Abstract:
The regularities of the manifestation of endothermic and exothermic effects during the transformations of perlite and austenite have been studied using differential scanning calorimetry. The enthalpy and entropy of eutectoid transformation at different heating and cooling rates were estimated by direct measurements. In particular, for a heating rate of 5 K/min $\Delta H$ = 2380 J/mol and the entropy of such a transition is $\Delta S$ = 2.32 J/(mol $\cdot$ K). It is suggested that in pre-eutectoid steels, when heated above the A$_{\mathrm{C1}}$ point (the critical point in the Fe–C state diagram when heated), the transition of perlite to austenite and the transition of excess ferrite to austenite occurs by its own set of mechanisms, each of which is realized at different temperatures in the intercritical (between points A$_{\mathrm{C1}}$ and A$_{\mathrm{C3}}$) temperature range. An explanation of the independence of the temperature of the A$_{\mathrm{C1}}$ point from the carbon content in Fe–C alloys is proposed.
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