NANO-PRECIPITATION STRENGTHENED ULTRA-HIGH STRENGTH CORROSION RESISTANT STRUCTURAL STEELS

A nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steel possesses a combination of strength and corrosio n resistance comprising in combination, by weight, about : 0.1 to 0.5 % carbon (C), about 8 to 17 % cobalt (Co), 0 to about 10 % nickel (Ni), about 6 to 12 % chromium (Cr), less than about 1 % silicon (Si), less than about 0.5 % manganese (Mn), and less than about 0.15 % copper (Cu), with additives selected from the group comprising about : less than 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 combinations thereof, with additional additives selected from the group comprising about : 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 combinatio ns thereof, impurities of less than about : 0.02 % sulfur (S), 0.012 % phosphoru s (P), 0.015 % oxygen (O) and 0.015 % nitrogen (N), the remainder substantiall y iron (Fe), incidental elements and other impurities. The alloy is strengthen ed by nanometer scale M2C carbides within a fine lath martensite matrix from which enhanced chemical partitioning of Cr to the surface provides a stable oxide passivating filmfor corrosion resistance. The alloy, with a UTS in excess of 280 ksi, is useful for applications such as aircraft landing gear, machinery and tools used in hostile environments, and other applications wherein ultrahigh-strength, corrosion resistant, structural steel alloys are desired.