| 摘要 |
PROBLEM TO BE SOLVED: To produce an extra-low carbon steel having a specified value or lower of T. [O] concn. in the molten steel in a mold by regulating a specified ratio or lower of (FeO+MnO) concn. in slag in a ladle and a specified value or higher of basicity ((CaO)/(SiO2)) in the slag in a tundish and a specified ratio or lower of nitrogen concn. in the atmosphere in a tundish. SOLUTION: The molten steel in the ladle is introduced into the tundish from the bottom part of the ladle and supplied into the mold from a nozzle arranged at the bottom part of the tundish to execute a continuous casting. It is regulated to be <=5 wt.% of (FeO+MnO) concn. >=0.5 of the basicity ((CaO)/(SiO2)) and <=20 vol.% of the nitrogen concn. in the atmosphere, and in this way, the ultra-high clean and extra-low carbon steel having <=10 ppm [O] concn. in the molten steel in the mold is obtd. In the case of evaluating inclusion caused by the leakage of air into the tundish, as the evaluating index concn., the oxygen concn. in the atmosphere is not used but the nitrogen concn. is used.
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