等轴晶移动对宏观偏析影响的数值模拟

Numerical simulation of macro-segregation with equiaxed grains movement

建立了自由等轴晶移动对宏观偏析影响的数学模型,对铸锭凝固过程中的对流和溶质分布进行了数值模拟.在模型中按照临界固相分数将糊状区分为紧密树枝晶和自由等轴晶两个不同的区域.对带冒口铸钢锭的宏观偏析进行了数值模拟,并同实验结果进行了比较.与假设糊状区内固相静止的模型相比,考虑等轴晶移动的模型得到的溶质分布结果与实验结果更接近.在凝固过程中,等轴晶随液体流动并在铸锭的底部中心聚集,在凝固后的铸锭中形成锥形的负偏析.还发现,在铸锭的中心靠上的区域形成正偏析,在铸锭的外部区域形成负偏析.

A mathematical model of equiaxed grains movement and macro-segregation has been built to analyze the fluid flow and species distribution during the metal solidification. The mushy zone was divided into dendrites region and free equiaxed grains region by the dendritic coherency point. Macro-segregation of a steel ingot in a rectangular mold with a riser was simulated and the calculation result was compared with that of an experiment. It shows that the species distribution obtained by the grain movement model is more consistent with experiment comparing to that by the solid skeleton model in mush. The equiaxed grains move with the fluid and accumulate at the bottom center of the ingot during solidification. The cone-shape negative segregation forms after solidification. The positive segregation in the upper center and the negative segregation in the exterior region of the ingot are found at the same time.