Alloy for Mud Motor Shaft Applications with High Strength, High Impact Toughness and Excellent Fatigue Life

A steel alloy having a unique combination of strength, toughness, and fatigue life, said alloy consisting essentially of, in weight percent,

• C
• about 0.15 to about 0.27
• Mn
• about 1.8 to about 2.2
• Si
• about 0.8 to about 1.0
• Cr
• about 1.95 to about 2.25
• Ni
• about 0.6 to about 0.8
• Mo + ½W
• about 0.15 to about 0.25
• Cu
• about 0.4 to about 0.6
• V + 5/9 × Nb
• about 0.25 to about 0.45
• and the balance 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 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.