It is a forging process for steels which comprises pre-treating a steel, such as by heat treatment or plastic working, and then hot forging the treated or worked steel at a temperature in the range from 450℃ to the Acl transformation point of the steel.
Hot forging is the plastic deformation of metal at a temperature and strain rate such that recrystallization occurs simultaneously with deformation, thus avoiding strain hardening. For this to occur, high work piece temperature (matching the metal's recrystallization temperature) must be attained throughout the process. A form of hot forging is isothermal forging, where materials and dies are heated to the same temperature. In nearly all cases, isothermal forging is conducted on superalloys in a vacuum or highly controlled atmosphere to prevent oxidation.