Effect of AlN and Al₂O₃ on Properties of CaO–Al₂O₃–BaO–CaF₂–Li₂O System Mold Fluxes

As low-density high-strength steel is widely used in industrial production, the formation of internal inclusions and their impact on CaO–Al₂O₃–BaO–CaF₂–Li₂O slag properties have become research hotspots. Utilizing ASPEX analysis and thermodynamic calculations, it was found that 95 pct of the inclusions consisted of AlN, with AlN–MnS and AlN–Al₂O₃ complex inclusions predominantly characterized by AlN. These inclusions ranged in size from 1–3, 1–5, and 1 to 3 µm, respectively, in which AlN predominantly precipitated in the molten steel. The addition of AlN and Al₂O₃ significantly increased the slags’ viscosity, break temperature, and melting temperature. Notably, the reduction in Li₂O content and the increase in Al₂O₃ content due to AlN introduction promoted the precipitation of the high-melting-point 11CaO·7Al₂O₃·CaF₂ phase and left some un-melted AlN, substantially degrading the slag properties. Excessive Al₂O₃ addition exacerbated the advance precipitation of the 11CaO·7Al₂O₃·CaF₂ and increased its precipitation amount, which also deteriorated the slag properties. However, for slags with high (CaO + BaO) content, the impact of AlN and Al₂O₃ was minimal. This study provides critical insights for optimizing high-Al steel production and ensuring high-quality continuous casting, with significant implications for the steel industry.