| Themes > Science > Physics > Cryogenics > Applications of Cryogenics > Deep Cryogenic Tempering > The Cryogenic Process |
The parts are cooled at a controlled rate to -320°F over a period of hours. Upon reaching this temperature, the chamber is flooded with liquid nitrogen to ensure an even temperature throughout the chamber. The parts are held at this temperature for a minimum of 20 hours, after which the temperature in the chamber is slowly allowed to return to ambient. The temperature is carefully controlled to avoid thermal shock as well as frost and condensation. Cryogenic processing is not a substitute for heat treatment, but rather an extension of the heating - quenching - tempering cycle. Normally, when an item is quenched, the final temperature is ambient. The only reason for this is that most heat treaters do not have cooling equipment. There is nothing metallurgically significant about ambient temperature. The cryogenic process continues this action from ambient temperature down to -320 degrees. In most instances the cryogenic cycle is
followed by a heat tempering procedure. As all alloys do not have the same
chemical constituents, the tempering procedure varies according to the
material's chemical composition, thermal history and/or a tool's
particular service application. |
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