High strength, tough alloy steel

Claim 1

A high strength, tough alloy steel consisting essentially of from about 0.20 to about 0.35 weight % carbon, about 3.0 to 4.5 weight % chromium, and at least 1 weight % of at least one other substitutional alloying element selected from the group consisting of nickel, manganese, molybdenum, cobalt, silicon, aluminum, and mixtures thereof, and the remainder iron, said steel being characterized by a microstructure of uniformly dispersed martensite crystals, the major portion of which are in dislocated form, said martensite crystals being formed by martensite transformation from austenite, said steel including a maximum alloy content below that which lowers the martensite transformation temperature to below about 250° C., said steel being characterized by a yield strength of at least about 180,000 psi, a room temperature Charpy impact energy of at least about 19 ft-lbs. and a plane strain fracture toughness (K Ic ) of at least about 80 KSI-in 1/2 , said martensite crystals being separated from each other by substantially continuous thin boundary films of stabilized retained austenite essentially free of carbides, and including autotempered carbides dispersed in said martensite.