| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet which is improved in all of the elongation (EL), stretch-flanging property (λ), and bending properties (R) with a good balance, is excellent in the overall workability, and has tensile strength of 980 MPa or more, and to provide a technique for manufacturing the high-strength cold-rolled steel sheet. SOLUTION: A metal structure of the steel sheet is made a mixed structure including bainite, residual austenite, and tempered martensite. When the metal structure is observed with a scanning electron microscope, the bainite has a composite structure of bainite formed in a high temperature region in which the average distance between neighboring residual austenite and/or carbide is 1μm or more and bainite formed in a low temperature region in which the average distance between the residual austenite and/or carbide is less than 1μm. When the area rate of the bainite formed in a high temperature region based on the whole metal structure is made a and the sum of the area ratio of the bainite formed in a low temperature region and the tempered martensite based on the whole metal structure is made b, a is 20 to 80%; b is 20 to 80%; and a+b is 70% or more. COPYRIGHT: (C)2011,JPO&INPIT
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