METHOD FOR MANUFACTURING ULTRA LOW PHOSPHOROUS AND SULFUR STEEL

摘要

PURPOSE: A method for manufacturing ultra low phosphorous and sulfur steel is provided which easily controls sulfur of steel by improving desulfurization patterns during refining of molten steel outside a furnace. CONSTITUTION: The method for manufacturing ultra low phosphorous and sulfur steel comprising 80 ppm or less of P and 30 ppm or less of S comprises the steps of tapping the refined molten steel into a ladle(2) after refining molten steel(5) in a converter; refining the molten steel received in the ladle(2) outside the furnace; and degassing the molten steel refined outside the furnace, wherein the step of refining the molten steel(5) outside the furnace further comprises the steps of determining a temperature increasing amount of the molten steel(5) from the measured temperature and a target temperature by measuring a temperature of the molten steel in which constituents are adjusted after adjusting target constituents of molten steel(5) received in the ladle(2); increasing a temperature of the molten steel as much as the determined temperature increasing amount as lower blowing an agitation gas in the range of 3 to 10 Nm¬3/hr; simultaneously strongly lower blowing the agitation gas to 10 to 30 Nm¬3/hr after the temperature increase of the molten steel and upper blowing the agitation gas in the range of 70 to 80 Nm¬3/hr by descending a lance(4) to 2/3 of a ladle height; and performing second desulfurization by injecting 0.8 to 1.1 kg of Ca-Si per ton of molten steel into the molten steel in the blowing condition of the agitation gas.