Study of the Heat Transfer Behavior and Naturally Deposited Films in Strip Casting by Using Droplet Solidification Technique

Oxide films that naturally deposit on the surface of the twin-roll mold during strip casting greatly influence the heat transfer from molten steel pool to the mold wall, which further affect the quality of casting product. In this study, a droplet solidification technique has been developed to simulate the initial process of solidification and film deposition during strip casting process. The results suggest that the maximum heat flux increases firstly (to 5201.5 kW/m² for industrial pure Fe and to 4242.1 kW/m² for stainless steel) and then decreases (to 4700.3 kW/m² for industrial pure Fe and to 2037.8 kW/m² for stainless steel) with the repeat of dropping tests. Furthermore, the roughness and thickness of the films formed on the surface increase with the successive addition of the solidifying material on the prior film. The compositions of the films are detected mainly as oxides containing O, Fe, Si, Mn, S, and Cu for the industrial pure Fe sample and they are O, Si, S, Mn, Cr, and Cu for the stainless steel sample. The deposited film with a thickness (54 μm for industrial pure Fe and 82 μm for stainless steel) and a roughness (24.5 nm for industrial pure Fe and 36.6 nm for stainless steel) allows a better wetting behavior between the molten steel and mold surface, resulting in an increase of actual contact area, and an enhancement of nucleation rate, which then in turn promote the interfacial heat transfer during the initial solidification of molten steel.