| 摘要 |
PURPOSE:To obtain the steel sheet for motorcar, etc. having superior press moldability, weather resistance and high strength, by regulating the condition of heat treatment and processing at hot rolling, coiling, cold rolling, annealing, etc. of steel slab containing a suitable amount of Si, Mn and coexisting with P, Cu. CONSTITUTION:Ingot or continuous casting slab containing C; 0.01-0.20wt%, Si; 0.3-3.0%, Mn; 0.2-1.2% (where, Mn/Si>1) and P; 0.03-0.20%, Cu; 0.2- 1.2% in a single or composite state, is manufactured. Finish hot rolling of the above slab is carried out at a temperature of Ar3 point or more and rolled slab is coiled at a tmeperature of 600 deg.C or less after cooling at a speed of 30 deg.C/sec or more. Next, temperature is raised at a speed of 150 deg.C/hr or less after carrying out descaling and cold rolling and then, annealing is carried out at 650-800 deg.C. By the above steel composition and treating and processing condition, cold rolled steel sheet is obtained excellent in strength, processing property and weather resistance. |
