| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength steel strip of excellent formability and a method for manufacturing the same. SOLUTION: This steel has contains C, Si and Mn of predetermined amount, the mean grain size of ferrite is≤15μm, the mean r-value is≥1.5, the hole expanding ratio is≥50%, and the tensile strength (MPa) x ductility (%) is≥20,000. Hot rolling is completed at Ar<SB>3</SB>transformation point or higher temperature, a steel strip coiled at≤550°C is cold-rolled at the draft of≥35% and < 75%, heated at the mean heating speed of 4-100°C/hr, and annealed with the maximum attainable temperature of 600-800°C. The steel strip is again cold-rolled at the draft of≥35% and < 75% after cooling, continuously annealed with the maximum attainable temperature of 730-850°C, cooled at the speed of≥3°C/sec, and subjected to overaging for≥3 minutes and < 10 minutes in the temperature range of 450-300°C. COPYRIGHT: (C)2004,JPO
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