Form This specification covers a premium aircraft-quality@ low-alloy steel in the form of bars@ forgings@ and forging stock. Application These products have been used typically for parts requiring through hardening to a minimum hardness of 50 HRC in section thicknesses up to 12 inches (305 mm) with a combination of high strength@ fatigue resistance@ ductility@ and thermal stability for operation in the range of -100 to +1000 ??(-73 to +538 ??@ but usage is not limited to such applications. Certain design and processing procedures may cause these products to become susceptible to stress-corrosion cracking after heat treatment; ARP1110 recommends practices to minimize such conditions.