| 摘要 |
<P>PROBLEM TO BE SOLVED: To produce a high-tensile cold-rolled steel plate excellent in ductility, work hardenability and stretch-flange formability. <P>SOLUTION: The method comprises: preparing a slab having a chemical composition including: by mass, >0.020% and <0.30% C, >0.10% and ≤3.00% Si, >1.00% and ≤3.50% Mn, ≤0.10% P, ≤0.010% S, ≤2.00% sol. Al, and ≤0.010% N; hot rolling the slab in such a manner that the rolling reduction at the final one pass exceeds 15% and rolling is finished within the temperature zone ≥A<SB POS="POST">r3</SB>point; cooling to the temperature zone ≤780°C within 0.4 second after completion of rolling; winding at the temperature zone exceeding 400°C; cold rolling the obtained hot-rolled steel sheet; then performing soaking treatment at a temperature zone of (Ac<SB POS="POST">3</SB>point-40°C) or above; cooling by ≥50°C at a cooling rate of <10.0°C/s then cooling down to a temperature zone of ≤500°C to ≥300°C; and annealing for ≥30 s at the temperature zone to produce the cold-rolled steel plate with a metal structure in which the main phase is low-temperature transformation-generating phase, and the second phase includes a residual austenite and polygonal ferrite. <P>COPYRIGHT: (C)2013,JPO&INPIT |
