Research on the Metallurgical Properties of Fluorine-Containing Refining Slag and Its Fluoride-Free Design

In view of the large use of calcium fluoride in LF refining process， an optimization scheme of fluorine-free refining slag system is proposed.Calculated by FactSage software， the optimal composition of the fluorine-free refining slag was determined to be： the mass fraction of CaO：52%-58%， SiO2：8%-12%， Al2O3：25%-35%， MgO：5%-7%， with a basicity of 4-6 and a （CaO）/（Al2O3）ratio of 1.5-2.0. Compared to the original slag system， the new fluorine-free slag system can be completely melted at 1 500 ℃， reducing the melting temperature by 60 ℃， and has a Mannesmann index of approximately 0.15， which meets the performance requirements of LF refining slag. Using the optimized slag system in the actual production， the application of the optimized slag system resulted in a 24% reduction in total oxygen content， a 21.3% reduction in nitrogen content， a 22.9% reduction in the number of inclusions during refining process， and a 22.4% reduction in the number of inclusions during the tundish process compared to the pre-optimization slag system. The results demonstrate that the fluorine-free slag system not only significantly improves the cleanliness of molten steel and enhances the quality of steel but also aligns with current development trend of environmental protection and energy saving， reducing the corrosion of metallurgical equipment and environmental pollution， thus offering significant environmental protection and economic benefits. This study provides a viable solution for steel enterprises to achieve efficient refining processes and significantly improve the cleanliness and quality of steel without using calcium fluoride.