Naturally Deposited Oxide Films in Near-Net-Shape Casting: Importance, Mechanisms of Formation, and Prediction of Their Composition

In near-net-shape casting technologies for steel, solidification occurs under conditions of direct contact between the processed metal and the mold. Because of the elimination of the use of mold powder in strip casting, oxide films can deposit from the solidifying steel onto the mold surface and affect the casting process. The interface between the mold and the shell of the casting represents the main thermal resistance to heat extraction during the initial phase of solidification when the cast surface is created. Deposited oxide or sulfide films play a very important role in the determination of casting productivity and stability of operations. Moreover, as the cause of many as-cast defects is related to heat transfer, these films can affect cast surface quality. In this article the possible formation mechanisms of oxide deposits are considered, with particular attention to the role of vaporization and liquation. Based on these two mechanisms, a model was developed to predict the composition of oxide films that deposit on water-cooled copper molds during casting. The agreement between measured and predicted film composition is reasonably good, suggesting that these two mechanisms might be the main mechanisms for the deposition of oxide films on the mold surface of near-net-shape casting technologies. Experimental results provide evidence that vaporization and reaction with the shrouding atmosphere is also a possible and relevant mechanism of film deposition.