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

Abstract

Provided herein is a martensitic stainless steel seamless pipe, intended for oil country tubular goods, having high strength, and excellent sulfide stress corrosion cracking resistance. A method for producing such a martensitic stainless steel seamless pipe is also provided. The martensitic stainless steel seamless pipe for oil country tubular goods has a composition that contains, in mass %, C: 0.035% or less, Si: 0.5% or less, Mn: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cu: 2.6% or less, Ni: 5.3 to 7.3%, Cr: 11.8 to 14.5%, Al: 0.1% or less, Mo: 1.8 to 3.0%, V: 0.2% or less, N: 0.1% or less, and the balance Fe and unavoidable impurities, and in which C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti satisfy the predetermined relations.

1 . A martensitic stainless steel seamless pipe for oil country tubular goods,
 the martensitic stainless steel seamless pipe having a composition that comprises, in mass %, C: 0.035% or less, Si: 0.5% or less, Mn: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Cu: 2.6% or less, Ni: 5.3 to 7.3%, Cr: 11.8 to 14.5%, Al: 0.1% or less, Mo: 1.8 to 3.0%, V: 0.2% or less, N: 0.1% or less, and the balance Fe and unavoidable impurities, and that satisfies the following formula (4) with the following formulae (1), (2), and (3),   the martensitic stainless steel seamless pipe having a yield stress of 758 MPa or more.
   −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)
 
   In the formulae (1) to (3), C, Mn, Cr, Cu, Ni, Mo, W, Nb, N, and Ti represent the content of each element in mass % (the content being 0 (zero) percent for elements that are not contained).
   −10≤formula (1)≤45, −0.25≤formula (2)≤−0.20, and 0.10≤formula (3)≤0.20  Formula (4)
 
   
     
     
         2 . The martensitic stainless steel seamless pipe for oil country tubular goods according to  claim 1 , wherein the composition further comprises, in mass %, at least one selected from Ti: 0.19% or less, Nb: 0.25% or less, W: 1.1% or less, and Co: 0.45% or less. 
     
     
         3 . A method for producing the martensitic stainless steel seamless pipe for oil country tubular goods of  claim 1 ,
 the method comprising:   making a steel pipe out of a steel pipe material;   subjecting the steel pipe to quenching in which the steel pipe is heated to a temperature equal to or greater than the Ac 3  transformation point, and air cooled to a cooling stop temperature of 100° C. or less at a cooling rate of 0.1° C./s or more; and   tempering the steel pipe at a temperature equal to or less than the Ac 1  transformation point.   
     
     
         4 . A method for producing the martensitic stainless steel seamless pipe for oil country tubular goods of  claim 2 ,
 the method comprising:   making a steel pipe out of a steel pipe material;   subjecting the steel pipe to quenching in which the steel pipe is heated to a temperature equal to or greater than the Ac 3  transformation point, and air cooled to a cooling stop temperature of 100° C. or less at a cooling rate of 0.1° C./s or more; and   tempering the steel pipe at a temperature equal to or less than the Ac 1  transformation point.