Effects of rapid heating on the phase transformation and grain refinement of a low-carbon mciroalloyed steel

The present study aims to clarify the possibility of rapid heating in the preparation of low-carbon ultrafine (UFG) steel. The effects of heating rate on the phase transformation, microstructure and precipitation of a low-carbon microalloyed steel were elaborately investigated. The results manifest that rapid heating potentially provides a simple and innovative process for the preparation of UFG steels just by increasing the heating rate. The parent austenite grains were refined due to the more reserved (Nb, Ti, V)C precipitates and dislocations within a short heating process by rapid heating. However, an effective holding time was proposed in the rapid heating to ensure the refined austenite grains. Moreover, the synthetic influences of initial increased grain boundaries and redissolved (Nb, Ti, V)C carbides provoked the abnormal grains with weakened thermostability. Redissolution of (Nb, Ti, V)C carbides were apparent during austenite nucleation at a slow heating rate, and it was verified during the isothermal holding stage by rapid heating. In addition, the austenitic phase transition occurred at higher temperature with the increase of heating rate, by which the transformation rate was accelerated.