Refinement of coarse grained austenite in Nb-V-Ti microalloyed steel during roughing rolling

The refinement of coarse grained austenite in a Nb-V-Ti microalloyed steel during roughing rolling of a medium thin slab casting and direct rolling process was investigated by considering the austenite grain size distribution. The evolution of grain size distribution was analysed by taking into account dynamic recrystallisation (DRX), static recrystallisation (SRX) and metadynamic recrystallisation (MDRX), strain induced precipitation and retained strain. The results indicated that the initial coarse austenite was significantly refined during roughing rolling. Static recrystallisation is the main post-dynamic softening mechanism during all interpass intervals, but SRX+MDRX may also take place at certain times. The microstructural homogeneity of microalloyed steel produced in this work is better than that in steel produced by thin slab and direct rolling (TSDR) process. This is associated with a higher reheating temperature, a higher entry temperature and a larger reduction due to increased slab thickness in this work compared with the TSDR process.