OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 The structure of the material was analyzed using the software package “SIAMS 800”. Some obtained results are reflected in [10, 11, 15, 16]. Results and discussion Specimens cut across the rolled direction were deformed under slow loading at a rate not exceeding 0.1 mm/s. Specimen No.2 was deformed by 1.5 %, specimen No.3 was deformed by 3.0 %, specimen No.4 was deformed by 4.5 %, specimen No.5 was deformed by 6.6 %. Specimen No.1 was not deformed, so it had the lowest magnitudes of internal stress. This difference from the theory is due to the direction, in which the specimen was cut from a plate of rolled metal. Deformation means the change in the length of the specimen expressed as a percentage of the original size. The microstructure of the specimen being investigated is shown in fig. 1. a b Fig. 1. Microstructure of the specimens at magnification of 500X: а – specimen No. 1; b – specimen No. 3 When analyzing the microsections, it was found that the structure is presented by a ferrite-perlite mixture in the ratio of 81.7 % ferrite and 18.3 % perlite. The structure corresponds to score 8 according to GOST 8233: the minimum grain score is 8, the maximum grain score is 13; grains occupying the largest area on a microsection correspond to a score of 11. When rolling the metal, grains are pulled out in the rolling direction and, consequently, internal stresses are redistributed; its maximum magnitude will also be observed in this direction, as evidenced by diffraction patterns (fig. 2). The specimens were stretched at a rate of 0.1 mm/min. Table 1 shows the results of determining the basic mechanical characteristics for specimen No.5. Since the specimens were cut across the rolling direction, it is natural to assume that the lowest magnitude of internal stresses will be observed in the initial state in the longitudinal direction relative to the external load. During deformation, redistribution of stresses may occur and its magnitude may increase (fig. 4). Fig. 4 shows that with increasing plastic strain of the specimens there is an increase in the magnitude of internal residual stresses in the direction of rolling. After deforming the specimens, corrosion tests were carried out, the results of which are shown in fig. 5. The tests were carried out in a thermostat at a constant temperature. To clarify the data obtained, the experiment was carried out twice. Specimens were preliminary prepared by electrochemical etching. It can be seen that the corrosion rate increases with increasing material strain, which is also due to the increase in the magnitude of internal stresses (fig. 6).
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