BETHLEHEM AIR-4 is a medium alloy air-hardening tool steel having low deformation, high wear resistance and hardness, deep hardening properties and adequate toughness for severe service. It has excellent free-machining characteristics. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on forming, heat treating, machining, and joining. Filing Code: TS-129. Producer or source: Bethlehem Steel Corporation.