| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet which has high press-formability suitable for an automotive outer panel such as a hood, a door, a fender and a side panel, does not form a streaky defect thereon after having been plated, shows no poor appearance in the cold-rolled state, and has a tensile strength of a 340 MPa grade or higher, though there have not been such a high-strength cold-rolled steel sheet and a galvanized steel sheet as to satisfy all properties of strength, formability, brittleness resistance in secondary forming and surface properties (surface roughening resistance and uniform platability), in a high grade, and to provide a manufacturing method therefor. SOLUTION: This steel sheet has a chemical composition comprising, by mass%, 0.0005% or more but less than 0.004% C, 0.5% or less Si, 0.1-2.5% Mn, 0.06% or less P, 0.05% or less S, 0.1% or less sol. Al, 0.006% or less N, (N/14×48×0.5)% to (0.02+N/14×48)% Ti, and 0.04-0.20% Nb, while controlling the contents of Ti and Nb so as to satisfy the relational expression of 2≤Nb/Ti≤20, and the balance Fe with unavoidable impurities; and has an (r) value of which the minimum value is 1.0 or more, and an (r) value of 1.5 or more in a direction of 45 degrees by angle with respect to a rolling direction. COPYRIGHT: (C)2007,JPO&INPIT
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