Electric resistance welded steel tube for heat treatment and method for manufacturing the same

Abstract

An electric resistance welded steel tube for heat treatment can be used as a highly durable material even after quenching treatment by rapid heating for hollow stabilizers or the like and a method for manufacturing such an electric resistance welded steel tube. A steel tube material, which has a composition constituted by, in mass percent, C: 0.15 to 0.40%, Si: 0.05 to 0.50%, Mn: 0.30 to 2.00%, Al: 0.01 to 0.10%, Ti: 0.001 to 0.04%, B: 0.0005 to 0.0050%, and N: 0.0010 to 0.0100% with Ti and N satisfying (N/14)<(Ti/47.9).

1 . An electric resistance welded steel tube for heat treatment that is excellent in terms of flatness, comprising an electric resistance welded portion having a bond width of 25 μm or less. 
   
   
       2 . An electric resistance welded steel tube for heat treatment that is excellent in terms of flatness, comprising an electric resistance welded portion having a bond width of 25 μm or less, wherein the electric resistance welded steel tube has a composition constituted by, in mass percent:
 C: 0.15 to 0.40% Si: 0.05 to 0.50%   Mn: 0.30 to 2.00% Al: 0.01 to 0.10%   Ti: 0.001 to 0.04% B: 0.0005 to 0.0050%, and   N: 0.0010 to 0.0100%   
     as well as Fe and unavoidable impurities as the balance and Ti and N satisfy (N/14)<(Ti/47.9). 
   
   
       3 . The electric resistance welded steel tube according to  claim 2 , further comprising one or more selected from, in mass percent, Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, and Cu: 1.0% or less. 
   
   
       4 . The electric resistance welded steel tube according to  claim 2 , further comprising either or both of, in mass percent, Nb: 0.2% or less and V: 0.2% or less. 
   
   
       5 . A method for manufacturing an electric resistance welded steel tube for heat treatment, comprising:
 forming a steel tube material into an almost cylindrical open pipe, the steel tube material being a steel sheet having a composition constituted by, in mass percent:   C: 0.15 to 0.40% Si: 0.05 to 0.50%   Mn: 0.30 to 2.00% Al: 0.01 to 0.10%   Ti: 0.001 to 0.04% B: 0.0005 to 0.0050%, and   N: 0.0010 to 0.0100%   
     with Ti and N satisfying (N/14)<(Ti/47.9) as well as Fe and unavoidable impurities as the balance;
 forming an electric resistance welded steel tube by bonding the ends of the open pipe to each other by induction resistance welding with heat input controlled so that the bond width will fall within the range of 30 to 65 μm; 
 heating the electric resistance welded steel tube to a temperature equal to or higher than the Ac 3  transformation temperature; and 
 diameter-reducing rolling the heated electric resistance welded steel tube with rolling reduction expressed by an outer diameter ratio being greater than (1−25/the bond width before diameter-reducing rolling (μm))×100% such that the bond width will be 25 μm or less. 
 
   
   
       6 . The method according to  claim 5 , wherein the composition further comprises one or more selected from, in mass percent. Cr: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, and Cu: 1.0% or less. 
   
   
       7 . The method according to  claim 5 , wherein the composition further contains either or both of, in mass percent, Nb: 0.2% or less and V: 0.2% or less. 
   
   
       8 . The electric resistance welded steel tube according to  claim 3 , further comprising either or both of, in mass percent, Nb: 0.2% or less and V: 0.2% or less. 
   
   
       9 . The method according to  claim 6 , wherein the composition further contains either or both of, in mass percent, Nb: 0.2% or less and V: 0.2% or less.