| 摘要 |
PURPOSE:To obtain a high corrosion resistant /high workability/high tensile strength cold rolled steel sheet excellent in elongation-flanging properties by forming a chromated layer with specified coating weight and a solid lubricating film layer on the surface of a steel sheet contg. specified amounts of C, Si, Mn, Nb, Al and S and having a specified crystalline structure. CONSTITUTION:Steel contg., by weight, 0.03 to 0.15% C, <=0.05% Si, 0.50 to 1.20% Mn, 0.005 to 0.045% Nb, 0.005 to 0.l00% Al and <=0.010% S is subjected to hot rolling, is thereafter subjected to >=50% cold rolling and is annealed at 720 to 780 deg.C for 20 to 60S by continuous annealing. In this way, the steel sheet having a structure in which uniform and fine recrystallized ferrite having <=20mum average grain size lies by >=95% area ratio is obtd. On the surface of this steel sheet, a chromated layer with 40 to 200mg/mm<2> coating weight expressed in terms of metallic Cr having <=5mg/m<2> akkali elutable Cr content is formed. On the surface, a solid lubricating film layer with 0.1 to 5.0g/m<2> coating weight contg. 0.05 to 40% in total of inorganic and organic lubricating grains contained respectively by 0.05 to 30% and 0.05 to 20% is formed. |
