Optimum Composition of CaO-SiO₂-Al₂O₃-MgO Slag for Spring Steel Deoxidized by Si and Mn in Production

The relations between plasticity of inclusions and contents of oxygen, aluminum, and sulfur in molten steel were overall discussed by thermodynamics and FactSage software. Then, the optimum compositions of slag were obtained and the activities of components of refining slag system were analyzed. Finally, experiments were carried out based on the results of calculation. According to the relations, it could achieve better effect to improve basicity R (R = CaO/SiO₂ by mass pct) and C/A (C/A = CaO/Al₂O₃ by mass pct) in the low melting temperature [≤1673 K (≤1400 °C)] region of refining slag as far as possible. For the CaO-SiO₂-Al₂O₃-MgO slag, the optimum compositions are MgO: 5–9 pct, CaO: 47.4–50.2 pct, SiO₂: 41.9–45.6 pct and Al₂O₃: ≤2.79 pct, respectively, in which the basicity is at the range of 1.0 to 1.19 and C/A is above 9.0. It is proved by experiments that the plasticity of inclusions and the contents of [O], [Al], and [S] can be controlled effectively by the optimum composition of refining slag, and the high cleanness is achieved in spring wire rods.