Alloy 800,Incoloy 800 ,N08800

Alloy 800HT (Welding),Incoloy 800HT Wire,N08811

Introduction to Alloy 800HT (Incoloy 800HT Wire, UNS N08811) for Welding Applications

Alloy 800HT, commercially known as Incoloy 800HT and classified under UNS N08811, is a nickel-iron-chromium superalloy engineered for exceptional performance in high-temperature and corrosive environments. Distinguished from standard Alloy 800 by its optimized chemistry (higher carbon, controlled aluminum and titanium content) and heat treatment, it delivers superior creep resistance, oxidation resistance, and mechanical strength at temperatures up to 850°C (1560°F). Incoloy 800HT wire, a critical form of this alloy, is widely used as welding filler material and precision components in industries relying on high-temperature stability—such as petrochemical, power generation, and aerospace. Its compatibility with welding processes (e.g., TIG, MIG) and ability to match the base metal’s high-temperature properties make it a preferred choice for joining Alloy 800HT structures.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N08811 adheres to stringent standards like ASTM B409 (for nickel-alloy wire), ASME SB409, and AWS A5.14 (for welding filler metals), ensuring consistent high-temperature performance and weldability. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

30.0 - 35.0

Enhances high-temperature ductility, corrosion resistance, and alloy stability.

Chromium (Cr)

19.0 - 23.0

Forms a protective chromium oxide (Cr₂O₃) layer, resisting oxidation and sulfidation at high temperatures.

Iron (Fe)

Balance

Reduces alloy cost while maintaining mechanical strength and thermal conductivity.

Carbon (C)

0.06 - 0.10

Improves creep and stress rupture strength by stabilizing grain boundaries (key distinction from standard Alloy 800).

Aluminum (Al)

0.15 - 0.60

Works with titanium to form precipitates (e.g., TiAl₃) for grain refinement and oxidation resistance.

Titanium (Ti)

0.15 - 0.60

Prevents intergranular corrosion and enhances high-temperature creep resistance; controlled to avoid brittle phase formation.

Manganese (Mn)

≤ 1.5

Improves hot workability and weldability without compromising high-temperature properties.

Silicon (Si)

≤ 1.0

Aids in deoxidation during melting and reduces oxide formation in welds.

Copper (Cu)

≤ 0.75

Minimized to avoid hot cracking in welds and maintain oxidation resistance.

Phosphorus (P)

≤ 0.03

Reduced to prevent brittleness and intergranular corrosion in welded joints.

Sulfur (S)

≤ 0.015

Minimized to avoid hot cracking during welding and reduce corrosion susceptibility.

Cobalt (Co)

≤ 1.0

Controlled to limit alloy cost and maintain thermal stability.

2. Physical Properties

Incoloy 800HT wire exhibits stable physical properties across its operating temperature range (-200°C to 850°C), making it suitable for both cryogenic pre-weld preparation and high-temperature service. Key properties are:

Property

Value

Test Condition

Density

7.94 g/cm³

Room temperature (25°C)

Melting Point Range

1350 - 1400°C

-

Thermal Expansion Coefficient

13.5 × 10⁻⁶/°C

20 - 100°C; 16.8 × 10⁻⁶/°C (20 - 800°C)

Thermal Conductivity

11.2 W/(m·K)

100°C; 23.4 W/(m·K) (800°C)

Electrical Resistivity

1.12 × 10⁻⁶ Ω·m

Room temperature (25°C); 1.38 × 10⁻⁶ Ω·m (800°C)

Modulus of Elasticity

195 GPa

Room temperature (tensile); 150 GPa (800°C)

Poisson’s Ratio

0.30

Room temperature

Curie Temperature

≈ -10°C

Below this temperature, the alloy is ferromagnetic (irrelevant for high-temperature applications).

Stress Rupture Strength

120 MPa

1000 hours at 700°C; 45 MPa (1000 hours at 800°C)

3. Production Process of Incoloy 800HT Wire (with Welding-Grade Focus)

The manufacturing of Incoloy 800HT wire—especially for welding applications—requires strict process control to ensure weld integrity, low impurity levels, and consistent dimensional accuracy. Key steps include:

3.1 Raw Material Melting & Purification

Melting: High-purity raw materials (nickel, chromium, iron, etc.) are melted via vacuum induction melting (VIM) followed by vacuum arc remelting (VAR). This dual-melting process eliminates gaseous impurities (e.g., oxygen, nitrogen) and segregations, critical for preventing weld porosity.

Casting: Molten alloy is cast into ingots, which are homogenized at 1150 - 1200°C for 4 - 6 hours to uniformize chemistry and eliminate grain boundary inhomogeneities.

3.2 Hot Working & Cold Drawing (Welding Wire Optimization)

Hot Rolling: Ingots are hot-rolled into rods (diameter: 12 - 60 mm) at 1050 - 1150°C, followed by air cooling to retain a fine-grained microstructure.

Cold Drawing: Hot-rolled rods are cold-drawn through diamond dies in multiple passes to achieve welding-grade wire diameters (typically 0.8 mm - 4.0 mm for TIG/MIG applications). Intermediate annealing (950 - 1050°C for 30 - 45 minutes, water-quenched) is performed to relieve work hardening and ensure ductility—critical for smooth wire feeding during welding.

3.3 Heat Treatment (Weld Compatibility Enhancement)

Solution Annealing: Final cold-drawn wire undergoes solution annealing at 1050 - 1100°C for 15 - 30 minutes, then rapid water quenching. This process dissolves unwanted precipitates (e.g., carbides) and produces a uniform austenitic microstructure, matching the base Alloy 800HT’s phase composition for consistent weld strength.

Stress Relieving (Optional): For precision welding wires, stress relieving at 400 - 600°C for 1 - 2 hours (slow-cooled) reduces residual stresses, preventing wire deformation during welding.

3.4 Surface Finishing & Welding-Grade Quality Inspection

Surface Treatment: Wire surfaces are cleaned via pickling (nitric-hydrochloric acid solution) to remove oxide scales, then passivated (chromate treatment) to enhance corrosion resistance and prevent contamination of weld pools.

Welding-Specific Quality Control:

Impurity Testing: Gas chromatography to detect trace gases (O₂ < 50 ppm, N₂ < 100 ppm) that cause weld porosity.

Dimensional Precision: Laser measurement for diameter tolerance (±0.02 mm) and roundness (≤0.01 mm) to ensure uniform arc stability.

Mechanical Testing: Tensile strength (≥550 MPa at room temperature) and elongation (≥30%) to verify ductility for welding.

Weldability Validation: Trial TIG welds to check for crack formation, fusion quality, and post-weld mechanical strength.

4. Product Applications (with Welding Focus)

Incoloy 800HT wire’s unique combination of high-temperature strength, oxidation resistance, and weldability makes it indispensable in industries requiring reliable performance under extreme heat. Key applications include:

4.1 Welding Filler Material (Primary Application)

TIG/MIG Welding: Used as filler wire (per AWS ERNiFeCr-2 specification) for joining Alloy 800HT components—such as petrochemical reactor vessels, power plant boiler tubes, and heat exchanger shells. Ensures weld joints match the base metal’s creep resistance and oxidation resistance at 700 - 850°C.

Overlay Welding: Applied as cladding wire to protect carbon steel or low-alloy steel components (e.g., furnace liners, exhaust manifolds) from high-temperature corrosion and erosion.

4.2 Petrochemical & Refining Industry

Cracking Furnace Components: Wire-wound heating elements and thermocouple sheaths for ethylene cracking furnaces (operate at 800 - 850°C, resist naphtha and steam corrosion).

Reactor Internals: Precision wire mesh filters and support springs for high-temperature hydrogenation reactors (resist H₂S and hydrocarbon-induced corrosion).

4.3 Power Generation

Fossil Fuel Power Plants: Boiler superheater tube connections (welded with Incoloy 800HT wire) and turbine exhaust duct components (withstand flue gas temperatures up to 750°C).

Nuclear Power: Auxiliary system components (e.g., coolant circulation pipes) and welding filler for steam generators—low neutron absorption and resistance to primary coolant (borated water) corrosion.

4.4 Aerospace & Defense

Jet Engine Components: Small-diameter wire for manufacturing combustion chamber liners and afterburner parts (resist high-temperature exhaust gases and thermal cycling).

Rocket Propulsion Systems: Welding filler for liquid rocket engine fuel lines (operate at cryogenic pre-launch temperatures and high post-ignition heat).

4.5 Heat Treatment & Industrial Furnaces

Furnace Heating Elements: Coiled Incoloy 800HT wire for electric resistance furnaces (used in metal heat treatment, operate at 800 - 850°C with air or inert gas atmospheres).

Furnace Retorts: Wire reinforcement for ceramic retorts (prevents thermal shock cracking in high-temperature sintering processes).

4.6 Other High-Temperature Applications

Automotive (Heavy-Duty): Exhaust system sensors and catalytic converter components for diesel trucks (resist high-temperature exhaust and sulfur oxide corrosion).

Chemical Processing: Wire-wound agitator shafts for high-temperature acid digestion tanks (resist sulfuric and nitric acid vapors at 600 - 700°C).

Conclusion

Alloy 800HT (Incoloy 800HT Wire, UNS N08811) stands out as a high-performance material for high-temperature and welding applications, thanks to its optimized chemistry, strict manufacturing controls, and exceptional creep/oxidation resistance. As a welding filler wire, it ensures robust, temperature-matched joints for critical Alloy 800HT structures, while its versatility extends to precision components in petrochemical, power, and aerospace industries. For custom requirements—such as specialized wire diameters (down to 0.5 mm) for micro-welding or modified surface finishes for enhanced weldability—tailored production processes are available to meet specific application needs.

Packing of Standard Packing:

 Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 896 gallon liquid totes Special package is available on request.