Abstract NAK 55 is a very clean steel for use in plastic and rubber molds were impact resistance is not critical in design. Its age-hardening gives very high strength and good wear resistance. Tight tolerance are obtained with consistent expansion and contraction properties. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on heat treating, machining, and joining. Filing Code: SA-481. Producer or source: International Mold Steels.