PURPOSE: To make a fine inclusion composition in a rolled product soft MgO-Al2 O3 series by executing continuous casting and rolling to molten metal which is prepared to contain the specific C, Mn, O, Al contents with a converter, vacuum degassing treatment and the specific ladle refining treatment.
CONSTITUTION: After adjusting the content of C of steel about 0.03% C with the converter, the components in the molten steel is made to ≤0.01% C, ≤0.05% Mn, ≥150ppm O and ≤20ppm Al through the vacuum degassing treatment. After that, by the ladle refining treatment, CaO and CaF2 are injected at 2-7kg/ ton in total based on the weight of molten steel. By this method, the components in the molten steel is made to ≤0.01% C, ≤0.05% Mn, 120-200ppm O and ≤20ppm Al. After that, the molten steel is subjected to a continuous casting process to produce a slab and then a final rolled product is obtd. The shape of the inclusion is controlled and the composition of fine inclusion in the above rolled product is made to MnO-Al2O3 series and the product is softened in quality, workability of the steel product is improved and the development of surface defect is prevented.
YAMAGUCHI FUKUYOSHI
HONMA HIROYUKI
SUGIMARU SATOSHI
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