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@ with section thickness of 0.375 inch (9.50 mm) and under at the time of heat treatment@ requiring a through-hardening steel capable of developing hardness as high as 50 HRC when properly hardened and tempered and also parts of greater thickness but requiring proportionately lower hardness@ but usage is not limited to such applications.