| 摘要 |
PURPOSE: A cold rolled steel sheet and a method for manufacturing the same are provided to reduce manufacturing cost, improve productivity and obtain superior formability and fatigue properties by low temperature annealing an ultra low carbon aluminum killed steel in which a weight ratio of Mn/S and an atomic ratio of B/N are controlled in a continuous annealing method, and properly controlling a texture ratio of steel. CONSTITUTION: The cold rolled steel sheet having superior fatigue properties contains 0.0035 wt.% or less of C, 0.5 to 1.0 wt.% of Mn, 0.007 to 0.015 wt.% of S, 0.04 to 0.10 wt.% of Al, 0.0035 wt.% or less of N, 0.0005 to 0.0025 wt.% of B and a balance of Fe and other inevitable impurities, wherein a weight ratio of Mn/S is 60 to 100, an atomic ratio of B/N is 0.7 to 1.5, and a texture ratio of {I(222)+I(211)}/{I(200)} is 11.0 to 15.5. The method for manufacturing the cold rolled steel sheet having superior fatigue properties comprises the processes of terminating hot rolling at a final hot rolling temperature of 890 to 940 deg.C after reheating an aluminum killed steel containing 0.0035 wt.% or less of C, 0.5 to 1.0 wt.% of Mn, 0.007 to 0.015 wt.% of S, 0.04 to 0.10 wt.% of Al, 0.0035 wt.% or less of N, 0.0005 to 0.0025 wt.% of B and a balance of Fe and other inevitable impurities, wherein a weight ratio of Mn/S is 60 to 100, and an atomic ratio of B/N is 0.7 to 1.5; cold rolling the coiled steel to a reduction ratio of 85 to 89% after coiling the hot rolled aluminum killed steel at a temperature of 620 to 720 deg.C; and continuous annealing the cold rolled steel in the temperature range of a recrystallization temperature to 800 deg.C.
|
