| 摘要 |
PURPOSE: A method for manufacturing a high strength bake-hardenable cold rolled steel sheet is provided. The high strength bake-hardenable cold rolled steel sheet has a bake-hardened amount of 3-6kgf/mm¬2, average r value higher than 2.0, an elongation value at yield point 0.1wt.% or less when aged for 1 hour at 10 0°C. CONSTITUTION: The method includes the steps of: (i) spheroidizing a steel slab comprising C 0.0020-0.0030%, Si 0.02wt.% or less, Mn 0.07-0.2wt.%, P 0.05-0.08wt.%, S 0.008wt.% or less, sol-Al 0.02-0.06wt.%, N 0.0035wt.% or less, Nb 0.008-0.012wt.%, V 0.02-0.1wt.% and inevitable impurities at higher than 1200°C; conducting finish hot-rolling in the temperature range of 900 to 950°C; (iii) coiling in the temperature of 700 to 750°C; (iv) conducting cold-rolling at a reduction ratio of 75 to 80%; (v) continuous annealing in the temperature range of 830 to 850°C; and (vi) temper rolling at a reduction ratio of 1.3 to 2.0%.
|
