Patent ID: 8647564

Claim:
A high-strength steel plate, comprising: carbon (C): 0.03 to 0.10% by weight, silicon (Si): 0.1 to 0.4% by weight, manganese (Mn): 1.8 wt % or less, nickel (Ni): 1.0 wt % or less, titanium (Ti): 0.005 to 0.03 wt %, niobium (Nb): 0.02 to 0.10 wt %, aluminum (Al): 0.01 to 0.05 wt %, calcium (Ca): 0.006 wt % or less, nitrogen (N): 0.001 to 0.006 wt %, phosphorus (P): 0.02 wt % or less, sulfur (S): 0.005 wt % or less, and the balance of iron (Fe) and other inevitable impurities, wherein a microstructure of the steel plate comprises acicular ferrite and bainite as a main microstructure and an austenite/martensite (M&A) as a second phase, and wherein the acicular ferrite has a grain size of 10 μm (micrometers) or less (excluding 0), and the bainite has a packet size of 5 μm (micrometers) or less (excluding 0), wherein the microstructure of the steel comprises substantially no polygonal ferrite.