PRODUCTION OF LOW Al AND EXTRA-LOW SULFUR STEEL

摘要

PROBLEM TO BE SOLVED: To reduce S concn. in molten steel to a specified value in a short time without executing Al deoxidation and also without developing inclusions, by injecting powdery material of Ca and CaO blended at a specified ratio to C content in the molten steel onto the surface of the low Al molten steel having a specified Al concn. under reduced pressure. SOLUTION: The powdery material of Ca and CaO blended whose wt. ratio Ca/CaO is regulated to the formula related to C content in the molten steel -2C+0.45>=Ca/CaO>=-1.9C+0.2, is injected onto the surface of the molten steel having <0.01 wt.% Al concn. under reduced pressure having <= about 100 Torr. Ca is used in a form of metallic Ca or the alloy of Ca-Si alloy, Ca-Fe alloy, etc. and the mixture with CaO is preferably <= about 2 mm grain diameter. Further, the injection of the powdery material is preferably performed at about 0.1-1.5 kg/t min top-blow speed in the distance of about 20-200 cm from the molten steel surface. In this way, S concn. in the molten steel is lowered to <=10 ppm within about 5 min to obtain the low Al and extra-low sulfur steel.