Cold rolled steel sheet with ultra-high strength, and manufacturing method therefor

Abstract

Provided are a cold rolled steel sheet with ultra-high strength, and a manufacturing method therefor. In an exemplary embodiment, a cold rolled steel sheet with ultra-high strength includes an amount of 0.10 to 0.40 wt % of carbon (C), an amount of 0.10 to 0.80 wt % of silicon (Si), an amount of 0.6 to 1.4 wt % of manganese (Mn), an amount of 0.01 to 0.30 wt % of aluminum (Al), an amount greater than 0 and less than or equal to 0.02 wt % of phosphorus (P), an amount greater than 0 and less than or equal to 0.003 wt % of sulfur (S), an amount greater than 0 and less than or equal to 0.006 wt % of nitrogen (N), an amount greater than 0 and less than or equal to 0.05 wt % of titanium (Ti) in, an amount of 0 to 0.05 wt % of niobium (Nb), an amount of 0.001 to 0.003 wt % of boron (B), and the balance of iron (Fe) and other inevitable impurities, wherein the cold rolled steel sheet has a microstructure comprising tempered martensite and has a 900 bending workability (R/t) of 1.5 or less, and the mass ratio (Nb/Ti) of niobium (Nb) to titanium (Ti) is 1.5 or less.