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Incoloy 800HT

UNS N08811, Alloy 800HT, W.Nr. 1.4959, Incoloy® 800HT
Note that the designation “ Incoloy®” is registered trademarks of the Special Metals Corporation group of companies. 


The mechanical properties of UNS N08810 and UNS N08811, combined with their resistance to high temperature corrosion, make these alloys exceptionally useful for many applications involving long-term exposure to elevated temperatures and corrosive atmospheres. Incoloy 800H and Incoloy 800HT have significantly higher creep and rupture strength than Incoloy 800. The base elements in three alloys are the same, only carbon, aluminum and titanium differ slightly. The carbon content of Incoloy 800 is 0.10% max with no limit on the lower end. The carbon content for Incoloy 800H is 0.05 to 0.10%. The carbon content for Incoloy 800HT is further restricted to 0.06 – 0.10%. In addition to the controlled carbon content, Incoloy 800H and 800HT receive a high-temperature annealing treatment that produces an coarser grain size. The annealing treatment and restricted chemical composition are responsible for these alloys having greater creep and rupture strength.  

  • In Hydrocarbon Processing: Catalyst tubing, convection tubing, pigtails, outlet manifolds, and quenching-system piping for steam/hydrocarbon reforming
  • In Ethylene Production: Convection and cracking tubes, pigtails
  • In Oxy-alcohol Production: Tubing in hydrogenation heaters
  • In Vinyl Chloride Monomer Production: Cracking tubes, return bends and inlet and outlet flanges
  • In Heat-treating Furnaces: Radiant tubes, muffles, retorts, and assorted furnace fixtures
  • In Power Generation: Steam superheating tubing
  • In Gas-cooled Nuclear Reactors: High temperature heat exchangers
Chemical Composition (%)
Material Ni Cr Fe C Mn S Al Ti
N08811 30.0-35.0n 19.0-23.0 39.5 min 0.06-0.10 1.50 max 0.015 max 0.25-0.60 0.25-0.60
Mechanical Property
Material Tensile strength Yield strength 0,2 Elongation Hardness HB30
N08811 531 N/mm² 200 N/mm² 52% 127HB
Corrosion Resistance

Incoloy 800, 800H, 800HT contains the same nickel, chromium, and iron contents and generally display similar corrosion resistance. Please note, Because Alloy 800H, 800HT are used for their high-temperature strength, corrosive environments to which these alloys are exposed normally involve high temperature reactions such as oxidation and carburization. 

Heat Treatment

Same as the Incoloy 800, Incoloy 800H, 800HT is a nickel-iron-chromium alloy known for its excellent resistance to oxidation, carburization, and high-temperature corrosion. Heat treatment can be used to enhance certain properties of the alloy, such as grain size control and stress relief. The common heat treatment processes for Alloy 800H, 800HT  is annealing, solution treatment and stress relieving. It's important to note that the specific heat treatment parameters may vary depending on the form and condition of the alloy material, as well as the desired properties for a particular application. 

Heating and Pickling

Before heating, Incoloy 800H, 800HT to be heated must be cleaned of oil, paint, grease, shop soil and other foreign substances. When heating, all operations must be performed in a low-sulfur atmosphere. If heating is performed in an open air environment, It is necessary to use low-sulfur fuel and maintain in a reducing condition in the furnace atmosphere, to prevent excessive oxidation. 


Because of the readiness with which chromium is oxidized into a refractory oxide by air, carbon dioxide or water vapor, Incoloy 800H, 800HT cannot be bright annealed in the usual industrial annealing furnace, the alloy is normally annealed in box or muffle furnaces using prepared reducing atmospheres. Low-sulfur natural gas burned with a deficiency of air, It produces a thin, adherent, green-black film of oxide on the material, these oxide films and scales can be removed by pickling. Please note, because of Alloy 800H, 800HT inherent resistance to chemical attack, specialized pickling procedures are needed.

Hot and Cold Forming

The recommended temperature range of hot forming is 1600 to 2200°F (870–1200°C). Heavy forging should be done at temperatures down to 1600°F (870°C) and light working can be accomplished down to 1600°F (870°C).  No working should be done between 1200 to 1600°F (650–870°C). However, they are subject to some carbide precipitation in the 1000 to 1400°F (540–760°C) temperature range and should be rapidly cooled through that range when sensitization is a concern. Cooling after hot working should be air cool or faster. Heavy sections may become sensitized during cooling from the hot-working temperature, and therefore be subject to intergranular corrosion in certain media.


Incoloy 800H, 800HT is austenitic and have a face-centered cubic crystallographic structure, typically require more power to deform, proper temperature control during deformation is the most important factor in achieving hot malleability. Pleae note that its necessary for Alloy 800H, 800HT to performe large amounts of cold work before annealing, the work-hardening rates for these alloys are somewhat lower than for the common grades of austenitic stainless steels.


Incoloy 800H and Incoloy 800HT are readily machined by standard methods. Turning operations can be performed with high metal removal rates, good tool life, and good surface finish using coated carbide tools. Good results have also been obtained with high-speed-steel tools, which are better for interrupted cutting. 


Like Incoloy 800, Incoloy 800H and 800HT have the same good weldability. Both are normally used for applications requiring high creep-rupture strength and should be joined with welding products that have suitable strength characteristics for the intended service temperatures, the optimum welding product choice depends on the specific service temperatures involved and the properties needed in the welded joint. For temperatures up to 1450°F (790°C), INCO-WELD A Electrode is used for shielded-metal-arc welding, and INCONEL Filler Metal 82 is used for gas-shielded welding. For service temperatures over 1450°F (790°C), INCONEL Welding Electrode 117 and INCONEL Filler Metal 617 are recommended. 

Product Forms
  • Bar & Rod
  • Plate & Sheet
  • Coil & Strip
  • Pipe & Tube
  • Fitting: Flange, Tee, Elbow, Reducer etc.
  • Forging: Ring, Shaft, Circle, Block etc.

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