ATI 13-8 Alloy (UNS S13800) is a precipitation hardening stainless steel that combines excellent strength, good toughness, and good general corrosion resistance. It is a through-hardening alloy, which allows it to be used in parts with large cross sections, where yield strengths in excess of 200 ksi (1,380 MPa) may be required. Good transverse toughness properties are achieved by tight chemical composition control (to prevent the formation of delta phase), low carbon content (to minimize grain boundary precipitation), and double vacuum melting (to reduce alloy segregation). Since the rate of cooling from the solution temperature is not critical, large cross sections can be air-cooled. This alloy is produced by a primary vacuum induction melt process (VIM), followed by a consumable vacuum arc remelting (VAR) step.

Typical uses are aircraft parts, rocket engine mounts, nuclear reactor parts, landing gear components, high performance shafts, and petrochemical parts that require high strength combined with good resistance to stress corrosion.