Form This specification covers an aircraft-quality@ low-alloy steel in the form of bars@ forgings@ flash-welded rings@ and stock for forging or flash-welded rings. Application These products have been used typically for parts 0.50 inch (12.7 mm) and under in nominal section thickness at time of heat treatment@ requiring a through-hardened steel capable of developing hardness as high as 50 HRC when appropriately heat treated and for parts of greater thickness but requiring proportionately lower hardness@ 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.