| 摘要 |
PROBLEM TO BE SOLVED: To obtain a cast piece which does not depend on the contents of Mn, Si and Al and small in defects caused by inclusions by controlling the number of oxide inclusions with specified size and the number of alumina cluster inclusions in a of carbon steel contg. specified rations of C, Mn, Si, P, S, Al, Ti, Ca, N, oxygen, and the balance iron with inevitable impurities to not more than the specified value. SOLUTION: This carbon steel has a compsn. contg., by weight, 0.001 to 0.2% C, 0.01 to 0.5% Mn, 0.001 to 0.5% Si, 0.001 to 0.3% P, 0.0005 to 0.05% S, 0.006 to 0.1% Al, 0.005 to 0.06% Ti, 0.0005 to 0.01% Ca, 0.0005 to 0.01% N, 0.0005 to 0.0050% oxygen, and the balance iron with inevitable impurities. In the slab, the number of oxide inclusions of >=53μm is >=200 pieces/kg, and the number of alumina cluster inclusions is <=20 pieces/kg. C deoxidation is executed in an evacuated atmosphere, furthermore, Ti and Ca are successively added thereto, oxygen in the molten steel is removed, and, thereafter, Al is added to suppress the growth of the crystal grains of the steel.
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