NASA TECHNICAL

hlEMORANDUM

(SASA-TH-1-73375) T P i S l E L S S COShOSICY 1377-~121% ~ b 5 ~ S I B Y C E A N f THE C R Y C C E b I C Z Z U F E S A l U ~ E E L C B A b i l C I l P F C E E E i I I B S CF HCT E O L L E C h I T F C B I c 32 BAS R A T E E i t L (PASB) 24 p HC 3@2/CE 101

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TEE STRESS CORROSION RES ISTPNCE PND THE CRYCGEF: IC TEI\'PERATURE MECHAN i C A L PROPERTIES OF HCT ROLLED NITRONIC 32 BAR MATERIAL

By J. W. Montano Materials and Processes Laboratory

April 19;:

NA!iA

Gelvge C. Marsh&// Space Fhght Center

MLars!3aU Space F@t Center, Aldhdma

MSFC - F o r m 3l9U ( R e v June 1971)

https://ntrs.nasa.gov/search.jsp?R=19770014270 2018-07-05T17:55:53+00:00Z

NASA TM X-73375 I . T T L E AND SUBTITLE 5. REPORT DATE

h e Shes Corrosion Resisb~ce and , llpril 1977 The Cryogenic Tempemtore Mecttanical Properties of 6. PERFORM~MG ORGANIZATION COOL

Hot Rolled Nitronic 32 Bar Material 1. AVTnOR(S) a. PERFL '411.5 ORGAN1 ZATION REPORT I

J. W. Montano - ). PERFORMING ORGANlZATtON NAME AND ADDRESS t o . iVORK UNIT NO.

NASA - George C. Marshall Space Flight Center Marshall Space Flighi Center, AL 35812

- 1 1. CONTRACT 5.. GRANT NO. I- 13. T Y P r OF REPOR. & PERIOD COVEREC

2. SPONSORING AGENCY NAME AND .-DRESS Tecbnica l Mem-randum

National Aeronautics and Space Administration Washington, D. C.

I CPONSOR!HG AGENCY COOE

I

5. SUPPLEMENTARY NOTES

Work performed by Mater:als and Processes Laboratory, Science and Engicetring

. A~STRACT This report presents the ambient and cryogenic temperature mechanical properties and the ambient temperat-#re stress corrosion properties of hot rolled and centerless ground Nitronic 32 stainless steel bar material.

The mechanical properties of longitudinal specimens were evaluate& at test tempemtures f r m ambient to liquid hydrogen. The tensile test data indicated increasing smooth tensile strength with decreasing temperature to liquid hydrogen temperature. However, below -200'~ (- 1 2 9 . 0 ~ ~ ) the notched tensile strength decreased slightly and below -320'~ ( - 196 .0~~ ) the decrease was signifi- cant. The elo~gation and reduction of area decreased drastically at temperatures below - 2 0 0 ~ ~ (- 129.0'~). The Charpy V-notched impact enesy decreased steadily with decreasing test temperature.

Stress corrosion tests were performed on longitudinal tensile specimens stressed to 0, 75, and 90% of the 0.2% yield srrength and on transverse "C"- ring specimens stressed to 75 and 90% of the yield strength and exposed to: a l temat immersion in a 3.5% NaCl bath, humidity cabinet environ ment, and a 596 sol t spray atmosphere. The longitudinal tensile specimens experienced no corrosive attack; however, the "CU- rings exposed to the alternate immersion and to the salt spray experiened some shallow etching and pitting, respectively. Small cracks appeared in two of the tlC"- rings a f k r one month exposure to tile salt spray. Metallographlc examination did not reveal the branchias phenomenon associated with stress corrosion cracking.

7. KE'f WORDS 1 18. DISTRIBUTION STATFMENT

Cryogenic Temperature Unclassified - Unlimited Altemcte Immersion Humidity Sol t Spray Metal lography

19. SECUR'TY CLASSIF. (d t h t ~ r*pd..1, 20. SECURITY CLASSIF. (of thl* PO*) 2 i . NO. OF PAbES 22. PRICE

Unclassified Unclassified 2 2 NTIS ~ B F C . Form 3291 (*Y 1969)

TABLE OF CONTENTS

kF

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SUMMARY 1

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

EQUIPMENT AND MECHANICAL TEST SPECIMENS . . . . . . . . . . . . . 3

STRESS CORROSION E S T PROCEDURE AND TEST SPECIMENS ...... 3

......................... RESULTS AND DISCUSSION 4

1 . MECHANICAL PROPERTIES EVALUATION ........... 4

2 . METALLOGRAPHY OF AS RECEIVED BAR MATERIAL ..... 4

. . . . . . . . . . . . . . . 3 . STRESS CORROSION EVALUATION 4

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

LIST OF TABLES

Table Page

I Chemical Composition of Nitronic 32 Stainless Steel Alloy Bar 8

I I Low Temperature Mechanical Properties of Nitronic 32 Stainless 9 Steel Longitudinal Tensile Specimens 0.250- lnch (0.635 cm) Diameter - Machined from a 1.00- lnch (2.54 cm) Diameter, Hot Rolled and Centerless Ground Bar

11 1 Low Temperature Impact Energy of Nitronic 32 Stainless Steel 10 Charpy V-Notched impact Specimens per Federal Test Method STD No. 151 - Machined from a 1.00- lnch (2.54 cm) Diameter Bar

I \/ Mechanical Properties of Ni tronic 32 Stainless Steel Lo~~ i t ud ina l I 1 Tensile Specimens 0.1250- Inch (0.3175 cm) Diameter - Machined from o 1 -00- lnch (2.54 cm) Diameter, Hot Rolled and Centerless Grwnd Bar [E>.psed to Various Environments]

Title P 0 s e

Smooth Tensile Test Specimen Configuration . . . . . . . . . . . . . 12

V-Notch Tensile Test Specimen Configuration . . . . . . . . . . . . 12

Stress Corrosion Test Specimen Configurations . . . . . . . . . . . . 13

Low Temperature Mechanical Properties of Hot Rolled Nitronic 32 Stainless Steel Specimens M a c h i d from a 1.00- Inch (2.54 an) Diameter Bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Low Temperature Kotched Properties of Hot Rolled Nitronic 32 Stainless Steel tlar Specimens . . . . . . . . . . . . . . . . . . . . 15

Microstructure of Nitronic 32 Skinless Steel Bar . . . . . . . . . . 16

Nltronic 32 Stainless Steel Specimens Stressed to 90% of Yield Strengh, Exposed for 180 Dars to:

a. Alternate Immersion

b. Salt Sproy

c. Humidity Environments . . . . . . . . . . . . . . . . . 17

Nibonic 32 Stainless Steel Cracked "C"- Ring and Microstructure After 180 Ooys ~f Sal t Spray - Stressed to 75% of Yield Strength . . 18

Technical Menlorandurn X-73375

SUMMARY

This report presetits the ambient and cryogeaic temperature mechanical properties and ambient tempemture stress corrosion properties of hot rolled and cecterless ground Nitronic 32 stainless steel bar material. Test specimens were manufactured frun a 1 -00- inch [2.54 un) dio-.-ieter bar.

The mechanical property tests were periogned at tem ratures of 75'~ (?3.9Oc), 8e OOF (-17.8~~). -100'~ (-73.0°c), -200 F (-129.0 C), - 3 2 0 ~ ~ (-196O~)and -423O~ (-252 .PC). These tests included smooth tensile (ultimate, yield, modulus, elongation and reduction of area), V-notched tensile (notched tensile strength and notthed/unnotched tensile ratio), and Charpy V-notched impact. The test data indi- cate an increase in smooth tensile proper'ies with decreasing tempemture. Below -200'~ (-129.0'~) the notched tensile sirengh decreased moderately to liquid nitrogen temperature, then drastically between liquid nitrogen and liquid hydrogen temperatures. The elongation and reduction of area decreased drastically below - 2 0 0 ~ ~ (-129.0~~). The Charpy V-notched inpact energy decreased steadily with decreasing test temperature decreasing to a minimum individual test value of 15 f t - Ibs (20.3 Joules) at the lowest impact test temperature of - 3 2 0 ~ ~ (- 196'~).

Results of h e 180 day alternate immersion, salt spray and humidity tests on longitudinal tensile specimens (stressed to 0, 75, and 90% of the 0.2% yield strength) and tror~sverse "C"- rings (stressed to 75, and 90% of the yield strength), indicate that the alloy has excellent resistance to stress corrosion cracking when tested in the longitudinal direction. The design of the "C"- ring specimens made them vulnerable to an end grain attack which caused some shallow etching and pitting of the specimens exposed to the alternate immer- sion and to the salt spray environments. Metallographic examination of the pits did n ~ t reveal tC? branching phenomenon associated with stress corrosion cracking.

l NTRODUCTION

Nitronic 32 (formerly know- as 18-2 Mn), an austenitic stainless steol developed by Armco Steel Company, i s an alloy from a new family of stainless steels in which manganese and nitrogen are substituted for a portion of the usual nickel content. This hitronic stainless was chosen for evaiuatim due to i t s unusually high yield strength in the hot rolled bar cmdition, its good corrosion resistance, and its excellent anti-gal ling properties. I t i s also lighter than most stainless steels and less costly when compured to type 304 stainless steel . Nitronic 32 stainless steel i s an iron base alloy containing approximately 18% chromium, 1.6% nickel, 12% manganese, 0.5% silicon, 0.100h carbon, and 0.34% nitrogen. The chemical composition of the 1.00- iilch (2.54 cm) diameter bar material shown i n Table I i s from Armco Steel Company's heat number 536480. This alloy as supplied in the hot rolled and centerless ground condition i s sold for marine applications sucl: as propeller shafts, and i s also designated as Aqua-Met 18.

EQUIPMENT AND MECHANICAL TEST SPEC!MENS

The equipment used in the mechanical properties evaluation i s described in a report by the author (Ref. 1). Tensile specimens, smooth and V-notched, are illustrated in Figures 1A and 10 , respectively. The Charpy V-notched specimen configuration was in accordance with Federal Test Method Standard No. 151A Method 222.1 .

STRESS CORROSION TEST PROCEDURE AND TEST SPECIMENS

The equipment and the test procedure used in the alternate immersion (A.I.) stress corrosion test i s described i n a report by Humphries (Ref. 2;. The A.I. bath i s a 3.5% NaCl solution maistained at a pH of 6.5- 7.2, a temperature of 80O~ + ZOF

(27 '~ + 1°C), and a water purity per ASTM-D-1193-7 Type II. The A.I. cycle i s 10 minutes in solution and 50 minutes out of solution. The salt spray test utilized the procedures of ASTM-B-117-64, "Standard Method of Salt Spray (Fog) Testing, I' which specifies a 5% salt solution at a pH of 6.5- 7.2 and a temperature of 95 '~ (35'~). The humidity test was conducted in a cabinet maintained at 98% relative humidity and a temperature of 95 '~ (35'~).

The longitudinal tensile specimens and the transverse "C"- rings illustrated in Figure 1 C were degreased with acetone, stressed, then recleaned with ace tone prior to the 180 day exposure in the corrosive environments. Tlne stress applied to the tensile specimens was 0, 75, and 90% of the 0.2% yield strength while {he "C"- ring specimens were stressed to 75 and 90% of the yield strength. Unstressed tensile specimens were also exposed to the same environments.

The stress corrosion testing schedule i s outlined below:

Test Applied 3 tress Specimens Per Specimen % of 0.2% Y .S . Stress Level Environments

Tensile 0, 75, 90 4 A.I., Salt Spray, Humidity

#*CI~ - :ing 75, 90 4 A.I., Salt Spray

"C" - ring 75, 90 3 Humidity

RESULTS AND DISCUSSION

1. Mechanical Properties Evaluation

The tensi!e test resvlts of the ambient through cryogenic temperature mechanical properties evaluation and the Charpy V-notched impact data are tabulated in Tables II and Ill, respectively. These properties are also plotted in Figures 2- 3.

Table I1 contains test data on hot rolled and centerless ground bar material tensile specimens. These tensile test data indicate an increase in ultimate tensile and 0.2% yield strengths with decreasing temperature. Below - 2 0 0 ~ ~ (- 129. O'C) there i s a drastic decrease in elongation (percent in 4 diameters) and reduction of area. The notch tensile strength (NTS) increased with decreasing test temperature to -200'~ (-129.0'~). Below that temperalure to liquid nitrogen temperature there was a moderate decrease in the NTS. Between liquid nitrogen and liquid hydrogen tempera- tures there was a drastic reduction of N T S resulting in a notched/unnotched tensile ratio of 0.53 at -423'~ (-252.8'~).

Table Ill indicates a steady decrease in Charpj V-notched impact energy with decreasing tsmperature, dropf ing from an ambient temperature average impact energy of 155.0 ft - Ibs (210.1 Joules) to a liquid nitrogen temperature average impact energy of 20.1 f t - Ibs (27.3 Joules). The variation in impact energy within a given tempera- ture rcnge can be attributed to the hot working and centerless grinding of the bar.

2. Metallography of As Received Bar Material

Figure 4 shows the microstruck-e of the longitudinal and transverse directions of the hot rolled and centerless ground bar material. The grains are extremely smoll and are free from any precipitated carbides in the grain boundaries. The stringer material shown in the longitudinal microstructure i s typical of the Ni+ronic stainless steels s x h as Nitronic 33 and Nitronic 60. Previous analysis of these nitronic steel 3trin~ei-s by Energy Dispersive Analysis of X-rays (EDAX) revealed them to contain the deoxidation additives, aluminum orld calcium.

3. Stress Corrosion Evaluation

Table IV contains test dc;ta prior to and after 18C days exposure to the following environments:

(1) A1temo.e Immersion - 3.5Oh NaCl Bath, 80'~ (27'~)

(2) Sal t Spray Cabinet - 5.096 NaCl Fog, O ~ O F (35'~)

(3) Hdmiaity Cabinet - 98% Relative Humidity, 95'~ (35'~)

3. Stress Corrosion Fvaluation (Cont'd)

These data indicate that the longitudinal tensile specimens were not susceptible to stress corrosion cracking, even when stressed to 90% of the 0.2% yield strength and exposed for 180 days to the environments listed above. However, after 180 days exposure to the various environments there was an increase in the mechanical properties of the 0% stressed specimens due, possibly, to aging.

These data i n Table IV obtained from 0.1250- inch (0.3175 cm) diameter bar specimens also indicate the variable depth of hardening obtained by hot rolling. When the tensile test data i n Table IV i s compared with the tensile test results in Table II, obtained from 0.250- inch (0.635 cm) diameter bar specimens, the effects of hot rolling, specimen size, and specimen location become more evident. Thc varioble strengths are reflected in the specimen size and specimen location as taken from the bar edge or center.

Figure 5 illustrates iypical tensile and "C" - ring specimens stressed to 90% of the 0.2% yield strengths and exposed to the corrosive environments, listed above, for 180 days.

The "C" - ring specimens exposed to the alternate immersion experienced only superficial etching. After approximately four months exposure small shallow etching was &served on the specimens surface and after 180 days exposure shallow pits were present.

The "C" - ring specimens exposed to the salt spray experienced some pitting . Small cracks appeared in two of the "C" - ring specimens after one month exposure to the salt spray, however neither of these specr~ens failed in 180 days exposure.

Figure 6 illustrates the resultant corrosive attack caused by the end grain surface pitting. The "2" - ring specimen shown in Figure 6 was stressed to 75% of the 0.2% yield strength and exposed for i80 days to the salt spray. As previously mentioned minute cracks and pitting began in the "C"- ring after one month exposure.

The humidity cabinet environment produced no rusting, pitting, cracking, or failures i n the stressed "C" - ring specimens.

CONCLUSIONS

Based upon the results of this evaluation of Nitronic 32 stainless steel hot rolled and centerless ground bar material specimens, the following conclusions are drawn:

(1) The ultimate tensile and 0.2% yield strengths of the longitudinal tensile specimens increased with decreasing temperature to liquid hydrogen temperature.

(2) The elongation (percent in 4 diameters) and reduction of area indicated excel lent ducti l i ty from ambient temperature to -200O~ (- 129.0"~).

(3) The notched to unnotched tensile ratios (Kt = 5.8) remained above 1.00 from ambient to liquid nitrogen temperature.

(4) Charpy V-notched impact eneigy decreased with decreasing temperature, yet remained above 35 .O f t - ibs (47.4 Joules) a t -200'~ (- 129. G'c).

(5) Considering the overall mechanical properties obtained in this evaluation, Nitronic 32 stainless steel al loy bar i t 1 the hot rolled and centerless ground condition could be utilized in tension applications from ambient temperature to -200'~ (- 129.0"~).

(6) Nitronic 32 stainless steel hot rolled and centerless ground bar material, as tested in this program, i s not susceptible to stress corrosion cracking in the longi- tudinal direction, even when stressed to 90% of the 0.2% yield strecgth and exposed ts 180 days of moisture and chloride environments.

(7) Transveise "C" - ring specimens exposed to alternate immersion and to the salt spray environments experienced shallow surface etching and pitting, respec- tively. I f lengthy exposure to a chloride environment i s anticipated, protection should be provided to prevent a cor;osive end grain attack.

(8) Considering the overail stress corrosion data obtained in this evaluation, N i t r ~ n i c 32 stainless steel al loy bars [ 1.00- inch (2.54 cm) diameter] in the hot rolled and centerless ground condition could be utilized in applications whrtre 300 series stainless corrosion resistance i s needed, yet additional strength i s required.

REFERENCES

1. Montano, J. W .: "A Mechanical and Stress Corrosion Evaluation of Custom 455 Stainless Steel Alloy," TMX-64682, August 2, 1972.

2. Humphries, T. 5 .: "Procedures for Externally Loading and Corrosion Testing Stress Corrosion Specimens, " TMX-53483, June 29, 1966.

TABLE I

CHEMICAL COMPOSITION OF NlTRONlC 32 STAINLESS STEEL ALLOY BAR*

- - - - --

Analysis Fe C r Mn N i S i C P S N Other Eiement:

Nominal Main 18.00 12.00 1.60 0.50 0.10 - --. 0.34 -

Arrnco Main 17.86 12.24 1.50 0.57 0.10 0.019 0.005 - 0.38

MS FC Main 17.7 12.2 1.6 0.50 0.10 0.015 0.007 0.33 -

' Armco Heat No. 536480

TABLE II

LOW TEMPERATURE MECHANICAL PKOPERTIES OF NlTRONlC 32 STAINLESS STEEL LONGlTUDlNAL TENSILE SFECIMENS -- -- 0.250 INCH (0.635CM) DIAkETER - - MACHINED i---.- FROM, A 1.00 INCH (2.54 -- CM) DIA. HOT ROLLED AND CEIJTERLESS GROUND BAR

4 - - test Ultimate .P? Offset Elongation Reduction Fracture Malults N/U* No.

Ternperowre Tensile Strength Yield Strength 1.00- In (2.54 cm) of Area Strength X 10- Tensile of OF ec) - ~ S I ( G N / ~ ) KSI ( G N / ~ ? ) - - 40% - % KSI (GN/~?) PSI ( G N / ~ ~ ) Ratio Tesb - -- --- -

- -- -

Average Stress Concentration Factor Kt = 5.8

TABLE Ill

LOW TEMPEWTURE IMPACT ENERGY OF NlTRONlC 32 STAINLESS STEEL CHARPY V-NOTCHED IMPACT SPECilviEiuS PER FEDERAL TEST METHOD STC. NO. 151

MACHINED FROM A 1.00 - INCK (2.54 CM) DIANtESkR BAR

Test Charpy V-Notched Temperature Impact Energy

OF r c j Ft - Lbs (Joijles) 160.Q 244 .O

75 (+23.9) 132.0 179.0 141 .O 191.2 167.0 226.4

I

Avg . 155.0 210.1

Avg . 125.4 ?70.0

-

Avg . 79.1 107.2

-200 (- 129.0) 35.0 47.4 38.0 51.5 46.0 42.4 46.5 63.0

5 i

Avg . 41 .4 56.1 *

Avg . 20.1 27.3

TABLE IV

MECHANICAL PROPERTIES CF :\IITROFJIC 32 STAINLESS STEEL LONGITUDIN/r,L TENSILE SPECIMENS 0.1250 INCH (0.3175 CM) DIAMETER - MACHOJED FROM A 1.00 INCH (2.54 CM) DIA. HOT ROLLED A N D CENTERLESS GROliAD BAR

(STRESSED A N D EXPOSED TO C0RRO;IVE ENVIRONMENTS FOR 180 DAYS)

Applied Stress Ultimcte 0.2% Offset Elongation Reduction Fracture Moduks Nutnber Pe~cent of Tensile Strength3 Yie ld Strength 0.5 - In. (1.27 cm) of Area Strength X10- of

YieldStreogth KSI (GN,/me-) KSI ( G N / ~ ~ ) - -- - --- 40% '36 KSI ( G N / ~ ~ ) PSI ( c N / ~ ~ ) Tcttr - -- -- -- -- A, R.sceived Mechanical Pronerties 1

Alternate Immersion - 3.5 Percent NaCl Bath 8 0 ' ~ (27 '~)

Salt Spray Cabinet 95 '~ (35'~)

Humidity Cabinet 95'~ (35'~) 98% H.H.

Armco Heat Nu. 536480

'AS Received Mechanical Property determination made on 0% Stressed o rd OOh Exposed Specimens.

.375R (.952) r .250 (.635) 1/2-20 Thds/lnch (No Metric Equivalent)

I 16

-

-- I - 1.312 (3.332) - I

- 2.700 (6 ;8) -----I Dimensions in Inches (Dimensions in Centimeters)

FIGURE 1A - SMOOTH f ENSILE SPLCIMEN CONFIGURATION

Notch R a d ~ u s 0015 + 0000 -. 0C05 1 /2-20 Thds/ln ( 0038 + 0060 - 001 3j Thread Both Ends

(No Metrlc Eqi;ivale:it) 250 + 00 1 - 000 -

( 635 + 002 - 000) Chamfer

050 ( 127)

-7 I

Dimens~ons In Inches D!mens~ons In Centimeters (

12

FIGURE 10 V--NOTCHED TENSILE SPEC!MEN Cf.lNflGURATiON

'No Mclrnc E q ~ t v o l e n t i

lh-20 Thds/lnch

7 - Dimensions In Inches

' Dom~ns~ons I* C e m r ~ m e ~ e r s ~

(. 5 1 0 ) DRILL - 2 0 1 D'A.

TnRu B o r n SIDES^

D:MENSIONS IN INCHES Dlrnenr~ons In Centimeters ( )

FIGURE 1C - STRESS CORROSION TEST SPECIMEN CONFIGURATIONS

Temperature, deg C

Hot Rolled (Aqua-Met 18) 6ar Spectmens - 1 930

0.250-Inch (0.635 Cm) Diameter - 1.793

- 1.655

- 1.517

2 - 1.379 ;

- 1.241 \ 3

- 3 - 4 0

Elongat~on (4D%) o -

VI P - 2 0 0 3 - - 10 & 8

14 Temperature, deg Fahr FIGURE 2 - LOW TEMPtRPTURE MECHANICAL PROPERT!ES OF HOT ROLLED NITRONIC 32 STAINLiSS STEEL SPECIMENS MACHINED FROM A 1 00 INCH 12 54 CM) DIAMETER BAR

Temperature, deg C

Charpy Impact

APPROVAL

THE STRESS CORROSION RESISTANCE AND THE CRYOGENIC TEMPERATURE MECHANICAL PROPERTIES OF

HOT ROLLED NlTRONlC 32 BAR MATERIAL

J . W . Mon tono

'%e information i n this report has been reviewed for security classification. Revie;; of any i n f ~ m t i o n concerning Department of Defense or Atomic Energy Commission programs hus been made by the MSFC Security Classification Officer. This report, i n i t s entirety, has been determined to be unclassified.

This document has also been reviewed and approved for technical accurcrcy.

Chief, Metallurgy Research Branch

Director Materials and Processes Laboratory

*U.S. GOVERNMENT PRINTING OFFICE 1977-7000491225 REGION NO. 4