METHOD FOR REFINING EXTRA LOW SULFUR STAINLESS STEEL BY CONTROLLING SLAG COMPOSITION AND MOLTEN STEEL CONDITIONS TO INCREASE DESULFURIZATION EFFICIENCY

摘要

PURPOSE: To provide a method for refining extra low sulfur stainless steel, the method capable of increasing desulfurization efficiency by properly controlling slag composition and molten steel conditions to overcome the limitations of inefficient desulfurization capability in conventional desulfurization technology and impurity removal capability according to sulfur pickup in the postprocess. CONSTITUTION: In an AOD(argon oxygen decarburization) refining method of stainless steel for lowering concentration of sulfur, the method for refining extra low sulfur stainless steel comprises a step of supplying 1.16 to 1.33 Nm¬3 of oxygen per 1 kg of carbon in molten steel and 0.8 to 0.84 Nm¬3 of oxygen per 1 kg of silicon into the molten steel so that carbon and silicon are removed, and controlling temperature of the molten steel in a range of 1680 to 1720 deg.C; a step of controlling content of silicon to a range of 0.3 to 0.6 wt.% by adding silicon to the molten steel to remove oxygen in slag and molten steel; a step of adding 30 to 50 kg of Al/ton-slag to the molten steel; a step of adding quicklime to the molten steel to control a ratio of CaO/SiO2 in a slag composition to a range of 2.0 to 3.0; and a step of desulfurizing the molten steel for 8 to 12 minutes while blowing an Ar gas into the molten steel in a blowing rate of 0.2 to 0.6 Nm¬3/min of Ar gas per ton of molten steel after adding fluorite to the molten steel in an amount corresponding to 20 to 30 wt.% of an addition amount of quicklime.