Comparison of Dynamic Recrystallization in Blooms between Conventional Rolling and Hot-Core Heavy Reduction Rolling Process

Hot-core Heavy Reduction Rolling (HHR2) is a new technology that improves the core quality of blooms by using a heavy reduction roller at the solidification end. Dynamic recrystallization (DRX) is expected to optimize the microstructure in this process. But the difference of DRX characteristic between HHR2 and conventional hot rolling (CHR) is an unclear problem. Herein, the differences of DRX behavior between two rolling processes are studied. If two rolling processes are carried out under the same deformation temperature and strain rate, the work hardening in CHR samples is greater than that in HHR2. Moreover, DRX occurrence in HHR2 lags behind the CHR process due to lower growth rate of dislocation density achieved in HHR2. By using DRX models, the DRX area and DRX volume fractions in bloom are calculated. The great temperature gradient and low strain rate decrease the DRX critical strain in the HHR2 process. The DRX region is mainly around the core of the HHR2 bloom, where the DRX volume fraction achieves 41.8%. The maximum value of DRX volume fraction in CHR bloom only achieves 20.1% because the great strain rate and uniform temperature lead to a low level of deformation permeability.