You must temper the steel after your hardening process Before cryo treating, then temper again. The cryo treat in my experience does several things: it will relieve a little stress, raise the Rockwell hardness# by 1 or 2 points therefore requiring retempering, and refine the internal grain structure of the steel.
This process is not required though and I have heard some outlandish claims as to its effectiveness, but on most "stainless" and air hardening steels it helps a lot. Just my :2cents: