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

1 . A high-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding, characterized by containing, by wt %, 
 C: 0.03-0.14%,    Si: 0.30% or less,    Mn: 0.8-2.0%,    P: 0.02% or less,    S: 0.005% or less,    Al: 0.001-0.040%,    N: 0.0010-0.0100%,    Ni: 0.8-4.0%,    Ti: 0.005-0.030%, and    Nb: 0.003-0.040%,    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    
   
   
       2 . A high-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding according to  claim 1 , characterized by fturther containing, by wt %, 
 one or more of:    Ca: 0.0003-0.0050%,    Mg: 0.0003-0.0050%, and    REM: 0.001-0.030% and    contains at least 1 00/mm 2  of oxide particles containing    O: 0.0010-0.0050%    and having a equivalent circle diameter of 0.005 to 0.5 μm.    
   
   
       3 . A high-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding according to  claim 1 , characterized by further containing, by wt %, 
 B: 0.0005-0.0050%.    
   
   
       4 . A high-strength thick steel plate excellent in low temperature toughness at heat affected zone resulting from large heat input welding according to  claim 1 , characterized by further containing, by wt %, 
 one or more of:    Cr: 0.1-0.5%,    Mo: 0.01-0.5%,    V: 0.005-0.10%, and    Cu: 0.1-1.0%.