Incoloy 800H is a high-temperature variant of Incoloy 800. It has a controlled carbon content (0.05–0.10 percent, compared to 0.10 percent maximum for standard 800) and is solution annealed at a higher temperature to produce a coarse grain size (ASTM 5 or coarser). These modifications significantly improve creep-rupture strength at temperatures above 650°C (1,200°F).

The nominal chemical composition is: nickel 30.0–35.0%, chromium 19.0–23.0%, iron balance, carbon 0.05–0.10%, plus smaller amounts of manganese, silicon, and aluminum + titanium (0.15–0.60%).

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 800H offers excellent oxidation resistance up to 1,100°C (2,000°F), good resistance to carburization and sulfidation, and superior creep strength for long-term high-temperature service. It is not precipitation hardenable; strengthening comes from solid solution and grain size control.

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: petrochemical reformer and cracking furnace tubes, ethylene cracking tubes, high-temperature heat exchangers, power plant superheater and reheater tubing, and furnace components such as radiant tubes and retorts.

Comparison with Incoloy 800: 800H has higher creep strength above 650°C, but similar oxidation resistance and corrosion properties. For applications below 650°C, standard 800 is sufficient. For the highest creep performance, Incoloy 800HT (with tighter control of aluminum, titanium, and carbon) may be specified.

Selection guidance: Choose Incoloy 800H for high-temperature components (650–1,100°C) requiring long-term creep resistance, such as furnace tubing and petrochemical heaters. For lower temperatures or less demanding creep conditions, standard 800 is more economical. For severe carburizing environments, consider alloys with higher chromium.