Simulation of phase transformations in high carbon pearlite steel at various cooling rates

The paper reports on the experimental research into the austenite decomposition in high carbon steel at a constant temperature and rates of cooling. The study was carried out by the methods of dilatometry, micro-durometry, optical and scanning microscopy. From the dilatometric curves it is apparent they are sufficiently presented by the Kolmogorov-Avrami equation in a temperature range from 700 to 550 °С, and by the logistic function for temperatures ranging 500 to 250 °С. The data of the dilatometric analysis were used to draw isothermal and continuous cooling transformation diagrams of phase conversions. It has been pointed out an isothermal diagram to comprise four C-curves of pearlite and bainite transformations, which are approximated by second- and third-degree polynomials. The critical temperatures of austenite, bainite, and martensite transformations have been determined, being 711, 550 and 196 °С, respectively. Considering the data obtained experimentally, a mathematical model of austenite decomposition has been developed for a constant cooling rate, and volume fractions of structure-phase components estimated theoretically, demonstrating the congruence with experimental results. The suggested mathematical model can be adopted to calculate a structure-phase composition in industrial differential heat treatment of rails. The authors are grateful to Vladimir Sarychev, Egor Polevoy and Victor Gromov who took an active part in the preparation of the manuscript. This work is supported by the Russian Foundation for Basic Research (RFBR) [project number 19-32-60001] and President grant for State Support to young researches [grant number МK-118.2019.2].