Incoloy 800HT – UNS N08811
Iron-nickel-chromium alloy for creep and oxidation at high temperature
Fe-Ni-Cr alloy of the 800 family with controlled carbon (0.06 – 0.10%), Al+Ti of 0.85 to 1.20% and a coarse grain obtained by solution annealing above 1,150 °C. This combination gives the highest creep and rupture strength of the family. It resists oxidation and carburization. Usually supplied dual certified 800H/800HT. By composition (Fe ≥ 39.5%) it is also classified as a high-alloy austenitic stainless.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N08811 (800H: N08810; 800: N08800) |
| W.Nr./EN | 1.4959 – X8NiCrAlTi32-21 (800H: 1.4958) |
| DIN | X8NiCrAlTi32-21 |
| JIS | NCF 800HT |
| Trade names | Incoloy 800HT (Special Metals), Nicrofer 3220 HP (VDM), Alloy 800HT |
| Others | Dual certification 800H/800HT |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM B408 |
| Forging | ASTM B564 |
| Plate | ASTM B409; ASTM A240 |
| Tube | ASTM B407 (seamless), B163 (exchanger), B514/B515 (welded) |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5). Fe-Ni-Cr alloy in which iron predominates by weight: under Section XV Note 5 and Chapter 72 Note 1(e) it is classified as stainless steel (7219, 7222, 7304), not as a Chapter 75 nickel alloy.
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM B408 / B564 (UNS N08811)
| Element | Range (%) |
|---|---|
| Ni | 30.0 – 35.0 |
| Cr | 19.0 – 23.0 |
| Fe | ≥ 39.5 |
| C | 0.06 – 0.10 |
| Al | 0.25 – 0.60 |
| Ti | 0.25 – 0.60 |
| Al + Ti | 0.85 – 1.20 |
| Mn | ≤ 1.50 |
| Si | ≤ 1.0 |
| Cu | ≤ 0.75 |
| S | ≤ 0.015 |
Mechanical properties
solution annealed (ASTM B564 / B408)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 172 MPa |
| Tensile strength | ≥ 448 MPa |
| Elongation | ≥ 30% |
| Grain size | ASTM No. 5 or coarser |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.94 g/cm³ |
| Melting range | 1,357 – 1,385 °C |
| Modulus of elasticity | 196 GPa |
| Thermal conductivity (20 °C) | 11.5 W/m·K |
| Thermal expansion (20–100 °C) | 14.4 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Designed for creep above ~600 °C, up to 899 °C per ASME (II-D) and up to ~1,000 °C per European standards (EN/VdTÜV); oxidation and carburization resistance up to ~1,100 °C. Below ~600 °C the plain 800 alloy (N08800) is adequate. |
| Heat treatment | Solution annealing at ≥ 1,149 °C (usual range 1,150 – 1,200 °C) until ASTM grain size No. 5 or coarser is reached, with rapid cooling. Not age hardenable. |
| Welding | Up to ~790 °C: AWS ERNiCr-3 (FM 82) and ENiCrFe-2 (Inco-Weld A type). Above ~790 °C: ERNiCrCoMo-1 (FM 617) and ENiCrCoMo-1 (electrode 117). |
| Machining | Comparable to high-alloy austenitic stainless: work hardens; use carbide, positive feed and coolant. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Steam reformer pigtails and headers (hydrogen, ammonia, methanol)
- Superheaters and reheaters
- High-temperature heat exchangers
- Muffles, retorts and baskets for heat treatment furnaces
- Petrochemical and cracking furnaces
- Carburizing and nitriding furnace components
Alternatives: Incoloy 800 (N08800) below ~600 °C, with no creep requirement; Inconel 600/601 for nitriding or severe cyclic oxidation; Inconel 617 when more creep resistance is needed; 310/253MA stainless as a lower-cost option.
Incoloy 800HT: complete guide
What Incoloy 800HT is
Incoloy 800HT belongs to the family of nickel alloys, in the iron-nickel-chromium group for high temperature. It is the version of Incoloy 800 with the highest creep resistance: carbon controlled between 0.06 and 0.10%, the sum of aluminum and titanium between 0.85 and 1.20% and high-temperature solution annealing, which produces ASTM grain size 5 or coarser, raise the allowable stresses above 600 °C.
800, 800H and 800HT
800 (N08800) is the basic, annealed alloy, for use up to about 600 °C. 800H (N08810) adds carbon of 0.05 to 0.10% and a coarse grain, and 800HT (N08811) further adds control of Al + Ti, with the highest creep values. For creep design, 800H or 800HT must be specified.
Mechanical properties
Solution annealed, ASTM B408 requires a minimum yield strength of 172 MPa, minimum tensile strength of 448 MPa, minimum elongation of 30% and ASTM grain size 5 or coarser. The room-temperature minimums are lower than those of annealed 800 precisely because of the coarse grain; the alloy's advantage lies in the creep allowable stresses given by the design code.
Corrosion and limits of use
800HT resists oxidation in air up to about 1,100 °C and has good resistance to carburization, moderate nitriding and sulfidation, in the latter superior to high-nickel alloys such as Inconel 600. In aqueous corrosion it behaves like a high-nickel austenitic, with good stress corrosion resistance. Use under load is defined by the creep stresses of the design standard, up to 899 °C per ASME and up to about 1,000 °C per European standards.
Applications
Tubes and headers of hydrogen and ammonia reforming furnaces and ethylene pyrolysis, radiant tubes, heat exchangers and superheaters, heat treatment furnace components, retorts, supports and grids, and power generation and high-temperature chemical process equipment. For less severe creep, 310S; for severe carburization, Inconel 601.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing or annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of Incoloy 800HT?
Per ASTM B408 / B564 (UNS N08811): Ni 30.0 – 35.0; Cr 19.0 – 23.0; Fe ≥ 39.5; C 0.06 – 0.10; Al 0.25 – 0.60; Ti 0.25 – 0.60.
Which standards cover Incoloy 800HT?
Bar: ASTM B408. Forging: ASTM B564. Plate: ASTM B409; ASTM A240. Tube: ASTM B407 (seamless), B163 (exchanger), B514/B515 (welded).
Up to what temperature can Incoloy 800HT be used?
Designed for creep above ~600 °C, up to 899 °C per ASME (II-D) and up to ~1,000 °C per European standards (EN/VdTÜV); oxidation and carburization resistance up to ~1,100 °C. Below ~600 °C the plain 800 alloy (N08800) is adequate.
Which materials can replace Incoloy 800HT?
Incoloy 800 (N08800) below ~600 °C, with no creep requirement; Inconel 600/601 for nitriding or severe cyclic oxidation; Inconel 617 when more creep resistance is needed; 310/253MA stainless as a lower-cost option.
