Dynamic recrystallization behavior and microstructural evolution in a Mn–Cr gear steel

Using a Gleeble 1500 hot simulator, the dynamic recrystallization (DRX) behavior and changes of DRX grain size of a Mn–Cr type gear steel have been investigated at deformation temperatures of 900–1150 °C, strain rates of 0.1–1 s−1, and initial austenite grain sizes of 70–150 μm. The experimental results show that the Mn–Cr gear steel exhibits a typical DRX behavior under higher deformation temperatures, lower strain rates and smaller initial austenite grain sizes. The DRX takes place under the conditions with Zener–Hollomon parameter (Z) less than a critical value Zc. The DXR grains are formed by the bulging mechanism. By regression analysis, activation energy and stress exponent were determined to be 378.6 kJ/mol and 5.8, respectively. The complete DRX grain size is a power law function of Z with an exponent of −0.25. The reason why Z parameter determines uniquely the DRX grain size was analyzed.