Effect of Nitro-Carburizing Treatment on Wear Mechanism and Friction of Steel/WC-Co Sliding Couple

In this work, tribological behavior and material degradation mechanisms of Nitro-carburized AISI H11 hot work tool steel were investigated during sliding against cemented tungsten carbide (WC/Co). The diffusion layer with an iron-nitrocarbide (Fe (N,C)) compound layer was developed on pre-hardened tool steel by a low temperature Ferritic Nitro-Carburizing (FNC) process in a gas medium. The X-ray diffraction analysis, microhardness testing, and optical microscopy were employed to indicate the properties of the compound and diffusion layers. Friction and wear tests were carried out by using the pin-on-disk technique under severe wear condition, and a wear map was provided for different load and sliding distance. Results of SEM secondary and backscatter imaging of wear scar together with EDS analysis of wear debris showed insignificant two-body abrasion wear system and oxide tribo-film on the nitro-carburized samples. In the case of the hardened sample, intensive plastic deformation on the surface, adhesion, and disk materials transfer developed three-body abrasive wear and a degradation mechanism. It was concluded that a lower material degradation rate and the friction coefficient of nitro-carburized steel in comparison with the hardened sample can be related to the formation of a protective oxide layer and a gradual increase in hardness from surface to substrate.