I don't have data on brake rotor material but I can tell you that on properly heated tool steels it does absolutly nothing. If it is a cast wrought, rolled or forged or whatever matrial you have, what you want in a situation like this is low residual stress and toughness with just enough hardness that surface seizures or galling won't happen. After 1 thermal cycle above the annealing temp of any part of the rotor any possible claimed benifit would be erased. At temp way below melting temp most metals start creeping and trying to relieve the stresses present, applied or residual. M-7 tool steel has half its room temp strength at 500 something Degree F! It is considered a high hot strength tool steel. Brake rotors get like 3X this on the surface of the friction zone. The problem happens whenever the metal cools down from these temperatures. It is impossible to make every portion cool at the same rate. This causes zones of tension and compresion. Compression on the surface of things is usually good because that is where there is usually the highest concentration of defedts and stress risers. Cracks can't form under comprression. Compression shot peening vibro peening and coldworking all do this by mechanically modifying the surface. Brake rotors have all sorts of cross sectional variation and heating and cooling rates. This is where residual stress builds and even chemical changes happen in the material.
By rotors of the best material and hope that there is as much as possible geometric and residule stress symmetry. Oh yeah, and after making you brakes glow all sorts of colors don,t come to a complete stop. This is the best way to get things going out of round no matter what the material. Got the idea why I think cryo treating is a waist.