Alloy 800H/HT®


Alloy 800H/800HT® are two individual solid solution strengthened, iron-nickel-chromium alloys typically offered as one, dual certified alloy meeting the chemical composition requirements of both alloys. The primary difference between Alloys 800H and 800HT® is the restricted aluminum and titanium content in 800HT®, which results in higher creep and stress rupture properties. Both Alloy 800H and 800HT® are generally considered to be superior to the base Alloy 800 (UNS N08800) because of greater creep and stress rupture properties and a more restrictive C wt% range.

With its high nickel and chromium content, Alloy 800H/800HT® provides excellent resistance to oxidation, carburization and sulfidation and is commonly used in applications that involve long-term exposure to high temperatures. Heat treatment and power generation are two common industries where Alloy 800 H/HT® is used with typical applications found in superheater and reheater tubing, headers, pigtails, outlet manifolds and sheathing for heating elements. Alloy 800H/800HT® also has excellent resistance to nitric acid at concentrations up to 70% and has good resistance to organic media like formic, acetic and propionic acids.

INCOLOY® and 800HT® are registered trademarks of Special Metals Corporation.

Chemical Composition

Chemical Composition (wt%)

Iron 39.5 min Aluminum 0.15 to 0.60
Nickel 30.0 to 35.0 Titanium 0.15 to 0.60
Chromium 19.0 to 23.0 Carbon 0.06 to 0.10
Manganese 1.5 max Phosphorus 0.045 max
Silicon 1.0 max Sulfur 0.015 max
Copper 0.75 max Other Al + Ti = 0.85 to 1.20

Physical Properties

Physical properties for Alloy 800H/800HT®

Density, lb/in3 0.287
Melting Temperature 2475°F to 2525°F
Specific Heat, Btu/lb ˚F 0.11
Permeability @ 70°F for Annealed Material 1.014 (200 Oersted)
Curie Temperature -175°F
Elastic Modulus @ 75°F (Tension) 28.50 X 103 ksi
Elastic Modulus @ 1600°F (Tension) 19.20 X 103 ksi
Electrical Resistivity @ 70°F 595 Ω•circ mil/ft
Electrical Resistivity @ 1800°F 776 Ω•circ mil/ft

Mechanical Properties

All properties in this table are for material in the solution annealed condition (hot worked and cold worked) and are from the governing ASTM specification.

0.2% Yield Strength, min. (ksi) 25
Tensile Strength, min. (ksi) 65
Elongation, min. (%) 30

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