High-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding

Abstract

The present invention provides a high-strength thick steel plate having a plate thickness of 50 to 80 mm and a tensile strength of 490 to 570 MPa which is able to realize an excellent HAZ toughness even when welding with a heat input of 20 to 100 kJ/mm is conducted and is characterized by containing, by wt %, 0.03-0.14% of C, 0.30% or less of Si, 0.8-2.0% of Mn, 0.02% or less of P, 0.005% or less of S, 0.8-4.0% of Ni, 0.003-0.040% of Nb, 0.001-0.040% of Al, 0.0010-0.0100% of N, and 0.005-0.030% of Ti, where Ni and Mn satisfy equation [1], and the balance of iron and unavoidable impurities: Ni/Mn≧10×Ceq−3 (0.36<Ceq<0.42)  [1] where,  Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15

Dependencies are inferred from the claim text.