Form: This Specification covers an aircraft-quality@ low-alloy steel in the form of bars@ forgings@ flash welded rings@ and stock for forging and flash welded rings. Application: Primarily for parts with section thickness of 0.50 in (12.7 mm) or less 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 for parts of greater thickness requiring proportionately lower hardness.