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 FactSage 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. Experimental 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. © All right reserved.