METHOD FOR PRODUCING HIGH-STRENGTH Cr-Ni ALLOY SEAMLESS PIPE

Abstract

A method for producing a high-strength Cr—Ni alloy seamless pipe comprising preparing an alloy billet with a chemical composition consisting, by mass %, of C: 0.05% or less, Si: 1.0% or less, Mn: less than 3.0%, P: 0.005% or less, S: 0.005% or less, Cu: 0.01 to 4.0%, Ni: 25% or more and less than 35%, Cr: 20 to 30%, Mo: 0.01% or more and less than 4.0%, N: 0.10 to 0.30%, Al: 0.03 to 0.30%, O (oxygen): 0.01% or less, REM (rare earth metal): 0.01 to 0.20%, and the balance being Fe and impurities, and satisfying the formula N×P/REM≦0.10, wherein P, N and REM represent the contents (mass %) of P, N and REM, respectively. The pipe is hot worked using cross roll piercing, solution heat treated, and cold worked. The pipe is excellent in hot workability, stress corrosion cracking and does not laminate during cross piercing.

1 . A method for producing a high-strength Cr—Ni alloy seamless pipe, comprising: preparing an alloy billet that has a chemical composition consisting, by mass %, of C: 0.05% or less, Si: 1.0% or less, Mn: less than 3.0%, P: 0.005% or less, S: 0.005% or less, Cu: 0.01 to 4.0%, Ni: 25% or more and less than 35%, Cr: 20 to 30%, Mo: 0.01% or more and less than 4.0%, N: 0.10 to 0.30%, Al: 0.03 to 0.30%, O (oxygen): 0.01% or less, REM (rare earth metal): 0.01 to 0.20%, and the balance being Fe and impurities, and satisfying the following formula (1);
 hot working to make a seamless material pipe on the basis of a cross roll piercing process; 
 subjecting a solution treatment; and 
 cold working.
     N×P/REM≦ 0.10   formula (1)
 
 
 wherein P, N and REM in formula (1) represent the contents (mass %) of P, N and REM, respectively. 
 
     
     
         2 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 1 , wherein the billet has a chemical composition that further contains, by mass %, Si: 0.3% or less and/or Mn: 0.7% or less. 
     
     
         3 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 1 , wherein the billet has a chemical composition that further contains, by mass %, one or more elements selected from at least one group of the following first group to third group in place of part of Fe.
 First group: W: less than 8.0%, 
 Second group: Ti: 0.5% or less, Nb: 0.5% or less, V: 0.5% or less and Zr: 0.5% or less, 
 Third group: Ca: 0.01% or less and Mg: 0.01% or less. 
 
     
     
         4 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 2 , wherein the billet has a chemical composition that further contains, by mass %, one or more elements selected from at least one group of the following first group to third group in place of part of Fe.
 First group: W: less than 8.0%, 
 Second group: Ti: 0.5% or less, Nb: 0.5% or less, V: 0.5% or less and Zr: 0.5% or less, 
 Third group: Ca: 0.01% or less and Mg: 0.01% or less. 
 
     
     
         5 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 1 , wherein the yield strength after cold working is 900 MPa or more in terms of the 0.2% yield stress. 
     
     
         6 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 2 , wherein the yield strength after cold working is 900 MPa or more in terms of the 0.2% yield stress. 
     
     
         7 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 3 , wherein the yield strength after cold working is 900 MPa or more in terms of the 0.2% yield stress. 
     
     
         8 . The method for producing a high-strength Cr—Ni alloy seamless pipe according to  claim 4 , wherein the yield strength after cold working is 900 MPa or more in terms of the 0.2% yield stress.