Dilatometric study of critical points of 13X11N2V2MF steel

At the heating and cooling rates up to 30$^\circ$ C/min, dilatograms for different heat treatment regimes for high-strength martensitic 13X11N2V2MF steel are recorded, and its critical points are determined. At low heating rates, the temperature of formation of austenite A$_{\mathrm {C1}}$ is 750$^\circ$ C, but its position depends on the heating rate and uniformity of the sample composition in volume, and can reach 810$^\circ$ C. It is shown that the temperature of the beginning of cooling, the duration of soaking and the presence of temperature stops, if they are accompanied by the release of carbide particles from the austenite, have a significant effect on the martensitic point of the steel under study. The second method of measurement A$_{\mathrm {C1}}$ used in the study is based on the analysis of the dependence of the hardness of hardened steel samples on the tempering temperature for a fixed duration of tempering (2 hours). As long as the holding temperature does not exceed A$_{\mathrm {C1}}$, processes lead to a decrease in hardness in the samples. However, once the elevated temperature passes through the critical point, along with the tempering of the preserved martensite, the formation of austenite crystals begins, which, after abrupt cooling in water, again leads to an increase in hardness. Therefore, the minimum hardness corresponds to the temperature of A$_{\mathrm {C1}}$. This method gave the same result: A$_{\mathrm {C1}}$ = 750$^\circ$ C, which is the same as dilatometry.