4140 steel hardening

[ttao]

I always meet the problem about hardening 4140 steel at my work. I used to induction or flame harden 4140 heat treaded and stress released (HTSR) steel to HRC 54-56 but someone told me I should use 4140 annealed steel because if I use pre-hardened material, I need anneal it first and then re-harden it. I knew that the core of annealed 4140 likes mild steel, which is not I wanted. My past experience also told me that it does not need to anneal 4140 preharden steel before re-hardening. I am looking for suggeston that what is the adventage and what is application for hardening each material. Thanks for you help.

 

[ornerynorsk]

I have used much pre-hardened 4140 (~32RC) for various tooling applications and had it flame hardened with no problems. Most everything I work with has a cross sectional thickness of greater than 2 inches, and the very reason of not annealing it is to maintain that core hardness for overall strength and longevity of the tool. Did the person who suggested annealing have any experience with the material? I'm interested to hear what other posters have to share about this.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.