Studies on Hot Deformation Behavior and Dynamic Recrystallization in a High Al Ferritic Low-Density Steel

Hot deformation behavior of a high Al ferritic low-density steel (Fe-11wt.%Al-10wt.%Mn-1wt.%C) was investigated using hot compression tests up to a true strain of 0.69 at strain rates of 0.001-0.1 s(-1) in a Gleeble thermomechanical simulator. When deformed at 900 degrees C the steel is ferritic and mostly dynamic recovery was observed. The samples hot compressed at 1000 and 1100 degrees C exhibited a dual phase microstructure (ferrite + austenite) and an appreciable amount of dynamic recrystallization (DRX) was observed in both the phases. There was a significant refinement in microstructure when the alloy was deformed in the intercritical region. The activation energy of dynamic recrystallization for the alloy was calculated to be 272.08 kJ mol(-1). The ferrite phase exhibited continuous dynamic recrystallization (CDRX) whereas the austenite exhibited discontinuous dynamic recrystallization (DDRX). A constitutive equation for predicting the flow stress values corresponding to a particular strain during hot deformation was derived using the basic Zener-Hollomon equation. Average absolute relative error (AARE) value of 6.2% and correlation coefficient (R) value of 0.97 were obtained indicating a high accuracy of the formulated constitutive relation. The DRX fractions were calculated from Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation as well as grain orientation spread (GOS <= 1 degrees) criterion. Fractions obtained for different deformation conditions by the two methods were compared.