Influence of heating rate and intercritical annealing temperature on the austenite formation of a cold rolled dual-phase steel

This study investigated austenite formation in a cold-rolled dual-phase steel through thermal experiments in a dilatometer and a Gleeble machine, applying various intercritical annealing temperatures and different heating rates in a 60 % cold-rolled ferrite-pearlite banded microstructure. The microstructural characterization revealed that the transformation of lamellar pearlite into ferrite and spheroidized cementite aggregates started before the onset of austenite formation. Different degrees of overlap between the recrystallization of ferrite-pearlite structure and austenite formation processes were observed, depending on the applied heating rates, which affected the austenite formation mechanisms and the microstructure morphology. This study showed that if the heating rate applied in an intercritical annealing cycle of a cold-rolled ferrite-pearlite microstructure is high enough, the austenite can be nucleated in the spheroidized cementite- ferrite aggregates and at ferritic grain boundaries, including the unrecristallized ones. image