Effect of Hot Rolling Reduction on Dynamic Recrystallization of Nb-V Bearing HSLA Steel: Physical Simulation and Microtexture Evolution

In the present study, the effect of hot rolling reduction ratio on dynamic recrystallization (DRX) of Nb-V bearing high-strength low-alloy (HSLA) steel was investigated. The hot rolling process was simulated physically by performing single- and double-hit plane strain compression using a thermo-mechanical simulator under similar conditions as experienced in the plant. The austenite no-recrystallization temperature (T-NR) value of the steel was determined through multi-hit plane strain compression in Gleeble simulator as well as using the actual rolling mill log data. The T-NR value (similar to 940-945 degrees C) obtained from both the methods were found to be in good agreement. The rolling reduction was varied in the range of 40-50% in the initial two passes. The kinetics of DRX were evaluated using the Avrami relationship. The dynamic recrystallization behavior was characterized by microtexture analysis using electron backscattered diffraction. The critical strain required for the instigation of DRX in the Nb-V HSLA steel was found to be similar to 0.15. Furthermore, a true strain of similar to 0.8, equivalent to 50% reduction in thickness was required in first pass for complete recrystallization to occur in the chosen steel. The grain orientation spread (GOS) analysis confirmed the presence of recrystallized grains with GOS values less than 2 degrees in the specimens deformed with 40-50% and 50-40% reduction schemes between first two passes of rolling.