TIG mild steel onto HARDENED STEEL?

By barryh Date 05-16-2001 14:40

I need some advise, I need to weld a MT5 taper onto the center of a 12" faceplate
the MT5 is factory made and hardened, the plate is 3/8" mild steel. I have a nice TIG setup,
Miller Dialarc HF, how can I do this weld without having problems, can it be done?

I will be grateful for any advise.

This face plate will be chucked in a huge wood lathe with a 100lb to 200 lb piece of wood
bolted to it, so I need to be sure the weld will hold and the taper won't fracture after the
welding is done.

thanks,
Barry

By G.S.Crisi (****)

Date 05-22-2001 13:38

I don't know whether I'm still on time to give you an advice. If so, I'll tell you that you can NOT weld hardened steel.
Reason 1. The surface is too hard and it won't accept a weld.
Reason 2. The heat input would remove the hardening.
What you should do is to normalize the hardened piece, i.e., submit it to a thermal treatment called "normalizing" which will completely remove all of the hardening, weld it to the mild steel and case harden it again. In doing this, the piece that was normalized will harden again but the mild steel will not, because it doesn't have the sufficient carbon content.
Giovanni S. Crisi
Sao Paulo - Brazil