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420ss Hydrogen embrittlement

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tmalinski

Mechanical
Oct 14, 2002
424
I make a small stamped sheetmetal component out of 420ss annealed. Its .030 thick and has several small holes pierced thru in the annealed state. These parts then get heat-treated to 48-52Rc with a deep freeze and double temper process. After heat treat the parts are formed to a gentle S curve like ribbon candy (no hard bends). Then we Stress Relieve them at 700 deg F for 1 hr.
My qustion is, Does the stress relieve process itself reduce or aggrivate the potential for Hydrogen Embrittlement?

thanks,
Tom

Tom Malinski
Dell Prec 670, Xeon 3.8,2GB Ram, Nvidia Quadra FX 3450/4000 SDI
SWorks Pro & PDMWorks 2007 SP3.0
 
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Heating Type 420 stainless steel to 700 F (370 C) means that you are essentially tempering it a third time, because this is the maximum tempering temperature used to obtain 48-52 HRC. There will not be much stress relief at that temperature, so I don't think it will do much to either reduce or increase the chance for delayed fracture.
 
It will reduce hydrogen, since diffusion is so fast at 700. There is still the risk that the material contained hydrogen earlier in the process and you developed microcracking during earlier operations.

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If you have any concerns related to delayed cracking from hydrogen perform a wet fluorescent MT. If the parts have no reportable indications, they should be good to use.
 
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