Stress relief 316LS 1

[MagBen]

Anyone knows the possible physics behind this?
I did stress relief annealing (800, 850, 900, 950F/ 4hous) on heavily cold worked flat 316 LS bars. It was found tensile and yield strengths were increased considerably! It seemed unlikely the test variation issue because all 4 temperatures had similar results.

 

[EdStainless]

How magnetic is the cold worked bar?
How magnetic are the aged samples?
I think that you know where I am going with this.
The yield strengths are neither here no their, small changes in residual stress will change the yield.
How much did the UTS change?
And what about the elong?

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

Ed, I thought too there might be some martensitic transform, but both CW and annealed bars had not response to a permanent magnet. I will try to run a subtle permeability test to see if any small ferromagnetism gained.
UTS increased by 10ksi, Yield by 20ksi, EL decreased by 1.5-2 %

 

[MagBen]

Perm was measured less than 1.01, practically no martensitic or ferritic phase.
some residual stress moved from edge to middle upon annealing (mid-radius tension was tested, bar size is around 1.5x0.5'')?

 

[MagBen]

carbide precipitates at 800F even? could that increase strength level?

 

[EdStainless]

It is possible that the strain combined with the temp could give a little precipitation.
What shape are these?
Were all of the tests done in the same orientation/direction?
I am beginning to think that small changes like this are all related to residual stress.

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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

well, 20ski increase is not a very small change.
Ed, how do you think it is related to residual stress? And yes, the purpose was to decrease residual stress (or make stress distributed more uniformly) to alleviate the deformation after grinding. It is flat bar at 1.5x0.5''. Tension test is always along the drawing direction.

 

[EdStainless]

You said high strength. In tubing we commonly see changes of 10-15ksi in UTS related to stress from cold work.
After all if there was residual tensile stress in the bar to start with that would 'assist' you in pulling the tensile samples.
Remove that stress and you have to pull harder.


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P.E. Metallurgy, Plymouth Tube

 

[MagBen]

this is something i never thought of! Thanks Ed, regardless if or not this is a correct statement!