Numerical Modeling of Austenite Transformations in Steel during Continuous Cooling

The processes occurring in bainitic-martensitic steel during continuous cooling from the austenitization temperature at a rate of 0.1–1.0°С/s were analyzed by numerical modeling of supercooled austenite transformations. The Austin–Rickett equation and the additivity rule were used to calculate the fraction of bainite formed during cooling at a given rate. The temperature dependence of the Austin–Rickett equation parameters n and k was determined experimentally from the kinetics of isothermal transformation of austenite at different temperatures. Based on the statistical analysis of similar dependences for a number of steels, it was shown that at a temperature above the martensite onset temperature, the n(t) dependence can be described by the Gauss equation, while at a temperature below the martensite onset temperature, the n(t) dependence is predominantly linear. It is shown that the temperature dependence of the equilibrium fraction of bainite in steel is determined from the thermodynamic condition of quasi-equilibrium of the α and γ phases. It is established that in numerical modeling of bainite formation during continuous cooling, it is necessary to take into account the shift of the n(t) dependence to the region of lower temperatures.