Incoloy 800 fasteners are widely used in high-temperature and corrosive service environments where strength, oxidation resistance, and structural stability are critical. As a nickel-iron-chromium alloy, Incoloy 800 offers excellent resistance to carburization, oxidation, and nitriding, making it a reliable choice for heat-processing and petrochemical industries.

This blog provides a technically accurate overview of Incoloy 800 fastener specifications, based strictly on established ASTM, ASME, and internationally recognized material standards.

1. What is Incoloy 800?

Incoloy 800 is a nickel-iron-chromium alloy designed for high-temperature structural applications. It is designated as:

• UNS N08800

The alloy maintains stable austenitic structure and resists scaling and oxidation at elevated temperatures. It is commonly used in environments involving prolonged exposure to temperatures above 600°C.

“Incoloy” is a trademark historically associated with Special Metals Corporation, though the alloy is produced globally under the UNS designation N08800.

2. Chemical Composition of Incoloy 800 (UNS N08800)

According to ASTM material specifications, the typical chemical composition is:

ElementComposition (%)Nickel (Ni)30.0 – 35.0Chromium (Cr)19.0 – 23.0Iron (Fe)≥ 39.5 (Balance)Carbon (C)≤ 0.10Manganese (Mn)≤ 1.50Silicon (Si)≤ 1.00Sulfur (S)≤ 0.015Copper (Cu)≤ 0.75Aluminum (Al)0.15 – 0.60Titanium (Ti)0.15 – 0.60

The balanced nickel and chromium content provides resistance to oxidation and carburization, while aluminum and titanium contribute to structural stability.

3. Standards for Incoloy 800 Fasteners

Incoloy 800 fasteners are manufactured in accordance with recognized ASTM and ASME standards depending on application:

Bolting Standards:

• ASTM B408 – Nickel-Iron-Chromium Alloy Rod, Bar, and Wire (basis material for fasteners)
• ASTM A193 Grade B407 – Alloy-Steel and Stainless Steel Bolting for High-Temperature or High-Pressure Service
• ASTM A194 Grade 8 (when applicable for nuts in certain assemblies)

Under ASTM A193, Incoloy 800 bolting is designated as:

• ASTM A193 Grade B407 (UNS N08800)

ASME Equivalent:

• ASME SB408 (material)
• ASME SA193 B407 (bolting)

These standards define chemical composition, mechanical properties, heat treatment conditions, and marking requirements.

4. Mechanical Properties

Mechanical properties vary depending on condition and product form. Typical minimum mechanical properties for Incoloy 800 (annealed condition, per ASTM specifications) include:

PropertyMinimum ValueTensile Strength520 MPaYield Strength (0.2% offset)205 MPaElongation30%

For bolting under ASTM A193 B407, specific strength requirements are defined by the standard depending on diameter and condition.

5. Physical Properties

PropertyApproximate ValueDensity7.94 g/cm³Melting Range1350 – 1400°CModulus of Elasticity196 GPaThermal Conductivity~11.5 W/m·K at 100°CElectrical Resistivity~0.98 µΩ·m at 20°C

These properties allow Incoloy 800 fasteners to perform reliably in elevated-temperature applications.

6. High-Temperature Performance

Incoloy 800 fasteners provide:

• Resistance to oxidation at high temperatures
• Resistance to carburization and nitriding
• Structural stability during long-term exposure to elevated temperatures
• Good creep and stress rupture strength

The alloy is commonly used in service temperatures up to approximately 1100°C in oxidizing environments, depending on specific application conditions.

7. Corrosion Resistance

Incoloy 800 exhibits:

• Resistance to oxidation and scaling
• Good resistance to many organic and inorganic acids
• Resistance to chloride stress corrosion cracking (better than many austenitic stainless steels)
• Resistance to carburizing atmospheres

It performs well in high-temperature aqueous and steam environments.

8. Types of Incoloy 800 Fasteners

Common fastener forms include:

• Hex bolts
• Stud bolts
• Heavy hex nuts
• Socket head cap screws
• Threaded rods
• Anchor bolts

Threading standards typically comply with ASME B1.1 (Unified threads) or ISO metric standards depending on region.

9. Applications of Incoloy 800 Fasteners

Due to its high-temperature and corrosion resistance, Incoloy 800 fasteners are widely used in:

• Petrochemical plants
• Heat exchangers
• Power generation facilities
• Industrial furnaces
• Steam superheater components
• Chemical processing equipment
• Oil and gas installations

They are particularly valuable where stainless steels may lose strength or suffer oxidation at elevated temperatures.

10. Difference Between Incoloy 800, 800H, and 800HT

Incoloy 800 has related grades:

• UNS N08810 (800H)
• UNS N08811 (800HT)

These variants have controlled carbon and grain size requirements to improve creep resistance at elevated temperatures.

However, standard Incoloy 800 (UNS N08800) is commonly used for general high-temperature fastener applications.

Key Advantages of Incoloy 800 Fasteners

• Excellent high-temperature oxidation resistance
• Good mechanical strength at elevated temperatures
• Resistance to carburization and nitriding
• Good structural stability
• Suitable for pressure and heat-processing equipment

Conclusion

Incoloy 800 fasteners (UNS N08800), manufactured according to ASTM A193 Grade B407 and ASTM B408 standards, provide dependable performance in high-temperature and corrosive service environments. With a nickel-iron-chromium composition and stable austenitic structure, they offer a reliable solution for petrochemical, power generation, and heat-processing industries.