HIGH STRENGTH AND LOW YIELD RATIO STEEL SHEET HAVING EXCELLENT LOW TEMPERATURE TOUGHNESS AND MATHOD FOR MANUFACTURING THE SAME

According to the present invention, a high strength and low yield ratio steel sheet comprises: at least one type selected in a group including 0.04-0.10 wt% of carbon (C), 2.4-2.8 wt% of manganese (Mn), 0.01-0.6 wt% of silicon (Si), 0.005-0.5 wt% of aluminum (Al), 0.005-0.1 wt% of niobium (Nb), 0.005-0.1 wt% of titanium (Ti), 0.02 wt% or less of phosphorus (P), 0.01 wt% or less of sulfur (S), 10-40 ppm of boron (B), 15-150 ppm of nitrogen (N), 60 ppm or less of calcium (Ca), 1.0 wt% or less of copper (Cu), 0.01-2.0 wt% of nickel (Ni), 0.05-1.0 wt% of chromium (Cr), 1.0 wt% or less of molybdenum (Mo), 0.3 wt% or less of vanadium (V); and the remainder consisting of Fe and inevitable impurities. 본 발명은 건축구조물, 기계구조물 등의 소재로 사용되는 구조용 강재에 관한 것으로서, 보다 상세하게는 저온 인성이 우수한 저항복비 고강도 강재 및 이의 제조방법에 관한 것이다.