Iron-Nickel-Chromium Superalloy with Excellent Oxidation, Carburization & Stress-Corrosion Resistance | ASTM B407 | Special Alloys
Strengthening
Solid Solution
Max Service Temp
~1100 °C
What is Incoloy 800? Incoloy 800 (UNS N08800 / W.Nr. 1.4876) is a nickel-iron-chromium superalloy engineered for high-temperature structural stability and outstanding resistance to oxidation, carburization, and sulfidation. Its balanced chemistry — 30–35% Ni, 19–23% Cr, balance Fe with Ti/Al stabilization — produces a fully austenitic microstructure that does not form the embrittling sigma phase even after prolonged exposure at 649°C (1200°F). Incoloy 800 maintains useful strength up to 1100°C and resists chloride stress-corrosion cracking better than standard 300-series stainless steels, making it the workhorse alloy for heat exchangers, furnace components, carburizing equipment, heating-element sheathing, and nuclear steam-generator tubing. HT PIPE supplies Incoloy 800 in seamless pipes, plates, welded pipes, forged fittings, flanges, and round bars with full EN 10204 3.1 certification.
Nickel (Ni)
30.0 – 35.0%
Austenitic matrix stabilizer
Chromium (Cr)
19.0 – 23.0%
Oxidation resistance
Iron (Fe)
≥ 39.5%
Balance — cost-effective base
Ti + Al
0.30 – 1.20%
Stabilizers — prevent sensitization
Tensile Strength (min)
≥520 MPa
75 ksi
Yield Strength (min)
≥205 MPa
30 ksi
Elongation (min)
≥30%
Highly ductile
Density
7.94 g/cm³
0.287 lb/in³
Melting Range
1357–1385°C
2475–2525°F
Incoloy 800: The Versatile Fe-Ni-Cr Workhorse for 600°C+ Service
Incoloy 800 (UNS N08800) was introduced in the 1950s as a cost-effective alternative to fully nickel-based alloys, replacing the more expensive Inconel 600 in many applications where iron could substitute for nickel without compromising high-temperature performance. The alloy’s 30–35% nickel content is sufficient to stabilize a fully austenitic structure, while the 19–23% chromium provides a self-healing Cr₂O₃ passive film that resists oxidation up to 1100°C and carburization in process streams containing hydrocarbons.
The deliberate addition of titanium (0.15–0.60%) and aluminum (0.15–0.60%) stabilizes the alloy against sensitization. These elements preferentially form TiC and AlN precipitates at high temperature, leaving no free carbon to form harmful chromium carbides at grain boundaries during cooling. This stabilization enables Incoloy 800 to retain corrosion resistance in the as-welded condition and prevents intergranular attack in polythionic acid service — a critical requirement in refinery applications.
A key metallurgical advantage: Incoloy 800 does not form the embrittling sigma phase even after thousands of hours at 649°C (1200°F). This distinguishes it from 300-series stainless steels, which become brittle after long exposure in the 425–815°C sigma range. For applications requiring higher creep-rupture strength above 600°C, the controlled-carbon variants Incoloy 800H (N08810) and Incoloy 800HT (N08811) are specified.
Five Defining Advantages of Incoloy 800
1. High-Temperature Stability
Maintains strength up to 1100°C. No sigma-phase embrittlement after prolonged exposure at 649°C — a critical advantage over 300-series stainless steels.
2. Oxidation & Carburization Resistance
19–23% Cr forms stable Cr₂O₃ film. Resists oxidizing atmospheres to 1100°C and carburizing environments to 980°C.
3. Chloride SCC Resistance
Superior to 304/316 stainless in chloride stress-corrosion cracking. Suitable for steam-generator tubing and water chemistry.
4. Ti/Al Stabilization
Titanium + aluminum prevent sensitization. As-welded corrosion resistance retained. Polythionic-acid resistant for refinery service.
5. Cost-Effective Ni Content
30–35% Ni (vs 72% in Inconel 600) delivers comparable performance at lower cost for high-temperature structural applications.
Chemical Composition — ASTM B409 UNS N08800
Incoloy 800’s balanced Ni-Fe-Cr chemistry with Ti/Al stabilization defines its high-temperature performance. The iron balance (≥39.5%) makes the alloy significantly more economical than Inconel grades while retaining austenitic stability:
| Element |
Min (%) |
Max (%) |
Role |
| Nickel (Ni) ★ |
30.0 |
35.0 |
Austenitic stabilizer. Provides chloride SCC resistance and high-temperature structural stability. |
| Chromium (Cr) ★ |
19.0 |
23.0 |
Forms protective Cr₂O₃ passive film. Primary defense against oxidation, sulfidation, and carburization at elevated temperature. |
| Iron (Fe) ★ |
39.5 |
Balance |
Cost-effective balance element. Replaces nickel without sacrificing austenitic stability. |
| Titanium (Ti) ★ |
0.15 |
0.60 |
Stabilizer — preferentially forms TiC, prevents Cr₂₃C₆ sensitization. Enables as-welded corrosion resistance. |
| Aluminum (Al) ★ |
0.15 |
0.60 |
Forms Al₂O₃ sub-layer beneath Cr₂O₃ film. Enhances oxidation and carburization resistance. |
| Carbon (C) |
— |
0.10 |
Controlled low level. Higher carbon (0.05–0.10%) in 800H/800HT for creep strength. |
| Manganese (Mn) |
— |
1.50 |
Deoxidizer; improves hot workability. |
| Silicon (Si) |
— |
1.00 |
Deoxidizer. Controlled to maintain corrosion resistance and weldability. |
| Copper (Cu) |
— |
0.75 |
Residual. Maintained low to preserve high-temperature performance. |
| Sulfur (S) |
— |
0.015 |
Ultra-low for hot workability and weld integrity. |
★ Starred elements define Incoloy 800’s high-temperature performance — Ni, Cr, Fe are the structural base; Ti and Al are the stabilizers
Mechanical Properties — Room Temperature (Annealed)
Incoloy 800 is a solid-solution strengthened alloy. The combination of nickel, chromium, and iron in the austenitic matrix provides good room-temperature strength and retains significant strength at elevated temperatures. For applications above 600°C requiring higher creep-rupture performance, 800H or 800HT with controlled carbon and grain size is specified.
| Condition |
UTS (MPa) |
YS (MPa) |
Elongation (%) |
Hardness |
| Annealed (min) |
≥520 |
≥205 |
≥30 |
≤200 HB |
| Typical (20°C) |
~600 |
~295 |
~44 |
~138 HB |
Elastic Constants & Physical Constants (Annealed at 20°C)
| Elastic / Physical Constant |
Value |
Unit |
| Modulus of Elasticity (Tension, E) |
197 |
GPa (28.5 × 10³ ksi) |
| Shear Modulus (G) |
76 |
GPa (11.0 × 10³ ksi) |
| Poisson’s Ratio (ν) |
0.29 |
— |
Physical Properties — UNS N08800
Incoloy 800’s physical properties reflect its iron-rich composition — the density of 7.94 g/cm³ is lower than fully nickel-based alloys (8.89 g/cm³ for Inconel 600), reducing component weight and cost. The alloy is non-magnetic in all conditions.
| Property |
Value |
Unit |
| Density |
7.94 |
g/cm³ (0.287 lb/in³) |
| Melting Range |
1357 – 1385 |
°C (2475 – 2525 °F) |
| Thermal Conductivity (at 100°C) |
11.4 |
W/m·K |
| Specific Heat (at 20°C) |
460 |
J/kg·K |
| Electrical Resistivity (at 20°C) |
0.989 |
μΩ·m |
| Coeff. of Thermal Expansion (20–100°C) |
13.1 |
μm/m·°C |
| Magnetic Permeability |
< 1.001 |
Non-magnetic |
Heat Treatment Procedures
Incoloy 800 is supplied in the solution-annealed condition. The standard annealing temperature is lower than 800H/800HT because Incoloy 800 does not require coarse grain size for creep performance. For applications requiring higher elevated-temperature creep strength, upgrade to 800H or 800HT.
Step 1 — Solution Anneal
980 – 1040 °C + Rapid WQ/AC
Hold ~1 hr per 25 mm section thickness. Water quench or rapid air cool. Dissolves secondary phases and restores full ductility after cold work.
Step 2 — Stress Relief (optional)
400 – 450 °C, 1–2 hr, air cool
For machined components requiring dimensional stability. Below precipitation range — does not compromise corrosion resistance.
Step 3 — Post-Weld
As-Welded Acceptable
Ti/Al stabilization prevents sensitization. As-welded corrosion resistance is acceptable for most service. Solution anneal recommended for severe environments.
CRITICAL NOTES:
For service above 600°C with creep-rupture requirements, upgrade to
Incoloy 800H (N08810) or
800HT (N08811) with controlled carbon and coarse grain size.
Avoid dwelling at 425–815°C for extended periods — while Incoloy 800 does not form sigma phase, prolonged exposure can promote minor carbide precipitation.
Cold work >10% requires re-annealing before service to restore full corrosion resistance and ductility.
Corrosion Resistance — Multi-Environment Performance
Incoloy 800’s corrosion resistance spans both high-temperature gaseous environments and aqueous media. The 19–23% chromium provides the protective oxide film for elevated-temperature service, while the 30–35% nickel content delivers superior resistance to chloride stress-corrosion cracking compared to austenitic stainless steels.
Oxidation Resistance ★ — DEFINING STRENGTH
Excellent oxidation resistance up to 1100°C (2010°F) in air, steam, and combustion atmospheres. The Cr₂O₃ film is self-healing and remains protective through thermal cycling. Al₂O₃ sub-layer from the aluminum addition enhances adhesion and resists spalling. Incoloy 800 outperforms 304/316 stainless steels by 200–300°C in continuous oxidation service.
Carburization Resistance
Outstanding resistance to carburization in hydrocarbon-containing environments up to 980°C (1800°F). The alloy is widely used in petrochemical furnace tubing, ethylene cracker coils, and carburizing furnace components where carbon uptake would embrittle conventional stainless steels.
Chloride Stress-Corrosion Cracking (SCC)
Superior to 304/316 austenitic stainless steels in chloride SCC resistance. The 30–35% nickel content raises the SCC threshold, making Incoloy 800 suitable for steam-generator tubing in nuclear and fossil-fuel power plants where chloride contamination of water is a concern.
Aqueous Corrosion
Good resistance to nitric acid, organic acids, and alkaline solutions. Excellent in high-purity water chemistry used in nuclear steam generators. Not recommended for service in hydrochloric or hydrofluoric acids — for these environments, Incoloy 825 with Mo+Cu additions is the correct choice.
Intergranular Corrosion (IGC)
Ti/Al stabilization prevents sensitization in the as-welded condition. Passes ASTM A262 Practice A and E tests. The Ti/C ratio > 7:1 ensures carbon is bound as TiC rather than forming Cr₂₃C₆ at grain boundaries, providing polythionic-acid resistance for refinery service.
Performance Comparison — Incoloy 800 vs 304SS vs 316SS
| Environment |
Incoloy 800 |
304 SS |
316 SS |
| Max Oxidation Temp (air) |
1100°C |
870°C |
870°C |
| Carburization Resistance |
Excellent |
Poor |
Poor |
| Chloride SCC Resistance |
Good |
Poor (>60°C) |
Moderate |
| Sigma-Phase Embrittlement |
Immune |
Susceptible |
Susceptible |
| HCl Resistance |
Limited |
Poor |
Poor |
Green = excellent; Red = unacceptable. For HCl/H₂SO₄ service, choose Incoloy 825 or Hastelloy grades.
Incoloy 800 Family Selection Guide — 800 vs 800H vs 800HT
The three Incoloy 800 grades share the same Ni-Fe-Cr base chemistry but differ in carbon control, Al+Ti content, and grain size requirements. These subtle differences determine which variant is appropriate for specific temperature and stress conditions:
| Alloy |
Carbon (C) |
Al + Ti |
Grain Size |
Optimal Service |
Relative Cost |
| Incoloy 800 |
≤0.10% |
0.30–1.20% |
Not specified |
<600°C |
$$ |
| Incoloy 800H |
0.05–0.10% |
0.30–1.20% |
ASTM 5 or coarser |
600–760°C |
$$$ |
| Incoloy 800HT |
0.06–0.10% |
0.85–1.20% |
ASTM 5 or coarser |
760–982°C |
$$$$ |
| Selection Guide |
Higher C = creep strength |
Higher Al+Ti = precipitation strength |
Coarser grain = creep life |
Temperature dictates grade |
800HT premium |
Incoloy 800 Positioning: "General-Purpose High-Temperature Workhorse"
Choose Incoloy 800 for service below 600°C without creep-rupture requirements — heat exchangers, heating-element sheathing, furnace fixtures, and chemical process equipment. For higher temperatures with sustained stress, upgrade to
800H (600–760°C) or
800HT (760–982°C). For reducing acid service, choose
Incoloy 825 with Mo+Cu additions.
Key Applications
Incoloy 800 is the workhorse alloy for high-temperature structural and heat-transfer applications where oxidation, carburization, and chloride SCC resistance are required simultaneously:
| Application |
Components & Conditions |
| Heat Exchangers ★ |
Shell-and-tube exchangers, air coolers, condensers for petrochemical and chemical processes operating at 400–600°C. Resistant to oxidation and chloride SCC. |
| Furnace Components |
Furnace muffles, retorts, baskets, trays, fixtures for heat-treatment equipment. Withstands thermal cycling and oxidizing atmospheres to 1100°C. |
| Heating Element Sheathing |
Protective sheathing for electric resistance heating elements in industrial and domestic appliances. Excellent oxidation resistance and electrical insulation compatibility. |
| Nuclear Steam Generator Tubing ★ |
Tubing for nuclear steam generators and pressurized water reactors. Chloride SCC resistance essential for long-term primary water chemistry service. |
| Petrochemical Process Piping |
Catalyst handling, hydrocarbon processing, reformer piping. Resists polythionic acid attack during shutdowns due to Ti/Al stabilization. |
| Carburizing Equipment |
Carburizing furnace retorts, muffles, and fixtures. Resists carbon uptake that would embrittle conventional stainless steels. |
Applicable Standards & Specifications
| Standard |
Product Form / Scope |
Notes |
| ASTM B409 / ASME SB-409 |
Plate, Sheet, Strip — Ni-Fe-Cr alloys |
Primary flat-product spec. Covers UNS N08800. |
| ASTM B407 / ASME SB-407 |
Seamless Pipe & Tube — Ni-Fe-Cr alloys |
Seamless pipe primary spec |
| ASTM B163 / ASME SB-163 |
Seamless Condenser & Heat-Exchanger Tubes |
Heat exchanger tube spec |
| ASTM B408 / ASME SB-408 |
Rod, Bar — Ni-Fe-Cr alloys |
Round bar and wire products |
| ASTM B514 / B515 |
Welded Pipe & Tube — Ni-Fe-Cr alloys |
Welded pipe/tube products |
| ASTM B366 / ASME SB-366 |
Wrought Welded Fittings |
Butt-weld and socket-weld fittings |
| ASTM B564 / ASME SB-564 |
Nickel Alloy Forgings (Flanges, Fittings) |
Pressure vessel service |
| DIN W.Nr. 1.4876 |
X10NiCrAlTi32-20 — European Werkstoff equivalent |
European project specification |
Available Product Forms from HT PIPE
We supply Incoloy 800 in solution-annealed condition with EN 10204 3.1 certification on every shipment. ASTM A262 intergranular corrosion testing per heat is available on specification. Contact us for current availability and project quotations.
| Product Form |
Specification & Range |
| Seamless Pipes & Tubes |
½″–12″ NB, Sch 10S–Sch 80S. ASTM B407 UNS N08800. Solution-annealed. |
| Plates & Sheets |
0.5–50 mm thickness. ASTM B409 UNS N08800. Solution-annealed. Custom cut-to-size available. |
| Welded Pipes |
ASTM B514/B515 UNS N08800. Full range of sizes. As-welded or solution-annealed per requirement. |
| Forged Fittings |
ASTM B366 UNS N08800. Butt-weld and socket-weld. Elbows, tees, reducers, caps, stub ends. |
| Flanges |
ASTM B564 UNS N08800. 150#–1500#. Weld neck, blind, slip-on, lap joint, long weld neck, orifice. |
| Round Bars |
6–300 mm diameter. ASTM B408 UNS N08800. Hot-finished and cold-drawn. Solution-annealed. |
HT PIPE Project Experience — Incoloy 800
Case Study: Petrochemical Heat Exchanger Bundle — 4.2 Tons Incoloy 800 Seamless Tube
HT PIPE supplied 4.2 tons of Incoloy 800 seamless tubes (ASTM B407, OD 25.4 mm × WT 2.11 mm, lengths 6.1 m) to a Middle East petrochemical refinery for a shell-and-tube heat exchanger bundle replacement in 2024. The exchanger handles preheated crude oil (inlet 510°C) against cooling medium, with cyclic operation causing thermal fatigue on prior 321 stainless steel bundles.
Material selection justification: Incoloy 800 was chosen over 321 SS based on three factors:
Higher oxidation resistance at 510°C — 800’s Cr₂O₃ + Al₂O₃ composite scale outperforms Ti-stabilized stainless
Immunity to sigma-phase embrittlement at 510°C — 321 SS forms sigma after 5,000+ hours
Ti/Al stabilization provides polythionic-acid resistance during shutdowns (refinery service)
Delivery: Full EN 10204 3.1 certification with chemical analysis, mechanical testing, hydrostatic test (200 bar), and PMI on every tube. ASTM A262 Practice A intergranular corrosion test passed on all 8 heats. Solution-annealed at 980°C with rapid air cool. Delivered in 12 weeks. Exchanger has operated 18 months with no tube failures, extending planned run length from 18 to 36 months between turnarounds.
For additional project references matching your specific application, contact our technical sales team.
Frequently Asked Questions — Incoloy 800
Q1: What is the difference between Incoloy 800 and 800H?
Incoloy 800H (UNS N08810) has a controlled carbon range of 0.05–0.10% (vs ≤0.10% max for 800) and requires coarse grain size (ASTM 5 or coarser). These two changes produce significantly higher creep-rupture strength above 600°C. Choose Incoloy 800 for service below 600°C without creep requirements; choose 800H for 600–760°C sustained-load service. Full 800H material guide →
Q2: Can Incoloy 800 replace 304 or 316 stainless steel?
Yes — Incoloy 800 is a direct upgrade over 304/316 SS for service above 425°C, in carburizing atmospheres, or in chloride-containing environments above 60°C. It provides 200–300°C higher oxidation resistance, immunity to sigma-phase embrittlement, and superior chloride SCC resistance. The trade-off is 2–3× higher material cost. For routine ambient or mild-temperature aqueous service, 304/316 SS remains more economical.
Q3: What is the maximum service temperature for Incoloy 800?
In oxidizing atmospheres, Incoloy 800 resists oxidation up to 1100°C (2010°F). In carburizing environments, the limit is ~980°C (1800°F). For reducing or sulfidizing environments, the limit is lower (typically ~600°C) due to chromium sulfide formation. For pressure-bearing components with sustained loads above 600°C, upgrade to 800H or 800HT for creep-rupture performance.
Q4: Does Incoloy 800 require post-weld heat treatment?
No — Incoloy 800 can be used in the as-welded condition for most applications. The Ti/Al stabilization prevents sensitization by forming TiC preferentially over Cr₂₃C₆ at grain boundaries. For severe service (polythionic acid, strong oxidizing media), a full solution anneal at 980–1040°C + rapid cool is recommended. Use matching filler metal ERNiCr-3 (AWS A5.14) or ERNiCrFe-2 for welding.
Q5: Is Incoloy 800 magnetic?
No. Incoloy 800 is non-magnetic with a permeability below 1.001 in the solution-annealed condition. The high-nickel austenitic structure is fully stable at all temperatures, making 800 suitable for applications where magnetic interference must be avoided. Cold work may slightly increase permeability but the alloy remains essentially non-magnetic.
Request a Quote for Incoloy 800 (UNS N08800)
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