Browsing by Author "Plitchenko, Serhii O."

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Influence of Current Shunting and Technological Parameters of Spot Welding on the Strength of Joints of Dimensional Products
    (Dniprovsky State Technical University, Kamianske, 2024) Nosov, Denys; Peremitko, Valerii; Plitchenko, Serhii O.; Makarenko, Mykola; Shevtsov, Viktor
    ENG: The effect of current shunting and technological parameters of spot welding on the strength of joints of dimensional products was studied. Experiments were carried out using a spot contact welding machine type MT-1614. As the main material to be joined, structural carbon steel of the 08Yu brand was chosen in the form of plates of various thicknesses. After welding, samples were made for testing according to standard techniques for shearing, tearing, or twisting. The experimental part of the study included determining the dependence of the fracture force and weld nugget diameter on the welding current, the distance between welded spots, and the duration of the welding current pulse. It was determined that the optimal welding current to ensure high strength of welded points is 7400…8000 A. Exceeding this value leads to a decrease in strength, especially when the distance between welded spots increases. The duration of the welding current pulse also plays a significant role: the optimal increase in strength is observed with pulses lasting 0.18…0.22 s. for currents of 7900…8200 A. The dependence of the diameter of the welded spot on the distance between the welded spots and the duration of the pulse was also established. A significant increase in the distance between the welded points leads to a decrease in their diameter. On the other hand, the duration of the current pulse in the range of 0.22...0.24 s increases the diameter of the points to 22 % on average. Based on the results of the experiments, mathematical models were developed that quantitatively evaluate the influence of the investigated parameters on the strength and diameter of the welded spot. Practical recommendations include optimizing welding parameters and implementing mathematical models in the production process to predict the quality of welded joints. The obtained results will contribute to improving the quality of welded joints and the efficiency of production processes in the manufacture of large-scale products.
  • Thumbnail Image
    Item
    Influence of Hot Plastic Deformation on Properties of the Carbon Steel
    (Dnipro University of Technology, Dnipro, Ukraine, 2024) Vakulenko, Ihor O.; Plitchenko, Serhii O.
    ENG: Purpose. Determination of the influence of hot plastic deformation degree on the set of carbon steel properties. Methodology. Steel with 0.6 % carbon was used for the study. The steel structure corresponded to the state after compression at 1,240 °C. Mechanical properties were determined by the tensile curve, friction stress of the ferrite crystal lattice and resistance of interphase boundary pearlite to propagation of deformation were estimated. Findings. Depending on the structural state of austenite, dispersion of pearlite colonies is accompanied by different rates of change in the properties of carbon steel. For pearlite formed from austenite after annealing, the strain hardening coefficient and maximum ductility are inversely proportional. For pearlite formed from austenite with preserved substructure after hot deformation, the strain hardening coefficient and maximum ductility are related through the proportional relationship. Originality. Preservation of the substructure of hot-deformed austenite affects propagation deformation in pearlite of the steel. Against the background of decreasing friction stress of the ferrite crystal lattice, there is an increase in resistance of ferrite-cementite boundary of the pearlite to the spread of deformation. Practical value. For carbon steels with a pearlite structures, the accelerated increase in ductility from maintaining the proportion of hot work hardening of the austenite will improve technology for manufacturing rolled products of large sections. When producing thermally strengthened rolled products, achieving a simultaneous increase in strength and plastic properties is ensured by increasing ability of metal to strain hardening.
  • Thumbnail Image
    Item
    Influence of the Isothermal Transformation Temperature on the Structure and Properties of Low-Carbon Steel
    (Український державний університет науки і технологій, Дніпро, 2024) Vakulenko, Ihor O.; Plitchenko, Serhii O.; Asgarov, Khangardash; Lytvynov, Bohdan V.; Orak, Abdulkadir; Umur, Hakan
    ENG: Purpose. The study is aimed at evaluating the effect of the isothermal transformation temperature on the structure and properties of low-carbon steel. Methodology. The material for the study was a 3 mm diameter wire made of mild steel with the following chemical composition: 0.21% C, 0.47% Mn, 1.2% Si, 0.1% Cr, 0.03% S, 0.012% P. The 0.3 m long wire samples were subjected to austenitizing at 920 °C for 8...9 min, after which they were held iso-thermally for 11 min at temperatures of 650...200 °C, followed by cooling in air. The strength, plastic properties, and strain hardening coefficient were determined from the analysis of tensile curves. Findings. It was found that a decrease in the temperature of isothermal transformation, starting from 450...400 °C, increases the amount of Widmannstätten ferrite due to the disappearance of polyhedral ferrite grains. At the same time, the number of areas with locally located dispersed cementite particles similar to pearlite colonies increases, and bainite crystals appear. Against the background of a sharp decrease in the strain hardening coefficient in the range of 450...400 °C, the ability of the bainite phase to undergo plastic deformation should be considered one of the reasons for the delay in den-sity reduction. Originality. The effect of steel hardening with a decrease in the pearlite transformation temperature is based on the grinding of ferrite grains, an increase in the amount of Widmannstätten ferrite, and the dispersion of pearlite colonies. The strengthening effect of steel with a bainite structure is based on an increase in the degree of supersaturation of the solid solution with carbon atoms and dispersion hardening by particles of the carbide phase. Practical value. The optimal structural state of steel intended for the manufacture of such critical elements as a sup-port beam, railroad car bogie, etc. is a mixture of phase components with different dispersion and morphology, and their quantitative ratio is determined by the operating conditions of a particular product.
  • Thumbnail Image
    Item
    Phenomenon of the Softening Cold-Deformed Low-Carbon Steel during Alternating Bending
    (Dniprovsky State Technical University, Kamianske, 2024) Vakulenko, Ihor O.; Sukhomlyn, Volodymyr; Plitchenko, Serhii O.; Serkan, Dal; Gurin, Illia
    ENG: For cold-rolled low-carbon steel, detected softening during alternating bending is accompanied by an increase in ductility and ability to strain hardening. The softening process is accompanied by a change at morphology of ferrite grains. Elongated grains after cold rolling acquire a shape close to a polyhedron after alternating bending. Compared to the strength properties, for which a maximum decrease corresponds to four bending cycles, the ductility and strain hardening ability of the metal continue to increase even after eight cycles. The non-monotonic nature of change in dislocation density depending on the number of bending cycles indicates complex substructural changes in cold-rolled metal, which has a dislocation cellular structure varying degrees of the perfection.
  • Thumbnail Image
    Item
    Structural Changes during Thermal Strengthening of the Railway Wheel
    (National University Zaporizhzhia Polytechnic, Zaporizhzhia, 2024) Vakulenko, Ihor O.; Plitchenko, Serhii O.; Gubarev, S.; Khlebnikov, A.
    ENG: Purpose. Justification of mechanism of the structure transformations in the carbon steel of the railway wheel during disk thermal strengthening. Research methods. The material for the study was carbon steel of a railway wheel with a content of 0.57 % C, 0.65 % Si, 0.45 % Mn, 0.0029 % S, 0.014 % P and 0.11 % Cr. The railway wheel was heated to temperatures higher than Ac3, kept at this temperature to complete austenite homogenization process, and disk was rapidly cooled to the specified temperature. Degree defectiveness structure of the metal after accelerated cooling was assessed using technique of X-ray structural analysis. Strength stress, yield stress and relative elongation of the carbon steel were determined at stretching at rate of deformation 10-3 s-1. Results. At accelerated cooling of the carbon steel, the sources of strengthening are the processes of blocking mobile dislocations due to the condensation of carbon atoms on them and dispersion strengthening from the formed particles of the carbide phase. At temperatures of termination of forced cooling of carbon steel above 300…350 °C, the reduction rate of strength properties is determined by the excess of total effect of softening from decomposition of the solid solution, acceleration of spheroidization and coalescence of cementite particles over the blocking of dislocations by carbon atoms and dispersion hardening. Scientific novelty. The level of strength and plasticity characteristics of carbon steel of the railway wheel disc, depending on the temperature end forced cooling, is determined by the ratio of the influence of degree super saturation of the solid solution and the dispersion strengthening by carbide phase. Practical value. For temperatures termination of accelerated cooling of 200…300 °C, degree of super saturation of the solid solution is the main factor that determines the level of strength and plasticity characteristics. When manufacturing an all-rolled railway wheel, the strength limit of the disc metal can be increased by accelerated cooling to the middle range of temperature.