Steel material and oil-well steel pipe
View Patent ↗A steel material for oil country tubular goods that has a high strength and excellent SSC resistance is provided. The steel material according to this invention contains, in mass %, C: more than 0.45 to 0.65%, Si: 0.10 to 1.0%, Mn: 0.1 to 1.0%, P: 0.050% or less, S: 0.010% or less, Al: 0.01 to 0.1%, N: 0.01% or less, Cr: 0.1 to 2.5%, Mo: 0.25 to 5.0%, and Co: 0.05 to 5.0%, and satisfies expressions (1) and (2), and contains 90% or more of tempered martensite by volume ratio: C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15−Co/6+α≥0.70 (1) (3C+Mo+3Co)/(3Mn+Cr)≥1.0 (2) Effective B=B−11(N−Ti/3.4)/14 (3) where, α in expression (1) is 0.250 when effective B (mass %) defined by expression (3) is 0.0003% or more, and is 0 when effective B is less than 0.0003%.
1. A steel material comprising a chemical composition consisting of, in mass %,
C: more than 0.45 to 0.65%,
Si: 0.10 to 1.0%,
Mn: 0.1 to 1.0%,
P: 0.050% or less,
S: 0.010% or less,
Al: 0.01 to 0.1%,
N: 0.01% or less,
Cr: 0.1 to 2.5%,
Mo: 0.25 to 5.0%,
Co: 0.05 to 5.0%,
Cu: 0 to 0.50%,
Ni: 0 to 0.50%,
Ti: 0 to 0.030%,
Nb: 0 to 0.15%,
V: 0 to 0.5%,
B: 0 to 0.003%,
Ca: 0 to 0.004%,
Mg: 0 to 0.004%,
Zr: 0 to 0.004%, and
rare earth metal: 0 to 0.004%,
with a balance being Fe and impurities, and satisfying expressions (1) and (2),
wherein the microstructure comprises, by volume ratio, 90% or more of tempered martensite:
C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15−Co/6+α≥0.70 (1)
(3C+Mo+3Co)/(3Mn+Cr)≥1.0 (2)
Effective B=B−11(N−Ti/3.4)/14 (3)
where, α in expression (1) is 0.250 when effective B (mass %) defined by expression (3) is 0.0003% or more, and is 0 when the effective B is less than 0.0003%, where a content (mass %) of a corresponding element is substituted for each symbol of an element in expression (1) to expression (3).
2. The steel material according to claim 1 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
3. An oil-well steel pipe comprising a chemical composition according to claim 1 , and a wall thickness of 15 mm or more.
4. The steel material according to claim 1 , wherein the chemical composition contains one or more types of element selected from a group consisting of:
Cu: 0.02 to 0.50%, and
Ni: 0.02 to 0.50%.
5. The steel material according to claim 4 , wherein the chemical composition contains:
B: 0.0003 to 0.003%.
6. The steel material according to claim 5 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
7. The steel material according to claim 4 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
8. The steel material according to claim 4 , wherein the chemical composition contains one or more types of element selected from a group consisting of:
Ti: 0.003 to 0.030%,
Nb: 0.003 to 0.15%, and
V: 0.005 to 0.5%.
9. The steel material according to claim 8 , wherein the chemical composition contains:
B: 0.0003 to 0.003%.
10. The steel material according to claim 9 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
11. The steel material according to claim 8 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
12. The steel material according to claim 1 , wherein the chemical composition contains one or more types of element selected from a group consisting of:
Ti: 0.003 to 0.030%,
Nb: 0.003 to 0.15%, and
V: 0.005 to 0.5%.
13. The steel material according to claim 12 , wherein the chemical composition contains:
B: 0.0003 to 0.003%.
14. The steel material according to claim 13 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
15. The steel material according to claim 12 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.
16. The steel material according to claim 1 , wherein the chemical composition contains:
B: 0.0003 to 0.003%.
17. The steel material according to claim 16 , wherein the chemical composition contains, in mass %, one or more types of element selected from a group consisting of:
Ca: 0.0003 to 0.004%,
Mg: 0.0003 to 0.004%,
Zr: 0.0003 to 0.004%, and
rare earth metal: 0.0003 to 0.004%.