LAUSR

The motion of free grains has a significant influence on the solidification structure, solute distribution, and defects of large casts. However, few studies have modeled the solidification structure of large casts considering grain motion. In this paper, taking into account the motion of free grains, a multiscale cellular automaton model is proposed to predict the solidification structure of continuously cast billets. The model is validated with experimental measurements. Then, the proposed model is adopted to investigate the solidification structure evolution of a wire steel 82b cast by a bow-type continuous caster with a billet section size of 160 mm × 160 mm. The results show that the growth of columnar grains in inner arc of billet strand is promoted by the sedimentation of free equiaxed grains. But the columnar grains in outer arc of strand are blocked once free grains nucleate before them. Thus, asymmetric morphology of solidification structure in the 82b billet with casting speed of 1.8 m/min is quantitatively determined and the length of the columnar grains in the inner arc and the outer arc of strand is 57.0 mm and 31.0 mm, respectively. Moreover, compared with the difference of cooling intensity between inner arc and outer arc in secondary cooling zone, the motion of free grains dominates the asymmetric morphology in the 82b billet.