| 摘要 |
PROBLEM TO BE SOLVED: To quickly and stably produce an extra-low carbon steel excellent in the cleanliness by using an RH vacuum-degassing apparatus. SOLUTION: In a method for producing the extra-low carbon steel with a vacuum-degassing refining in the RH vacuum-degassing apparatus 1, inert gas is blown into molten steel 3 at >=30 Nl/min.ton of molten steel circulating quantity while controlling >=70 kg/Hr.ton at 300 torr pressure in the vacuum vessel 5, >=40 kg/Hr.ton at 200 torr, >=25 kg/Hr.ton at 100 torr, >=12 kg/Hr.ton at 50 torr and >=10 kg/Hr.ton at 10 torr, and also, the vacuum decarburizing refining is executed by controlling the dissolved oxygen concn. in the molten steel to 300-500 ppm.
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