Nimonic 86: Oxidation & Carburization Resistance up to 1000°C

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Overview

Nimonic 86 (UNS N07306) is a solid-solution-strengthened nickel-chromium-molybdenum alloy developed specifically for high-temperature service where resistance to oxidation, carburization, and sulfidation is more critical than high creep strength. It belongs to the Nimonic family of nickel-base alloys originally developed by Mond Nickel Company in the United Kingdom, and it has been widely adopted in gas turbine combustion systems, industrial furnace fixtures, and petrochemical reforming equipment operating at temperatures up to 1000°C (1832°F).

The defining feature of Nimonic 86 is its carefully balanced chemistry: approximately 25% chromium provides the foundation for a protective chromium oxide scale, while 10% molybdenum significantly improves resistance to reducing sulfidizing and carburizing environments. The small but critical addition of cerium (typically 0.03–0.10%) dramatically improves the adhesion and spallation resistance of the oxide scale during severe thermal cycling. This rare-earth effect is why Nimonic 86 outperforms many conventional Ni-Cr alloys in applications with frequent start-stop thermal transients.

Unlike precipitation-hardened superalloys such as Nimonic 80A, Nimonic 90, or Waspaloy, Nimonic 86 derives its strength primarily from solid-solution strengthening and is normally used in the solution-annealed condition. This gives it excellent ductility, outstanding formability, and good weldability using matching nickel-base filler metals. The trade-off is lower room-temperature strength and minimal creep resistance compared to age-hardened grades, but this is acceptable for the static and lightly stressed components where it is typically specified.

The alloy is produced by vacuum induction melting (VIM) followed by vacuum arc remelting (VAR) or electroslag remelting (ESR) to achieve the cleanliness required for high-temperature oxidation resistance. Hot working is performed in the 1050–1200°C range, and the alloy is solution annealed at approximately 1100–1150°C followed by rapid cooling to retain a homogeneous austenitic microstructure. Cold forming is readily accomplished in the annealed condition, and the material can be welded by gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and resistance welding techniques using nickel-chromium-molybdenum filler metals.

At Hangbo Alloy Group, Nimonic 86 is supplied as sheet, strip, plate, seamless tube, welded tube, round bar, and custom forgings per BS HR4, BS HR204, AMS 5869, ASTM B670, DIN 17742, and VdTÜV 499. We provide full material certification including chemical analysis, mechanical testing, and metallographic examination on request.

Chemical Composition (BS HR4 / AMS 5869)

The chemistry of Nimonic 86 is optimized for high-temperature surface stability rather than precipitation strengthening. The high chromium content forms a protective Cr₂O₃ scale, while molybdenum improves resistance in reducing and sulfidizing conditions. Cerium is the key rare-earth addition that anchors the oxide scale to the metal substrate during thermal cycling. Carbon is kept low to avoid sensitization and to maintain corrosion resistance in the as-welded condition.

Element	Min %	Max %
Nickel (Ni)	Balance	Balance
Chromium (Cr)	24.0	26.0
Molybdenum (Mo)	9.0	11.0
Cobalt (Co)	—	2.5
Aluminum (Al)	—	0.30
Titanium (Ti)	—	0.30
Iron (Fe)	—	2.0
Manganese (Mn)	—	1.0
Silicon (Si)	—	1.0
Carbon (C)	—	0.10
Cerium (Ce)	0.03	0.10
Sulfur (S)	—	0.015
Phosphorus (P)	—	0.02

Physical Properties

Nimonic 86 has a face-centered cubic (FCC) austenitic structure that remains stable throughout its service temperature range. The alloy has a relatively high density due to the substantial nickel, chromium, and molybdenum content, and its thermal expansion coefficient is comparable to other nickel-base high-temperature alloys. Moderate thermal conductivity and good emissivity contribute to reduced thermal gradients in combustion hardware.

Property	Value	Unit
Density	8.53	g/cm3
Melting Range	1330 - 1390	°C
Specific Heat (20°C)	460	J/kg·K
Thermal Conductivity (20°C)	11.0	W/m·K
Electrical Resistivity (20°C)	1.18	μΩ·m
Modulus of Elasticity (20°C)	220	GPa
Mean CTE (20–1000°C)	15.5	μm/m·°C
Mean CTE (20–500°C)	13.8	μm/m·°C

Mechanical Properties at Room Temperature

Nimonic 86 is normally supplied in the solution-annealed condition, which gives it moderate strength and excellent ductility. The values below are typical for sheet, strip, and plate products in the annealed condition. Because the alloy is not precipitation-hardened, its strength decreases gradually with increasing temperature, but it retains sufficient load-bearing capacity for static components such as heat shields, combustion liners, and retorts.

Property	Value
Tensile Strength	730 MPa (106 ksi)
Yield Strength (0.2% offset)	300 MPa (44 ksi)
Elongation in 2 inches	45%
Reduction of Area	55%
Hardness	85 - 95 HRB
Young's Modulus	220 GPa

Heat Treatment Conditions

Nimonic 86 is used almost exclusively in the solution-annealed condition. No aging treatment is required or recommended, since the alloy is not designed to develop precipitation strengthening. The standard heat treatment is:

• Solution Anneal: Heat to 1100–1150°C (2012–2102°F), hold for sufficient time to dissolve any residual secondary phases, then water quench or rapid air cool. This produces a soft, homogeneous austenitic microstructure with optimum formability and corrosion resistance.
• Stress Relief: Occasionally applied after severe forming or welding at 850–950°C, followed by air cooling. Care must be taken not to precipitate sigma phase or carbide films at grain boundaries.
• Hot Working: Initial forging and rolling are performed at 1050–1200°C. Avoid prolonged exposure below 950°C to prevent the formation of deleterious intermetallic phases.

Hangbo Alloy Group supplies Nimonic 86 with full heat treatment certification and can perform additional ultrasonic testing, dye penetrant inspection, and dimensional inspection according to customer specifications.

High-Temperature Performance

Nimonic 86 is primarily selected for its outstanding surface stability at high temperatures rather than for high load-bearing capacity. Its maximum recommended service temperature in air is approximately 1000°C, with short-term excursions to 1050°C possible in low-stress components. The combination of high chromium and molybdenum provides excellent resistance to oxidation, carburization, and sulfidation in both oxidizing and reducing combustion atmospheres.

Temperature (°C)	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation (%)
20 (Room)	730	300	45
600	520	210	48
700	440	180	50
800	360	150	52
900	280	120	55
1000	200	90	58

Thermal Cycling & Scale Adhesion

One of the most important performance characteristics of Nimonic 86 is its resistance to oxide spallation during thermal cycling. The cerium addition segregates to the oxide-metal interface, reducing void formation and improving the mechanical keying of the Cr₂O₃ scale. In cyclic oxidation tests between room temperature and 1000°C, Nimonic 86 typically shows lower weight loss and better scale retention than binary Ni-Cr alloys and many stainless steels. This makes it particularly suitable for combustion chambers, afterburners, and furnace components that experience repeated heating and cooling cycles.

Corrosion Resistance

Nimonic 86 offers a broad spectrum of corrosion resistance in aggressive high-temperature environments. The alloy's performance is dominated by the synergistic effects of chromium, molybdenum, and cerium:

Resistance to Specific Media:

• Oxidation Resistance: Forms a protective chromium-rich oxide scale that remains stable in air and combustion gases up to 1000°C. The cerium addition improves scale adhesion and reduces spallation during thermal cycling.
• Carburization Resistance: The high nickel and chromium content, combined with the protective oxide scale, provides excellent resistance to carbon uptake in carburizing atmospheres such as cracked hydrocarbons and endothermic gas. This is critical for furnace components and petrochemical reformer tubes.
• Sulfidation Resistance: Molybdenum significantly improves resistance to sulfidation in sulfur-containing combustion gases and reducing environments. Nimonic 86 performs better than many austenitic stainless steels in low-oxygen, high-sulfur conditions.
• Nitridation Resistance: The stable Cr₂O₃ scale offers good protection in ammonia and nitrogen-rich atmospheres at elevated temperatures, though service limits should be confirmed for each specific environment.
• Chloride-Induced Attack: While not primarily designed for aqueous chloride service, the high chromium and molybdenum content provides moderate resistance to pitting and stress corrosion cracking compared with conventional stainless steels.

Applications

Nimonic 86 is used wherever high-temperature surface stability, thermal fatigue resistance, and moderate strength are required. Its applications span aerospace, power generation, industrial heat treatment, and petrochemical processing:

• Gas Turbines: Combustion chamber liners, transition ducts, afterburner components, flame tubes, and heat shields. The alloy withstands the severe thermal cycling and oxidizing combustion products found in aircraft and industrial engines.
• Industrial Furnaces: Muffles, retorts, radiant tubes, furnace belts, heat treatment baskets, and fixtures. The carburization resistance is especially valuable in heat treatment furnaces used for automotive and aerospace components.
• Petrochemical Processing: Reformer tubes, catalyst support grids, and internal components in steam methane reformers. The alloy resists carburization and sulfidation in the complex reducing-oxidizing atmospheres encountered in hydrogen production.
• Waste Incineration: Grates, combustion chamber walls, and boiler tubes in municipal and hazardous waste incinerators. The alloy tolerates the corrosive, halogen-containing flue gases and thermal shock associated with waste combustion.
• Power Generation: Components in coal-fired and biomass-fired boilers, including superheater tubes, soot blower lances, and burner nozzles, where resistance to sulfidation and ash corrosion is critical.

Available Product Forms

Hangbo Alloy Group manufactures and supplies Nimonic 86 in a comprehensive range of product forms and sizes, all supported by material test reports and third-party inspection. Our typical supply scope includes:

• Sheet & Strip: AMS 5869, BS HR204, thickness 0.1 mm to 6.0 mm, cold-rolled and solution annealed, available in coils, cut lengths, and precision slit widths.
• Plates: ASTM B670, BS HR4, thickness 3 mm to 50 mm, hot-rolled and solution annealed, with ultrasonic testing available on request.
• Round Bars: BS HR4, diameters 6 mm to 250 mm, hot-rolled, forged, or cold-drawn, solution annealed and pickled.
• Seamless Tubes: OD 6 mm to 219 mm, wall thickness 0.5 mm to 25 mm, for combustion liners, heat exchangers, and furnace tubes.
• Forgings: Custom flanges, rings, discs, and complex shapes per customer drawing, solution annealed and with full traceability.
• Welding Wire: Matching nickel-chromium-molybdenum filler metals in diameters 0.8 mm to 5.0 mm, precision layer-wound for GTAW and GMAW applications.

Related Standards

Standard	Description
BS HR4	Sheet and Plate
BS HR204	Sheet, Strip, and Plate
AMS 5869	Sheet and Strip, Solution Annealed
ASTM B670	Plate, Sheet, and Strip
DIN 17742	Wrought Nickel-Chromium-Molybdenum Alloy
VdTÜV 499	German Material Approval for Pressure Equipment
ASME Code Case	Boiler and Pressure Vessel Applications (where applicable)

Nimonic 86 vs. Other High-Temperature Alloys

Selecting the right alloy for a high-temperature component depends on the balance between mechanical load, thermal cycling severity, and environmental corrosiveness. Nimonic 86 occupies a specific niche: it is not as strong as precipitation-hardened superalloys, but it offers better oxidation and carburization resistance than many solid-solution alloys at comparable cost.

Alloy	UNS	Max Temp (Air)	Key Strength	Best For
Nimonic 86	N07306	1000°C	Oxidation / carburization resistance	Combustion liners, furnace fixtures
Nimonic 80A	N07080	815°C	High creep strength	Gas turbine blades, bolts
Nimonic 90	N07090	870°C	Very high creep strength	Discs, turbine blades
Inconel 600	N06600	1100°C	Oxidation resistance	Furnace components, nuclear
Haynes 230	N06230	1150°C	Oxidation + creep strength	Combustors, hardware

Frequently Asked Questions

Contact Us for Nimonic 86

Hangbo Alloy Group maintains mill-direct supply of Nimonic 86 sheet, strip, plate, bar, tube, and forgings in standard and custom sizes. Our technical team can assist with material selection, specification review, heat treatment certification, and export documentation. We support customers in aerospace, power generation, industrial heat treatment, and petrochemical industries with reliable quality and fast delivery.

For quotations, material certifications, or technical consultation, contact our sales team or call +86-136-1165-6360. We typically respond within 10 minutes.