Slag rim structure and phase formation mechanism in molds during the continuous casting of high-Mn high-Al steel

The slag-steel reaction between low basicity mold flux and high-Mn and high-Al steel results in changes to the composition and properties of the mold flux, forming a slag rim at the meniscus of the mold during continuous casting. In this study, the slag rim was divided into five layers comprising the glass, columnar crystals, fine crystals, coarse crystals, and sinter layers from mold to molten steel based on their morphological features. Compared to the original slag, the Al2O3 content in the slag rim significantly increased and the SiO2 content decreased, thereby increasing the Al2O3/SiO2 mass ratio from 0.05 to 5.52. Phases with high melting points, such as Na2O.CaO.2Al2O3 and LiAlO2, were identified in the slag rim. According to crystallization process calculations using FactSage, these phases were the primary causes of slag rim formation. Thus, new slags with a low O/F mass ratio were subsequently designed to mitigate the generation and growth of Na2O.CaO.2Al2O3. These new compositions reduced the melting point and viscosity, thereby ensuring sufficient fluidity in slags with a high Al2O3/SiO2 mass ratio.