3. Influence of the main gases used in heat treatment

3.1 Different heat treatment atmospheres

Depending on the heat treatment involved, the atmosphere plays a different role. A distinction is made between :

• heat treatments designed to modify properties in the mass (such as annealing, austenitizing before quenching and tempering) where the atmosphere must be inert with respect to the metal;

• thermochemical treatments where interaction is desired.

In the case of heat treatment in the mass, no physico-chemical interaction is desired between the surface of the metal part and the atmosphere. Thus, the gaseous atmospheres used in furnaces are generally made up of mixtures of several inert or neutral gases (nitrogen (N _...