Browsing by Author "Yilmaz, A. F."

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Determination of the Causes of Rolling Surface Damage during Operation of the Railway Wheels
(Dnipro University of Technology, Dnipro, 2025) Vakulenko, Ihor O.; Plitchenko, Serhii O.; Yilmaz, A. F.
ENG: Purpose. Substantiation of the mechanism of damage formation on the rolling surface of railway wheels by different strength levels to determine optimal structural state of the carbon steel. Methodology. The material for study was steel from rim fragments of the railway wheels with a carbon concentration of 0.61 and 0.69 % and other chemical elements within the range of the grade composition. Samples for mechanical tests were subjected to thermal hardening to obtain different structural states. The microstructure was examined under light and electron microscopes, using quantitative metallography techniques. Metal wear was determined under dry friction conditions, with different degrees of slippage, on a machine of the SMC-2 type. Hardness was estimated by the Rockwell method, and micro hardness of structural components – on a PMT-3 micro hardness tester. Findings. Based on the analysis of the wheel-rail interaction, it was determined that resulting inhomogeneity at distribution of plastic deformation and heating temperature in the plane of the contact surface are due to the development of slippage processes. Heating the metal to temperatures higher than onset of phase transformations and subsequent accelerated cooling determine the mechanism of structural transformations. The difference between adjacent sections of the rolling surface with different structural states and corresponding level of strength determines conditions for the formation of a fracture center of the railway wheel during operation. Originality. Heating the metal to temperatures above onset of phase transformations from the wheel sliding along rail and subsequent forced cooling is the cause of formation of gradient of the structures from pearlite to martensitic-bainite. The cyclic nature of the change in the structural state of the metal from simultaneous influence elevated temperatures, high plastic deformations and phase transformations corresponds to the development of low-cycle fatigue processes. Plastic deformation of the rolling surface area with martensitic or bainite structures is accompanied by softening, and with pearlite structures – by a hardening process. Practical value. The obtained results of the development of phase transformations in carbon steel on rolling surface will be useful in determining optimal structural state of the railway wheels of different strength levels.