1Cr18Ni9Ti不锈钢双辊薄带凝固组织区的形成机理

Forming mechanism of solidification structure zone on 1Crl8Ni9Ti stainless steel twin-roll thin strip

在双辊薄带连铸实验和薄带凝固组织特征分析的基础上,结合对薄带凝固组织区的模拟预测结果,研究了1Cr18Ni9Ti不锈钢双辊薄带凝固组织区(特别是等轴晶区)的形成机理.结果表明:1Cr18Ni9Ti不锈钢双辊薄带凝固组织中的等轴晶区不但在凝固类型为半固态时形成,在轧制或理想型时也能形成.其形成机理为,熔池中悬浮游离晶体的沉积、聚集以及在枝晶生长前沿的长大和薄带离开二铸辊最小间隙(铸辊出口)后,薄带/空气界面换热系数骤然降低抑制了柱状枝品的生长,并促使薄带中部未凝固熔体中游离晶体的择优长大.

On the basis of twin-roll thin strip continuous casting experiments and solidification structure characteristic analysis of thin strip and combining with the simulation results of effects of technological parameters, the forming mechanism of solidification structure zone (especially equiaxed crystal zone) on 1Cr18Ni9Ti stainless steel twin-roll thin strip was investigated. The results show that the equiaxed crystal zone in the solidification structure of 1Cr18Ni9Ti stainless steel twin-roll thin strip was formed possibly under the condition of semi-solid solidification type and the rolling solidification type or the ideal solidification type. The forming mechanism of the equiaxed crystal zone was associated with the sedimentation and accumulation of free crystals in the molten pool and the growth of the accumulation crystals onto the dendritic solidification fronts, and the suppression of the growth of columnar dendritic and the preferential growth of free crystals in unsolidied layer near the strip center by the abrupt decrease of heat transfer coefficient on the strip surface after leaving roll nip.