Investigations of the structural components of rail joints, obtained by contact butt welding using burning-off, which are revealed on the surface of kinks after the destruction of the compounds during static bending tests and after destruction in operating conditions, were carried out. Analysis of the microstructure and chemical heterogeneity of the fracture surface was carried out with the help of a scanning electron microscope JEOL JIB-Z4500, equipped with an attachment for energy-dispersive analysis. The analysis showed that the main structural defects were poor penetration and inclusions of iron-manganese silicates that significantly reduced the parameters for mechanical tests of welded joints. Their presence in welded joints is unacceptable. Clusters of inclusions of aluminosilicates, so-called matte spots, and oxide films of a more complex composition are formed in the compound on the basis of non-uniformly distributed nonmetallic inclusions of the metal of the rail.
The results of a study of the change in the microstructure of welded joints of rail steel are presented. Comparison of various methods of structural factor analysis is presented. Comparative studies of various methods of analyzing the structural factor in welded joints of K76F rail steels according to GOST R 51685-2013 are considered. It has been established that for this series of experiments, a decrease in hardness of the surface of the welded joint, as well as an increase in Barkhausen MP noise, is 65-75% of the mean value. That indicates the presence of tensile residual stresses in this zone. A coarse-grained structure of primary austenite grains with a grain score of 2 ... 3 is observed along the joint line and adjacent metal layers. A solid grid of ferrite precipitates is clearly observed along the grain boundaries of the primary austenite that indicates the low plastic properties of this section. As a result of conducted studies, it was found that the microstructure of the metal in the heat affected zone of the welded rail joint after the flash welding is represented by plate and globular perlite. The change in hardness in the heat affected zone is associated with a change in the interlamellar distance of perlite that in turn depends on the cooling conditions, i.e. thermal cycle of welding. Control of the thermal cycle during butt flash welding of rails will allow one to form the optimal structure in the welded joint.
The structure, phase composition, and morphology of the surface layers of structural 1020, 1050, 1060 steels of the steel modified by the cathode spot of the welding arc are studied with the help of electron and optical microscopy. It is shown that the treatment of the cathode spot of the arc leads to grain refinement in the surface layer and causes its hardening. As a result of this treatment, partial or complete amorphization of the surface layer is possible.
Abstract. This paper describes a discrete model of a standard airframe part. The model is intended for determining the junctures between the design elements of a node (unit) in the pre-assembly procedures. We herein propose an algorithm selecting base surfaces for basing the product being assembled; selections are made on the basis of the 3D model of such product.
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