HIGH STRENGTH COLD ROLLED STEEL SHEET HAVING EXCELLENT STRETCH FLANGE ABILITY AND METHOD FOR MANUFACTURING THE SAME

摘要

The present invention relates to a high strength cold rolled steel sheet with excellent stretch flange property, and a manufacturing method thereof. The high strength cold rolled steel sheet comprises: 0.05-0.2 wt% of carbon (C); 0.05-0.1 wt% of silicon (Si); 1.5-2.0 wt% of manganese (Mn); 0.03 wt% or less of phosphorus (P); 0.015 wt% or less of sulfur (S); 0.02 wt% or less (excluding 0 wt%) of aluminum (Al); 0.1 wt% or less (excluding 0 wt%) of niobium (Nb); 0.01 wt% or less of nitrogen (N); and the remaining consisting of iron (Fe) and inevitable impurities. If Do is designated as an initial hole diameter (mm) and Dh is designated as a post-breakage hole diameter (mm); a hole expansion rate (%) λ, indicated in the relational expression 1 below, is not less than 45%. The relational expression 1: λ = (Dh-Do)/Do*100