High-strength steel plate for pressure vessel having excellent toughness after post weld heat treatment and manufacturing method thereof

Provided is a high-strength steel plate for a pressure vessel having excellent low temperature toughness after a post weld heat treatment (PWHT). The high-strength steel plate for a pressure vessel includes: by wt %, 0.02-0.15% of carbon (C), 0.05-0.50% of silicon (Si), 1.0-2.0% of manganese (Mn), 0.005-0.1% of aluminum (Al), 0.015% or less of phosphorus (P), 0.0015% or less of sulfur (S), 0.01-0.03% of niobium (Nb), 0.01-0.03% of vanadium (V), 0.01-0.03% of titanium (Ti), 0.005% or less of chromium (Cr), 0.005% or less of molybdenum (Mo), 0.02-0.50% of copper (Cu), 0.05-0.60% of nickel (Ni), 0.0002-0.0010% of boron (B), 0.0035-0.0065% of nitrogen (N), and a balance of iron (Fe) and other inevitable impurities. A microstructure of the high-strength steel plate includes a complex structure of ferrite having an area fraction of 35-40% and a balance of bainite, and the bainite has a packet size of 15 μm or less.