Incoloy 800HT (UNS N08811)

Incoloy 800HT (also specified as UNS N08811 / W.Nr. 1.4959) is an austenitic nickel-iron-chromium heat-resistant alloy engineered for long-term service in high-temperature, high-stress applications. With controlled additions of aluminium and titanium (Al+Ti 0.85–1.2 %) and a controlled coarse grain size (ASTM 5 or coarser), it offers significantly improved creep-rupture strength over Incoloy 800H above about 700 °C, combined with good oxidation resistance and resistance to a wide range of hot acidic and alkaline media.

Overview

• Category: Austenitic heat-resistant alloy (Ni-Fe-Cr, Al + Ti strengthened)
• Standards: ASTM B409, B408, B407; ASME SB-409, SB-408, SB-407; UNS N08811; W.Nr./EN 1.4959; Code Case 1325
• Available forms: Round bar / rod, plate, sheet, pipe & tube, forgings, and custom profiles to order

Chemical Composition (wt%)

Physical Properties

Mechanical Properties

Excellent yield strength and good creep and crack resistance above approximately 700 °C.

Fabrication & Welding

• Hot working: 1050–1200 °C with uniform heating; air cool or water cool after working.
• Cold working: Good cold-formability (cold rolling, cold drawing, stamping), with a moderate work-hardening rate.
• Welding: Readily welded by GTAW (TIG), electron-beam welding, resistance welding and other conventional processes.
• Post-weld heat treatment (PWHT): to avoid grain-boundary cracking caused by stress relaxation above 538 °C, heat-treat at 899 °C after welding, holding for 1 hour per 25 mm of thickness (minimum 0.5 hour per 25 mm), then air cool.

Heat Treatment

• Annealing: anneal at a minimum of 1149 °C to achieve a coarse grain size of ASTM 5 or coarser (this coarse grain is key to the alloy's creep-rupture strength).
• PWHT: as described above, 899 °C per thickness-based holding time, then air cool.

Key Features

• Excellent high-temperature strength above 600 °C in both tensile and yield terms, able to carry high stresses and strains;
• Good oxidation resistance: chromium together with controlled aluminium and titanium forms a dense protective oxide film at high temperature;
• Good corrosion resistance in hot acidic and alkaline media, including sulfuric, nitric and hydrofluoric acid environments;
• Resistant to chloride and sulfide attack at elevated temperature.

Corrosion Resistance

• Good tolerance of a wide range of hot acidic and alkaline media;
• Maintains good corrosion performance in chloride-bearing and sulfur-bearing environments.

Typical Applications

• Petrochemical: high-temperature reactors, furnace tubes, pigtails, valves and other critical components (ethylene / steam-reformer furnace service);
• Aerospace: jet-engine combustors, turbine blades and other high-temperature components;
• Power generation: high-temperature steam piping and heat exchangers.

For detailed datasheets, mill certificates (EN 10204 3.1) or inquiries on specific sizes and tolerances, please contact our sales & engineering team.