Steel material, oil-well steel pipe, and method for producing steel material

1. A steel material having:

a chemical composition consisting of, in mass %,

C: 0.26 to 0.50%,

Si: 0.05 to 0.50%,

Mn: 0.05 to 1.00%,

P: 0.025% or less,

S: 0.0100% or less,

Al: 0.005 to 0.100%,

Cr: 0.30 to 1.50%,

Mo: 0.25 to 1.50%,

Ti: 0.002 to 0.050%,

B: 0.0001 to 0.0050%,

N: 0.002 to 0.010%,

O: 0.0100% or less,

V: 0 to 0.30%,

Nb: 0 to 0.100%,

Ca: 0 to 0.0100%,

Mg: 0 to 0.0100%,

Zr: 0 to 0.0100%,

Co: 0 to 0.50%,

W: 0 to 0.50%,

Ni: 0 to 0.50%, and

Cu: 0 to 0.50%,

with the balance being Fe and impurities,

an amount of dissolved C within a range of 0.010 to 0.050 mass %,

a yield strength within a range of 862 to less than 965 MPa, and

a yield ratio of 90% or more.

2. The steel material according to claim 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

V: 0.01 to 0.30%, and

Nb: 0.002 to 0.100%.

3. The steel material according to claim 2 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ca: 0.0001 to 0.0100%,

Mg: 0.0001 to 0.0100%, and

Zr: 0.0001 to 0.0100%.

4. The steel material according to claim 3 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Co: 0.02 to 0.50%, and

W: 0.02 to 0.50%.

5. The steel material according claim 4 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

6. The steel material according claim 3 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

7. The steel material according to claim 2 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Co: 0.02 to 0.50%, and

W: 0.02 to 0.50%.

8. The steel material according claim 7 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

9. The steel material according claim 2 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

10. The steel material according to claim 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ca: 0.0001 to 0.0100%,

Mg: 0.0001 to 0.0100%, and

Zr: 0.0001 to 0.0100%.

11. The steel material according to claim 10 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Co: 0.02 to 0.50%, and

W: 0.02 to 0.50%.

12. The steel material according claim 11 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

13. The steel material according claim 10 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

14. The steel material according to claim 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Co: 0.02 to 0.50%, and

W: 0.02 to 0.50%.

15. The steel material according claim 14 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

16. The steel material according claim 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:

Ni: 0.02 to 0.50%, and

Cu: 0.01 to 0.50%.

17. The steel material according to claim 1 , wherein the steel material is in an oil-well steel pipe.

18. A method for producing the steel material according to claim 1 , comprising:

a preparation process of preparing an intermediate steel material containing a chemical composition consisting of, in mass % C: 0.26 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010%, O: 0.0100% or less, V: 0 to 0.30%, Nb: 0 to 0.100%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, Co: 0 to 0.50%, W: 0 to 0.50%, Ni: 0 to 0.50%, and Cu: 0 to 0.50%, with the balance being Fe and impurities,

a quenching process of, after the preparation process, cooling the intermediate steel material that is at a temperature in a range of 800 to 1000° C. at a cooling rate of 300° C./min or more; and

a tempering process of holding the intermediate steel material after quenching at a temperature in a range of 670° C. to an A c1 point for 10 to 180 minutes, and thereafter cooling the intermediate steel material at an average cooling rate in a temperature region from 600° C. to 200° C. of 5 to 100° C./sec.

19. The method for producing the steel material according to claim 18 , wherein the preparation process includes:

a starting material preparation process of preparing a starting material containing a chemical composition consisting of, in mass %, C: 0.25 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010%, O: 0.0100% or less, V: 0 to 0.30%, Nb: 0 to 0.100%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Zr: 0 to 0.0100%, Co: 0 to 0.50%, W: 0 to 0.50%, Ni: 0 to 0.50%, and Cu: 0 to 0.50%, with the balance being Fe and impurities, and

a hot working process of subjecting the starting material to hot working to produce an intermediate steel material.