It depends on how the cryo freezing is done. The idea is to 'stress relieve' the cast components by gradually reducing the temp them increasing it.
I suspect it takes many hours of gradual cooling then warming to do this. If this was done quickly, you would just simply amplify the existing internal stresses.
Engines actually get stress relieved every time you drive your car. All the engine parts are heated then gradually cooled when you switch the engine off.
Lots of engine builders know than 'seasoned' or used cast components frequently are stronger than new ones.
However, there are other, proven ways to stress relieve components, such as shot peening.
Benefits of Shot Peening:
Compressive Stresses
Cold Working
Shot Peening increases resistance to
……fatigue failure
…corrosion fatigue
…hydrogen assisted cracking
…cavitation erosion
…stress corrosion cracking
…galling
…fretting
Shot Peening Helps with
……surface texturing
…intergranular corrosion resistance
…closing of porosity
…testing of bond coatings
…work hardening
…increased strength
…increased durability
Although the process of Shot Peening has evolved and become very technical, it still employs the age-old principles of pre-stressing and work-hardening a material to create a harder and more durable material.
Today, Shot Peening involves bombarding a material with small spherical media called shot. Each piece of shot is the modern day version of the hammer/ stone used in the past. As the Shot Peening is performed, the atoms on the surface of the metal become crowded and try to restore the metal's original shape by pushing outward. This pulls, towards the surface, the atoms in the deeper layers, which resist the outward pull, thereby creating internal tensile stress that keeps the part in equilibrium with the compressive stress on the surface. The tensile stresses, resulting from Shot Peening, deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start on the interior.