ev UDC 669.15The paper addresses the action of a high-temperature hydrogen-containing fluid on mechanical properties of a low-alloy carbon hypopearlitic steel 09G2S which is used for the manufacture of a gasoline-producing reactor vessel for a catalytic reformer unit. The vessel metal had 180,000 running hours at a hydrogen-containing fluid temperature 280°C and pressure 4.0 MPa. It is demonstrated that a long-term operation of the material in contact with gaseous hydrogen has caused its natural ageing. Further hydrogen saturation of test specimens at 580°C and 10 MPa for 17 h has resulted in a so-called hydrogen-induced strain hardening of the material. The influence of gaseous hydrogen on the state of carbide phases in the base metal and weld is studied by the x-ray spectrum analysis and nuclear gamma resonance method. The amount of a carbide phase (cementite) in steel has been found to grow due to natural ageing at elevated temperatures. The high-temperature hydrogen saturation makes the cementite decomposition process more intensive, and no cementite recovery occurs even when the material is heated up to 580°C.Introduction. The interaction between commercial steels and hydrogen was the subject of numerous studies [1][2][3][4][5][6][7] which have demonstrated that the physicochemical action of hydrogen on the metal, which is accompanied by chemical interaction of the gas with the alloy's individual components and phases, tend to cause irreversible microstructural alterations in the metal. Also, a unique effect of the structural factor on the behavior of alloys in a hydrogen medium was noted more than once. Archakov [5] substantiates the conclusion that the hydrogen resistance of steels depends on the nature of the carbide phase that governs the metal-carbon interatomic bond strength as well as on the presence of other elements dissolved in the phase.The processes of carbide precipitation and growth are known to depend on the structure. Due to the difference in their rates at the grain boundaries and in the matrix (the maximum rate is at the grain boundaries and minimum one in the matrix precipitates), carbides are redistributed between the body and boundaries of the grains, predominantly at the grain boundaries. The concentration of carbides at the grain boundaries or their accumulation inside a grain has been found to promote localization of absorbed hydrogen, which in turn impairs the microstructure stability, degradation of properties and local fracture in the material. Specifically, the researchers [4, 5] point out a deteriorated cementite stability (due to the domination of covalent bond and a low concentration of electron gas in this iron-carbon compound) and the possibility of dissolution of less stable carbides under certain conditions: the cementite decomposition at elevated hydrogen temperatures and pressures, which is accompanied by the methane formation and steel decarburization.Considering that the process equipment of oil refinery facilities has to work under the conditions of hydrogenation proce...

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620.178.15/625.143 and N. Ya. OpravkhataThe analysis of the mechanical state of the materials of a new rail and a rail after long-term operation are performed on the basis of the obtained data on the distributions of hardness over the cross sections of rails and the spread of the characteristics of hardness.Keywords: residual and contact stresses, hardness, spread of values of the characteristics of hardness. Introduction.In the course of operation, the materials of heavy-duty structures undergo various types of changes. Thus, in new products, we observe the processes of adjustment of the components with intense wear of the working surfaces, as well as the processes of adaption of the upper layers of the materials to the modes of operation, temperature conditions, etc. The indicated adaptation leads to irreversible structural changes in the materials, which, as a rule, increase their serviceability [1]. The subsequent long-term operation promotes the initiation and development of defects in the materials of the workpieces. It is clear that all these processes are typical, in particular, of the materials of wheel-rail systems.The structural inhomogeneity of structural materials prior to operation manifests itself in the spread of values of its mechanical characteristics in local volumes. A noticeable structural inhomogeneity of the material of the rail in the intact state caused by the technological processes of its manufacturing (rolling, thermomechanical treatment of the entire rail or its head, etc.) increases in the course of operation. The inhomogeneity of the mechanical properties of structural materials over the cross section of any product is estimated according to the distribution of the values of hardness. In this case, the analysis of inhomogeneity of the properties of materials is performed both on the basis of direct values of hardness [2, 3] and by using statistical methods [4][5][6]. The approaches extensively used in practice enable one to monitor (without significant costs) both the state of load-carrying elements and the accumulation of defects in the local zones of structures without their destruction [4].If a wheel rests on a rail, then a three-dimensional stressed state is formed in the central part of its head. In the case of hunting of a train, the contact zone shifts toward the working fillet. In this case, one may observe the realization of two-point contact as a result of the interaction of the wheel flange with the rail. This leads to the formation of a stressed state close to pure shear [7]. The action of numerous factors of different nature affecting the stress-strain state of the railway bed results in the necessity of a large number of replacements of defective and highly defective rails in the railway tracks and frequent failures of rails, which is especially dangerous for the mainline railways with fast motion of passenger and heavy freight trains.The levels of operating loads and the fields of residual stresses play a significant role in the operation of rails. In passing all ...

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