Browsing by Author "Proidak, Svitlana V."

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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.
The Influence Mechanism of Ferrite Grain Size on Strength Stress at the Fatigue of Low-Carbon Steel
(Дніпропетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпропетровськ, 2014) Vakulenko, Ihor O.; Proidak, Svitlana V.
EN: Purpose. Explanation of the influence mechanism of ferrite grain size on the fatigue strength of low-carbon steel. Methodology. Material for research is the low-carbon steel with 0.1% of carbon contnent. The different size of ferrite grain was obtained due to varying the degree of cold plastic deformation and temperature of annealing. The estimation of grain size was conducted using methodologies of quantitative metallography. The microstructure of metal was investigated under a light microscope with increase up to 1 500 times. As a fatigue response the fatigue strength of metal – a maximal value of load amplitude with endless endurance limit of specimen was used. Fatigue tests were carried out using the test machine «Saturn-10», at the symmetric cycle of alternating bend loading. Findings. On the basis of research the dependence for fatigue strength of low-carbon steel, which is based on an additive contribution from hardening of solid solution by the atoms of carbon, boundary of the ferrite grain and amount of mobile dislocations was obtained. It was established that as the grainy structure of low-carbon steel enlarges, the influence of grain size on the fatigue strength level is reduced. For the sizes of grains more than 100 mcm, basic influence on fatigue strength begins to pass to the solid solution hardening, which is determined by the state of solid solution of introduction. Originality. From the analysis of the obtained dependences it ensues that with the increase of ferrite grain size the required amount of mobile dislocations for maintenance of conditions for spreading plastic deformation becomes less dependent from the scheme of metal loading. Practical value. The obtained results present certain practical interest when developing of recommendations, directed on the increase of resource of products work from low-carbon steels in the conditions of cyclic loading. Estimation of separate contribution of the studied processes of structural changes with fatigue load allows one to choose a rational solution – to use the hardening effect from the ferrite alloying or to change the grain size of ferrite.
Influence of Perlite Dispersion of Carbon Steel on the Fatugue Processes
(Springer, 2018) Vakulenko, Ihor O.; Kawalek, Anna; Vakulenko, Leonid I.; Proidak, Svitlana V.
EN: Using the example of carbon steel with perlite structure it was determined the influence nature of the ferrite layer thickness of perlite on the angular coefficient of tangent at a certain point of the fatigue curve. Based on the analysis of the obtained dependencies, it is determined that the value of angular coefficient of the tangent can be used to evaluate the resource of limited endurance of the metal under conditions of cyclic loading.
Influence of Self-Tempering Temperature on Strength of Railway Wheel Disk after Accelerated Cooling
(Дніпропетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпропетровськ, 2016) Vakulenko, Leonid I.; Bolotova, Daria M.; Proidak, Svitlana V.; Gryshchenko, Mykola A.; Vakulenko, Ihor O.
ENG: Purpose. The paper aims at estimation of resource of strength increase for railway wheel disk. Methodology. The material for research was carbon steel of railway wheel containing 0.57%C, 0.65%Si, 0.45%Mn, 0.0029%S, 0,014%P, 0,11%Cr. A railway wheel was heated to the temperatures above Ac3 and was held at this temperature until the completion of аustenite homogenization processes and then the disk was cooled at a growing rate to a certain temperature. A temperature interval of completion of the speed-up wheel disk cooling was 200-450 C. Structure was studied with the use of research methods under electronic and light microscopes. After accelerated cooling the estimation of metal structure imperfection degree was carried out with the use of X-ray structural analysis method. The stress and yielding limit of carbon steel were determined at tension, at a speed of deformation10− − 3 1 s. The microhardness of steel structural components was estimated using the microhardness tester of PMT-3 type. Findings. The properties complex of railway wheel carbon steel depending on the temperature of the accelerated cooling termination is determined by the correlation of soften and work-hardening processes development. The effect of work-hardening is based on blocking of mobile dislocations due to a precipitation carbon atoms and dispersion work-hardening from the formed particles of carbidic phase. At the temperatures of the accelerated cooling termination of carbon steel higher than 300-350 C the decrease rate of strength properties is determined by the exceeding of total soften effect (from disintegration of solid solution, acceleration of spheroidithation and coalescence of cementite particles) above the dislocations blocking by the carbon atoms and dispersion work-hardening. Originality Authors proved that the strength level of the railway wheel carbon steel from the temperature of accelerated cooling completion is determined by the influence ratio of the solid solution satiety degree and dispersion work-hardening from a carbidic phase. For the temperatures of accelerated cooling termination 200-300 C a decrease of solid solution satiety degree is a basic factor, which determines the level of the strength characteristic. Practical value. When making the whole-rolled railway wheel one can increase the strength limit of disk metal using the accelerated cooling to the middle interval of temperatures, which was successfully proven by authors.
Investigation of Slide Mechanism of Tread During Operation of Railway Wheel
(Silesian University of Technology, Gliwice, Silesia, Poland, 2016) Vakulenko, Ihor O.; Proidak, Svitlana V.; Perkov, Oleg N.
ENG: Causes of reasons and explanation of mechanism forming damages of railway wheels tread were investigated. At slipping on contact surfaces wheel-rail a between by simultaneous development of processes of work-hardening and softening metal determines the terms of origin damages of railway wheels tread were fixed.
Softening of Hardened Medium-Carbon Steel During Heating
(Дніпровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпро, 2019) Vakulenko, Ihor O.; Proidak, Svitlana V.; Vakulenko, Leonid I.; Grischenko, Nikolaj A.
EN: Purpose. The work is aimed to clarify the softening mechanism during the heating of martensite hardened carbon steel, which is of practical importance, especially in the development of the production technology of rolled products with different levels of hardening. Methodology. The samples after martensite hardening were tempered at the temperatures of 300-500˚С. The microstructure was investigated under the electron microscope. Thin foils were made using the Bolman and tweezer methods in chlorous-acetic solution and Morris reagent. Phase distortions of crystalline lattice were determined by the methods of X-ray structural analysis, using the diffractometer. The cold-worked layer of metal after grinding was removed by electrolytic dissolution. Tensile strength brake of the metal was determined using the tensile diagrams of samples using the Instron type machine. Microhardness was measured using the PMT-3 device with indentation load 0.49 N. Findings. When heating the hardened steel to a temperature of 300˚C, the softening effect is mainly related to the rate of reduction of the accumulated as a result of martensitic transformation, density of the crystalline structure defects. The total result is caused by the development of dislocations recombination and strengthening because of the emergence of additional number of cementite particles during the martensitic crystals decomposition. Starting from the heating temperatures of 400˚C and above, the development of polygonization processes in the ferrite is accompanied by the emergence of additional sub-boundaries, which enhance the effect of metal strengthening. With increase in the heating temperature of the hardened steel, the level of strength properties is determined by the progressive softening from the decrease in carbon atoms saturation degree of the solid solution, dislocations density and increase in the size of cementite particles over the effect of strengthening from hindering of mobile dislocations by carbon atoms and the emergence of additional sub-boundaries. Originality. For the tempering temperature of 300-400˚C, the absence of the phase distortion change indicates the emergence of additional factor in strengthening the metal from the formation of sub-boundaries and the dispersion strengthening from the carbide particles. Practical value. The given explanation of the mechanism of structural transformations in the process of tempering in the average temperature range of the hardened carbon steel can be used to optimize the technology of thermal strengthening of rolled metal.
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, Khangardash
ENG: 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.
The Transformation of Structure Steel with Thermal Strengthening of the Disk Railway Wheel
(Karabuk University, Karabuk, Turkey, 2019) Vakulenko, Ihor A.; Proidak, Svitlana V.; Raksha, Serhii V.; Akay, M.; Cug, Harun; Askerov, Khangardas
ENG: On the example of the carbon steel, issues of structuring in the process of accelerated cooling are considered. The emerging gradient of structures at different distances from the surface of the heat transfer is presented in the form of a dependence, which is adequate to the effect of the temperature of individual heating during the release of steel after the quenching. It is shown that after the forced cooling is stopped, the increase of distance from the cooling surface accompany higher the tempering temperature of the metal. In the volumes of the metal, the microstructure close to the middle of the disk wheel is formed by the diffusion mechanism.