| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tension cold-rolled steel sheet having≥900 MPa tensile strength and excellent in elongation, stretch-flangeability and balance between the strength, extension and stretch-flangeability, and to provide a method of producing the high tension cold-rolled steel sheet. SOLUTION: The high tension cold-rolled steel sheet is produced by subjecting steel having composition containing 0.08-0.20% C, 0.01-1.5% Si, 0.1-2.5% Mn,≤0.08% P,≤0.005% S, 0.01-0.08% Al, 0.01-0.05% Ti, 0.001-0.005% N and the balance Fe with inevitable impurities to an annealing treatment of a prescribed condition, after hot-rolling and cold-rolling in order, and the high tension cold-rolled steel sheet thus produced is characterized in that the steel sheet has a dual-phase composed of 5-15% ferritic phase and the balance tempered martensitic phase by an area ratio, while the ferritic phase has a grain diameter of≤10μm, and≥60% ferrite grains of the whole ferrite grains is non contact with the other ferrite grains. COPYRIGHT: (C)2011,JPO&INPIT
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