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 900-1150degreesC, strain rates of 0.1-1 s(-1), and initial austenite grain sizes of 70-150 mum. 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 Z(c). The DXR grains are formed by the bulging mechanism. By regession 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. (C) 2004 Elsevier B.V. All rights reserved.