1995 Volume 35 Issue 6 Pages 771-777
In order to elucidate the formation of solidification structure in twin roll process, casting experiments 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 thicknesses of the strip and the dendritic zone increase, 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 columnar dendrite zone is formed when the solidifying shells are contacting with rolls. An unsolidified layer remained in the strip solidifies under slow cooling rate after leaving roll nip to form a equiaxed zone. 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 small 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.
