Stress Relieving 304L

[PhilScrimp]

I have a 304L SS weldment that will require machining after fabrication. There is some distortion in the weldment that is outside the required tolerances. If the weldment is constrained inside the tolerance, welded to keep it constrained, and then low temperature stress relieved (700-800F), will it hold the constrained shape after stress relieving and cutting the welds?

 

[btrueblood]

Are you maintaining the constraint through both welding and stress relief? Then maybe. But the act of machining may also introduce stress and/or stress relief all by itself, so...the answer is (as always) try it and see.

 

[EdStainless]

You won't get stress relief at those temperatures.
If you over constrain the part when welding you risk hot cracking.
You need to look at the weld sequence and heat inputs to try to maintain shape.

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P.E. Metallurgy, Plymouth Tube

 

[PhilScrimp]

The thought was (probably a bad one) to use a strong-back across a flange face and bolts to pull it inside the tolerance. Once inside the tolerance, tack or stitch weld the parts. Send the parts through stress relief. The tack/stitch welds would be removed after stress relieving.

 

[Chumpes]

hi
stress relief of austenitic stainless steels could eventualy be conducted at (roughly) 900-950°C (1650-1750F), and as Ed points, 700-800F is not a stress relief temperature for SS (nor for CS !)

 

The purpose of stress relief is not to correct distortion. Managing distortion is done during the design and welding stages. Strong-backing mentioned by PhilS is a brute-force but effective method.

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

 

[MagBen]

A further question:
If it (Type 304) is heavily cold worked, could stress relief (no effect on tensile, but with a slightly decrease in hardness) help? I am having flatness/warp issue after cold worked flat bars were ground.

 

[EdStainless]

How were they straightened Ben?
SR on heavily cold worked SS is a dicey situation.
I have done it at 900-950F.
It shouldn't change tensile or hardness, but the parts may become slightly less ferromagnetic.
I would also be suspicious of your grinding, it is easy to 'grind in' stresses.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Ed, thanks for reply.
We use 2-roll straightener. The extra or non-uniform stress could be from either from drawing or from straightening. Bars without straightening or less straightening seem perform better.
yes, there is aggressive grinding. we are trying to roll, instead of drawing to get better surface such that there is no or less aggressive grinding.
Less ferro is actually a benefit for application.
Not sure if a SR can help. I can do some experiment but afraid it would be hard to assess, other factors could take leading main roles

 

[EdStainless]

You would be better off stretching them to straighten them.
Try to SR a sample and see what happens to the magnetic properties.

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P.E. Metallurgy, Plymouth Tube

 

[Chumpes]

dear Ed,
can you please confirm your statement about austenitic stainless steel PWHT temperature ?
you said 900-950F and i believe if is 900-950°C
thanks
regards

 

[EdStainless]

This is not PWHT, this is just trying to reduce peek local residual stress.
You can get rid of the worst of the local peak stresses by soaking at 900-950F.
IT won't give you full stress relief, but it will knock down the highest areas.
If you are going to 900C you might as well do an actual anneal at 1050C.
One issue with the higher temps is that if you get rapid or uneven cooling you will end up with high residual stresses. And at those temps you will get some distortions so you are back to trying to straighten again.

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P.E. Metallurgy, Plymouth Tube

 

If it is really a problem just go for a full anneal as EdS says. That would give the SS material a fresh start on all potential issues of concern.
You should then qualify a new welding procedure.

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

 

[PhilScrimp]

So, does anyone have recommendations of a company or firm that I could work with to develop a heat treat procedure that would work best with my application?

 

[EdStainless]

Where are you located?
I have worked with the guys at Solar and had very good results.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Have also used Solar with great results. Heat treatment parameters were developed by Solar personnel and myself.

 

[PhilScrimp]

I'm in MS. Thanks! I will investigate that group.