| 摘要 |
PROBLEM TO BE SOLVED: To stably produce an extra-low sulfur steel having little inclusion and excellent cleanliness with an efficiently desulfurizing reaction. SOLUTION: In the producing method of the extra-low sulfur steel with the combination of a converter 3 and an RH vacuum degassing apparatus 5, when molten steel 6 obtd. with the converter refining is tapped into a ladle 4 from the converter, Al is added into the molten steel to deoxidize the molten steel so that soluble Al in the molten steel becomes >=0.03 wt.%, and also, the adding quantity of Mn alloy into the molten steel is regulated to <=2.0 kg/ton of molten steel in terms of pure Mn content and after tapping, slag reforming agent containing Al is added into the slag 7 in the ladle so that the pure Al content in the slag reforming agent 8 becomes >=0.1 kg/kg of slag. In the refining in the following RH vacuum degassing apparatus, firstly, oxygen is fed into a vacuum vessel to burn the Al and raise the temp. of the molten steel and successively, Mn alloy and desulfurizing agent are added into the molten steel after >=5 min from the completion of oxygen feeding, Then, during the interval from the completion of oxygen feeding to the completion of refining in the RH vacuum degassing apparatus, the stirring energy with the circulating flow is regulated to >=6 WH/ton of molten steel.
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