Numerical Evaluation for Influence of Ca Treatment and Slag Composition on Compositional Changes in Non-metallic Inclusion Using Coupled Reaction Model for Ladle Treatment

Nonmetallic inclusions significantly affect the final quality of steel production. Mg-Al spinel inclusions, which are known for their high deformability, are particularly detrimental. Thus, controlling these favorable liquidus inclusions, such as Ca-Al inclusions, is crucial. The evolution of Ca-Al inclusions is primarily driven by the [Ca] source in molten steel, which is supplied by slag or the addition of Ca to the molten steel. Inclusions exhibit three physical behaviors: flotation into the slag, entrapment from the slag, and agglomeration within each inclusion. A numerical model grounded in a coupled reaction model was established to investigate these inclusion behaviors, with a focus on the evolution of the Ca-Al system inclusions. These findings indicate that the [Ca] concentration in molten steel drives the evolution of Ca-Al inclusions, but the rate of evolution is limited by the mass transfer rate of the Ca source into the inclusion. Moreover, slag composition, particularly the higher basicity and slags enriched with Ca sources, such as CaF2, significantly influence the inclusion composition, reaching a composition closer to the liquid phase. Additionally, it was found that the physical behavior of inclusions, particularly entrapment from slag, plays a crucial role in controlling the inclusion composition. This study further discusses methods for controlling the liquidus composition of inclusions.