Martensitic stainless steel seamless pipe for oil country tubular goods, and method for manufacturing same

Abstract

The invention provides a martensitic stainless steel seamless pipe for oil country tubular goods having a yield stress of 758 MPa (110 ksi) or more, and excellent sulfide stress corrosion cracking resistance and a method for manufacturing the same. The martensitic stainless steel seamless pipe for oil country tubular goods having a yield stress of 758 MPa or more has a composition that contains, in mass %, C: 0.010% or more, Si: 0.5% or less, Mn: 0.05 to 0.24%, P: 0.030% or less, S: 0.005% or less, Ni: 4.6 to 8.0%, Cr: 10.0 to 14.0%, Mo: 1.0 to 2.7%, Al: 0.1% or less, V: 0.005 to 0.2%, N: 0.1% or less, Ti: 0.06 to 0.25%, Cu: 0.01 to 1.0%, and Co: 0.01 to 1.0%, in which C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti satisfy the predetermined relations, and the balance is Fe and incidental impurities.

1 . A martensitic stainless steel seamless pipe for oil country tubular goods having a yield stress of 758 MPa or more,
 the martensitic stainless steel seamless pipe having a composition that comprises, in mass %, C: 0.010% or more, Si: 0.5% or less, Mn: 0.05 to 0.24%, P: 0.030% or less, S: 0.005% or less, Ni: 4.6 to 8.0%, Cr: 10.0 to 14.0%, Mo: 1.0 to 2.7%, Al: 0.1% or less, V: 0.005 to 0.2%, N: 0.1% or less, Ti: 0.06 to 0.25%, Cu: 0.01 to 1.0%, and Co: 0.01 to 1.0%, in which the values of the following formulae (1), (2), and (3) satisfy the formulae (4) below, and the balance is Fe and incidental impurities:
   −109.37C+7.307Mn+6.399Cr+6.329Cu+11.343Ni−13.529Mo+1.276W+2.925Nb+196.775N−2.621Ti−120.307,  Formula (1)
 
   −0.0278Mn+0.0892Cr+0.00567Ni+0.153Mo−0.0219W−1.984N+0.208Ti−1.83,  Formula (2)
 
   −1.324C+0.0533Mn+0.0268Cr+0.0893Cu+0.00526Ni+0.0222Mo−0.0132W−0.473N−0.5Ti−0.514,  Formula (3)
 
   wherein C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti represent the content of each element in mass %, and the content is 0 (zero) for elements that are not contained,
   −35.0≤value of formula (1)≤45.0,
 
   −0.600≤value of formula (2)≤−0.250, and
 
   −0.400≤value of formula (3)≤0.100.  Formulae (4)
 
   
     
     
         2 . The martensitic stainless steel seamless pipe for oil country tubular goods according to  claim 1 , wherein the composition further comprises, in mass %, one or two selected from Nb: 0.1% or less, and W: 1.0% or less. 
     
     
         3 . The martensitic stainless steel seamless pipe for oil country tubular goods according to  claim 1 , wherein the composition further comprises, in mass %, one, two or more selected from Ca: 0.010% or less, REM: 0.010% or less, Mg: 0.010% or less, and B: 0.010% or less. 
     
     
         4 . A method for manufacturing a martensitic stainless steel seamless pipe for oil country tubular goods,
 the method comprising:   forming a steel pipe from a steel pipe material of the composition of  claim 1 ;   quenching the steel pipe by heating the steel pipe to a temperature equal to or greater than an Ac 3  transformation point, and cooling the steel pipe to a cooling stop temperature of 100° C. or less; and   tempering the steel pipe at a temperature equal to or less than an Ac 1  transformation point.   
     
     
         5 . The martensitic stainless steel seamless pipe for oil country tubular goods according to  claim 2 , wherein the composition further comprises, in mass %, one, two or more selected from Ca: 0.010% or less, REM: 0.010% or less, Mg: 0.010% or less, and B: 0.010% or less. 
     
     
         6 . A method for manufacturing a martensitic stainless steel seamless pipe for oil country tubular goods,
 the method comprising:   forming a steel pipe from a steel pipe material of the composition of  claim 2 ;   quenching the steel pipe by heating the steel pipe to a temperature equal to or greater than an Ac 3  transformation point, and cooling the steel pipe to a cooling stop temperature of 100° C. or less; and   tempering the steel pipe at a temperature equal to or less than an Ac 1  transformation point.   
     
     
         7 . A method for manufacturing a martensitic stainless steel seamless pipe for oil country tubular goods,
 the method comprising:   forming a steel pipe from a steel pipe material of the composition of  claim 3 ;   quenching the steel pipe by heating the steel pipe to a temperature equal to or greater than an Ac 3  transformation point, and cooling the steel pipe to a cooling stop temperature of 100° C. or less; and   tempering the steel pipe at a temperature equal to or less than an Ac 1  transformation point.   
     
     
         8 . A method for manufacturing a martensitic stainless steel seamless pipe for oil country tubular goods,
 the method comprising:   forming a steel pipe from a steel pipe material of the composition of  claim 5 ;   quenching the steel pipe by heating the steel pipe to a temperature equal to or greater than an Ac 3  transformation point, and cooling the steel pipe to a cooling stop temperature of 100° C. or less; and   tempering the steel pipe at a temperature equal to or less than an Ac 1  transformation point.