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 0.50 in. (12.5 mm) or less in thickness at time of heat treatment requiring a through-hardening steel capable of developing hardness as high as 35 HRC when properly hardened and tempered and also for parts of greater thickness requiring proportionately lower hardness.