Clipped form of cryogenic treatment, in which hardened parts are ramped slowly down to around minus 185 to minus 196 °C, held for many hours, warmed back and tempered. It converts retained austenite and is credited with better wear life in knives, dies and cutting tools. On many floors, sending parts to cryo is used loosely for any sub-zero step.
Knife blanks are back from cryo, get them into the temper oven at 400 before they sit overnight.
The slow ramp is the point: dunking a hardened part straight into liquid nitrogen is a reliable way to crack it.
Also heard as
- cryogenic treatment
- deep cryogenic treatment
- DCT
Related terms
Sub-zero treatment
Chilling hardened steel well below room temperature to turn retained austenite into martensite.
Retained austenite
Austenite that fails to transform during the quench and survives at room temperature inside hardened steel.
Tempering
Reheating hardened steel below its lower critical temperature to trade some hardness for toughness.