Alloy 800H/800HT / UNS N08810 & N08811 / W.Nr. 1.4958 & 1.4959
Incoloy 800 H/HT
Incoloy 800H and 800HT are high-performance iron-nickel-chromium alloys that offer superior strength and durability. Both alloys are solid solution strengthened and meet the chemical composition requirements of each other, making them often offered as dual certified. The main difference between 800H and 800HT lies in their restricted aluminum and titanium content in 800HT, which leads to higher creep and stress rupture properties.
Compared to base alloy 800 (UNS N08800), Incoloy 800H/800HT offers improved creep and stress rupture properties and a more restrictive carbon weight percent range. 800H limits carbon weight percent from a maximum of 0.1% in base alloy 800 to a range of 0.5% to 0.1%. 800HT further restricts the carbon weight percent to a range of 0.6% to 0.1%. Additionally, grain size restrictions are also in place for Incoloy 800H/800HT, but not for base alloy 800.
Industries and Applications
Incoloy 800H/800HT® is an ideal choice for demanding applications requiring high-temperature resistance. This iron-nickel-chromium based solid solution strengthened alloy is widely used in industries such as heat treatment and power generation. Known for its resistance to oxidation, carburization, and other elevated temperature corrosion, 800H/800HT® is commonly used in various applications, including superheater and reheater tubing, headers, pigtails, outlet manifolds, and sheathing for heating elements. The alloy’s quality and superior properties are recognized by the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, which approves the use of 800H/800HT® in pressure vessels and vessel components.
Resistance to Corrosion
Incoloy 800H/800HT® is a high-performing, iron-nickel-chromium alloy that offers exceptional resistance to oxidation, carburization, and sulfidation due to its high nickel and chromium content. The nickel content also enhances its resistance to nitriding, although it may be lower compared to other alloys with a higher nickel content like Alloy 600. This alloy’s chromium content makes it highly resistant to nitric acid, up to 70% concentration, and provides good resistance to organic acids such as formic, acetic, and propionic acids.
Fabrication and Heat Treatment
For optimum results in working with Incoloy 800H/800HT® alloy, it’s important to follow specific temperature guidelines during hot and cold working processes. Hot working temperatures should range from 1600°F to 2200°F, with heavier forming best performed above 1850°F. Avoid forming between 1200°F and 1600°F, and consider preheating tools and dies to 500°F to prevent chill. Rapid cooling is recommended after hot working to minimize time spent at temperatures between 1000°F and 1400°F. Cold working should only be done on annealed material, with additional stress relief or annealing heat treatments potentially needed depending on the amount of strain induced.
To prevent negative impacts on mechanical properties, care should be taken in selecting the right annealing temperature and duration. If the material will undergo more than 20% deformation and requires a final anneal, fine-grain starting stock should be considered. Stress relief can occur at temperatures between 1000°F and 1600°F, and should last a minimum of 1 hour per inch of material or 1.5 hours at 1600°F. The recrystallization anneal is performed at 2100°F to 2200°F.
Incoloy 800H/HT – Applicable Specifications
| Form | ASTM | ASME | Other |
|---|---|---|---|
Incoloy 800 H/HT Plate & Sheet |
B409 | SB409 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Strip |
B409 | SB409 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Pipe |
B407 | SB407 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Tube |
B163 | SB163 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Bar |
B408 | SB408 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Forging |
B564 | SB564 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Welding Wire |
B408 | SB408 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Fittings |
B366 | SB366 | NACE MR0175/ISO 15156 |
Incoloy 800 H/HT Flange |
B564 | SB564 | NACE MR0175/ISO 15156 |
Common Trade Names
The trademark INCOLOY® and 800HT® belongs to the Special Metals Corporation group of companies.
Key Properties
(in annealed condition)
| Tensile strength: | |
| Yield strength: | |
| Elongation: |
Chemical Composition (%)
| Element | Incoloy 800H | Incoloy 800HT |
|---|---|---|
| Ni | 30.0-35.0 | 30.0-35.0 |
| Cr | 19.0-23.0 | 19.0-23.0 |
| Fe | 39.5-46.0 | 39.5-46.0 |
| C | 0.1-0.5 | 0.06-0.1 |
| Mn | 1.0 max | 1.0 max |
| Si | 1.0 max | 1.0 max |
| Al | 0.15-0.6 | 0.15-0.5 |
| Ti | 0.15-0.6 | 0.15-0.5 |
| S | 0.015 max | 0.015 max |
| P | 0.03 max | 0.03 max |
| Cu | 0.75 max | 0.75 max |
| Nb | 0.15-0.5 | 0.15-0.5 |
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