Tribological criterion of the quality of nitrided steels and alloys

The mechanism and kinetics of surface layer destruction during friction, as well as tribotechnical characteristics (level of surface destruction, friction coefficient, ultimate load-bearing capacity) depend on the structure, phase composition and properties of the surface operational layer, which are formed as a result of intense contact elastic-plastic deformation. The paper presents the results of assessing the conditions of the surface layer performance during friction of structural steels and alloys subjected to nitriding. A tribological criterion for the quality of the surface nitrided layer has been developed, an integrated approach to assessing the tribological efficiency of chemical-thermal treatment of structural steels and alloys has been proposed. The studies of the nitrided surface included the following stages: 1) based on the developed tribological criterion containing micro- and macroscopic characteristics of the material of the contact deformation zone during friction, the choice of its processing modes to ensure an acceptable level of surface destruction under test conditions of a heavily loaded mating; 2) using the surface plastic deformation method, assessing the ability of the nitrided layer (formed as a result of processing according to the selected mode) to perceive surface plastic deformation without destruction, which serves as a justification for the modes of chemical-thermal treatment; 3) assessing the ultimate performance of the nitrided surface layer under friction and wear conditions (maximum permissible (at which the pair operates stably) and critical (after which the pair is inoperative, but its operation is possible under short-term overloads) pressures, the average total wear intensity of the sliding friction pair in contact under load as a whole, and friction losses). The results obtained can be used to optimize the technological process of chemical-thermal treatment of tribotechnical parts.