CRUST | Browsing by Author "Vakulenko, Ihor O."

Browsing by Author "Vakulenko, Ihor O."

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The Calculation of Stress Intensity Factor Steel of Railway Wheels
(Silesian University of Technology, Katowice, Poland, 2020) Vakulenko, Ihor O.; Proydak, Svetlana V.; Askerov, Hangardas
EN: From an analysis of the dependence complex of carbon steel properties on structural parameters, it was found that for an isostructural state, the influence of austenite grain size on impact strength exceeds the dependence on carbon content. As a result of explaining correlation relationships between individual mechanical characteristics, to evaluate critical stress intensity factor, a relationship is proposed based on the use of impact strength. The proportionality coefficient in proposed dependence is determined by ratio of elongation to narrowing at tensile test.
Concept of Determining the Friction Stir Welding Mode
(Національний гірничий університет, Дніпро, 2018) Vakulenko, Ihor O.; Plitchenko, Serhii; Murashova, Nataliia H.; Bohomaz, Volodymyr M.
ENG: Purpose. To determine the optimal mode of friction stir welding of aluminum alloy. Methodology. 2.5 mm thick plates made of aluminum alloy AMg5 with chemical content of alloying elements within grade composition were used as a material for the research. Friction stir welding was carried out using specially designed equipment with a preselected form and dimensions of working tool. At different ratios of the working tool rotation frequency the forces of pressing and speed of its movement along the connecting edges determined the metal heating degree and the quality of welded joint formation. Temperature of the connecting edges heating was determined by thermocouples immersed in metal at different distances from the welded joint. Rotational speed of the working tool was from 800 to 1600 min-1 with the effort of pressing to the plate surface from 580 to 1370 N and the speed of movement along the joint of 50 mm/min. Findings. On the basis of different ratios of the working tool rotation speed and pressing to the connecting edges, there were determined conditions for achieving the effect of constant softening during friction stir welding. In order to achieve a high level of welding joint quality during friction stir welding it is necessary to carry out the process at high revolutions of the working tool and low levels of pressing to the connecting edges. Originality. At the constant speed of the working tool rotation proportional increase in alloy temperature from increasing the level of its pressing to the connecting edges is disturbed by achievement of conditions of the dynamic softening processes development. Practical value. The concept of choosing the technological parameters of welding process is determined, when it is preferred to increase in speed of the working tool rotation when the level of its pressing to the connecting edges decreases.
Determination Activation Energy of Friction Stir Welding
(WRTYS, Kyiv, 2017) Vakulenko, Ihor O.; Plitchenko, Serhii
EN: According to the technology of friction stir welding (FSW) heating of the edges is equal to 0.85-0.9 from the melting temperature of metal (T). Increase in temperature is accompanied by increased degree of the metal stirring, which leads to ambiguous influence on the metal density and concentration of cavities at different distances from the welding joint. At the same time, the temperature gradient across the section of joint leads to a different speed of recrystallization processes development and forming of structural heterogeneity in metal edges. Thus, the relevant question is to determine the optimal scheme of metal edges heating during the implementation of FSW technology. Material for the study was alloy AMg5. For different ratio of rotation speed and pressure on operating tool there were obtained the conditions of superplastic state of alloy at the temperatures of heating at the level of 0.45-0.5 from T, which corresponds to the beginning of dynamic recrystallization development during FSW. At the same time, it was evaluated the energy of activation (EA) of FSW process. Using the analysis of the obtained results it was determined the fact that when reaching the same temperature of alloy heating the EA value of FSW process decreases with increasing the rotation frequency of the operating tool and decreasing the degree of its pressing to the edges of welding joint. On the basis of the above mentioned the development of FSW technology should be directed toward the use of high speed rotations of the operating tool and low levels of its pressing to the alloy edges.
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.
Electric Pulse Treatment of Welded Joint of Aluminum Alloy
(Дніпроопетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпроопетровськ, 2013) Vakulenko, Ihor O.; Nadezhdin, Yurii L.; Sokirko, V. A.; Volchok, I. P.; Mitiaev A. A.
EN: Purpose. Explanation of the redistribution effect of residual strengthes after electric pulse treatment of arc welding seam of the aluminum alloy. Methodology. Alloy on the basis of aluminium of АК8М3 type served as the research material. As a result of mechanical treatment of the ingots after alloy crystallization the plates with 10 mm thickness were obtained. After edge preparation the elements, which are being connected were butt welded using the technology of semiautomatic argon arc welding by the electrode with a diameter of 3 mm of AK-5 alloy. Metal structure of the welded joint was examined under the light microscope at a magnification of 200 and under the scanning electronic microscope «JSM-6360 LA». The Rockwell hardness (HRF) was used as a strength characteristic of alloy. Hardness measuring of the phase constituents (microhardness) was carried out using the device PМТ-3, with the indenter loadings 5 and 10 g. The crystalline structure parameters of alloy (dislocation density, second kind of the crystalline lattice distortion and the scale of coherent scattering regions) were determined using the methods of X-ray structural analysis. Electric pulse treatment (ET) was carried out on the special equipment in the conditions of the DS enterprise using two modes A and В. Findings. On the basis of researches the previously obtained microhardness redistribution effect in the area of welded connection after ET was confirmed. As a result of use of the indicated treatment it was determined not only the reduction of microhardness gradient but also the simultaneous hardening effect in the certain thermal affected areas near the welding seam. During study of chemical composition of phase constituents it was discovered, that the structural changes of alloy as a result of ET first of all are caused by the redistribution of chemical elements, which form the connections themselves. By the nature of the influence the indicated treatment can be comparable with the thermal softening technologies of metallic materials. Originality. The observed structural changes of alloy and related to them microhardness change in the areas near the welding seam after ET are conditioned by both the change of morphology of structural constituents and the redistribution of chemical elements. In case of invariability of chemical elements correlation in the phase constituents of alloy the reduction effect of gradient microhardness should be far less. Practical value. In practice, the negative effect of the wares embrittlement made using the casting technologies, excluding the pressure casting and quite difficult selection of chemical composition of alloy can be significantly reduced during the treatment of alloy with electric pulses.
Evaluation of the Influence of Dispersion of Pearlite on the Fatigue of Carbon Steel
(Springer Link, 2020) Askerov, Khangardas; Vakulenko, Ihor O.
EN: It is shown that the slope of a tangent to the fatigue curve can be used to analyze the effect of dispersion of pearlite on the fatigue strength of carbon steel. For a constant thickness of the ferrite-pearlite layer, we established an inversely proportional relationship between the indicated parameter and the density of accumulated dislocations. We also estimated the mechanism of influence of the dispersion of pearlite on the transition from low- to high-cycle fatigue of carbon steel.
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.
Fractographic Analysis of the Destroyed Side Frame of the Truck of a Wreight Wagon
(ПОСВІТ, Дрогобич, 2020) Vakulenko, Ihor O.; Kuzin, Nickolai O.; Vakulenko, Leonid I.
EN: The initial inspection of damaged frame in fracture revealed two sections with characteristic structural features. The area with traces of slight corrosion, representing a smooth surface, corresponds to the gradual movement of fatigue crack. The rest of fracture surface with signs of a dynamic destroy has a qualitatively different structure. The fatigue part occupies approximately 30% of the total cross-sectional area. The propagation front of fatigue crack, after reaching the outer and inner surfaces of vertical wall from the side of wheel, reaches half the length lower horizontal wall. The focus of origin fatigue crack, located in lower inner corner, when moving from vertical wall to horizontal part of the side frame, is difficult obtain access when visually inspecting the frame trolley.
Influence Hot Plastic Deformation on the Structure and Properties of Carbon Steel of the Railway Wheel
(Politechnika Śląska, 2023) Vakulenko, Ihor O.; Plitchenko, Serhii; Bolotova, Daria M.; Asgarov, Khangardash
ENG: The study is devoted to the explanation of the influence of hot plastic deformation on the properties of railway wheels. The shape of individual elements of the wheel provides for a different degree of hot compression, which determines the mechanism for the development of the recrystallization at austenite. With a decrease in the degree of the hot deformation, a certain proportion of grains with a low energy of linear stretching are formed in austenite. As a result, of the low mobility of such boundaries, the likelihood of preservation of part of the substructural state of the austenite increases, which should affect the formation of a colony of perlite during the cooling of the carbon steel. Against background preservation and a dependence of strength properties on the dispersion of the pearlite colony, the appearance in austenite of grain boundaries with a low energy of linear tension leads to a qualitative change in the plastic properties of railway wheel steel. The increase in plasticity of carbon steel with an increase in dispersion of the pearlite colony is due to a decrease in the effect of solid solution hardening and an increase in the role of the ferrite-cementite interface in the development processes of strain hardening carbon steel. The results obtained can be useful for improving the technology of manufacturing all-rolled railway wheels.
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 Chemical Compounds on the Forming of Welding ARC
(Дніпропетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпропетровськ, 2014) Vakulenko, Ihor O.; Plitchenko, Serhii; Makarevich, D. M.
EN: Purpose. The purpose of work is a comparative analysis of chemical compounds influence on the process of forming arc welding and condition of its burning. Methodology. A wire with diameter 3 mm of low carbon steel with contain of carbon 0.15% was material for electrode. As chemical compounds, which determine the terms of arc welding forming the following compounds were used: kaolin; CaCO3 with admixtures of gypsum up to 60%; SiO2 and Fe − Si with the iron concentration up to 50%. Researches were conducted using the direct electric current and arc of reverse polarity. As a source of electric current a welding transformer of type PSO-500n was used. On the special stand initial gap between the electrode and metal plate was 1-1.5 mm. The inter electrode space was filled with the probed chemical compound and the electric arc was formed. At the moment of arc forming the values of electric current and arc voltage were determined. After the natural break of electric arc, the final gap value between electrodes was accepted as a maximal value of arc length. Findings. Experimentally the transfer of metal in interelectrode space corresponded to the tiny drop mechanism. According to external signs the relation between maximal arc length and the power of electric current has the form of exponential dependence. Specific power of electric arc at the moment of arc forming per unit of its length characterizes the environment in the interelectrode space. Originality. 1) Based on the analysis of influence of the studied chemical compounds on the formation processes of electric arc the inversely proportional relationship between the power of the electric current and the maximum arc length until the moment of its natural break is defined. 2) Ratio between the maximal arc length and the power of electric current, with the sufficiently high coefficient of correlation is submitted to the exponential dependence. Influence of the compounds under study on the process of electric arc forming is determined using the indexes of degree of the above mentioned correlation. 3) The value of specific power of electric current at the moment of electric arc forming per unit of arc length can be accepted as the parameter, which characterizes the state of interelectrode space environment. Practical value. In the conditions of identical adjusting force of electric current the sequence of location of the studied compounds in the order of increase of their influence on the process of arcing is determined. Minimum influence is observed from kaolin, and maximal one – from Fe − Si .
Influence of Cooling Rate on the Strength of the Rims of Railway Wheel
(Springer Science, Business Media, New York, 2016) Vakulenko, Ihor O.
ENG: It is shown that the intense cooling (with rates of 2-9°C/sec) of wheel rims after their hot rolling in a rolling mill increases the yield limit and the ultimate strength of the metal. It is also established that, in the absence of supersaturation of the solid solution with carbon atoms in the course of this kind of cooling, the mechanical properties of carbon steel are determined solely by the internal stresses caused by the phase hardening of ferrite in pearlite and the state of ferrite-cementite boundaries.
Influence of Grain Size Ferrite on Speed of Distribution Sonic Vibrations in Alloy Steel
(China, 2016) Vakulenko, Ihor O.; Nadezhdin, Yurii L.; Sokyrko, V. A.; Yaremchuk, A.
ENG: On the example of steel XI8TI after cold rolling and annealing influence of grain size ferrite and texture is investigational on speed of distribution sonic vibrations. Character influence of grain size and texture is set on correlation of hardness and speed of distribution sonic vibrations.
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.
Influence of Hot-Reduction Parameters on the Steel Austenite Structure of a Railway Wheel
(Politechniki Śląskiej, Poland, 2016) Vakulenko, Ihor O.; Bolotova, Daria M.; Perkov, Oleg N.; Lisnyak, Alex G.
ENG: The formation of grain structures with boundaries similar to substructures is one of the factors contributing to grain refinement in hot-reduction carbon steel. At the forming of a rim, the slight cooling-down (100-150°C) of the surface volumes is sufficient to increase their strength characteristics. After that, an increase in the magnitude of the hot-hardening of metal in the central rim volumes will lead to the formation of a more uniform fine-grain austenite structure over the rim section.
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.
Influence of Shock Voltage from the Electric Discharge on the Fatigue Endurance of Carbon Steel in Water
(Дніпропетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпропетровськ, 2015) Vakulenko, Ihor O.; Lisnyak, Alex G.; Perkov, Oleg N.; Hai, Xu Xiao
ENG: Purpose. The research supposes the explanation of influence of stress impulses from an electrical discharge in water on the level of the limited endurance at a cyclic loading of the thermally work-hardened carbon steel. Methodology. Material for research was steel 45 (0,45 % carbon) with сoncentration of chemical elements within the limits of steel composition. Specimens for tests are made as plates in 1 thick, width 15 and length 120-180 mm. The structural state of steel corresponded to quenching on a martensite from the normal temperatures of annealing and tempering at 300 C, duration of 1 h. Microstructure was investigated with the use of electronic microscopy, the density of dislocations was estimated on the methods of X-ray analysis. Hardness was measured on the method of Rockwell (scale of «C»). A cyclic loading was carried out in the conditions of symmetric bend on a tester «Saturn-10» at a temperature +20 C. The treatment by shock voltage from the electrical discharge was carried out in water on setting of bath type «Iskra-23», used for cleaning of castings manufactures. Electric impulses were formed at 15-18 kV with energy of 10-12 kJ and amplitude of 1-2 GPа. Findings. As a result of processing pulses of a pressure wave of heat-strengthened steel 45 found the increase of endurance under the cyclic loading corresponds to an increased amount of accumulated dislocations on the fracture surface. The use of Coffin–Manson Equation allowed finding the decrease of deformation per cycle of loading as a result of arising stress from an electrical discharge in water. On the fracture surface (after pulse exposure) was found the increased number of dislocations, located in different crystallographic systems, that is a testament to the rather complicated development of dislocation transformations in the structure of steel, which provide an increase of endurance at a fatigue. The increase of the limited endurance became as a result of impulsive treatment largely related with the number change of mobile dislocations. For the area of low-cyclic fatigue the growth of amplitude of loading is accompanied with the decrease of distinction in the values of the limited endurance (before and after the treatment of shock voltage). Originality. For the field of high-cycle fatigue, the result of shock voltage of carbon steel with the structure of the improvements, the increase of limited endurance is accompanied with a decrease in deformation per cycle. As far as growth of amplitude of stress cycle the effect of increase of endurance from treatment of metal by the shock voltage declines. Practical value. Treatment of metal by the impulses of pressure waves from an electrical discharge in water can be used for the time extending of exploitation details of the rolling stock, which are subjects of the cyclic loading.
Influence of Structural Parameters of Low-Carbon Steel on Electric Arc Burning
(Дніпропетровський національний університет залізничного транспорту імені академіка В. Лазаряна, Дніпро, 2017) Vakulenko, Ihor O.; Plitchenko, Serhii; Murashova, Nataliia H.
EN: Purpose. The article is aimed to evaluate the influence of structural parameters of low-carbon steel on arcing process.Methodology. The values of the micro- and substructure characteristics of the electrode wire metal were changed by varying the parameters of heat treatment and cold deformation by drawing. The degree of plastic deformation was obtained by drawing blanks from different initial diameter to final dimension of 1 mm. The thermal treatment was carried out in electric chamber furnace of the SNOL-1,6.2,5.1/11-IZ type. The temperature was measured by chromel-alumel thermocouple and the electromotive force was determined using the DC potentiometer. In order to obtain the substructure of different dispersion degree the steel (after quenching from temperatures and tempering at 650°C for 1 hour) was subjected to cold drawing to reduction 17 – 80%. To form structure with different ferrite grain size the steel after drawing was annealed at 680°C for 1 hour. The microstructure was examined under a light and electron transmission microscope UEMV-100K at the accelerating voltage 100 kV. The grain and subgrain sizes were evaluated using the methodologies of quantitative metallography. A welding converter of the PSG-500 type was used to study the arc welding process of direct and reverse polarities. Findings. The experimentally detected value of the welding current, which depends on the degree of deformation during wire drawing, under conditions of stable arc burning of direct polarity is about an order of magnitude lower than the calculated value. Similar difference was found for the arc of reverse polarity: the experimental value of the welding current is 5...6 times less than the calculated value. Dependence analysis shows that, regardless of the polarity of the welding arc, a good enough agreement between the calculated and experimental values of the welding current is limited to deformations of 60%. For deformation degrees of more than 60%, the differences are explained by qualitative changes in the dislocation cell structure. Originality. In the conditions of stable arcing of different polarity for the electrode of low-carbon steel, an extreme dependence of welding current on the degree of cold plastic deformation was observed. Practical value. Influence of ferrite grain size of electrode wire on the value of welding current is much greater than that from substructure presence.
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.