Claims
- 1. A heat resistant steel which comprises, by mass %, C: 0.01-0.25%, Cr: 0.5-8%, V: 0.05-0.5%, Si: not more than 0.7%, Mn: not more than 1%, Mo: not more than 2.5%, W: not more than 5%, Nb: not more than 0.2%, N: not more than 0.1%, Ti: not more than 0.1%, Ta: not more than 0.2%, Cu: not more than 0.5%, Ni: not more than 0.5%, Co: not more than 0.5%, B: not more than 0.1%, Al: not more than 0.05%, Ca: not more than 0.01%, Mg: not more than 0.01%, Nd: not more than 0.01%, with Fe and impurities accounting for the balance, the chemical composition of which satisfies the relations (1) and (2) given below and in which, among precipitates inside grains, precipitates having an average diameter of not more than 30 nm are present at a density of not less than 1/μm3:
- 2. The heat resistant steel according to claim 1, wherein the amount of V among the metal elements constituting each grain boundary precipitate is not less than 2% by mass and the value of the ratio between the length of the minor axis and major axis “minor axis/major axis” thereof is not less than 0.5.
- 3. The heat resistant steel according to claim 1, wherein the chemical composition further satisfies the following relations (3) to (5):
- 4. The heat resistant steel according to claim 2, wherein the chemical composition further satisfies the following relations (3) to (5):
- 5. The heat resistant steel according to claims 2, wherein the contents of Mo and W give a value of Mo (%)+0.5W(%) of 0.01-2.5% and the content of Nb is 0.002-0.2%.
- 6. The heat resistant steel according to claims 3, wherein the contents of Mo and W give a value of Mo (%)+0.5W(%) of 0.01-2.5% and the content of Nb is 0.002-0.2%.
- 7. The heat resistant steel according to claims 4, wherein the contents of Mo and W give a value of Mo (%)+0.5W(%) of 0.01-2.5% and the content of Nb is 0.002-0.2%.
- 8. The heat resistant steel according to claim 4, wherein at least one of the following content requirements is satisfied: the N content of 0.001-0.1%, the Ti content of 0.001-0.1%, the Ta content of 0.002-0.2%, the Cu content of 0.01-0.5%, the Ni content of 0.01-0.5% and the Co content of 0.01-0.5%.
- 9. The heat resistant steel according to claim 4, wherein the content of B is 0.0001-0.1%.
- 10. The heat resistant steel according to claim 4, wherein the content of Al is 0.001-0.05%.
- 11. The heat resistant steel according to claim 4, wherein at least one of the following content requirements is satisfied: the Ca content of 0.0001-0.01%, the Mg content of 0.0001-0.01% and the Nd content of 0.0001-0.01%.
- 12. The heat resistant steel according to claim 7, wherein at least one of the following content requirements is satisfied: the N content of 0.001-0.1%, the Ti content of 0.001-0.1%, the Ta content of 0.002-0.2%, the Cu content of 0.01-0.5%, the Ni content of 0.01-0.5% and the Co content of 0.01-0.5%.
- 13. The heat resistant steel according to claim 7, wherein the content of B is 0.0001-0.1%.
- 14. The heat resistant steel according to claim 7, wherein the content of Al is 0.001-0.05%.
- 15. The heat resistant steel according to claim 7, wherein at least one of the following content requirements is satisfied: the Ca content of 0.0001-0.01%, the Mg content of 0.0001-0.01% and the Nd content of 0.0001-0.01%.
- 16. The heat resistant steel according to claims 7, wherein at least one of the following content requirements is satisfied: the N content of 0.001-0.1%, the Ti content of 0.001-0.1%, the Ta content of 0.002-0.2%, the Cu content of 0.01-0.5%, the Ni content of 0.01-0.5%, the Co content of 0.01-0.5%, and the contents of B and Al are 0.0001-0.1% and 0.001-0.05%, respectively, and further, at least one of the following content requirements is satisfied: the Ca content of 0.0001-0.01%, the Mg content of 0.0001-0.01% and the Nd content of 0.0001-0.01%.
- 17. The heat resistant steel according to claim 16, wherein the contents of the impurities P and S are not more than 0.03% by mass and not more than 0.015% by mass, respectively.
- 18. A heat resistant steel excellent in strength at elevated temperatures which comprises, by mass %, C: 0.01-0.25%, Cr: 0.5-8%, V: 0.05-0.5%, Si: not more than 0.7% and Mn: not more than 1%, with Fe and impurities accounting for the balance, in which coherent precipitates having an average diameter of not more than 30 nm as confirmable upon observation of a section of the steel using a transmission electron microscope at an accelerating voltage of not lower than 100 kV are present inside grains at a density of not less than 1/μm3 and in which grain boundary precipitates of at least one species selected from among cementites, M7C3 carbides and M23C6 carbides are present at grain boundaries, the amount of V among the metal elements constituting each grain boundary precipitate being not less than 2% by mass, the value of the ratio between the length of the minor axis and major axis “minor axis/major axis” thereof being not less than 0.5.
- 19. The heat resistant steel according to claim 18, which further comprises an element or elements of one or more groups selected from the groups (a) to (g) listed below in lieu of part of Fe:
(a): one or more selected from among Nb: 0.002-0.2%, Ti: 0.001-0.1% and Ta: 0.002-0.2% by mass; (b): N: 0.001-0.1% by mass; (c): one or both of Mo: 0.01-2.5% and W: 0.02-5% by mass; (d): B: 0.0001-0.1% by mass; (e): one or more selected from among Co: 0.01-0.5%, Ni: 0.01-0.5% and Cu: 0.01-0.5% by mass; (f): Al: 0.001-0.05% by mass; and (g): one or both of Ca: 0.0001-0.01% and Mg: 0.0001-0.01% by mass.
- 20. The heat resistant steel according to claim 19, wherein the contents of P and S as impurities are not more than 0.03% and not more than 0.015% by mass, respectively.
Priority Claims (2)
Number |
Date |
Country |
Kind |
2000-093827 |
Mar 2000 |
JP |
|
2001-021239 |
Jan 2001 |
JP |
|
Parent Case Info
[0001] This application claims priority under 35 U.S.C. § §119 and/or 365 to Japanese Patent Application Nos. 2000-093827 and 2001-021239 filed in Japan on Mar. 30, 2000 and Jan. 30, 2001, respectively, the entire content of which is herein incorporated by reference.