3. Heating conversions

Heating transformations can be studied from two different angles, depending on the initial structural state and the objective:

• the steel is in one of the structural states (more or less out of equilibrium) resulting from the different conditions under which the γ → α transformation may have taken place, and we wish, by reheating, to bring about a limited and controlled return to the equilibrium state at ambient temperature (and above all to bring about hardening precipitation); this point will be dealt with in the paragraph "tempering out-of-equilibrium structures";

• the steel is in a state more or less approaching equilibrium, and reheating is intended to bring it to the austenitic state, as part of its processing; this point will be dealt with in the "α → γ transformations"...