High-strength steel material for oil well and oil well pipes
There is provided a high-strength steel material for oil well having a chemical composition consisting, by mass percent, of C: 0.60-1.4%, Si: 0.05-1.00%, Mn: 12-25%, Al: 0.003-0.06%, P: ≤0.03%, S: ≤0.03%, N: <0.1%, Cr: ≥0% and <5.0%, Mo: ≥0% and <3.0%, Cu: ≤0% and <1.0%, Ni: ≥0% and <1.0%, V: 0-0.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: ≥0% and <0.005%, Mg: ≥0% and <0.005%, B: 0-0.015%, the balance: Fe and impurities, wherein Nieq [=Ni+30C+0.5Mn] is 27.5 or higher, a metal micro-structure is a structure consisting mainly of an FCC structure, a total volume fraction of ferrite and α′ martensite is less than 0.10%, and a yield strength is 862 MPa or higher.
1. A high-strength steel material for oil well having a chemical composition consisting, by mass percent, of
C: 0.85 to 1.4%,
Si: 0.05 to 1.00%,
Mn: 12 to 25%,
Al: 0.003 to 0.06%,
P: 0.03% or less,
S: 0.03% or less,
N: less than 0.1%,
V: 0 to 0.5%,
Nb: 0 to 0.5%,
Ta: 0 to 0.5%,
Ti: 0 to 0.5%,
Zr: 0 to 0.5%,
Ca: 0% or more and less than 0.005%,
Mg: 0% or more and less than 0.005%,
B: 0 to 0.015%, and
one or more elements selected from
Cr: 0.1% or more and less than 5.0%,
Mo: 0.1% or more and less than 3.0%,
Cu: 0.1% or more and less than 1.0%, and
Ni: 0.1% or more and less than 1.0%, and
the balance: Fe and impurities,
wherein Nieq defined by the following Formula (i) is 32.7 or higher,
a metal micro-structure is a structure consisting of
a total volume fraction of ferrite and α′ martensite: less than 0.10%,
a volume fraction of ε martensite: 10% or less,
the balance: an FCC structure, and
a yield strength is 862 MPa or higher;
the high-strength steel material for oil well, has
a) sulfide stress-corrosion cracking resistance (SSC resistance) defined as having no rupture after being immersed in Solution A for at 24° C. for 336 hours,
b) stress corrosion cracking resistance (SCC resistance) defined as having no rupture after being immersed in Solution A for at 60° C. for 336 hours, and
c) a corrosion rate of 1.5 g/m 2 h or lower after being immersed in Solution A for at 24° C. for 336 hours,
wherein solution A is a 5% NaCl+0.5% CH 3 COOH aqueous solution, 1-bar H 2 S saturated, as specified in NACE TM0177-2005;
Nieq=Ni+30C+0.5Mn (i)
where, each symbol Ni, C and Mn in the formula represents a content of the element contained in the high-strength steel material by mass percent, and is made zero in a case where the element is not contained.
2. A high-strength steel material for oil well having a chemical composition consisting, by mass percent, of
C: 0.85 to 1.4%,
Si: 0.05 to 1.00%,
Mn: 12 to 25%,
Al: 0.003 to 0.06%,
P: 0.03% or less,
S: 0.03% or less,
N: less than 0.1%, and
one or more elements selected from
V: 0.005 to 0.5%,
Nb: 0.005 to 0.5%,
Ta: 0.005 to 0.5%,
Ti: 0.005 to 0.5%,
Zr: 0.005 to 0.5%,
Ca: 0.0003% or more and less than 0.005%,
Mg: 0.0003% or more and less than 0.005% and
B: 0.0001 to 0.015%, and
one or more elements selected from
Cr: 0.1% or more and less than 5.0%,
Mo: 0.1% or more and less than 3.0%,
Cu: 0.1% or more and less than 1.0%, and
Ni: 0.1% or more and less than 1.0%, and
the balance: Fe and impurities,
wherein Nieq defined by the following Formula (i) is 32.7 or higher,
a metal micro-structure is a structure consisting of
a total volume fraction of ferrite and α′ martensite: less than 0.10%,
a volume fraction of ε martensite: 10% or less,
the balance: an FCC structure, and
a yield strength is 862 MPa or higher;
the high-strength steel material for oil well, has
a) sulfide stress-corrosion cracking resistance (SSC resistance) defined as having no rupture after being immersed in Solution A for at 24° C. for 336 hours,
b) stress corrosion cracking resistance (SCC resistance) defined as having no rupture after being immersed in Solution A for at 60° C. for 336 hours, and
c) a corrosion rate of 1.5 g/m 2 h or lower after being immersed in Solution A for at 24° C. for 336 hours,
wherein solution A is a 5% NaCl+0.5% CH 3 COOH aqueous solution, 1-bar H 2 S saturated, as specified in NACE TM0177-2005;
Nieq=Ni+30C+0.5Mn (i)
where, each symbol Ni, C and Mn in the formula represents a content of the element contained in the high-strength steel material by mass percent, and is made zero in a case where the element is not contained.
3. The high-strength steel material for oil well according to claim 1 , wherein the yield strength is 965 MPa or higher.
4. Oil well pipes, which are comprised of the high-strength steel material for oil well according to claim 1 .
5. Oil well pipes, which are comprised of the high-strength steel material for oil well according to claim 3 .
6. Oil well pipes, which are comprised of the high-strength steel material for oil well according to claim 2 .