Residual stresses exist in all metals and metal components. But why does cryogenic treatment relieve these stresses? The answer is found in observations made by Einstein and Bose of Germany. Both of these noted physicists observed that matter is at its most relaxed state or condition when it has the least amount of kinetic energy. The process of freezing is not one of putting cold into an object. Rather, it is the removal of heat. When we remove heat, we are removing energy and slowing down the molecular activity (kinetic energy) of the object being frozen. This is evident to every high school science student who studies the effects of heat – and its removal – on water.
Absolute zero, which is –459º F or 0º Kelvin is that point where no further energy can be extracted. Many people believe that at absolute zero there is no kinetic energy at all. This is not the case. But absolute zero provides a theoretical point where matter (or material) is at its most relaxed state.
Cryogenic treatment with liquid nitrogen does not get the material to its absolute lowest temperature, but when we bring materials to –300º F to –320º F for extended periods, we have removed a large amount of the object’s latent heat, slowed down its kinetic energy, and relieved or relaxed many of the residual stresses that exist within it. At this point, cryogenic treatment has relieved residual stresses.
There are a large number of cryogenic stress relieving approaches or profiles that are in use today. We provide customers the choice of using our standard stress relieving process profile or we will follow a customized recipe. These usually involve a heating or warming cycle that is repeated multiple times in sequence.