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 mu m, 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<middle dot>7Al2O3<middle dot>CaF2 phase and left some un-melted AlN, substantially degrading the slag properties. Excessive Al2O3 addition exacerbated the advance precipitation of the 11CaO<middle dot>7Al2O3<middle dot>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.