High-strength seamless stainless steel pipe for oil well

Abstract

To provide a high-strength seamless stainless steel pipe for oil well that has high strength, is excellent in hot workability, has excellent carbon dioxide gas corrosion resistance, and is excellent in SSC resistance under a low temperature environment. A high-strength seamless stainless steel pipe for oil well having a composition containing the particular components, the balance being Fe and unavoidable impurities, and satisfying certain expressions, having a number density of an inclusion having a major axis of 5 μm or more and 0.5<Ti/(Ti+Al+Mg+Ca)<1.0 of 0.5 per mm2 or more and 3 per mm2 or less, and having a yield strength of 655 MPa or more, wherein in 0.5<Ti/(Ti+Al+Mg+Ca)<1.0, Ti, Al, Mg, and Ca represent the contents (% by mass) of the elements in the inclusion, and an element that is not contained is designated as 0.

1 . A high-strength seamless stainless steel pipe for oil well having a composition containing, in terms of % by mass,
 C: 0.002-0.05%,   Si: 0.05-0.50%,   Mn: 0.04-1.80%,   P: 0.030% or less,   S: 0.002% or less,   Cr: 11.0-14.0%,   Ni: 3.0-6.5%,   Mo: 0.5-3.0%,   Al: 0.005-0.10%,   V: 0.005-0.20%,   Ti: 0.01-0.20%,   Co: 0.01-1.0%,   N: 0.002-0.15%, and   O: 0.010% or less,   
       the balance being Fe and unavoidable impurities, and satisfying the following expression (1) and the following expression (2),
  having a number density of an inclusion having a major axis of 5 μm or more and 0.5<Ti/(Ti+Al+Mg+Ca)<1.0 of 0.5 per mm 2  or more and 3 per mm 2  or less, and having a yield strength of 655 MPa or more, 
  wherein in 0.5<Ti/(Ti+Al+Mg+Ca)<1.0, Ti, Al, Mg, and Ca represent the contents (% by mass) of the elements in the inclusion, and an element that is not contained is designated as 0,
   Cr+0.65Ni+0.6Mo+0.55Cu−20C≥15.0  (1)
 
   Cr+Mo+0.3Si−43.3C−0.4Mn—Ni−0.3Cu−9N≤11.0  (2)
 
 
 
       wherein Cr, Ni, Mo, Cu, C, Si, Mn, and N represent the contents (% by mass) of the elements, and an element that is not contained is designated as 0. 
     
     
         2 . The high-strength seamless stainless steel pipe for oil well according to  claim 1 , wherein the high-strength seamless stainless steel pipe further contains, in addition to the composition, in terms of % by mass, one kind or two kinds selected from
 Cu: 0.05-3.0% and   W: 0.05-3.0%.   
     
     
         3 . The high-strength seamless stainless steel pipe for oil well according to  claim 1 , wherein the high-strength seamless stainless steel pipe further contains, in addition to the composition, in terms of % by mass, one kind or two or more kinds selected from
 Nb: 0.01-0.20%,   Zr: 0.01-0.20%,   B: 0.0005-0.01%,   REM: 0.0005-0.01%,   Ca: 0.0005-0.0025%,   Sn: 0.02-0.20%,   Ta: 0.01-0.1%, and   Mg: 0.002-0.01%.   
     
     
         4 . The high-strength seamless stainless steel pipe for oil well according to  claim 1 , wherein the high-strength seamless stainless steel pipe has an average prior austenite grain diameter of 40 μm or less. 
     
     
         5 . The high-strength seamless stainless steel pipe for oil well according to  claim 2 , wherein the high-strength seamless stainless steel pipe further contains, in addition to the composition, in terms of % by mass, one kind or two or more kinds selected from
 Nb: 0.01-0.20%,   Zr: 0.01-0.20%,   B: 0.0005-0.01%,   REM: 0.0005-0.01%,   Ca: 0.0005-0.0025%,   Sn: 0.02-0.20%,   Ta: 0.01-0.1%, and   Mg: 0.002-0.01%.   
     
     
         6 . The high-strength seamless stainless steel pipe for oil well according to  claim 2 , wherein the high-strength seamless stainless steel pipe has an average prior austenite grain diameter of 40 μm or less. 
     
     
         7 . The high-strength seamless stainless steel pipe for oil well according to  claim 3 , wherein the high-strength seamless stainless steel pipe has an average prior austenite grain diameter of 40 μm or less. 
     
     
         8 . The high-strength seamless stainless steel pipe for oil well according to  claim 5 , wherein the high-strength seamless stainless steel pipe has an average prior austenite grain diameter of 40 μm or less.