Assessment of the effect of the steels structure dispersion on its magnetic and mechanical properties

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 As is known, the properties of alloys in the solid state are determined by its crystal structure, chemical composition and by all types of structural disorders manifested in the form of inhomogeneities [1]. The structure inhomogeneities or chemical composition leads to a deviation of the material properties in the local part. This signi fi cantly affects the reliability and service life of the equipment. Considering that the operation of equipment and structures made of structural steels occurs in most cases under constant external loads, which are of a multi-component nature, then there is a rapid intensi fi cation of material destruction processes, leading to emergencies. A lot of research is being carried out on the development of methods for determining the mechanical properties of steels [2-6]. Nowadays there are methods of non-destructive testing based on the analysis of magnetic parameters. It allows determining the steel mechanical properties, in addition to destructive tests [7, 8]. It is proposed to use the steel coercive force as a diagnostic criterion for the hardness and tensile strength in the study [7]. However, this approach has its own nuances. There is no uniform dependence of mechanical properties and coercive force for different grades of steel [7]. It indicates a difference in the structure and properties of the phase components, which signi fi cantly affect the formation of mechanical properties and coercive force. There are methods for monitoring mechanical properties. They are based on the analysis of the ultrasonic vibration propagation by the controlled object [9]. The connection of the diagnostic criteria with the mechanical properties and structural features of the steel has been considered for a long time. The diagnostic criteria show the magnitude of the steel mechanical properties. There are research works that consider the in fl uence of the structure dispersion (inhomogeneity) on the mechanical properties. Inhomogeneity is the presence of different grains in the structure at the same time. For example, the in fl uence of an ultra- fi ne-grained or fi ne-grained structure of simple carbon steel on the yield strength is considered. [10]. The process of accumulation and occurrence of dislocations and its effect on the steel strength is analyzed in [11] from a statistical point of view for eutectic steel with an ultra- fi ne-grained or fi ne-grained structure. The study of changes in plastic deformation for austenitic steel with a high manganese content and different average grain size is re fl ected in [12]. The in fl uence of substructure development on deformation hardening of steel (Fe -17.5 Mn -8.3 Al -0.74 C -0. 14Si) is evaluated in [13]. It is noted that substructures during re fi nement make signi fi cant changes in the strength properties. The intragrain orientation inhomogeneity and inhomogeneity of the stress state are highlighted as important areas for the future studies in [14]. There are works [15, 16], in which the samples being studied are obtained by an additive method, in addition to the works, in which the study is carried out on alloys, obtained by conventional metallurgical methods. In these works, the in fl uence of microstructural features, namely mesostructure descriptors, which describe the features of mesostructural inhomogeneity on mechanical properties from the point of view of quantitative evaluation, is considered. Despite the fact that in the works listed above, some statistical analysis of the effect of structural heterogeneity on mechanical properties was carried out, there is no veri fi cation of the dependencies put forward as the results. In this study, the in fl uence exerted by the structure dispersion not only on the value of the ultimate strength, but also on the value of the coercive force and internal stresses of structural steels 15KhSND , 09G2S , St3 is considered. The in fl uence is assessed by the analysis of correlation dependencies between the ultimate strength, coercive force, the value of internal stresses and the uneven-grained factor, acting as a criterion for the structure dispersion. The studied structural steels are widely used for the manufacture of various metal structures, pipeline transport, storage tanks for oil and petroleum products. To determine the relationship between the considered values, it is necessary to analyze the effect of heat treatment on the value of coercive force, tensile strength, internal stresses and the uneven-grained factor; and to determine the correlation relationship between these parameters and to explain changes of these parameters during heat treatment.