Application of Plasma Electrolytic Nitriding to Improve Wear Resistance of R6M5 High-Speed Steel

The feasibility of using plasma electrolytic treatment to improve the wear resistance of R6M5 high-speed steel has been demonstrated by combining anodic nitriding at 550°C with air quenching from 1230°C and subsequent three-stage tempering at 555°C. Structural and phase transformations in the surface layers of the steel after high-temperature air quenching and three-stage tempering, as well as their influence on tribological behavior in a friction pair with hardened tool steel, were studied using X-ray diffraction and scanning electron microscopy. The most pronounced reduction in the friction coefficient (by a factor of 3) and in weight loss due to wear (by a factor of 11), compared with the untreated sample, occurs after 10 min of nitriding followed by quenching and tempering under oxidative wear conditions observed at a load of 10 N and a sliding speed of 1.44 m/s. The modified layer of nitrided steel after tempering exhibits a finely dispersed structure of high-alloy martensite retaining part of the austenite and containing inclusions of iron, vanadium, and chromium nitrides, as well as tungsten carbide, with a microhardness reaching 1240 HV. At both lower and higher sliding speeds in the studied friction pairs, wear is dominated by fatigue mechanisms involving dry friction and plastic contact.