糊状区结构与通道偏析的形成机理

Structure of mushy zone and formation mechanism of channel segregation

用Ｐｂ－５％Ｓｎ合金在Φ７０ｍｍ×１２０ｍｍ的圆柱锭上模拟大型钢锭中经常出现的通道偏析．根据糊状区特征结构分析流动稳定性，研究通道偏析的形成机理．结果表明：通道偏析是糊状区富集溶质的液相由于密度倒置形成的局部对流所引起．斑点偏析的形成位置取决于决定局部Ｒａ的糊状区结构．Ａ偏析的生长方向取决于凝固界面的推进作用．

Channel segregation constantly occuring in large steel ingot was simulated with Pb 5%Sn alloy, using a Φ 70 mm×120 mm cylindrical mold. Based on the peculiar structure of mushy zone, the stability of fluid flow was analyzed, and the mechanism of formation of channel segregation was studied furthermore. The results are summarized as follows: Channel segregation of different types is caused by the local convection of solute riched liquid which is driven by the density inversion within mushy zone. The location of origin of freckle is determined by the Rayleigh number which signifies the structure of mushy zone. The growing orientation of A type segregation is affected by the pushing action of solidification interface.