VACUUM REFINING OF HIGH CLEAN EXTRA-LOW NITROGEN STEEL

摘要

PROBLEM TO BE SOLVED: To produce a high clean extra-low nitrogen steel in high efficiency and high yield by simultaneously top-blowing at least one kind of Ca alloy and metallic Ca and CaO.Al2 O3 base flux onto the molten steel surface under vacuum condition. SOLUTION: A pre-mixed material of the Ca alloy and the CaO.Al2 O3 base flux is injected onto the molten steel surface from a top-blown lance arranged in the vacuum degassing vessel by using an inert gas as the carrier. The point of time of injection is desirably after adding a deoxidizer and the alloy. As the Ca alloy, Ca-Si alloy is exemplified. The flux is desirably to be pre-melted one, and when the flux invades into the molten steel, the reaction can quickly be started. CaO concn. in the flux is desirably 50-95 wt.%. Further, the mixed ratio of the Ca alloy or the metallic Ca to the flux is preferably by weight from 3:97 to 25:75.