A nanocarbide precipitation strengthened ultrahigh-strength, corrosionresistant, structural steel possesses a combination of strength and corrosionresistance comprising in combination, by weight, about: 0.1 to 0.3% carbon(C), 8 to 17% cobalt (Co), 0 to 5% nickel (Ni), 6 to 12% chromium (Cr), lessthan 1% silicon (Si), less than 0.5% manganese (Mn), and less than 0.15%copper (Cu), with additives selected from the group comprising about: lessthan 3% molybdenum (Mo), less than 0.3% niobium (Nb), less than 0.8% vanadium(V), less than 0.2% tantalum (Ta), less than 3% tungsten (W), and combinationsthereof, with additional additives selected from the group comprising about:less than 0.2% titanium (Ti), less than 0.2% lanthanum (La) or other rareearth elements, less than 0.15% zirconium (Zr), less than 0.005% boron (B),and combinations thereof, impurities of less than about: 0.02% sulfur (S),0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen (N), theremainder substantially iron (Fe), incidental elements and other impurities.The alloy is strengthened by nanometer scale M2C carbides within a fine lathmartensite matrix from which enhanced chemical partitioning of Cr to thesurface provides a stable oxide passivating film for corrosion resistance. Thealloy, with a UTS in excess of 280 ksi, is useful for applications such asaircraft landing gear, machinery and tools used in hostile environments, andother applications wherein ultrahigh-strength, corrosion resistant, structuralsteel alloys are desired.
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