The effect of temperature on microstructure during ultra-rapid annealing of severely deformed low-carbon steel

Ultra rapid annealing (URA) is an effective method to control and refinement of microstructure in steel. In this research, URA of severely deformed low carbon steel with the heating rate of 200 oC/s up to different subcritical and intercritical temperatures are performed. The results show that the recrystallization is not completed during URA in subcritical temperature range due to increase in start temperature of recrystallization. URA up to 730 oC leads to interaction between ferrite recrystallization and phase transformation, and consequent grain refinement. During URA, fine recrystallized ferrite grains are surrounded by fine massive austenite phases which are transformed to pearlites after cooling. These austenite phases pin the grain boundaries and lead to form thermally-stable microstructure in higher intercritical URA.