Patent ID: 8128763

Claim:
A bake hardenable cold-rolled steel sheet with high strength and superior aging resistance, comprising, by weight %, the following components homogenized together: C: 0.0025˜0.0035%; Si: 0.02% or less; Mn: 0.2˜1.2%; P: 0.05˜0.11%; S: 0.01% or less; Soluble Al: 0.08˜0.12%; N: 0.0025% or less; Ti: 0.005˜0.018%; Mo: 0.1˜0.2%; B: 0.0005˜0.0015%; and the balance of Fe and other unavoidable impurities, wherein the steel sheet is Nb free and satisfies Equation 1: Ti*[Effective Ti]=Total Ti−(48/14)N−(48/32)S≦0 (1), wherein the steel sheet has a bake hardening degree (BH) of 30 MPa or more, an aging index (AI) of 30 MPa or less, a DBTT of −30° C. or less at a drawing ratio of 2.0, and a crystal grain size of ASTM No. 9 or more.