Retreatment of Steel

[TChronos]

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?

 

[Metalguy]

No, but watch closely for decarb.

 

[TVP]

I agree with Metalguy. Decarb is your enemy.

 

[israelkk]

Grain size increase is a problem you have to avoid too

 

[TChronos]

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.

 

[Metalguy]

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.

 

[unclesyd]

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.