Steel

Abstract

A steel according to an aspect of the present invention includes, as a chemical composition, by unit mass %, C: 0.15% to 0.40%, Mn: 0.10% to 1.50%, S: 0.002% to 0.020%, Ti: 0.005% to 0.050%, B: 0.0005% to 0.0050%, Bi: 0.0010% to 0.0100%, P: 0.020% or less, N: 0.0100% or less, Si: 0% or more and less than 0.30%, Cr: 0% to 1.50%, Al: 0% to 0.050%, Mo: 0% to 0.20%, Cu: 0% to 0.20%, Ni: 0% to 0.20%, Nb: 0% to 0.030%, and a remainder including Fe and impurities.

1 . A steel comprising, as a chemical composition, by unit mass %,
 C: 0.15% to 0.40%,   Mn: 0.10% to 1.50%,   S: 0.002% to 0.020%,   Ti: 0.005% to 0.050%,   B: 0.0005% to 0.0050%,   Bi: 0.0010% to 0.0100%,   P: 0.020% or less,   N: 0.0100% or less,   Si: 0% or more and less than 0.30%,   Cr: 0% to 1.50%,   Al: 0% to 0.050%,   Mo: 0% to 0.20%,   Cu: 0% to 0.20%,   Ni: 0% to 0.20%,   Nb: 0% to 0.030%, and   a remainder including Fe and impurities.   
     
     
         2 . The steel according to  claim 1 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
 Si: 0.01% or more and less than 0.30%,   Cr: 0.01% to 1.50%, and   Al: 0.001% to 0.050%.   
     
     
         3 . The steel according to  claim 1 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
 Mo: 0.02% to 0.20%,   Cu: 0.02% to 0.20%,   Ni: 0.02% to 0.20%, and   Nb: 0.002% to 0.030%.   
     
     
         4 . The steel according to  claim 1 ,
 wherein a N fixation index I FN  defined by the following Expression 1 is 0 or more,
     I   FN =[Ti]−3.5×[N]  (Expression 1)
 
   where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.   
     
     
         5 . The steel according to  claim 1 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         6 . The steel according to  claim 2 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
 Mo: 0.02% to 0.20%,   Cu: 0.02% to 0.20%,   Ni: 0.02% to 0.20%, and   Nb: 0.002% to 0.030%.   
     
     
         7 . The steel according to  claim 2 ,
 wherein a N fixation index I FN  defined by the following Expression 1 is 0 or more,
     I   FN =[Ti]−3.5×[N]  (Expression 1)
 
   where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.   
     
     
         8 . The steel according to  claim 3 ,
 wherein a N fixation index I FN  defined by the following Expression 1 is 0 or more,
     I   FN =[Ti]−3.5×[N]  (Expression 1)
 
   where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.   
     
     
         9 . The steel according to  claim 6 ,
 wherein a N fixation index I FN  defined by the following Expression 1 is 0 or more,
     I   FN =[Ti]−3.5×[N]  (Expression 1)
 
   where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.   
     
     
         10 . The steel according to  claim 2 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         11 . The steel according to  claim 3 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         12 . The steel according to  claim 4 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         13 . The steel according to  claim 6 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         14 . The steel according to  claim 7 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         15 . The steel according to  claim 8 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.   
     
     
         16 . The steel according to  claim 9 ,
 wherein a Ti—Nb-based precipitate generation index I P  defined by the following Expression 2 is 0.0100 or less,
     I   P =0.3×[Ti]+0.15×[Nb]−[N]  (Expression 2)
 
   where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.