| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet which is not influenced by the variation of chemical composition and has a small variation in mechanical properties (strength and ductility in particular), and a method for manufacturing the same.SOLUTION: A high-strength cold-rolled steel sheet has a component composition including, by mass%, 0.10-0.25% C, 0.5-2.0% Si, 1.0-3.0% Mn, 0.1% or less P, 0.01% or less S, 0.01-0.05% Al, 0.01% or less N, and the balance comprising Fe with inevitable impurities, and has a structure comprising ferrite as a soft first phase at an amount of 20-50%, by an area ratio, and the reminder being tempered martensite and/or tempered bainite as a hard second phase. The total area of ferrite particles having an average particle diameter of 10-25 μm occupies 80% or more of a sum of areas of all the ferrite particles, the dispersion number of cementite particles existing in all the ferrite particles and having a circle-equivalent diameter of 0.3 μm or more is more than 0.15 piece and 1.0 piece or less per 1 μmof the ferrite, and the tensile strength is 980 MPa or more. |
