| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a super-high strength cold-rolled steel sheet having excellent bending properties and lagging destruction resistance and having a small thickness. <P>SOLUTION: Provided is the super-high strength cold-rolled steel sheet having excellent bending properties, which contains 0.15 to 0.30% of C, 0.01 to 1.8% of Si, 1.5 to 3.0% of Mn, 0.05% or less of P, 0.005% or less of S, 0.005 to 0.05% of Al, 0.005% or less N, and the balance Fe with inevitable impurities, and has a soft steel sheet surface layer part meeting the following formulae: Hv(S)/Hv(C)=0.8 (1) (wherein Hv(S) represents the hardness of the soft steel sheet surface layer part, and Hv(C) represents the hardness of the steel sheet center part); 0.10≤t(S)/t≤0.30 (2) (wherein t(S)represents the thickness of the soft steel sheet surface layer part; and t represents the thickness of the sheet), wherein the soft steel sheet surface layer part contains tempered martensite at a ratio of vol.90% or more, the structure of the central part of the steel sheet comprises tempered martensite, and the tensile strength of the steel sheet is 1,270 MPa or more. <P>COPYRIGHT: (C)2011,JPO&INPIT</p> |
