Effect of Oxidation on Surface Properties of AISI H13 Tool Steel Nitrided by Atmospheric-Pressure Plasma

Abstract

Atmospheric-pressure plasma nitriding of AISI H13 tool steel is performed using a dielectric barrier discharge method. As the surface of the sample nitrided by atmospheric-pressure plasma is oxidized, the surface characteristics are considered to be different from those of conventional plasma nitriding in a vacuum. In this study, the surface properties of the nitrided layer such as tribological properties generated by atmospheric-pressure plasma nitriding are investigated. The results show that the surface and cross-sectional hardness of the nitrided sample increase as the amount of nitrogen gas increases. By contrast, the surface and cross-sectional hardness of the nitrided sample increase as the amount of hydrogen gas decreases. Moreover, the surface luster of the nitrided samples changes unlike the untreated samples; however, the surface roughness of all the nitrided samples is similar to that of the untreated samples. When compared with an untreated sample, the friction coefficient and wear resistance of the nitrided sample are improved. For this reason, we consider that the nitriding in this research also causes oxidation by oxygen, similar to oxynitriding. Samples with oxidation film formed by atmospheric-pressure plasma nitriding have excellent wear resistance and friction coefficient, demonstrating the superiority of atmospheric-pressure plasma nitriding for treating small components.