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: These products have been used typically 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@ but usage is not limited to such applications. This steel may become notch-sensitive when heat treated to a tensile strength level of 240 ksi (1655 MPa) or higher.