DH 21 is a hot work die steel with excellent heat check resistance, excellent mechanical properties at high temperatures, excellent temper resistance, excellent oxidation resistance, and excellent nitriding properties. The alloy was developed to extend the life of aluminum die cast molds. This datasheet provides information on composition, physical properties, and hardness. It also includes information on heat treating. Filing Code: TS-695. Producer or source: International Mold Steel Inc.