Dynamic recrystallization and precipitation behaviors during hot deformation of a κ-carbide-bearing multiphase Fe-11Mn-10Al-0.9C lightweight steel

The dynamic recrystallization (DRX) and dynamic precipitation (DP) of grain boundary/intra-granular (GB/IG) kappa-carbides in a novel medium-Mn lightweight steel are investigated by conducting compression tests over a wide range of temperatures (800-1100 degrees C) and strain rates (0.001-10 s(-1)). Two types of distinct flow behaviors have been observed: the flow curves show typical DRX features at high temperatures (>= 950 degrees C), whereas the flow stress shows the significant softening after peak stress at low temperatures (<= 900 degrees C), which is closely associated with the DP of GB/IG kappa-carbides. According to the distinguished flow behaviors, two constitutive equations have been developed for the low and high temperature regimes, showing disparate hot deformation energy (Q) values (i.e. 600.58 kJ/mol and 355.51 kJ/mol). At low temperatures, the kappa-carbides inhibit dislocation motion, and the pinning effect of fine GB kappa-carbide particles retards the austenite grain boundary migration, which greatly improves the peak stress level and thus increases the energy barrier (i.e. Q). Furthermore, the volume fraction and grain size of GB kappa-carbides increase with the decrease in strain rate, resulting in the consumption of stored deformation energy, which coupled with the continuous DRX (CDRX) in delta-ferrite are responsible for the significant softening. The DRX takes place more sufficiently with increasing temperature, and the deformation induced alpha-ferrite transformation (DDT) and morphology evolution of delta-ferrite are observed at 950 degrees C and 1100 degrees C, respectively.