How to estimate strength increase from cold work

[nickjk]

Is there any way to estimate increase of tensile and yield strength due to cold work (hydro-form) and shot peening.

I am currently making thin wall (.020") tubular blanks (1.037 O.D.) from 304/304L stainless in the annealed condition. The blanks are hydro-formed with a perimiter elongation of approx 11%. There are multiple small .062" radius's formed to the blanks wall during hydroform.
After hydro-forming I would like to have the blanks shot peened to increase fatigue characteristics and cold work.

The material in the annealed condition has a tensile strength of approx 81,000 psi and a yield strength of approx 30,500 psi.

I have seen data showing 304 at 1/2 hard having tensile strength of 150,000 psi and yield strength of 110,000 psi and at full hard tesile of 185,000 psi and yield strength of 140 psi.

An FEA study on the design shows a maximum tensile bending stress of 90,000 psi. I was told that the peening process would put the tensile surface into approx compression by 30,000 psi when no load is applied.

Any input or advise would greatly be appreciated.

Thank you,

Nickjk

 

[Metalguy]

Try contacting Metal Improvement Co. (MIC).

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[nickjk]

I have a meeting with Metal Improvement Co. on Thursday.
They are the source I plan on having do the shot peening.
Thank you
Nickjk

 

[EdStainless]

you will be no where near 1/2 hard.
use your FEA to determine local strains, then look at work hardening curves to estimate what the strength will be.
If you want fatigue you also need a few other things:
1. start with clean steel, not standard 304L
2. achieve the best surface possible in the areas of crack initiation, electropolish


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Plymouth Tube

 

[nickjk]

EdStainless,
304L was selected based on its corrosion resistance and formability properties.

"you will be no where near 1/2 hard."
even with the 11% elongation during hydroforming?


Would I look at local strains with load applied or during hydroforming?
I will research the work hardening curves for 304.
What about the work hardening caused by shot peening?

Thank you,
Nickjk

 

[EdStainless]

the peening work should be rather shallow.
11% isn't that much on 304, look at the reductions in cold rolling and wire drawing.

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Plymouth Tube

 

[Guest102023]

Heat-to-heat variation in mechanical properties and work hardening rates is considerable for the austenitic stainless steels.