Статті КПММ
Permanent URI for this collection
ENG: Articles
Browse
Browsing Статті КПММ by Author "Bolotova, Daria M."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Formation of Carbon Steel Structure During Hot Plastic Deformation(Dnipro National University of Railway Transport named after Academician V. Lazaryan, Dnipro, 2020) Vakulenko, Ihor O.; Bolotova, Daria M.; Proidak, Svitlana V.; Askerov, Hangardas; Cug, H.; Tchaikovska, H. O.EN: Purpose. The main purpose of the work is to determine the peculiarities of the development of recrystallization processes of carbon steel austenite depending on the degree of hot plastic deformation and to develop proposals for improving the structural state of the metal of the railway solid-rolled wheel. Methodology. Two carbon steels of a railway wheel with a minimum and maximum carbon content of 0.55 and 0.65 % and other chemical elements within the grade composition of the steel 60 were used as research material. Samples in the form of cylinders with a diameter of 20 mm and a height of 40 mm were heated in a muffle furnace, exposed for a certain time to equalize the temperature across the cross section of the sample. After that, the samples were subjected to hot compression on Instron type test machine. The temperature interval of hot compression of the samples was 950–1100 ºС, with deformation degrees in height in the range of 10–40%. The strain rate was 10-3–10-2 sec-1 . A standard etching was used to detect the boundaries of the austenite grains. Structural studies were performed using Epikvant type light microscope at magnifications sufficient to determine the structure of austenite grains. The grain size of austenite was determined by the methods of quantitative metallography. Findings. In the case of hot compression of the railway wheel blank, increasing the concentration of carbon atoms only within the grade composition of the steel is sufficient to increase the average austenite grain size, which confirms the proposals to limit the carbon content in the metal of railway wheels. The formation of a certain degree of austenite structural heterogeneity at the cross section of the rim or hub of the railway wheel is due to a change in the development mechanism of recrystallization processes depending on the deformation value. Under conditions of the same degree of hot plastic deformation, the replacement of one-time compression by fractional one is accompanied by a violation of the conditions of formation of the recrystallization nucleus. As a result of the specified replacement of the scheme of hot plastic deformation we obtain reduction in the austenite grain size. Originality. Based on a study of the development of collective recrystallization processes during the hot compression of carbon steel of the railway wheel, it was determined that the increase in carbon content contributes to the austenite grain increase. After hot compression of the wheel blank, the structural inhomogeneity of austenite that occurs is determined by a change in the mechanism of recrystallization processes development. During deformations above the critical degree, the recrystallization nuclei are formed and successively grow, which leads to the structure refinement. In the case of deformations below the critical value, the growth of austenite grains occurs according to the coalescence mechanism, according to which fragments of boundaries with large disorientation angles consistently disappear. Practical value. For austenite grain refining in massive elements of solid-rolled railway wheel we offer to replace one-time hot compression by fractional one.Item Influence of the Shock Wave of Electric Discharge on the Fatigue Characteristics of Thermally Hardened Steel(springer, 2018) Vakulenko, Ihor O.; Bolotova, Daria M.; Hryshchenko, Mykola A.ENG: The procedure of treatment of thermally hardened steel by pulses of shock waves from electric discharges in water increases its hardness and the limited fatigue strength. As a result of the action of shockwave pulses, the number of dislocations increases. This guarantees the propagation of deformation in a cycle, which promotes the increase in cyclic fatigue strength.Item Influense of the Shock Wave Treatment on Fatigue Carbon Steel(Print ABC, Netanya, Israel, 2017) Vakulenko, Igor A.; Lisnyak, Alexander G.; Griaznova, Ludmila; Bolotova, Daria M.EN: The process of introducing additional number of dislocations in the heat-hardened steel after shock wave pulse treatment apparently is not accompanied by the development of dislocation annihilation. Furthermore, implementation of the deformation per cycle for the area of high-cycle fatigue is ensured by the participation of more dislocations. Thus, in the process of shock wave pulse treatment, the vast number of introduced dislocations is mobile and able to interact with further cyclic loading or it takes place additional unlock of previously fixed dislocations after hardening and tempering. Overall, on the destruction surface after treatment with shock wave pulses it is found increased number of dislocations that are located in different crystallographic slip systems. They can be seen as evidence of the development of quite complex dislocation reactions that increases the metal limited endurance during cyclic loading.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.Item Structural Changes at Metal of a Railway Wheel Along Rolling Surface(Nevsehir University, Turkey, 2021) Vakulenko, Igor A.; Kurt, Bulent; Bolotova, Daria M.; Colova, O.ENG: As a result rolling of the hardened carbon steel without slipping, only due to normal loading, a decrease in hardness is observed. The observed decrease in hardness is due to the development of softening processes during plastic deformation. Additional slippage at the contact points of the samples accelerates development of softening effects in the hardened metal. It has been found that softening during rolling of a quenched metal is accompanied by a refinement of the coherent scattering regions, increase in internal stresses, and increase at number of crystal structure defects.