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

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Fig. 7. Dependence of the coercive force on the tempering temperature of the investigated steels processes of decay for the martensitic structure and the presence of cementite components in various mag- netic states. There are known works [28, 29], in which the magnetic parameters of steel were used to determine structural changes: coercive force, magnetic permeability, relaxation coercive force, differential magnetic permeability, etc. The experimentally established correlation between the magnetic properties of a ferromagnet, the structure and mechanical properties is shown in [30]. However, it should be noted that regularities of this kind are determined only for a certain class of steels, for example, carbon steels 30 , 35 , 45 , U8 , U10 , U12 subjected to quenching and tempering at different temperatures [31]. The signi fi cant in fl uence of heat treatment on the structure and properties of steel, which can be considered on the coercive force and hardness, is shown in [29]. When analyzing the relationship, correlation dependences of magnetic and mechanical properties for steels belonging to different groups, the dependences cease to be of a general direct nature, and it is often dif fi cult to determine the properties of interest. This is due to the fact that the structures formed during heat treatment and their characteristics (the amount, distribution and properties of martensite, retained austenite, carbides) are more dependent on the interaction of alloying elements that are part of the steel, their percentage content, including carbon, the nature as well as magnitude of temperature in fl uences [32]. It is necessary to make an assessment by statistical and regression analysis to understand the in fl uence of the structure dispersion on the magnetic and mechanical properties of steel. Figures from 8 to 10 show the dependences of the uneven-grained factor on various parameters characterizing the steel properties. They are obtained in laboratory conditions. In addition, these graphs show the predicted values for the Y - value of the uneven-grained factor calculated from the magnitude of internal stresses. The regression analysis for the data in Figure 8 [33, 34] allows obtaining the information about regres- sion statistics. Its main indicators are shown in Table 3. The R -squared or the determination coef fi cient in the analysed model is 0.885. It suggests that the used parameters have a relationship that with a probability of 88.5% can be explained using the proposed model. Because the determination coef fi cient is greater than 0.5, then the relationship is considered satisfactory. ε is the standard error for the regression model. This value shows how much the predictions of the val- ues for the parameter Y do not correspond to the true value. Usually, the permissible limits de fi ned on the base of ε lies within +/- 2-3 values.