Seamless steel pipe suitable for use in sour environment
The seamless steel pipe according to the present disclosure includes a base material and a decarburized layer formed on the surface of the base material. The chemical composition of the base material consists of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.01 to 1.00%, P: 0.0300% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.20%, Mo: 0.30 to 1.50%, Ti: 0.002 to 0.050%, V: 0.01 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0001 to 0.0050%, N: 0.0100% or less, O: 0.0050% or less, and with the balance being Fe and impurities. The base material has a yield strength of 655 MPa or more, and a yield ratio of 85.0% or more. The decarburized layer has a depth of 150 μm or less.
1. A seamless steel pipe, comprising a base material and a decarburized layer formed on a surface of the base material, wherein
a chemical composition of the base material consists of, in mass %,
C: 0.20 to 0.50%,
Si: 0.05 to 0.50%,
Mn: 0.01 to 1.00%,
P: 0.0300% or less,
S: 0.0100% or less,
Al: 0.005 to 0.100%,
Cr: 0.30 to 1.20%,
Mo: 0.30 to 1.50%,
Ti: 0.002 to 0.050%,
V: 0.01 to 0.30%,
Nb: 0.002 to 0.100%,
B: 0.0001 to 0.0050%,
N: 0.0100% or less,
O: 0.0050% or less,
Ca: 0 to 0.0100%,
Mg: 0 to 0.0100%,
Zr: 0 to 0.0100%,
rare earth metal: 0 to 0.0100%,
Co: 0 to 0.50%,
W: 0 to 0.50%,
Cu: 0 to 0.50%,
Ni: 0 to 0.50%, and
with the balance being Fe and impurities, wherein
a yield strength of the base material is 655 MPa or more,
a yield ratio of the base material is 85.0% or more, wherein
the decarburized layer has a depth of 15 to 150 μm.
2. The seamless steel pipe according to claim 1 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Ca: 0.0001 to 0.0100%,
Mg: 0.0001 to 0.0100%,
Zr: 0.0001 to 0.0100%, and
rare earth metal: 0.0001 to 0.0100%.
3. The seamless steel pipe according to claim 2 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Co: 0.02 to 0.50%, and
W: 0.02 to 0.50%.
4. The seamless steel pipe according to claim 3 , wherein
the decarburized layer has a depth of 15 to 130 μm.
5. The seamless steel pipe according to claim 3 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Cu: 0.02 to 0.50%, and
Ni: 0.02 to 0.50%.
6. The seamless steel pipe according to claim 5 , wherein
the decarburized layer has a depth of 15 to 130 μm.
7. The seamless steel pipe according to claim 2 , wherein
the decarburized layer has a depth of 15 to 130 μm.
8. The seamless steel pipe according to claim 2 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Cu: 0.02 to 0.50%, and
Ni: 0.02 to 0.50%.
9. The seamless steel pipe according to claim 8 , wherein
the decarburized layer has a depth of 15 to 130 μm.
10. The seamless steel pipe according to claim 1 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Co: 0.02 to 0.50%, and
W: 0.02 to 0.50%.
11. The seamless steel pipe according to claim 10 , wherein
the decarburized layer has a depth of 15 to 130 μm.
12. The seamless steel pipe according to claim 10 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Cu: 0.02 to 0.50%, and
Ni: 0.02 to 0.50%.
13. The seamless steel pipe according to claim 12 , wherein
the decarburized layer has a depth of 15 to 130 μm.
14. The seamless steel pipe according to claim 1 , wherein
the chemical composition of the base material contains one or more elements selected from the group consisting of, in mass %:
Cu: 0.02 to 0.50%, and
Ni: 0.02 to 0.50%.
15. The seamless steel pipe according to claim 14 , wherein
the decarburized layer has a depth of 15 to 130 μm.
16. The seamless steel pipe according to claim 1 , wherein
the decarburized layer has a depth of 15 to 130 μm.
17. The seamless steel pipe according to claim 1 , wherein
the seamless steel pipe is an oil-well steel pipe.