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.

中文翻译：

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带晶粒运动的连铸坯凝固组织的数值模拟

自由晶粒的运动对大型铸件的凝固组织、溶质分布和缺陷有显着影响。然而，很少有研究对考虑晶粒运动的大型铸件的凝固结构进行建模。在本文中，考虑到自由晶粒的运动，提出了一种多尺度元胞自动机模型来预测连铸坯的凝固组织。该模型通过实验测量进行了验证。然后，采用所提出的模型研究了由弓形连铸机铸造的钢坯截面尺寸为 160 mm × 160 mm 的 82b 线材的凝固组织演变。结果表明，自由等轴晶粒的沉降促进了钢坯内弧柱状晶粒的生长。但是一旦自由晶粒在它们之前成核，股线外弧中的柱状晶粒就会被阻塞。由此定量确定了82b钢坯在拉速为1.8 m/min时凝固组织的不对称形态，铸坯内弧和外弧柱状晶粒的长度分别为57.0 mm和31.0 mm。此外，与二次冷却区内弧和外弧冷却强度的差异相比，自由晶粒的运动主导了82b钢坯的不对称形貌。