| 摘要 |
PROBLEM TO BE SOLVED: To provide a vacuum decarburizing method, with which the decarburizing speed is increased, in a method of obtaining an extra-low carbon steel <=30 ppm carbon content by using an RH vacuum degassing apparatus. SOLUTION: When vacuum refining is carried out, gaseous hydrogen or the like is mixed in inert gas for circulation, while regulating the maximum value of the hydrogen concentration in the exhaust gas to 2-20 vol.%. Further, for reducing the internal defect in a product slab and the breakout times in a continuous casting apparatus caused by the hydrogen content in the molten steel, the hydrogen concentration in the exhaust gas at the end period of the refining under the vacuum, is regulated to <=1.0%.
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