Accelerated test program results show which precipitation hardening stainless steels are resistant to stress corrosion cracking. In certain cases stress corrosion susceptibility was found to be associated with the process procedure

Humphries, T. S.

Nelson, E. E.

English

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June 1970	 Brief 70-10140 
NASA TECH BRIEF 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Stress Corrosion Cracking Evaluation

of Precipitation-Hardening Stainless Steel 
Flat Tensile Specimens Loaded in a Constant Span Fixture 
Precipitation-hardening (PH) stainless steels, such 
as the hardenable chromium stainless steels, under 
conditions of tensile stress and a corrosive environ-
ment suffer stress corrosion. As with most metals, 
the stress corrosion cracking susceptibility normally 
increases with increasing hardness or strength. How-
ever, the stress corrosion susceptibility is not governed
solely by hardness or strength of the material, but it 
appears to be associated with the processes used to 
obtain the desired material characteristics. Because 
of the limited amount of available test data, a program 
was initiated to evaluate the stress corrosion resistance 
of the more frequently used PH stainless steels in a cor-
rosive environment.
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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The PH stainless steels evaluated in this investiga-
tion were PH 13-8 Mo, PH 14-8 Mo, 15-5 PH, PH 
15-7 Mo, 17-4 PH, 17-7 PH, A-286, Almar 362, AM-
350, and Unitemp 212 in the form of bar stock and/or 
sheet. Three types of specimens were required to test 
the material in at least two directions of grain orien-
tation. Flat tensile specimens, loaded by constant 
deflection, were used for testing sheet material; round 
tensile specimens, stressed in direct tension, were used 
for testing the longitudinal direction of all bar stock 
and the transverse direction of two inch or greater 
diameter bar; and C-rings, utilizing the constant d- 
flection method, were used for testing the transverse 
direction of bar stock of less than two inch diameter. 
The specimens were deflected or strained the cal-
culated amount in order to reach the desired stress 
levels (see Fig.). After undergoing a cleaning cycle, 
they were placed in a ferris wheel type alternate im-
mersion tester containing a 3.5% solution (deionized 
water) of sodium chloride; the 10 minute immersion 
cycle was followed by a 50 minute drying period. This 
test phase continued for six months or until a failure 
occurred. The mechanical properties of the PH stain-
less steels were measured in both directions of testing 
at a stress level from 25 to 100% of the directional 
yield strength. Duplicate unstressed tensile specimens 
were exposed under identical conditions for compara-
tive control. 
The results of this accelerated test program indi-
cated: (1) The precipitation hardening PH 13-8 Mo, 
PH 14-8 Mo, 15-5 PH, 17-4 PH, A286, Almar 362, 
and Upitemp 212 stainless steels were highly resistant 
to stress corrosion cracking. (2) Alloys PH 15-7 Mo
and 17-7 PH were susceptible to stress corrosion crack-
ing in all heat treat conditions tested except Ch 900, 
and AM-350 was resistant in Condition SCT 1000 but 
susceptible in Condition SCT 850. (3) Precipitation 
hardening stainless steels appeared to be less resistant 
to stress corrosion cracking in the transverse direction 
of grain orientation than in the longitudinal direc-
tion. (4) The stress corrosion cracking susceptibility 
of the precipitation hardening stainless steels generally 
increased with increasing hardness or strength, but in 
certain cases appeared to be associated with the pro 
cess procedure used to obtain these properties. Alloy 
17-7 PH stainless steel exhibited the highest resistance 
to stress corrosion cracking in Condition CH 900, 
and this condition gave the highest hardness and 
strength of any of the conditions tested. 
The stress corrosion cracking resistance should 
be determined, for the precipitation hardening stain-
less steels in all recommended process and heat treat 
conditions because of the effect of these conditions on 
the resistance to stress corrosion cracking. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B70-10140 
Patent status: 
No patent action is contemplated by NASA. 
Source: T. S. Humphries and E. E. Nelson 
Marshall Space Flight Center 
(M FS-20667)
[1 
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Brief 70-10140	 Category 04


Stress corrosion cracking evaluation of precipitation-hardening stainless steel

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