VACUUM DEGASSING APPARATUS AND SECONDARY REFINING APPARATUS FOR MOLTEN STEEL

PROBLEM TO BE SOLVED: To provide a vacuum degassing apparatus and a secondary refining apparatus for molten steel using the same which can complete desulfurization in a short time while performing vacuum degassing treatment under reduced pressure as well as suppressing melting loss of refractories in a vacuum tank even if the desulfurization is carried out.SOLUTION: A vacuum degassing apparatus 21 used for secondary refining of molten steel has: a vacuum chamber 1 (a straight body vacuum chamber) having a single tubular dip tube 9 at the bottom; and a tuyere 2 for blowing gas over the entire circumference of an inner circumference of the tubular dip tube 9. A secondary refining apparatus for molten steel has the vacuum degassing apparatus 21, a ladle 5, and the tuyere 2 provided on the inner periphery of the tubular dip tube 9 as only means for supplying gas into the molten steel. The relationship between the number N of the tuyeres 2 and the diameter D(m) on the inner side of the tubular dip tube satisfies the following expression (1). 4D+2≤N≤12D...(1)SELECTED DRAWING: Figure 4 【課題】減圧下で真空脱ガス処理を行いつつ、短時間で脱硫を完了することができ、さらに脱硫を行っても真空槽内耐火物の溶損を抑制できる真空脱ガス処理装置及びそれを用いた溶鋼の二次精錬装置を提供する。【解決手段】溶鋼の二次精錬に用いる真空脱ガス処理装置２１であって、下部に単一の筒状浸漬管９を有する真空槽１（直胴型真空槽）を有し、筒状浸漬管９の内周に全周にわたってガスを吹き込む羽口２が設けられている真空脱ガス処理装置２１。真空脱ガス処理装置２１と、取鍋５とを有し、溶鋼中にガスを供給する手段として筒状浸漬管９の内周に設けた羽口２のみを有する溶鋼の二次精錬装置。羽口２の数Ｎと筒状浸漬管内側直径Ｄ（ｍ）との関係が下記（１）式を満足する。４Ｄ＋２≦Ｎ≦１２Ｄ ・・・（１）【選択図】図４