EE-RM/STD-00-550 COMMENT 86
The information and data in this bulletin are accurate to the best of

our knowledge and belief, but are intended for general information

only. Applications suggested for the materials are described only

to help readers make their own evaluations and decisions, and are

neither guarantees nor to be construed as express or implied

warranties of suitability for these or other applications.

Data referring to mechanical properties and chemical analyses

are the result of tests performed on specimens obtained from

specific locations of the products in accordance with prescribed

sampling procedures; any warranty thereof is limited to the values

obtained at such locations and by such procedures. There is no

warranty with respect to values of the materials at other locations.

AK Steel, the AK Steel logo, TRAN-COR and CARLITE are registered

trademarks of AK Steel Corporation.

Copyright© 2000 AK Steel Corporation.

 EE-RM/STD-00-550 COMMENT 86

2 

The information and data in this bulletin are accurate to the best of 

our knowledge and belief, but are intended for general information 

only. Applications suggested for the materials are described only 

to help readers make their own evaluations and decisions, and are 

neither guarantees nor to be construed as express or implied 

warranties of suitability for these or other applications. 

Data referring to mechanical properties and chemical analyses 

are the result of tests performed on specimens obtained from 

specific locations of the products in accordance with prescribed 

sampling procedures; any warranty thereof is limited to the values 

obtained at such locations and by such procedures. There is no 

warranty with respect to values of the materials at other locations. 

AK Steel. the AK Steel logo, TRAN-COR and CARLITE are registered 

trademarks of AK Steel Corporation. 

Copyright© 2000 AK Steel Corporation. 
AK Steel Oriented

and A

Electrical Steels

:lectri

Oriented electrical steels are iron-silicon alloys that were

developed to provide the low core loss and high permeability required for more efficient and economical electrical transformers. First produced commercially by AK

Steel, these magnetic materials exhibit their superior

magnetic properties in the rolling direction. This directionality occurs because the steels are specially processed to create a very high proportion of grains within

the steel which have similarly oriented atomic crystalline structures relative to the rolling direction.

In iron-silicon alloys, this atomic structure is cubic

and the crystals are most easily magnetized in a direction parallel to the cube edges. By a combination of precise steel composition and rigidly controlled cold rolling

and annealing procedures, the crystals of these oriented

electrical steels are aligned with their cube edges nearly

parallel to the direction in which the steel is rolled. Consequently, they provide superior permeability and lower

core loss when magnetized in this direction. This phenomenon is clearly illustrated by Figure 3 which shows

the polydirectional permeability of AK Steel Oriented

Electrical Steels.

AK Steel Oriented Electrical Steels are used most

effectively in transformer cores having wound or sheared

and stamped laminations with the magnetic flux path

entirely, or predominately, in the rolling direction. They

also are used in large generators and other apparatus

when the design permits the directional magnetic characteristics to be used efficiently. Since the inception of

the oriented grades in 1933, AK Steel Research has continued to develop new and improved grades to provide

the electrical industry with core materials for the manufacture of more efficient electrical apparatus.

9

AK Steel TRAN-COR H High-Permeability Electrical

Steels offer an outstanding degree of grain orientation.

The result is far lower core loss than possible with conventional grain-oriented electrical steels.

In addition, these "super-oriented" materials provide

better permeability, particularly at higher operating inductions, and the potential for producing less noisy core

structures due to lower magnetostriction.

` Steel

ie -Jectrical Steels

The inherent characteristics of grain-oriented electrical

steels plus AK Steel's long-time experience in producing these materials yield a valuable and unique combination of advantages over nonoriented electrical steels.

Lower Core Loss and Higher

Permeability in the Rolling Direction

AK Steel Oriented Electrical Steels give the transformer

designer a choice of grades that have much lower core

loss in the rolling direction than nonoriented grades.

This low core loss is also combined with high permeability even at high inductions. All the advantages

of lower core loss can be used without the penalty of

lower permeability at high flux densities.

Laser Scribing Refines Domains

Laser scribing AK Steel TRAN-COR H Electrical Steels

provides additional beneficial core loss reductions

through domain refinement. In this process, a highly

focused Nd:YAG laser beam rapidly scans the material

surface perpendicular to the rolling direction. The resulting thermal shock produces compressive

microstrains in the material which generate new

domain walls. By forcing the existing domains to

subdivide, the refined domain wall spacing requires less

movement during AC magnetization, thereby reducing

core loss in the steel.

In addition to Domain Refined TRAN-COR H-0 and

H-1 Electrical Steels, AK Steel Oriented M-3 Electrical

Steel (CARLITE 3 coated material only) is available in

the domain refined condition.

 EE-RM/STD-00-550 COMMENT 86

AK Steel Oriented 

and TRAN .. COR H 

Electrical Steels 

Oriented electrical steels are iron-silicon alloys that were 

developed to provide the low core loss and high permeability required for more efficient and economical electrical transformers. First produced commercially by AK 

Steel, these magnetic materials exhibit their superior 

magnetic properties in the rolling direction. This directionality occurs because the steels are specially processed to create a very high proportion of grains within 

the steel which have similarly oriented atomic crystalline structures relative to the rolling direction. 

In iron-silicon alloys, this atomic structure is cubic 

and the crystals are most easily magnetized in a direction parallel to the cube edges. Bya combination of precise steel composition and rigidly controlled cold rolling 

and annealing procedures, the crystals of these oriented 

electrical steels are aligned with their cube edges nearly 

parallel to the direction in which the steel is rolled. Consequently, they provide superior permeability and lower 

core loss when magnetized in this direction. This phenomenon is clearly illustrated by Figure 3 which shows 

the polydirectional permeability of AK Steel Oriented 

Electrical Steels. 

AK Steel Oriented Electrical Steels are used most 

effectively in transformer cores having wound or sheared 

and stamped laminations with the magnetic flux path 

entirely, or predominately, in the rolling direction. They 

also are used in large generators and other apparatus 

. when the design permits the directional magnetic characteristics to be used efficiently. Since the inception of 

the oriented grades in 1933, AK Steel Research has continued to develop new and improved grades to provide 

the electrical industry with core materials for the manufacture of more efficient electrical apparatus. 

AK Steel TRAN-COR H High-Permeability Electrical 

Steels offer an outstanding degree of grain orientation. 

The result is far lower core loss than possible with conventional grain-oriented electrical steels. 

In addition, these "super-oriented" materials provide 

better permeability, particularly at higher operating inductions, and the potential for producing less noisy core 

structures due to lower magnetostriction. 

The inherent characteristics of grain-oriented electrical 

steels plus AK Steel's long-time experience in producing these materials yield a valuable and unique combination of advantages over non oriented electrical steels. 

Lower Core Loss and Higher 

Permeability in the Rolling Direction 

AK Steel Oriented Electrical Steels give the transformer 

designer a choice of grades that have much lower core 

loss in the rolling direction than non oriented grades. 

This low core loss is also combined with high permeability even at high inductions. All the advantages 

of lower core loss can be used without the penalty of 

lower permeability at high flux densities. 

Laser Scribing Refines Domains 

Laser scribing AK Steel TRAN-COR H Electrical Steels 

provides additional beneficial core loss reductions 

through domain refinement. In this process, a highly 

focused Nd:YAG laser beam rapidly scans the material 

surface perpendicular to the rolling direction. The resulting thermal shock produces compressive 

microstrains in the material which generate new 

domain walls. By forcing the existing domains to 

subdivide, the refined domain wall spacing requires less 

movement during AC magnetization, thereby reducing 

core loss in the steel. 

In addition to Domain Refined TRAN-COR H-O and 

H-1 Electrical Steels, AK Steel Oriented M-3 Electrical 

Steel (CAR LITE 3 coated material only) is available in 

the domain refined condition. 3 
Stress-relief annealing will nullify the beneficial

effects of laser scribing domain refinement. These

materials are most appropriate for stacked-core

applications where stress-relief annealing is not needed.

Superior Lamination Factor

The lamination or stacking factors of AK Steel Oriented

Electrical Steels are remarkably good. As a result,

efficient use of core volume for carrying magnetic flux

is obtained.

Shipped Insulated

AK Steel Oriented Electrical Steels are supplied with

glass-type insulation formed during the final stages of

manufacture and/or additionally applied inorganic insulation. The former is usually adequate for wound cores

of the type used in distribution transformers.

Oriented and TRAN-COR H Electrical Steels also are

supplied with CARLITE 3 Insulation. This coating supplies a beneficial tensile stress which contributes to the

significantly better magnetic properties and decreased

stress sensitivity of these materials. CARLITE 3 Insulation, applied to any of the oriented and TRAM-COR H

grades, provides high interlaminar resistivity with minimal effect on lamination factor.

Stress-Relief Anneal May Be Required

The type of material, design considerations and fabrication practices dictate the potential need for annealing to

achieve satisfactory magnetic performance in various

applications. When needed, only a low-temperature,

1400-1550°F (760-843°C) stress-relieving anneal with

proper furnace atmosphere conditions is required to

optimize magnetic properties and remove the harmful

effects of punching, shearing or winding.

When appropriate annealing procedures are

followed, high insulation resistance is retained after

stress relief annealing.

Due to the nature of the CARLITE 3 Insulation application process, the resulting low-stress product normally

eliminates the need to stress-relief anneal laminations

for stacked core structures.

Assured Quality

AK Steel Oriented Electrical Steels are supplied with

magnetic properties fully developed at the mill by a

special high-temperature heat treatment. Transformer

manufacturers may design to known electrical characteristics established by grading tests at the mill.

F---

Grade and Thickness

AK Steel Oriented and TRAN-COR H Electrical Steels

are produced in the following grades and nominal

thicknesses:

AK Steel Oriented M-2: 7 mils (0.007")

AK Steel Oriented M-3: 9 mils (0.009")

AK Steel Oriented M-4: 11 mils (0.011 ")

AK Steel Oriented M-6: 14 mils (0.014")

AK Steel TRAN-COR H-0: 9 mils (0.009")

AK Steel TRAN-COR H-1: 11 mils (0.011 ")

Grades and thicknesses listed are available in the form

of coils subject to the following limits:

Widths from 3/4" to 34". (Above 34" up to 36 ", please

inquire.)

Average coils weigh approximately 260-350 pounds

per inch of width.

Surface Insulations

Three types of surface insulations on AK Steel Oriented

Electrical Steels meet specific design and fabrication

requirements. First is the insulation provided by the magnesium-silicate coating formed during annealing, called

Mill-Anneal Insulation. Then, there are two types of special AK Steel CARLITE Insulation - CARLITE 3 and Punching Quality CARLITE Insulations. TRAN-COR H Electrical

Steels are supplied only with CARLITE 3 Insulation.

 EE-RM/STD-00-550 COMMENT 86

4 

Stress-relief annealing will nullify the beneficial 

effects of laser scribing domain refinement. These 

materials are most appropriate for stacked-core 

applications where stress-relief annealing is not needed. 

Superior Lamination factor 

The lamination or stacking factors of AK Steel Oriented 

Electrical Steels are remarkably good. As a result, 

efficient use of core volume for carrying magnetic flux 

is obtained. 

Shipped Insulated 

AK Steel Oriented Electrical Steels are supplied with 

glass-type insulation formed during the final stages of 

manufacture and/or additionally applied inorganic insulation. The former is usually adequate for wound cores 

of the type used in distribution transformers. 

Oriented and TRAN-COR H Electrical Steels also are 

supplied with CAR LITE 3 Insulation. This coating supplies a beneficial tensile stress which contributes to the 

significantly better magnetic properties and decreased 

stress sensitivity of these materials. CAR LITE 3 Insulation, applied to any of the oriented and TRAN-COR H 

grades, provides high interlaminar resistivity with minimal effect on lamination factor. 

Stress-Relief Anneal May Be Required 

The type of material, design considerations and fabrication practices dictate the potential need for annealing to 

achieve satisfactory magnetic performance in various 

applications. When needed, only a low-temperature, 

1400-1550°F (760-843°C) stress-relieving anneal with 

proper furnace atmosphere conditions is required to 

optimize magnetic properties and remove the harmful 

effects of punching, shearing or winding. 

When appropriate annealing procedures are 

followed, high insulation resistance is retained after 

stress relief annealing. 

Due to the nature of the CAR LITE 3 Insulation application process, the resulting low-stress product normally 

eliminates the need to stress-relief anneal laminations 

for stacked core structures. 

Assured Quality 

AK Steel Oriented Electrical Steels are supplied with 

magnetic properties fully developed at the mill by a 

special high-temperature heat treatment. Transformer 

manufacturers may design to known electrical characteristics established by grading tests at the mill. 

Grade and Thickness 

AK Steel Oriented and TRAN-COR H Electrical Steels 

are produced in the following grades and nominal 

thicknesses: 

AK Steel Oriented M-2: 7 mils (0.007") 

AK Steel Oriented M-3: 9 mils (0.009") 

AK Steel Oriented M-4: 11 mils (0.011") 

AK Steel Oriented M-6: 14 mils (0.014") 

AK Steel TRAN-COR H-O: 9 mils (0.009") 

AK Steel TRAN-COR H-1: 11 mils (0.011") 

Grades and thicknesses listed are available in the form 

of coils subject to the following limits: 

Widths from 3/4" to 34". (Above 34" up to 36", please 

inquire.) 

Average coils weigh approximately 260-350 pounds 

per inch of width. 

Surface Insulations 

Three types of surface insulations on AK Steel Oriented 

Electrical Steels meet specific design and fabrication 

requirements. First is the insulation provided by the magnesium-silicate coating formed during annealing, called 

Mill-Anneal Insulation. Then, there are two types of special AK Steel CAR LITE Insulation - CAR LITE 3 and Punching Quality CAR LITE Insulations. TRAN-COR H Electrical 

Steels are supplied only with CAR LITE 3 Insulation. 
Mill-Anneal Insulation

This insulative coating forms in the final mill-annealing

operation at very high temperatures. It is a tightly

adherent, magnesium-silicate type of coating corresponding to ASTM C-2 Insulation. Mill-Anneal Insulation provides insulative properties suitable for transformers operated at flux densities where the induced voltage is about 10 volts per turn or less (as in distribution

transformers normally used by public utilities). This

glass-like surface supplies good resistance to abrasion

in winding into core form, and will withstand the

recommended stress-relieving anneal without loss

of insulative value. No danger of transformer oil

contamination exists with this coating. Prolonged

exposure to oils or air at transformer operating temperatures does not endanger insulating qualities.

AK Steel Oriented grades usually are used with a

mill-anneal finish for wound or formed transformer cores,

except in larger ratings where the insulation or flatness

of a CARLITE 3 product may be required. However, where

the induced volts per turn may be unusually high or

where the strip width exceeds 10 inches, the increased

resistance of CARLITE 3 Insulation may be worthwhile.

CARLITE Insulation

CARLITE Insulations are inorganic coatings produced by

combined thermal and chemical surface treatments.

They provide thin, uniform coverage of the surface with

a high-resistance film that protects against energy loss

from induced currents. To permit these insulations to

be used in a broader range of applications, two types of

CARLITE Insulation are available: CARLITE 3 for sheared

laminations and Punching Quality CARLITE.

AK Steel-developed CARLITE 3 Insulation consists

of a special insulative coating applied over the MillAnneal finish produced in annealing. It has higher

insulative properties than Punching Quality CARLITE

Insulation, and corresponds to ASTM C-5 Insulation.

CARLITE 3 Insulation is applied to both TRAN-COR H

and regular grain oriented materials and is intended for

materials that will be used in the form of sheared laminations for power transformers and other apparatus with

high volts per turn.

For AK Steel Oriented M-2 (.007"), a much lighter

CARLITE 3 insulative coating is applied when thermal

flattening is specified. This product is called M-2 Light

CARLITE, or M-2 LC, and is intended for wound-core

applications only.

Punching Quality CARLITE Insulation is a product

variant designed to give good die life by removing the

Mill-Anneal finish before applying CARLITE Insulation.

Although the punching quality product has an insulative

quality of the ASTM C-5 type, it provides lower insulation resistance than CARLITE 3 Insulation (C-5 over C2), but affords adequate resistance for applications

where volts per turn are moderate. It is not recommended where very high surface insulation is required.

The effect of CARLITE coatings on lamination factor

is quite small. CARLITE coatings retain their insulative

capability after stress-relief annealing if suitable annealing procedures are followed. CARLITE coatings will

not contaminate transformer oils, nor is there any deterioration of the insulative coating in either oils or air at

operating temperatures.

Surface Insulation Curves

Figure 1 shows the variation of surface insulation resistance versus pressure and provides a guide to users

interested in knowing the relative insulative capabilities

of the available surface finishes. Resistance values are

typical of those which should be equalled or surpassed

in most tests made on such surfaces by the Franklin

Test (ASTM A717). However, the user should recognize

that the normally small variations in mill oxide and coating thickness within a lot necessitate allowing for some

test values lower as well as higher than those shown in

the curves.

 EE-RM/STD-00-550 COMMENT 86

MiII·Anneallnsulation 

This insulative coating forms in the final mill-annealing 

operation at very high temperatures. It is a tightly 

adherent, magnesium-silicate type of coating corresponding to ASTM C-2 Insulation. Mill-Anneal Insulation provides insulative properties suitable for transformers operated at flux densities where the induced voltage is about 10 volts per turn or less (as in distribution 

transformers normally used by public utilities). This 

glass-like surface supplies good resistance to abrasion 

in winding into core form, and will withstand the 

recommended stress-relieving anneal without loss 

of insulative value. No danger of transformer oil 

contamination exists with this coating. Prolonged 

exposure to oils or air at transformer operating temperatures does not endanger insulating qualities. 

AK Steel Oriented grades usually are used with a 

mill-anneal finish for wound or formed transformer cores, 

except in larger ratings where the insulation or flatness 

of a CAR LITE 3 product may be required. However, where 

the induced volts per turn may be unusually high or 

where the strip width exceeds 10 inches, the increased 

resistance of CAR LITE 3 Insulation may be worthwhile. 

CAR UTE Insulation 

CAR LITE Insulations are inorganic coatings produced by 

combined thermal and chemical surface treatments. 

They provide thin, uniform coverage of the surface with 

a high-resistance film that protects against energy loss 

from induced currents. To permit these insulations to 

be used in a broader range of applications, two types of 

CAR LITE Insulation are available: CAR LITE 3 for sheared 

laminations and Punching Quality CAR LITE. 

AK Steel-developed CARUTE 3 Insulation consists 

of a special insulative coating applied over the MillAnneal finish produced in annealing. It has higher 

insulative properties than Punching Quality CAR LITE 

Insulation, and corresponds to ASTM C-5 Insulation. 

CAR LITE 3 Insulation is applied to both TRAN-COR H 

and regular grain oriented materials and is intended for 

materials that will be used in the form of sheared laminations for power transformers and other apparatus with 

high volts per turn. 

For AK Steel Oriented M-2 (.007"), a much lighter 

CAR LITE 3 insulative coating is applied when thermal 

flattening is specified. This product is called M-2 Light 

CAR LITE, or M-2 LC, and is intended for wound-core 

applications only. 

Punching (luality CARLilE Insulation is a product 

variant designed to give good die life by removing the 

Mill-Anneal finish before applying CAR LITE Insulation. 

Although the punching quality product has an insulative 

quality of the ASTM C-5 type, it provides lower insulation resistance than CAR LITE 3 Insulation (C-5 over C2), but affords adequate resistance for applications 

where volts per turn are moderate. It is not recommended where very high surface insulation is required. 

The effect of CAR LITE coatings on lamination factor 

is quite small. CAR LITE coatings retain their insulative 

capability after stress-relief annealing if suitable annealing procedures are followed. CAR LITE coatings will 

not contaminate transformer oils, nor is there any deterioration of the insulative coating in either oils or air at 

operating temperatures. 

Surface Insulation Curves 

Figure 1 shows the variation of surface insulation resistance versus pressure and provides a guide to users 

interested in knowing the relative insulative capabilities 

of the available surface finishes. Resistance values are 

typical of those which should be equalled or surpassed 

in most tests made on such surfaces by the Franklin 

Test (ASTM A717). However, the user should recognize 

that the normally small variations in mill oxide and coating thickness within a lot necessitate allowing for some 

test values lower as well as higher than those shown in 

the curves. 

5 
Figure 1 i r°°^tor

Typical surface insulation characteristics of AK Steel Lamination factor is the measure of compactness of an

Oriented Electrical Steels at various pressures as electrical steel core. This is also referred to as "stacking

determined by the Franklin Test. factor" and "space factor." Lamination factor is the

ratio of the equivalent "solid" volume, calculated from

.70 1.0 2.0 3.0 5.0 weight and density of the steel, to the actual volume of

100 the compressed pack, determined from its dimensions.

'7-

.07

Special processing gives AK Steel Oriented Electri-

.1 cal Steels (either with Mill-Anneal finish or CARLITE

types of insulation) exceptionally and consistently high

lamination factors.

.2

.3

.4

.5

.6

.95

.98

200 300 500 700 1000

TEST PRESSURE - psi

Test Method . The lamination factor of electrical steels

is determined from measurements of a stack of Epstein

strips under known pressure in accordance with ASTM

A 719. Figure 2 illustrates how the ASTM lamination

factor varies as a function of pressure for the most widely

used forms of AK Steel Oriented Electrical Steels. The

values shown are representative of the lamination factor determined by this test.

Figure 2

99

TEST PRESSURE-MPa

07 .14 .35 .7 1.4 3.5 7.0

i9

P^peo 01Y' pA^' \

(1^ C

^i 6^^ , a4 M.3 .

tE 9 \.^zUW^e

loll

TEST PRESSURE-psi

 EE-RM/STD-00-550 COMMENT 86

figure 1 

Typical surface insulation characteristics of AK Steel 

Oriented Electrical Steels at various pressures as 

determined by the Franklin Test. 

.70 1.0 2.0 3.0 5.0 

100 I I I 

f- .07 

70 

f- .1 

Cil 50 Q) 

() 

co 

't: 

:::l 

U) 

i'-. 

~ ~ r..!!-4lil.rr~ 

Lamination factor is the measure of compactness of an 

electrical steel core. This is also referred to as "stacking 

factor" and "space factor." Lamination factor is the 

ratio of the equivalent "solid" volume, calculated from 

weight and density of the steel, to the actual volume of 

the compressed pack, determined from its dimensions. 

Special processing gives AK Steel Oriented Electrical Steels (either with Mill-Anneal finish or CARLITE 

types of insulation) exceptionally and consistently high 

lamination factors. 

Test Method. The lamination factor of electrical steels 0 30 

$ -.....:: Iv fr--. .2 is determined from measurements of a stack of Epstein ~ 

c 20 0 

r-- '';::; 

co 

c 

'E .3 

co 

.....I 

.... 

Q) 10 - .4 0.. 

NE 

u 7 

U) 

E 

.c 5 0 

I 

ill 

U 3 z 

~ (j) 2 (f.i 

ill 

0:: 

f\ 

~~ 

\" -

"'~. \ '\ ~ A) ~$ ... 

~ ~. ~ ~;.' - 1", i!'~ 

.5 

.6 

.7 

.8 

Z 

0 

.....I 

~ 

::) 

(j) 

z .7 ill 

U « u.. .5 0:: 

::) 

(j) 

IZ 

ill .3 0:: 

ct 

\ ~ '\ 

~ ~ 

~ ~ l\. f-

'\ '\ 

I\. 

\ f-

~ 

\ 

.9 

.95 

a... 

« .2 

f- .98 

.1 

100 200 300 500 700 1000 

TEST PRESSURE - psi 

6 

U) 

Q) 

.... 

Q) 

0.. 

E 

« 

I 

Iz 

ill 

0:: 

0:: 

::) 

u 

I-

(j) 

ill 

Iz 

:::J 

::.::: 

Z 

« 

0:: 

u.. 

strips under known pressure in accordance with ASTM 

A 719. Figure 2 illustrates how the ASTM lamination 

factor varies as a function of pressure for the most widely 

used forms of AK Steel Oriented Electrical Steels. The 

values shown are representative of the lamination factor determined by this test. 

figure 2 

TEST PRESSURE-MPa 

9g0r7 __ ~.1r4 ____ ~.35~ __ ~~~~ __ ~,3.~5 __ ~7.0 

95.51·'::-0-----:2f-::0-------::5'=-0 -------:-:1 0!-=-0----::-20':-::0-----::-l50~0 ---:-:-:1 000 

TEST PRESSURE-psi 
Physical Properties

Representative Mechanical Properties

Ultimate Tensile Strength, psi (MPa)

in rolling direction

Yield Strength, psi (MPa)

in rolling direction

Percent Elongation in 2 inches (50.8 mm)

in rolling direction

Microhardness (Knoop Hardness Number, HK)

Equivalent Rockwell B Scale Hardness

Modulus of Elasticity, psi (MPa)*

in rolling direction

at 20 degrees to rolling direction

at 45 degrees to rolling direction

at 55 degrees to rolling direction

at right angles to rolling direction

*Values may vary as much as plus or minus 5%

Physical Properties

Density, grams per cubic centimeter

Electrical Resistivity, microhm-centimeters

Saturation Value of Ferric Induction*

(B-H) in kilogausses

Curie Temperature, °F (°C)

*Effective value for coated specimen.

Oriented TRAN-COR H

51,000 (352) 52,000 (359)

48,000 (331) 50,000 (345)

9 11

167 173

81 83

17,700,000 (122,000) 16,500,000 (113,800)

20,800,000 (143,000) 20,000,000 (138,000)

34,300,000 (236,000) 35,000,000 (241,000)

37,500,000 (258,000) 40,000,000 (276,000)

29,000,000 (219,500) 29,500,000 (203,000)

Oriented TRAN-COR H

7.65 7.65

51 50

20.0 19.9

1375 (746) 1380 (749)

 EE-RM/STD-00-550 COMMENT 86

Representative Mechanical Properties 

Ultimate Tensile Strength, psi (MPa) 

in rolling direction 

Yield Strength, psi (MPa) 

in rolling direction 

Percent Elongation in 2 inches (50.8 mm) 

in rolling direction 

Microhardness (Knoop Hardness Number, HK) 

Equivalent Rockwell B Scale Hardness 

Modulus of Elasticity, psi (MPa)* 

in rolling direction 

at 20 degrees to rolling direction 

at 45 degrees to rolling direction 

at 55 degrees to rolling direction 

at right angles to rolling direction 

*Values may vary as much as plus or minus 5% 

Phvsical Properties 

Density, grams per cubic centimeter 

Electrical Resistivity, microhm-centimeters 

Saturation Value of Ferric Induction* 

(B-H) in kilogausses 

Curie Temperature, DF (DC) 

*Effective value for coated specimen. 

Oriented 

51,000 (352) 

48,000 (331) 

9 

167 

81 

17,700,000 (122,000) 

20,800,000 (143,000) 

34,300,000 (236,000) 

37,500,000 (258,000) 

29,000,000 (219,500) 

Oriented 

7.65 

51 

20.0 

1375 (746) 

TRAN-COR H 

52,000 (359) 

50,000 (345) 

11 

173 

83 

16,500,000 (113,800) 

20,000,000 (138,000) 

35,000,000 (241,000) 

40,000,000 (276,000) 

29,500,000 (203,000) 

TRAN-COR H 

7.65 

50 

19.9 

1380(749) 

1 
M .,®. , 'ate Loss

For grading purposes, core loss tests on AK Steel transformers designed for these types of materials. Test

Oriented and IRAN-COR H Electrical Steels are made results agree closely with those made on single-phase

at inductions of 15 and 17 kilogausses. This testing transformers with stress-free cores having no joints.

procedure approximates the operating conditions in

Maximum Core Loss*

60 Hertz

AK Steel Test Thickness

Grade Specimen inches

Watts per lb

15 kG 17 kG

Watts per kg

15kG 17kG

Oriented M-2 (1) .007

Oriented M-3 (1) .009

Oriented M-4 (1) .011

Oriented M-6/PQ (1) .014

TRAN-COR H-0 (1) .009

TRAN-COR H-1 (1) .011

TRAN-COR H-0 DRt (2) .009

TRAN-COR H-1 DRt (2) .011

.405 -

.445 .70

.51 .74

.66 .94

.60

.66

.39 .535

.425 .57

.89 -

.98 1.54

1.12 1.63

1.46 2.07

50 H

Watts per Ib

15 kG 17 kG

.31 -

.34 .53

.39 .56

.50 .71

ertz

Watts per kg

15 kG 17 kG

.68 -

.75 1.17

.85 1.24

1.11 1.57

1.01

1.11

.65 .90

.71 .96

1.32 - .46

1.46 - .50

.86 1.18 .30 .41

.94 1.26 .32 .43

(1) Annealed Condition, Epstein type test specimen

(2) As-sheared single sheet test specimen.

*Customer has option of specifying either 15 or 17 kG inductions for 9-mil M-3, 11-mil M-4, 14-mil M-6, 9-mil H-0 DR, and 11-mil H-1 DR.

tDR designates domain refinement by laser scribing.

Typical core losses of AK Steel Oriented and TRAN-COR H Electrical Steels are significantly lower than the maximum limits. Contact AK Steel for

computer spread sheet for typical core loss and exciting power.

The core loss and exciting power of the AK Steel Oriented and TRAN-COR H grades are determined by magnetic tests performed in accordance with

general procedures approved by the American Society forTesting and Materials.

The following conditions apply:

1. Epstein Specimens

a. Sheared parallel to the rolling direction of the steel from fully processed coils.

b. Annealed again after shearing to relieve stresses per ASTM A 876.

c. Tested after stress-relief anneal per ASTM A 343.

2. Single Sheet Specimens

a. Sheared parallel to the rolling direction of the steel from fully processed coils.

b. Tested as-sheared per ASTM A 804.

3. Density of all grades - 7.65 grams/cm3 per ASTM A 34.

ASTM A 664 is a grade identification system for electrical steels. While this system has not been widely adopted by the manufacturers and consumers

of electrical steels, it is used in ASTM A 876 to designate various grades of grain oriented electrical steel. The following is a listing of the corresponding

AK Steel and ASTM grades of grain oriented electrical steels.

AK Steel grade 7-mil M-2 is approximately equivalent to ASTM Core Loss Type 18G041.

AK Steel grade 9-mil M-3 is approximately equivalent to ASTM Core Loss Types 23G045 and 23H070.

AK Steel grade 1 1-mil M-4 is approximately equivalent to ASTM Core Loss Types 27G051 and 27H074.

AK Steel grade 14-mil M-6 is approximately equivalent to ASTM Core Loss Types 35G066 and 35H094.

AK Steel grade 9-mil H-0 is approximately equivalent to ASTM Core Loss Type 23P060.

AK Steel grade 11-mil H-1 is approximately equivalent to ASTM Core Loss Type 27P066.

AK Steel grade 9-mil H-0 DR is approximately equivalent to ASTM Core Loss Type 23Q054.

AK Steel grade 11 -mil H-1 DR is approximately equivalent to ASTM Core Loss Type 270057.

 EE-RM/STD-00-550 COMMENT 86

8 

For grading purposes, core loss tests on AK Steel 

Oriented and TRAN-COR H Electrical Steels are made 

at inductions of 15 and 17 kilogausses. This testing 

procedure approximates the operating conditions in 

transformers designed for these types of materials. Test 

results agree closely with those made on single-phase 

transformers with stress-free cores having no joints. 

Maximum Core Loss* 

60 Hertz 50 Hertz 

AK Steel Test Thickness Watts per Ib Watts per kg Watts per Ib Watts per kg 

Grade Specimen inches 

Oriented M-2 (1) .007 

Oriented M-3 (1 ) .009 

Oriented M-4 (1 ) .011 

Oriented M-6/PQ (1) .014 

TRAN-COR H-O (1) .009 

TRAN-COR H-l (1) .011 

TRAN-COR H-O DRt (2) .009 

TRAN-COR H-l DRt (2) .011 

(1) Annealed Condition, Epstein type test specimen 

(2) As-sheared single sheet test specimen. 

15 kG 17 kG 

.405 -

.445 .70 

.51 .74 

.66 .94 

- .60 

- .66 

.39 .535 

.425 .57 

15 kG 17 kG 15 kG 17 kG 15 kG 

.89 - .31 - .68 

.98 1.54 .34 .53 .75 

1.12 1.63 .39 .56 .85 

1.46 2.07 .50 .71 1.11 

- 1.32 - .46 -

- 1.46 - .50 -

.86 1.18 .30 .41 .65 

.94 1.26 .32 .43 .71 

*Customer has option of specifying either 15 or 17 kG inductions for 9-mil M-3, II-mil M-4, 14-mil M-6, 9-mil H-O DR, and II-mil H-l DR. 

tOR designates domain refinement by laser scribing. 

Typical core losses of AK Steel Oriented and TRAN-COR H Electrical Steels are significantly lower than the maximum limits. Contact AK Steel for 

computer spread sheet for typical core loss and exciting power. 

17 kG 

-

1.17 

1.24 

1.57 

1.01 

1.11 

.90 

.96 

The core loss and exciting power of the AK Steel Oriented and TRAN-COR H grades are determined by magnetic tests performed in accordance with 

general procedures approved by the American Society forTesting and Materials. 

The following conditions apply: 

1. Epstein Specimens 

a. Sheared parallel to the rolling direction of the steel from fully processed coils. 

b. Annealed again after shearing to relieve stresses per ASTM A 876. 

c. Tested after stress-relief anneal per ASTM A 343. 

2. Single Sheet Specimens 

a. Sheared parallel to the rolling direction of the steel from fully processed coils. 

b. Tested as-sheared per ASTM A 804. 

3. Density of all grades - 7.65 grams/cm3 per ASTM A 34. 

ASTM A 664 is a grade identification system for electrical steels. While this system has not been widely adopted by the manufacturers and consumers 

of electrical steels, it is used in ASTM A 876 to designate various grades of grain oriented electrical steel. The following is a listing of the corresponding 

AKSteel and ASTM grades of grain oriented electrical steels. 

AK Steel grade 7-mil M-2 is approximately equivalent to ASTM Core Loss Type 18G041. 

AK Steel grade 9-mil M-3 is approximately equivalent to ASTM Core Loss Types 23G045 and 23H070. 

AK Steel grade II-mil M-4 is approximately equivalent to ASTM Core Loss Types 27G051 and 27H074. 

AK Steel grade 14-mil M-6 is approximately equivalent to ASTM Core Loss Types 35G066 and 35H094. 

AK Steel grade 9-mil H-O is approximately equivalent to ASTM Core Loss Type 23P060. 

AK Steel grade II-mil H-l is approximately equivalent to ASTM Core Loss Type 27P066. 

AK Steel grade 9-mil H-O DR is approximately equivalent to ASTM Core Loss Type 23Q054. 

AK Steel grade II-mil H-l DR is approximately equivalent to ASTM Core Loss Type 270057. 
Stress-Relief Annealing

General Requirements

A mill anneal develops the full magnetic potential and

reduces harmful elements in AK Steel Oriented Electrical Steel. Stress relief annealing relieves stresses thermally after the steel has been fabricated into its final

size and shape. In stress-relief annealing, the user should

first recognize that the parameters of time, temperature

and atmosphere are not interchangeable with those for

annealing of semiprocessed grades of nonoriented silicon steels or carbon steels.

Basically, stress relief is accomplished by heating

the laminations or fabricated parts to the 1400-1550°F

(760-845°C) range, followed by cooling to room temperature. The stress relief must be done under time,

temperature and ambient atmosphere conditions that

will avoid even minute adverse changes in the steel

chemistry and prevent excessive thermal gradients that

might reintroduce stresses into the steel or perhaps

distort its shape. Cores or laminations usually can be

removed from the protective annealing atmosphere at

about 600-700°F (315-370°C) without ill effects.

Insulation

AK Steel Oriented Electrical Steels are supplied with

either a Mill-Anneal finish or CARLITE types of insulation. TRAN-COR H Electrical Steels are supplied with

CARLITE 3 Insulation. Surface finish has a very important bearing on the selection of the proper annealing

atmosphere.

The Mill-Anneal finish (sometimes referred to as

glass film) is developed at very high temperatures in a

hydrogen atmosphere. Consequently, it is completely

compatible with hydrogen-nitrogen mixtures ranging

from 0 to 100 percent nitrogen without adversely

affecting the interlaminar resistance quality of the

electrical steel. However, for economy and safety,

the hydrogen content usually is maintained below

10 percent. Vacuum annealing gives very satisfactory

results with a Mill-Anneal surface, but may be too costly.

The insulative quality of CARLITE types of

insulation is best maintained or enhanced by an atmosphere that is neutral or slightly oxidizing to iron.

Pure, dry nitrogen is recommended for batch annealing

CARLITE types of insulated material when the cycle time

requires hours.

Continuous stress relief of slit widths or single

laminations may be carried out in an air atmosphere

if exposure time is only a matter of minutes. Vacuum

annealing of CARLITE types of insulated material is not

recommended.

Atmosphere Conditions to Avoid

AK Steel Oriented Electrical Steels are produced under

very exacting limits and careful control of composition,

rolling and annealing. Consequently, these steels are

extremely low in impurities such as carbon and oxygen.

Destructive magnetic effects will ensue if either of these

impurities are reintroduced into the steel by the user.

Any annealing atmosphere which contains carbon or

oxygen compounds may contaminate the steel with

these elements. If they are present in the annealing

atmosphere or evolved from lubricants or other foreign

matter within the annealing chamber, the best magnetic

quality will not be obtained. For instance, contamination with carbon can occur if the annealing atmosphere

has an equilibrium value with the steel of greater than

.0025 percent carbon and if the steel is so exposed for

any appreciable length of time when it is at temperatures over 1200°F (650°C).

Oxygen compounds, such as water vapor, oxidize

silicon in oriented steels even under conditions highly

reducing to iron. Long exposure to conditions oxidizing

to silicon can undermine glass film by continued oxidation of silicon, especially at or near the exposed edges.

Oxidation is not only somewhat harmful to magnetic

properties, but it also causes growth in the steel thickness which can cause excessive tightening of uncut

wound cores. This results in dimensional difficulties and

deleterious stress effects in reassembly of wound cores

after cutting.

 EE-RM/STD-00-550 COMMENT 86

General Requirements 

A mill anneal develops the full magnetic potential and 

reduces harmful elements in AK Steel Oriented Electrical Steel. Stress relief annealing relieves stresses thermally after the steel has been fabricated into its final 

size and shape. In stress-relief annealing, the user should 

first recognize that the parameters of time, temperature 

and atmosphere are not interchangeable with those for 

annealing of semiprocessed grades of nonoriented silicon steels or carbon steels. 

Basically, stress relief is accomplished by heating 

the laminations or fabricated parts to the 1400-1550°F 

(760-845°C) range, followed by cooling to room temperature. The stress relief must be done under time, 

temperature and ambient atmosphere conditions that 

will avoid even minute adverse changes in the steel 

chemistry and prevent excessive thermal gradients that 

might reintroduce stresses into the steel or perhaps 

distort its shape. Cores or laminations usually can be 

removed from the protective annealing atmosphere at 

about 600-700°F (315-370°C) without ill effects. 

Insulation 

AK Steel Oriented Electrical Steels are supplied with 

either a Mill-Anneal finish or CAR LITE types of insulation. TRAN-COR H Electrical Steels are supplied with 

CAR LITE 3 Insulation. Surface finish has a very important bearing on the selection of the proper annealing 

atmosphere. 

The Mill-Anneal finish (sometimes referred to as 

glass film) is developed at very high temperatures in a 

hydrogen atmosphere. Consequently, it is completely 

compatible with hydrogen-nitrogen mixtures ranging 

from 0 to 100 percent nitrogen without adversely 

affecting the interlaminar resistance quality of the 

electrical steel. However, for economy and safety, 

the hydrogen content usually is maintained below 

10 percent. Vacuum annealing gives very satisfactory 

results with a Mill-Anneal surface, but may be too costly. 

The insulative quality of CARLITE types of 

insulation is best maintained or enhanced by an atmosphere that is neutral or slightly oxidizing to iron. 

Pure, dry nitrogen is recommended for batch annealing 

CAR LITE types of insulated material when the cycle time 

requires hours. 

Continuous stress relief of slit widths or single 

laminations may be carried out in an air atmosphere 

if exposure time is only a matter of minutes. Vacuum 

annealing of CAR LITE types of insulated material is not 

recommended. 

Atmosphere Conditions to Avoid 

AK Steel Oriented Electrical Steels are produced under 

very exacting limits and careful control of composition, 

rolling and annealing. Consequently, these steels are 

extremely low in impurities such as carbon and oxygen. 

Destructive magnetic effects will ensue if either ofthese 

impurities are reintroduced into the steel by the user. 

Any annealing atmosphere which contains carbon or 

oxygen compounds may contaminate the steel with 

these elements. If they are present in the annealing 

atmosphere or evolved from lubricants or other foreign 

matter within the annealing chamber, the best magnetic 

quality will not be obtained. For instance, contamination with carbon can occur if the annealing atmosphere 

has an equilibrium value with the steel of greater than 

.0025 percent carbon and if the steel is so exposed for 

any appreciable length of time when it is at temperatures over 1200°F (650°C). 

Oxygen compounds, such as water vapor, oxidize 

silicon in oriented steels even under conditions highly 

reducing to iron. Long exposure to conditions oxidizing 

to silicon can undermine glass film by continued oxidation of silicon, especially at or near the exposed edges. 

Oxidation is not only somewhat harmful to magnetic 

properties, but it also causes growth in the steel thickness which can cause excessive tightening of uncut 

wound cores. This results in dimensional difficulties and 

deleterious stress effects in reassembly of wound cores 

after cutting. 

9 
Do not use unmodified exothermic atmospheres

obtained from the partial combustion of natural gas or

similar hydrocarbons. They are oxidizing to silicon during the entire annealing cycle. In addition, they usually

are carburizing in part of the heating and cooling cycles

even when noncarburizing at the soak temperature.

Satisfactory annealing atmospheres can be produced

from natural gas or similar hydrocarbons only by (1)

complete combustion and removal of carbon dioxide and

water vapor or (2) partial combustion followed by conversion of the CO to CO2 with steam and final removal of

CO2 and water vapor by scrubbing and drying. Process

(1) results in essentially pure nitrogen and process (2)

results in nitrogen containing 3 to 10 percent hydrogen.

Mill-Anneal

Oriented steel with a Mill-Anneal finish is used primarily

for wound and formed transformer cores. The material

normally has some residual coil set which can be tolerated in the manufacture of wound cores, but this curvature is undesirable for punched or sheared laminations

that are subsequently stacked.

Annealing Furnaces

Two general types of furnaces, batch type and continuous batch type, are widely used for stress-relief annealing of wound or formed cores made from oriented electrical steel with a Mill-Anneal finish.

Batch-Type Furnaces

Required Features - Batch furnaces have advantages,

particularly where the volume of steel being annealed at

any one time is small, production is intermittent, or core

sizes being annealed vary considerably. Such furnaces

can provide considerable flexibility and the opportunity

to vary the cycle from charge to charge. With tightfitting inner covers that isolate the annealing space, it is

possible to maintain accurate control of the atmosphere

surrounding the charge at all times and yet maintain

atmosphere flow rates at economical levels. Heat input

to the furnace charge must be adjustable so that temperature variations can be controlled properly. This is

necessary to ensure that the lagging temperature at the'

bottom center of the charge is sufficient without the

top temperature exceeding the maximum desirable for

the anneal conditions. Furnaces with recirculating fans

are particularly advantageous for annealing wound cores

since they permit more uniform heating of the charge

and shorter annealing cycles.

Inner Covers - Always use inner covers with box furnaces to protect against contamination from furnace

brickwork or combustion products. Covers should be

made from material of very low carbon content such as

Types 304L or 316L stainless steel. The cover preferably should fit tightly with a base plate of comparable

material. The metal base which covers the brick furnace base, plus the removable cover, should form a

metallic enclosure for the charge within which there is

no brickwork. Atmosphere inlet and outlet pipes are

usually placed in the base and located to ensure positive flow around the charge. The joint between the inner cover and base may be sealed with sand. When the

furnace is a "bell" type, it is advantageous to flange the

inner cover. This provides a seal outside the furnace

where it may be kept cool enough to maintain a positive seal with water.

Piling the Charge - Exercise care in piling the charge

in batch furnaces to ensure that the charge receives the

maximum exposure to direct radiation from the heat

source. Conduction of heat within cores takes place principally along the plane of the strip. Heat is radiated to or

from the exposed cut edges of the strip rather than

through strip surfaces. As a result, cores in the heat

shadow of others may take substantially longer to be

heated. This can cause severe temperature variations

to exist within the furnace. However, such variations

can be minimized by the shape and design of the annealing chamber considering the usual makeup of the

charge, or by using forced recirculation of the heated

atmosphere.

 EE-RM/STD-00-550 COMMENT 86

10 

Do not use unmodified exothermic atmospheres 

obtained from the partial combustion of natural gas or 

similar hydrocarbons. They are oxidizing to silicon during the entire annealing cycle. In addition, they usually 

are carburizing in part of the heating and cooling cycles 

even when noncarburizing at the soak temperature. 

Satisfactory annealing atmospheres can be produced 

from natural gas or similar hydrocarbons only by (1) 

complete combustion and removal of carbon dioxide and 

water vapor or (2) partial combustion followed by conversion of the CO to CO2 with steam and final removal of 

CO2 and water vapor by scrubbing and drying. Process 

(1) results in essentially pure nitrogen and process (2) 

results in nitrogen containing 3 to 10 percent hydrogen. 

MiII·Anneal 

Oriented steel with a Mill-Anneal finish is used primarily 

for wound and formed transformer cores. The material 

normally has some residual coil set which can be tolerated in the manufacture of wound cores, but this curvature is undesirable for punched or sheared laminations 

that are subsequently stacked. 

Annealing Furnaces 

Two general types of furnaces, batch type and continuous batch type, are widely used for stress-relief annealing of wound or formed cores made from oriented electrical steel with a Mill-Anneal finish. 

Batch·Tvpe Furnaces 

Required Features - Batch furnaces have advantages, 

particularly where the volume of steel being annealed at 

anyone time is small, production is intermittent, or core 

sizes being annealed vary considerably. Such furnaces 

can provide considerable flexibility and the opportunity 

to vary the cycle from charge to charge. With tight-fitting inner covers that isolate the annealing space, it is 

possible to maintain accurate control of the atmosphere 

surrounding the charge at all times and yet maintain 

atmosphere flow rates at economical levels. Heat input 

to the furnace charge must be adjustable so that temperature variations can be controlled properly. This is 

necessary to ensure that the lagging temperature at the' 

bottom center of the charge is sufficient without the 

top temperature exceeding the maximum desirable for 

the anneal conditions. Furnaces with recirculating fans 

are particularly advantageous for annealing wound cores 

since they permit more uniform heating of the charge 

and shorter annealing cycles. 

Inner Covers - Always use inner covers with box furnaces to protect against contamination from furnace 

brickwork or combustion products. Covers should be 

made from material of very low carbon content such as 

Types 304L or 316L stainless steel. The cover preferably should fit tightly with a base plate of comparable 

material. The metal base which covers the brick furnace base, plus the removable cover, should form a 

metallic enclosure for the charge within which there is 

no brickwork. Atmosphere inlet and outlet pipes are 

usually placed in the base and located to ensure positive flow around the charge. The joint between the inner cover and base may be sealed with sand. When the 

furnace is a "bell" type, it is advantageous to flange the 

inner cover. This provides a seal outside the furnace 

where it may be kept cool enough to maintain a positive seal with water. 

Piling the Charge - Exercise care in piling the charge 

in batch furnaces to ensure that the charge receives the 

maximum exposure to direct radiation from the heat 

source. Conduction of heat within cores takes place principally along the plane of the strip. Heat is radiated to or 

from the exposed cut edges of the strip rather than 

through strip surfaces. As a result, cores in the heat 

shadow of others may take substantially longer to be 

heated. This can cause severe temperature variations 

to exist within the furnace. However, such variations 

can be minimized by the shape and design of the annealing chamber considering the usual makeup of the 

charge, or by using forced recirculation of the heated 

atmosphere. 
Atmosphere Flow Rate -To avoid exposing cores made

from glass film material to danger of growth and tightening from oxidation of either the silicon or iron constituents of the material, eliminate oxygen from the atmosphere as early as possible in the cycle. Thereafter,

provide maximum protection against oxidation during

the entire annealing cycle. This may require that the

annealing chamber be thoroughly purged of oxygen quite

rapidly at the start of the heating cycle. The amount

depends upon the gas volume involved (volume inside

the inner cover minus the charge volume). It is a good

practice to provide at least 10 volume changes by the

time the charge has heated to 1000°F (540°C). Then,

the atmosphere flow rate can be reduced to about five

volume changes per hour until the charge cools to at

least 700°F (370°C).

Temperature Cycle -Annealing time should be as short

as possible without producing excessive thermal gradients. Proper time must take into account the size and

weight of cores being annealed and their relative

degree of exposure to heating and cooling. For instance,

100-pound cores with good exposure to the heating and

cooling sources might require a minimum of six to eight

hours to go from room temperature to the annealing temperature and back to 700°F (370°C) without experiencing thermal strains. With a lesser degree of exposure, it

might require 10 hours for equivalent results. A temperature of about 1450-1500°F (790-820°C) is usually

adequate for stress relief of most wound cores. It is usually desirable to hold or soak at 1500°F (820°C) until the

desired minimum temperature is reached at the most

protected location within the charge. If cores are not

well exposed, this soaking period may be up to two hours

in length. With maximum exposure, it might be as short

as one-half hour. Furnace heat input should be adjusted

so that the heating rate is not too great when approaching the soaking temperature. Rapidly forcing cores

up to temperatures with extra high heat input is never

advisable. It may be desirable to begin the cooling cycle

at a controlled rate if the natural cooling rate of the furnace is so rapid it might cause thermal strain.

If cores are fabricated by cold-working procedures

that produce plastic deformation of a relatively large

percentage of the core volume, it may be desirable to

employ a slightly higher soaking temperature for the

anneal. A temperature of about 1550°F (845°C) will

assure all the stress relief possible for drastically strained

steel. However, this higher temperature should not be

used unless experimentation with the cores being annealed shows that it is definitely beneficial.

Continuous Batch-Type Furnaces

Continuous furnaces usually yield best results in high

production volume, primarily because relative exposure

of cores or laminations to the heat source is much greater

than in box furnaces, resulting in minimum annealing

time and maximum exposure to the protective atmosphere. These furnaces usually fit well into automated

production lines, but are less flexible and less economical than box furnaces or batch-type furnaces for varied

or low-volume production.

Continuous furnaces must have several controlled

heating and cooling zones with individual control. These

permit the heating rate to be adjusted so that heating

and cooling gradients, particularly going into and out of

the maximum temperature region of the cycle, will not

be large enough to produce stress effects or distortion

in the core. Unlike batch furnaces, continuous furnaces

cannot be kept sealed for the entire cycle. So, atmosphere flow rates usually are substantially larger than

for batch furnaces of equivalent volume. Separate

entrance and exit chambers may be needed to

minimize admission of air into the furnace when the

charge is introduced or removed.

Special Precaution for Annealing Wound Cores

Exercise care to maintain the shape of rectangular or

formed cores during annealing. Unless the cores come

out of the anneal stress-free and in a shape that minimizes the reintroduction of stresses in assembly or as a

result of framing, then even the most careful attention

to other features of the stress-relieving treatment may

be wasted.

11

 EE-RM/STD-00-550 COMMENT 86

Atmosphere flow Rate- To avoid exposing cores made 

from glass film material to danger of growth and tightening from oxidation of either the silicon or iron constituents of the material, eliminate oxygen from the atmosphere as early as possible in the cycle. Thereafter, 

provide maximum protection against oxidation during 

the entire annealing cycle. This may require that the 

annealing chamber be thoroughly purged of oxygen quite 

rapidly at the start of the heating cycle. The amount 

depends upon the gas volume involved (volume inside 

the inner cover minus the charge volume). It is a good 

practice to provide at least 10 volume changes by the 

time the charge has heated to 1000°F (540°C). Then, 

the atmosphere flow rate can be reduced to about five 

volume changes per hour until the charge cools to at 

least 700°F (370°C). 

Temperature Cycle - Annealing time should be as short 

as possible without producing excessive thermal gradients. Proper time must take into account the size and 

weight of cores being annealed and their relative 

degree of exposure to heating and cooling. For instance, 

1 ~O-pound cores with good exposure to the heating and 

cooling sources might require a minimum of six to eight 

hours to go from room temperature to the annealing temperature and back to 700°F (370°C) without experiencing thermal strains. With a lesser degree of exposure, it 

might require 10 hours for equivalent results. A temperature of about 1450-1500°F (790-820°C) is usually 

adequate for stress relief of most wound cores. It is usually desirable to hold or soak at 1500°F (820°C) until the 

desired minimum temperature is reached at the most 

protected location within the charge. If cores are not 

well exposed, this soaking period may be up to two hours 

in length. With maximum exposure, it might be as short 

as one-half hour. Furnace heat input should be adjusted 

so that the heating rate is not too great when approaching the soaking temperature. Rapidly forcing cores 

up to temperatures with extra high heat input is never 

advisable. It may be desirable to begin the cooling cycle 

. at a controlled rate if the natural cooling rate of the furnace is so rapid it might cause thermal strain. 

If cores are fabricated by cold-working procedures 

that produce plastic deformation of a relatively large 

percentage of the core volume, it may be desirable to 

employ a slightly higher soaking temperature for the 

anneal. A temperature of about 1550°F (845°C) will 

assure all the stress relief possible for drastically strained 

steel. However, this higher temperature should not be 

used unless experimentation with the cores being annealed shows that it is definitely beneficial. 

Continuous Batch-Type Furnaces 

Continuous furnaces usually yield best results in high 

production volume, primarily because relative exposure 

of cores or laminations to the heat source is much greater 

than in box furnaces, resulting in minimum annealing 

time and maximum exposure to the protective atmosphere. These furnaces usually fit well into automated 

production lines, but are less flexible and less economical than box furnaces or batch-type furnaces for varied 

or low-volume production. 

Continuous furnaces must have several controlled 

heating and cooling zones with individual control. These 

permit the heating rate to be adjusted so that heating 

and cooling gradients, particularly going into and out of 

the maximum temperature region of the cycle, will not 

be large enough to produce stress effects or distortion 

in the core. Unlike batch furnaces, continuous furnaces 

cannot be kept sealed for the entire cycle. So, atmosphere flow rates usually are substantially larger than 

for batch furnaces of equivalent volume. Separate 

entrance and exit chambers may be needed to 

minimize admission of air into the furnace when the 

charge is introduced or removed. 

Special Precaution for Annealing Wound Cores 

Exercise care to maintain the shape of rectangular or 

formed cores during annealing. Unless the cores come 

out of the anneal stress-free and in a shape that minimizes the reintroduction of stresses in assembly or as a 

result of framing, then even the most careful attention 

to other features of the stress-relieving treatment may 

be wasted. 

11 
CARLITE Types of Insulation Finish

A thermal flattening treatment is an integral part of the

process for the application of CARLITE 3 Insulation.

Because of the special insulation and flatness, material

with CARLITE types of insulation is used primarily for

flat sheared laminations and punchings. If CARLITE 3

types of finish offer special advantages, they can be

used for wound cores. However, when used for wound

cores, instead of Mill-Anneal Finish, the stress-relief

anneal should be in an oxygen-free nitrogen atmosphere

and the maximum charge temperature should never

exceed 1500°F (820°C). If the atmosphere contains

hydrogen, it should be kept below five percent to avoid

deterioration of insulative capabilities.

Batch-Type Furnaces

When annealing flat, sheared laminations for stacked

transformer cores in batch-type furnaces, care of

annealing bases and stacking plates, as well as the heating and cooling rates, become especially critical.

Unless such laminations are extremely flat after annealing, strains will be built into the transformer when the

laminations are stacked and clamped together.

Flat lamination production requires that the furnace

base must be maintained flat, and piling plates must be

flat and of adequate thickness to give firm support.

Shearing burrs must be kept very small or removed. This

prevents the accumulation of burr buildup that causes

the sheared edges of the laminations to stack higher

than the body of the laminations. Avoid furnaces that

require laminations to be stacked rather high for effective use of furnace space. Bowed laminations may

result from the accumulative burr buildup in high stacks

of laminations.

Practical experience shows that heating and cooling rates, together with the width of the laminations,

have an important influence in maintaining lamination

flatness in batch annealing. This is particularly true

where only one edge of the lamination is exposed to

direct radiation from the heat source. Rapid temperature changes create thermal gradients in the charge and

nonuniform thermal expansion or contraction. This may

result in the production of wavy laminations if the thermally induced forces exceed the yield point of the steel

which is relatively low at elevated temperatures. Once

developed, such waviness cannot be removed readily

in a reanneal and will cause increased core loss in the

assembled transformer.

To prevent thermal distortions, keep temperature gradients small when laminations are quite wide and the

charge is near the maximum temperature during both

heating and cooling. For 10-inch-wide (254 mm) laminations heated almost entirely from one edge (as might

be the situation where the charge is piled several stacks

wide), this might require that the edge heating rate not

exceed 40°F (22°C) per hour at 1400°F (760°C). Yet, with

the temperature at 1200°F (650°C) and the same piling

arrangement, the heating and cooling might be at 80°F

(44°C) per hour with safety.

On the other hand, with 5-inch-wide (127 mm) laminations and heating from one edge, the heating and

cooling rate at the exposed edge might safely be

about 150°F (85°C) per hour at 1400°F (760°C) and

300°F (165°C) per hour at 1200°F (650°C) without

causing thermal distortion. With single-width stacks

exposed to equal heating from opposite edges, these

heating rates could be up to four times as fast.

 EE-RM/STD-00-550 COMMENT 86

12 

CARLilE Types of Insulation finish 

A thermal flattening treatment is an integral part of the 

process for the application of CAR LITE 3 Insulation. 

Because of the special insulation and flatness, material 

with CAR LITE types of insulation is used primarily for 

flat sheared laminations and punchings. If CAR LITE 3 

types of finish offer special advantages, they can be 

used for wound cores. However, when used for wound 

cores, instead of Mill-Anneal Finish, the stress-relief 

anneal should be in an oxygen-free nitrogen atmosphere 

and the maximum charge temperature should never 

exceed 1500°F (S20°C). If the atmosphere contains 

hydrogen, it should be kept below five percent to avoid 

deterioration of insulative capabilities. 

Batch·Type Furnaces 

When annealing flat, sheared laminations for stacked 

transformer cores in batch-type furnaces, care of 

annealing bases and stacking plates, as well as the heating and cooling rates, become especially critical. 

Unless such laminations are extremely flat after annealing, strains will be built into the transformer when the 

laminations are stacked and clamped together. 

Flat lamination production requires that the furnace 

base must be maintained flat, and piling plates must be 

flat and of adequate thickness to give firm support. 

Shearing burrs must be kept very small or removed. This 

prevents the accumulation of burr buildup that causes 

the sheared edges of the laminations to stack higher 

than the body of the laminations. Avoid furnaces that 

require laminations to be stacked rather high for effective use of furnace space. Bowed laminations may 

result from the accumulative burr buildup in high stacks 

of laminations. 

Practical experience shows that heating and cooling rates, together with the width of the laminations, 

have an important influence in maintaining lamination 

flatness in batch annealing. This is particularly true 

where only one edge of the lamination is exposed to 

direct radiation from the heat source. Rapid temperature changes create thermal gradients in the charge and 

nonuniform thermal expansion or contraction. This may 

result in the production of wavy laminations if the thermally induced forces exceed the yield point of the steel 

which is relatively low at elevated temperatures. Once 

developed, such waviness cannot be removed readily 

in a reanneal and will cause increased core loss in the 

assembled transformer. 

To prevent thermal distortions, keep temperature gradients small when laminations are quite wide and the 

charge is near the maximum temperature during both 

heating and cooling. For 10-inch-wide (254 mm) laminations heated almost entirely from one edge (as might 

be the situation where the charge is piled several stacks 

wide), this might require that the edge heating rate not 

exceed 40°F (22°C) per hour at 1400°F (760°C). Yet, with 

the temperature at 1200°F (650°C) and the same piling 

arrangement, the heating and cooling might be at SO°F 

(44°C) per hour with safety. 

On the other hand, with 5-inch-wide (127 mm) laminations and heating from one edge, the heating and 

cooling rate at the exposed edge might safely be 

about 150°F (S5°C) per hour at 1400°F (760°C) and 

300°F (165°C) per hour at 1200°F (650°C) without 

causing thermal distortion. With single-width stacks 

exposed to equal heating from opposite edges, these 

heating rates could be up to four times as fast. 
In any event, the recommended maximum charge

temperature for flat laminations with CARLITE types of

insulation should not exceed 1450°F (790°C), except that

CARLITE 3 Insulation can withstand temperatures up to

1500°F (820°C). If all parts of the charge reach 1400°F

(760°C), this is usually adequate for stress relief of material. The requirements for inner covers, purging of the

annealing chamber and flow rate of the protective (nitrogen) atmosphere are generally the same as those

recommended for Mill-Anneal finish.

Continuous Batch-Type Furnaces

Small punched laminations are usually continuously

batch annealed in trays, frequently with the plane of the

laminations vertical. Consequently, they do not pose the

same temperature gradient problems encountered with

large sheared laminations. A soaking temperature in the

range of 1400-1450°F (760-790°C) is usually sufficient

to remove the shearing strains present in oriented grades

with CAR LITE types of surface insulation.

When continuous furnaces are employed for stress

relief of oriented materials, it is most important that the

temperature of the furnace zones and the speed of the

charge through the furnace are suited to producing a

desirable time-temperature cycle for the charge. Laminations are often introduced into the furnace with the

first zone at maximum temperature. However, for best

flatness, it might be found that the first zone in the furnace should not exceed a temperature of 1200-1300°F

(650-704°C). Likewise, when laminations are at a temperature over 1300°F (704°C), the gradient between adjacent zones should not be more than about 150°F (85°C)

during heating or 100°F (55°C) during cooling. This prevents excessive temperature gradients with the attended

possibilities of distortion of shape or thermal strain.

At temperatures substantially under 1200°F (650°C),

cooling in continuous furnaces may usually be as rapid

as desired. Temperature cycles should be checked by

placing thermocouples in the most shaded part of the

charge before deciding on final temperature and speed

for different charges.

A continuous flow of annealing gas should be maintained through the furnace. The charge may exit from

the protective atmosphere at 600-700°F (315-370°C).

Continuous Furnaces - Single Thickness Annealing

Excellent results can be obtained by continuous annealing of slit widths which are later cut to lamination length

or by the continuous annealing of single laminations

on a suitable conveyor. Heating and cooling must be

uniform from the plane of the strip, and conditions

conducive to good flatness must be maintained. An air

atmosphere can be used because the entire cycle

requires only a few minutes. Temperatures in the range

of 1450-1550°F (790-845°C) are usually employed.

 EE-RM/STD-00-550 COMMENT 86

In any event, the recommended maximum charge 

temperature for flat laminations with CAR LITE types of 

insulation should not exceed 1450°F (790°C), exceptthat 

CAR LITE 3 Insulation can withstand temperatures up to 

1500°F (820°C). If all parts of the charge reach 1400°F 

(760°C), this is usually adequate for stress relief of material. The requirements for inner covers, purging of the 

annealing chamber and flow rate of the protective (nitrogen) atmosphere are generally the same as those 

recommended for Mill-Anneal finish. 

Continuous Batch-Type Furnaces 

Small punched laminations are usually continuously 

batch annealed in trays, frequently with the plane of the 

laminations vertical. Consequently, they do not pose the 

same temperature gradient problems encountered with 

large sheared laminations. A soaking temperature in the 

range of 1400-1450°F (760-790°C) is usually sufficient 

to remove the shearing strains present in oriented grades 

with CAR LITE types of surface insulation. 

When continuous furnaces are employed for stress 

relief of oriented materials, it is most important that the 

temperature of the furnace zones and the speed of the 

charge through the furnace are suited to producing a 

desirable time-temperature cycle for the charge. Laminations are often introduced into the furnace with the 

first zone at maximum temperature. However, for best 

flatness, it might be found that the first zone in the furnace should not exceed a temperature of 1200-1300°F 

(650-704°C). Likewise, when laminations are at a temperature over 1300°F (704°C), the gradient between adjacent zones should not be more than about 150°F (85°C) 

during heating or 100°F (55°C) during cooling. This prevents excessive temperature gradients with the attended 

possibilities of distortion of shape or thermal strain. 

At temperatures substantially under 1200°F (650°C), 

cooling in continuous furnaces may usually be as rapid 

as desired. Temperature cycles should be checked by 

placing thermocouples in the most shaded part of the 

charge before deciding on final temperature and speed 

for different charges. 

A continuous flow of annealing gas should be maintained through the furnace. The charge may exit from 

the protective atmosphere at 600-700°F (315-370°C). 

Continuous Furnaces· Single Thickness Annealing 

Excellent results can be obtained by continuous annealing of slit widths which are later cut to lamination length 

or by the continuous annealing of single laminations 

on a suitable conveyor. Heating and cooling must be 

uniform from the plane of the strip, and conditions 

conducive to good flatness must be maintained. An air 

atmosphere can be used because the entire cycle 

requires only a few minutes. Temperatures in the range 

of 1450-1550°F (790-845°C) are usually employed. 

13 
Summary of Recommended Annealing Procedures

The principal requirements for stress-relieving of AK Steel

Oriented and TRAN-COR H Electrical Steels according

to the type of material are shown in the following procedures chart:

Annealing Procedures

CARLITE Type

Insulation (for

Mill-Anneal flat laminations)

Insulation (for Punching Quality

wound cores) only CARLITE 3

Maximum 1550°F 1450°F 1500°F

Charge (845°C) (790°C) (820°C)

Temperature

Minimum 1450°F

Charge (790°C) 1400°F (760°C)

Temperature

Atmosphere Dry nitrogen Dry nitrogen Dry nitrogen

with 0 to 10% H2 with 0 to 2% H2 with 0 to 5% H2

Time Minimum necessary to reach temperature in coldest part of

charge without imposing thermal strain from excessive

heating and cooling gradients.

Special Meticulously avoid Keep piling plates flat and give strict

Precautions oxidation as well attention to avoiding excessive

as carburization. temperature gradients in 1300-

Always use inner 1450°F (704-790°C) range. Avoid

covers in furnaces. exposure to hydrogen over 2% (5%

for CARLITE 3)

Figure 3

For advice on annealing specific sizes of laminations or

cores with specified piling arrangements, ask our

AK Steel specialists for technical assistance.

Core D esign

AK Steel Oriented and TRAM-COR H Electrical Steels offer

outstanding magnetic properties when the flux path is

parallel to the direction in which the steel was rolled.

This is due primarily to their highly perfected "grain

orientation."

However, this same orientation that improves magnetic characteristics in the rolling direction impairs

magnetic properties when the flux path is not parallel to

the rolling direction. This is illustrated in Fig. 3.

Polydirectional Permeabilities of AK Steel Oriented Electrical Steels

PERMEABILITY, u

at B= 15,000 Gausses

FLUX DENSITY and

Permeability

50°

70°

9

°

Figure 3. Tests made on Epstein samples cut at various angles to rolling direction, stress annealed after shearing.

Negligible joint effects. Assumed density 7.65 grams per cubic centimeters.

3

Angle From

Rolling Direction

50 °

70°

90°

14

 EE-RM/STD-00-550 COMMENT 86

14 

Summary of Recommended Annealing Procedures 

The principal requirements for stress-relieving of AK Steel 

Oriented and TRAN-COR H Electrical Steels according 

to the type of material are shown in the following procedures chart: 

Annealing Procedures 

CARLITE Type 

Insulation (for 

Mill-Anneal flat laminations) 

Insulation (for Punching Quality 

wound cores) only CAR LITE 3 

Maximum 1550°F 1450°F 1500"f 

Charge (845°C) (790°C) (820°C) 

Temperature 

Minimum 1450°F 

Charge (790°C) 1400°F (760°C) 

Temperature 

Atmosphere Dry nitrogen Dry nitrogen Dry nitrogen 

with 0 to 10% Hz with 0 to 2% Hz with 0 to 5% Hz 

Time Minimum necessary to reach temperature in coldest part of 

charge without imposing thermal strain from excessive 

heating and cooling gradients. 

Special Meticulously avoid Keep piling plates flat and give strict 

Precautions oxidation as well attention to avoiding excessive 

as carburization. temperature gradients in 1300-

Always use inner 1450°F P04-790°C) range. Avoid 

covers in furnaces. exposure to hydrogen over 2% (5% 

for CAR LITE 3) 

Figure 3 

For advice on annealing specific sizes of laminations or 

cores with specified piling arrangements, ask our 

AK Steel specialists for technical assistance. 

AK Steel Oriented and TRAN-COR H Electrical Steels offer 

outstanding magnetic properties when the flux path is 

parallel to the direction in which the steel was rolled. 

This is due primarily to their highly perfected "grain 

orientation." 

However, this same orientation that improves magnetic characteristics in the rolling direction impairs 

magnetic properties when the flux path is not parallel to 

the rolling direction. This is illustrated in Fig. 3. 

Figure 3. Tests made on Epstein samples cut at various angles to rolling direction, stress annealed after shearing. 

Negligible joint effects. Assumed density 7.65 grams per cubic centimeters. 
Note how rapidly the permeability at 15 kilogausses is

reduced when the direction of magnetic flux departs

substantially from the rolling direction. For example,

the magnetizing force must be about 100 times as

large to produce an induction of 15 kilogausses in the

45-degree direction as in the rolling direction.

Tape wound or spirally wound cores are the ideal

core form forthe oriented electrical steel grades because

the flux path is in the rolling direction. Design allowances will have to be made for the effects of any joints

in the magnetic circuit and other basic differences

between cores and Epstein test values. Stresses introduced by fabricating or assembly operations after stressrelief annealing also must be taken into consideration in

design. Fabrication methods which cause a very large

percentage of the core volume to be deformed beyond

the elastic limit should be avoided. These methods may

cause some slight permanent deterioration of magnetic

properties not recoverable in subsequent stress-relief

annealing.

In stacked core, the presence of joints and flux paths

in unfavorable directions make precise core design less

simple. The successful use of oriented grades demands

careful core design to minimize, or eliminate if possible,

all magnetic paths in unfavorable directions and high

reluctance in joints.

For approximating the excitation requirements and

losses of a particular core shape, break up the magnetic

path into parallel-grain, cross-grain and corner sections,

and calculate each section separately. Then combine

values for all sections to obtain the total for the core.

In small stacked cores, any flux paths not in the

rolling direction should be limited to relatively short

sections such as corners of conventional cores with

fairly long windows. In E and I assemblies, the legs

of the E and all of the I laminations should be blanked

in the rolling direction. Where E and I cores operate at

rather high inductions, it is often helpful to widen the

back of the E by as much as 35 percent to reduce flux

density, because here the flux path is transverse to the

rolling direction.

When stacking small E and I cores of oriented

material, interleaving of laminations one at a time is

desirable for best results at low and moderate

inductions. Cores operated at high inductions can be

stacked two or three laminations at a time.

Effects -'

The detrimental effects of stress introduced into laminations by shearing, forming, riveting or other fabricating operations is almost always extremely important

with oriented materials. These effects usually can be

eliminated by a suitable stress-relieving anneal after

fabrication to final shape (see section on Stress-Relieving Anneal). Great care must then be exercised to

assemble the stress-free laminations to avoid any appreciable stress due to bending in assembly. When

stress-relief annealing is impractical, or when some

stresses in assembly are unavoidable, these shortcomings must be compensated for by design allowance.

r ect o

r 3

Joints in a magnetic core can greatly increase the total

excitation requirements especially when operating at

inductions where the permeability of the material itself

would normally be very high. In cases where flux is

forced to pass perpendicularly to the laminations as in

areas adjacent to gaps formed by abutting laminations,

core loss may be increased appreciably. To reduce such

losses, care should be taken to minimize the number of

joints and the reluctance associated with them. Where

lowest exciting current is of prime importance and where

the path length in "iron" is relatively short as in small

cores, designers can profit by giving major consideration to improving the joints in their design.

It of Wave Forms

If the flux wave form is not closely sinusoidal, harmonic

components of flux will cause an increase in core loss

and exciting current because of increased eddy

currents and skin effect. These increases become

comparatively large if the exciting current is forced to

approach sinusoidal wave shape at moderate and high

inductions, because then the flux wave form will be

approaching relatively square wave shape. Since

harmonic components of flux cause increases in both

the "in-phase" and quadrature components of exciting

current, the operating a-c flux-current loop will be somewhat widened and altered in shape from that for

sinusoidal flux.

15

 EE-RM/STD-00-550 COMMENT 86

Note how rapidly the permeability at 15 kilogausses is 

reduced when the direction of magnetic flux departs 

substantially from the rolling direction. For example, 

the magnetizing force must be about 100 times as 

large to produce an induction of 15 kilogausses in the 

45-degree direction as in the rolling direction. 

Tape wound or spirally wound cores are the ideal 

core form for the oriented electrical steel grades because 

the flux path is in the rolling direction. Design allowances will have to be made for the effects of any joints 

in the magnetic circuit and other basic differences 

between cores and Epstein test values. Stresses introduced by fabricating or assembly operations after stressrelief annealing also must be taken into consideration in 

design. Fabrication methods which cause a very large 

percentage of the core volume to be deformed beyond 

the elastic limit should be avoided. These methods may 

cause some slight permanent deterioration of magnetic 

properties not recoverable in subsequent stress-relief 

annealing. 

In stacked core, the presence of joints and flux paths 

in unfavorable directions make precise core design less 

simple. The successful use of oriented grades demands 

careful core design to minimize, or eliminate if possible, 

all magnetic paths in unfavorable directions and high 

reluctance in joints. 

For approximating the excitation requirements and 

losses of a particular core shape, break up the magnetic 

path into parallel-grain, cross-grain and corner sections, 

and calculate each section separately. Then combine 

values for all sections to obtain the total for the core. 

In small stacked cores, any flux paths not in the 

rolling direction should be limited to relatively short 

sections such as corners of conventional cores with 

fairly long windows. In E and I assemblies, the legs 

of the E and all of the I laminations should be blanked 

in the rolling direction. Where E and I cores operate at 

rather high inductions, it is often helpful to widen the 

back of the E by as much as 35 percent to reduce flux 

density, because here the flux path is transverse to the 

rolling direction. 

When stacking small E and I cores of oriented 

material, interleaving of laminations one at a time is 

desirable for best results at low and moderate 

inductions. Cores operated at high inductions can be 

stacked two or three laminations at a time. 

The detrimental effects of stress introduced into laminations by shearing, forming, riveting or other fabricating operations is almost always extremely important 

with oriented materials. These effects usually can be 

eliminated by a suitable stress-relieving anneal after 

fabrication to final shape (see section on Stress-Relieving Anneal). Great care must then be exercised to 

assemble the stress-free laminations to avoid any appreciable stress due to bending in assembly. When 

stress-relief annealing is impractical, or when some 

stresses in assembly are unavoidable, these shortcomings must be compensated for by design allowance. 

Joints in a magnetic core can greatly increase the total 

excitation requirements especially when operating at 

inductions where the permeability of the material itself 

would normally be very high. In cases where flux is 

forced to pass perpendicularly to the laminations as in 

areas adjacent to gaps formed by abutting laminations, 

core loss may be increased appreciably. To reduce such 

losses, care should be taken to minimize the number of 

joints and the reluctance associated with them. Where 

lowest exciting current is of prime importance and where 

the path length in "iron" is relatively short as in small 

cores, designers can profit by giving major consideration to improving the joints in their design. 

Effects Wave Forms 

If the flux wave form is not closely sinusoidal, harmonic 

components of flux will cause an increase in core loss 

and exciting current because of increased eddy 

currents and skin effect. These increases become 

comparatively large if the exciting current is forced to 

approach sinusoidal wave shape at moderate and high 

inductions, because then the flux wave form will be 

approaching relatively square wave shape. Since 

harmonic components of flux cause increases in both 

the "in-phase" and quadrature components of exciting 

current, the operating a-c flux-current loop will be somewhat widened and altered in shape from that for 

sinusoidal flux. 

15 
f CJs r ix

A factor usually overlooked, but not always negligible

in core design, is the ratio of maximum to minimum

length of magnetic path. If this ratio is too much greater

than unity, the elements of shortest magnetic path

length may be operating at exciting forces (NI/1) excessively higher than those for the longest elements

of magnetic path. This will cause greatly increased flux

density at the inside periphery of the core compared

with that computed for the mean path length.

This non-uniformity of flux density in the core in

turn causes the wave form of the flux at the extremes

of the magnetic path to be distorted - even when

the total flux is sinusoidal. As a result, effects of

nonsinusoidal wave form will be present, to a degree,

depending upon the departure of the path length ratio

from unity and the moderating effects of the joint

reluctance along the maximum and minimum paths.

Steel

AK Steel Corporation

703 Curtis Street

Middletown, OH 45043-0001

Electrical Steels Customer Service

P.O. Box 1609

Butler, PA 16003-1609

Phone .................................................. 724-284-2800

www.aksteel.com

© 2000 AK Steel Corporation

Conversion of

The following conversion factors may be useful

in the application of data on AK Steel Oriented

and TRAN-COR H Electrical Steels:

Core loss at 50 Hertz ^ Core loss at 60 Hertz x

0.76

Kilogausses = Flux Lines per square inch

6450

Oersteds = Ampere-turns per inch

2.02

Webers = Flux Lines

108

Teslas = Kilogausses

10

Teslas = Flux Lines per square inch

64,500

Ampere/meter = Oersteds

0.01257

AK Steel Sales Offices

Atlanta, GA-Southeast Region ............. 770-514-0023

Baltimore, MD ..................................... 410-612-1338

Charlotte, NC ....................................... 704-662-0786

Chicago, IL-West Central Region ......... 630-368-0001

Cincinnati, OH- Mideast Region ........... 513-683-5300

Detroit, MI-North Central Region ......... 248-641-7595

Grand Rapids, MI ................................. 616-949-5278

Nashville, TN-Southwest Region ......... 615-771-3134

New England ....................................... 401-658-3468

Pittsburgh, PA ...................................... 412-635-9835

Tulsa, OK .............................................. 918-298-2272

International Sales-Houston, TX ... 281-872-8741

Specialty Stainless and Electrical

Commercial-Buda, PA ...................... 800-381-5663

7180-0139 7/00

 EE-RM/STD-00-550 COMMENT 86

A factor usually overlooked, but not always negligible 

in core design, is the ratio of maximum to minimum 

length of magnetic path. If this ratio is too much greater 

than unity, the elements of shortest magnetic path 

length may be operating at exciting forces (NII1) excessively higher than those for the longest elements 

of magnetic path. This will cause greatly increased flux 

density at the inside periphery of the core compared 

with that computed for the mean path length. 

The following conversion factors may be useful 

in the application of data on AK Steel Oriented 

and TRAN-COR H Electrical Steels: 

Core loss at 50 Hertz"" Core loss at 60 Hertz x 

0.76 

Kilogausses = Flux Lines per square inch 

6450 

This non-uniformity of flux density in the core in 

turn causes the wave form of the flux at the extremes 

of the magnetic path to be distorted - even when 

the total flux is sinusoidal. As a result, effects of 

nonsinusoidal wave form will be present, to a degree, 

depending upon the departure of the path length ratio 

from unity and the moderating effects of the joint 

reluctance along the maximum and minimum paths. 

Oersteds = Ampere-turns per inch 

2.02 

Webers = Flux Lines 

108 

Teslas = Kilogausses 

10 

Teslas = Flux Lines per square inch 

64,500 

AKSteel 

AK Steel Corporation 

703 Curtis Street 

Middletown, OH 45043-0001 

Electrical Steels Customer Service 

P.O. Box 1609 

Butler, PA 16003-1609 

Phone .................................................. 724-284-2800 

www.aksteel.com 

© 2000 AK Steel Corporation 

AK Steel Sales Offices 

Ampere/meter = Oersteds 

0.01257 

Atlanta, GA-Southeast Region ............. 770-514-0023 

Baltimore, MD ..................................... 410-612-1338 

Charlotte, NC ....................................... 704-662-0786 

Chicago, IL-West Central Region ......... 630-368-0001 

Cincinnati, OH- Mideast Region ........... 513-683-5300 

Detroit, MI-North Central Region ......... 248-641-7595 

Grand Rapids, MI ................................. 616-949-5278 

Nashville, TN-Southwest Region ......... 615-771-3134 

New England ....................................... 401-658-3468 

Pittsburgh, PA ...................................... 412-635-9835 

Tulsa, OK .............................................. 918-298-2272 

International Sales-Houston, TX ... 281-872-8741 

Specialty Stainless and Electrical 

Commercial-ButlEr, PA ...................... 800-381-5663 

7180-01397/00