Form: This specification covers a premium aircraft-quality alloy steel in the form of bars@ forgings@ and forging stock. Application: These products have been used typically for parts requiring a combination of high strength@ high toughness@ and weldability@ but usage is not limited to such applications. Product after heat treatment should attain a minimum tensile strength of 290 ksi (1999 MPa) and yield strength of 245 ksi (1689 MPa).