Modelling of dynamic recrystallization kinetics of 300M steel at high strain rates during hot deformation

The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization (DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely acquired. In this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173-1423 K with strain rates between 0.001-50 s (-1). Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.