Deep-desulphurizing slag system containing BaO and Li2O and method for producing ultralow-sulfur steel by adopting same

The invention relates to a steel-making technique in the metallurgy industry, in particular to a refining slag system containing BaO and Li2O and a method for producing ultralow-sulfur steel by adopting the same, and the refining slag system can be directly applied in LF furnace top slag to carry out desulphurization. By weight percent, the components of the slag system are as follows: 45 percent to 55 percent of CaO; 3 percent to 10 percent of SiO2; 18 percent to 30 percent of Al2O3; 5 percent to 12 percent of BaO; 0.2 percent to 2.0 percent of Li2O; and 3 percent to 8 percent of MgO. 2kg/t to 15 kg/t of deep-desulphurizing agent containing BaO and Li2O is added in a ladle or during tapping, 10kg/t to 15 kg/t of lime is also added, aluminum particles are adopted for deoxidization, and thereby the target slag system can be obtained. When an LP furnace adopts the slag system, the molten iron does not need to be preprocessed, a VD technique is adopted in the next step, and under the circumstance that the initial sulphur of LF molten steel is up to 200ppm, the sulphur content in the steel can be stably controlled below 8ppm. Because calcium is adopted to treat the molten steel, the calcium content of continuously cast slab can be larger than or equal to 20ppm, thus satisfying the production of ultralow-sulfur steel varieties such as high-grade acid-resistant pipeline steel with Ca/S larger than or equal to 2.0.