1. Role of the atmosphere

The role of the atmosphere in heat treatment is to control the physico-chemical characteristics of the surface of treated parts. This role depends on the type of treatment chosen and the desired interaction between the gas and the metal surface.

In the case of heat treatments designed to modify "core" metallurgical properties (annealing, tempering, gas quenching), the atmosphere must protect the metal surface from any undesirable reactions (such as oxidation, carburization, decarburization) and must convey heat between the treated metal and the hot (resistors, radiant tubes) and cold (fans, exchangers, water jackets, quenching zones) parts of the process. The atmospheres used for this type of treatment are either inert atmospheres with respect to the treated metal (N ₂ , Ar, He), or reducing atmospheres (H _...