Effect of low-temperature ion–plasma nitriding time on the tribomechanical properties of 30kh13 martensitic stainless steel

Abstract

This study investigates the effect of low-temperature ion–plasma nitriding time on the microstructure, phase composition, and functional properties of 30Kh13 martensitic stainless steel. The samples were treated at 400 °C for 3, 4, and 5 h in an atmosphere of dissociated ammonia. Using X-ray diffraction analysis, Vickers microhardness measurements, as well as tribological and corrosion tests, the patterns of structural evolution and their relationship with tribological characteristics were established. It was shown that increasing the nitriding time results in the sequential formation of expanded martensite (α′N), γ′-Fe₄N and ε-Fe_2-3N nitrides, while 5 h of treatment additionally leads to the formation of CrN nitrides, causing chromium depletion of the surface layer.It was determined that the 4 h nitriding regime provides the most favorable combination of structural homogeneity and functional properties. Under this condition, the surface microhardness increases up to 948 HV, the coefficient of friction decreases to 0.46, and the wear volume is reduced by more than three times compared to the initial state. Corrosion tests demonstrated that this regime is characterized by the lowest corrosion current density (4.13 μA/cm²) and a more positive corrosion potential (−0.12 V), which is attributed to the absence of CrN nitrides and the formation of a stable passive film.Thus, low-temperature ion–plasma nitriding at 400 °C for 4 h represents the optimal regime for improving the wear and corrosion resistance of 30Kh13 steel.