| 摘要 |
PROBLEM TO BE SOLVED: To provide a high carbon steel sheet having reduced anisotropy of workability in the rolling direction, also having excellent hardenability, and suitable for an automobile field. SOLUTION: The steel sheet has a composition comprising, by mass, >0.2 to 0.70% C, 0.01 to 0.8% Si, 0.1 to <2.0% Mn, 0.003 to 0.030% P, 0.0001 to 0.008% S, 0.005 to 0.07% Al, 0.0001 to 0.02% N, 0.0001 to 0.0030% O, and the balance inevitable impurities, and, in which the following A value is≤0.008, and, provided that the sheet thickness in the cross-section of the sheet thickness parallel to the rolling direction is defined as t, (i), in the cross-section of 4/10 to 6/10t, the area ratio of nonmetallic inclusions with a length of≥100μm is≤0.1%, and (ii), in the cross-sectional region, the area ratio of the carbides in which the carbide diameter exceeds the following B value is≤10% of the carbides in the region: A value=O+S+0.033Al; the O, S and Al denote the contents of respective elements; and the B value(μm)=1.5×C%+0.5. COPYRIGHT: (C)2011,JPO&INPIT
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