Abstract: According to the actual situation of a steel mill, the process defect of Al killed steel smelting by RH refining furnace was introduced. Though the slag modification treatment of the molten steel after the converter，the oxidation property of steel slag was reduced, the fluidity of steel slag was improved and the adsorption capacity of the steel slag to inclusion was increased. The slag modification, decreasing adding aluminum amount and reinforced protective casting were adopted to reduce the content of inclusion in the molten steel sufficiently, improving the quality of the casting billet and obtaining good protective casting. After optimization, the continuous casting heats increased from 8 heats to 18 heats in a casting times, the purity of that molten steel was greatly improved and the grade of Al2O3 inclusion formation was reduced, so that the annual defect rate of rolling was reduced from 1.27 % to 0.49 % in 2017.

Key words: Al killed steel , RH refining；modification of top slag；Al addition amount；protection casting, castability of liquid steel