Study of the Effect of Gas Nitriding Time on Microstructure and Wear Resistance of 42CrMo4 Steel

Abstract

Prior studies have noted that gas nitriding has a considerable effect for wear resistance. The aim of this paper is to study the influence of gas nitriding time (12, 24, 36 and 48 h) in the wear behaviour of 42CrMo4 steel. It has been assessed by micro hardness, pin-on-disc tribosystem, and SEM through the nitrided layer for each nitriding time. The study relates to the performance of the compound layer and the diffusion layer with respect to adhesive wear. The results were analyzed in terms of the weight lost during wear, for nitrided steel with and without the compound layer, and for untreated steel. It has been observed that wear rate varies as a function of the tests conditions due to the presence of different wear mechanisms. Thus, for short tests conditions wear rate depends on two mechanisms: plastic deformation and adhesive wear, whereas for large tests conditions the mechanisms controlling wear rate are abrasive and oxidative wear. Furthermore, this study contains an analysis of the wear mechanisms of a nitrided part, founded on scanning electron microscopy (SEM) observations of the wear traces at various stages of the evolution of wear. The SEM examination of worn surfaces revealed signatures for the adhesion, abrasion, delamination and tribochemical (oxidative) modes of wear. This is an important issue for future research.