Dynamic recrystallisation behaviour and microstructural evolution in a Mn-Cr gear steel

Using a Gleeble 1500 hot simulator, the dynamic recrystallisation (DRX) behaviour 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 70-150μm. The experimental results show that the Mn-Cr gear steel exhibits a typical DRX behaviour under higher deformation temperatures, lower strain rates and smaller initial austenite grain sizes. The DRX takes place under conditions such that the Zener-Hollomon parameter Z is less than a critical value Z c . By regression analysis, activation energy and stress exponent were determined to be 378 kJ mol -1 and 5·8 respectively. The DRX grain size is a power law function of Z with an exponent of -0·25. The reason why the Z parameter determines uniquely the DRX grain size was analyzed.