best way to determine if SS has been cryo treated

[AndrewTT]

Lets say that you have a part made from UNS-S31600 and this part gets cryo treated for stress relief. Visually this part looks no different before or after cryo treatment. If you wanted to have a test in place to determine if a part had been cryo treated or not, in case there was ever any confusion, how would you do it? The cryo process should turn austenite into martensite.

Thanks.

 

[EdStainless]

316 should be 100% austenite, period.
If there was residual delta ferrite then the material was never properly annealed.
I won't ask why someone thinks cryo treating a single phase alloy could have any impact on residual stress or any other property of 316. This material is used in liquid He service because there are no phase changes.
But the answer is that there is no way to tell because the treatment does exactly nothing in this material.

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P.E. Metallurgy, Plymouth Tube

 

EdS is correct.
You are confusing austenitic 316SS with a ferritic, hardenable steel.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[arunmrao]

The OP is confusing about cryo treatment for Tool Steels. In tool steels,, typically the retained austenite is converted into martensite, but then in 316 austenite remains stable all along and does not form martensite.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[AndrewTT]

Correction: the material is UNS-J92800. The cryo process is doing something to this part b/c it performs much better in boiling MgCl2 stress-cracking test with cryo treatment than without treatment.

 

[EdStainless]

So these are castings, have they been solution heat treated after casting?
How were they cooled? (this is the source of the residual stresses.
How much retained delta ferrite is there in them?
You can get some stress equalization (the places of highest stress go down, the lowest rise slightly) by doing temperature cycles over the range of a few hundred degrees. That may be the effect that you are seeing in this material.
We used to use a couple of cycles between -75F and 400F for this. It made the parts more stable.

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P.E. Metallurgy, Plymouth Tube

 

[AndrewTT]

Solution Annealed = yes.
how were they cooled = unknown.
how much retained delta ferrite is there = unknown.

Back to the original question. Is there a "quick" way to determine if a part has been cryo treated or not (the MgCl2 test is not quick)?

Thank you.