Also referred to as Alloy 800, Incoloy 800 is a popular nickel-iron-chromium alloy. This alloy is commonly used in environments where the temperatures go up to 1100° F. The Incoloy 800/H/HT tends to be mostly used in environments where the aspect of oxidation and corrosion resistance is highly crucial.

Incoloy 800H basically has the same composition as Alloy 800, but enjoys a superior resistance to creep rupture in comparison to it. High temperature anneals of titanium, aluminum and carbon are added to the composition of Incoloy 800H, so as to enhance its strength. These additives aid in augmenting the temperature resistance capacity, durability, as well as properties of carbonization and oxidation resistance in the Incoloy 800H.

Incoloy 800 HT is known to have the same chemical makeup as Incoloy 800 H, but the quantities of titanium, aluminum, and carbon present in it tend to differ. While the carbon levels in Incoloy 800 H is greater, Incoloy 800 HT has more titanium and aluminum content. This factor provides 800 HT even superior resistances to the high-temperature environment.

The Incoloy 800 800H 800HT alloys tend to be used in extremely high temperature environments like heat-treating equipment, chemical and nuclear vessels and industrial furnaces. While typical stainless steels may creep and crack in such environments, Incoloy 800H and 800HT are able to stay perfectly stable.

The common forms in which Incoloy 800 800H 800HT are generally available

  • Sheet
  • Plate
  • Bar
  • Pipe and tube (welded and seamless)
  • Fittings ( which can include flanges, slip-ons, socket welds, elbows, tees, caps, crosses, reducers, etc)
  • Wire

Alloy 800 (UNS N08800) Chemical Composition, %

NiCrFeCAlTiAl+Ti
30.0-35.019.0-23.039.5 min.10 max.15-.60.15-.60.30-1.20

Alloy 800H (UNS N08810) Chemical Composition, %

NiCrFeCAlTiAl+Ti
30.0-35.019.0-23.039.5 min.05-.10.15-.60.15-.60.30-1.20

Alloy 800HT (UNS N08811) Chemical Composition, %

NiCrFeCAlTiAl+Ti
30.0-35.019.0-23.039.5 min.06-.10.25-.60.25-.600.85-1.2

Mechanical Properties
Typical room temperature Tensile Properties of Annealed Material

ProductTensile (ksi).2% Yield (ksi)Elongation (%)
Rod & Bar75-10030-6060-30

ASTM Specifications

AlloyPipe SmlsPipe WeldedTube SmlsTube WeldedSheet/PlateBarForgingFitting
Alloy 800 (UNS N08800)B407B154B163B515B409B408B564B366
Alloy 800H (UNS N08810)B407B154B163B515B409B408B564B366
Alloy 800HT (UNS N08811)B407B154B163B515B409B408B564B366

Incoloy 800 800H 800HT Applications

  • Petrochemical and chemical processing: The process equipment that is used for the production of ethylene dichloride, ethylene, oxy-alcohol, nitric acid, ketene, and acetic anhydride
  • Petroleum refining: Hydrodealkylation units and steam/hydrocarbon reformers
  • Power Generation: Piping systems in coal-fired power plants, high-temperature heat exchangers and steam super-heaters in gas-cooled nuclear reactors
  • Thermal Processing Fixtures: Fixtures, retorts, muffles and radiant tubes for heat-treating furnaces

Corrosion Resistance

Incoloy 800H and 800HT have quite high nickel and chromium content, which invariably provides them with good aqueous corrosion resistance. The corrosion resistance capacity of these alloys is similar to 304 when used in organic and nitric service. The 800H and 800HT alloys must not be used in sulfuric acid service. These alloys are ideally subjected to chromium carbide precipitation if used in service for a prolonged time and exposed to the temperature range of 538 – 760°C/ 1000 – 1400°

As the Incoloy 800H and 800HT have primarily been developed for superior temperature strength, these grades tend to be typically exposed to corrosive environments that involve high-temperature reactions like carburization and oxidation. 

Machining

Incoloy 800 800H 800HT sheets should typically be machined in the annealed condition. As these alloys tend to be prone to work-hardening, only low cutting speeds should be used when working on them. The cutting tool should additionally be engaged at all times. In order to avoid any contact with the previously formed work-hardened zone, it is important to ensure an appropriate cut depth.

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