Effect of Alternate Electromagnetic Stirring on Macrostructure Evolution in Thin-Slab Continuous Casting

Abstract

Strand electromagnetic stirring (SEMS) is widely applied in thin-slab continuous casting to promote the equiaxed crystal ratio (ECR). However, the effects of alternate electromagnetic stirring on the evolution of solidification macrostructure and ECR remain poorly understood. And the formation of the equiaxed crystal region beneath the stand and equiaxed-to-columnar transition (ECT) have been overlooked in most previous models. This study first introduces a novel equiaxed-columnar solidification model to comprehensively analyze the effects of alternate electromagnetic stirring in thin-slab continuous casting. A complete macrostructure feature of the slab, including the equiaxed crystal region beneath the strand, ECT, well-developed columnar dendrites, columnar-to-equiaxed transition, and center equiaxed crystal zone, could be simulated accurately. The multiphase model was validated by the measured ECR and columnar growing direction from a pickling corrosion experiment. Results showed that alternate stirring could improve the ECR effectively. The ECR was increased by 26 pct compared to the one-way stirring when the switching period of alternate stirring was 8–12 seconds. A multi-vortex flow structure was observed in the secondary cooling zone, which could increase the residence time of the molten steel and the nucleation rate. Furthermore, the vortex-shedding behavior of the upper recirculation alleviated the remelting of equiaxed crystals during the sedimentation. The behavior of multiphase flow under alternate SEMS is a novel finding. These preliminary results are encouraging and should be validated in other continuous casting processes.