Stainless steel for oil wells and stainless steel pipe for oil wells
View Patent ↗A stainless steel for oil wells which has excellent high-temperature corrosion resistance and can stably obtain a strength of not less than 758 MPa is provided. The stainless steel for oil wells contains, by masse, C: not more than 0.05%, Si: not more than 1.0%, Mn: 0.01 to 1.0%, P: not more than 0.05%, S: less than 0.002%, Cr: 16 to 18%, Mo: 1.8 to 3%, Cu: 1.0 to 3.5%, Ni: 3.0 to 5.5%, Co: 0.01 to 1.0%, Al: 0.001 to 0.1%, O: not more than 0.05%, and N: not more than 0.05%, the balance being Fe and impurities, and satisfies Formulas (1) and (2): Cr+4Ni+3Mo+2Cu≧44 (1) Cr+3Ni+4Mo+2Cu/3≦46 (2) where each symbol of element in Formulas (1) and (2) is substituted by the content (mass %) of a corresponding element.
1. A stainless steel for oil wells comprising, by mass %,
C: not more than 0.05%,
Si: not more than 1.0%,
Mn: 0.01 to 1.0%,
P: not more than 0.05%,
S: less than 0.002%,
Cr: 16 to 18%,
Mo: 1.8 to 3%,
Cu: 1.0 to 3.5%,
Ni: 3.0 to 5.5%,
Co: 0.01 to 1.0%,
Al: 0.001 to 0.1%,
O: not more than 0.05%, and
N: not more than 0.05%, the balance being Fe and impurities, and satisfying Formulas (1) and (2):
Cr+4Ni+3Mo+2Cu≧44 (1)
Cr+3Ni+4Mo+2Cu/3≦46 (2)
where each symbol of element in Formulas (1) and (2) is substituted by a content, in mass %, of a corresponding element.
2. The stainless steel for oil wells according to claim 1 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
V: not more than 0.3%,
Ti: not more than 0.3%,
Nb: not more than 0.3%, and
Zr: not more than 0.3%.
3. The stainless steel for oil wells according to claim 1 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
W: not more than 1.0%, and
rare earth metal (REM): not more than 0.3%.
4. The stainless steel for oil wells according to claim 2 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
W: not more than 1.0%, and
rare earth metal (REM): not more than 0.3%.
5. The stainless steel for oil wells according to claim 1 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
Ca: not more than 0.01%, and
B: not more than 0.01%.
6. The stainless steel for oil wells according to claim 2 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
Ca: not more than 0.01%, and
B: not more than 0.01%.
7. The stainless steel for oil wells according to claim 3 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
Ca: not more than 0.01%, and
B: not more than 0.01%.
8. The stainless steel for oil wells according to claim 4 , wherein
the stainless steel for oil wells contains, in place of some of Fe, one or more kinds of elements selected from the group consisting of
Ca: not more than 0.01%, and
B: not more than 0.01%.
9. The stainless steel for oil wells according to claim 1 , wherein
a metal micro-structure of the stainless steel for oil wells contains, by volume ratio, not less than 10% and less than 60% of ferrite phase, not more than 10% of retained austenite phase, and not less than 40% of martensite phase.
10. The stainless steel for oil wells according to any one of claims 1 to 8 , wherein
the stainless steel for oil wells has a yield strength of not less than 862 MPa.
11. The stainless steel for oil wells according to claim 9 , wherein
the stainless steel for oil wells has a yield strength of not less than 862 MPa.
12. An oil well pipe manufactured from the stainless steel for oil wells according to claim 1 .
13. An oil well pipe manufactured from the stainless steel for oil wells according to claim 9 .
14. An oil well pipe manufactured from the stainless steel for oil wells according to claim 10 .
15. An oil well pipe manufactured from the stainless steel for oil wells according to claim 11 .