Originally Posted By: ed good
please define case?

My understanding is that this process, color case hardening, is done because the steel of the part does not have enough carbon in it to harden by conventional heat treating. I believe given the correct conditions created by this process, carbon defuses into the part. It seems to have been shown to require a low carbon steel for carbon to diffuse into the part and it seems to have been shown to only penetrate a few thousands?

Are you thinking that a crack formed in that few thousands on the surface, or did the entire part become somehow brittle and crack? If the entire part cracked, was it a good candidate to attempt this process, or was the process done incorrectly, or some of both? Possibly, not entirely related to just tempering?