Incoloy 800HT is a high-temperature variant of Incoloy 800, with tighter control of carbon (0.06–0.10 percent), aluminum (0.15–0.60 percent), and titanium (0.15–0.60 percent), plus a coarse grain size (ASTM 5 or coarser). These modifications provide significantly improved creep-rupture strength and enhanced resistance to high-temperature embrittlement compared to both standard Incoloy 800 and 800H.

The nominal chemical composition is: nickel 30.0–35.0%, chromium 19.0–23.0%, iron balance, carbon 0.06–0.10%, aluminum 0.15–0.60%, titanium 0.15–0.60%, and smaller amounts of manganese and silicon.

Key mechanical properties (typical, annealed condition):

● Tensile strength: 450–650 MPa

● Yield strength (0.2% offset): 170–240 MPa

● Elongation: 30–45%

● Density: 7.94 g/cm³

Incoloy 800HT offers excellent oxidation resistance up to 1,100°C (2,000°F), good resistance to carburization and sulfidation, and superior creep-rupture strength, particularly for long-term service above 650°C (1,200°F). The controlled Al+Ti content forms fine carbides and promotes a stable microstructure.

Common standards: ASTM B408 (plate, sheet, strip), B407 (seamless pipe/tube), B409 (welded tube), B564 (forgings), ASME SB-408, SB-407, SB-409. Also covered under ASME Code Case 1325 for Section I construction.

Typical applications include:

● Petrochemical industry: reformer and cracking furnace tubes, pigtails, and manifolds.

● Power generation: superheater and reheater tubing in ultra-supercritical plants.

● Heat treatment: furnace components, radiant tubes, and retorts.

● High-temperature heat exchangers and pressure vessels.

Comparison with Incoloy 800 and 800H: 800HT has the highest creep-rupture strength of the three, especially for long-term exposure above 650°C. For applications below 650°C, standard 800 is sufficient. For moderate high-temperature creep, 800H offers a balance. For the most demanding high-temperature service (e.g., steam methane reforming), 800HT is preferred.

Selection guidance: Choose Incoloy 800HT for long-term high-temperature service (650–1,100°C) where maximum creep resistance is required, such as reformer tubes and high-pressure superheaters. For less severe conditions, 800H or standard 800 may be more economical.