A nanocarbide precipitation strengthenedultrahigh-strength, corrosion resistant, structural steelpossesses a combination of strength and corrosion resistancecomprising in combination, by weight, about: 0.1 to 0.3%carbon (C), 8 to 17% cobalt (Co), 5 to 10% nickel (Nl), 6 to12% chromium (Cr), less than 1% silicon (Sl), less than 0.5%manganese (Mn), and less than 0.15% copper (Cu), withadditives selected from the group comprising about: lessthan 3% molybdenum (Mo), less than 0.3% niobium (Nb), lessthan 0.8% vanadium (V), less than 0.2% tantalum (Ta), lessthan 3% tungsten (W), and combinations thereof, withadditional additives selected from the group comprisingabout: less than 0.2% titanium (Ti), less than 0.2%lanthanum (La) or other rare earth elements, less than 0.15%zirconium (Zr), less than 0.005% boron (B), and combinationsthereof, impurities of less than about: 0.02% sulfur (S),0.012% phosphorus (P), 0.015% oxygen (O) and 0.015% nitrogen(N), the remainder substantially iron (Fe), incidentalelements and other impurities. The alloy is strengthened bynanometer scale MZC carbides within a fine lath martensitematrix from which enhanced chemical partitioning of Cr tothe surface provides a stable oxide passivating film forcorrosion resistance. The alloy, with a UTS in excess of280 ksi, is useful for applications such as aircraft landinggear, machinery and tools used in hostile environments, andother applications wherein ultrahigh-strength, corrosionresistant, structural steel alloys are desired.
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