Microstructure evolution and its influence on thermoplasticity of wide and thick continuous casting slab with heavy reduction

After the heavy reduction (HR) process was carried out at the solidification end of the continuous casting slab, the austenite grains were refined by recrystallization, which improved the thermoplasticity of the slab. However, the reduction in deformation during the HR process initiated stress concentration at the slab surface, and the crack risk increased. To effectively evaluate the risk of slab surface cracks under these complex conditions, the effect of the HR on the austenite recrystallization and thermoplasticity of a microalloyed slab surface was investigated by 15-pass reduction thermal simulation according to the wide and thick slab continuous casting process. The softening fraction was introduced as a global internal variable to quantitatively analyze various recrystallized re-refined grains. After the critical strain reaches the critical strain of dynamic recrystallization, a variety of recrystallization modes alternately occur. Among them, the contribution rate of dynamic crystallization to the later refinement reaches more than 50%. The contribution rates of static recrystallization and metadynamic recrystallization to grain refinement are almost the same. The thermoplasticity of the slab surface first increases and then decreases with increasing reduction pass. It was verified by transmission electron microscopy that the main reason for the decrease in thermoplasticity is that the dislocation multiplication rate increases, resulting in a sharp increase in stress and a decrease in thermoplasticity.