The Effect of Oxidation Process After Nitrocarburization on Tribological Properties of AISI 4140 Steel

Abstract

In this study, microstructure, microhardness and tribological properties were investigated after nitrocarburisation process (on the AISI 4140 steel) which was the oxidation processes based on simultaneous diffusion of carbon and nitrogen atoms. Although the nitrocarburisation process has many advantages, different post-treatment heat treatment techniques are needed to improve the corrosion and tribological properties of the materials in particular. As a result of the nitrocarburization + oxidation processes, 3 different zones were formed on the outermost surface of the material. These zones were obtaining of respectively as; about 5 mm thick oxide layer, just below it, about 5 mm thick compound layer consisting of nitride and carbides and diffusion zone rich in carbide. Wear behavior on the entire surface of the material was improved by means of a harder diffusion zone, nitrocarburization and oxidation layers than the main phase. Thus, the wear resistance is also improved, as well as the coefficient of friction.