Regularities of wear of austenitic steel AISI 321 strengthened by nitrogen ions

The results of the study of the structure, microhardness, and data from tribological tests of AISI 321 steel samples treated with nitrogen ions at various temperatures are presented. It is shown that the ion nitriding of steel forms hardened layers with a thickness of $3$ to $18$ microns, characterized by increased hardness (up to $1400$ HV $0.05$) and containing nitrogenous austenite $\gamma_N$, as well as nitride phases $\gamma'_N$ and CrN. It is established that during the friction of steel samples with a hardened layer, the transition from the stage of gradual slow wear of the azo-tated layer to its accelerated wear occurs when the layer thickness decreases to $3$–$5$ microns. It is concluded that accelerated wear of thin modified layers is caused by plastic deformation of the substrate and phase $\gamma\to\alpha$ transformation in it, which leads to cracking of the surface layer.