Formation of Solidification Structure in the Twin Roll Casting Process of 18Cr-8Ni Stainless Steel

In order to elucidate the formation of solidification structure in twin roll process, experiments of the strip casting of SUS304 austenitic stainless steel were done by using a laboratory scale twin roll caster. In the cast strips, there exist two kinds of solidification structures ; columnar dendrite and equiaxed crystal zones. With increasing contact time between roll and metal, the thickness of dendritic zone increases, while that of equiaxed zone is kept almost constant. With increasing initial roll gap, only the equiaxed zone is enlarged. Furthermore, effects of the superheat of molten steel and the roll supporting force on the formation of solidification structure have been made clear.The dendritic zone is formed when the solidifying shells are contacting with rolls. On the basis of the experimental results and theoretical analysis of heat transfer in the strip, it has been deduced that, under the conditions of relatively high superheat of molten metal and low roll supporting force, the equiaxed zone results from the preferential growth of free crystals ahead of the dendritic solidification front, with the abrupt decrease in the heat transfer coefficient on strip surface after the strip goes away from rolls.