| 摘要 |
<p>A cold-rolled steel sheet for outer panels and the like of an automobile body, a galvannealed steel sheet using the cold-rolled steel sheet, and a method for manufacturing the same are disclosed. The high strength cold-rolled steel sheet with superior bake hardenability, comprises, by weight%: C: 0.0016 ~ 0.0025%; Si: 0.02% or less; Mn: 0.2 ~ 1.2%; P: 0.05 ~ 0.11%; S: 0.01% or less; Sol. Al: 0.08 ~ 0.12%; N: 0.0025% or less; Ti: 0.008 ~ 0.018%; Mo: 0.1 ~ 0.2%; B: 0.0005 ~ 0.0015%; and the balance of Fe and other unavoidable impurities. The steel sheet satisfies Equations 1 and 2: Ti * Effective Ti = Total Ti - 48 / 14 �¢ N - 48 / 32 �¢ S ‰¤ 0 C * amount of solute carbon in grain boundaries GB - C + amount of solute carbon in crystal grains G - C = Total C ppm - C in TiC = 8 ˆ¼ 15 ppm
[in Equation 2, GB-C (that is, the amount of solute carbon in the grain boundaries) is 5 - 10 ppm, and G-C (that is, the amount of solute carbon in the crystal grains) is 3 - 7 ppm], and
wherein the steel sheet has ASTM No. of 9 or more, a bake hardenability value (BH) of 30 MPa or more, an aging index (AI) of 30 MPa or less, and a tensile strength of 340 ~ 390 MPa.</p> |
