Hot deformation behavior of a 4Al alumina-forming austenitic heat-resistant steel: Constitutive equation, prediction model, processing map and dynamic recrystallization mechanism

Alumina-forming austenitic (AFA) heat-resistant steel has exhibits excellent performance and has extended application prospects. To study the hot deformation characteristics of a novel Fe-15Cr-27Ni-4Al-based AFA heat-resistant steel, thermal compression experiments were performed at a 900 to 1200 °C temperature range and a 0.001-10 s -1 strain rate range on Gleeble-3800 thermal-mechanical simulator. An improved Arrhenius-type constitutive model and a dynamic recrystallization (DRX) kinetic model was established, and its accuracy for predicting the high-temperature flow behaviors was verified. The thermal processing maps based on the dynamic materials model (DMM) were constructed and microstructure evolutions were investigated. The result shows that the stress decreases with the increase of temperature or the decrease of strain rate. Furthermore, under the premise of allowing certain errors, the improved constitutive model and the DRX kinetic model better describe the hot flow behavior and DRX process, respectively. As the temperature and strain rate increases, DRX is more likely to occur. At the same temperature, the degree of DRX decreases with increasing the strain rate up to 0.1 s -1 , whereas an opposite trend is exhibited when the strain rate is greater than 0.1 s -1 , which is closely related to a change in DRX mechanism. Eventually, based on the analysis of thermal processing maps and microstructure evolutions, the optimal thermal processing parameters were determined.