The Relationship of Technological Processes Based on Plasma Electrolytic Treatment with Structural Changes and Tribological Properties of the Tool High-Speed Steel Surface

A technology has been proposed to increase the hardness and wear resistance of M2 high-speed tool steel by combining low-temperature nitrocarburizing using anodic plasma electrolytic treatment, stepwise heating in plasma electrolysis with a change in the polarity of the workpiece, high-temperature hardening in air and triple tempering release. The structure, phase and elemental composition of the surface layers of high-speed steel after plasma electrolytic treatment with quenching, as well as subsequent tempering, were studied using the methods of x-ray, SEM and EDX analysis. Tribological tests were carried out under dry friction conditions with assessment of the friction coefficient and weight wear, as well as calculation of the microgeometry of the worn surface to assess contact stiffness and determine the wear mechanism. It has been shown that the formation of a structure of highly alloyed martensite with nitride inclusions after nitrocarburizing with quenching and the release of finely dispersed carbides during subsequent tempering leads to hardening of the surface layer to 1090-1100 HV after quenching and to 1350-1380 HV after subsequent tempering. The nitrogen concentration in the surface layer as a result of low-temperature nitrocarburizing reaches up to 13 wt.%. The greatest reduction in the friction coefficient (2.1 times) and weight wear (5.5 times) compared to the untreated sample occurs after plasma electrolytic treatment for 10 minutes, followed by quenching and triple tempering. Contact hardness similarly increases by 1.73-1.83 times after quenching and by 2.37-2.70 times after quenching and triple tempering. The wear occurring in the friction pairs under study is defined as fatigue wear during dry friction and plastic contact.