Form: This specification covers a premium aircraft-quality@ low-alloy steel in the form of bars@ forgings@ mechanical tubing@ flash welded rings@ and stock for forging or flash welded rings. Application: Primarily for heat treated parts@ which may be welded during fabrication@ requiring through-hardening to high strength levels and which may be used at operational stress levels approaching the yield strength. Steel may become notch-sensitive when heat treated to a tensile strength level of 240@000 psi (1655 MPa) or higher.