ATI S240 alloy (UNS S11900) is a martensitic precipitation-hardening stainless steel with tensile strength of 240 ksi (1,655 MPa), high fracture toughness, and good corrosion and stress corrosion cracking resistance. ATI S240 alloy has strength and toughness properties that are comparable to other commercial steels in this class, but it also offers:

• Simple processing; can be thermal mechanically processed similarly to other precipitation-hardened stainless steels such as 13-8 and 15-5 alloys, and does not require "deep freeze" or cryogenic treatment to achieve the high tensile strength.

• Improved corrosion and stress corrosion cracking resistance compared with other steels of similar strength

• Lower raw materials and processing costs (no cobalt; no complicated heat treatment)

Good transverse toughness properties are achieved by tight chemical composition control, low carbon content, and double vacuum melting. The alloy is produced by vacuum induction melting (VIM), followed by vacuum arc remelting (VAR). This melt practice ensures excellent macro- and micro-cleanliness, and tight compositional control. The strengthening mechanism (precipitation hardening in a martensitic matrix) makes it possible to achieve uniform strengthening in heavy sections. Strength and ductility levels can be tailored to the application by varying the aging temperature. ATI S240 alloy is available as ingot, billet, block, round bar, rolled shapes and rectangles, rolled and drawn rod, and wire.