A thermal process mainly carried out on ferrous materials that have been forged, cast or hot rolled. Following the heat treatment the steel has a more controlled grain structure and is more stable and predictable in its further manufacturing processes.
By heating the component to its equivalent hardening temperature the microstructure changes, transforming the unrefined ferrite grains into small austenitic grains. During the slow cooling cycle the austenitic grains revert back to refined ferrite.
This process can be performed in air or an inert atmosphere to prevent oxidation and decarburization.