Originally Posted By: 2-piper
.....it is given the Quench from still above its critical temp, which is necessary for it to harden. This high carbon layer which is hardened is known as "The Case"....


Thanks 2-piper, this is what I was curious about. Some formation of nice colors seem to be done at a temperature that is below critical. Do you have a ballpark on what critical temps. might be. Again, just wondering not trying to stir anything.