Form: This specification covers a nitriding grade of aircraft-quality low-alloy steel in the form of heat treated bars and forgings@ and of forging stock. Application: Primarily for nitrided parts requiring high surface hardness@ resistance to heat@ and less distortion than parts made from steel requiring quenching to case harden. This steel may be case hardened in dissociated ammonia gas to give a minimum case hardness of 900 HV.