OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 а b c d Fig. 6. Inclusions of manganese sulfide in a 09Mn2Si steel sample at an after medium-temperature tempering (500 oС): a – inclusions in a micrograph obtained using a scanning electron microscope; b – the distribution of manganese in the micrograph shown in a; b – the distribution of manganese in the micrograph shown in a; c – the distribution of carbon in the micrograph shown in a; d – the distribution of sulfur in the micrograph shown in a Conclusions 1. When analyzing the results obtained, it is found that in the low-alloy low-carbon structural steel 09Mn2S, in most cases, there are non-metallic inclusions such as manganese sulfide. These inclusions are formed during steel production in the area of grain boundaries and have spherical form. When this steel is heated to the temperatures of the intercritical transition, in which a ferritic-martensitic structure is formed, this compound does not undergo significant changes. These inclusions significantly affect the strength and corrosive behavior. Manganese sulfide acts as the initiation point of the corrosion process. 2. It is found that carbon diffused from the main matrix forms a halo around the inclusions with a strong distortion of the crystal lattice. This leads to a change in the composition of the material in the local area, and, consequently, to a difference in mechanical and corrosion properties. 3. With an increase in the tempering temperature, the defect structure of the crystal lattice decreases due to a decrease in the number of dislocations and the decomposition of the unstable phase of martensite. As a result, internal stresses are reduced. However, there is a deformation of less strong inclusions of manganese sulfide. It begins to take on an elongated shape. This leads to an increase in the corrosive area. At high tempering, as a result of a decrease in the defect structure and the completion of the process of martensite decomposition, back diffusion of carbon into the depleted regions occurs. As a result, an increase in the concentration of this element is observed around the inclusions. These processes lead to some increase in the resistance of the material to corrosion processes.
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