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NBS MONOGRAPH 18

Heat Treatment and Properties

of Iron and Steel

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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UNITED STATES DEPARTMENT OF COMMERCE . Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Dirictor

Heat Treatment and Properties of

Iron and Steel

Thomas G. Digges and Samuel J. '^senberg

National Bureau of Standards Monograph 18

Issued October 3, 1960

Supersedes Circular 495

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington 25, D.C, - Price 35 cents
Contents

Page

1. Introduction 1 2. Properties of iron 1 2.1. Transformation temperatures 1 2.2. Mechanical properties 2

3. Alloys of iron and carbon 2

3.1. Iron-carbon phase diagram 2

3.2. Correlation of mechanical properties with

microstructures of slowly cooled carbon

steels 4

4. Decomposition of ausenite 5

4.1. Isothermal transformation 6

a. To pearlite 6

b. To bainite 7

c. To martensite 7

4.2. Continuous cooling 7

5. Heat treatment of steels 8

5.1. Annealing 9

a. Full annealing 9

b. Process annealing 9

c. Spheroidizing 10

5.2. Normalizing 11

5.3. Hardening 11

a. Effect of mass 11

5.4. Tempering 12

5.5 Case hardening 13

a. Carburizing 13

b. Cyaniding 14

c. Carbonitriding 15

d. Nitriding 15

5.6. Surface hardening 15

a. Induction hardening 15

b. Flame hardening 16

5.7. Special treatments 16

a. Austempering 16

b. Martempering 16

c. Cold treatment 16

6. Hardenability 17

7. Heat treatment of cast irons 18

7.1. Relieving residual stresses (aging) 20

7.2. Annealing 20

a. Malleabilizing 20

7.3. Normalizing, quenching, and tempering 20

7.4. Special heat treatments 21

II

8. Practical considerations

8.1. Furnaces and salt baths

a. Protective atmospheres

b. Temperature measurement and control

8.2. Quenching media and accessories

8.3. Relation of design to heat treatment

9. Nomenclature and chemical compositions of steels.

9.1. Structural steels

9.2. Tool steels

9.3. Stainless and heat resisting steels

10. Recommended heat treatments

10.1. Structural steels 10.2. Tool steels 10.3. Stainless and heat resisting steels

a. Group I—Hardenable chromium

steels (martensitic and magnetic).

b. Group II—-Nonhardenable chro- mium steels (ferritic and magnetic)

c. Group III—-Nonhardenable chro- mium-nickel and chromiumnickel-manganese steels (austenitic and nonmagnetic)

11. Properties and uses of steels 11.1. Structural steels

a. Plain carbon structural steels

b. AUoy structural steels

11.2. Tool steels 11.3. Stainless and heat resisting steels

a. Group I—Hardenable chromium

steels (martensitic and magnetic).

b. Group II—Nonhardenable chro- mium steels (ferritic and magnetic)

c. Group III—Nonhardenable chro- mium-nickel and chromiumnickel-manganese steels (austenitic and nonmagnetic)

d. Semi-austenitic stainless steels

12. Selected references.

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Heat Treatment and Properties of Iron and Steel

Thomas G. Digges and Samuel J. Rosenberg

This ^lonograph has been prepared to give an understanding of heat treatment principally to those unacquainted with this subject. To this end, the basic theoretical and practical principles involved in the heat treatment of iron and steel are presented in simplified form.

1. Introduction

The Xational Bureau of Standards receives

many requests for general information concerning

the heat treatment of iron and steel and for directions and explanations of such processes. This

Monograph has been prepared to answer such

inquiries and to give in simplified form a working

knowledge of the basic theoretical and practical

principles involved in the heat treatment of iron

and steel. The effects of various treatments on

the structures and mechanical properties of these

materials are described. Many theoretical aspects

are discussed only briefly or omitted entirely, and

in some instances, technical details have been

neglected for sunplicity. The present Monograph

supersedes Circular 495, which was published in 1950.

Heat treatment may be defined as an operation

or combination of operations that involves the

heating and cooling of a solid metal or alloy for the

purpose of obtaining certain desirable conditions

^ or properties. It is usually desired to preserve, as

"I nearly as possible, the form, dimensions, and

m surface of the piece being treated.

m Steels and cast irons are essentially alloys of

Mjl iron and carbon, modified by the presence of other

m elements. Steel may be defined as an alloy of u'on

3j[i and carbon (with or without other alloymg ele- ments) containing less than about 2.0 percent of

I carbon, usefidly malleable or forgeable as initially

isj cast. Cast iron may be defined as an alloy of u'on and carbon (with or without other alloying ele- ments) containing more than 2.0 percent of carbon,

not usefully malleable or forgeable as initially cast. For reasons that will be apparent later, the dividing line between steels and cast irons is taken at

2.0 percent of carbon, even though certam special

steels contain carbon in excess of this amount. In

addition to carbon, fom^ other elements are nor- J maUy present in steels and in cast irons. These

are mangnaese, silicon, phosphorus, and sulfiu". Steels may be broadly classified into two types,

(1) carbon and (2) alloy. Carbon steels owe their

properties chiefly to the carbon. They are fre- quently called straight or plain carbon steels. Alloy steels are those to which one or more alloying

elements are added in sufficient amounts to modify

certain properties. The properties of cast iron

also may be modified by the presence of alloying

elements—such irons are called alloy cast irons.

2. Properties of Iron

Since iron is the basic element of steel, a knowledge of some of its properties is a prerequisite to an understanding of the fimdamental pi"inciples

underlying the heat treatment of steels.

2.1. Transformation Temperatures

If a molten sample of pure u"on were allowed to cool slowly and the temperature of the iron were measured at regular intervals, an idealized (equilibrium) time-temperature plot of the data would

appear as shown in figure 1. The discontinuities

(temperature arrests) in this curve are caused by

physical changes in the U'on. The first arrest at 2,800° F marks the temperature at which the iron freezes. The other arrests (known as transformation temperatures or criti- cal points) mark temperatm-es at which certain

internal changes take place in the solid iron.

Some of these temperatures are very important

in the heat treatment of steel. The atoms in all solid metals are arranged

in some definite geometric (or crystallographic)

pattern. The atoms in iron, immediately after

freezing, are arranged in what is termed the bodycentered cubic system. In this crystal structure

TIME Figure 1. Idealized cooling curve for pure iron.
the unit cell consists of a cube with an ii'on atom

at each of the eight corners and another in the

center (fig. 2, a). Each of the many individual

grains (crystals) of which the solid metal is composed is built up of a very large number of these

unit cells, all oriented alike in the same grain.

This high-temperatui'e form of iron is known as delta (5) iron.

o b Figure 2. Crystal structure of iron.

(a) Body-centered cubic (alpha and delta iron); (b) Face-centered cubic (gamma iron).

At 2,550° F (the A4 point), iron undergoes an

alio tropic transformation (fig. 1); that is, the ar- rangement of the atoms in the crystal changes.

The new crystal structure is face-centered cubic,

and the unit cell again consists of a cube with an

iron atom at each of the eight corners, but with an iron atom in the center of each of the six faces

instead of one in the center of the cube (fig. 2, b).

This form is known as gamma (7) iron. At 1,670°

F (the A3 point), h-on undergoes another allo- tropic transformation and reverts to the bodycentered cubic system (fig. 2, a). This structure,

which is crystallographically the same as delta

iron, is stable at all temperatures below the A3

point and is known as alpha (a) iron (fig. 5, A).

The arrest at 1,420° F (known as the A2 point)

is not caused by an allotropic change, that is, a change in crystal structure. It marks the temperature at which iron becomes ferromagnetic and is therefore termed the magnetic transition. Above

this temperature iron is nonmagnetic.

These various temperature arrests on cooling

are caused by evolutions of heat. On heating,

the arrests occur in reverse order and are caused

by absorption of heat. The critical points may be

detected also by sudden changes in other physical

properties, for instance, expansivity or electrical conductivity.

2.2. Mechanical Properties

Iron is relatively soft, weak, and ductile and

cannot be appreciably hardened by heat treat- ment. Its tensile strength at room temperature is about 40,000 lb/in.\ its yield strength is about

20,000 Ib/in.^, and its Brinell hardness is about 80. The modulus of elasticity is about 29,000,000

Ib/in.^. The strength and hardness can be in- creased, with corresponding decrease in ductility,

by cold working.

3. Alloys of Iron and Carbon

The properties of iron are affected very markedly by additions of carbon. It should be realized

that in discussing iron-carbon alloys, we actually

are dealing with plain carbon steels and cast irons.

3.1. Iron-Carbon Phase Diagram

The complete iron-carbon phase (or constitutional) diagram represents the relationship between temperatures, compositions, and structures

of all phases that may be formed by iron and

carbon under conditions of equilibrium (very slow

cooling). A portion of this diagram for alloys

ranging up to 6.7 percent of carbon is reproduced

in figure 3; the upper limit of carbon in cast iron

is usually not in excess of 5 percent. The left- hand boundary of the diagram represents pure iron

(ferrite), and the right-hand boundary represents

the compound iron carbide, FcsC, commonly called

cementite.

The beginning of freezing of the various ironcarbon alloys is given by the curve ABCD, termed

the liquidus curve. The ending of freezing is given by the curve AHJECF, termed the solidus curve. The freezing point of iron is lowered by

the addition of carbon (up to 4.3%) and the re- sultant alloys freeze over a range in temperature

instead of at a constant temperature as does the

pure metal iron. The alloy containing 4.3 percent

of carbon, called the eutectic alloy of iron and

cementite, freezes at a constant temperature as indicated by the point C. This temperature is 2,065° F, considerably below the freezing point of

pure iron.

Carbon has an important effect upon the trans- formation temperatures (critical points) of iron. It raises the A4 temperature and lowers the A3. This efl^ect on the A3 temperature is very important

in the heat treatment of carbon and alloy struc- tural steels, while that on the A4 is important in the heat treatment of certain high alloy steels,

particularly of the stainless types.

It is possible for solid iron to absorb or dissolve

carbon, the amount being dependent upon the

crystal structure of the iron and the temperature.

The body-centered (alpha or delta) iron can dis- solve but little carbon, whereas the face-centered

(gamma) iron can dissolve a considerable amount,

the maximum being about 2.0 percent at 2,065°

F (fig. 3). This solid solution of carbon in gamma

iron is termed austenite. The solid solution of

carbon in delta iron is termed delta ferrite, and

the solid solution of carbon in alpha iron is termed

alpha ferrite, or, more simply, ferrite. The mechanism of solidification of iron-carbon

alloys, especially those containing less than about

0.6 percent of carbon, is rather complicated and

is of no importance in the heat treatment of carbon

steels and cast irons. It is sufficient to know that

all iron-carbon alloys containing less than 2.0 per- cent of carbon (that is, steel) will, immediately

or soon after solidification is complete, consist of

2
3600 —

STEELS CAST IRONS

CARBON, %

6.7 % C

FiGT'RE 3. Iron-carbon phase diaqravt.

the single phase austenite. Cast ii-ons will consist

of two phases immediately after solidification

austenite and cementite. Under some conditions

this cementite formed on cooling through the temperature horizontal ECF will decompose partly or completely into austenite and grapliite.

The part of the iron-carbon diagram that is con- cerned with the heat treatment of steel is reproduced on an expanded scale in figure 4. Regardless of the carbon content, steel exists as austenite

above the line GOSE. Steel of composition S

(0.80% of carbon) is designated as "eutectoid"

steel, and those with lower or higher carbon as "hypoeutectoid" and ''hypereutectoid," respectively.

A eutectoid steel, when cooled at very slow rates from temperatures within the austenitic field, undergoes no change until the temperature horizontal

PSK is reached. At this temperature (known as the Ai temperature), the austenite transforms completely to an aggregate of ferrite and cementite

having a typical lamellar structure (fig. 5, D and

E). This aggregate is known as pearlite and the

Ai temperature is, therefore, frequently- referred

to as the pearlite point. Since the Ai transformation involves the transformation of austenite to

pearlite (which contains cementite—FesC), pure

iron does not possess an Ai transformation (fig. 4).

Theoretically, iron must be alloyed with a minimum of 0.03 percent of carbon before the first minute traces of pearlite can be formed on cooling

(point P, fig. 4). If the steel is held at a temperature just below A], (either during coohng or

heating), the carbide in the pearhte tends to coalesce into globules or spheroids. This phenomenon, known as spheroidization, will be dis- cussed subsequently.

Hypoeutectoid steels (less than 0.80% of car- bon), when slowly cooled from temperatures above

the A3, begin to precipitate ferrite when the A3

line {GOS—fig. 4) is reached. As the temperature

drops from the A3 to Ai, the precipitation of ferrite increases progressively and the amount of the

remaining austenite decreases progressively^, its carbon content being increased. At the Ai temperature the remaining austenite reaches eutectoid

composition (0.80% of carbon—point S, fig. 4)

and, upon further coohng, transforms completely

into pearlite. The microstructures of slowly cooled

hypoeutectoid steels thus consist of mixtures of

3
2200

2000

1800

1600

2065° F

0,6 08 1-0 CARBON,

2.0

Figure 4. Phase diagram for carbon steels.

ferrite and pearlite (fig. 5, B and C). The lower

the carbon content, the higher is the temperature

at which ferrite begins to precipitate and the

greater is the amount in the final structure. Hypereutectoid steels (more than 0.80% of car- bon) , when slowly cooled from temperatures above

the Acta, begin to precipitate cementite when the

Acm line (SE—fig. 4) is reached. As the temperature di-ops from the Acm to Ai, the precipitation of

cementite increases progressively and the amount

of the remaining austenite decreases progressively, its carbon content being depleted. At the

Ai temperature the remaining austenite reaches

eutectoid composition (0.80% of carbon) and,

upon further cooling, transforms completely into

pearlite. The microstructures of slowly cooled

hypereutectoid steels thus consist of mixtures of

cementite and pearlite (fig. 5, F). The higher the

carbon content, the higher is the temperature at which cementite begins to precipitate and the

greater is the amount in the final structure. The temperature range between the Ai and A3

points is called the critical or transformation

range. Theoretically, the critical points in any

steel should occur at about the same temperatures on either heating or cooling very slowly. Practically, however, they do not since the A3 and Ai

points, afi^ected but slightly by the rate of heating,

are affected tremendously by the rate of cooling.

Rapid rates of heating raise these points only

slightly, but rapid rates of cooling lower the temperatures of transformation considerably. To

differentiate between the critical points on heating

and cooling, the small letters "c" (for "chauffage"

from the French, meaning heating) and "r" (for

"refroidissement" from the French, meaning cooling) are added. The terminology of the critical points thus becomes Acs, Ars, Aci, Ari, etc. The

letter "e" is used to designate the occurrence of the

points under conditions of extremely slow cooling on the assumption that this represents equihbrium

conditions ("e" for equilibrium); for instance, the

Acs, Aci, and Accm3.2. Correlation of Mechanical Properties

With Microstructures of Slowly Cooled

Carbon Steels

Some mechanical properties of pearlite formed

during slow cooling of a eutectoid (0.80% of carbon)

steel are approximately as follows

Tensile strength—115,000 Ib/inl

Yield strength—60,000 Ib/inl

Brinell hardness number—200.

The amount of pearlite present in a slowly

cooled hypoeutectoid steel is a linear function of

the carbon content, var3dng from no pearlite, when

no carbon is present (the very slight amount of

carbon soluble in alpha iron may be neglected),

to all pearlite at 0.80 percent of carbon. The bal- ance of the structure of hypoeutectoid steels is composed of ferrite, the mechanical properties of

which were given in a preceding section. Since

the mechanical properties of aggregates of ferrite and pearlite are fimctions of the relative amounts

of these two constitutents, the mechanical properties of slowly cooled hypoeutectoid steels are also

4
Fk.i re .3. Miri ostructural constituents of slowly cooled carbon steels. A, Ferrite (a iron). All grains are of the same composition. XIOO. B, 0.25% carbon. Light areas are ferrite grains. Dark areas are pearlite. XIOO.

C, 0.5% carbon. Same as B but higher carbon content results in more pearlite and less ferrite. XIOO. D, 0.8% carbon. All pearUte. XIOO. E, Same as D. At higher magnification the lamellar structure of pearlite is readily observed. XoOO.

r, 1.3% carbon. Pearlite plus excess cementite as network. XIOO.

All etched with either picral or nital.

linear functions of the carbon content, varying between those of iron at no carbon to those of pearlite

at 0.80 percent of carbon (fig. 6).

4. Decomposition of Austenite

In alloys of iron and carbon, austenite is stable

only at temperatures above the Aei (1,330° F).

Below this temperature it decomposes into mixtures of ferrite (a iron) and cementite (iron carbidej. The end product or final structui-e is greatly influenced by the temperature at which the

transformation occurs, and this, in turn, is influenced by the rate of cooling. Since the mechanical

properties may be varied over a wide range, depending on the decomposition products of the

parent austenite, a knowledge of how austenite

decomposes and the factors influencing it is neces- sary for a clear imderstanding of the heat treat- ment of steel. The progressive transformation of

austenite under conditions of equilibrium (extremely slow cooling) has been described. Practicall}^, however, steel is not cooled under

equilibrium conditions, and consequently the

critical points on coohng always occur at lower

temperatoores than indicated in figure 4.

5
120

100

._ 80

60

40

20

200

160

120

80

100 FERR TE .

PEARL.ITE

0.2 0.4 0.6 CARBON, PERCENT

100

0.8

Figure 6. Relation of mechanical properties and structure

to carbon content of slowly cooled carbon steels.

If samples of steel, say of eutectoid carbon content for the sake of simplicity, are cooled from

above the Aei at gradually increasing rates, the

corresponding Ar transformation occurs at lower

and lower temperatures (fig. 7). This transformation is distinguished from that occurring under

extremely slow rates of cooling (Ai'i) by the designation Ar'. As the rate of cooling of this steel is increased, an additional transformation (termed the

Ar" or Ms) appears at relatively low temperatures

(about 430° F). If the rate of coohng is still fur- ther increased, the Ar' transformation is suppressed entirely and only the Ar" transformation

is evident. It should be noted that the temperature of the Ar" is not affected by the rate of cooling, whereas the temperature of the Ar' may be

depressed to as low as about 1,050° F in this particular steel. The product of the Ar' transformation is fine pearlite. As the temperature of the Ar' is gradually lowered, the lamellar structure of the resulting

pearlite becomes correspondingly finer and the

steel becomes harder and stronger. The product

of the Ar" transformation is martensite (fig. 9, A, and 15, A), which is the hardest and most

1330

1050

430

AUSTENITE

MARTENSITE

INCREASED RATE OF COOLING Figure 7. Schematic illustration showing the effect of rate of cooling on the transformation temperatures and de- composition products of austenite of eutectoid carbon

steel.

brittle of the transformation products of austenite

and is characterized b}^ a typical acicular structure. The phenomenon of the occurrence of both the

Ar' and Ai-" transformations is known as the

split transformation. The resultant microstructures of steels cooled at such rates as to undergo

a split transformation consist of varying amounts

of fine pearlite and martensite (fig. 9, C). The

actual amounts of these two constitutents are functions of the rates of cooling, the slower rates re- sulting in more pearlite and less martensite, and

the faster rates resulting in more martensite and ! less pearlite.

|

4.1. Isothermal Transformation

| The course of transformation of austenite when

the steel is quenched to and held at various con- ' stant elevated temperature levels (isothermal,

transformation) is conveniently shown by a diagram known as the S-curve (also termed the TTT

diagram—for time, temperature, and transforma-'

tion) . Such a diagram for eutectoid carbon steel

is shown in figure 8 and the discussion of this

figure will be confined to steel of this particular

composition.

i a. To Pearlite

, Austenite containing 0.80 percent of carbon,

cooled quickly to and held at 1,300° F, does not f begin to decompose (transform) until after about

15 min, and does not completely decompose until

after about 5 hr (fig. 8). Thus, at temperatures

just below the Aci, austenite is stable for a considerable length of time. The product of tlie deconxposition of austenite at this temperatm'e is coarse pearlite of relatively low hardness. If the

austenite is quickly cooled to and held at a some- what lower temperature, say 1,200° F, decomposition begins in about 5 sec and is completed after

6
1400

1200

1000

800

600

400

200

_I [ Ae,

|aUSTEN(TE(A)_1

0.5 I TIME, SECONDS Figure 8. Isothermal transformation diagram (S-curve) for eutecioid carbon steel. (Metals Handbook, 1948 edition, page 608.) The hardness of the structures formed at the various temperatures is given by the scale on the right.

about 30 sec, the resultant pearlite being finer and

harder than that formed at 1,300° F. At a temperature of about 1,050° F, the austenite decomposes extremely rapidly, only about 1 sec

elapsing before the transformation starts and 5

sec before it is completed. The restdtant pearlite

is extremel}' fine and its hardness is relatively

high. This region of the S-cm've where decomposition of austenite to fine pearlite proceeds so

rapid!}' is termed the "nose" of the cm-ve.

b. To Bainite

If the austenite is cooled unchanged to temperatures below the nose of the S-curve (1,050° F), the

time for its decomposition begins to increase (fig. 8). The final product of decomposition now is not pearlite, but a new acicular constituent called bainite (fig. 15, E) possessing unusual toughness

with hardness even greater than that of very fine pearUte.

Depending on the temperature, then, a certain

finite interval of time is necessary before austenite

starts to transform into either pearhte or bainite.

Additional time is necessar}' before the transformations are completed.

c. To Martensite

If the austenite is cooled unchanged to relatively

low temperatures (below about 430° F for the

eutectoid carbon steel under consideration), partial

transformation takes place instantaneously; the

product of transformation is martensite. Austenite transforms into martensite over a temperature range and the amount that transforms

is a function of the temperature. Only minute

amounts will so transform at about 430° F;

practically aU of the austenite will be transformed

at about 175° F. The beginning of this trans- formation range is termed the 2vlg (martensite—

start) and the end of the range is termed the Mf

(martensite—finish). As long as the temperature

is held constant within the Mg—^Mf range, that

portion of the austenite that does not transform

instantaneously to martensite remains untransformed for a considerable length of time, eventually

transforming to bainite.

In ordinary heat treatment of the plain carbon

steels, austenite does not transform into bainite.

Transformation of the austenite takes place either

above or at the nose of the S-cm-ve, forming pearlite, or in passing through the Mg^—Mf range, forming martensite, or both. It is evident that in order

for austenite to be transformed entirely into martensite, it must be cooled sufficiently rapidly so that the temperature of the steel is lowered past the nose of the S-curve in less time than is necessary

for transformation to start at this temperature.

If this is not accomplished, part of the steel trans- forms into pearlite at the high temperature (Ai-'), and the remainder transforms into martensite at the low temperatm-e (Ar" or Mg—Mf temperature

range). This explains the phenomenon of the

split transformation described previously.

4.2. Continuous Cooling

Figure 9 represents a theoretical S-curve on

which are supermiposed five theoretical cooling

curves. Cm-ves A to E represent successively

slower rates of cooling, as would be obtained, for

instance, by cooling in iced brine, water, oil, air, and m the furnace, respectively.

The steel cooled according to cmwe E begins to transform at temperature ti and completes trans- formation at the final product is coarse pearlite

with relatively low hardness. When cooled ac- cording to cm*ve D, transformation begins at U

and is completed at U; the final product is fine pearlite ancl its hardness is greater than the steel cooled according to curve E. When cooled ac- cording to curve C, transformation begins at U

and is only partially complete when temperature

ta is reached; the product of this partial trans- formation is very fine pearlite. The remainder of

the austenite does not decompose until the Mg temperature is reached, when it begins to transform

to martensite, completing this transformation at the Mf temperature. The final structm-e is then

a mixture of fine pearlite and martensite (typical

of incompletely hardened steel—frequently termed

"slack quenched" steel) with a higher hardness

than was obtained with the steel cooled according

to curve D. The rate of cooling represented by

cm-ve B is just sufficient to intersect the nose of

the S-cm-ve, consequently only a minute amount

of the austenite decomposes into fine pearlite at temperature i?; the remainder of the austenite is unchanged until the martensite transforrnation

range is reached. If the steel is cooled at a slightly

faster rate, so that no transformation takes place

at the nose of the S-cm-ve, the steel is completely

hardened. This particular rate is termed the criti- cal cooling rate and is defined as the slowest rate

at which the steel can be cooled and yet be corn- pletely hardened. Since this rate cannot be di548691—60 2 7
L "

. -«a. _. , ..J Figure 9. Schematic diagram illustrating the relation be- tween the S-ciirve, continuous cooling curves, and result- ing microstructures of eutectoid carbon steel. Microstructiu-es: A, martensite; B, martensite with a trace of very fine pearlite (dark); C, martensite and very fine pearlite; D, fine pearlite; E,

coarse pearlite. All etched with nital. X500.

rectly determined, the rate indicated by curve B,

producing only a trace of fine pearlite (fig. 9, B),

is frequently used as the critical cooling rate. The

hardness of the resultant martensite is equivalent

to the maximum that can be obtained. Samples

cooled at a faster rate, such as that indicated by

cm-ve A, are also completely martensitic but no

harder than the sample cooled according to the

critical coolmg rate. It will be noted that the rate at which a steel cools tlu-ough the temperature range in the vicinity

of the nose of the S-cm-ve is of critical importance.

Somewhat slower rates of cooling above and below

this temperature range can be tolerated and yet

obtain a completely hardened steel, provided that

the cooling through the temperature interval at the nose of the S-curve is suflSciently fast. In

practice, however, steels are usually cooled rapidly

from the quenching temperature to relatively low

temperatures (about 500° F) and then allowed

to cool in air. Although the above discussions of the decomposition of austenite have been limited to a steel of

eutectoid composition, other steels behave in a similar manner, the temperatures and times of

reactions being di^fferent. In hypoeutectoid steels, free ferrite plus pearlite are formed if transformation begins above the temperature range of the nose of the S-curve; the amount of free ferrite decreases as the temperature of transformation

approaches the nose of the curve. In hypereutectoid steels, free cementite plus pearlite are formed

if transformation occurs above the nose. The time

for the start of the transformation at the nose in- creases as the carbon increases up to the eutectoid

composition, and then decreases with further in- crease in carbon. That is, the nose is shifted to the right (with respect to the time axis, fig. 8) as the carbon is increased to 0.8 percent and to the left with further increase in carbon content, j The temperature of formation of bainite is not \ appreciably affected by carbon content, but the

time for its formation increases with the carbon.

Both the Mg and Mf temperatures are markedly . lowered by increasing carbon content, as is shown

for Mg in figm-e 10. The Mi temperatures of the

plain carbon steels have not been adequately determined ; available information indicates that the

Mf of high carbon steels is actually below room < temperature. Slight amounts of austenite are i frequently retained in quenched steels, especially : in the higher carbon grades, even when cooled to i room temperature. i

5. Heat Treatment of Steels

All heat-treating operatures consist of subjecting a metal to a definite time-temperature cycle, ' which may be divided into three parts: (1) Heat- ' ing, (2) holding at temperature (soaking), and '

(3) cooling. Individual cases vary, but certain

fundamental objectives may be stated.

The rate of heating is not particularly important I unless a steel is in a highly stressed condition, such

as is imparted by severe cold working or prior

hardening. In such instances the rate of heating

should be slow^. Frequently this is impracticable, j- since furnaces may be at operating temperatures, i but placing the cold steel in the hot furnace may i cause distortion or even cracking. This danger :

8
1000

800

200

0 1 \ \ 1 1 1 1 1 0 0.20 0.40 0.60 0.80 1.00 1.20 1.40 CARBON,

Figure 10. Influence of carbon on the start of the martensite (Ms) transformation of high-purity iron-carbon

alloys.

(Dlgges, Trans. Am. Soc. Metals 28, 597 (1940).)

can be ininiinized by the use of a preheating

furnace maintained at a temperature below the Ai. The steel, preheated for a sufficient period, then can be transferred to the fm-nace at operating

temperature. This procedure is also advantageous

when treating steels having considerable variations

in section thickness or very low thermal conductivity.

The object of holding a steel at heat-treating

temperature is to assure uniformity of temperature

throughout its entire volume. Obviously, thin

sections need not be soaked as long as thick

sections, but if different thicknesses exist in the same piece, the period required to heat the thickest

section uniformly governs the time at temperatm-e.

A rule frequently used is to soak % hr/in. of thickness. The structm-e and properties of a steel depend

upon jts rate of coolmg and this, in turn, is governed by such factors as mass, quenching media,

etc. It must be realized that the thicker the

section, the slower will be the rate of cooling re- gardless of the method of cooling used except in such operations as induction hardening to be

discussed later.

5.1. Annealing

Annealing is a process involving heating and

cooling, usually applied to produce softening.

The term also refers to treatments intended to

alter mechanical or physical properties, produce

a definite microstructm-e, or remove gases. The

temperature of the operation and the rate of

cooling depend upon the material being annealed

and the purpose of the treatment.

a. Full Annealing

Full annealing is a softening process in which

a steel is heated to a temperature above the trans- formation range (Acs) and, after being held for

a sufficient time at this temperature, is cooled

slowly to a temperatm-e below the transformation

range (Ari). The steel is ordinarily allowed to cool slowly in the furnace, although it may be

removed and cooled in some medium such as mica, lime, or ashes, that insm'es a slow rate of

cooling.

Since the transformation temperatures are af- fected by the carbon content, it is apparent that

the higher carbon steels can be fully annealed at lower temperatures than the lower carbon steels. In terms of the diagram shown in figure 4, steels must be heated to above the Ime GOSK. The temperature range normally used for full annealing

is 25 to 50 deg F above this line (the upper

critical), as shown in figm'e 11.

Figure 11. Reconnnended temperature ranges for heat

treating plain carbon steels. The microstructures of the hypoeutectoid steels that result after full annealmg are quite similar

to those shown for the equilibrium conditions (fig. 5, B and C). Eutectoid and hypereutectoid steels frec^uently spheroidize partially or completely on

full annealing (see later section and fig. 12, D).

b. Process Annealing

Process annealing, frequently termed stressrelief annealing, is usually applied to cold-worked

low carbon steels (up to about 0.25% of carbon)

to soften the steel sufficiently to allow fiu-ther coldworking. The steel is usually heated close to, but

below, the Aci temperature (fig. 11). If the steel

is not to be further cold-worked, but relief of internal stresses is deshed, a lower range of temperature will suffice (about 1,000° F). Rate of coohng

is immaterial.

This type of anneal will cause recrystallization

and softening of the cold-worked ferrite grains,

but usually will not affect the relatively small

amounts of cold-worked pearlite. Typical struc- tures of cold-worked, process-annealecl, and fully

annealed low-carbon steel are shown in figure 12,

A, B, and C, respectively.

I
Figure 12. Representative microstructures of carbon steels. A,':Low carbon steel (0.1% C) as cold-worked. Both ferrite (light) and pearlite (dark) are severely deformed. XIOO. B, Same as (A) after process aimealing at 1,200° F. The ferrite is recrystallized (grains are equi-axed), but pearlite is not affected by this treatment. XIOO. C, Same as (A) after full aimeaUng at 1,650° F. All traces of cold working are eliminated, and the ferrite grains are larger than in (B). XIOO. D, High carbon steel (1.1% 0) as spheroidized. All the carbon is present in the form of spheroids or slightly elongated particles of cementlte in a matrix of

ferrite. X500. E, Hypoeutectoid steel (0.5% G) as normalized at 1,600° F in ?4-in. round (center area). Because of the rapid rate of air cooling such a small section, the

pearlite is quite fine and relatively little free ferrite is formed. X600.

F, Same steel as (E) but normalized in IVi-XQ. round (center area). The slower rate of cooling due to the larger section results in coarser pearlite and more

free ferrite. X500.

All etched in picral.

c. Spheroidizing

Spheroidizing is a process of heating and cool- ing steel that produces a rounded or globular form

of carbide m a matrix of ferrite. It is usually

accomj)lished by prolonged heating at temperatures just below the Aci (fig. 11), but may be facil- itated by alternately heating to temperatures just

above the Aci and cooling to just below the Ari. The final step, however, should consist of holding

at a temperature just below the critical (Ari). The

rate of cooling is immaterial after slowly cooling

to about 1,000° F. The rate of spheroiclization is affected by the

initial structure. The finer the pearlite, the more

readily spheroidization is accomplished. A martensitic structure is very amenable to spheroidization.

This treatment is usually applied to the high

carbon steels (0.60% of carbon and higher). The

purpose of the treatment is to improve machinability and it is also used to condition high-carbon steel for cold-drawing into wire. A typical microstructure of spheroidized high carbon steel is shown

in figure 12, D.
5.2. Normalizing

Normalizing is a process in which a steel is heated, to a temperature above the Acs or the Acm

(fig. 11) and then cooled in still aii-. The pm"pose

of the treatment is to obliterate the effects of any

previous heat treatment (including the coarse- grained structure sometimes resulting from high

forging temperatures) or cold-working and to insure a homogeneous austenite on reheating for hardening or full annealing. The resultant struc- tures are pearlite or pearlite with excess ferrite or cementite, depending upon the composition of the

steel. They are different from the structm'es

resulting after annealing in that, for steels of the same carbon content in the hypo- or hypereutectoid ranges, there is less excess ferrite or cementite

and the pearlite is finer. These are the results of

the more rapid cooling.

Since the type of structm'e, and, therefore, the

mechanical properties, are affected by the rate of

cooling, considerable variations may occur in

normalized steels because of differences in section

thickness of the shapes being normalized. The

effect of section thickness on the structure of a normalized 0.5-percent-carbon steel is shown in figure 12, E and F.

5.3. Hardening

Steels can be hardened by the simple expedient

of heating to above the Aca transformation, holding long enough to insure the attainment of uniform temperatm'e and solution of carbon in the

austenite, and then cooling rapidly (quenching).

Complete hardening depends on cooling so rapidly

(fig. 9, A and B) that the austenite, which otherwise would decompose on cooling through the Ari,

is maintained to relatively low temperatm-es.

When this is accomplished, the austenite trans- forms to martensite on cooling through the Ms

Mi range. Rapid cooling is necessary only to the

extent of lowering the temperature of the steel to well below the nose of the S-curve. Once this has

been accomplished, slow cooling from then on,

either in oil or in air, is beneficial in avoiding dis- tortion and cracking. Special treatments, such as time quenching and martempering, are designed

to bring about these conditions. As martensite is quite brittle, steel is rarely used in the as-quenched

condition, that is, without tempering.

The maximum hardness that can be obtained

in completely hardened low^-alloy and plain car- bon structural steels depends primarily on the

carbon content. The relationship of maximum

hardness to carbon content is shown in figure 13.

a. Effect of Mass

Previous discussion of the formation of martensite has neglected the influence of mass. It must

be realized that even with a sample of relatively

small dimensions, the rate of abstraction of heat

is not uniform. Heat is always abstracted from

the surface layers at a faster rate than from the

interior. In a given cooling medium the cooling

rate of both the surface and interior decreases as the dimensions of a sample increase and the pos70

0 I 1 \ \ ! 1 1 1 1 1 1 0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 CARBON ,7o Figure 13. Relation of maximum attainable hardness of quenched steels to carbon content.

(Burns, Moore, and Archer, Trans. Am. Soc. Metals 26, 14 (1938)). sibility of exceeding the critical cooling rate (fig. 9, B) becomes less. To overcome this, the steel may be quenched in a medium having a very

high rate of heat abstraction, such as iced brine,

but, even so, many steels have a physical restric- tion on the maximum size amenable to complete

hardening regardless of the quenching medium.

The marked effect that mass has upon the hardness of quenched steel may be illustrated by measuring the hardness distribution of different size rounds of the same steel quenched in the same

medium. Curves showing the distribution of

hardness in a series of round bars of different sizes of 0.5-percent-carbon steel are shown in figure 14.

30

l/2"0

3/4"d \

"d

'

1 1/2 \ \ \

f

J

2 10RADIUS, INCHES 12

Figure 14. Variation in hardness in different size rounds

of 0.5-percent-carbon steels as quenched from 1,630° F

in water.

(Jomlny, Hardenabillty of alloy steels. Am. Soc. Metals, p. 75, 1939.) 11
The quenching medium used was water; the

quenching temperatm-e was 1,530° F. The rate of

coohng decreased as the diameters of the bars

increased. Only the }^-in. round hardened completely through the cross section, whereas with

the 4-iu. round the critical cooling rate was not

attained even at the surface.

5.4. Tempering

Tempering (sometimes called drawing) is the

process of reheating hardened (martensitic) or normalized steels to some temperature below the

lower critical (Aci). The rate of cooling is immaterial except for some steels that are susceptible

to temper brittleness.^

As the tempering temperature is increased, the

martensite (fig. 15, A) of hardened steel passes

through stages of tempered martensite (fi.g. 15, B

and C) and is gradually changed into a structure

consisting of spheroids of cementite in a matrix of

ferrite, formerly termed sorbite (fig. 15, D). These | changes are accompanied by a decreasing hardness

and increasing toughness. The tempering temper-^

ature depends upon the desired properties and the

purpose for which the steel is to be used. If con1 Temper brittleness is manifested as a loss of toughness (observed only by- impact tests of notched bars) after slow cooling from tempering temperatures

of 1,100° F or higher, or after tempering in the temperature range between

approximately 850° and 1,100° F. It is most pronounced in alloy steels that contain manganese or chromium and usually can be prevented by rapid quenching from the tempering temperature. The presence of molybdenum

is beneficial in counteracting the tendency toward temper brittleness.

Figure 15. Microstructures and corresTponding hardness of heat-treated high carbon steel. A, As quenched in brine; martensite, Rockwell C hardness=67. X500. B, Same as A after tempering at 400° F; tempered martensite, Rocliwell C hardness=61. X500.

C, Same as (A) after tempering at 800° F; tempered martensite, Rockwell C hardness=45. X500. D, Same as (A) after tempering at 1,200° F; tempered martensite, Rockwell C hardness=25. X500.

E, Quenched in lead at 650° F; bainite, Rockwell C hardness=49. X500.

F, Heat-treated steel showing decarburized surface layer (Ught area) that did not respond to hardening. XIOO.

All etched in 1% nital. 12
siderable hardness is necessary, the tempering

temperatui-e should be low; if considerable toughness is required, the tempering temperatm-e shoiild

be high. The effect of tempering on the hardness

of fullv hardened carbon steels is shown in figiu-e 16.Proper tempering of a hardened steel requires a

certain amount of time. At any selected tempering temperatiu-e, the hardness drops rapidly at

fii'st, gradually decreasing more slowly as the tune

is prolonged. The effect of time at different tempering temperatiu'es upon the residtant hardness

of a eutectoid carbon steel is shown in figm'e 17. Short tempering periods are generally undesirable

70

60

50

40

30

20

10

*— —

0.8()7oNN

IRBON N

>Ov l.2%CARB0

0.35 °/o CARBO

200 400 600 800 1000 TEMPERING TEMPERATURE °F

1200 1400

Figure 16. Effect of tempering temperature on the hardness of carbon steels of different carbon content.

Specimens were tempered for 1 hr. (Bain, Functions of the allojing elements in steel, Am. Soc. Metals, p. 38, 1939.)

70

60

o: 50

40

30

____400°F

600°F -_.M0°F

^^^OO^F

10 SECOND

1/2 2 5 HOURS

25

TIME AT TEMPERING TEMPERATURE Figure 17. Effect of time at tempering temperature on

the hardness of 0.8-percenl-carbon steel. {Logarithmic

time scaled)

(Bain, Functions of the alloying elements in steel, Am. Soc. Metals, p. 233,

1939.)

and should be avoided. Good practice requires

at least hr (or, preferably, 1 to 2 lir) at tempering

temperature for any hardened steel. The necessity for tempering a steel promptly

after hardening cannot be overemphasized. If fully hardened steel is allowed to cool to room

temperature dming hardening there is danger that

the steel may crack. Carbon steels and most of

the low aUoy steels should be tempered as soon as they are cool enough to be held comfortably in the

bare hands. Steels should not be tempered before

they cool to this temperatm-e because in some

steels the Mi temperatiire is quite low and untransformed austenite may be present. Part of all of

this residual austenite will transform to martensite on cooling from the tempering temperature so that

the final structure will consist of both tempered

and untempered martensite. The brittle un- tempered martensite, together with the internal

stresses caused by its formation, can easily cause

failm-e of the heat-treated part. When it is possible that such a condition exists, a second tempering treatment (double tempering) should be given

to temper the fresh martensite formed on cooling

after the initial tempering treatment.

If structmal steels are to be used in the nor- malized condition, the normalizing operation is frequently followed by heating to a temperatm-e

of about 1,200° to 1,300° F. The purpose of this

treatment, which is also designated as tempering,

is to relieve internal stresses resulting on cooling

from the normalizing temperature and to improve

the ductUity.

5.5. Case Hardening

Case hardening is a process of hardening a

ferrous alloy so that the surface layer or case is made substantially harder than the interior or

core. The chemical composition of the surface

layer is altered during the treatment by the addition of carbon, nitrogen, or both. The most

frequenth' used case-hardening processes are car- bm-izing, cj'aniding, carbonitriding, and nitriding.

a. Carburizmg

Carbm-izing is a process that introduces carbon

into a solid ferrous alloy by heating the metal in contact with a carbonaceous material to a temperature above the Acs of the steel and holding

at that temperature. The depth of penetration of

carbon is dependent on temperature, tmie at temperature, and the composition of the carburizing

agent. As a rough indication, a carburized depth

of about 0.030 to 0.050 in. can be obtained in

about 4 hr at 1,700° F, depending upon the type

of carburizing agent, which may be a solid, liquid, or gas. Since the primary object of carbm-izing is to secm-e a hard case and a relatively soft, tough

core, only low-carbon steels (up to a maximum of about 0.25% of carbon), either with or without

alloying elements (nickel, chromium, manganese,

13
molybdenum), are normally used. After car- burizing, the steel will have a high-carbon case graduating into the low-carbon core (fig. 18).

A variety of heat treatments may be used subsequent to carburizing, but all of them involve

quenching the steel to harden the carburized sur- face layer. The most simple treatment consists

of quencliing the steel directly from the carburizing temperature; this treatment hardens both

the case and core (insofar as the core is capable

of being hardened). Another simple treatment,

and perhaps the one most frequently used, consists

of slowly cooling from the carburizing temperature, reheating to above the Ac3 of the case (about

l,425°F),and quenching; this treatment hardens

the case only. A more complex treatment is to double quench—first from above the Aca of the

core (about 1,650° F for low-carbon steel) and

then from above the Acs of the case (about 1,425°

F) ; this treatment refines the core and hardens the

case. The plain carbon steels are almost always

quenched in water or brine; the alloy steels are usually quenched in oil. Although tempering

following hardening of carburized steel is sometimes omitted, a low-temperature tempering treat- ment at about 300° F is good practice.

It is sometimes desirable to carburize only cer- tain parts of the surface. This can be accomplished by covering the surface to be protected

against carburizing with some material that pre- vents the passage of the carburizing agent. The

most widely used method is copper plating of the

surfaces to be protected. Several proprietary

solutions or pastes, which are quite effective in

preventing carburization, are also available.

The commercial compounds commonly used for

pack (solid) carburizing contain mixtures of

carbonate (usually barium carbonate), coke

(diluent), and hardwood charcoal, with oil, tar, or molasses as a binder. Mixtures of charred

leather, bone, and charcoal are also used.

The carburizing action of these compounds is diminished during use and it is necessary to add

new material before the compound is reused. Addition of one part of unused to three to five parts

of used compound is common practice. The parts

to be carburized are packed in boxes (or other

suitable containers) made of heat-resistant alloys,

although rolled or cast steel may be used where

long life of the box is not important. The Hd of

the box should be sealed with fire clay or some

other refractory to help prevent escape of the

carburizing gas generated at the carburizing temperature. The depth and uniformity of case is affected by the method of packing and design of

the container.

Liquid carburizing consists of case hardening

steel or iron in molten salt baths that contain

mixtures principally of cyanides (violently poisonous), chlorides, and carbonates. The case produced by this method contains both carbon and

nitrogen, but principally the former. The temperatiu-es used range from about 1,550° to 1,650° F

or higher, depending upon the composition of the

bath and the desired depth of case. At 1,650° F

a case depth of about 0.010 to 0.015 in. can be

obtained in 1 hr; about 0.020 to 0.030 in. can be obtained in 4 hr. Considerably deeper cases can be obtained at higher temperatm-es with longer

periods of time. After carburizing, the parts must

be quenched just as in solid carburizing, but it is usual to do this directly from the molten bath.

In all present-day commercial gas carburizing,

two or more hydrocarbons are used in combination for supplying the carbon to the steel. The

hydrocarbons used are methane, ethane, propane,

and oil vapors. The steel parts are placed in

sealed containers through which the carburizing

gases are circulated; the temperatures used are in

the neighborhood of 1,700° F. Average expectation for depth of case in gas-carburized steel is illustrated in figure 19. After carburizing, the

parts must be quench hardened.

b. Cyaniding

A hard, superficial case can be obtained rapidly on low-carbon steels by cyaniding. This process

involves the introduction of both carbon and nitroHYPOEUTEGTOID ZONE

Figure 18. Structure of a carburized steel. The specimen was cooled slowly from the carburizing temperature. Etched with nital. X75.

14
S 0.080 I

t-a.Q 0.060 u

05<

0.040

0.020

0 l__ 1 1 1 1 1 1 1 0 4 8 12 16 20 24 28 CARBURIZINGTIME , HOURS Figure 19. Relation of time and temperature to carbon

penetration in gas carhiirizing.

(Metals Handbook, 1939 edition, p. 1041.) gen into the surface layers of the steel. Steels to be cyanided normally are heated in a molten bath

of cyanide-carbonate-cliloride salts (usually containing 30 to 95% of sodium cyanide) and then

quenched in brine, water, or mineral oil; the temperature of operation is generally within the range

of 1 ,550 ° to 1 ,600 ° F. The depth of case is a function of time, temperature, and composition of the

cyanide bath; the time of immersion is c^uite short

as compared with carburizing, usually varjang

from about 15 min to 2 hr. The ma.ximum case depth is rarely more than about 0.020 in. and the

average depth is considerably less. Steels can be cyanided also by heating to the

proper temperatm-e and dipping in a powdered

cyanide mixture or sprinkling the powder on the

steel, followed by quenching. The case thus

formed is extremely thin.

Cyaniding salts are violent poisons if allowed to come in contact with scratches or wounds; they are

fatally poisonous if taken internally. Fatally poi- sonous fumes are evolved when cyanides are brought into contact with acids. Cyaniding baths

should be equipped with a hood for venting the

gases evolved during heating and the work room

should be well ventilated. Molten cyanide should never be permitted to come in contact with sodium

or potassium nitrates commonly used for baths for tempering as the mixtures are explosive. Furthern^ore, care is necessary in preparing a salt bath and

the work pieces should be completely dry before

placing in the molten bath. The advice of salt manufacturers should be obtained and followed in

the operation and maintenance of salt baths.

c. Carbonitriding

Carbonitriding, also termed gas cyaniding, dry

cyaniding, and ni-carbing, is a process for case hardening a steel part in a gas-carburizing atmosphere that contains ammonia in controlled percentages. Carbonitriding is used mainly as a low-cost

substitute for cyaniding and, as in cyanidiiag, both

carbon and nitrogen are added to the steel. The

process is carried on above the Aci temperature of

the steel, and is practical up to 1,700° F. Quenching in oil is sufficiently fast to attain maximum

surface hardness; this moderate rate of cooling

tends to minimize distortion. The depth to which

carbon and nitrogen penetrate varies Avith temperatm-e and time. The penetration of carbon is approximately the same as that obtained in gas

carburizing (fig. 19).

d. Nitriding

The nitriding process consists in subjecting machined and heat-treated steel, free from surface

decarburization, to the action of a nitrogenous

medium, usuallv ammonia gas, at a temperature of

about 930° to 1,000° F, whereby a very hard sur- face is obtained. The surface-hardening effect is due to the absorption of nitrogen and subseqeunt

heat treatment of the steel is unnecessary. The

time required is relatively long, normally being

1 or 2 da^'s. The case, even after 2 dsLjs of nitriding, is generally less than 0.020 in. and the highest

hardness exists in the surface layers to a depth of only a few thousandths of an inch.

Special low-alloy steels have been developed for

nitriding. These steels contain elements that

readily com.bine with nitrogen to form nitrides,

the most favorable being aluminum, chromium,

and vanadium. Molybdenum and nickel are used

in these steels to add strength and toughness. The

carbon content usually is about 0.20 to 0.50 percent, although in some steels, where high core hardness is essential, it may be as high as 1.3 percent.

Stainless steels also can be nitrided.

Because nitriding is carried out at a relatively

low temperature, it is advantageous to use quenched and tempered steel as the base material.

This gives a strong, tough core with an intensely

hard wear-resisting case—much harder, indeed,

than can be obtained by quench hardening either

carbm'ized or cyanided steel. Although warpage is not a problem during

nitriding, steels increase slightly in size during

this treatment. Allowance can be made for this growth in the finished article. Protection against

nitriding can be eft'ected by tin, copper, or bronze

plating, or by the application of certain paints.

5.6. Surface Hardening

It is frequently desirable to harden only the

surface of steels without altering the chemical

composition of the surface layers. If a steel contains sufficient carbon to respond to hardening, it

is possible to harden the surface layers only byvery rapid heating for a short period, thus conditioning the surface for hardening by quenching.

a. Induction Hardening

In induction hai'dening, a high-frequency cur- rent is passed through a coil surrounding the steel,

the surface layers of which are heated by electro548691—60 .3 15
magnetic induction. The depth to which the

heated zone extends depends on the frequency of

the current (the lower frequencies giving the

greater depths) and on the duration of the heating

cycle. The time required to heat the surface layers

to above the Acg is surprisingy brief, frequently

being a matter of only a few seconds. Selective

heating (and therefore hardening) is accomplished

by suitable design of the coils or inductor blocks.

At the end of the heating cycle, the steel is usually

quenched by water jets passing through the

inductor coils. Precise methods for controlling

the operation, that is, rate of energy input,

duration of heating, and rate of cooling, are necessary. These features are incorporated in induction hardening equipment, which is usually

entirely automatic in operation. Figure 20 shows

the hardened layer in induction hardened steel.

Figure 20. Macrograph of induction hardened gear teeth.

Original size, 4-in. diameter (Osborn).

b. Flame Hardening

Flame hardening is a process of heating the

surface layers of steel above the transformation

temperature by means of a high-temperature flame

and then quenching. In this process the gas flames

impinge directly on the steel surface to be hardened. The rate of heating is very rapid, although

not so fast as with induction heating. Plain

carbon steels are usually quenched by a water

spray, whereas the rate of cooling of alloy steels may be varied from a rapid water quench to a slow

air cool depending on the composition.

Any type of hardenable steel can be flame

hardened. For best results, the carbon content

should be at least 0.35 percent, the usual range

being 0.40 to 0.50 percent.

5.7. Special Treatments

a. Austempering

Austempering is a trade name for a patented

heat-treating process. Essentially, it consists of

heating steel to above the Acg transformation temperature and then quenching into a hot bath held

at a temperatm-e below that at which fine pearlite

would form (the nose of the S-curve, fi.g. 8), but

above the Mg temperature (fig. 10). The product

of isothermal decomposition of austenite in this temperature region is bainite. This constituent

combines relatively high toughness and hardness.

A typical microstructure of austempered steel is shown in figure 15, E.

Tlie austempering process has certain limitations

that make it impracticable for use with many

steels. In order to assure a uniform structure (and

hence uniform properties), it is essential that the

entire cross section of the steel be cooled rapidly

enough so that even the center escapes transformation at the nose of the S-curve. In carbon steels the time required to start transformation at the nose of the S-curve is extremely short, so that only

relatively small sections (about %-in. maximum

thickness) can be successfully hot quenched in austempering baths. The time required for trans- formation of the austenite of alloy steels to fine pearlite is usually longer, and hence larger sections can be successfully austempered (about 1 in. maximum). However, the time required for transformation to bainite frequently becomes

inordinately long with many alloy steels and the

process of austempering, therefore, is generally

impracticable for these steels.

b. Martempering

Martempering consists of heating a steel to above its Acs transformation and then quenching

into a bath held at a temperature approximately

equal to that of its Mg. The steel is maintained

in the hot bath until its temperature is essentially

uniform and then is cooled in air. Severe internal stresses develop in steel during

hardening. Steel contracts during cooling but

undergoes a marked expansion when the austenite

transforms to martensite. Since a quenched steel must cool from the surface inward, various portions transform at different times. The steel is thus subjected to a variety of differential expansions and contractions, resulting in considerable

internal stress. By equalizing the temperature

throughout the section before transformation takes

place, and then cooling slowly through the mar- .] tensite (M.,—-Mf) range, the internal stresses are i considerably reduced. This is the prime objective

of martempering.

c. Cold Treatment

The Mj temperature of many alloy steels is so low that complete transformation of austenite to martensite does not occur on quenching to room

16
temperature or on cooling after tempering. This

retained austenite may be partially or completely

transformed by cooling below atmospheric temperatm'es and such treatment is called "cold treat- ment." The beneficial effects of cold treatment

have not been fully explored. It is known that

the retained austenite of highly alloyed steels is frequently difficult to transform. Cooling these

steels to low temperatm'es (to the temperature of

solid CO2 or even lower) immediately after the

quench is sometimes efi'ective in transforming the

retained austenite, but with the concomitant danger of cracking. When the cold treatment is applied after tempering, the retained austenite is considerably more resistant to transformation. If cold treatment is used, the steel should always be

tempered afterwards.

Repeated alternate heating to a temperatm'e

slightly below that used in tempering and cooling

to a subzero temperature in a refrigerated iced

brine, carbon dioxide, liquid air, or lic|uid nitrogen

is commonly used for transforming the retained

austenite (dimensional stabilization) of steel gages, especially those of the ball-bearing type

composition (AISI 52100).

6. Hardenability

Hardenability is the property that determines

the depth and distribution of hardness induced in

steel by quenching. It is increased by increasing

carbon and by the addition of all the common alloying elements (except cobalt), provided that these

elements are completely dissolved in the austenite

at quenching temperatures. The elements most

frequently used for this purpose are manganese,

chromium, and molybdenum. Hardenability is also enhanced by increased grain size^ and homogeneity of the austenite. However, a coarse- grained austenite increases the tendency of a steel

to distort and crack durmg heat treatment.

Coarse-grained steels also are less tough than fine- grained steels. A clear distinction must be draum between the

maximum hardness obtainable m a steel and its hardenability. In straight carbon and low-alloy

steels, the maximum hardness is a function of car- bon content only (fig. 1.3), whereas hardenability

is concerned primarily with the depth of hardening.

Numerous methods have been proposed and

used for determining the hardenability of steel.

2 The grain size tliat influences hardenability is that grain size of the

austenite that exists at the quenching temperature. It is usually measured

unrler the microscope in terms of the number of grains per square inch at a

m;ignific;ition of XIOO. The common range of grain size numbers is as follows (note that the larger the number, the finer is the grain size; i.e., the more grains there are per square inch): Grain size no. (American Society for Grains/in.^ Testing Materials) at XIOO

1 = H to m 2 UA to 3

3 3 to 6

4 6 to 12

5 12 to 24

6 24 to 48

7 48 to 96

8 90 to 192 Numbers 3 and under are considered as coarse grain, numbers 4 and 5 as intermediate, and numbers 'j and higher as fine-grain steels.

The selection of a method depends largely upon

the information desired and the range in hardenability of the steels. For a fundamental study, hardenability is often

measured in terms of the critical cooling rate (fig. 9, B), but the standard end-quench (Joniiny) test

is widely used commercially. In the end-quench

test a bar of steel 1 ui. in diameter by 4 in. long,

previously normalized and machined to remove

the decarbm'ized surface, is heated to the hardening temperature for 30 min. It is then quickly

transferred to a fixture that holds the bar in a

vertical position and a jet of water under controlled conditions immediately is directed against

the bottom end only. The end of the bar is thus

cooled very quickly while cross sections remote

from the end are cooled more slowly, the rate of

cooling being dependent upon the distance from

the c^uenched end. After coolmg is completed, two

diametrically opposite flats about in. wide are ground the length of the bar and Rockwell hardness measurements are made at intervals of Ke. in. on the flat surfaces so prepared. The relationship of hardness to distance from the ciuenched

end is an indication of the hardenability (fig. 21).

The conditions of the end-quench test have been

standardized and the rates of cooling at various

distances from the quenched end have been determined and are shown at the top of figure 21. It is thus possible to correlate hardness with cooling

rate, which is a function of the distance from the

water-cooled end. The cooling rates at various

positions in different size rounds when quenched

in still oil and in still water also have been determined. Correlations can be made, therefore, between the hardness obtained at various positions on the end-quench bar and positions of equivalent

hardness of round bars quenched in still oil or water (assuming that points of equal hardness

COOLING RATE AT I300°F , °F/SEC

310 125 32 16 10.2 7.0 4.8 3.9 3.4 3.2 3.10

60

10

490|l95 55 ' 22 12.4 8.4 5.6 4.3 3.6 3.3 3.15

1 1 1 1 1 1 1 1

C

1 1 1 1

B

A

1 1 1

1

1 1 1 1 1 1 1

1 0 4 8 12 16 20 24 28 32 36 40

DISTANCE FROI«l QUENCHED END , 1/16 IN. Figure ,21. Hardenability ctirves for different steels with

the same carbon content.

A, Shallow hardening; B, intermediate hardening; C, deep hardening. The cooling rates shown in this figure are according to the results of Boegehold and Weinman, N.D.R.C. Report OSRD No. 3743, p. 42 (June 1, 1944).

17
have the same coohng rate). Figui'e 22 shows this

relationship between the distances on the endquenched bar and various locations for equivalent

hardnesses in round bars quenched in still oil; figiu"e 23 shows corresponding relations for bars

quenched in still water.

If the hardenability (end-quench) curve of a

steel is known, it is possible to ascertain from this curve and the curves given in figures 22 and 23

whether or not a selected size round made from

the steel will have a desired hardness at its surface,

% radius, K radius, or center, when quenched

either in still oil or water. Conversely, the hardness values as determined at various positions in rounds after quenching in oil or water can be used

to advantage in approximating the degree of hardenability of a steel suitable for replacement of

similar parts.

0 I— I \ \ 1

1 1 \ 1 1 1 0 2 4 6 8 10 12 14 16 18 20 22 24

DISTANCE FROM WATER QUENCHED END, I/I6IN. FiGUEE 22. Relation between distances on the end-quench

bar and various locations for equivalent hardnesses or cooling rates in ro\md bars quenched in still oil. (Metals Handbook, 1948 edition, p. 492.)

<

SURFACE / 3/4

ADIUS /}

^1/2 WDIUS J

/XENTER

O 2 4 6 8 10 12 14 16 18 20

DISTANCE'FROM WATER QUENCHED END. 1/16 IN. Figure 23. Relation between distances on the end-quench

bar and various locations for equivalent hardnesses or cooling rates in round bars quenched in still water.

(Metals Handbook, 1948 edition, p. 492.)

The standard end-quench test is most useful

for steels of moderate hardenability, that is, the

low-alloy steels. For shallow hardening steels,

such as plain carbon, a modification of this test (the L-type bar) is used.

7. Heat Treatment of Cast Irons

Cast irons are of three general types, gray, white,

and nodular. The terms gray and white are i descriptive of the characteristic appearances of the

fractures and nodular is descriptive of the shape of

the graphite particles.

In gray iron a large proportion of the carbon is present as graphitic or uncombined carbon m the

form of flakes. The small proportion of carbon

that is present as combined carbon or cementite I is in the form of pearlite just as in a steel. Depending on the amount of combined carbon, the

matrix of cast iron may be similar to a hypoeutectoid steel with varying amounts of free ferrite and

graphite flakes dispersed throughout (fig. 24, A,

B, and C). If the amount of combined carbon is about 0.8 percent, the matrix will be entirely

pearlitic ; if the amount is greater, the matrix will be similar to a hypereutectoid steel. In white iron most, if not all, of the carbon is present as cementite (fig. 24, D). The dividing

line between white and gray cast iron is not clearly

defined and irons possessing characteristics of both

are called mottled cast iron. Whether a cast iron will be gray or white depends on two factors—composition and rate of

cooling. Certain elements tend to promote the

formation of graphitic carbon; the most important of these are silicon, nickel, and sulfur. Others

tend to promote the formation of combined

carbon ; the most important of these are chromium,

molybdenum, vanadium, and manganese. Rapid

solidification and cooling, such as result from thin

sections cast in sand or larger sections cast against

chills, promote the formation of white iron. Iron

so produced is frequently termed chilled iron. ; Because of variations in the rate of solidification i and cooling, castings may be white at the surface

layers, mottled immediately below, and gray in the interior. In nodular cast iron, also known as "ductile

iron," "nodular graphite iron," "spherulitic iron,"

and "spheroidal graphite iron," the graphite is present in the form of nodules or spheroids (fig. 24, E and F). These nodules form during solid- ification due to the treatment of the molten u'on, just prior to casting, with a few hundredths percent

usually of either magnesium or cerium ; the sulfur I content must be below about 0.015 percent for ! the treatment to be effective with these elements.

Nodular iron and gray iron have the same total carbon content. The mechanical properties of

nodular iron can be varied by alloying.

Cast irons may be given a variety of heat ' treatments, depending on the compositions and

18
• ^ •

Figure 24. Microstructure of cast irons.

A, Gray iron. The dark flakes are graphite. XJnetched. XIOO.

B, Same as (A). Etched with picral. XIOO.

C, Same as fB). The matrix consists of pearlite with a small amount of free ferrite (white) and is similar to a hypoeuteetoid steel. The appearance of the graphite flakes is not affected by the etchant. X500. X50?'

iron. The white needles are cemcntite; the dark areas are pearlite; the dark spheroidal areas are the eutectlc (Ledeburite). Etched with picral. E, Nodular iron. The dark nodules are graphite; the white matrix is ferrite. Etched with picral. XIOO.

F, Pearlitic nodular iron. Xodular graphite (dark) in a pearlitic matrix. Etched with picral. XIOO. G, Malleable iron. The dark nodules are graphite; the white matrix is ferrite. Etched with picral. XIOO. H, Pearlitic malleable iron. Nodular graphite (dark) in a pearlitic matrix. Etched with picral. XIOO.

19
desired properties. The principles of the heat

treatments applied to cast iron are similar to those

already discussed for steels.

7.1. Relieving Residual Stresses (Aging)

The heat treatment that relieves residual stresses

is commonly called "aging," "normalizing," or "mild annealing;" the term "stress relieving" is more accurately descriptive. This treatment can be accomplished by heating the cast iron to between 800° and 1,100° F, holding at temperature

from 30 min. to 5 hr, the time depending on the

size and temperature, and cooling slowly in the

furnace. _ Such treatment will cause only a slight

decrease in hardness, very little decomposition of

cementite, and only a slight change in the strength

of the metal.

7.2. Annealing

Sometimes it is desirable to soften castmgs in order to facilitate machinmg. The temperature

range most commonly used for this purpose is 1,400° to 1,500° F, although temperatures as low

as 1,200° to 1,250° F have been used satisfactorily.

Highly alloyed irons are sometimes annealed at temperatures as high as 1,800° F. In all annealing, care should be taken to prevent oxidation of

the casting and coolmg should be slow.

In general, softenmg for machinability is ac- companied by a decrease in strength and in the

amount of combined carbon, and by an increase in graphite content. Irons that contain carbideforming elements (such as chromium, molybdenum, vanadium, and manganese) are more

resistant to softening than the ordinary gray iron

and, therefore, must be annealed at considerably

higher temperatures. Completely annealed ordinary gray cast iron has a Brinell hardness of 120

to 130, and completely annealed alloy irons may

have a Brmell hardness of 130 to 180, depending on the composition.

The matrix of nodular iron can be made completely ferritic by heating at 1,300° F for 1 to

5 hr, depending on composition, size of castmg,

and amount of pearlite in the as-cast structure; cooling from the annealmg temperature can be at any convenient rate. If massive or primary

carbides are present m the as-cast structure, they

may be converted to spheroidal graphite by

heating at 1,600° to 1,700° F for 1 to 5 hr. Slowly cooling from this temperature range to about 1,275° F and holding from 3 to 5 hr will convert the matrix to ferrite. Nodular iron with

a ferritic matrix has the desirable combination of

maximum machinability, toughness, and ductility.

The hardness of ferritic nodular iron varies with

the alloy content from a low of about 130 Brinell

to a high of about 210 Brinell.

a. Malleabilizing

Malleabilizing (also termed graphitizing) is a

process of annealing white cast iron m such a way

that the combined carbon is wholly or partly trans- formed to graphite in the nodular form (fig. 24,

G and H) instead of the flaky form that exists in gray cast iron. The nodular form of carbon is called temper or free carbon. In some instances,

part of the carbon is lost in the malleabilizing

process. White iron that is to be malleabilized should

contain all its carbon in the combined form. Any

carbon present as graphitic carbon (and hence in the form of flakes) will not be affected by the

graphitizmg treatment and is undesirable in the

final structure. The temperatures used in malleabilizing usually

range from about 1 ,500° to 1 ,650° F. Time at temperature is quite long, frequently being as much

as two to three days. Holdmg at this temperature

causes the decomposition of the cementite into

austenite plus rather rounded forms of graphite.

If the iron is then cooled very slowly through the

critical range (less than 10° F/hr), the resultant structure will consist of ferrite plus temper carbon.

Cooling less slowly through the transformation

range, or using an iron containing an alloying

element that retards graphitization, results in a

final product containing various amounts of pearlite plus ferrite with, of course, temper carbon. Irons having a pearlitic structure plus temper car- bon are known as pearlitic malleable irons (fig. 24,

H). As might be expected, pearlitic malleable

irons are susceptible to heat treatment in the same manner as steels.

7.3. Normalizing, Quenching, and Tempering

When heated to above the critical temperature

(line SK, fig. 3), cast iron consists of austenite

plus excess cementite or graphite and the austenite can be transformed in the same manner as in

steel. Although irons that are almost completely

graphitic (the common soft gray irons) can be

hardened, this is not customary. Such irons must

be held at temperatures well above the critical for long periods of tune in order to assure the solution

of carbon in the austenite.

For optimum results, the graphite flakes should

be small and uniformly distributed and the matrix

should be peaiiitic with not too much free ferrite (combined carbon from about 0.50 to 0.80%).

Castings should be heated uniformly to the quenchmg temperature, which usually ranges from 1,500°

to 1,600° F. The quenching medium commonly

used is oil; water is used to a limited extent and some alloy castings may be quenched in air. The

iron, as quenched, generally has a lower strength

than as cast, but the strength is increased by

tempering in the range of 350° to 1,200° F. Softening proceeds uniformly as the tempering

temperature is mcreased above about 350° to 1,200° F. A pearlitic matrix can be produced in nodular

iron as cast or by normalizing. The normalizing

treatment consists of heating to 1,600° to 1,650° F

20
holding at temperature for solution of carbon,

followed by cooling in air. The mechanical

properties of the normalized irons vary with the

composition, fineness, and amoimts of pearlite;

heavy sections are lower m hardness and higher

in ductility than light sections. The Brinell

hardness numbers range from about 200 to 275.

Martensitic or bainitic structures are produced

in nodular iron by quenching from 1,600° to 1,700° F m oil or water. The kons as quenched

have high strengths but low ductility. However,

the ductility of the as-quenched u'on can be

materially increased (strength and hardness decreased) by tempermg at about 1,000° to 1,300° F.

7.4. Special Heat Treatments

Subject to the same limitations as steels, cast

irons can be flame-hardened, mduction-hardened,

austempered, martempered, or nitrided.

8. Practical Considerations

Satisfactory heat treatment of steel (and iron)

requires fmnaces that have uniform controlled

temperatm'es, means for accm-ate temperatm^e

measurement, and for protecting the surface of the

material from scaling or decarburizing. Proper

quenching equipment is needed also.

8.1. Furnaces and Salt Baths

There are many different types and sizes of

furnaces used in heat treatment. As a general

rule, furnaces are designed to operate in certain

specific temperature ranges and attempted use in

other ranges frequently results in work of inferior

quality. In addition, using a furnace beyond its rated maximum temperature shortens its life and

may necessitate costly and time-consummg repau's.

Fuel-fired furnaces (gas or oil) recj[uire an- for proper combustion and an air compressor or blower is therefore a necessary adjunct. These

furnaces are usually of the muffle type, that is, the

combustion of the fuel takes place outside of and

around the chamber in which the work is placed.

If an open muffle is used, the furnace should be

designed so as to prevent the duect impingement

of flame on the work.

In furnaces heated by electricity the heating

elements are generally in the form of wire or ribbon. Good design requires incorporation of

additional heating elements at locations where

maximum heat loss may be expected. Such

furnaces commonly operate up to a maximum

temperature of about 2,000° F. Fm-naces operating at temperatures up to about 2,500° F usually

employ resistor bars of sintered carbides.

Furnaces intended primarily for tempering may

be heated by gas or electricity and are frequently

equipped with a fan for cuculating the hot air.

Salt baths are available for operating at either

tempering or hardening temperatures. Depending on the composition of the salt bath, heating can be conducted at temperatures as low as 325° F

to as high as 2,450° F. Lead baths can be used in

the temperature range of 650° to 1,700° F. The

rate of heating in lead or salt baths is much faster than in fm-naces.

a. Protective Atmospheres

It is often necessary or desirable to protect steel or cast ii'on from surface oxidation (scaling) and

loss of carbon from the surface layers (decarburization, fig. 15, F) . Commercial furnaces, therefore, are generally equipped with some means of

atmosphere control. This usually is in the form

of a bm'ner for burning controlled amounts of gas

and au" and directing the products of combustion

into the fmiiace muffle. Water vapor, a product of

this combustion, is detrunental and many furnaces

are equipped with a means for eliminating it. For

furnaces not equipped with atmosphere control, a variety of external atmosphere generators are

available. The gas so generated is piped into the

furnace and one generator may supply several

fm-naces. If no method of atmosphere control is available, some degree of protection may be

secured by covering the work with cast u-on borings or chips.

Since the work in salt or lead baths is surrounded

by the liquid heating medium, the problem of

preventing scaling or decarburization is simplified.

b. Temperature Measurement and Control

Accm-ate temperature measurement is essential

to good heat treating. The usual method is by means of thermocouples; the most common basemetal couples are copper-Constantan (up to about

700° F), iron-Constantan (up to about 1,400° F),

and Chromel-Alumel (up to about 2,200° F).

The most common noble-metal couples (which can be used up to about 2,800° F) are platinum

coupled with either the alloy 87 percent platinum—

13 percent rhodium or the alloy 90 percent

platinum—^10 percent rhodium. The temperatures quoted are for continuous operation.

The life of thermocouples is afl'ected by the

maximum temperature (which may frequently

exceed those given above) and by the furnace

atmosphere. Iron-Constantan is more suited for use in reducing and Chromel-Alumel in oxidizing

atmospheres. Thermocouples are usually encased

in metallic or ceramic tubes closed at the hot end

to protect them from the furnace gases. A

necessary adjunct is an instrument, such as a

millivoltmeter or potentiometer, for measuring the

electromotive force generated by the thermocouple.

In the interest of accurate control, the hot

junction of the thermocouple should be placed as

close to the work as possible. The use of an

automatic controller is valuable in controlling the

temperature at the desired value.

21
If temperature-measuring equipment is not

available, it becomes necessary to estimate temperatures by some other means. An inexpensive,

yet fairly accurate method involves the use of

commercial crayons, pellets, or paints that melt

at various temperatures witlain the range 125° to 1,600° F. The least accurate method of temperature estimation is by observation of the color

of the hot hearth of the furnace or of the work.

The heat colors observed are affected by many

factors, such as the conditions of artificial or natural light, the character of the scale on the

work, etc. Steel begins to appear dull red at about 1,000° F,

and as the temperature increases the color changes

gradually through various shades of red to orange, to yellow, and finally to white. A rough

approximation of the correspondence between

color and temperature is indicated in figure 25.

It is also possible to secure some idea of the

temperature of the piece of steel in the range used

for tempering from the color of the thin oxide film

that forms on the cleaned surface of the steel when

heated in this range. The approximate temperature-color relationship is indicated on the lower

portion of the scale in figure 25. Since steel becomes nonmagnetic on heating

through the A2 temperature, the proper annealing

and hardening temperature for medium and highcarbon steels can be estimated magnetically.

8.2. Quenching Media and Accessories

Quenching solutions act only through their

ability to cool the steel. They have no beneficial

chemical action on the quenched steel and in themselves impart no unusual properties. Most re- quirements for quenching media are met satis- factorily by water or aqueous solutions of inorganic

salts such as table salt or caustic soda, or by some

type of oil. The rate of cooling is relatively rapid

during quenching in brine, somewhat less rapid

in water, and slow in oil. Brine usually is made of a 5- to 10-percent solution of salt (sodium chloride) in water. In addition to its greater cooling speed, brine has the

ability to "throw" the scale from steel during

quenching. The cooling ability of both water and

brine, particularly water, is considerably affected

by their temperature. Both should be kept cold

well below 60° F. If the volume of steel being

quenched tends to raise the temperature of the

bath appreciably, the quenching bath should be

cooled by adding ice or by some means of

refrigeration.

There are many specially prepared quenching

oils on the market; their cooling rates do not vary

widely. A straight mineral oil with a Saybolt

viscosity of about 100 at 100° F is generally used.

Unlilce brine and water, the oils have the greatest

cooling velocity at a slightly elevated tempera2700

2600

Z 1400

2500

2400 1

2300

2200

2 100

2000 -

1900

1800

1700

1600

1500 -

1400

1300

1200

1100

100 0

-

900

800

700

600

50 0 -

1500

•c

— 1300

Color of

Hot Body

1200

1 100

1000

White

Yellow

900

800

— 700

— 600

Orange

Light Cherry

Full Cherry

Dork Cherry

Dark Red 500

400

Temper

Colors

300 Blue

Purple Brown 200 Strow

100

400

300

200

100

Figure 25. Temperature chart indicating conversion of Centrigrade to Fahrenheit or vice versa, color temperature

scale for hardening-temperature range, and temperingtemperature range.

22
tui-e—about 100° to 140° F—because of their

decreased viscosity at these temperatures.

Wlien steel is quenched, the liquid in immediate

contact with the hot surface vaporizes; this vapor

reduces the rate of heat abstraction markedly.

Vigorous agitation of the steel or the use of a

pressure spray c^uench is necessary to dislodge

these vapor films and thus permit the desired rate

of coohng.

Shallow hardeiiing steels, such as plain carbon

and certain varieties of alloy steels, have such a high critical coohng rate that they must be

quenched in brine or water to effect hardening.

In general, intricately shaped sections should not

be made of shallow liardening steels because of the

tendency of these steels to warp and crack during

hardening. Such items should be made of deeper

hardening steels capable of being hardened by

quenching in oU or air. A variety of different shapes and sizes of tongs

for handling hot steels is necessary. It should be

remembered that cooling of the area contacted by

the tongs is retarded and that such areas may not

harden, particularly if the steel being treated is very shallow hardening. Small parts may be

wired together or quenched in baskets made of

wire mesh.

Special quenching jigs and fixtures are fre- quently used to hold steels during quenching in a manner to restrain distortion.

When selective hardening is desired, portions of

the steel may be protected by covering with alundum cement or some other insulating material.

Selective hardening may be accomplished also by

the use of water or oil jets designed to direct the

quenching medium on the areas to be hardened.

This also is accomplished by the induction and

flame-hardening procedures previously described,

particularly on large production jobs.

8.3. Relation of Design to Heat Treatment

Internal strains arise from many causes, but the

most serious are those developed cluring quenching

by reason of differential cooling and from the

increase in volume that accompanies the martensitic transformation. These stresses are fre- quently sufficient to distort or crack the hardened

steel. Since temperature gradients are largely a

III function of the size and shape of the piece being

quenched, the basic principle of good design is to plan shapes that will keep the temperature gradient throughout a piece at a minimum during

j quenching.

Because of the abruptness in the change of

section, some shapes are impractical to harden,

without cracking or distortion, by quenching in

water, but a certain latitude in design is permissible

when using an oil-hardening or air-hardening steel

J K

Figure 26. Examples of good and bad designs from stand- point of hardening by heat treatment {Palmer and Luerssen, Tool steel simplified, p. 392, 1948).

A, End view of an undercutting form tool incorrectly designed. B, The same tool better designed from the viewpoint of heat treatment. Heavy sections have been lightened by drilling holes, thus insuring more

uniform cooling. The fillet at (a) minimizes danger of cracking at the sharp

re-entrant angle. Where a fillet is not allowable, treatment as shown at

(b) is helpful. C, Cracking will tend to occur at the sharp roots of the keyways. D, Fillets at the roots of the keyways will reduce the tendency toward

cracking. The incorporation of the two additional keyways, even though

uimecessary in actual service, helps balance the section and avoid warping.

E, A blanking die with the center rib heavier than the surrounding areas. This may cause warping on quenching.

F, The same die with holes drilled in the center rib to equaUze the amount

of metal throughout the die, thus eliminating warpage difficulties. G, A stem pinion with a keyway about one-half the diameter of the stem. The base of the keyway is extremely sharp, and the piece is further weakened by a hole drilled through the center of the stem near the keyway. The base

of the keyway should be filleted and hole re-located. H, A dangerous design consisting of a thin collar adjoining a thick section. When hardening such pieces, the thin section often warps or cracks at the junction with the hub. Extremely generous fillets and diiUing holes through

the hub to lighten its mass will be helpful.

J, When hardening, the concentration of strains at the junction of the two

holes in the center are apt to cause failure. Such holes should be plugged

before hardening. K, A blanking die poorly desig-ned. Crack will occur from point of fork prong to setscrew hole. The position of the setscrew hole should be changed

to eliminate cracking.

23
Other things being equal, temperature gradients

are much lower in shapes quenched in oil than in

water, and are still less in air. Thus a certain

design may be perfectly safe for one type of steel, or one type of coolant, and unsafe for another.

Errors in design reach farther than merely

affecting the internal strains during hardening.

A sharp angle or notch serves to greatly concentrate the stresses applied during service, and the

design of the part may be entirely responsible for concentrating the service stresses at a point

aheady weakened by internal strains produced

during hardening. Concentration of ser\^ice stresses frequently parallels coilcentration of heattreating strains and is frequently caused and cm'ed

by the same combination of chcumstances.

A part is properly designed, from a standpoint

of heat treatment, if the entire piece can be heated

and cooled at approximately the same rate dm-ing

the heat-treating operations. Perfection in this regard is unattainable because, even in a sphere,

the surface cools more rapidly than the interior. The designer should, however, attempt to shape

parts so that they will heat and cool as uniformly

as possible. The greater the temperatm^e differ- ence between any two points in a given part during

quenching, and the closer these two points are

together, the greater will be the internal strain

and, therefore, the poorer the design.

When large and small sections are unavoidable

in the same piece, the thick part frequently can be

lightened by drilling holes through it. Where

changes in section are eiicountered, angles should

be filletted generously. Some examples of poor

and good design are shown in figure 26.

9. Nomenclature and Chemical

Compositions of Steels

9.1. Structural Steels

In order to facilitate the discussion of steels, some familiarity with their nomenclature is desirable. A numerical index, sponsored by the Society of Automotive Engineers (SAE) and the American

Iron and Steel Institute (AISI), is used to identify

the chemical compositions of the structural steels. In this system, a four-numeral series is used to designate the plain carbon and alloy steels; five numerals are used to designate certain types of

alloy steels. The first two digits indicate the

type of steel, the second digit also generally (but

not always) gives the approximate amount of the

major alloying element and the last two (or tliree)

digits are intended to indicate the approximate

middle of the carbon range. However, a deviation from the rule of indicatmg the carbon range

is sometimes necessary.

The series designation and types are summarized

as follows:

Series designation Types lOxx Nonsulphurized carbon steels llxx Resulphuri-zed carbon steels (free machining)

12xx Rephosphorized and resulphurized carbon

steels (free machining)

13xx Manganese 1.75%

*23xx Nickel 3.50 %

*25xx Nickel 5.00%

31xx Nickel 1.25%, chromium 0.65%

33xx Nickel 3.50%, chromium 1.55%

40xx Molybdenum 0.20 or 0.25%

41xx Chromium 0.50 or 0.95%, molybdenum 0.12

or 0.20%

43xx Nickel 1.80%, chromium 0.50 or 0.80%,

molybdenum 0.25%

44xx Molybdenum 0.40%

45xx Molybdenum 0.52%. 46xx Nickel 1.80%, molybdenum 0.25%

47xx Nickel 1.05%, chromium 0.45%, molybde- num 0.20 or 0.35%

48xx Nickel 3.50%, molybdenum 0.25%

50xx Chromium 0.25, 0.40 or 0.50%

50xxx Carbon 1.00%, chromium 0.50%

51xx Chromium 0.80, 0.90, 0.95, or 1.00 %o 51xxx Carbon 1.00%, chromium 1.05%

52xxx Carbon 1.00%, chromium 1.45%

61xx Chromium 0.60, 0.80 or 0.95%, vanadium

0.12%, 0.10% min., or 0.15% min.

81xx Nickel 0.30%, chromium 0.40%, molybdenum 0.12%

86xx Nickel 0.55%, chromium 0.50%, molybdenum 0.20%

87xx Nickel 0.55%, chromium 0.50%, molybdenum 0.25%

88xx Nickel 0.55 %o, chromium 0.50%, molybdenum 0.35%

92xx Manganese 0.85%, silicon 2.00%, chromium

Oor 0.35%

93xx Nickel 3.25%, chromium 1.20%, molybdenum 0.12%

94xx Nickel 0.45%, chromium 0.40%, molybdenum 0.12%

98xx Nickel 1.00%, chromium 0.80%, molybdenum 0.25%

Not included in the current list of standard steels. Listings of the SAE-AISI type numbers and

chemical composition limits of the standard and

tentative standard structural steels (complete as I of February 1960) are given in table 1. The SAE i' numbers are the same as the AISI numbers, except

that the latter may be given a letter prefix to in- dicate the method of manufacture. These prefixes and their meanings are as follows: B denotes

acid bessemer carbon steel, C denotes basic open

hearth or basic electric furnace carbon steels, E

denotes electric furnace alloy steels. Small quantities of certain elements are present

in alloy steels that are not specified as required.

These elements are considered as incidental and

may be present to the maximum amounts as I' follows: copper, 0.35 percent; nickel, 0.25 percent;

chromium, 0.20 percent; molybdenum, 0.06 percent.

24
The list of standard steels is altered from time to time to accommodate steels of proven merit and

to provide for changes in the metallm-gical and

engineering requirements of industry.

Alany of the alloy structm-al steels are manufactm'ed to meet certain specified limits in hardenability as determmed by the standard end-quecnh

test. Such steels, table 2, are designated by the

letter "H" following the SAE-AISI number. The

chemical composition limits of these steels have

been modified somewhat from the ranges or limits

applicable to the same grades when specified by

chemical composition only. The hardenability of an "H" steel is guaranteed by the manufacturer

to fall within a hardenability band having maximum and minimum limits as shown by two limiting hardenability curves for that particular

steel.

Table 1. Composition limits of standard steels NONEESULPHURIZED CARBON STEELS "

Designation number Chemical composition limits, percent Designation number Chemical composition limits, percent

AISI SAE C Mn P(max) S(max) AISI SAE C Mn P(max) S(max)

C 1008 1008 0. 10 max 0. 25/0. 50 0.040 0. 050 C 1039 1039 0. 37/0. 44 0. 70/1.00 0.040 0. 0.50 C 1010 1010 .08/0.13 . 30/0. 60 .040 .050 C 1040 1040 . 37/0. 44 . 60/0. 90 .040 .050 C 1011 . 08/0. 13 . 60'0. 90 .040 .050 C 1041 1041 . 36/0. 44 1. 35/1. 65 .040 .050 C 1012 1012 . 10/0. 15 . 30/0. 60 .040 .050 C 1042 1042 . 40/0. 47 0. 60/0. 90 .040 .050 C 1015 1015 . 13/0. 18 . 30/0. 60 .040 .050 C 1043 1043 . 40/0. 47 . 70/1. 00 .040 .050 C 1016 1016 . 13/0. 18 . 60/0. 90 .040 .050 C 1045 1045 . 43/0. 50 . 60/0. 90 .040 .050 C 1017 1017 . 15/0. 20 . 30/0. 60 .040 .050 C 1046 1046 . 43/0. 50 . 70/1. 00 .040 .050 C 1018 1018 . 15/0. 20 . 60/0. 90 .040 .050 C 1048 1048 . 44/0. 52 ]. 10/1.40 .040 .050 C 1019 1019 . 15/0. 20 . 70/1. 00 .040 .050 C 1049 1049 . 46/0. 53 . fiO/0. 90 .040 .050 C 1020 1020 . 18/0. 23 . 30/0. 60 .040 .050 C 1050 1050 . 48/0. 55 . 60/0. 90 .040 .050 C 1021 1021 . 18/0. 23 . 60/0. 90 .040 .050 C 1051 . 45/0. 56 . 85/1. 15 .040 .050 C 1022 1022 . 18/0. 23 .70/1.00 .040 .050 C 1052 1052" . 47/0. 55 1. 20/1. 50 .040 .050 C 1023 1023 . 20/0. 25 . 30/0. 60 .040 .050 C 1053 . 48/0. 55 0. 70/1. 00 .040 .050 C 1024 1024 . 19/0. 25 1. 35/1. 65 .040 .050 C 1055 1055 . 50/0. 60 . 60/0. 90 .040 .050 C 1025 1025 . 22/0. 28 0. 30/0. 60 .040 .050 C 1060 1060 . 56/0, 65 . 60/0. 90 .040 .050 C 1026 1026 . 22/0. 28 . 60/0. 90 .040 .050 C 1070 1070 . 65/0. 75 . 60/0. 90 .040 .050 C 1027 1027 . 22/0. 29 1. 20/1. 50 .040 .050 C 1078 1078 . 72/0. 85 . 30/0. 60 .040 .050 C 1029 . 25/0. 31 0. 60/0. 90 .040 .050 C 1080 1080 . 75/0. 88 . 60/0. 90 .040 .060 C 1030 1030 . 28/0. 34 . 60/0. 90 .040 .050 C 1084 1084 . 80/0. 93 . 60/0. 90 .040 .050 C 1031 . 28/0. 34 . 30/0. 60 .040 .050 C 1085 1085 . 80/0. 93 . 70/1. 00 .040 .060 C 1033 1033 . 30/0. 36 . 70/1. 00 .040 .050 C 1086 1086 . 80/0. 93 . 30/0. 50 .040 .060 C 1035 1035 . 32/0. 38 . 60/0. 90 .040 .050 C 1090 1090 . 85/0. 98 . 60/0. 90 .040 .060 C 1036 1036 . 30/0. 37 1. 20/1. 50 .040 .050 C 1095 1095 . 90/1. 03 . 30/0. 50 .040 .060 C 1037 1037 . 32/0. 38 0. 70/1. 00 .040 .050 C 1038 1038 . 35/0. 42 . 60/0. 90 .040 .050

RESULPHURIZED CARBON STEELS b

Designation number Chemical composition limits, percent Designation number Chemical composition limits, percent

AISI SAE C Mn P(max) S AISI SAE C Mn P(ma.\) s

C 1108 1108 0. 08/0. 13 0. 50/0. 80 0. 040 0. 08/0. 13 C 1126 1126 0. 23/0. 29 0. 70/1. 00 0. 040 0. 08/0. 13 C 1109 1109 . 08/0. 13 . 60/0. 90 .040 . 08/0. 13 C 1132 1132 . 27/0. 34 1. 35/1. 65 .040 . 08/0. 13 C 1110 . 08/0. 13 . 30/0. 60 .040 . 08/0. 13 C 1137 1137 . 32/0. 39 1.35/1.66 .040 . 08/0. 13 C 1113 . 10/0. 16 1.00/1.30 .040 . 24/0. 33 C 1138 1138 . 34/0. 40 0. 70/1. 00 .040 . 08/0. 13 C 1115 1115 . 13/0. 18 0. 60/0. 90 .040 . 08/0. 13 C 1139 1139 . 35/0. 43 1.35/1.65 .040 . 12/0. 20 C 1116 1116 . 14/0. 20 1. 10/1.40 .040 . 16/0. 23 C 1140 1140 . 37/0. 44 0. 70/1. 00 .040 . 08/0. 13 C 1117 1117 . 14/0. 20 1.00/1.30 .040 . 08/0. 13 C 1141 1141 . 37/0. 45 1.35/1.66 .040 . 08/0. 13 C 1118 1118 . 14/0. 20 1.30/1.60 .040 . 08/0. 13 C 1144 1144 . 40/0. 48 1.36/1.66 .040 . 24/0. 33 C 1119 1119 . 14/0. 20 1.00/1.30 .040 .24/0. 33 C 1146 1145 . 42/0. 49 0. 70/1. 00 .040 . 04/0. 07 C 1120 1120 . 18/0. 23 0. 70/1. 00 .040 . 08/0. 13 C 1146 1146 . 42/0. 49 . 70/1. 00 .040 . 08/0. 13 C 1125 . 22/0. 28 . 60/0. 90 .040 . 08/0. 13 C 1151 1151 . 48/0. 65 . 70/1. 00 .040 . 08/0. 13

ACID BESSEMER RESULPHURIZED CARBON STEEL"

Designation number Chemical composition limits, percent

AISI SAE C Mn P S

B nil nil 0. 13 max 0. 60/0. 90 0. 07/0. 12 0. 08/0. 16 B 1112 1112 . 13 max . 70/1. 00 . 07/0. 12 . 16/0. 23 B 1113 1113 . 13 max . 70/1. 00 . 07/0. 12 . 24/0. 33

REPHOSPHORIZED AND RESULPHURIZED CARBON STEELS ^

Designation numljer Chemical composition limits, percent

AISI SAE C Mn P S

C 1211 nil 0. 13 max 0. 60/0. 90 0. 07/0. 12 0. 08/0. 15 C 1212 1112 .13 max . 70/1. 00 . 07/0. 12 . 16/0. 23 C 1213 1113 . 13 max . 70/1. 00 . 07/0. 12 . 24/0. 33 *C 12L14 12L14 . 16 max .80/1.20 . 04/0. 09 . 25/0. 35

*Lead=0J.5/0.35 percent. See footnotes at end ol table.

il

25
Table 1. Composition limits of standard steels—Continued

OPEN HEARTH AND ELECTRIC FURNACE ALLOY STEELS »

Designation number Chemical composition limits, percent

AISI SAE C Mn P (max) S (max) Si

1330 1330 0. 28/0. 33 1.60/1 90 0. 040 0. 040 0. 20/0. 35

1335 1335 . 33/0. 38 1. 60/1. 90 .040 .040 . 20/0. 35 1340 1340 . 38/0. 43 1. 60/1. 90 .040 .040 . 20/0. 35

1345 1345 . 43/0. 48 1. 60/1. 90 .040 .040 . 20/0. 35

3140 3140 . 38/0. 43 0. 70/0. 90 . 040 . 040 . 20/0. 35 E 3310 3310 . 08/0. 13 . 45/0. 60 .026 .026 . 20/0. 35

4012 4012 . 09/0. 14 . 75/1. 00 .040 .040 . 20/0. 36 4023 4023 . 20/0. 25 . 70/0. 90 .040 .040 . 20/0. 35 4024 4024 . 20/0. 25 . 70/0. 90 . 040 *. 036/. 050 . 20/0. 35 4027 4027 . 25/0. 30 . 70/0. 90 .040 .040 , 20/0. 35 4028 4028 . 25/0. 30 . 70/0. 90 .040 *. 035/. 050 . 20/0. 35 4037 4037 . 35/0. 40

. 70/0. 90 . 040 .040 . 20/0. 35 4042 4042 . 40/0. 45 . 70/0. 90 . 040 . 040 . 20/0. 35 4047 4047 '. 45/o! 50 ] 70/0. 90 .040 !040 '. 20/0. 36 4063 4063 . 60/0. 67 . 75/1. 00 .040 .040 . 20/0. 35

4118 4118 . 18/0. 23 . 70/0. 90 .040 .040 . 20/0. 35 4130 4130 . 28/0. 33 . 40/0. 60 .040 .040 . 20/0. 35 4135 4135 . 33/0. 38 . 70/0. 90 . 040 040 20/0. 36 4137 4137 '. 35/o! 40 '. 70/0. 90 .040 .040 '. 20/0. 35 4140 4140 . 38/0. 43 .75/1.00 .040 .040 . 20/0. 35 4142 4142 .40/0.45 . 75/1.00 . 040 . 040 20/0. 35 4145 4145 '. 43/o! 48 '. 76/1. 00 .040 .040 '. 20/0. 35 4147 4147 . 45/0. 50 76/1 00 . 040 . 040 . 20/0. 35 4150 4150 '. 4810. 53 '. 75/L 00 !040 !040 '. 20/o! 35

4320 4320 . 17/0. 22 . 45/0. 65 .040 .040 . 20/0. 35 4337 4337 . 35/0. 40 . 60/0. 80 .040 .040 . 20/0. 35 E 4337 . 35/0. 40 . 65/0. 85 . 025 . 025 . 20/0. 35 4340 4340 '. 38/o! 43 ! 60/o! 80 !040 .'040 '. 20/o'. 35 E 4340 E 4340 . 38/0. 43 . 65/0. 85 .026 .025 . 20/0. 35

4422 4422 . 20/0. 25 . 70/0. 90 .040 .040 . 20/0. 36 4427 4427 . 24/0. 29 . 70/0. 90 .040 .040 . 20/0. 35

4520 4520 . 18/0. 23 . 45/0. 65 . 040 . 040 20/0. 36

4615 4615 . 13/0. 18 .46/0. 65 .040 .040 . 20/0. 35 4617 4617 . lU/U. . 45/0. 65 . 040 . 040 90/0 3'i 4620 4620 . 17/0. 22 '. 45/o! 66 !040 !040 . 20/0. 36 4621 4621 . 18/0. 23 . 70/0. 90 .040 .040 . 20/0. 35

4718 4718 . 16/0. 21 . 70/0. 90 .040 .040 . 20/0. 35 4720 4720 . 17/0. 22 . 50/0. 70 .040 .040 . 20/0. 36

4815 4816 . 13/0. 18 . 40/0. 60 .040 .040 . 20/0. 35

4817 4817 . 16/0. 20 . 40/0. 60 .040 .040 . 20/0. 36 4820 4820 . 18/0. 23 . 50/0. 70 .040 .040 . 20/0. 36

5015 6015 . 12/0. 17 . 30/0. 50 .040 .040 . 20/0. 35 5046 5046 . 76/1. 00 . 040 . 040 . ZU/U. 90/0 oo^5

5115 5116 .13/0.18 . 70/0. 90 .040 .040 . 20/0. 35

5120 5120 .17/0.22 . 70/0. 90 .040 .040 . 20/0. 35

5130 5130 . 9S/n ^o/u. oo 70/0 QO , 040 . 040 on/A 5132 6132 . 30/0. 35 . 60/0. 80 !040 ]040 . 20/0. 35 5135 5135 . 33/0. 38 . 60/0. 80 .040 .040 . 20/0. 35

5140 5140 . 38/0. 43 . 70/0. 90 .040 .040 . 20/0. 35 5145 5145 . 43/0. 48 . 70/0. 90 . 040 040 . 90/0 ^u/u. oo 5147 5147 '. 46/o! 52 '. 70/0. 95 !040 !040 . 20/0. 35

5150 70/0 QO . 040 040 9n /n ^ . zu/u. oo

5165 5156 . 60/0. 60 . 70/0. 90 !040 ]040 . 20/0. 35

5160 5160 . 65/0. 65 .75/1.00 .040 .040 . 20/0. 35 E 50100 50100 . 96/1. 10 . 25/0. 45 .025 .025 . 20/0. 35 E 51100 61100 . 96/1. 10 . 25/0. 45 .026 .025 . 20/0. 35 E 52100 62100 . 96/1. 10 . 26/0. 46 .026 .025 . 20/0. 35

6118 6118 . 16/0. 21 . 50/0. 70 .040 .040 . 20/0. 36

6120 6120 . 17/0. 22 . 70/0. 90 .040 .040 . 20/0. 36 6150 6150 . 48/0. 63 . 70/0. 90 .040 .040 . 20/0. 36

8115 8116 . 13/0. 18 . 70/0. 90 .040 .040 . 20/0. 36

8615 8616 . 13/0. 18 . 70/0. 90 .040 .040 . 20/0. 36

8617 8617 . 15/0. 20 . 70/0. 90 .040 .040 . 20/0. 35

8620 8620 . 18/0. 23 . 70/0. 90 .040 .040 . 20/0. 35 8622 8622 . 20/0. 25 . 70/0. 90 .040 .040 . 20/0. 35 8625 8625 . 23/0. 28 . 70/0. 90 .040 .040 . 20/0. 36 8627 8627 . 2.5/0. 30 . 70/0. 90 .040 .040 . 20/0. 36

8630 8630 . 28/0. 33 . 70/0. 90 .040 .040 . 20/0. 35

8637 8637 . 36/0. 40 . 75/1. 00 .040 .040 . 20/0. 35 8640 8640 . 38/0. 43 .75/1.00 .040 .040 . 20/0. 35 8642 8642 . 40/0. 45 .75/1.00 .040 .040 . 20/0. 36

8645 8646 . 43/0. 48 . 75/1. 00 .040 .040 . 20/0. 35

8660 8660 . 48/0. 53 . 75/1. 00 .040 .040 . 20/0. 35 8656 8665 . 50/0. 60 . 75/1. 00 .040 .040 . 20/0. 35 8660 8660 . 55/0. 65 .75/1.00. .040 .040 . 20/0. 35

Ni Cr Mo

1. 10/1. 40

3. 25/3. 76

1. 66/2. 00

1. 66/2. 00

1. 65/2. 00

1. 66/2. 00

1. 65/2. 00

1. 65/2. 00

1. 6.5/2. 00

1. 65/2. 00

1. 65/2. 00

0. 90/1. 20

. 90/1. 20

3. 26/3. 76

3. 25/3. 75

3. 25/3. 75

0. 20/0. 40

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

0. 55/0. 75

1. 40/1. 75

0. 40/0. 60

. 80/1. 10

. 80/1. 10

. 80/1. 10

. 80/1. 00

. 80/1. 10

. 80/1. 10

. 80/1. 10

. 80/1. 10

40/0. 60

70/0. 90

70/0. 90

70/0. 90

70/0. 90

. 35/0. 55

. 35/0. 66

.30/0 50

. 20/0 35

.70/0 90

.70/0 90

.80/1 10 .75/1 00

.80/1 05

.70/0 90

.70/0 90

.85/1 15 .70/0 90

.70/0 90

.70/0 90

.40/0 60

.90/1 15

1.30/1 60

.60/0 70

.70/0 90

.80/1 10

.30/0 60

.40/0 60

.40/0 60

.40/0 60

.40/0 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

0. 15/0. 25

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 08/0. 15

. 15/0. 26

. 16/0. 25

. 15/0. 25

. 15/0. 26

. 15/0. 26

. 15/0. 25

. 16/0. 26

. 15/0. 26

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 36/0. 45

. 35/0. 45

. 45/0. 60

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 30/0. 40

. 16/0. 26

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 08/0. 16

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 26

. 15/0. 26

. 15/0. 26

. 16/0. 25

. 16/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 16/0. 25

,15/0.25

See footnotes at end of table. 26
Table 1. Composition limits of standard steels—Continued

OPEN HEARTH AND ELECTRIC FURNACE ALLOY STEELS «—Continued

Designation number Chemical composition limits, percent

Aisr SAE Mn P (max) S (max) Ni Cr Mo

8720 8735

8740

8742

8822

9255

9260

9262 E 9310

9840 9850

8720

8740

8742

8822

9255

9260

9262

9310

9840

9850

0. 18/0. 23

. 33/0. 38

. 38/0. 43

. 40/0. 45

. 20/0. 25

. 50/0. 60

. 55/0. 65

. 55/0. 65

. 08/0. 13

. 38/0. 43

. 48/0. 53

0. 70/0. 90

.75/1.00

.75/1.00

. 75/1. 00

. 75/1. 00

. 70/0. 95

. 70/1. 00

.75/1.00

. 45/0. 65

. 70/0. 90

. 70/0. 90

0.040

.040

.040 .040

.040

.040

.040 .040

.025

.040

.040

0.040

.040 .040

.040

.040

.040

.040 .040

.025

.040

.040

0. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

1.80/2.20 1.80/2.20

1. 80/2. 20

0. 20/0. 35

. 20/0. 35

. 20/0. 35

0. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

. 40/0. 70

3. 00/3. 50

0. 85/1. 15

.85/1.15

0. 40/0. 60

. 40/0. 60

. 40/0. 60

. 40/0. 60

.40/0.60

.25/0.40

1. 00/1. 40

0. 70/0. 90

. 70/0. 90

0. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 30/0. 40

.08/0.15

. 20/0. 30

. 20/0. 30

BORON STEELS »

These steels can be expected to have 0.0005 percent minimum boron content.

Designation number Chemical composition limits, percent

AISI SAE Mn P (max) S (max) Ni Cr Mo

50B40

50B44 oOB46

.5OB50 50B60 51B60

81B45 86B45

94B15

94B17

94B30

94B40

50B40

50B44

50B46

50B50

50B60 51B60 81B45

86B45

94B15

94B17

94B30

94B40

0. 38/0. 43

. 43/0. 48

. 43/0. 50

. 48/0. 53

. 55/0. 65

. 55/0. 65

. 43/0. 48

. 43/0. 48

. 13/0. 18

. 15/0. 20

. 28/0. 33

. 38/0. 43

0. 75/1. 00

. 75/1. 00

. 75/1. 00

.75/1.00

. 75/1. 00

.75/1.00

. 75/1. 00

. 75/1. 00

. 75/1. 00

. 75/1. 00

.75/1.00

. 75/1. 00

0.040

.040

.040

.040

.040

.040

.040

.040

.040 .040

.040

.040

0.040

.040 .040

.040

.040

.040

.040

.040

.040

.040

.040

.040

0. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

.20/0.35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

0. 20/0. 40

. 40/0. 70

. 30/0. 60

. 30/0. 60

. 30/0. 60

.30/0.60

0. 40/0. 60

. 40/0. 60

. 20/0. 35

. 40/0. 60

. 40/0. 60

. 70/0. 90

. 35/0. 55

. 40/0. 60

. 30/0. 50

. 30/0. 50

. 30/0. 50

. 30/0. 50

0. 08/0. 15

. 15/0. 25

. 08/0, 15

. 08/0. 15

. 08/0. 15

. 08/0. 15

NITRIDING STEEL «

Designation number Chemical composition ranges and limits, percent

AISI SAE C Mn P (max) S (max) Si AI Cr Mo V

0. 38/0. 43 0. 50/0. 70 0.040 0. 040 0. 20/0. 40 0. 95/1. 30 1. 40/1. 80 0. 30/0. 40

» SUicon: When silicon is required, the following ranges and limits are com- monly used: Standard steel designations Silicon ranges or limits Up to C 1015 excl 0.10% max. C 1015 to C 1025 incl 0.10% max, 0.10/0.20%, or 0.15/0.30% Over C 1025 0.10/0.207o or 0.15/0.30% Copper: When required, copper is specified as an added element to a stand- ard steel. Lead: When required, lead is specified as an added element to a standard

steel.

^ Silicon: When sUicon is required, the following ranges and limits are commonly used: Standard steel designations SiUcon ranges or limits Up to C 1113 excl 0.10% max.

C1113 and over 0.10%, max, 0.10/0.20%, or 0.15/0.30%. Lead: When required, lead is specified as an added element to a stand- ard steel.

" Silicon: Because of the technological nature of the process, acid bessemer

steels are not produced with specified silicon content. Lead: When required, lead is specified as an added element to a stand- ard steel. —

^ Silicon: It is not common practice to produce these steels to specified

limits for silicon. Lead: When required, lead is specified as an added element to a stand- ard steel.

" Grades shown in the above list with prefix letter E generally are manufactured by the basic electric furnace process. All others are normally manufactured by the basic open hearth process but may be manufactured by the basic electric furnace process with adjustments in phosphorus and

sulphur. The phosphorus and sulphur limitations for each process are as follows: Basic electric furnace 0.025 maximum percent Basic open hearth 0.040 maximum percent Acid electric furnace 0.050 maximum percent Acid open hearth _-- 0.050 maximum percent Minimum silicon limit for acid open hearth or acid electric furnace alloy

steel is 0.15 percent. Small quantities of certain elements are present in aUoy steels which are not

specified or required. These elements are considered as incidental and may,

be present to the following maximum amounts: Copper, 0.35 percent; nickel

0.25 percent; chromium, 0.20 percent, and molybdenum, 0.06 percent. Where minimum and maximum sulphur content is shown it is indicative

of resulpliurized steels.

27
Table 2. Standard H-steels OPEN HEARTH AND ELECTRIC FURNACE STEELS

Designation number Chemical composition limits, percent

AISI

1330 H

1335 H

1340 H

3140 H

3310 H

4027 H

*4028 H

4037 H

4042 H

4047 H

4063 H

4118 H

4130 H

4135 H

4137 H

4140 H

4142 H

4145 H

4147 H

4150 H

4320 H

4337 H

4340 H

E4340 H

4520 H

4620 H

4621 H

4718 H

4720 H

4815 H

4817 H

4820 H

5046 H

5120 H

5130 H

5132 H

5135 H

5140 H

5145 H

5147 H

5160 H

5155 H

5160 H

6118 H

6120 H

6150 H

8617 H

8620 H

8622 H

8625 H

8627 H

8630 H

8637 H

8640 H

8642 H

8645 H

8650 H

8655 H

8660 H

8720 H

8740 H

8742 H

8822 H

9260 H

9262 H

9310 H

9840 H

9850 H

SAE

1330 H

1335 H

1340 H

3140 H

3310 H

4027 H

*4028 H

4037 H

4042 H

4047 H

4063 H

4118 H

4130 H

4135 H

4137 H

4140 H

4142 H

4145 H

4147 H

4150 H

4320 H

4337 H

4340 H

E4340 H

4520 H

4620 H

4621 H

4718 H

4720 H

4815 H

4817 H

4820 H

5046 H

5120 H

5130 H

5132 H

5135 H

5140 H

5145 H

5147 H

5150 H

5155 H

5160 H

6118 H

6120 H

6150 H

8617 H

8620 H

8622 H

8625 H

8627 H

8630 H

8637 H

8640 H

8642 H

8645 H

8650 H

8655 H

8660 H

8720 H

8740 H

8742 H

8822 H

9260 H

9262 H

9310 H

9840 H

9850 H

0. 27/0. 33

. 32/0. 38

. 37/0. 44

.37/0. 44

. 07/0. 13

. 24/0. 30

. 24/0. 30

. 34/0. 41

. 39/0. 46

. 44/0. 51

. 59/0. 69

. 17/0. 23

. 27 '0. 33

. 32/0. 38

. 34/0. 41

. 37/0. 44

. 39/0. 46

. 42/0. 49

. 44/0. 51

. 47/0. 54

. 17/0. 23

. 34/0. 41

. 37/0. 44

. 37/0. 44

. 17/0. 23

. 17/0. 23

. 17/0. 23

. 15/0. 21

. 17/0. 23

. 12/0. 18

.14/0. 20

. 17/0. 23

. 43/0. 50

. 17/0. 23

. 27/0. 33

. 29/0. 35

. 32/0. 38

. 37/0. 44

. 42/0. 49

. 45/0. 52

. 47/0. 54

. 50/0. 60

. 55/0. 65

. 15/0. 21

. 17/0. 23

. 47/0. 54

. 14/0. 20

. 17/0. 23

. 19/0. 25

. 22/0. 28

. 24/0. 30

. 27/0. 33

. 34/0. 41

. 37/0. 44

. 39/0. 46

. 42/0. 49

. 47/0. 54

. 50/0. 60

. 55/0. 65

. 17/0. 23

. 37/0. 44

. 39/0. 46

. 19/0. 25

. 55/0. 65

. 55/0. 65

. 07/0. 13

. 37/0. 44

. 47/0. 54

Mn

1. 45/2. 05

1. 45/2. 05

1. 45/2. 05

0. 60/1. 00

. 30/0. 70

. 60/1. 00

. 60/1. 00

. 60/1. 00

. 60/1. 00

. 60/1. 00

. 65/1. 10 .60/LOO

. 30/0. 70

. 60/1. 00

. 60/1. 00

. 65/1. 10

. 65/1. 10 .65/1.10

. 65/1. 10

. 65/1. 10

. 40/0. 70

. 55/0. 90

. 55/0. 90

. 60/0. 95

. 35/0. 75

. 35/0. 75

. 60/1. 00

. 60/0. 95

. 45/0. 75

. 30/0. 70

. 30/0. 70

. 40/0. 80

. 65/1. 10

. 60/1. 00

. 60/1. 00

. 50/0. 90

. 50/0. 90

.60/1.00

. 60/1. 00

. 60/1. 05

. 60/1. 00

. 60/1. 00

. 65/1. 10

. 40/0. 80

. 60/1. 00

.60/1.00

. 60/0. 95

. 60/0. 95

. 60/0. 95

. 60/0. 95

. 60/0. 95

. 60/0. 95

.70/1.05

.70/1.05

. 70/1. 05

.70/1.05

.70/1.05

. 70/1. 05

.70/1.05

. 60/0. 95

. 70/1. 05

. 70/1. 05

. 70/1. 05

. 65/1. 10

. 65/1. 10

. 40/0. 70

. 60/0. 95

. 60/0. 95

0. 20/0. 35

. 20/0. 35

. 20/0. 35

.20/0.35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

.20/0.35

.20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

.20/0.35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20/0. 35

1. 70/2. 20

1. 70/2. 20

0. 20/0. 35

. 20/0. 35

. 20/0. 35

Ni

1.00/1.45

3. 20/3. 80

1. 55/2. 00

1. 55/2. 00

1. 55/2. 00

1. 55/2. 00

1. 55/2. 00

1. 55/2. 00

0. 85/1.25

0. 85/1. 25

3. 20/3. 80

3. 20/3. 80

3. 20/3. 80

0. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 65

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

. 35/0. 75

2. 95/3. 55

0. 80/1. 20

. 80/1. 20

Cr

0. 45/0. 85

1. 30/1. 80

0. 30/0 70

.75/1 20

.75/1 20

.75/1 20

.75/1 20

.75/1 20

.75/1 20

.75/1 20

.75/1 20

.35/0 65

. 65/0. 95

.65/0 95

.65/0 95

Mo

. 30/0. 60

. 30/0. 60

. 13/0. 43

. 60/1. 00

. 75/1. 20

. 65/1. 10

. 70/1. 15 .60/1.00

. 60/1. 00

. 80/1. 25

. 60/1. 00

. 60/1. 00

. 60/1. 00

. 40/0. 80

. 60/1. 00

. 75/1. 20

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 35/0. 65

. 20/0. 50

1. 00/1. 45

0. 65/0. 95

. 65/0. 95

0. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 08/0. 15

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 45/0. 60

. 20/0. 30

. 20/0. 30

. 30/0. 40

. 15/0. 25

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 15/0. 25

. 20/0. 30

. 20/0. 30

. 20/0. 30

. 30/0. 40

. 08/0. 15

. 20/0. 30

. 20/0. 30

See footnote at end of table.

28
Table 2. Standard H-steels—Continued

BORON H-STEELS

These steels can be expected to hare 0.0005 percent minimum boron content

Designation number Chemical composition limits, percent

AISI SAE Mn Ni Cr Mo

5'1B40 H

50B44 H

5l)B46 H

oiiBoO H

.511B6O H

51B60 H

81B45 H

s<:,B45 H

94B15 H

94B17 H

94B30 H

94B40 H

S0B40 H

50B44 H

50B46 H

50B50 H

50B60 H

51B60 H

81B45 H

86B45 H

94B15 H

94B17 H

94B30 H

94B40 H

0. 37/0. 44

. 42/0. 49

. 43/0. 50

. 47/0. 54

. 55/0. 65

. 55/0. 65

. 42/0. 49

. 42/0. 49

. 12/0. 18

. 14/0. 20

. 27/0. 33

. 37/0. 44

0. 65/1. 10

. 65/1. 10

. 65/1. 10

. 65/1. 10

. 65/1. 10

. 65/1. 10

.70/1.05

.70/1.05

.70/1.05

. 70/1. 05

. 70/1. 05

. 70/1. 05

0. 20/0. 35

. 20/0. 35

. 20/0. 35

. 20'0. 35

. 20/0. 35

. 20/0. 35

.20/0.35

.20/0. 35

.20/0.35

. 20/0. 35

. 20/0. 35

. 20/0. 35

0. 15/0. 45

. 35/0. 75

.25/0. 65

. 25/0. 65

. 25/0. 65

. 25/0. 65

0. 30/0. 70

. 30/0. 70

. 13/0. 43

. 30/0. 70

. 30/0. 70

. 60/1. 00

.30/0.60

. 35/0. 65

. 25/0. 55

. 25/0. 55

. 25/0. 55

. 25/0. 55

0. 08/0. 15

. 15/0. 26

. 08/0. 15

. 08/0. 15

.08/0. 15

. 08/0. 15

•Sulphur content 0.03.5/0.0.50 percent.

Tlie phosphorus and sulphur limitations for each steelmaking process are

as follows: Basic electric furnace .--0.026 percent ma.\imum

Basic open hearth 0.040 percent ma.xiraum Acid electric furnace 0.050 percent ma.ximum

Acid open hearth 0.050 percent maximum.

Minimum silicon limit for acid open hearth or acid electric furnace alloy

steel is 0.15 percent. Small quantities of certain elements are present in alloy steels which are not specified or required. These elements are considered as incidental and may be present to the following maximum amounts: Copper, 0.35 percent;

nickel, 0.25 percent; chromium, 0.20 percent; and molybdenum, 0.06 percent.

9.2. Tool Steels

Technically, any steel used as a tool may be

termed a tool steel. Practically, however, the term

is restricted to steels of special composition that

are usually melted in electric furnaces and manufactm-ed expressly for certain types of services.

The current commonly used tool steels have

been classified by the American Iron and Steel

Institute into six major groups and each commonly

accepted group or subgroup has been assigned an

alphabetical letter. Methods of quenching, applications, special characteristics, and steels for particular industries were considered in this type

classification of tool steels which is as follows:

Group Symbol and type Water hardening- - W

Shock resisting S

rO—-Oil hardening

Cold work < A—Medium alloy

[T>—High carbon—high chromium

Hot work H— (H 1 to H 19 incl. chromium base, H 20 to H 39 incl. tungsten

base, H 40 to H 59 incl. molybdenum base)

TT- ; „ , f T—Tungsten base High speed |M-Mol?bdenum base

f L—-Low alloy

Special purpose < F—^Carbon tungsten

[ P—Mold steels (P 1 to P 19 incl. low carbon, P 20 to P .39 incl. other types)

The AISI identification and type classification of tool steels is given in table 3. Each major

group, identified by a letter symbol, may contain

Table 3.

Identification and type classification of tool steels

Desig- nationIdentifying elements, percent AISI C Mn Si Cr Ni v W Mo Co WATER HARDENING

Wl

W2

W3

W4

W5

W6

W7

"0.60/1.40 ".60/1.40

1.00

".60/1.40

1.10 1.00

1.00

0.25

.50 0.25

.60

.25 .50

.26 .20

SHOCK RESISTING

SIS2

S3

S4S5

0.50

.50 .50 .55

.55

1.50 2.60 1.00 0.50 0.75 1.00 0.80

.80 2.00

2.00 .40

COLD WORK; OIL HARDENING

0102

06

07

0.90

.90

1.46

1.20

1.00

1.60 0.50 0.60

1.00 0.25

.75 1.75

COLD WORK; MEDIUM ALLOY AIR HARDENING

A2A4

A5A6

A7

1.00

1.00 1.00 0.70

2. 25

5. 00

1.00

1.00

1.00

5.25

1.00

1.00

1.00

1.00

1.00

2.00

3.00

2.00

4. 75 bl.OO

See footnotes at end of table.

29
Table 3. Identification and type classification of tool steels—-Continued

Desig- nation

Identifying elements, percent Desig- nation

Identifying elements, percent AISI C Mn Si Cr Ni V W Mo Co

AISI C Mn Si Cr Ni V W Mo Co COLD WORK; HIGH CARBON—HIGH CHROMIUM

DlD2

D3

D4

D5D6

D7

1.00 1.50

2. 25 2.25

1.50

2. 25

2. 35

12.00

12.00

12.00

12.00 12.00

12.00

12.00

1.00

1.00

1.00

1.00 3.00

1.00 1.00 4.00 1.00 HOT WORK; CHROMIUM BASE

HU

H12

H13 H14

H15 H16

0. 35 .35

.35

.40

.40

.55

5.00

5.00

5.00

5.00

5.00

7.00

0.40

.40 1.00

1.50

1.50 1.501.50

5.00

5. 00

7.00 HOT WORK; TUNGSTEN BASE

H20

H21 H22 H23

H24 H25

H26

0. 35

.35 .35

.30 .45

.25

.50

2.00

3.50

2. 00

12. 00

3.00

4.00

4.00

9.00

9.00

11.00

12.00

15. 00

15.00 1.00 18. 00 HOT WORK; MOLYBDENUM BASE

H41 H42

H43

0.65

.60 .55

4.00

4.00

4.00

1.00

2. 00

2.00

1.50

6.00

8.00

5.00 8.00 HIGH SPEED; TUNGSTEN BASE

TlT2

T3

T4

T5

T6

T7T8

T9

T15

0.70

.80

1.05 0.75

.80

.80

.75

.75 1.20

1.50

4.00 4.00

4.00

4.00

4. 00

4.50

4.00 4.00

4.00 4.00

1.00

2. 00

3.00

1.00 2.00

1.50 2.00

2.00

4.00

5. 00

18.00

18. 00

18.00 18.00 18.00

20.00

14.00

14.00

18.00

12. 00

5. 00

8. 00

12.00

5.00

5. 00

a number of individual types that are identified

by a suffix number following the letter symbol.

The percentages of the elements shown in the table

for each type are not to be considered as the mean

of the composition ranges of the elements. Steels

of the same type, manufactured by various producers, may differ in analysis from the values

listed and may contain elements not listed in the

type identification.

9.3. Stainless and Heat Resisting Steels

The stainless and heat resisting steels possess

relatively high resistance to oxidation and to at- tack by corrosive media at room and elevated

temperatures and they are produced to cover wide

ranges in mechanical and physical properties.

They are melted exclusively by the electric furnace

process. A three-numeral system is used to identify

stainless and heat resisting steels by type and

according to four general classes. The first digit

indicates the class and last two digits indicate

HIGH SPEED; MOLYBDENUM BASE

Ml 0. 80 M2 .80 M3 LOO M4 L30 M6 0. 80 M7 1.00 M8 ° 0.80 MIO .85 M15 1, 50 M30 0.80 M33 .90 M34 .90 M35 .80 M36 .80

4. 00

4. 00

4. 00

4. 00

4. 00

4. 00

4. 00

4. 00

4. 00

4,00

3. 75 4.00

4. 00

4. 00

1.00

2. 00

2. 70 4.00

1.50 2.00

1.50

2. 00

5.00 L25

1.15

2. 00

2.00

2. 00

1.50

6. 00

6. 00

5.50 4.00

1.75

5. 00

6. 50 2.00 L 50

2. 00

6. 00

6.00

8. 00

5. 00

5. 00

4. 50 5.00

8. 75

5. 00

8. 00

3. 50 8.00

9. 50

8. 00

5.00

5. 00

12. OO

5. 00

5. 00

8.00

8. 00

5. 00

8.00

SPECIAL PURPOSE; LOW ALLOY

LIL2

L3

L4

L5

L6

L7

1.00

1 0. 50/1. 10 1.00 L 00

1.00

0. 70 1.00

0. 60 1.00

0. 35

1.25 1.00

1.50

1. 50 1.00 0.75

1.40

0.20

.20

.25

0. 25

b. 25 .40

1. 50

SPECIAL PURPOSE; CARBON TUNGSTEN

Flr2r31.00

1.25

1.25

1. 25

3. 50 0.75 3. 50

SPECIAL PURPOSE: MOLD STEELS—LOW CARBON

PIP2

P3

P4

P5

P6

0.10

.07

.10 .07

.10

.10

2. 00

0. 60

5. 00

2. 25 1.50

0. 50

1.25 0.20

3.50

SPECIAL PURPOSE; MOLD STEELS—OTHER TYPES

P20 0. 30 0.75 0. 25

I "Varying carbon contents may be available. bAt producer's option. •Cb, 1.2.5%.

type. Modification of types are indicated by

suffix letters. The meaning of this AISI system

is as follows:

Series designation Classes 2xx Chromium-nickel-manganese steels; nonhardenable, austenitic and nonmagnetic

3xx Chromium-nickel steels; nonhardenable,

austenitic and nonmagnetic

4xx Chromium steels; hardenable, martensitic and magnetic

4xx Chromium steels; nonhardenable, ferritic and magnetic

5xx Chromium steels; low chromium heat resist- ing.

The chemical composition ranges and liniits of

the standard stainless and heat resisting steels are given in table 4.

10. Recommended Heat Treatments

10.1. Structural Steels

A listing of recommended heat treatments for many of the steels listed in tables 1 and 2 are given

in tables 5 and 6. Treatments for the standard ,

30
C3 =3 aa

ilM

oo

; IS ss Nlli iii

If

gg ggggg

SS still

sssss sssss sssss mil iiiit iiiit

--•=22 d223S S^^^^

ss SSSgg sssss sssss sssss sssss sssss sssss ss

^^^^^ S2i:2?j ??'S'3;'?32 22£'iSS ddddsj SSSS?? -^-^ Ifffi iifif Ifill Iiiit

88 SSSSS SSSSS sssss SSSSS sssss sssss sssss ss

„-^_:m-; d ^^^^^

ii iiili iiiii iiiii iiiii iiiil iiifi iiiii §§

ii iisss gsifg iiiii iiiii iiiii essee iiiii ii

I

SS sssss sssss sssss sssss sssss ?5ssss5 sssss ss

r-"d (NciciN^i c^cNriricii cificsriN !NCM>i^ri ^-Jrt^-; ^I^-^-J^- ^-^^-^-^

ii iiiii MM IMM IMi MM iiiii iSiSi ii

ss sssss sssss g^SSS sssss sssss S|S£;3 SSSig te2 0= ' 0°

m mm mm MM hmi -iiiss isill mih si
Table 5. Recommended heat treatments for carburizing grade steels

AISI or SAE number

1008 to 1024; 1108 to 1120; 1211 to 1214.

_

3310.

4012 to 4024; 4118.

4422 and 4427; 8822.

4520.

4320; 4615 to 4621; 4718 and 4720.

4815 to 4820.

5015; 5115 and 5120..

6118 and 6120.

8115; 8615 to 8622; 8720; 8822; 9310; 94B15 and 94B17.

Carbuiizing temperature

1, 650/1, 700

1, 650/1, 700

1, 650/1, 700

1, 650/1, 700

1,650/1, 700

1, 650/1, 700

1, 650/1, 700

1, 650/1, 700

1, 650/1, 700

1, 650/1, 700

Cooling method

Brine or water . Water or oil Cool slowly

....do

Oil ....do Cool slowly.

....do

Oil ....do Cool slowlv.

....do

Oil ...-do Cool slowly. ....do

Oil .-..do Cool slowly.

.....do

Oil ...-do Cool slowlv. ....do OU

...-do Cool slowly. .do

Oil .-..do Cool slowly.

....do

Oil ....do. Cool slowly. ....do OU

....do Cool slowly- ....do

Reheat

1, 400/1, 450

1, 400/1, 450

1, 650/1, 700

1, 375/1, 425

1, 375/1, 425

1, 525/1, 575

1, 425/1, 475

1,425/1,475

, 1, 600/1, 650

1, 450/1, 500

1, 450/1, 500

1, 625/1, 675

1, 475/1, 525

1, 475/1, 525

1, 650/1, 700

1, 425/1, 475

1, 375/1, 425

1, 525/1, 575

1, 350/1, 400

1, 350/1, 400

1, 550/1, 600

1, 425/1, 475

1, 425/1, 475

1, 600/1, 650

1, 450/1, 500

1, 450/1, 500

1, 600/1, 650

1, 450/1, 500

1, 450/1, 500

1, 550/1, 600

Cooling medium 2d reheat Cooling medium

Brine or water. do Water or oil

OU.

.do. .do.

OU.

.do.

.do.

OU.

.do.

.do.

OU.

.do.

.do.

OU.

.do. .do.

OU.

.do.

.do.

OU.

.do.

-doOil or water. do

OU...

OU.

.do.,

.do..

1,400/1,450

1, 375/1, 425

1, 425/1, 475

1, 450/1, 500

1, 475/1, 525

1, 375/1, 425

1, 350/1, 400

1, 425/1, 475

1, 450/1, 500

1,450/1,500

Brine or water.

Oil.

OU.

OU.

OU.

OU.

OU.

OU.

Oil or water.

OU.

Tempering

temperature

° F

250/300

250/300

250/300

250/300

250/300

250/300

250/300

250/300

300/400

250/300

Ml

Table 6. Recommended heat treatments for heat treating grade steels

(No tempering treatments are given, as these temperatures depend upon the desired hardness)

AISI or Normalizing Annealing Hardening Quenching AISI or Normalizing Armealing Hardening Quenching

lllj SAE temperature temperature temperatui'e medium SAE temperatui-e temperature temperature medium to number number

0 p "F "F op op op

1030 1,626/1,725 1,525/1,575 1,550/1,600 Water or brine. 6046 1,600/1,700 1,476/1,525 1,500/1,560 OU.

1040 1,600/1,700 1,476/1,526 1,500/1,550 Do. 5130 1,600/1,700 1,600/1,660 1,550/1,600 Oil or water.

1050 1,550/1,650 1,450/1,500 1,475/1,525 Do. 6146 1,600/1,700 1,475/1,526 1,626/1,575 OU.

' llD 1060 1,500/1,600 1,425/1,475 1,460/1,600 Do. 6160 1,600/1,700 1,450/1,500 1,600/1,650 Do.

1070 1, 500/1 600 1,425/1,475 1,450/1,500 Do. 50100 1,600/1,700 1,400/1,450 1,450/1,600 Do.

«f 1080 1,475/1,575 1,375/1,425 1,400/1,460 Do. 51100 1,600/1,700 1,400/1,450 1,476/1,525 Do.

1090 1,475/1,575 1,375/1,425 1,400/1,450 Do. 52100 1,600/1,700 1,400/1,450 1,500/1,550 Do. ' (T 1132 1,625/1,725 1,526/1.575 1,550/1,600 Do. 6160 1,600/1,700 1,500/1,550 1 , 650/1, 600 Do.

1140 1,600/1,700 1,475/1,525 1,600/1,660 Do. 8630 1,600/1,700 1,500/1,550 1,626/1,575 Do. ill 1151 1,550/1,650 1,460/1,500 1,475/1,525 Do. 8646 1, 600/1, 700 1,476/1,525 1,600/1,650 Do.

Pl 1330 1,600/1,700 1,500/1,550 1,525/1,676 Oil or water. 8660 1,600/1,700 1,450/1,500 1,475/1,525 Do. «il 1340 1,550/1,650 1,476/1,626 1,500/1,550 Do. 8735 1,660/1,700 1,500/1,550 1,526/1,575 Do.

a 3140 1,650/1,650 1,475/1,525 1,475/1,525 OU. 8742 1,600/1,700 1,600/1,650 1,525/1,575 Do.

4028 1,600/1,700 1,525/1,575 1,550/1,600 OU or water. 9260 1,600/1,700 1,500/1,660 1,550/1,600 Do. to 4042 1,550/1,660 1,475/1,625 1,600/1,560 Oil. 9840 1,600/1,700 1,476/1,626 1,500/1,560 Do. 1 9860 1,600/1,700 1,475/1,525 1,500/1,550 Do. ' ki 4063 1,550/1,650 1,450/1,500 1,475/1,525 Do.

4130 1,600/1,700 1,525/1,575 1, 560/1, 600 Oil or water. us 4140 1,600/1,700 1,500/1,550 1, 626/1, 676 Oil. ([ 4150 1,600/1,700 1,475/1,525 1,600/1,650 Do.

to

s

4340 1,600/1,700 1,600/1,650 1,500/1,550 Do.

steels that are omitted can be estimated by interpolation (also see fig. 11). Where different

quenching media are suggested, the smaller sec32

tions may harden satisfactorily in the slower

quenching medium. The upper end of the heat

treating ranges should always be used for large
I size sections. The inclusion of normalizing and

annealing temperatm-es does not imply that these

treatments are necessarily a prelude to hardening.

For hardening, the general rule is to place the

cold steel in a fui'nace containing a slightly oxidizing atmosphere or neutral salt bath at the hardening temperature and let it heat natmally, hold

hx/'m of thickness, and then quench; it is sometimes

advisable to warm intricate sections or complex

shapes before putting them into the high temperatui'e unit and to remove fi'om the quenching

medium while still warm. Usually, the quenched

piece should be allowed to cool until it can be

comfortably held in the bare hand and then immediately tempered. To minimize cracking, it is sometimes desirable to temper the quenched piece

before it reaches room temperatm-e ; a double temper (i.e., repeating the treatment) is recommended

for this condition.

For carburizing, most of the steels may be given

either (1) a single, (2) double, or (3) triple treat- ment as is indicated in table 5. The time at the

carburizing temperature will vary depending upon

the temperature used and the desired thickness of

the case. The relation between time, temperature and case depth is illustrated m figm'e 19.

10.2. Tool Steels

Recommended heat treatments for the different

types of tool steels are summarized in table 7. The time the steel is at the normalizing temperature, after being heated uniformly through, varies

from about 15 min for a small section to about 1 hr for large sizes; cooling from the normalizing

temperature is in still air. For annealing, the

upper range in temperatm-e is recommended for

large and the lower limit for small sections. The

time the steel is at the annealing temperature,

after being heated uniformly through, ranges from

about 1 hr for thin sections of carbon or low alloy

to about 4 hr for heavy sections of high alloy

steel. Cooling from the annealmg temperatiire

through the transformation range should not ex- ceed about 75° F/hr for the carbon and low alloy

and 50° F/hr for the high alloy steels. For hardening, the protective atmosphere, rate

of heating, hardening temperature, time at temperature, and rate of cooling vary with the composition of the steels. A general rule is to heat the

plain carbon and low alloy steels rapidly m a fiu"- nace having a slightly oxidizing atmosphere or in a neutral salt bath at the hardening temperature,

hold K hr/in of thickness, and then quench. The

high alloy steels, such as the T and M types, are usually preheated to minimize distortion and

cracking and then heated rapidly in a furnace

containing a highly carburizing atmosphere or in a molten bath at the hardening temperature, held

at temperature for time as indicated in the table,

and then quenched. Tools should be tempered

immediately after quenching; a double temper is recommended for the high alloy steels.

The carbm'izing steels (type P) may be (1) quenched dhectly from the carburizing temperatm*e; (2) quenched directly from the carburizing

temperature followed by quenching from the

recommended hardening temperature; (3) slowly

cooled from the carburizing temperature followed

by quenching from the recommended hardening

temperatm*e; or (4) slowly cooled from the car- bmizing temperature, reheated to the carburizing

temperature and quenched, followed by reheating to and quenching from the recommended hardening

temperatm-e. For most pm-poses, method (3) is generally suitable. Tempering should follow in

all cases.

10.3. Stainless and Heat Resisting Steels

The response of stainless and heat resistihg

steels to heat treatment depends upon their composition. The general methods employed are

similar to those used with other steels and no

special equipment is needed. Heat treatment

may be performed in any conventional electric,

gas fired, oil fired, salt bath, or induction furnace

in which the requhed temperatures can be

obtained. Precautions should be taken to avoid

exposure of the steel to the direct flame of the

burners. Conditions that will result in carburization of the surface of the steel should be avoided.

In general, oxidizing furnace atmospheres are

preferred. Bright, scale-free heat treatment is possible by the use of specially prepared and

controlled atmospheres.

The stainless steels may be divided into three

general groups 'as follows:

a. Group I—Hardenable Chromium Steels (Martensitic

and Magnetic)

These steels respond to heat treatment in a manner similar to most lower alloy steels and will,

by suitable thermal treatment, develop a wide

range of mechanical properties. The tempering

range of 700° to 1000° F. should be avoided

because it is conducive to increased brittleness.

b. Group II—Nonhardenable Chromium Steels (Ferritic and Magnetic)

These steels are essentially nonhardenable by

heat treatment. They develop their maximum

softness, ductility and corrosion resistance in the

annealed condition.

c. Group III—Nonhardenable Chromium-Nickel and

Ghromium-Nickel-Manganese Steels (Austenitic and

Nonmagnetic)

These steels are essentially nonmagnetic and

cannot be hardened by heat treatment. Cold

working develops a wide range of mechanical

properties and some of these steels, in the severely

cold worked condition, may become slightly

magnetic. They are annealed by rapidly cooling

(air or water) from high temperatures to develop

maximum softness and ductility as well as corrosion resistance.

Recommended heat treatments for the steels listed in table 4 are given in table 8.

33
Table 7. Recommended heat treatments for tool steels

Normalizing

temperature

Annealing

Temperature

Brinell hardness number

Hardening

Preheating temperature Quenching

temperature Quenchingmedium

Tempering

Temperature

o p

1,450/1, 700

1,450/1, 700 »

1, 450/1, 700 »

1, 450/1, 700 ^

1, 450/1, 700 > 1,450/1,700"

1, 450/1, 700 >

(«) C)

. Col

(")

1, 500/1, 600

1, 500/1, 550

1, 600/1, 650

1,600/1,650

600/1,650

600/1, 650

600/1,650

600/1, 650

600/1, 650

600/1, 650

600/1, 650

1, 375/1, 450

1, 400/1, 450

1,400/1,450

1,375/1,450

1, 400/1, 450

1, 400/1, 450

1, 400/1, 450

1, 450/1, 500

1, 400/1, 450

1, 450/1, 600

1, 400/1, 450

1, 400/1, 450

1, 400/1, 450

1,375/1,425

1, 400/1, 450

1, 450/1, 500

1,550/1,600

1, 350/1, 400

1, 350/1, 400

1, 350/1, 375

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 550/1, 650

1, 550/1, 650

1, 550/1, 650

1, 600/1, 650

1, 550/1, 600

1,600/1,650

1,600/1,650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1,600/1,650

1, 600/1, 650

1, 500/1, 600

1,550/1,650

1, 500/1,600

1,600/1,650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1, 600/1, 650

1,500/1,600

1,600/1,650

1,600/1,650 1,600/1,650

1, 500/1, 600

1, 500/1, 600

1,550/1,600

1, 500/1, 600

1,600/1,650

1,600/1,650

1,600/1,650

1,600/1,650

1,600/1,660 1,600/1,650

1, 426/1, 475

1, 400/1, 450

1, 450/1, 500

1,425/1,475

1,425/1,475

1, 400/1, 450

1,450/1,500

(BHN)

169/202 169/202

163/202

169/202 163/202

163/202

163/202

183/229

192/217

183/212

192/229

192/229

183/212

183/212

183/217

192/217

202/229

200/241

228/265

217/248

235/262

207/248

217/255

217/255

217/265 223/256

217/255

235/262

192/229

192/229

192/229 207/236

207/229

212/241 207/236

207/235

207/235 213/255

217/241 207/236

217/241 207/235

207/235

207/235

217/255

223/255

229/269

229/269

235/275

248/293 217/256

229/255

235/277 241/277

207/235

212/241 223/255

223/255

248/277 217/255

217/241 207/236

241/277

236/269 236/269 235/269

235/269

235/269

179/207

163/196

174/201

179/207 183/223

183/212

183/212

o p

(•>) m

C)

(")

C")

C-)

('')

(•>) 1, 100/1, 200

1, 100/1, 200

1, 100/1, 200

1, 300/1, 400

1, 100/1, 200

1,100/1,200

1, 100/1, 200

1, 100/1, 200

1,360/1,450

1, 150/1, 250

1, 100/1, 200

1, 100/1, 200

1, 400/1, 500

1,400/1,500

1, 400/1, 600

1, 400/1, 500

1, 400/1, 500

1, 400/1, 500

1, 400/1, 500

1, 400/1, 500

1, 400/1, 600

1, 400/1, 500

1, 400/1, 500

1, 400/1, 500

1, 600/1, 600

1, 500/1, 600

1,600/1,600

1, 500/1, 600

1, 500/1, 600

1, 600/1, 600

1,500/1,600

1, 500/1, 600

1, 600/1, 600

1, 360/1, 650

1, 360/1, 650

1, 360/1, 650

1, 500/1, 600

1, 500/1, 600

1, 500/1, 600

1, 500/1, 600

1, 600/1, 600

1, 500/1, 600

1, 500/1, 600

1, 500/1, 600

1, 500/1, 600

1, 600/1, 600

1, 350/1, 550

1, 350/1, 550

1, 350/i, 550

1, 350/1, 550

1, 400/1, 600

1,350/1, 650

1, 400/1, 650

1, 350/1, 550

1, 500/1, 600

1,350/1,550

1, 360/1, 550

1, 350/1, 550

1, 350/1, 550

1, 350/1, 550

(")

C-)

C')

(")

(") C)

(")

o p

1, 426/1, 475

1, 450/1, 500

1, 450/1, 500

1, 425/1, 475

1, 425/1, 475

1, 450/1, 500

1, 450/1, 500

1, 650/1, 800

<l 1,550/1,650

1, 500/1, 600

/<i 1,600/1,700 V 1, 650/1, 750

<i 1, 600/1, 700

1, 450/1, 500

"i 1, 400/1, 476

<i 1, 450/1, 500

fl, 450/1, 525

11, 650/1, 625

1, 700/1, 800

1, 600/1, 600

1, 450/1, 650

1, 525/1, 600

1, 750/1, 800

1,775/1,850

1, 800/1, 875

1,700/1,800

1, 776/1, 860

1, 800/1, 875

1, 700/1, 750

1, 850/1, 950

1, 825/1, 875

1,825/1,875

1, 825/1, 900

I, 850/1, 950

2, 100/2, 300

<! 2, 050/2, 160

e 2, 000/2, 200

e 2, 000/2, 200

' 2, 000/2, 200

e 2, 200/2, 325

< 2, 000/2, 250

' 2, 100/2,300

e 2, 150/2, 300

d 2, 000/2, 175

i

2, 050/2, 225

2, 000/2, 175

» 2, 300/2, 375

e 2, 300/2, 375

0 2, 250/2, 326

' 2, 300/2, 375

< 2, 325/2, 400

e 2, 325/2, 400

" 2, 300/2, 350

< 2, 300/2, 375

« 2, 275/2, 325

« 2, 200/2, 300

e 2, 150/2, 225

e 2, 176/2, 250

e 2, 200/2, 250

o 2, 200/2, 250

« 2, 150/2, 200

s 2, 150/2, 240

' 2, 200/2, 300

e 2, 150/2, 225

e 2, 175/2, 250

2, 200/2, 250

« 2, 200/2, 250

' 2, 200/2, 250

" 2, 225/2, 275

« 2, 225/2, 275

1, 450/1, 550

II, 450/1, 550

11, 560/1,700

fl, 426/1, 500 U, 500/1, 600

1,475/1,600

1,450/1,600

1, 450/1, 560

1, 500/1, 600

Brine or water. do

-dodo

do

do

do

Oil Brine or water. -..do —_do Oil.—

_.._do

Oil .__.do- ___.do. WaterOil

Air..-do.

.do.

-do. .do.

Air..

Oil.

Air..

-do.

OilAir.,

.doAir -- do

do

do

Air, or oil do

do

do

do- do

do .- doAir, oil, or salt- do

do

do —

Oil, au-, or salt. dodo

dodo- - do

.do

.do

-do - -do

Oil, air, or salt- do

dodo

do .—

do- .-

-do

.do

.do .do - .do -do

-do. -do

Oil or water.. Water

Oil Water

Oil Oil or water.

Oil do

do

o p

300/650

300/650

300/660 300/660

300/650

300/650

300/660

400/1, 200

300/800 300'600

350/800

350/800

300/500

300/500 300/600

325/550

350/1. 000

300/800

300/800

300/800

300/1, 000

400/1,000

400/1, 000

400/1, 000

400/1, 000

400/1, 000

400/1, 000

300/1, 000

000/1, 200

000/1, 200

000/1, 200

100/1, 200

100/1, 200

050/1, 250

100/1,250

100/1, 250

100/1, 250

200/1, 500

050/1. 200

050/1, 260

050/1, 250

050/1, 200

050/1, 200

050/1, 200

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100 000/1,100

000/1,200

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

000/1, 200

000/1,100

000/1, 100

000/1, 100

000/1, 100

000/1, 100

300/600

300/1, 000

300/600

300/600

300/600

300/1, 000

300/600 See footnotes at end of table.

34
Table 7. Recommended heat treatments for tool steels—Continued

AISI

type

N'ormalizing temperature

Annealing Hardening Tempering

Temperature

Brinell hardness numberPreheating temperature Quenching

temperature Quenchingmedium Temperature

Rockwell

hardness number

FlF2F3

" F

1, 600/1, 650

1, 600/1, 650

1,600/1,650

o p

1,400/1,475

1,450/1,500

1, 450/1, 500

{BHN)

183/207

207/235

212/248

° F

1, 100/1, 200

1, 100/1, 200

1, 100/1, 200

o p

1, 500/1, 600

1,500/1.600

1, 500/1, 600

Water or brine.

° F

300/500

300/500

300/500

(Rc)

64/60

66/62

66/62 do Water, brtue, or oil

CARBURIZIN-Q GRADES

AISI

type

ISTormalizing temperature

Annealing

Carburizing temperature

Hardening Tempering

Temperature Hardness Temperature Quenching medium Temperature Rc of case op ° F (BHIST) 0 p ° F ° p

PI 1. 350/1, 650 81/100 1, 650/1, 700 1,450/1,475 Water or brine -„ 300/500 64/58 P2 1, 350/1. .500 103/123 1, 650/1, 700 1.525/1,550 Oil 300/500 64/58 P3 1, 350/1, .500 109/137 1, 650/1, 700 1, 475/1. 525 do 300/500 64/58 P4 1,600/1.650 116/128 1, 775/1, 825 1, 775/1, 825 Air - 300/500 64/58 P5 1, 550/1.600 105/110 1, 650/1, 700 1, 550/1, 600 Oil or water 300/500 64/58 P6 1. 550/1, 600 190/210 1, 650/1. 700 1, 4.50/1, 500 Oil 300/450 61/58 P20 1625 to 1675 1, 400/1, 450 150/180 1,600/1,650 1, 500/1, 600 do 300/500 64/58

' N'ormalizing:

0.60 to 0.75% C, 1500° F;

.75 to .90% C, 1450° F;

.90 to 1.10% C, 1600° F;

1.10 to 1.40% C, 1600° to 1700° F.

j Preheating not necfessary.

» Do not normalize.

^ Do not soalv.

e Time at hardening temperature, 2 to 5 min.

' Double tempering recommended,

e Normalizing not required.

Table 8. Recommended heat treatments for stainless and heat resisting steels GROUP I. HARDENABLE CHROMIUM STEELS (MARTENSITIC AND MAGNETIC)

AISI

Annealing » Hardening i> Stress relieving Tempering

type Temperature Hardness Temperature Hardness Temperature Hardness Temperature Hardness

403

410

414

416 416 Se

420

431 440 A

440 B

440 C

.501

"F

1..5.50;1,650

1. .5,50/1. 6.50

= 1, 200/1, 300

1, .5.50/1, 650

1, 550/1, 6.50 1,6{|0'1,6.50 M. ir.n 1.22.^.

75/83 Rb

7.5/85 Rb

98 Rb/24 Rc

78/83 Rb

80/90 Rb

81 '89 Rb

'17 K 1, 24 Rc

IM '.15 Rb

:n 'M Rb

9.5/99 Rb

80/90 Rb

72/80 Rb

°F

1, 700/1, 850

1, 700/1, 850

1, 800/1, 950

1. 700/1, 850

1, 700/1, 8.50

1. 800/1. 900

1.800/1,950

1.8,50/1.9.50

1,8.50/1.9.50

1, 850/1, 950

1,600/1,700 m

39/43 Rc

39/43 Rc

42/47 Rc

40/44 Rc

39/43 Rc

53/56 Rc

42/46 Rc

55/58 Rc

57/59 Rc

60/62 Rc

35/45 Rc

op

450/700

450/700 450/700

450/700

450/700

300/700

450/700 300/700

300/700

300/700

40/37 Rc

40/37 Rc

44/40 Rc

40/37 Rc

40/37 Rc

53/48 Rc

42/36 Rc

56/51 Rc

58/53 Rc

60/55 Rc

°F

1, 000/1, 400

1,000/1.400

1,100/1,300 1,000/1.400

1,000/1.400

.34 Rc/86 Rb

34 Ec/86 Rb

29 Rc/99 Rb

34 Rc/86 Rb

34 Rc/8fi Rb

1. 000/1, 200 35 Rc/99 Rb

L ' K675

1, 1.600 400/1. 200 45/25 R 0 502 1.52.51,600

GROUP II. XOXHARDEXABLE CHROMIUM STEELS

(FERRITIC AND MAGfNETIC)

AISI

type

Annealing «

Temperature Hardness, Rb

°F

405 1, 350/1, 500 70/80 430 1. 400/1, 500 80/90 430 F 1,350/1, .500 80/90 430 F Se 1, 350/1, 500 80/90 446 1, 500/1, 600 80/90

GROUP III. NONIIARDENABLE CHROMIUM-NICKEL AND

CHROMIUM-NICKEL-MANGANESE STEELS (AUSTENITIC

AND NONMAGNETIC)

AISI Annealing AISI Aimcahng

type temperature

type temperatui'e

°F op

201 1, 850/2. 050 309 1,900/2, 050 202 1, 850/2, 0.50 309 S 1,900/2, 050

301 1,850/2,050 310 1, 900/2, ( 50 302 1, 850/2, 050 310 S 1,900/2, 050

302 B 1, 850/2, 050 314 2, 000/2, 100

303 1. 850/2, 050 316 1, 850/2, 050

303 Se 1, 850/2, 050 316 L 1. 850/2, 050

304 1, 850/2, 050 317 1, 850/2, 050 304 L 1, 850/2, 050 321 1, 750/1, 950 305 1, 850/2, 050 347 1,850/1. 950

308 1, 850/2, 050 348 1, 850/1, 950

Cool slowly to 1,100° F.

^ Although these steelsTTafden appreciably on air cooling, quenching in oil is preferable.

' Full annealing impractical; may he air cooled from indicated temperature.

<< Generally used in annealed condition only.

' Air fOOl. , 1, T>

' Cooling may be in air or by quenching in water. The resultant hardness of all of these steels will be in the range of approximately Rockell B I I to 90.

35
11. Properties and Uses of Steels

11.1. Structural Steels

The strength properties of heat treated

(quenched and tempered) structural carbon and

alloy steels are closely related to their hardness

and are surprisingly similar for a selected hardness

provided that the steels originally were hardened

throughout their cross sections. The relation of

tensile strength, yield strength, elongation, and

reduction of area to hardness is shown in figure 27. The tempering temperatures necessary to secure

certain hardness levels in steels are affected by

alloying elements, and two different steels may

have to be tempered at two different temperatures

to secui'e the same hardness. When this has been

accomplished, however, the strength and ductility

of the two steels will be quite similar. It must be

emphasized that these relationships are valid only

if the heat treated structures are tempered martensite. A steel that has been incompletely hardened

(that is, quenched at too slow a rate to prevent the

formation of some fine pearlite) may have, after tempering, a hardness and tensile strength equal

to that of a completely hardened and tempered

steel, but its yield strength and ductility will be

inferior.

HARDNESS .ROCKWELL C

5 70

25 30 35 40 45

< 60

u_O

g 40

30

od 10

- 220

<n

o.0 200 O

X 180

I-1 160

I-<oa 140

_iUJ^ "20

IiJ 100

1 1

1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1

REDUCTION OF AREA

ELONGATION

. 1 ] 1

1 1 1 _l L. _l L

UJ

t- 80

1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1

TENSILE STRENGT

lELD STRENGTH

1 1 1

1 1 1 1 1 J_J 1

1

1 1

1 ,1 L 1 1 1 t 240 280 320 360 400

BRINELL HARDNESS NUMBER 440

Figure 27. Tensile strength, yield strength, elongation,

and reduction of area as a function of hardness in struc- tural steels. Valid only for steels originally hardened throughout and then tempered. Although drawn as lines, the relationship between these properties is not

exact, and some deviations may be expected. 36

The modulus of elasticity of steel is the same as that of iron (about 29,000,000 Ib/m.^). It is not

affected by heat treatment or by the addition of

alloying elements. Since stiffness, or the resistance

to deformation under load, is a function of the

modulus of elasticity, it follows that the stiffness of steel cannot be changed by heat treatment or by alloying elements, provided that the total stress j is below the elastic limit of the steel in question.

Either heat treatment or alloying elements can

raise the elastic limit and thus apparently improve

the stiffness in that higher allowable unit stresses may be imposed on the steel.

a. Plain Carbon Structural Steels The plain carbon steels are the least costly and Is may be used for a variety of purposes. The lower

carbon grades (up to about 0.25% of carbon), fre- quently termed machmery steels, are used in the

hot- and cold-worked conditions and for carburizing. Except when carbm-ized, they are not very

responsive to hardening by heat treatment because

of the low carbon content. The medium carbon

steels (about 0.30 to 0.60%) are the forging grades

and are commonly used in the heat-treated condition. The higher carbon grades are the spring and

tool steels. Carbon steels are essentially shallow-hardening,

usually requiring a water or brine quench, although

very small sections may be successfully hardened

in oil. Even with the most drastic quench, they

cannot be hardened throughout even in moderate

(about %-in.) cross sections. Large cross sections

(about 4 in.) cannot be fully hardened even on

the surface except by induction or flame hardening.

b. Alloy Structural Steels From the viewpoint of heat treatment, the advantages accruing from the use of alloy steels are

threefold: (a) Increased hardenability, (b) retention of fine-grained austenite, and (c) retardation

of softening during tempering. j All of the alloying elements commonly used in f structural alloy steels are effective to varying \ degrees in displacing the S-curve to the right as . compared with plain carbon steels of similar car- bon contents. Consequently, they can be hardened

throughout in larger sections and, generally, by means of a milder quenching medium, such as oil. Because of the slower rates of quenching that can

be employed in hardening these steels, they are ; less likely to distort or crack during hardening [ than the plain carbon steels. The hardenability of alloy steels varies widely,

depending on the composition. Certain elements

and combinations of elements are very effective

in increasing hardenability. Of the five alloying

elements most generally used, and within the

amounts normally present m the structm-al steels,

nickel enhances hardenability but mildly, vanadium, chromium, manganese, and molybdenum

moderately to strongly, depending upon the

amount of alloy dissolved in the austenite at the
hardening temperatiu"e. Combinations of chi'O- mium, nickel, and molybdenum, such as are present in the 4300 series (table 1), result in very

deep hardeniag steels. The alloying elements that form stable carbides,

principally vanadium and molybdenum (and

chi-oniium to a lesser degree), are very effective in

inhibiting grain growth in austenite. These steels may be overheated to a considerable degree dming

heating for hardening without suffering grain

growth. This is deshable since martensite formed

from fine-gi'ained austenite is tougher than that

formed from coarse-grained austenite.

AUoying elements, particularly those that form

the more stable carbides, tend to retard the softening effects of tempering so that alloy steels must

frequently be tempered at higher temperatures

than carbon steels in order to secm'e the same

hardness. This is beneficial in conferring in- creased toughness, i.e., resistance to shock.

It is pertinent to note that manganese and nickel

lower the annealing and hardening temperatures,

and that chi'omium, molybdenum, and vanadium

raise these temperatm-es. Combinations of these

alloys may therefore, raise, lower, or have no effect on the heat-treating temperatures, depending on

the combinations of elements and their amounts.

The low carbon (up to about 0.25% of carbon)

alloy steels are used mainly as carburizing steels. The medium carbon (about 0.30 to 0.60% of car- bon) alloy steels find wide use as stressed members

in an almost infinite variety of structural parts.

Although some of these alloy steels containing

high carbon are used for certain special applications, the maximum amount of carbon present in

the alloy structural steels is generally about 0.5 percent.

11.2. Tool Steels

Practical experience has shown that in a majority of instances the choice of a tool steel is not limited to a single type or even to a particular

family for a working solution to an individual

tooling problem. It is desirable to select the

steel that will give the most economical overall

performance; the tool life obtained with each steel under consideration should be judged by weighing

such factors as expected productivity, ease of

fabrication, and cost. Hardness, strength, toughness, wear resistance,

and resistance to softening by heat are prime

factors that must be considered in selecting tool

steel for general applications. Many other factors

must be considered in individual applications;

they include permissible distortion in hardening,

permissible decarburization, hardenability, resist- ance to heat checking, machinability, grindability,

and heat treating requirements.

The straight carbon tool steels can be used for a

variety of purposes, depending upon the carbon

content and heat treatment. The lower carbon

ranges are used for tools where toughness and

resistance to shock are of primary importance;

these steels are usually tempered at temperatures

of 500° to 700° F or even higher. The higher

carbon ranges are used where the main requirements are hardness, resistance to abrasion, or

ability to hold a keen edge ; these steels are usually

tempered at temperatmes of 300° to 500° F. An addition of 0.20 to 0.50 percent of chromium

or of vanadium is frequently made to the carbon

tool steels. The chromium-bearing carbon steels have a greater depth of hardnening and are

slightly more wear-resistant than the chromiumfree steels of the same carbon content. Vanadium

decreases slightly the depth of hardening but

increases toughness. (This may appear contradictory to previous statements that alloying

elements increase hardenability. In the case of the

carbon-vanadium tool steels, the normal hardening

temperatures are too low to allow the solution of

vanadium carbide in the austenite. The presence

of undissolved carbides decreases hardenability).

The cutting ability, or the ability to hold an

edge, is closely related to the hardness. For most

purposes, therefore, cutting tools are used in a highly hardened condition. Excessive heat,

whether caused by heavy cutting or careless

gi-incling, will "draw the temper" (that is, decrease

the hardness) and ruin the tool, necessitating

rehardening and retempering. Since hardened

carbon steels soften rapidly under the influence of

heat, the carbon steels cannot be used as cutting

tools under conditions where an appreciable

amount of heat is generated at the cutting edge.

Theu' uses are limited to conditions entailing light cuts on relatively soft materials, such as brass,

aluminum, and unhardened low carbon steels. The ranges for the carbon content and some

typical applications of carbon tool steels are as

follows:

0.60 to 0.75 percent of carbon—Hot forming or heading dies for short runs, machinery parts,

hammers (sledges and pinch bars), concrete

breakers, and rivet sets. 0.75 to 0.90 percent of carbon—Hot and cold

sets, chisels, dies, shear blades, mining drill steel,

smiths' tools, set hammers, swages, and flatteners. 0.90 to 1.10 percent of carbon—Hand chisels,

small shear blades, large taps, granite drills, trimming dies, drills, cutters, slotting and milling tools,

mill picks, chcular cutters, threading dies, colcl header dies, jewelers' cold striking dies, blanking,

forming and drawing dies, and punches.

1.10 to 1.40 percent of carbon—Small cutters,

small taps, drills, reamers, slotting and planing

tools, wood-cutting tools, turning tools, and razors. Suitable tempering temperatures for carbon tool

steels are as follows:

300° to 375° F—Lathe tools and millmg cutters, scrapers, drawing mandrels, dies, bone-cutting

tools, engraving tools, gages, and threading dies. 375° to 500° F—Hand taps and dies, hand

reamers, di'ills, bits, cutting dies, pen knives, milling cutters, chasers, press dies for blanking and

forming, rock drills, dental and surgical instru37
ments, hammer faces, wood-carving tools, shear

blades, and hack saws. 500° to 700° F—Bending dies, shear blades,

chuck jaws, forging dies, tools for wood cutting,

hammers and drop dies, axes, cold chisels, coppersmith tools, screwdrivers, molding and planing

tools, hack saws, butcher knives, and saws. The high-speed steels are intended for use under

heavy cutting conditions where considerable heat

is generated. These steels are very complex, containing large amounts of alloying elements. The

high-speed steels, which harden from a very high

temperature (2,150° to 2,400° F), develop what

is termed "secondary hardness" after tempering

at about 1,050° to 1,100° F and maintain their

cutting edge at considerably higher temperature

than do carbon tool steels. Dies, depending on their use, can be made of a variety or steels. When intended for use at low

temperatures, even carbon steel may be satisfactory sometimes. For use at elevated temperatures,

certain minimum amounts of alloying elements are necessary and for the higher ranges of hot-working

temperatures, steels of the high-speed steel type

are frequently used.

The manufacture of dies usually involves such

considerable expense in machining that cost of

material and heat treatment form but a relatively

small proportion of the total. It is imperative,

therefore, that die steels be selected carefully and

properly heat treated. The so-called "nondeforming" tool steels (type O) are favorites for dies that

are not required to operate at elevated temperatures. These steels usually contain about 0.9 percent of carbon and 1.2 percent to 1.6 percent of

manganese. With the lower manganese content

they also contain about 0.5 percent each of chromium and tungsten. The expansion of these steels during hardening is much less than is experienced

with carbon steels, and the shrinlvage that occm-s during the initial stage of tempering is almost

sufficient to return the steel to its original size when it has been tempered at the proper temperatiu'e. The high carbon-high chromium steels (type D)

are frequently used for dies. This type contains

about 12 percent of chromium and 1.5 or 2.2 percent of carbon, the lower carbon steel being

air hardening. These steels also are nondeforming,

are more resistant to wear, and may be used at higher temperatures than the manganese nondeforming steels. They have the disadvantage of

requiring higher hardening temperatures (about

1,800° F).

11.3. Stainless and Heat Resisting Steels

Steels for high-temperature service must resist scaling and have high creep strength, that is, re- sistance to deformation under prolonged stress at elevated temperatures. Resistance to scaling is aided by the presence of chromium, aluminum, or

silicon, and heat-resistant steels invariably contain one or more of these elements. Resistance to creep

era!

lilt 11

Tv

is aided by elements that form stable carbides

such as tungsten, vanadium, molybdenum, anc chromium.

The stainless steels, often called corrosion-resist-,

ant steels, contain appreciable amounts of chro-^ mium (12% or more), either with or without otheii elements, the most important of which is nickel. The heat-resistant and corrosion-resistant steels

all belong to the same family, the terminology

frequently being dictated by the temperature of use. By common consent, this dividing temperature is taken at about 1200° F. The three general groups of stainless steels hav€|

markedly different characteristics, as follows:

a. Group I —Hardenable Chromium Steels (MartensitiCj^

and Magnetic)

The significant characteristic of this group is* f^ist that the steels respond to heat treatment in manner similar to most lower alloy steels. The

steels possess a pearlitic structure on slow cooling

and a martensitic (hardened) structure on rapid

cooling from within the austenitic field. The

chromium content varies from about 12 to 18

percent and the carbon content from less than 0.1 to over 1.0 percent; the higher chi'omium content

demands the higher carbon.

The mechanical properties of this group of

steels are markedly improved by heat treatment

and heat treatment is essential to realize their

corrosion-resistant properties. The only excep

tions are the low carbon, low chromium steels (types 403, 410, 416) which are corrosion resistant,

in the annealed condition, although heat treatment: decidedly improves mechanical properties.

Finishing of the martensitic steels has an im-- portant effect on corrosion resistance, since maxi

mum corrosion resistance is obtained only with

highly fi.nished surfaces. Grinding should be

done carefully, using a sharp wheel, light cuts and plenty of coolant. Grinding burrs and embedded scale serve as focal points for corrosion.

As a group, the martensitic stainless steels

resist many types of corrosive environments,

including the atmosphere, fresh water, mine'

water, steam, food acids, carbonic acid, crude

oil, gasoline, blood, perspiration, ammonia, and

sterilizing solutions.

Type 410 stainless is a general purpose steel' suitable for numerous applications where severe

corrosion is not a problem. Types 416 and 416L

are free-machining varieties of type 410. The

higher hardness of type 420 makes it suitable

for such uses as cutlery, surgical instruments,

valves, ball bearings, magnets, etc. Type 420F

is its free-machining counterpart. Where still greater hardness is required, type 440A, B, or C may be used; the last is the hardest of all the

stainless steels. Types 420 and 440 should be

used only in the hardened and stress-relieved

conditions. Type 431 is a structural stainless

steel capable of being used in the strength range

of 200,000 psi.

38
aveii

0 0

b. Group II—Nonhardenable Chromium Steels (Ferritic and Magnetic)

The distinguishing chai'acteristic of this group

s that these steels are ferritic at all temperatures

nd, therefore, incapable of being hardened by

iieat treatment. They can, however, be strengthjjened by cold working.

|; The ferritic steels develop coarse grained strucitm-es when subjected to temperatm-es above 1650°F

^"^ifor varying lengths of time. This grain growth,

'frequently objectionable because of concomitant

fjrittleness, cannot be eliminated by heat treat- jment alone. It can be corrected to some extent

'by cold working, followed by annealing.

I The ferritic steels have lower strength at

,ielevated temperatirres than the martensitic steels,

''*f|but resistance to scaling and corrosion is generally

Abetter. As a class, the ferritic stainless steels resist corrosion from food products, organic acids,

jsalt water, nitric acid, many fused salts and

j^'raolten nonferrous metals.

Type 430 stainless finds extensive use in automobile trim, chemical equipment, food containers,

iind furnace parts. If ease of machining is important, type 430F or 430F Se may be substiMjftuted. Where greater resistance to corrosion or

.Qtltoxidation is required, type 446 may be used.

c. Group III—Nonhardenable Chromium-Nickel and

Chromium-Nickel-Manganese Steels (Austenitic and

Nonmagnetic)

The steels in this group are austenitic at room

.-temperature and, hence, both nonhardenable by

• lieat treatment and nonmagnetic. They can,

liowever, be strengthened appreciably by cold

work. Depending upon the amount of cold

^v-ork, the tensile strength varies from about

. 80,000 psi for fully annealed material to as high

as 300,000 psi for severely work hardened steel; the highest strengths can be secured only with

^jftsmall cross sections. A stress-relieving treatment

Vof about 1 hr at 750° to 800° F after severe cold

vorking improves elastic properties without any

.idverse effect upon ductility. Cold work causes

partial transformation of austenite to ferrite, with

consequent appearance of magnetism, in some of

these steels. The austenitic steels have excellent coldforming properties and are extremely tough and

luctile, even at low temperatures. Their toughless makes machining of all but the free-machinng varieties difficult. As a group, the ausenitic stainless steels are the

nost corrosion resistant of all the stainless steels. They have excellent resistance to acetic, nitric,

and citric acids (liquid), foodstuffs, sterilizing

solutions, most of the organic chemicals and

lyestuffs, and a wide variety of inorganic chemicals. Typical applications are for outdoor trim,

kitchen equipment, dairy utensils, soda fountains,

and light weight transportation such as aircraft. This group of stainless steels should not be

discussed without some mention of intergranular

.jL fimbrittlement. If maintained in the temperature

- range of about 800° to 1,400° F, or if slowly cooled

through this range after annealing, some of these

steels precipitate carbides at the grain boundaries.

This is not deleterious unless the steel is either

simultaneously or subsequently exposed to acidified corrosive conditions, causing intergranular

corrosion. When this occurs, the steels lose their

metallic ring and become quite brittle. Type 302 stainless, with its higher carbon

content, is more prone to carbide precipitation than

is 304, which in turn is more susceptible than 304L.

Type 301, because of its lower alloy content, is quite susceptible to work hardening and is used

largely in the cold rolled or cold drawn form of

sheet, strip, and wire. Types 201 and 202 are quite

similar to types 301 and 302 in properties. The

former were developed primarily to conserve

nickel, then in short supply.

Types 305, 308, 309, and 310 contain progressively higher amounts of chromium and nickel and

are, therefore, superior to the lower alloy steels in corrosion and heat resistance.

Types 316 and 317 contain molybdenum. The

incorporation of this element increases resistance

to corrosion, particularly of the "pitting" type.

Types 321 and 347 were developed specifically to resist intergranular corrosion. This property

of the titanium-bearing steel (type 321) is generally

enhanced by a stabilizing heat treatment. This

treatment is not particularly necessary for the

columbium-bearing steels (types 347 and 348).

d. Semi-Austenitic Stainless Steels The semi-austenitic stainless steels, also called

precipitation hardening stainless steels, constitute

a special group for which no standard specifications

have as yet been adopted by AISI. These steels are of sufficient commercial importance, however,

to warrant some mention.

Essentially, the semi-austenitic stainless steels are steels in which, by careful control of composition and heat treatment, an austenite can be

produced having a stability intermediate between

that of the austenitic and martensitic types. After

a solution heat treatment these steels are austenitic

at room temperature and, therefore, readily

amenable to severe forming and working operations. Following fabrication, exposure to a

relatively low temperature conditions the austenite

for transformation to martensite on subsequent

cooling, with a marked increase in strength.

Depending on the composition and final properties

desired, the low temperature treatment may be

a two-step operation. The transformation of the

austenite to martensite in the first step results in

hardening of the matrix. In some compositions,

the matrix also contains elements that are in

supersaturated solid solution after this treatment.

The second operation, therefore, is designed to allow the solute elements to precipitate and to temper the martensite.

As these are proprietary steels, the manufacturers should be consulted for details of chemical

compositions, recommended heat treatments,

typical properties, and uses.

39
In preparing this monograph, the authors have

drawn liberally from the field of common knowledge and published information, especially from

the Metals Handbook, published by the American

Society for Metals, and the Steel Product Manuals

of the American Iron and Steel Institute. Grateful

acknowledgment is due to all metallurgists, both

known and unknown, whose work and study have

transformed the art of heat treating into a science.

The various photomicrographs used were prepared

by Carolyn R. Irish, a member of the staff of the

National Bureau of Standards.

12. Selected References

The following is a selected, but by no means complete,

list of books that contain information pertaining to the

subject of this Monograph. In addition, many manufacturers of steels and of equipment related to heat treating

have available excellent pamphlets and books. American Foundi'ymen's Society, The cast metals handbook, Am. Foundrymen's Soc, Chicago, 111. (1957) 316 pages. American Iron and Steel Institute Steel Products

Manuals, as follows: Carbon steel: Semi-finished for forging; Hot rolled and cold finished bars; Hot rolled deformed concrete reinforcing bars, July 1957; Suppl. Dec. 1957; Alloy steel: Semi-finished; hot rolled and cold

finished bars, July 1955; Suppl. July 1958; Tool steels, Apr.

1955; Suppl. Sept. 1959; Stainless and heat resisting

steels, June 1957; Suppl. Sept. 1959, Am. Iron and

Steel Inst., New York, N.Y. American Society for Metals, Metals handbook. Am.

Soc. Metals, Novelty, Ohio (1948) 1444 pages; with 1954

and 1955 supplements.

Edgar C. Bain, Functions of the alloying elements in

steel, Am. Soc. Metals, Novelty, Ohio (1939) 312 pages. R. M. Brick and Arthur Phillips, Structure and properties of allovs (McGraw-Hill Book Co., Inc., New York,

N.Y., 1949) 485 pages.

Malcolm S. Burton, Applied metallurgy for engineers

(McGraM'-HiU Book Co., Inc., New York, N.Y., 1956)

407 pages.

J. M. Camp and C. B. Francis, The making, shaping

and treating of steel, 7th edition U.S. Steel Corp., Pitts- burgh, Pa. (1957) 1048 pages. Walter Crafts, and John L. Lamont, Hardenability and | steel selection (Pitman and Sons, New York, N.Y., 1949) i 279 pages. John C. Everhart, et al. Mechanical properties of metals and alloys, NBS Circ. C447 (1943) 481 pages.

J. P. Gill, et al. Tool steels. Am. Soc. Metals, Novelty,

Ohio (1944) 577 pages. M. A. Grossmann, Principles of heat treatment, Am. i

' Soc. Metals, Novelty, Ohio (1953) 303 pages. I

A. W. Grosvenor, Editor, Basic metallurgy, vol. I, Am. I, Soc. Metals, Novelty, Ohio (1954) 697 pages.

' J. H. Hollomon and L. D. Jaffe, Ferrous metallurgical

design (John Wiley and Sons, Inc., New York, N.Y.,

1947) 346 pages. Samuel L. Hoyt, Metal Data (Reinhold Publishing

Corp., New York, N.Y., 1952) 526 pages. Carl A. Kej^ser, Basic engineering metallurgy, 2d edition

(Prentice-Hail, Inc., Englewood Cliffs, N.J., 1959) 507

pages. j|

Frank R. Palmer and George V. Luerssen, Tool steel simplified. Carpenter Steel Co., Reading, Pa. (1948) [' i 564 pages. i George Sachs and Kent R. Van Horn, Practical metal- i lurgy. Am. Soc. Metals, Novelty, Ohio (1940) 567 pages.

' Carl H. Samans, Engineering metals and their alloys, | (Macmillan Co., New York, N.Y., 1949) 913 pages, i Bradley Stoughton, Allison Butts, and Ardrey M. . Bounds, Engineering metallurgy (McGraw-Hill Book

Co., Inc., New York, N.Y., 1953) 479 pages. E. J. Teichert, Ferrous Metallurgy, vol. I—^Introduction

to ferrous metallurgy, 484 pages; vol. II—-The manufacture and fabrication of steel, 487 pages; vol. Ill—^Metallog- ! raphy and heat treatment of steel, 577 pages (McGrawHill Book Co., Inc., New York, N.Y., 1944). Carl A. Zapffe, Stainless steels. Am. Soc. Metals,

Novelty, Ohio (1949) 368 pages.

Washington, D.C. (March 18, 1960)

40

U.S. GOVERNMENT PRINTING OFFICE: 1960
THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories, in Washington,

D.C., and Boulder, Colo., is suggested in the following listing of the divisions and sections engaged

in technical work. In general, each section carries out specialized research, development, and engineering in the field indicated by its title. A brief description of the activities, and of the resultant

pubhcations, appears on the inside front cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instru- ments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instru- mentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic Technology. Length. Engineering Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular

Kinetics. Free Radicals Research.

Atomic Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Elec- tron Physics. Atomic Physics.

Radiation Physics Neutron Physics. Radiation Theory. Radioactivity. X-ray. High Energy

Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry

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and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

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Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning. Heating

and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat

Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems. Analog Systems. Applications Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures.

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials.

Gas Liquefaction.

Radio Propagation Physics. Upper Atmosphere Research. Ionosphere Research. Regular

Prediction Services. Sun-Earth Relationships. VHF Research. Radio Warning Services.

Airglow and Aurora. Radio Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Trophospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High-Frequency Electrical Standards. Radio Broadcast Service. Radio and

Microwave Materials. Atomic Frequency and Time Standards. Electronic Calibration Center. Microwave Circuit Standards.

Radio Communication and Systems. Low Frequency and Very Low Frequency Research.

High Frequency and Very High Frequency Research, Modulation Systems. Antenna Research.

Navigation Systems. Systems Analysis Field Operations.
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