Numerical simulation of slab centerline segregation with mechanical reduction during continuous casting process

The mechanical reduction is an effective way to improve the strand center segregation during the continuous casting process, while the effect of reduction parameters on solute transport phenomenon has rarely been addressed. In the present work, a two-phase solidification model coupling the thermal shrinkage and mechanical reduction was established to investigate fluid flow and solute distribution in the continuous casting slab. In the model, an integrated method was used to define solid deformation, which was dependent on the solidification behavior in the center. The results show that the solidified shell contracting outward by thermal shrinkage will be compressed to slab center with mechanical reduction and the enriched liquid steel transporting downwards is suppressed, resulting in the center segregation improvement. The reduction zone should cover the solidification range in the slab center, where the liquid fraction is between 0.95 and 0.01. The mechanical reduction applied in the earlier stage strongly influences the solidification end, while that in the later stage obviously affects center segregation evolution. Moreover, it is found that the solid phase still contracts intensively to slab surface, even the liquid phase has already solidified. Therefore, the mechanical reduction should also be applied in the subsequent cooling stage to avoid the center porosity formation. Besides the reduction amount and position, the slab stretching in the reduction zone is also another important factor influencing the improvement of center segregation.