| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength cold-rolled steel strip having low yield stress in the initial state before press forming, having high yield stress after the baking of coating subsequently to press forming, and having surface properties in which scale flaws are suppressed. SOLUTION: The cold-rolled steel strip has a chemical composition comprising 0.010 to 0.040% C,≤0.5% Si, 1.0 to 2.5% Mn,≤0.05% P,≤0.01% S, 0.001 to 0.15% sol.Al,≤0.008% N and 0.25 to 1.0% Cr, and the balance Fe with impurities, and satisfying Mn+Cr≥1.9, has a steel structure composed of ferrite as the main phase and a low temperature transformation formation phase as the second phase, and martensite in which the area ratio of the low temperature transformation formation phase is≥0.5%, has mechanical properties satisfying a yield ratio of≤0.65, and further has a scale flaw production rate of≤0.5%. COPYRIGHT: (C)2010,JPO&INPIT
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