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Incoloy 800HT (UNS N08811, Werkstoff 1.4959) is a fully austenitic nickel-iron-chromium alloy containing 30–35% Ni, 19–23% Cr, and controlled additions of aluminium (0.25–0.60%) and titanium, with carbon fixed between 0.06–0.10%. It is designed for long-term service above 600°C (1112°F) and is the preferred grade for applications where creep strength, oxidation resistance, and resistance to carburisation are required simultaneously. It is governed by ASTM B407 (pipe/tube), ASTM B409 (plate/sheet), and ASTM B564 (forgings).
800HT alloy has excellent creep strength above 1290°F. Alloy 800ht has similar high temperature properties to 800H alloy. Incoloy 800HT is resistant to a wide range of corrosive media. Its high nickel content makes it resistant to stress corrosion cracking in aqueous corrosive conditions. The high chromium content gives it better resistance to pitting and crevice corrosion cracking.
800HT has good corrosion resistance to nitric acid and organic acids, but limited corrosion resistance in sulfuric and hydrochloric acids. It has good corrosion resistance in both oxidizing and non-oxidizing salts, but pitting may be present in halides. It also has good corrosion resistance in water, steam, and mixtures of steam, air, and carbon dioxide.
Composition | Value |
Ni | 30.0-35.0 |
Cr | 19.0-23.0 |
Fe | ≥39.5 |
Al | 0.25-0.60 |
C | 0.06-0.10 |
Mn | ≤1.5 |
P | ≤0.04 |
Si | ≤1 |
S | ≤0.015 |
Al&Ti | ≤0.5-1.20 |
Cu | ≤0.75 |
Physical Properties | Value |
Density | 8.02 g/cm³ |
Specific heat | 460 J/Kg*K |
Intrinsic resistance | 99 μΩ·cm |
Thermal conductivity | 12.6 W/m*K |
Longitudinal elastic modulus | 19.7x104 MPa |
Curie point | -115 °C |
Magnetic properties | NO |
Melting point | 1357-1395 |
Physical Properties at High Temperatures
Temperatures | Thermal Conductivity (W/m*K) | Average Expansion Coefficient (10-6/℃) | Longitudinal Elastic Modulus (104 MPa) |
Normal Temperature | 12.6 | - | 19.7 |
100 °C | 14.1 | 14.6 | 19.3 |
200 °C | 16.1 | 15.9 | 18.7 |
300 °C | 17.8 | 16.4 | 18.0 |
400 °C | 19.3 | 16.8 | 17.3 |
500 °C | 20.6 | 17.0 | 16.7 |
600 °CC | 23.2 | 17.3 | 15.9 |
700 °C | 24.4 | 17.7 | 15.2 |
800 °C | 25.1 | 18.1 | 14.5 |
900 °C | 25.9 | 18.3 | 13.8 |
1000 °C | 26.7 | 18.6 | 13.1 |
Tensile, min, ksi[MPa] | Yield, min, ksi[MPa] | Elongation, %(min) |
65[450] | 25[170] | 30 |
High temperature resistance
Incoloy 800HT alloy has excellent high temperature resistance. It can maintain stability at high temperatures and is not easy to soften or flow. This ability makes it suitable for applications in various high temperature environments, such as furnace tubes, heating elements, annealing furnaces, heat treatment equipment and petrochemical units.
Corrosion resistance
Incoloy 800HT alloy has good corrosion resistance and can resist corrosion from a variety of corrosive media. It has good resistance to acidic solutions, alkaline solutions and chlorides. In addition, it can also maintain good corrosion resistance in oxidizing environments.
Based on these characteristics, 800HT alloy is widely used in chemical, petrochemical, oil refining, power and nuclear energy industries. It is used to manufacture reactors, pipelines, heat exchangers, storage tanks, pipelines and pickling equipment.
Anti-oxidation performance
Incoloy 800HT alloy has excellent anti-oxidation properties and can remain stable in high temperature and oxidizing environments. It can form a dense oxide film to effectively prevent the material from being oxidized. Therefore, it can be used to manufacture high temperature furnaces, burners and other high temperature equipment.
Crack and stress corrosion resistance
Incoloy 800HT alloy has good crack and stress corrosion resistance. It can remain stable in high temperature and corrosive environments and is not prone to cracks and stress corrosion cracking. This makes Incoloy 800HT alloy an important material in the oil refining, chemical and nuclear energy industries.
Manufacturing and processing
Incoloy 800HT alloy can be manufactured by conventional processes such as smelting, forging, heat treatment and cold working. During the manufacturing process, the composition and processing temperature of the alloy need to be strictly controlled to ensure the best performance and microstructure.
Processing processes include forging, hot rolling, cold drawing, welding, etc. During the welding process, appropriate welding materials and welding processes should be selected to avoid welding defects and stress corrosion cracking.
STANDARD | WERKSTOFF.NR. | UNS | JIS | BS | GOST | EN | OR |
Incoloy 800HT | 1.4959 / 1.4876 | N08811 | NCF 800HT | NA 15(HT) | ЭИ670 | X8NiCrAlTi32-21 | XH32T |
Product | Standard | Show |
Incoloy 800ht rod bars | ASTM B408, EN 10095 |  |
Incoloy 800ht plate/sheet/strip | ASTM A240, A480, ASTM B409, B906 |  |
Incoloy 800ht pipe tubes | ASTM B407 |  |
Incoloy 800ht fittings | ASTM B366 |  |
Incoloy 800ht forgings | ASTM B564, DIN 17460 |  |
Ethylene furnace quench boilers
Incoloy 800HT is selected for ethylene furnace quench boilers because it provides outstanding resistance to carburization and oxidation at temperatures up to 1100°C. It maintains excellent creep-rupture strength in the extremely hot, carbon-rich environment of ethylene cracking furnaces, preventing premature failure and ensuring long service life.
Hydrocarbon cracking
In hydrocarbon cracking processes, Incoloy 800HT is used due to its superior high-temperature strength and excellent resistance to carburization and nitridation. These properties allow it to withstand the aggressive, high-temperature atmospheres where hydrocarbons are cracked into lighter products without suffering from embrittlement or rapid degradation.
Industrial furnaces
Industrial furnaces require materials that can endure prolonged exposure to high temperatures and oxidizing or carburizing gases. Incoloy 800HT is preferred because of its stable microstructure, high creep strength, and outstanding oxidation resistance, which keep furnace components (such as radiant tubes and hangers) reliable and maintenance-free for extended periods.
Heat-treating equipment
In heat-treating equipment, Incoloy 800HT is chosen for its ability to resist thermal fatigue, oxidation, and carburization at elevated temperatures. It retains good mechanical properties even after repeated heating and cooling cycles, making it ideal for fixtures, baskets, and furnace internals that must perform consistently in heat-treatment operations.
Chemical and petrochemical processing
Incoloy 800HT is widely used in chemical and petrochemical processing because it offers excellent resistance to a wide range of corrosive environments at high temperatures, including organic acids, sulfur compounds, and chloride-containing media. Its high creep strength ensures structural integrity in reactors, piping, and other process equipment under demanding operating conditions.
Superheaters and re-heaters in power plants
Superheaters and reheaters in power plants operate at very high steam temperatures and pressures. Incoloy 800HT is selected for these components due to its exceptional creep-rupture strength, resistance to steam oxidation, and long-term microstructural stability, which prevent tube failures and extend the life of the power generation system.
Pressure vessels
Incoloy 800HT is ideal for pressure vessels operating at elevated temperatures because it combines high creep and rupture strength with excellent resistance to oxidation and general corrosion. It meets stringent design codes for high-temperature service while providing reliable performance and safety in pressurized, hot environments.
Heat exchangers
Heat exchangers made from Incoloy 800HT perform reliably in high-temperature service because the alloy offers superior thermal stability, resistance to oxidation and carburization on both process and utility sides, and high creep strength. This ensures efficient heat transfer and prevents tube wall thinning or cracking over long operating periods.
What is Incoloy 800HT?
Incoloy 800HT is a nickel-iron-chromium alloy (UNS N08811) designed for high-temperature structural applications requiring excellent oxidation resistance, carburization resistance, and creep rupture strength. It offers enhanced mechanical stability and improved high-temperature strength compared with standard Incoloy 800 grades.
What is Incoloy 800HT used for?
Incoloy 800HT is widely used in heat exchangers, furnace components, petrochemical processing equipment, pressure vessels, and power generation systems. Its excellent resistance to oxidation and high-temperature creep makes it suitable for demanding industrial environments.
What is the difference between Incoloy 800H and Incoloy 800HT?
The main difference between Incoloy 800H and Incoloy 800HT lies in the chemical composition control of carbon, titanium, and aluminum. Incoloy 800HT provides better creep rupture strength and superior performance in elevated temperature applications, making it more suitable for long-term service under high thermal stress.
Is Incoloy 800HT suitable for high-temperature service?
Yes, Incoloy 800HT is specifically developed for long-term exposure to temperatures above 600°C. It provides excellent oxidation resistance, structural stability, and creep strength, making it ideal for high-temperature service environments.
What are the main properties of Incoloy 800HT?
Incoloy 800HT offers excellent oxidation resistance, carburization resistance, high creep rupture strength, and good metallurgical stability at elevated temperatures. These properties make it a reliable alloy for high-temperature structural applications.
What standards does Incoloy 800HT comply with?
Incoloy 800HT conforms to UNS N08811 and is commonly supplied according to ASTM B409, ASTM B163, ASTM B407, and ASTM B564 standards, depending on the product form and application requirements.
In what forms is Incoloy 800HT available?
Incoloy 800HT is available in a variety of product forms, including plate, sheet, pipe, tube, round bar, flanges, and forgings. These forms are widely used in industries requiring reliable high-temperature alloy materials.
