The term heat treatment describes a process in which a work piece or part of a work piece is intentionally subjected to a specific time-temperature sequence. In some instances, the work piece may additionally be subjected to other physical and/or chemical influences. The aim of heat treatment is to impart properties to a work piece which are required for further processing steps or for the intended application.

This definition covers all thermal, thermo-chemical and thermo-mechanical processes for the treatment of work pieces with which mechanical material properties are to be selectively changed. Furthermore, the appearance of the surface of work pieces can be influenced. These properties are optimized by structural transformations on the surface or in the entire work piece and by chemical changes on the surface.

Heat treatment takes place in furnaces that are temperature controlled (heating, soaking and cooling steps), usually using a process gas atmosphere to prevent, e.g. undesirable discoloration or to alter the surface chemically.The influenceable properties are, e.g. deformability, residual stresses, hardness, toughness and surface condition.