Incoloy 800HT/UNS N08811/W.Nr. 1.4959/Alloy 800HT bar

Incoloy 800HT bar, designated as UNS N08811, material number W.Nr. 1.4959, and commonly known as Alloy 800HT, is a high-temperature nickel-iron-chromium alloy with controlled chemistry and mandatory heat treatment to optimize its creep and stress-rupture properties. It represents the highest strength variant within the Alloy 800 family, specifically engineered for long-term service under high stress at temperatures ranging from 600°C to 1150°C (1110°F to 2100°F). This bar stock is essential for machining critical components in reformer furnaces, heat exchangers, and other high-pressure, high-temperature systems in the petrochemical and power industries.

Introduction to Incoloy 800HT (Alloy 800HT)

Incoloy 800HT builds upon the specifications of Alloy 800H with even tighter compositional controls, particularly for aluminum, titanium, and carbon, and a mandatory high-temperature solution anneal to produce a coarse grain structure. The “HT” stands for “High Temperature,” reflecting its superior mechanical strength and creep resistance compared to standard 800 and 800H grades. The bar stock is the material of choice for applications where maximum load-bearing capability and microstructural stability over extended periods at extreme temperatures are non-negotiable.

Chemical Composition of Incoloy 800HT Bar

The enhanced high-temperature performance of Incoloy 800HT bar is guaranteed by its precise and narrowly defined chemical composition. Supplied by Shanghai NC Metal Materials Co., Ltd., the bar stock strictly adheres to specifications that include a mandatory minimum for the combined aluminum and titanium content.

Mechanical Properties of Incoloy 800HT Bar

Incoloy 800HT bar is characterized by its superior high-temperature strength and creep rupture properties, which are validated through specific heat treatment and grain size control. Room temperature properties are similar to 800H, but its elevated temperature performance is enhanced.

Key High-Temperature Property

Physical Properties of Incoloy 800HT Bar

The physical properties of Alloy 800HT bar are consistent with other grades in the 800 series and are used in thermal and mechanical design.

Notes / Condition

Standard Specifications, Bar Forms, and Available Sizes

Shanghai NC Metal Materials Co., Ltd. supplies Incoloy 800HT bar with the rigorous heat treatment and compositional controls required for the most demanding high-temperature structural applications.

Primary Applications of Incoloy 800HT Bar Stock

Machined or forged components from Incoloy 800HT bar are specified for the most critical high-temperature, high-stress services: Petrochemical & Chemical Processing: Catalytic reformer furnace tubes (especially outlet regions), steam methane reformer (SMR) tubes, pyrolysis furnace tubes, and associated headers and pigtails where maximum creep resistance is paramount. Power Generation: High-temperature bolting, superheater/reheater tube supports, and heat exchanger components in advanced thermal power systems. Industrial Heating: Load-bearing radiant tubes, retorts, and fixtures in high-temperature heat treatment furnaces operating under heavy loads. Nuclear Power: Selected high-temperature components in gas-cooled and advanced reactor designs.

Heat Treatment, Grain Size, and the (Al+Ti) Requirement

Three factors define Incoloy 800HT and ensure its properties: 1. Minimum Solution Anneal Temperature: The material must be heated to at least 1149°C (2100°F) to dissolve secondary phases and allow grain growth. 2. Coarse Grain Size: A minimum grain size of ASTM No. 5 (coarser) is mandatory. This coarse structure impedes creep deformation. 3. (Al + Ti) ≥ 0.85%: This is the critical compositional control for 800HT. This minimum level of strengthening/stabilizing elements ensures the formation of a stable, fine dispersion of precipitates (gamma prime) during service, which significantly enhances high-temperature strength. Shanghai NC Metal Materials Co., Ltd. ensures all three requirements are met.

Machining and Fabrication Considerations

Machining Incoloy 800HT bar requires techniques for coarse-grained, high-temperature austenitic alloys. Its coarse grain can lead to a slightly more variable and abrasive machining behavior compared to fine-grained materials. Best practices include: using rigid machine tools; sharp carbide inserts with positive geometry; moderate cutting parameters; and ample coolant. It is machined in the solution-annealed condition. Welding is possible but challenging; the high heat input of welding destroys the coarse grain structure in the heat-affected zone (HAZ), severely degrading creep properties. Post-weld heat treatment to restore the coarse grain is generally not feasible, so welding is often avoided for critical creep-resistant components.

Comparison within the Alloy 800 Family

Selecting the correct grade is crucial: Alloy 800: For general corrosion and heat resistance where high creep strength is not the primary design factor. Alloy 800H: For applications requiring good creep resistance, with mandatory coarse grain but without the stringent (Al+Ti) minimum. Alloy 800HT: For the most demanding creep-resistant applications, with mandatory coarse grain AND a guaranteed minimum (Al+Ti) content of 0.85% for maximum high-temperature strength and stability. Bar stock from Shanghai NC Metal Materials Co., Ltd. is clearly identified and certified to the specified grade.

Reference Pricing and Key Purchasing Factors

The price of Incoloy 800HT bar from Shanghai NC Metal Materials Co., Ltd. reflects its status as the premium, highest-performance grade within the 800 series, with additional processing and quality controls.