Fundamentals of Slag-Steel-Inclusion Multiphase Reactions for Producing Clean Steels During Secondary Refining and Continuous Casting Process

Abstract

The probability of alumina inclusion is strongly affected by slag chemistry and deoxidation practices. Moreover, the viscosity of the slag should also be carefully controlled to suppress this harmful inclusion at the secondary refining stage. The effect of physicochemical properties of FetO-bearing calcium aluminate based system RH slag on the removal rate of alumina inclusions in Al-killed steel has been investigated by considering the interfacial reaction between steel melts and the slag layer. The alumina removal rate is strongly proportional to the physicochemical factor of the slag. The addition of FetO to the RH slag with CaO/Al2O3≤1.3 effectively breaks the aluminate network structure, while the structure is less affected by the FetO in the slags with CaO/Al2O3≥1.6. Consequently, even though the FetO in the RH slag enhances the atomic oxygen pick-up (i.e., reoxidation) from slag to steel melt, it contributes to the inclusion absorption and dissolution by lowering viscosity of the slag in conjunction with the depolymerization of aluminate frame structure. Therefore, the relatively basic slag (i.e., CaO/Al2O3= 1.2-1.4) with appropriate amounts of FetO (T.Fe=7-9%) would be recommended as an operational window to improve the cleanliness of molten steel in RH degasser. © 2025 by the Association for Iron & Steel Technology.