| 摘要 |
PROBLEM TO BE SOLVED: To produce a high-tensile cold-rolled steel sheet excellent in ductility, work hardenability and stretch-flange formability. 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 such that the rolling is completed at a temperature zone of A<SB POS="POST">r3</SB>point or above; cooling to the temperature zone≤780°C within 0.4 second after completion of rolling; winding at the temperature zone below 400°C; performing annealing the hot-rolled steel plate obtained after winding by heating at the temperature zone≥300°C; cold rolling; performing soaking treatment at a temperature zone (Ac<SB POS="POST">3</SB>point-40°C) or above; then cooling down to a temperature zone of≥500°C to≥300°C; (preferably on this occasion, cooling by≥50°C at a cooling rate of <10.0°C/s); and annealing by holding 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. COPYRIGHT: (C)2013,JPO&INPIT |
