EXTRA HEAVY GAUGED STEEL PLATE HAVING EXCELLENT SURFACE QUALITY AND LAMELLAR TEARING RESISTANCE AND MANUFACTURING METHOD FOR THE SAME

摘要

Steel for ultra-thick pressure vessel according to an aspect of the present invention, by weight, carbon (C): 0.10 to 0.25%, silicon (Si): 0.05 to 0.50%, manganese (Mn): 1.0 to 2.0%, aluminum (Al): 0.005 to 0.1%, phosphorus (P): 0.010% or less, sulfur (S): 0.0015% or less, niobium (Nb): 0.001 to 0.03%, vanadium (V): 0.001 to 0.03%, titanium (Ti) ): 0.001 to 0.03%, Chromium (Cr): 0.01 to 0.20%, Molybdenum (Mo): 0.01 to 0.15%, Copper (Cu): 0.01 to 0.50%, Nickel (Ni): 0.05 to 0.50%, Calcium (Ca) ): 0.0005 to 0.0040%, including the remaining Fe and unavoidable impurities, the thickness direction elongation (ZRA) is 35% or more, the tensile strength is 450 to 620 MPa, and the maximum surface crack depth may be 2 μm or less.