Form: This specification covers an aircraft-quality@ low-alloy steel in the form of sheet@ strip@ and plate. Application: Primarily for heat treated parts and structures that may require welding during fabrication. Product may be through-hardened to a minimum tensile strength of 180@000 psi (1240 MPa) in sections 0.375 in. (9.50 mm) and under in nominal thickness and proportionately lower strength in heavier section thicknesses.