800H/HT®

Alloys 800H/HT®

UNS N08810 / UNS N08811 / W.Nr. 1.4959

COMMON TRADE NAMES: Incoloy® 800 H/HT, Sanicro® 31HT

Alloys 800H® and 800HT® are iron-nickel-chromium solid solution strengthened alloys with a nominal chemical composition of 42% iron, 34% nickel, and 22% chromium. These two grades are variations of the base grade 800 and are referred to by the tradenames Incoloy® 800H and Incoloy® 800HT and the universal designation UNS N08810 and N08811, respectively. 800H® and 800HT® share the high-temperature oxidation and carburization resistance of Alloy 800 but have enhanced creep and stress rupture properties.

Characteristics

Chemical Composition

Chemical Composition

The base composition of 800H/HT® is identical to the parent Alloy 800. However, in both 800H® and 800HT®, the levels of carbon, aluminum, and titanium are modified for improved creep resistance. The base 800 grade has a carbon range of 0 - 0.10%, while 800H® raises the minimum carbon level to 0.05%. Similarly, the base 800 grade has a combined aluminum and titanium content requirement of 0.30 - 1.20%, while 800HT® raises the minimum Al + Ti level to 0.85% and increases the minimum carbon to 0.06%.

Corrosion Resistance

Both grades share the corrosion resistant characteristics of the base grade Alloy 800, including good general corrosion resistance, as well as good resistance to reducing and oxidizing acids, organic acids, seawater, salts, and particularly excellent resistance to nitric acid. Alloy 800H® and 800HT® also exhibit excellent corrosion resistance to chloride stress corrosion cracking (SCC). However, alloys 800H® and 800HT® are not recommended for sulfuric acid service. Additionally, they are susceptible to chromium carbide precipitation along grain boundaries when subjected to temperatures in the range of 1000°F - 1400°F (538°C - 760°C).
Service Temperature

Elevated Temperature Resistance

800H® and 800HT® have outstanding resistance to oxidation, carburization, and sulfidation at temperatures up to 1800°F.
Mechanical Properties

Mechanical Properties

800H® and 800HT® are typically supplied in a low-strength solution annealed condition. While intended for high-temperature applications, they have excellent toughness down to cryogenic temperatures.

Heat Treatment

Alloys 800H® and 800 HT cannot be strengthened by heat treating. They are typically solution annealed at 2050°F - 2150°F (1121°C - 1177°C) followed by rapid cooling. Stress-relieving at 1000°F - 1600°F (538°C - 870°C) may also be performed after cold working to reduce residual stresses and prevent distortion.
Workability

Workability

Alloy 800H® and 800HT® can be cold worked using common methods and should be in the annealed condition prior to cold working. The large grain size produced in both grades from solution annealing can lead to “orange peel” surface roughening after cold working. Hot-working should be done above 1600°F (871°C).

Applications

Alloy 800H® and 800HT® are used at temperatures from 1100°F – 1800°F (593°C – 982°C) where creep and stress rupture failure is a concern. 800H® is typically used at the lower end of this range, while 800HT® is employed at the upper end. Applications include structural members, furnace equipment, heat exchangers, petrochemical vessels and piping, and aerospace. CRA offers specialty alloy 800H/HT® seamless pipe & tube for use in multiple industries and applications, including:

  • Heat Exchangers
  • Furnace Equipment
  • Aerospace
  • Petrochemical Vessels & Piping

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Chemical Composition

 CCrNiFeTiAlAl + Ti
N088100.05 - 0.119 - 2330 - 35≥ 39.50.15 - 0.60.15 - 0.60.3 - 1.2
N088110.06 - 0.119 - 2330 - 35≥ 39.50.25 - 0.60.25 - 0.60.85 - 1.2
(mass %)

Specifications

ASTM B407, ASME SB407

Specified Mechanical Properties in Solution Annealed Condition

Per ASTM B407
Tensile StrengthYield StrengthElongation
minimum, ksiminimum, ksiminimum, %
652530

Typical Physical & Mechanical Properties in Solution Annealed Condition

  70°F200°F400°F600°F800°F1000°F1200°F
Densitylbs/in30.287------
Thermal ExpansionX10-6/°F-7.98.899.29.59.6
Elastic Modulus103 ksi28.527.8226.8125.7124.6423.5222.37
Poisson Ratio-0.3390.3410.3530.3570.3630.3670.377
Thermal ConductivityBtu-in/h·ft2·°F8089103115127139152
Specific HeatBtu/lb·°F0.110.110.110.120.120.130.14
Yield Strengthksi25201714121211
Tensile Strengthksi65625857555244

Manufacturing Process

PROCESSDESCRIPTION
Steel MakingElectric Arc Furnace followed by Vacuum Oxygen Decarburization (VOD) or Argon Oxygen Decarburization (AOD).
Pipe MakingConventional Seamless Cold Finished Pipe and Tube Manufacturing Processes.
Heat TreatmentCannot be hardened by heat treatment. Typically provided in the solution annealed condition. Solution annealing may be optimized for intended application temperature range.

Related Alloys

As noted above, 800H® and 800HT® are creep-resistant variants of Alloy 800.

Product Availability

CRA offers this alloy in:
Seamless Pipe & Tube

MIN OD: 2-1/16″ (2.0625″)
MAX OD: 10-3/4″ (10.750”)
THICKNESS: Up to 1.925”
LENGTHS: Up to 70′

Standard & Non-Standard Sizes Available.

Manufactured Material Available as Quickly as 1 Week.

Non-Standard Mill Quantities Accommodated