A manufacturing method of a high-cleanness steel

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PROBLEM TO BE SOLVED : To manufacture a superclean steel by effectively floating up and separating while absorbing microperspective inclusion without generating alumina-series inclusion, etc. SOLUTION : A combined additional material constituted of rare earth metal elements(REM) and oxide of mullite(3Al2O3-2SiO2), etc., is added in molten steel. The rare earth metal elements and the mullite, are desirable to add in the range of 0.1-1.0 mass% of the molten steel, respectively. Further, it is desirable that preceding to addition of the additive materials, a treatment with a primary additional material is performed. In this result, while restraining the generation of the alumina-based inclusion, etc., the removal of the microperspective inclusion in the molten steel can effectively be performed and the superclean steel can be obtained. Further, due to the primary treatment, the additional quantity of the REM is reduced, and thus, the cleanliness of the molten steel can effectively be improved in the profitable cost. COPYRIGHT : (C)2009, JPO&INPIT