http://asm.asminternational.org/ht-echarts/3046_OMM120707_figure.pdf [Broken]ASM International said:Cold treatment of steel consists of exposing the ferrous material to subzero temperatures to either impart or enhance specific conditions or properties of the material.
Unlike heat treating, which requires that temperature be precisely controlled to avoid reversal, successful transformation through cold treating depends only on the attainment of the minimum low temperature (-84°C, or -120°F) and is not affected by lower temperatures. Typical cryogenic treatment consists of a slow cool-down (~2.5°C/min, or 4.5°F/min) from ambient temperature to liquid nitrogen temperature. When the material reaches approximately 80K (-315°F), it is soaked for an appropriate time (generally 24 h). At the end of the soak period, the material is removed from the liquid nitrogen and allowed to warm to room temperature in ambient air. Temperature can be controlled accurately and thermal shock to the material is avoided by conducting the cool-down cycle in gaseous nitrogen.
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