| 摘要 |
PURPOSE: An ultra high strength cold rolled steel sheet having excellent surface properties, a galvanized steel sheet, and a method for manufacturing the same are provided to improve the quality of edges and corners of slab and accordingly production yield. CONSTITUTION: An ultra high strength cold rolled steel sheet having excellent surface properties comprises C of 0.1-0.3%, Si of 0.1-1.5%, Mn of 2.0-3.0%, P of 0.001-0.10%, S of 0.010%, Al of 0.01-0.1%, Cr of 0.3-1.0%, B of 0.0010-0.0030%, Ti of 0.01-0.1%, and N of 0.001-0.01%. The cold rolled steel sheet also includes one or more selected from the group consisting of Nb of 0.02-0.05%, Mo of 0.01-0.2%, V of 0.01-0.2%, W of 0.01-0.2%, and Fe and inevitable impurities of the remaining amount. Ti and N satisfy the relation of 3.4 <= Ti/N <= 10. Nb, Mo, V, and W satisfy the relation of 0.02 <= Nb+0.2(Mo+V+W) <= 0.05. C, Mn, Si, and Cr satisfy the relation of 0.17 <= C+0.023Mn+0.062Si-0.009Cr <= 0.4. Nb, C, Al, and N satisfy the relation of 0.2 <= 124(Nb×C) + 2900(Al×N) <= 1.
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