REX AA is the original 18-4-1 high-speed steel, having been first introduced in the early 1990s. Melting practice and processing have been improved since that time, but nevertheless it is so properly balanced and the fundamental characteristics so sound, that it is still a standard, general-purpose high-speed steel. REX AA has a wide hardening range. This steel is less susceptible to soft skin during hardening than other types and has good red hardness and toughness. Among its many applications are boring tools, broaches, cutters, drills, gear cutters, lathe tools and woodworking knives. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on forming, heat treating, and machining. Filing Code: TS-426. Producer or source: Crucible Specialty Metals Division, Colt Industries.