Effect of CaO–Al₂O₃–SiO₂–MgO(–CaF₂) refining slag system on inclusions in silicon–manganese deoxidized spring steel.

This article investigates the influence of CaO–Al₂O₃–SiO₂–MgO refining slag composition on aluminum-containing (Al₂O₃) inclusions in silicon–manganese-deoxidised spring steel, aiming to optimize slag parameters for different grades of spring steel. Laboratory high-temperature equilibrium experiments combined with thermodynamic calculations showed that low basicity slag with low Al₂O₃ content effectively reduces the size and Al₂O₃ content of inclusions, making it suitable for high-end spring steel production. Medium basicity slags with moderate Al₂O₃ and CaF₂ additives improve slag fluidity and inclusion adsorption capacity, benefiting middle- and low-end spring steel, while high basicity slags tend to produce larger, high-Al₂O₃ inclusions despite controlling inclusion number density. The study concludes that refining slag adsorption capacity, related to viscosity and melting temperature, is key to controlling Al-containing inclusions, recommending slag basicity around 2–2.5 with about 10% Al₂O₃, MgO, and CaF₂ for balanced inclusion control and steel quality.