| 摘要 |
PURPOSE:To produce a high-strength cold-rolled steel sheet having baking hardenability and press formability in the stage of producing a low carbon steel sheet by performing an annealing treatment after hot rolling and cold rolling of a steel slab under specific conditions. CONSTITUTION:A steel slab contg. 0.02-0.10% C, <0.07% Si, 0.05-0.5% Mn, 0.03-0.20% P, 0.02-0.15% Al and 0.003-0.008% N is hot-rolled in such a way that the hot finish temp. attains the Ar3 transformation point or above of said steel to form a sheet material. The sheet is coiled at 450-630 deg.C. The sheet is cold-rolled after descaling to form a cold-rolled steel sheet having a prescribed sheet thickness. The sheet is held for 0.5-5hr at 450-600 deg.C during the time since starting of heating until the temp. rises to the annealing temp. in the stage of annealing. The heating stage in the force period till the holding stage is performed by open coil annealing at a heating rate of <=100 deg.C/hr and an annealing temp. of 710-820 deg.C. |
