International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The effect of inclusions and corrosion products on the mechanism of wear of railway wheels made of R7 steel and also of rails made of R7 steel M76. was studied. The research was carried out by several methods: metallographic, electron microscopy, X-ray, micro-X-ray spectral analysis. The features of the formation of wear particles near nonmetallic inclusions and corrosion products related to structural changes near the treads of railway wheels and rails as well as to the interaction of steel with the surrounding atmosphere during operation were investigated. The influence of various factors on the role of nonmetallic inclusions and corrosion products in the formation of wear particles is shown, which makes it possible to predict the nature of wear of the rolling surface of railway wheels and rails under various operating conditions. The main sources and the mutual influence of various factors on the formation of wear particles near nonmetallic inclusions and corrosion products have been established, which makes it possible to predict the nature of wear of the rolling surface of railway wheels and rails under various operating conditions.

The characteristics of crack growth near non-metallic inclusions under various loading conditions and the influence of laser treatment of steel on these processes are discussed. It is shown that crack development is accompanied by branching within fractured inclusions and in their clusters, as well as upon encountering structural defects in the steel matrix and dispersed second-phase particles. Conditions for crack growth inhibition associated with crack inhibition by plastic sulfides, the development of local relaxation processes in the steel matrix, and changes in the stress state are established. The influence of local microcomposite structures of the steel matrix, obtained under laser irradiation, on the inhibition of crack growth near non-metallic inclusions is demonstrated. The nature of crack growth near non-metallic inclusions was studied under various types of loading without laser irradiation and after preliminary laser treatment. Specimens of hot-rolled steel grades 08Al, 08Ti, 08, 08Cr18Ni10Ti, R7, M76, and GCr15 were subjected to tension and compression in vacuum at temperatures of 20…1200 °C using Instron-1195 and IMASH-9 units (grip movement speed of 1680 mm/min). Some steel specimens with polished surfaces were subjected to laser irradiation before deformation using GOS-30M and CVANT-16 units at pulse energy Wimp of 10…30 J. The heating rate was 105 °C/s, the pulse action time was (1.0…6.0).10-3 s, the cooling rate was 106 °C/s, and the radiation power density was 4 .104 kW/cm2.

The features of localization of severe plastic deformation in a steel matrix near non-metallic inclusions are studied. In the steel matrix, near inclusions and at the inclusion-matrix interphase boundaries, the nature of the stressed and deformed states changes, the strain increment is determined by the rotation angle of the inclusion during its movement in the plastic region. Processes of local structural transformations near non-metallic inclusions in steels exposing to intensive plastic deformation were investigated. The influence of non-metallic inclusions on the local refinement of the steel microstructure is an important effect during severe plastic deformation, which makes it possible to obtain additional nanostructural strengthening near the inclusions during the general refinement of grains to a submicrocrystalline state. It was shown the influence of non-metallic inclusions on mechanical properties of these steels.

The goal of this investigation was to research the nature of the formation of gradient and composite zones near non-metallic inclusions during laser treatment of the steels. The materials for investigation were commercial steels containing different non-metallic inclusions. The specimens of different steels were exposed to laser beaming on the installations GOS-30M. The research methods were applied: petrography, X-ray microscopy (MS-46 Cameca, “Nanolab – 7”) and optical microscopy (Neophot-31) to study steel matrix near non-metallic inclusions and to identify of the inclusions. Nanohardness of the steel matrix near inclusions (“Nano Indenter II”) was analyzed. Peculiarities of saturation of the steel matrix by elements of non-metallic inclusions during different regimes of laser action were investigated. It was shown the role of that process in the formation of local structure of steel matrix near non-metallic inclusions. The features of the formation of gradient and micro composite saturation zones of a steel matrix under conditions of abnormal mass transfer from nonmetallic inclusions during laser processing are discussed. The difference in the rates of abnormal mass transfer of chemical elements of non-metallic inclusions into a steel matrix at the moment of laser melting is shown.

During operation, under the influence of mechanical stress, temperature, and external environment, the initial structure of a railway wheel undergoes changes that lead to its fatigue-corrosion wear.
The wheels with different tread profiles that were removed from operation due to the maximum wear of the rims were studied. The studies were carried out using the metallographic method (Neophot-21) and scanning electron microscope JSM-35.
The causes of cracks and wear particles formation near the tread surface of railway wheels associated with phase and structural changes occurring during operation were analyzed. The possibilities of changing the tread profile due to uneven wear were established. It was shown that structural and phase changes near the tread surface are associated with the development of plastic shifts due to the action of external loads, thermal stresses during braking, and the formation of “white layers” when the metal is heated by the heat of braking and abrupt cooling when the brakes are turned off. The role of non-metallic inclusions and corrosion products of wheel steel in the formation of cracks near tread of railway wheels has been established.

The features of the chemical and phase composition, structure and transformations in boride inclusions in the steel 04H14Т3R1F, used for the manufacture of hexagonal pipe covers used during transportation to the place of regeneration and storage of spent fuel assemblies (FA) of nuclear power plants, have been studied. It has been established that steel 04H14Т3R1F contains two types of boride inclusions (Ti,Fe,Cr,V)2B with a shell of (Ti,Cr,V)2B and (Fe,Cr)2B, which have significant chemical heterogeneity. It is shown that in the process of hot deformation the phase and structural transformations occur: a change in the composition of borides due to the redistribution of elements, dynamic diffusion fragmentation and release of “satellite” particles, brittle destruction of borides, boride transformation. The behavior of boride inclusions and their influence on the mechanical properties of 04H14T3R1F steel at different plastic deformation temperatures was studied.

The features of high-speed primary recrystallization of the cold-worked steels with different chemical composition and structure in the laser impact zone are studied. It has been established that during laser heating of the cold-formed steels, either polygonization or primary recrystallization occurs, which has a dynamic character. It is shown that the range of degrees of cold rolling, at which the character of structure recovery changes from polygonization to recrystallization, increases from 25…30 to 50…60%. The effect of heredity of the cold deformation substructure is revealed. It has been found that the density of dislocations in the surface layer after laser exposure increases by more than an order of magnitude due to plastic shears that introduce forest dislocations. It is shown that in the zone of laser treatment there are signs of columnarity of recrystallized grains and subboundaries, as well as a crystallographic texture.

The features of the chemical and phase composition, structure and transformations in boride inclusions in the steel 04H14Т3R1F, used for the manufacture of hexagonal pipe covers used during transportation to the place of regeneration and storage of spent fuel assemblies (FA) of nuclear power plants, have been studied. It has been established that steel 04H14Т3R1F contains two types of boride inclusions (Ti,Fe,Cr,V)2B with a shell of (Ti,Cr,V)2B and (Fe,Cr)2B, which have significant chemical heterogeneity. It is shown that in the process of hot deformation the phase and structural transformations occur: a change in the composition of borides due to the redistribution of elements, dynamic diffusion fragmentation and release of “satellite” particles, brittle destruction of borides, boride transformation. The behavior of boride inclusions and their influence on the mechanical properties of 04H14T3R1F steel at different plastic deformation temperatures was studied.

The influence of non-metallic inclusions on the formation of defects in deformed steels and their role in providing crack resistance are considered. It is shown that non-metallic inclusions as stress and strain concentrators are one of the most dangerous sources of defect initiation in steels during pressure treatment. It has been established that the nature of cracks and the features of their growth near nonmetallic inclusions are determined by the type of inclusions, as well as by the scheme of the local stress state, which depends on the loading conditions. An analysis was made of the features of the initiation and development of the cracks near non-metallic inclusions of various types during tensile strain, compressive and bending deformation. It is shown that the most severe way of deformation for the inclusion-matrix system is tensile strain, the softest is compression.

Corrosion mechanism and rate of different chemical composition and structural condition of wheel steel were investigated. It was shown that “white layers”, variation in grain size and banding of wheel steel structure results in corrosion rate. Microstructure of steel from different elements of railway wheels after operation with corrosion was investigated. Wheel steel with addition of vanadium corroded more quickly than steel without vanadium. Non-metallic inclusions are the centres of corrosion nucleation and their influence on corrosion depends on type of inclusion. Mechanism of corrosion of wheel steel corrosion was discussed.

The features of recrystallization of steels with different chemical composition and type of crystal lattice under laser action were investigated. These processes are of great importance in high-speed laser heating and cooling, as well as in the formation of the microstructure of steels under the influence of residual heat.
It was found that recrystallization under laser action has signs of a dynamic process due to an increase in the dislocation density. In addition, the dislocation substructure of steel is inherited from the initial hot-deformed state. It is shown that the mechanism of laser recrystallization depends on the type of steel, chemical composition, and crystal lattice.
In different steels, the development of primary, collective, and secondary recrystallization was observed. In this case, the change in the grain structure of steels took place against the background of an increased density of dislocations and the formation of a cellular dislocation substructure.

The features of structural changes in the cove zone on the tread of worn out railway wheels were investigated. The influence of laser processing in pulsed and continuous mode on the nature of the structure and properties of wheel steel was shown. The influence of laser treatment on the increase in the hardness and wear resistance of wheel steel has been established. It was shown possibility and necessity of local laser hardening of cove zone of railway wheels tread by coming out of bainite structure. A method for improving the wear resistance of the tread by local laser treatment has been proposed.