EFFECT OF CASTING ATMOSPHERE ON THE FORMATION OF STRIP SURFACE IN TWIN-ROLL CASTING PROCESS

In order to elucidate effects of casting atmosphere on formation of strip surface in twin roil casting process, an experiment of the direct casting of SUS304 austenitic stainless steel under Ar, air and He gas atmospheres was performed using a laboratory scale twin roll easter. Furthermore, heat transfer from molten metal to casting roll was theoretically analyzed by taking account of gas film between the roll and metal. In the experiment, surface wrinkles of strip were observed under a critical casting velocity. This critical casting velocity decreased in order of Ar, air and He gases. This would come from that. fluctuation of the overall heat transfer coefficient in the case of He gas is smaller than Ar and air gases. In the case of air atmosphere, it has been very difficult to obtain better surface quality of strip because of formation of fine surface cracks. The control of casting atmosphere has been found to be very important for better surface quality of strip. It has been also considered that the thickness of the gas film between roll and metal under a steady state is related to the thickness of gas boundary layer on the roll surface, which is estimated by a boundary layer theory.