Alloy for mud motor shaft applications with high strength, high impact toughness and excellent fatigue life
A steel alloy is disclosed that provides a unique combination of strength, toughness, and fatigue life. The steel alloy has the following composition in weight percent: C about 0.15 to about 0.30 Mn about 1.7 to about 2.3 Si about 0.7 to about 1.1 Cr about 1.85 to about 2.35 Ni about 0.5 to about 0.9 Mo+½W about 0.1 to about 0.3 Cu about 0.3 to about 0.7 V+ 5/9×Nb about 0.2 to about 0.5. The balance of the alloy is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy. A hardened and tempered steel article made from the alloy is also disclosed.
1. A hardened and tempered steel article formed from a steel alloy consisting essentially of, in weight percent, about
C about 0.15 to about 0.30
Mn about 1.7 to about 2.3
Si about 0.7 to about 1.1
Cr about 1.85 to about 2.35
Ni about 0.5 to about 0.9
Mo+½W about 0.1 to about 0.3
Cu about 0.3 to about 0.7
V+ 5/9×Nb about 0.2 to about 0.5
and the balance is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy, said article providing a yield strength of at least about 180 ksi and a Charpy V-notch impact energy of at least about 25 ft-lbs wherein the article comprises a shaft or a constant velocity joint for a transmission drive unit of a drilling mud motor.
2. The steel article claimed in claim 1 wherein the alloy contains at least about 0.18% carbon.
3. The steel article claimed in claim 2 wherein the alloy contains not more than about 0.27% carbon.
4. The steel article claimed in claim 1 wherein the alloy contains at least about 1.8% manganese.
5. The steel article claimed in claim 4 wherein the alloy contains not more than about 2.2% manganese.
6. The steel article claimed in claim 1 wherein the alloy contains at least about 0.8% silicon.
7. The steel article claimed in claim 6 wherein the alloy contains not more than about 1.0% silicon.
8. The steel article claimed in claim 1 wherein the alloy contains at least about 1.95% chromium.
9. The steel article claimed in claim 8 wherein the alloy contains not more than about 2.25% chromium.
10. The steel article claimed in claim 1 wherein the alloy contains at least about 0.6% nickel.
11. The steel article claimed in claim 10 wherein the alloy contains not more than about 0.8% nickel.
12. The steel article claimed in claim 1 wherein the alloy contains at least about 0.15% (Mo+½W).
13. The steel article claimed in claim 12 wherein the alloy contains not more than about 0.25% (Mo+½W).
14. The steel article claimed in claim 1 wherein the alloy contains at least about 0.4% copper.
15. The steel article claimed claim 14 wherein the alloy contains not more than about 0.6% copper.
16. The steel article claimed in claim 1 wherein the alloy contains at least about 0.25% (V+ 5/9Nb).
17. The steel article claimed in claim 16 wherein the alloy contains not more than about 0.45% (V+ 5/9Nb).
18. The steel article claimed in claim 1 wherein the alloy consists essentially of
C about 0.21 to about 0.24
Mn about 1.95 to about 2.05
Si about 0.85 to about 0.95
Cr about 2.05 to about 2.15
Ni about 0.65 to about 0.75
Mo+½W about 0.18 to about 0.22
Cu about 0.45 to about 0.55
V+ 5/9×Nb about 0.30 to about 0.40
and the balance is iron, usual impurities, and residual amounts of other elements added during melting for deoxidizing and/or desulfurizing the alloy.