Form This specification covers a premium aircraft-quality@ low-alloy steel in the form of sheet@ strip@ and plate. Application These products have been used typically for parts@ that may be welded during fabrication@ requiring through-hardening to high strength levels and that may be used at operational stress levels approaching the yield strength@ but usage is not limited to such applications. Steel may become notch sensitive when heat treated to a tensile strength level of 240 ksi (1655 MPa) or higher.