Insight into effect of forced convection during slab casting on as-cast solidification structure

Solidification structure of casting strands significantly impacts the subsequent processing and service properties of the steel products, which correlates closely with the melt flow during the solidification process. Several abnormal solidification phenomena and segregation characteristics observed in slab casting are elucidated by referencing to their related flow patterns of molten steel calculated by a multi-field coupling model for actual casting conditions. Eventually, the effect of forced convection on the solidification structure was discussed. The results show that the forced convection generated by electromagnetic stirring and/or nozzle jet will remove the solute-enriched molten steel between the dendrite in front of the solidifying shell, and change solute distribution at the interface of dendrite tips, leading to the white bands and dendrite deflection. In the white band region, a dense dendrite structure without dendrite segregation appears. Moreover, forced convection results in a higher growth rate on the upstream side than the backflow side of the dendrite tip, promoting the columnar crystal deflection. In addition, dendrite fragmentation upon the forced convection during solidification will increase the equiaxed crystal ratio of the as-cast slab and the number of the spot-like semi-macrosegregation. The carbon extreme range decreased with the change in electromagnetic stirring process, indicating a significant improvement in the composition uniformity of the slab casting. It is suggested that the final quality of rolled products could be improved from the very beginning of casting and solidification through regulating the as-cast solidification structure.