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Item Influence Ferrite Grain Size on the Development of Discontinuons Flow at Lowcarbon Steel(Nevsehir University, Turkey, 2021) Vakulenko, Igor A.; Kurt, Bulent; Erdogdu, Ahmet Emrah; Asgarov, KhangardashENG: On example of low-carbon steel, it is shown that development of strain hardening processes, starting from the moment initiation of plastic deformation, determines nature behavior of the metal at all subsequent stages of loading. The conditions formation of deformation bands and reasons for the disappearance of intermittent yield section on the deformation curves are considered. The use of the dependence characteristics of strain hardening on the size ferrite grain made it possible to explain evolution structure of low-carbon steel at region of intermittent flow.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, HakanENG: 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.Item Strain Hardening of Low-Carbon Steel in the Area of Jerky Flow(Дніпровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпро, 2021) Vakulenko, Ihor O.; Bolotova, Daria M.; Proidak, Svitlana V.; Bulent, Kurt; Erdogdu, Ahmet Emrah; Chaikovska, H. O.; Asgarov, KhangardashENG: Purpose. The aim of this work is to assess the effect of ferrite grain size of low-carbon steel on the development of strain hardening processes in the area of nucleation and propagation of deformation bands. Methodology. Low-carbon steels with a carbon content of 0.06–0.1% C in various structural states were used as the material for study. The sample for the study was a wire with a diameter of 1mm. The structural studies of the metal were carried out using an Epiquant light microscope. Ferrite grain size was determined using quantitative metallographic techniques. Different ferrite grain size was obtained as a result of combination of thermal and termo mechanical treatment. Vary by heating temperature and the cooling rate, using cold plastic deformation and subsequent annealing, made it pos-sible to change the ferrite grain size at the level of two orders of magnitude. Deformation curves were obtained during stretching the samples on the Instron testing machine. Findings. Based on the analysis of stretching curves of low-carbon steels with different ferrite grain sizes, it has been established that the initiation and propagation of plastic de-formation in the jerky flow area is accompanied by the development of strain hardening processes. The study of the nature of increase at dislocation density depending on ferrite grain size of low-carbon steel, starting from the moment of initiation of plastic deformation, confirmed the existence of relationship between the development of strain harden-ing at the area of jerky flow and the area of parabolic hardening curve. Originality. One of the reasons for decrease in Luders deformation with an increase of ferrite grain size of low-carbon steel is an increase in strain hardening indicator, which accelerates decomposition of uniform dislocations distribution in the front of deformation band. The flow stress during initiation of plastic deformation is determined by the additive contribution from the frictional stress of the crys-tal lattices, the state of ferrite grain boundaries, and the density of mobile dislocations. It was found that the size of dis-location cell increases in proportion to the diameter of ferrite grain, which facilitates the development of dislocation annihilation during plastic deformation. Practical value. Explanation of qualitative dependence of the influence of ferrite grain size of a low-carbon steel on the strain hardening degree and the magnitude of Luders deformation will make it possible to determine the optimal structural state of steels subjected to cold plastic deformation.