It can have a profound effect on the mechanical properties of certain steels, provided their composition and prior heat treatment are such that they retain some austenite at room temperature.
[2] The transformation from austenite to martensite is mostly accomplished through quenching, but in general it is driven further and further toward completion as temperature decreases.
The transformation between these phases is instantaneous and not dependent upon diffusion, and also that this treatment causes more complete hardening rather than moderating extreme hardness, both of which make the term "cryogenic tempering" technically incorrect.
Many alloys that do not undergo martensitic transformation have been subjected to the same treatments as steels—that is, cooled with no provisions for cold work.
If any benefit is seen from such a process, one plausible explanation is that thermal expansion causes minor, but permanent deformation of the material.