| 摘要 |
PURPOSE: To produce a high strength cold rolled steel sheet capable of producing without troubles such as deterioration in the shape of the steel sheet by a contin uous annealing method and capable of withstanding severer deep drawing such as fender. CONSTITUTION: A slab having a compsn. contg., by weight, 0.0010 to 0.0030% C, <=0.50% Si, 0.02 to 0.80% Mn, 0.035 to 0.150% P, <=0.030% S, 0.025 to 0.100% sol.Al, 0.0005 to 0.0100% N and 0.007 to 0.020% Nb, furthermore satisfying 7.75×C-0.013<=Nb<=7.75×C+0.007, and the balance iron with inevitable impurities is subjected to finish rolling at the Ar3 or above and is coiled to form into a hot rolled steel strip, which is subjected to cold rolling and is subjected to recrystallization annealing under heating to 750 to 890 deg.C by a continuous annealing method. Next, at the time of executing cooling, it is cooled at least to 730 deg.C at 2 to <10 deg.C/s cooling rate to make an annealed sheet, and after that, it is subjected to skin-pass rolling of 0.5 to 3%.
|
