Incoloy 800, 800H, and 800HT are nickel-iron-chromium alloys with good strength and excellent resistance to oxidation and carburization in high-temperature exposure. These nickel steel alloys are identical except for the higher level of carbon in alloy 800H, and the addition of up to 1.20 percent aluminum and titanium in alloy 800HT. Incoloy 800 was the first of these alloys and it was slightly modified into Incoloy 800H. This modification was to control carbon (.05-.10%) and grain size to optimize stress rupture properties. Incoloy 800HT has further modifications to the combined titanium and aluminum levels (.85-1.20%) to ensure optimum high temperature properties.The nickel alloy is dual certified (800H/HT) and combines the properties of both forms. Incoloy 800H/HT alloy was intended for high temperature structural applications. The nickel content makes the alloys highly resistant to both chloride stress-corrosion cracking and to embrittlement from precipitation of sigma phase. The general corrosion resistance is excellent. In the solution annealed condition, alloys 800H and 800HT have superior creep and stress rupture properties. Today, most suppliers, including Mega Mex, only carry the dual certified 800H/HT alloy.

Incoloy 800 is primarily used in applications with temperatures up to 1100° F, while alloys 800H and 800HT are normally used in temperatures above 1100° F where resistance to creep and rupture is required. The chemical balance allows the nickel steel alloy to exhibit excellent resistance to carburization, oxidation and nitriding atmospheres. Incoloy 800HT will not become embrittled even after long periods of usage in the 1200-1600° F range where many stainless steels become brittle. Excellent cold forming characteristics typically associated with the nickel-chromium alloys are exhibited with 800HT. When cold formed extensively the grain size produces a visibly undulated surface called “orange peel”. Incoloy 800HT can be welded by the common techniques used on stainless steels.

ASTM Specifications

Alloy 800 (UNS N08800) Chemical Composition, %

Alloy 800H (UNS N08810) Chemical Composition, %

Alloy 800HT (UNS N08811) Chemical Composition, %