| 摘要 |
<p>The present invention relates to an ultra-high strength cold rolled steel sheet having excellent weldability and bendability and a method for manufacturing the ultra-high strength cold rolled steel sheet and, more specifically, an ultra-high strength cold rolled steel sheet having more than 980 Mpa of tensile strength enough to be used to manufacture cars and a method for manufacturing the ultra-high strength cold rolled steel sheet. An embodiment of the present invention provides the ultra-high strength cold rolled steel sheet which is composed of, in wt%: C: 0.08-0.105; Si: 0.05-0.6; Mn: 2.5-2.9; P: 0.001-0.10; S: 0.010% or less; Sol. Al: 0.01-0.10; N: 0.001-0.010; Cr: 0.2-0.6; B: 0.0010-0.0060; Sb: 0.001-0.10; Ti: 0.005-0.05; Nb: 0.003-0.08; and the remainder Fe and other inevitable impurities; and which has 0.28 or less of Ceq shown in the following formula 1, satisfies the conditions of the following formula 2, and includes bainite whose micro-structure is 30-40 area%, the remainder ferrite and martensite; and the method for manufacturing the ultra-high strength cold rolled steel sheet.[Formula 1] Ceq = C + Mn/20 + Si/30 + 2P + 4S [Formula 2] 60C - 0.2Si - 0.15Mn + 2.2Si×Cr - 0.7Cr <= 5.6 The present invention provides the ultra-high strength cold rolled steel sheet securing 980 Mpa of strength, which is an ultra-high level, and 12% of strain rate while having excellent weldability and bendability, and a method for manufacturing the ultra-high strength cold rolled steel sheet. [Reference numerals] (AA,CC,EE) Yield strength (MPa); (BB,DD,FF) Annealing temperature (°C)</p> |
