| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet manufacturable by a steel mass-production manufacturing process, having an extralow carbon concentration and an extralow Al concentration, an having high drawability, and to provide a method for refining a molten steel for the steel sheet. SOLUTION: The extralow carbon steel sheet has a chemical composition comprising, by mass, 0.0005 to 0.025% C, 0.003 to 0.15% Si, 0.3 to 2.5% Mn,≤0.15% P,≤0.02% S,≤0.006% N, 0.0002 to 0.005% sol.Al, 0.005 to 0.05% Ti, 0.020 to 0.20% Nb, and the balance Fe with impurities, and in which an Nb/Ti ratio is≥2.0, and inclusions satisfy inequalities (1) to (3): N<SB>Ti</SB>≥30 pieces/mm<SP>2</SP>(1), N<SB>Ti</SB>/(N<SB>Ti</SB>+N<SB>Al</SB>)≥0.80 (2), N<SB>Ti</SB>/N<SB>Total</SB>≥0.65 (3), wherein N<SB>Ti</SB>, N<SB>Al</SB>and N<SB>Total</SB>all denote inclusions with a major axis of≥1μm in the longitudinal face parallel to the rolling direction, and are the one comprising≥50% Ti oxide, the one comprising≥50% Al oxide and the average numerical density of all oxide inclusions, respectively. COPYRIGHT: (C)2009,JPO&INPIT
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