Oil well pipe for expandable tubular applications excellent in post-expansion toughness and method of manufacturing the same

Abstract

The invention provides an oil well pipe for expandable tubular applications excellent in post-expansion toughness and a method of manufacturing the oil well pipe. The oil well pipe for expandable tubular applications comprises, in mass %, C: 0.03 to 0.14%, Si: 0.8% or less, Mn: 0.3 to 2.5%, P: 0.03% or less, S: 0.01% or less, Ti: 0.005 to 0.03%, Al: 0.1% or less, N: 0.001 to 0.01%, B: 0.0005 to 0.003%, optionally comprises one or move of Nb, Ni, Mo, Cr, Cu and V, and further optionally comprises one or both of Ca and REM, satisfies the relationship A=2.7C+0.4Si+Mn+0.45Ni+0.45Cu+0.8Cr+2Mo≧1.8, has a balance of iron and unavoidable impurities, and is formed of tempered martensite structure. The manufacturing method according to the invention is characterized in subjecting a steel stock pipe of the foregoing composition to hardening from a temperature range of Ac 3 point+30° C. or greater and to tempering at a temperature of 350 to 720° C.

1 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness, which oil well pipe for expandable tubular applications comprises, in mass %:
 C: 0.03 to 0.14%,   Si: 0.8% or less,   Mn: 0.3 to 2.5%,   P: 0.03% or less,   S: 0.01% or less,   Ti: 0.005 to 0.03%,   Al: 0.1% or less,   N: 0.001 to 0.01%,   B: 0.0005 to 0.003%, and   the balance of iron and unavoidable impurities,   where A represented by Expression (1) below has a value of 1.8 or greater; and   is formed of tempered martensite structure:
   A=2.7C+0.4Si+Mn+0.45Ni+0.45Cu+0.8Cr+2Mo  (1), 
   where C, Si, Mn, Ni, Cu, Cr and Mo represent contents of the respective elements (in mass %).   
   
   
       2 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 1 , further comprising, in mass %, one or more of:
 Nb: 0.01 to 0.3%,   Ni: 0.1 to 1.0%,   Mo: 0.05 to 0.6%,   Cr: 0.1 to 1.0%,   Cu: 0.1 to 1.0%, and   V: 0.01 to 0.3%.   
   
   
       3 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 1 , further comprising, in mass %, one or both of:
 Ca: 0.001 to 0.01% and   REM: 0.002 to 0.02%.   
   
   
       4 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 1 , wherein S content of the oil well pipe for expandable tubular applications is 0.003 mass % or less. 
   
   
       5 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 1 , wherein the oil well pipe for expandable tubular applications is manufactured by hardening and tempering an electric-resistance-welded steel pipe. 
   
   
       6 . An oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 1 , wherein a minimum wall thickness of the oil well pipe for expandable tubular applications is not less than 95% of an average wall thickness thereof. 
   
   
       7 . A method of manufacturing an oil well pipe for expandable tubular applications excellent in post-expansion toughness, comprising:
 subjecting a steel stock pipe to hardening from a temperature range of Ac 3  point+30° C. or greater and to tempering at a temperature of 350 to 720° C., thereby giving it a tempered martensite structure,   the steel stock pipe comprising, in mass %,   C: 0.03 to 0.14%,   Si: 0.8% or less,   Mn: 0.3 to 2.5%,   P: 0.03% or less,   S: 0.01% or less,   Ti: 0.005 to 0.03%,   Al: 0.1% or less,   N: 0.001 to 0.01%,   B: 0.0005 to 0.003%, and   the balance of iron and unavoidable impurities,   where A represented by Expression (1) below has a value of 1.8 or greater; and   being formed of tempered martensite structure:
   A=2.7C+0.4Si+Mn+0.45Ni+0.45Cu+0.8Cr+2Mo  (1), 
   where C, Si, Mn, Ni, Cu, Cr and Mo represent contents of the respective elements (in mass %).   
   
   
       8 . A method of manufacturing an oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 7 , wherein the steel stock pipe further comprises, in mass %, one or more of:
 Nb: 0.01 to 0.3%,   Ni: 0.1 to 1.0%,   Mo: 0.05 to 0.6%,   Cr: 0.1 to 1.0%,   Cu: 0.1 to 1.0%, and   V: 0.01 to 0.3%, and   satisfies A=2.7C+0.4Si+Mn+0.45Ni+0.45Cu+0.8Cr+2Mo≧1.8.   
   
   
       9 . A method of manufacturing an oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 7 , wherein the steel stock pipe further comprises, in mass %, one or both of:
 Ca: 0.001 to 0.01% and   REM: 0.002 to 0.02%.   
   
   
       10 . A method of manufacturing an oil well pipe for expandable tubular applications excellent in post-expansion toughness according to  claim 7 , wherein the steel stock pipe is an electric-resistance-welded steel pipe.