Hangbo Alloy Group
Shanghai · Est. 2012
UNS N08800 / W.Nr. 1.4876 — Nickel-iron-chromium alloy with exceptional oxidation and carburization resistance up to 1100°C. The standard material for heat treatment furnace components, petrochemical cracking tubes, and nuclear steam generators.
Incoloy 800 (UNS N08800 / W.Nr. 1.4876) is a nickel-iron-chromium alloy designed for high-temperature structural applications requiring exceptional resistance to oxidation, carburization, and other forms of high-temperature corrosion. As the foundational grade of the Incoloy 800 series, it offers a unique combination of strength, metallurgical stability, and environmental resistance at temperatures up to 1100°C (2012°F) that has made it a workhorse material in the heat treatment, petrochemical, and nuclear power industries since its introduction in the 1950s by Special Metals Corporation.
The alloy's composition — approximately 32% nickel, 46% iron, and 21% chromium — represents an optimal balance: the high nickel content provides resistance to carburization and nitridation, the chromium content ensures oxidation resistance through the formation of a protective chromium oxide (Cr2O3) scale, and the iron base offers economic advantages over higher-nickel alloys without sacrificing essential performance properties. The carefully controlled carbon content and titanium-plus-aluminum additions provide stabilization against sensitization during long-term exposure at intermediate temperatures (450–850°C).
Incoloy 800 is the base grade of a family that includes Incoloy 800H (UNS N08810, with controlled carbon and larger grain size for improved creep resistance) and Incoloy 800HT (UNS N08811, with optimized aluminum-plus-titanium content for maximum creep-rupture strength). All three grades share the same nominal chemical composition limits but differ in their thermal processing and grain size control to achieve different property profiles.
The chemical composition of Incoloy 800 is designed to provide a stable austenitic structure with excellent resistance to high-temperature environmental attack. The nickel content (30–35%) is sufficient to maintain the austenitic structure while providing carburization resistance. The chromium content (19–23%) provides oxidation resistance, and the controlled titanium-plus-aluminum content provides stabilization against sensitization.
| Element | Min % | Max % |
|---|---|---|
| Nickel (Ni) | 30.0 | 35.0 |
| Chromium (Cr) | 19.0 | 23.0 |
| Iron (Fe) | Balance | Balance |
| Carbon (C) | — | 0.10 |
| Aluminum (Al) | 0.15 | 0.60 |
| Titanium (Ti) | 0.15 | 0.60 |
| Manganese (Mn) | — | 1.50 |
| Silicon (Si) | — | 1.0 |
| Copper (Cu) | — | 0.75 |
| Aluminum + Titanium | 0.30 | 1.20 |
| Phosphorus (P) | — | 0.020 |
| Sulfur (S) | — | 0.015 |
Incoloy 800 has a fully austenitic face-centered cubic (FCC) crystal structure that remains stable from cryogenic temperatures up to the melting point. The alloy does not undergo any phase transformations during heating or cooling, which contributes to its excellent dimensional stability during thermal cycling. The moderate thermal expansion coefficient and good thermal conductivity simplify design of furnace components and heat exchanger tubing.
| Property | Value | Unit |
|---|---|---|
| Density | 7.94 | g/cm3 |
| Melting Range | 1357–1385 | °C |
| Specific Heat (20°C) | 460 | J/kg·K |
| Thermal Conductivity (20°C) | 11.5 | W/m·K |
| Electrical Resistivity (20°C) | 0.99 | μΩ·m |
| Modulus of Elasticity (20°C) | 196 | GPa |
| Mean Coefficient of Thermal Expansion (20–100°C) | 14.2 | μm/m·°C |
| Mean Coefficient of Thermal Expansion (20–1000°C) | 18.2 | μm/m·°C |
Incoloy 800 is supplied in the solution-annealed condition (typically 980–1065°C) and offers good strength and ductility at room temperature. The mechanical properties below represent minimum values for solution-annealed plate per ASTM B409. The alloy is not age-hardenable; its strength is derived from solid-solution strengthening and grain size control.
| Property | Value |
|---|---|
| Tensile Strength (Rm) | 520 MPa (75 ksi) |
| Yield Strength, 0.2% offset (Rp0.2) | 207 MPa (30 ksi) |
| Elongation in 50 mm | 30% |
| Reduction of Area | 45% |
| Hardness (Rockwell B) | 75–90 HRB |
| Impact Strength (Charpy V-notch, RT) | >100 J |
| Shear Modulus | 74 GPa |
| Poisson's Ratio | 0.33 |
Incoloy 800 retains useful mechanical properties at elevated temperatures, though its strength decreases more rapidly above 650°C compared to precipitation-hardening superalloys. The alloy is primarily selected for its environmental resistance (oxidation, carburization) rather than for load-bearing capability at the highest temperatures. For applications requiring higher creep strength, Incoloy 800H or 800HT should be considered.
| Temperature (°C) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
|---|---|---|---|
| 20 (Room) | 520 | 207 | 30 |
| 200 | 470 | 175 | 32 |
| 400 | 440 | 155 | 34 |
| 600 | 380 | 140 | 36 |
| 800 | 200 | 120 | 45 |
| 900 | 130 | 80 | 55 |
| 1000 | 70 | 40 | 65 |
The primary reason for selecting Incoloy 800 is its outstanding resistance to high-temperature corrosion mechanisms that rapidly degrade standard stainless steels and lower-alloy materials. The combination of high nickel and chromium content, along with the controlled titanium and aluminum additions, provides a uniquely balanced resistance profile.
Incoloy 800 exhibits excellent oxidation resistance in air and combustion gases up to 1100°C. The 21% chromium content promotes formation of a dense, adherent chromium oxide (Cr2O3) scale that acts as a diffusion barrier, limiting further oxidation. Under cyclic thermal conditions, the scale remains adherent and does not spall excessively, providing reliable long-term protection. The alloy is widely used for furnace muffles, radiant tubes, and heat treatment baskets that experience repeated heating and cooling cycles.
The high nickel content (32%) provides superior resistance to carburization compared to standard stainless steels. In carburizing atmospheres at 800–1100°C, carbon atoms diffuse into the metal surface and form chromium carbides. In stainless steels with lower nickel content, this leads to severe embrittlement and loss of oxidation resistance. Incoloy 800's nickel-rich matrix significantly slows carbon diffusion, reducing the rate of carburization by a factor of 3–5 compared to Type 310 stainless steel. This property is critical for ethylene cracking furnace tubes and heat treatment furnace components.
The nickel content also provides excellent resistance to nitridation in ammonia-containing and nitrogen-rich atmospheres. This makes Incoloy 800 suitable for ammonia dissociation equipment, nitriding furnace components, and heat exchangers in ammonia plants.
Incoloy 800 offers moderate resistance to sulfidation in reducing sulfur-containing environments, though it is not as resistant as higher-nickel alloys such as Alloy 600. The chromium content provides some protection by forming chromium sulfide scales, but for severely sulfidizing conditions, alloys with higher chromium and nickel content should be considered.
A key advantage of Incoloy 800 over standard austenitic stainless steels is its resistance to sigma phase formation. Sigma phase is a brittle intermetallic compound that forms in Fe-Cr alloys after long-term exposure at 540–900°C, causing severe loss of ductility and toughness. The high nickel content of Incoloy 800 suppresses sigma phase formation, maintaining ductility after tens of thousands of hours at temperature.
Incoloy 800 is readily weldable using all common arc welding processes including GTAW (TIG), GMAW (MIG), SMAW (stick), and SAW (submerged arc). The recommended welding filler metal is ERNiCr-3 (AWS A5.14) / Inconel 82, which provides a weld deposit with corrosion and oxidation resistance matching the base metal. Preheating is generally not required, and post-weld heat treatment is not necessary for most applications, though stress relief at 900°C may be specified for thick sections or for applications involving stress corrosion cracking environments.
Hot working is performed at 1200–950°C. Cold forming is readily accomplished due to the alloy's good ductility in the annealed condition. The alloy work hardens at a rate between that of mild steel and Type 304 stainless steel. Solution annealing is performed at 980–1065°C followed by rapid cooling in air or water.
Incoloy 800's balanced properties have made it the standard material for a wide range of high-temperature industrial applications where both environmental resistance and structural integrity are required:
The Incoloy 800 family consists of three grades with identical nominal chemical composition but different thermal processing and resulting properties:
For most furnace component and non-load-bearing applications, Incoloy 800 provides excellent performance at lower cost. For pressure-containing components or applications where creep deformation must be minimized, 800H or 800HT should be specified.
Hangbo Alloy Group manufactures and supplies Incoloy 800 in the following product forms, conforming to ASTM, ASME, and EN specifications:
| Standard | Description |
|---|---|
| ASTM B409 | Plate, Sheet, and Strip |
| ASTM B408 | Bar and Rod |
| ASTM B407 | Seamless Pipe and Tube |
| ASTM B163 | Condenser and Heat Exchanger Tubes |
| ASTM B564 | Forgings |
| ASTM B366 | Fittings |
| ASME SB-409 | Boiler and Pressure Vessel Code — Plate |
| ASME SB-407 | Boiler and Pressure Vessel Code — Pipe |
| ASME SB-163 | Boiler and Pressure Vessel Code — Condenser Tubes |
| EN 10095 | Heat Resisting Steels and Nickel Alloys |
| ISO 4954 | Heat-Resisting Steels and Alloys |
Hangbo Alloy Group maintains extensive inventory of Incoloy 800 in all standard product forms and sizes. We can provide mill test certificates per EN 10204 3.1, third-party inspection reports (SGS, TUV, Lloyd's Register, DNV), and custom processing services including cutting, machining, and surface finishing.
For quotations, material certifications, or technical consultation on Incoloy 800, 800H, or 800HT for your application, contact our technical sales team or call +86-136-1165-6360. We typically respond within 10 minutes during business hours.
Request a quotation for Incoloy 800 bars, tubes, plates, or custom furnace components. ASTM/ASME certified material with full mill test certification.