Heat treated 431 or 19-9DL Steel

[mighoser]

Why are these two steels prohibited by most Military M&P Specs? For example: MIL-STD-1587C (page 10) I'm most interested in stainless alloy 431. What would warrant a complete prohibition and if it were to be used what steps should be taken? (NDI...???)

 

[mighoser]

It looks like the low strength heat treatment can be found in NASM3-20 bolts. Anyone know about 431 treated in the 200ksi range. Issues??

 

[metengr]

At this strength level, there is a significant increase in susceptibility to stress corrosion cracking and hydrogen embrittlement in certain environments.

 

[mighoser]

metengr,

Why a ban on all heat treated 431?

 

[metengr]

mighoser;
I'm not an aerospace standards expert, only a boiler and pressure vessel/Power Generation metallurgist. Just for kicks I did review the Carpenter web site (see at the end of this post), because they supply Type 431 stainless steel. Low and behold, they do reference this material for use in the following military specifications;

MIL-S-18732
AMS-5628

http://www.cartech.com/

You can register for free and locate Type 431 stainless steel under High Strength, Conventionally-Hardened Grades. An excellent technical database for future reference.

 

[mighoser]

Metengr,

Mil-s-18732 is inactive for new design. We do spec stainless 431 to ams-5628 but were required to get a waiver to use it. I wonder if this prohibition is the sum of several bad experiences with the alloy in the heat treated condition.