Optimization of CaO-SiO₂-Al₂O₃-MgO-CaF₂ refining slag in low-carbon and aluminum-containing 20Mn2 steel

Through analysis of samples taken in the refining process of low carbon and aluminum containing 20Mn2 steel,it was found that the melting point of the refining slag was high,substantial solid CaO and CaO-type inclusions existed in the steel and slag,leading to a decrease in absorption capacity of inclusions in the molten slag. Based on thermodynamic calculations utilizing Fact Sage software,the slag system was investigated and optimized by integrating the control of low-melting-point regions and reactions between slag and steel. The results show that 3% CaF₂ addition can decrease the melting temperature of the slag with CaO/Al₂O₃ mass ratio around 1. 5,and the melting point of the slag exhibits an initial decline and a subsequent rise with increasing CaF₂ content. The largest low-melting-point region is obtained through governing the MgO content in a vicinity of 5%. The oxygen content in the steel decreases with increasing CaO/Al₂O₃ mass ratio in the region of SiO₂ exceeding 30%,and decreases with increasing CaO content in the region of SiO₂ lower than 30%. The acid-soluble aluminum content increases with increasing Al₂O₃/SiO₂ mass ratio in the region of high SiO₂ content and increasing CaO/SiO₂ mass ratio in the region of low SiO₂ content. According to results from thermodynamic analysis,the optimized slag can be given as 50%-60% CaO,20%-35% Al₂O₃,5%-10% SiO₂,5%-8% MgO,and 0-5% CaF₂. Experi-mental results show that the melting point of the optimized slag declines,and there are apparent decreases in the number,area and mean diameter of inclusions in the steel.