Recrystallisation before austenitization for improved microstructure and properties in automotive steel sheets with high product of strength and elongation

Abstract

This study investigated the effect of recrystallization before austenitizing transformation (i.e., pre-recrystallization) on the microstructure and properties of 22Mn2Cr cold-rolled automotive steel sheets based on continuous annealing at 700 °C for various holding times. Subsequently, the samples were heated to an austenitizing temperature of ∼850 °C, which led to the formation of a fine austenite grains via nucleation at the dislocations during reheating. The austenite grain size was more refined when samples were pre-recrystallized at 700 °C for several minutes compared to those directly heated to 850 °C, which was attributed to combined grain refinement from recrystallization and austenite phase transformation. This refined austenite grain size led to a finer bainite grain size in the cooled final product. The strength of the steel decreased slightly (∼1200 MPa), but the elongation (∼19%) and product of strength and elongation (∼23 GPa%) were significantly enhanced by the pre-recrystallization treatment.