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Originally Posted by Ambush Master
Cool............Very Cool...........What about Cryogenic Tempering?!?! 
Later
Martin |
Freeze treatment (from -100F to -320F) after the initial hardening steps described above continues the transformation of the carbides for better and stronger steel. Said another way:
The deep freeze increases the driving force inside the steel to force the completion of the austenite to martensite transformation.
It is critical that this step is followed by a heat tempering cycle, well under the transformation point, to remove just a bit of hardness from the steel to keep it from being too brittle for use.
I use liquid nitrogen for the cryo step here, that's -320 F.
Personally I won't let steel set overnight from the deep freeze cycle but always get it right back up to room temp and into the first temper cycle to make sure it doesn't sit there and break itself because of the tremendous stresses being generated inside.