| 摘要 |
PURPOSE: A method for manufacturing bake hardenable galvannealed steel sheets with high formability, excellent bake-hardening capacity of higher than 3Kgf/mm¬2 and tensile strength of higher than 40 kg/mm¬2 is provided. CONSTITUTION: In a manufacture method of bake hardenable galvannealed steel sheets through hot rolling, hot coiling, cold rolling and annealing, the present invention is characterized in that the bake hardenable galvannealed steel sheets comprises C 0.0015 to 0.0025 wt.%, Mn 0.8 to 1.5 wt.%, P 0.08 to 0.12 wt.%, S 0.006 wt.% or less, N 0.003 wt.% or less, sol-Al 0.06 wt.% or less, Ti 0.010 to 0.016 wt.%, Nb 0.007 to 0.013 wt.%, Cr 0.02 wt.% or less, a balance of Fe and other inevitable impurities where N, Ti and C satisfy following inequality:(4/14xN wt%)<=Ti<=(48/14xN wt%)+(48/12xC wt%x0.6).
|
