PURPOSE: To melt an extremely high cleanliness steel to an extremely low carbon range without lowering decarburizing speed.
CONSTITUTION: A straight barrel type immersion tube 2 is dipped into a part of the surface of molten steel 4 in a ladle 1, and while making vacuum only in the immersion tube 2, refining is executed. At this time, stirring gas is supplied at 0.6-15 NL/(min.ton) from a gas blowing hole 3 arranged at a position deeper than 0.5H of the molten steel depth H in the immersion tube 2 and the ratio d/D of the inner diameter (d) of the immersion tube 2 to the inner diameter D of the ladle 1 is made to be 0.3-0.8, and the distance S between the lower end of the immersion tube 2 and the molten steel surface at out of the immersion tube 2 is made to be 0.03 H-0.3H and the distance L in the horizontal direction between the gas blowing hole 3 and the center of the immersion tube 2 is made to be 0.1d-0.5d and the distance L between the center of the immersion tube 2 and the center of the ladle 1 is made to be 0.02D-0.12D. Further, on the way of tapping the molten steel into the ladle 1 from a refining furnace or after tapping the molten steel, deoxidizing agent is added and after lowering (T.Fe) concn. in the slag 6 to ≤7%, it is desirable to dip the immersion tube 2 into a part of the nolten steel surface.
AOKI HIROYUKI
YONEZAWA KIMITOSHI
MIYAMOTO KENICHIRO
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