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Retreatment of Steel

Retreatment of Steel

Retreatment of Steel

(OP)
A batch of our torsion springs were heat treated to the wrong hardness (too soft-RC42 vs RC46-48). The metal is 9254. Is there any reason these couldn't be rehardened?

RE: Retreatment of Steel

No, but watch closely for decarb.

RE: Retreatment of Steel

I agree with Metalguy.  Decarb is your enemy.

RE: Retreatment of Steel

Grain size increase is a problem you have to avoid too

RE: Retreatment of Steel

(OP)
Is there a preferred approach to avoiding these problems, or will I have to wait until it's done and do some testing?

Also, these have already been shotpeened. I assume that will have to be redone.

RE: Retreatment of Steel

You will have to re-shot peen, that's for sure.  I wouldn't worry about the grain size either-the hardening temp. is low enough not to increase it in normal short time-at-temp.

By all means sacrifice a couple of springs and have a met. lab. look for decarb.  That can be a spring-killer, even on the 1st HT.

RE: Retreatment of Steel

What caused the low hardness, Austenizing temperature or Tempering Temperature?

I would not reharden unless I annealed the parts first.

Yes the shot-peening will have to be redone.  Be careful with your intensity as it will be different this time around.  I would talk with my shoot peening provider.
 
With a good atmosphere furnace and oil quenching Decarb should be no problem.
Watch where you take your hardness readings.

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