High strength, high fatigue structural steel

A high strength, fatigue-resistant steel alloy which is substantially free of titanium nitride and titanium carbonitride precipitates, the steel alloy consisting essentially of:

• about 10 to about 18 weight percent nickel;
• about 8 to about 16 weight percent cobalt;
• about 1 to about 5 weight percent molybdenum;
• about 0.5 to about 1.3 weight percent aluminum, at least a portion of the aluminum forming intermetallic precipitates with at least a portion of the nickel;
• about 1 to about 3 weight percent chromium;
• about 0.15 to about 0.25 weight percent carbon, at least a portion of the carbon forming uniformly dispersed carbides with at least a portion of the molybdenum and at least a portion of the chromium;
• less than about 0.10 weight percent titanium;
• and
• the balance being essentially iron with trace amounts of ordinarily present elements, including niobium, vanadium and tungsten;
• whereby the combination of the intermetallic precipitates formed by the aluminum, and the carbides formed by the carbon, chromium and molybdenum within the steel alloy provide enhanced yield strength of the steel alloy, and whereby the fatigue properties of the steel alloy are enhanced by the substantial absence of titanium which substantially precludes the formation of titanium nitride and titanium carbonitride precipitates within the steel alloy.

A high strength, fatigue-resistant article formed from a steel alloy which is substantially free of titanium nitride and titanium carbonitride precipitates, the steel alloy comprising:

• about 10 to about 18 weight percent nickel;
• about 8 to about 16 weight percent cobalt;
• about 1 to about 5 weight percent molybdenum;
• about 0.5 to about 1.3 weight percent aluminum;
• about 1 to about 3 weight percent chromium;
• up to about 0.3 weight percent carbon;
• less than about 0.10 weight percent titanium;
• and
• the balance being essentially iron with trace amounts of ordinarily present elements;
• whereby the substantial absence of titanium within the steel alloy enhances the fatigue properties of the article by substantially precluding the formation of titanium nitride and titanium carbonitride precipitates within the article, and whereby the presence of aluminum, chromium, and molybdenum within the steel alloy provide duplex strengthening of the article through the formation of intermetallic precipitates and a fine dispersion of carbides.