Hervé Chavanne

6 – Salt Bath Thermal Treating and Nitriding

Hardening, carburizing, and nitrocarburizing of steel are heat treatment processes usually carried out in baths of molten salts. This chapter describes the implementation of those techniques briefly. Special attention is devoted to the surface treatment of steel workpieces. As an example, the mechanism of fused salt nitriding is examined. As is shown, the quality control of the coating layers depends on several factors, such as temperature, processing time, cooling rate, and metallurgical state of the workpieces and their composition (carbon content and presence of alloying elements). The nitrogen chemical potential is explicited, and the role of the fused bath composition is analyzed on a thermodynamic basis. The results of nitriding experiences using various salt mixtures are given.