Incoloy 800H (UNS N08810): High-Temperature Nickel-Iron-Chromium Alloy

ASTM B407 / ASTM B163 · Published: 2026-06-01 · Updated: 2026-06-02

Incoloy 800H (UNS N08810) is a nickel-iron-chromium alloy designed for high-temperature structural applications up to 1,100°C. It is the solution-annealed and coarse-grain variant of Incoloy 800 — the controlled carbon content (0.05-0.10%) and grain size (ASTM 5 or coarser) provide superior creep and stress-rupture properties compared to standard 800. The alloy's defining characteristic is its resistance to sigma phase embrittlement at intermediate temperatures (550-850°C) where standard austenitic stainless steels (304H, 316H) become embrittled and unsuitable for load-bearing service.

Primary applications: ethylene furnace cracking tubes (operating at 850-950°C), hydrocarbon steam reforming tubes, petrochemical furnace components, and heat treatment furnace radiant tubes, muffles, and retorts. The alloy develops a protective chromium oxide scale that remains adherent under thermal cycling, providing oxidation resistance in air and combustion gases. Carburization resistance (resistance to carbon diffusion from hydrocarbon atmospheres) is superior to stainless steels due to the high nickel content — nickel does not form stable carbides, limiting carbon penetration. For applications above 1,000°C, Incoloy 800HT (UNS N08811) with tighter aluminum and titanium control provides enhanced creep strength.

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