| 摘要 |
PURPOSE:To prepare a cold rolled steel plate excellent in processability, by a method wherein a low carbon steel slab of which components are prescribed is hot rolled and, after winding up at a high temp., the outer peripheral temp. of the formed hot rolled coil is gradually cooled through a specific range. CONSTITUTION:Hot rolling is applied to a steel slab containing 0.005-0.07% C, 1.3% or less Si, 0.8% or less Mn, 0.1% or less, P, 0.01-0.1% Al and 10-80ppm N in a usual process and the hot rolled slab is wound up at 720 deg.C or more in a coil form while the wound-up hot rolled coil is subjected to heat holding treatment directly after winding-up to gradually cool the outer periphery part thereof at a cooling speed of 10 deg.C/min or less over a temp. range reaching 500 deg.C from 720 deg.C. By this method, the material qualities of the leading end part and the trailing end part can be secured to high levels equal to that of the central part. |
