| 摘要 |
<p>Disclosed are a high strength cold-rolled steel sheet having more than 980 MPa of tensile strength with excellent bendability and excellent formability, and a manufacturing method thereof. According to the present invention, a method of manufacturing a high strength cold-rolled steel sheet comprises: (a) a step for forming a hot-rolled steel by re-heating, hot-rolling, cooling, and winding a steel, and a slab, which consists of 0.05-0.25 wt% of C, 0.5-1.5 wt% of Si, 1.5-2.5 wt% of Mn, 0.01-0.05 wt% of P, 0.005 wt% or less of S, 0.1-0.7 wt% of Cr, 0.03-0.08 wt% of Mo, 60 ppm or less of N, residual Fe, and unavoidable impurities; (b) a step for forming a cold-rolled steel by cold-rolling the hot-rolled steel after pickling the hot-rolled steel; (c) a step for annealing heat treating the cold-rolled steel in an austenite single phase; and (d) a step for heat treating with a constant temperature after cooling the heat treated steel until 420-540°C. The cold-rolled steel manufactured thereby has 980 Mpa or more of tensile strength, 0.65 or more of a yield ratio, 15% or more of an elongation rate, and a minimum bending radius (R) is two times or less of a steel sheet thickness bending at 90°.</p> |
