Mathematical Modeling and Mechanism of Coarsening of Austenitic Grain at High-Temperature Heating of Alloyed Structural Steels

The influence of the heating rate of typical cemented steels 15KhGN2TA and 25KhGT on the growth of austenitic grain at long isothermal exposures in the process of high-temperature chemical-thermal treatment is studied. It is shown that the change in the heating rate of cemented steels in the temperature range α → γ of transformation at chemical and thermal treatment has a significant impact on the growth process of austenitic grain in them. The equations of regression are obtained that describe the dependence of the average size of austenitic grain on the heating rate, pre-ignition temperature and cementation temperature, which allow to select the modes of cementation of different steels. The phenomenological model is developed which describes the mechanism of formation and growth of austenitic grains in the steels at heating with different speeds. The conclusion is made that the slow heating of the steels in the interval of phase α → γ transformation contributes to the formation of a complex of small austenitic grains separated by high angular boundaries with impurity atoms adsorbed on them, which provides the increased stability of the grain structure to coalescence and reduces the rate of boundary migration at long term high-temperature austenization.