| 摘要 |
<p>A cold rolled steel sheet comprising C, Mn, S, Al, N, P, B, Ti, Nb and the balance of Fe and other unavoidable impurities which is capable of enhancing yield strength and lowering in-plane anisotropy by (Mn,Cu)S precipitates and AlN precipitates in bake-hardening type interstitial free steel, and a method for manufacturing the same are provided. A bake-hardening type cold rolled steel sheet with excellent yield strength comprises, by weight percent, 0.001 to 0.01% of C, 0.01 to 0.2% of Cu, 0.01 to 0.3% of Mn, 0.005 to 0.08% of S, 0.1% or less of Al, 0.004 to 0.02% of N, 0.2% or less of P, 0.0001 to 0.002% of B, 0.005 to 0.15% of Ti and 0.002 to 0.04% of Nb with the balance being Fe and other inevitable impurities, wherein the Cu, Mn, S, Al, N, C, Ti and Nb satisfy Cu+Mn=0.05 to 0.4, (Mn/55+Cu/63.5)/(S^*/32)=1 to 30, (Al/27)/(N^*/14)=1 to 10, and Cs(solute carbon) satisfies 5 to 30, wherein S^*=S-0.8Î(Ti-0.8Î(48/14)ÎN)Î(32/48), N^*=N-0.8Î(Ti-0.8Î(48/32)ÎS))Î(14/48), Cs=(C-NbÎ12/93-Ti^*Î12/48)Î10000, Ti^*=Ti-0.8Î((48/14)ÎN+(48/32)ÎS), and Ti^*=0 provided that Ti^*<0, and wherein (Mn,Cu)S precipitates and AlN precipitates have an average size of 0.2 mum or less.</p> |
