a nanocarbide precipitation strengthened ultrahigh - strength , corrosion resistant , structural steel possesses a combination of strength and corrosion resistance comprising in combination , by weight , about : 0 . 1 to 0 . 3 % carbon , 8 to 17 % cobalt , 0 to 10 % nickel , 6 to 12 % chromium , less than 1 % silicon , less than 0 . 5 % manganese , and less than 0 . 15 % copper , with additives selected from the group comprising about : less than 3 % molybdenum , less than 0 . 3 % niobium , less than 0 . 8 % vanadium , less than 0 . 2 % tantalum , less than 3 % tungsten , and combinations thereof , with additional additives selected from the group comprising about : less than 0 . 2 % titanium , less than 0 . 2 % lanthanum or other rare earth elements , less than 0 . 15 % zirconium , less than 0 . 005 % boron , and combinations thereof , impurities of less than about : 0 . 02 % sulfur , 0 . 012 % phosphorus , 0 . 015 % oxygen and 0 . 015 % nitrogen , the remainder substantially iron , incidental elements and other impurities . the alloy is strengthened by nanometer scale mzc carbides within a fine lath martensite matrix from which enhanced chemical partitioning of cr to the surface provides a stable oxide passivating film for 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 .