METHOD FOR MANUFACTURING COREX MOLTEN IRON INTO MOLTEN STEEL CONTAINING LOW PHOSPHORUS BY CONTROLLING RATIO OF L/L0, BOTTOM BLOWING FLOW RATE AND INJECTION CONDITIONS OF SUBSIDIARY RAW MATERIAL, FERROALLOY AND CaO

摘要

PURPOSE: To provide a method for manufacturing molten steel containing low phosphorus using COREX molten iron, the method for reducing generation of slag, suppressing slopping and preventing damage of the furnace body by properly controlling ratio of L/L0, bottom blowing flow rate and subsidiary raw material injection conditions per blowing sections and properly controlling injection conditions of ferroalloy and CaO in the tapping step. CONSTITUTION: The method is characterized in that during a period of time from the start of blowing to 10% of blowing, a ratio of L/L0(cavity depth/steel bath depth) is controlled to 0.48 to 0.50, a bottom blowing flow rate is controlled to 0.05 to 0.07 Nm¬3, and solidified slag with high basicity is dividingly injected twice into a converter in an injection quantity of 1.0 to 1.5 kg/ton of molten steel; during a period of time from 10% blowing to 20% blowing, the ratio of L/L0 is controlled to 0.47 to 0.49, and the bottom blowing flow rate is controlled to 0.03 to 0.05 Nm¬3; during a period of time from 21% blowing to 35% blowing, the ratio of L/L0 is controlled to 0.40 to 0.42, and the bottom blowing flow rate is controlled to 0.04 to 0.06 Nm¬3; during a period of time from 35% blowing to 80% blowing, the ratio of L/L0 is controlled to 0.39 to 0.47, the bottom blowing flow rate is controlled to 0.05 to 0.09 Nm¬3, and the solidified slag with high basicity is dividingly injected twice into the converter in an injection quantity of 1.0 to 1.5 kg/ton of molten steel; during a period of time from 80% blowing to blowing completion, the ratio of L/L0 is controlled to 0.31 to 0.47, the bottom blowing flow rate is controlled to 0.04 to 0.09 Nm¬3, and luppe is injected into the converter; at a blowing completion time point, a steel bath is strongly agitated by maintaining the bottom blowing flow rate to 0.08 to 0.11 Nm¬3 for 30 seconds to 2 minutes and 30 seconds; a recarburizer is injected into the converter before discharging molten steel; during a period of time from 20% discharging to 30% discharging, Mn based ferroalloy and 45 to 55% of CaO out of the total CaO injection quantity injected in the discharging step are injected into the converter; during a period of time from 50% discharging to 80% discharging, recarburizer, Al, Si based ferroalloy and 25 to 35% of CaO out of the total CaO injection quantity injected in the discharging step are injected into the converter; and after completion of discharging, 15 to 25% of CaO out of the total CaO injection quantity injected in the discharging step is injected into the converter.