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NATIONAL BUREAU OF STANDARDS REPORT

2427

on

Stress-Rupture Tests at 1 350 °F on Type 304 Stainless Steel

By

William D. Jenk ins

and

Wi 1 1 iam A. Wi 1 lard

Thermal Metallurgy Section

Metal 1 urgy Division

and

William J. Youden

Applied Mathematics Division

To

Test Methods Panel of the ASTM-ASME Joint Committee on the Effect of Temperature on the Properties of Metals

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions find Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards'; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

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Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.
NBS 259 (Rev. 3/1/50) United States department of Commerce

Washington

iSattonal pureau of ifetanbarbs

Report

Mo. 21*27

on

Stress-Rupture Tests at 1350°F on Type 304 Stainless Steel

By

Wt 1 1 lam 0. Jenkins

and

William A. Willard

Thermal Metallurgy Section

Metal lurgy Division

To

Test Methods Panel of the ASTM-ASME Joint Committee on the Effect of Temperature on the Properties of Metals

I* Introduction

Tests were made at the request of the Test Methods Panel to determine

the suitability of a heat of 304 stainless steel for use as calibrated

specimens for stress-rupture testing. It was requested that the tests be

made at 1350°F under a stress to give an average life of 100 hours on specimens selected to evaluate the uniformity of the bars processed from the heat.

II. Material and Testing Procedures

Fart of a basic electric heat (No* C-804) of 304 stainless steel was

supplied by Universal Cyclops Steel Corporation In the form of 15/16" square

(rounded corners) by 10-12' bars (9400 pounds) In the condition as annealed.

The heat was cast Into 8 Ingots, each weighing approximately 3150 pounds and

designated 1 to 8, Inclusively, In the order of pouring. The bars supplied

were processed from ingots 3, 4, 5, and 6. All bars were Identified as to

Ingot, and some were also Identified as to the position In the Ingot (top,

middle, bottom). The bars were annealed by the manufacturer by heating

2

at 1950-1 975 °F for 1 hour before quenching in water in three lots (A, B,

and C) as follows:

Lot A - all bars from ingot 3;' 1/3 of bars from ingot 6 .

Lot B - all bars from ingot 4; 1/3 of bars from ingot 6 .

Lot C - al 1 bars from ingot 5; 1/3 of bars from ingot 6 .

The chemical composition of the heat is given in table 1.

Hardness surveys (Rockwel 1 B) were made at room temperature on cross- sections prepared from some of the annealed bars as received. The values

ranged from about Rockwell B 69 to 72 with an average of approximately 71*

A metal log raph i c examination was also made on specimens of the bars,

as received, and on specimens after testing in creep at 1350°F.

Representative structures are shown in figure 1.

The form and dimensions of the stress-rupture specimens are given in

figure 2. These specimens were machined on centers in a lathe to a reduced

diameter of approximately 0.002 inch oversize and a slight taper (reduced

section approximately 0.001 inch less at the midpoint than at the shoulders)

according to a form block attached to the cross-slide of the lathe carriage;

light cuts were used to finish the reduced section to these dimensions. The

specimens were then finished to size by grinding on centers in a direction

parallel to the axis in a specially designed machine; the grinding wheels,

1 1/2 in. dia. x 1/4 In. wide, were made with a soft rubber binder and

grinding was dry at a speed of 2400 RPM.

The stress-rupture specimens were machined from the selected

Identified bars from the positions In the cross-section according to a test

program (table 2) that was statistically designed. The axis of specimens

from the “a" position in the cross section was the same as the axis of the

bars, and that corresponding to the "b" position was 5 / 16" from the outer

surface.

The specimens were heated in air overnight (approximately 16 hr.) to

about 1325°F and the temperature was raised, the following morning, to

1350°F. The specimens were held at temperature 1 to 1 1/4 hr. before

applying the desired load corresponding to a stress of 13*500 psi. A few

exploratory tests were made at stresses ranging from 13*000 to 14,600 psi

(table 3). The stress-rupture machines were of a multiple-lever type with

motorized jacks to prevent shock loading. Three stress-rupture units were

used; each was recently calibrated at room temperature with a proving ring.

Autographic strain-time data were obtained from direct-contact follow-up

type extensometers attached to shoulders of specially-designed adapters.
t ; ss - rt j !
- 3

-

The temperature was uniform over the length of the specimen and was maintained at \3'?0°F - 4°F throughout the test. The furnace (l6" long),

the lot of 22-gage Chromel -A1 umel thermocouple wire, and the potentiometer

used were also calibrated. A hot junction of one thermocouple was attached

to the center and the hot junction of another couple to the bottom end of

the reduced section of the specimen; new couples were used for each test.

III. Resul ts

The experimental results are summarized in tables 3 to 8 and figures

3 to 6.

- 4 -

IV, Statistical Analysis of Stress-Rupture Data of Table 5

by

William J. Youden

The data for the three ingots 3, 4, and 5 were examined as a group.

The average of the 18 tests (using averages where duplicates were available)

Is 100.3 hours. The averages for each of the three stress-rupfcure units are

1 11 1

102.8 100.5 97.6

The averages for the three bar positions Aa , Ab, Bb, are

Aa Ab Bb

101.6 97.7 101.6

The averages for the three ingots 3> 4, and 5 are

3 4 5

Unadjusted ave. 108.1 93.1 91.9

Adjusted ave. 105.3 103.0 92.6

The averages for the three positions In an ingot are

Top Center Bottom

Unadjusted ave. 111.5 92.2 97.1

Adjusted ave. 112.9 9^.7 93.3

The adjustments are made necessary because top positions were run on only two ingots, and the same was true for center and bottom positions. For

example, the center samples were taken from ingots 4 and the weaker ingots.

Statistical analysis showed that test specimens from the same position

in the same ingot showed a standard deviation of 11.0 hours. Specimens from

different positions chosen- from different ingots show a standard deviation

of 21.5 hours, just about twice that from specimens from the same part of

the same Ingot. The material Is definitely heterogeneous, but most of this

arises from the high values associated with specimens from the tops of Ingots.
'

.
- 5 -

This heterogeneity within ingots Is verified by the data on ingot 6 which

gives the following averages (based on three specimens)

Top ' Center Bottom

111.0 102.5 85.8

This ingot, however, shows differences in all three positions. The estimate

of error based on the triplicate specimens from the parts of this ingot is

8.0 hours, consistent with the 11.0 hours obtained above.

The analysis of these data show that three different sets of testing

equipment could be calibrated so that the results were within three percent

of the average for the three sets of equipment. The heterogeneity of the

material was avoided by assigning to each test equipment the same number of

specimens from each ingot and from each part of an ingot.

The preparation of the specimens is clearly adequate or the good

agreement between test equipments would not appear.

Specimens from different bars and from either the corner or center

of the cross section of a bar gave results that have a standard deviation

of 11 percent provided the bars are from the same part of the same ingot.

This standard deviation is doubled if the specimens come from different

parts of different ingots. A standard deviation of 20 hours means that

two results may easily differ by twice this amount. The four highest and

the four lowest results bear out this spread:

129. 1; 128 .9; 121.8; 114.1

76.3; 77.4; 78.0; 81.0

These eight are the extremes from 30 tests that average close to 100 hours.

The evidence shows that it Is possible to calibrate the test equipment much

closer than the variation shown by this material.

USC0MM-NBS-DC
.

.
Table l Chemical Composition (Percentage by Weight) of the

Steel Used, as furnished by Universal Cyclops Corp.

Ladle analysis

C - 0.071 Cr - 18.64

Mn - 1.76 Nl - IO.56

SI - 0.57 Mo- 0.18

s * 0.010 Co - 0.12

p - 0.023 Cu - 0.10

Check analysis on bar product

Ingot No. 4 6

C 0.069 0.069

Mn l .63 1 .67

SI 0.53 0.54

Cr 18.66 18.68

Nl 10 . 5^ IO.56
4
Table 2* Design of the Stress-Rupture Teat Program,,

Position Speci- Testing

in men ' ISquipment

Ingot Ingot Bar Position

I II III

(A a X

Top ]a b X

(B b X

(A a X

I Center

|

A b X

(b b X

/

A a X

Bottom / A b X

/ 1 B b X

/

A a X

Top

1

A b X

b X

( A a X

2 Center b X

( B b X

(

A a Bott om

1 A b

^ B b

/ A a X

Top

l A b X

b X

f

A a

3 Center

J A b

i B b

f A a X

Bottom

]

A b X

b X

r a a Top b

i B b

r A a X

U Center

1 A b X

b X

/

A a Bottom

)

A b X

l B b X

Ear A Bar A Bar B

15/16"

Position of specimen in cross section of bar
s'
Table

3*

Summary

of

Conditions

Used

and

Results

of

Exploratory

Stress-Rupture

Tests.

Specimens

Tested

at

1350°F

with

Different

Stresses*

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Summary

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Used

and

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Stress-Rupture

Tests,

Specimens

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13

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Ingot

Position

In Ingot Bar

Specimen

Pos 1 1 1 on Testing Equipment No,

Average

( Ingot)

A a 121.8

Top A b I 09.6

B b

* 101.7

A a 101.1

6 Middle A b 1 10.7 99.8

B b 95.8

A a 95.8

Bottom A b 77.4

B b 84.3

Top

A

A

a

b {,?!:? 89.8

B b 104.1

A a 103.3

5 Middle A b 81 96.1

B b 95.2

A a Bottom A b

a b

A a 129.1

Top A b 128.9

B b 114.1

A a

3 Middle A b 108.1

B b

A a 84.1

Bottom A b 98.2

B b 94.4

A a Top A b

B b

A a

4 Middle A b

|7o*

76.3 96.7

B b 110

A a 102.5

Bottom A b 111.8

B b m

Average (Testing Equipment) 103.7 100.5 96.2 100.1

Table 5». Effect of conditions used on the rupture time (hours). Specimens tested

at I350°F with stress of 13,500 psi.
. - "
Ingot

Pos 1 1 1 on

In Ingot Bar

Speci- men Position

Testing Equipment No.

~1 T~

Average

(ingot)

A a 0.17

Top A b ; 0.19

B b 0.24

A a .26

6 Middle A b .21 0.23

B b .21

A 3 .25

Bottom A b

B b .26

A a .22*

Top A b .25

B b .20

A a .21

5 Middle A b .32 .24

B b .23

A

" a Bottom A b

B ba .15

Top A b .16

B b .18

A a

3 Middle A b .20

S b

A a .26

Bottom A b ,2b

B b —

A a

Top A b

B b

A a .24*

4 Middle A b .24 .24

B b .24

Ar a .22

Bottom A b .22

8 b .26*

Average (Testing Equipment) .21 .22 .25 .23

* Average of 2 tests

Table 6. Effect of conditions used on the second-stage creep rate, percent per

hour. Specimens tested at 1350°F with stress of 13*500 psf.
% - .
Ingot

Position

In Ingot Bar

Spec l

men Position

Testing Equipment No* Average

( Ingot)

1 2 3

A a 29

Top A b 32 - B b 33

A a 56

6 Middle A b 31 33.2

B b A

A a 32

Bottom A b 3b

B b 37

A a 39*

Top A b 36

B b 32

A a 1+0 5 Middle A b bO 36.7

3 b 33

A a Bottom A b

B b

A a Top A b 26

B b 32.5

A a

3 Middle A b 3b. 5 3 b

A a 38

Bottom A b 36.5

B b 1+1 A a

Top A b

B b

A a 36*

b Middle A b 1+6.5 39.2

B b 37

A a 36

Bottom A b 39-5

3 b bo*

Average (Testing Equipment) 53 37 A 36.1 35.5 * Average of 2 tests.

Table 7 . Effect of conditions used on the elongation values (# In 1 l A Inch)

Specimens tested at 1350°F with stress of 13,500 ps I

f*os 1 1 1 on Spec!-

Average

( ingot)

In men Testing Equipment No.

Ingot ingot Bar Pos I t 1 on 1 2 3

A a 35

Top A b 39*5

B b *U»5

A a 43

6 Middle A b 42 41.7

a b 4l

A a 36

Bottom A b hk

B b *t}.5

A a ^9*

Top A b 59

B b bo

A a 44

5 Middle A b hh 42.4

B b 38.5

A a

Bottom A b

B b

A a 34

“To75~

Top A b

B b 36

A 3

3 Middle A b 39*9

B b

A a 42.5

Bottom A b 43

B b *3.5

A a Top A b

B h

A a 36,5*

4 Middle A b *0.5 41 .5

B b 4o

A a 40.5

Bottom A b *2.5

B b 4?*

Average (Testing Equipment) 39 A 41.5 42.4 41

* Average of 2 tests.

Table 8. Effect of conditions used on the reduction oT area values (percent).

Specimens tested at 1350°P with stress of 13*500 psl.
i

*• ^
igure 1 Structure of

Longi tudinal

acid (10$).

the steel as annealed and after testing at 1350°F to rupture,

sections. Etched in 5 parts HC1 (cone.) and 2 parts chromic

A. Initial structure, center of specimen.

B. Structure, center of specimen, at time

Co Structure, near fracture, at center of

129.1 hr. x 100

D. Same as C. x 500

E. Structure, near fracture, at center of

76.5 hr. x 100

F. Same as E. x 500

x 100

of application of stress, x 100

specimen, after rupture in

specimen, after rupture in

r JA

7*

8

NJ

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1 a

xr* *

3 r° z

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Figure 2. Form and dimensions of stress-rupture specimen.

50

40

30

20

10

0

40

30

20

10

0

i

re ». Strain-time curves for specimens tested at 1350°F with

a stress of 13*500 psi.

Final point on each curve indicates rupture

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Figure 5 . Strain-time curves for specimens tested at 1350°F with

different stresses.

STRESS,

psi

Figure .6 . Effect of stress on second-stage creep rate, rupture

time and ductility of specimens tested at 135Q°F.

Numbers adjacent to points Indicate the number of

values averaged at this stress.

U. vS. DEPARTMENT OK COMMERCE

Ltswls Ij. Stt-ritHM, Secretary

NATIONAL tUMftAU OF STANRAIIDH

A. V. Antlil, l)lrp.ct.or THE NATIONAL BUREAU OE STANBARBS

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® Office of Basic Instrumentation. p Office of Weights and Measures. BOULWIUl* COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction.

Bndlo Propagation PliyNicft. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Sun-Earth Relationships. VUE Research. Ionospheric Communication

Systems.

Studio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radii* Systems Application Engineering. Rndio-Mcleoroingy.

Iludio Standards. High Frequency Electrical Standards. Radio Broadcast Service, High

Frequency Impedance. Slwmlards. Electronic Calibration Center. Microwave Physics. Microwave

Circuit Stundards,