ATI 800™ (UNS N08800), ATI 800H™ (UNS N08810), and ATI 800AT™ (UNS N08811) alloys are nickel-iron-chromium alloys designed to resist oxidation and carburization at elevated temperatures. The nickel content, 32%, makes the alloys highly resistant both to chloride stress-corrosion cracking and to embrittlement from precipitation of sigma phase. The general corrosion resistance is excellent. In the solution annealed condition, the ATI 800H™ and ATI 800 AT™ alloys have superior creep and stress rupture properties. All three versions of the basic ATI 800™ alloy have been approved as materials of construction under ASME Boiler and Pressure Vessel Code, Section I-Power Boilers, Section III-Nuclear Vessels, and Section VIII-Unfired Pressure Vessels.

ATI 800™, ATI 800H™ and ATI 800AT™ alloys are identical except for the higher level of carbon (0.05 to 0.10 percent) in the ATI 800H™ alloy, and the addition of up to 1.00 percent aluminum + titanium in the ATI 800 AT™ alloy. The ATI 800™ alloy is normally used in service at temperatures to approximately 1100°F (593°C). The ATI 800H™ and ATI 800 AT™ alloys are normally used above approximately 1100°F where resistance to creep and stress rupture is required.