how critical is it NOT to use martensitic steels in condition A without heat treatment? 1

[glulambeam]

On the surface, 15-5 in condition A, AMS5659 has excellent strength properties (F.tu = 160 ksi, F.ty = 140 ksi on the AK Steel website (aksteel.com), etc)

I was told by one of the older materials engineers (now retired), that one should never use 15-5 in just its annealed condition due to...potential stress corrosion cracking issues that can crop up? How critical of a problem is this really, if we're talking about hardware that's going to live in a regular, non-marine clean room environment? The piece would be a #3-56 threaded rod subjected to a max preload of 300 lbs in its life.

 

[EdStainless]

Most of the PH stainless grades (semi-martensitic, 17-4, 13-8, 15-5 and so on) have very unreliable properties and very low low ductility when they are annealed. You should never use them in this condition if there is any load at all.
If those strength levels are fine then go ahead and have the material aged. Aging at H1150 will give you roughly the same strength, double the ductility, and assure what properties you actually have.
I presume that this is a thick part, why else would you be using 15-5PH. For thin parts the more common 17-4PH would be the first choice. There are really no advantages to using 15-5PH unless you have heavy sections.

To quote Armco (from 17-4 lit):
This alloy exhibits useful mechanical properties in Condition A. Tests at Kure Beach, NC, after 14 years show excellent stress corrosion resistance. Condition A material has been used successfully in numerous applications. The hardness and tensile properties fall within the range of those for Conditions H 1100 and H 1150. However, in critical applications, the alloy is used in the precipitation-hardened condition, rather than Condition A. Heat treating to the hardened condition, especially at the higher end of the temperature range, stress relieves the structure and may provide more reliable resistance to stress corrosion cracking than in Condition A.


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P.E. Metallurgy, Plymouth Tube

 

[metengr]

How critical of a problem is this really, if we're talking about hardware that's going to live in a regular, non-marine clean room environment? The piece would be a #3-56 threaded rod subjected to a max preload of 300 lbs in its life.

Condition A for 15-5 PH has lower ductility but very good strength properties. If what you have stated is accurate, Condition A would work.

 

[MagBen]

it is not recommended to use as condition A due to low toughness, poor impact strength and susceptibility to stress-corrosion cracking. as for strength, except for overaged condition, aged material should still have higher strength than solution annealed. one benefit though to use annealed material is no need to worry about contraction upon hardening. Also, material is often supplied with condition A.

 

[EdStainless]

In condition 'A' I have seen the yield strength very by a factor of 2, and elongations that are <2% are not uncommon.
Just don't do it.
Use H1150 and you can still easily machine after aging.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Sorry, but I have not seen elongations less than 2% for Condition A PH material we have ordered over the years. Sounds to me there was a problem with the Condition A treatment from the mill or the material itself was of poor quality. How the hell would you even form or weld in Condition A before aging heat treatment with elongations this low, as is typically done with typical material in Condition A treatment.

There is nothing wrong with using material in the Condition A treatment PROVIDED you understand the limitations.

 

[MagBen]

we do not have lots of data for condition A since people do not care much about properties at this condition, rather we offer capability properties with samples aged and tested longitudinal for small bars, transverse for large bars. A few customers order directly the aged material, samples are tested as shipped condition.
Condition A: longitudinal elongation normally >10%, transverse 2% not uncommon. Welding in A condition is normally fine.

 

[glulambeam]

Thanks for the inputs!

 

[tbuelna]

From MMPDS-01, section 2.6.7.0, "Heat Treatment — 15-5PH must be used in the heat-treated condition and should not be placed in service in Condition A."


I would agree with the recommendation to use the stock 15-5PH material in an H1150 condition. The material hardness in H1150 condition is Rc 28-37 per AMS 2759/3, which is readily machinable and even suitable for roll forming 3-56 UNJF-3A external threads.