Activation energy-based criteria of hot workability for 38MnVS6 steel

The activation energy, which reveals valuable information about the underlying deformation mechanisms associated with microstructural evolution, can be effectively employed to evaluate the hot workability of metals. Nevertheless, systematic research on establishing quantitative evaluation criteria of hot workability for steel based on the activation energy remains scarce in the literature. This work aims to address these issues by carrying out the hot compression test in the temperature range of 900–1200 °C and strain rate range of 0.01–5 s⁻¹. Considering the relationship between activation energy and hot deformation parameters, a modified constitutive model and a dynamic recrystallization (DRX) kinetic model were established to accurately quantify the flow behavior and DRX behavior of 38MnVS6 steel. Furthermore, the 3D activation energy maps were constructed and integrated with microstructural evolution mechanisms to investigate the hot workability of the tested materials. The results show that the activation energy is sensitive to the hot working parameters and reflects the development trend of DRX during the deformation. Combining with average grain size and activation energy maps, the criteria for evaluating the hot workability were proposed through analysis of microstructural evolution under different strains. When the strain exceeds 0.7, both grain size and activation energy criteria are employed to evaluate the hot workability. Based on the proposed criteria, the optimal hot deformation parameters of 38MnVS6 steel can be defined as the temperature range of 930–1075 °C and the strain rate range of 0.66–5 s⁻¹ at high strains with the fine and uniform DRX microstructure.