Since the 19th century the term heat treatment has meant a set of operations carried out on metal parts, comprising heating followed by soaking at steady temperature, then more or less rapid cooling to the ambient temperature. The parameters (time, temperature, etc.) vary according to the temperatures at which the material structure is modified. The monitoring curves can easily be shown by a graph.

The purpose of heat treatments is to give the steel particular properties suited to its implementation or use. Heat treatments can be classified into two types of treatment: balanced treatments, including homogenisation treatment and annealing, and unbalanced treatments, including quenching , tempering and structural hardening.

The effects of heat treatments are varied and enable steel characteristics and properties to be modified.