| 摘要 |
PURPOSE:To manufacture high strength cold rolled steel sheet excellent in press formability and baking hardenability, by the hot rolling and cold rolling of steel material having a ratio of Si/Mn not small than 1 to form steel sheet, then by cooling at a specific cooling rate after batch annealing. CONSTITUTION:Molten steel contg. 0.01-0.20% C, 0.7-3.0% Si, <=0.7% Mn, and having a ratio of Si/Mn not smaller than 1 is made into ingot, bloomed, or continuously cast to form a slab. The slab is finishing hot rolled at a temp. not lower than Ar3 transformation temp., descaled, and cold rolled at a reduction ratio not lower than 40%. After batch annealing at a temp. 650-800 deg.C, the slab is cooled rapidly at a rate not lower than 80 deg.C/hr thereby securing crystal arrangement preferable for formability, simultaneously manufacturing steel sheet excellent in tensile strength, formability, and baking hardenability by keeping the presence of carbide, the quantity of N in solid solution and C in solid solution at a proper value. Presence of 0.03-0.20% P and 0.015-0.15% Al further improves the above-described characteristics. |
