Steel for welded structure and producing method thereof

Abstract

A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.015 to 0.045%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.5 to 2.0%; Ni at a Ni content [Ni] of 0.10 to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; O at an O content [O] of 0.0015 to 0.0035%; and N at a N content [N] of 0.002 to 0.006%, and a balance composed of Fe and unavoidable impurities. In the steel for a welded structure, the P content [P] is limited to 0.008% or less, the S content [S] is limited to 0.005% or less, the Al content [Al] is limited to 0.004% or less, the Nb content [Nb] is limited to 0.005% or less, the Cu content [Cu] is limited to 0.24% or less, the V content [V] is limited to 0.020% or less, and a steel composition parameter P CTOD is 0.065% or less, and a steel composition hardness parameter CeqH is 0.235% or less.

1 . A steel for a welded structure, comprising the following composition:
 by mass %,   C at a C content [C] of 0.015 to 0.045%;   Si at a Si content [Si] of 0.05 to 0.20%;   Mn at a Mn content [Mn] of 1.5 to 2.0%;   Ni at a Ni content [Ni] of 0.73% to 1.50%;   Ti at a Ti content [Ti] of 0.005 to 0.015%;   O at an O content [O] of 0.0015 to 0.0032%; and   N at a N content [N] of 0.002 to 0.006%,   and a balance composed of Fe and unavoidable impurities,   wherein, a P content [P] is limited to 0.008% or less,   a S content [S] is limited to 0.005% or less,   an Al content [Al] is limited to 0.004% or less,   a Nb content [Nb] is limited to 0.005% or less,   a Cu content [Cu] is limited to 0.24% or less,   a V content [V] is limited to 0.020% or less, and   a steel composition parameter P CTOD  of a following equation (3) is 0.065% or less, and a steel composition hardness parameter CeqH of a following equation (4) is 0.200% or less, where
   P CTOD =[C]+[V]/3+[Cu]/22+[Ni]/67  (3)
 
   CeqH=[C]+[Si]/4.16+[Mn]/14.9+[Cu]/12.9+[Ni]/105+1.12[Nb]+[V]/1.82  (4).
 
   
     
     
         2 . The steel for welded structure according to  claim 1 , wherein Cu is included, by mass %, at the Cu content [Cu] of 0.03% or less. 
     
     
         3 - 4 . (canceled)