UNS N08811 DIN 1.4959 Inconel Round Bars

Product Description

UNS N08811 (universally known as Incoloy 800HT or W.Nr. 1.4959) is a premium nickel-iron-chromium solid-solution alloy designed specifically for high-temperature structural and creep-rupture applications.

While it is frequently grouped into the "Inconel" umbrella by suppliers, it technically belongs to the Incoloy family because its iron content ($>39.5%$) is higher than its nickel content. This specific elemental balance makes it far more cost-effective than pure nickel-base alloys, while still providing remarkable mechanical stability and oxidation resistance at extreme temperatures between 600C and 950C (1100F to 1740F).

Chemical Composition (Weight % per ASTM B408)

UNS N08811 is a sub-grade variant of the baseline Alloy 800. It features tightly restricted limits on carbon, aluminum, and titanium, along with a mandatory high-temperature solution annealing treatment to maximize grain growth.

Element	Iron (Fe)	Nickel (Ni)	Chromium (Cr)	Carbon (C)	Al + Ti	Aluminum (Al)	Titanium (Ti)
Percentage	39.5% min (Balance)	30.0 35.0%	19.0 23.0%	0.06 0.10%	0.85 1.20%	0.25 0.60%	0.25 0.60%

Why this specific modification matters:

• The High Carbon (0.060.10%): Positioned on the higher end of standard Alloy 800 to ensure high-temperature creep strength.

• The Al + Ti Window (0.851.20%): Combined concentration is held strictly within this range to ensure optimal solid-solution strengthening without triggering embrittling phases over long thermal exposures.

• The Base Matrix (Ni-Fe-Cr): Chromium provides excellent scaling and oxidation resistance, while the nickel content maintains an austenitic structure that resists carburization and nitriding in high-temperature gases.

Global Material Standards

Round bars processed from UNS N08811 are typical certified under the following industrial designations:

• UNS: N08811 (Alloy 800HT)

• Werkstoff Nummer (W.Nr.): 1.4959

• EN ISO Alphanumeric: X8NiCrAlTi32-21

• ASTM / ASME: B408 / SB408 (Standard Specification for Nickel-Iron-Chromium Alloy Rod and Bar)

• Design Pressure Codes: Approved under ASME Section VIII (Boiler and Pressure Vessel Code) for construction up to 899C (1650F).

Key Mechanical Profile & Creep Properties

Unlike age-hardenable superalloys (such as N09925), UNS N08811 cannot be hardened by heat treatment. Its strength at room temperature is relatively modest, but it is engineered to excel where standard alloys yield or creep over time.

• Grain Size Requirement: Must exhibit a coarse grain structure of ASTM No. 5 or coarser (typically achieved via high-temperature annealing). Large grains significantly reduce grain-boundary sliding, which is the primary cause of high-temperature creep deformation.

• Tensile Strength: $ge 500 text{ MPa}$ ($72 text{ ksi}$)

• Yield Strength (0.2% Offset): $ge 170 text{ MPa}$ ($25 text{ ksi}$)

• Elongation: $ge 30%$

Thermal Processing & Fabrication Insights

1. High-Temperature Solution Annealing

• Temperature: 1150C 1200C (2100F2190F) is mandatory for 800HT.

• Process: Soaked thoroughly to ensure complete recrystallization and controlled grain coarsening, followed by a rapid air cool or water quench.

2. Machining Characteristics

• UNS N08811 is gummy and work-hardens rapidly. It requires rigid machine setups, heavy duty cutting fluids, sharp tooling (preferably carbide), and a continuous feed rate. Never allow the tool to dwell or rub against the metal, as it will instantly glaze and harden the surface layer.

3. Welding Guidelines

• Commonly welded using matching composition filler metals like Inconel Filler Metal 82 or Welding Electrode 182. For maximum creep resistance in service above 760C (1400F), specialized filler metals like Inconel 617 or Haynes 230 are often specified to match the creep profile of the base metal.

Primary Applications for N08811 Round Bars

Because of its phenomenal structural stability when exposed to glowing-hot operating environments, UNS N08811 round bars are machined into:

• Petrochemical Processing: Steam/hydrocarbon reforming components, pigtails, header assemblies, and cracking tubes where long-term creep rupture resistance is vital.

• Industrial Furnace Components: Furnace retorts, conveyor rollers, radiant heating tubes, muffle elements, and internal structural fixtures.

• Power Generation Infrastructure: Superheater and reheater tubing attachments, heat exchanger components, and high-temperature piping hangers in coal, gas, and nuclear power plants.

• Thermal Processing Hardware: Nitriding furnace fixtures, carburizing baskets, and heat-treating jigs exposed to cyclical thermal loads.

Unmatched High-Temperature Performance

UNS N08811 / DIN 1.4959 Inconel Round Bars are engineered to perform exceptionally well under intense heat. Their advanced alloy composition and tolerance for temperatures up to 1385C make them the preferred choice for furnace components and heat treating equipment.


Superior Corrosion Resistance

These round bars display remarkable resistance to oxidation and corrosive atmospheres, even in the harshest industrial settings. This property makes them ideal for critical applications in chemical and petrochemical industries where exposure to aggressive chemicals and high operating temperatures is routine.


Tailored Dimensions and Finishes

Available in diameters from 5 mm to 200 mm and lengths from 100 mm to 6000 mm, these round bars can be customized as per project requirements. They are offered in peeled, turned, polished, bright, or black finishes, ensuring compatibility with diverse engineering needs.