I have a pin (4" length, 1.5" diameter) of 4340 that was heat treated to RC40 which requires rework: turning down the diameter about .004" to meet the drawing's spec. Does the part require heat treatment again (RC40 specified on drawing)? More importantly, can someone explain why heat treatment would be required again after rework is done? I don't think the machinist intends on annealing it before reworking. I'm not a manufacturing engineer and just trying to understand. Thanks!
I'm not convinced you're using the right words here.. One might case harden to a RC40 (Rockwell Hardness) I'm not sure one can heat treat the material (4340) to a Rockwell hardness of RC40.
Heat treating can create a higher hardness the difference being that the core of the material is hardened as well. If the surface being re-worked is case-hardened by QPQ, nitriding, etc.. and needs a RC40 hardness then yes a re-case harden process would need be done.
Case-hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal (called the "case") at the surface.
So, the big question is how or what process was utilized the harden the material?
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