Wear Kinetics of Steels with Diffusion Coatings in Rolling Friction
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WEAR KINETICS OF STEELS WITH DIFFUSION COATINGS IN ROLLING FRICTION P. V. Kaplun,1,2 V. A. Honchar,1 and T. V. Donchenko1
UDC 621.726
It is shown that the wear kinetics of steels with diffusion coatings under the conditions of rolling friction strongly depends on the physicomechanical properties and phase compositions of the coatings, hardness of the base, and the modes of thermal and thermochemical treatments. The dependence of the degree of wear on the number of loading cycles is always parabolic. The contact fatigue strength in rolling is strongly affected by the ratio of slip and deformation components of wear. The deformation component is predominant for low hardnesses of the surface and the base and results in the minimum contact fatigue strength. At the same time, the slip component prevails for high hardnesses of the base and corresponds to the highest contact fatigue strength under the conditions of rolling friction. Keywords: wear kinetics, ion nitriding, nitroquenching, medium, hardness, base.
Introduction The increase in the contact fatigue strength of tribosystems under the conditions of rolling is an urgent problem. Note that, in this case, structural elements, as a rule, fail as a result of wear and crumbling of the surface caused by the fatigue of the material. These processes were studied in numerous works [1–7] devoted mainly to the analysis of operation of homogeneous materials [1–4]. These materials have certain restrictions imposed on the possibility of increasing their wear resistance and contact fatigue strength under the conditions of rolling. The procedures most extensively used for increasing the service life under variable contact loads are carburizing and nitrocarburizing [6]. However, these are high-temperature procedures based on the use of hydrogencontaining saturation media, which negatively affects the characteristics of strength and service life of structural elements. As an alternative to these technologies, it is possible to apply the procedure of ion nitriding in hydrogen-free saturation media and complex technologies [5, 8–17]. It is known that the phenomenon of slip occurs in machine parts and units under the conditions of rolling. In this case, the process of wear can be described as a combination of plastic deformation of the contact surface and its rubbing as a result of slipping. Therefore, the total wear has two components caused by deformation and slip, respectively. The process of wear of homogeneous materials in rolling has three stages: running-in, accumulation of defects, and fracture [1–3, 5]. These stages depend on the action of numerous factors determined by the properties of the materials, conditions of operation, etc. In the presence of coatings, the total wear also depends on the following additional factors: the physicomechanical properties and phase compositions of the coatings [8, 16], hardness of the base [14], residual stresses in the surface layers [14, 16], ambient medium [13, 15], participation of hydrogen in the technological process of application of
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