There are two varieties of sub-zero or cold treatments performed on metals, the first treatment is used to maximize the hardening transformation (transformation of retained austenite to untempered martensite), especially in the case of highly alloyed steels. It consists of cooling the parts to approximately –120°F /-84°C, followed by tempering, it also provides a measure of dimensional stability.

The second is more oftened known as deep-cryogenics and goes beyond what sub-zero accomplishes. These processes necessitate temperatures in the neighbourhood of -300°F and cycles must be carefully executed in multi-staged fashion so as to approach the process temperatures very gradually. The same care and attention is required when returning to ambient conditions. In certain cases (following a theory of micro-carbides being precipitated) both wear-resistance and toughness have been known to increase dramatically.