Material Family

Nickel-Iron-Chromium Austenitic Alloy (Solid-Solution Strengthened, High-Temperature Optimized)

Premium grades for high-temperature, load-bearing applications.

Common Designations

800H: UNS N08810, Incoloy 800H, W.Nr. 1.4958
800HT: UNS N08811, Incoloy 800HT, W.Nr. 1.4959

The "HT" grade has tighter controls on aluminum and titanium for optimal creep strength. "Incoloy" is a trademark of Special Metals Corporation.

Distinguishing Feature

Guaranteed Enhanced Creep Rupture Strength at temperatures above 540°C (1000°F).

This is the primary reason to specify 800H/HT over standard 800 for high-temperature designs.

Chemical Composition (Typical wt.%)

Common Elements:
Ni: 30.0 - 35.0
Cr: 19.0 - 23.0
Fe: ≥ 39.5 (Balance)
C: 0.05 - 0.10
Key Differences:
Aluminum (Al): 0.15 - 0.60
Titanium (Ti): 0.15 - 0.60
800HT Requirement: (Al + Ti) must be 0.85 - 1.20

Controlled Carbon (C) is key for strength. 800HT's required (Al+Ti) sum ensures optimal precipitation strengthening for the best creep performance.

Mechanical Properties (Annealed Plate, Room Temp)

Tensile Strength (Rm): 450 - 600 MPa (min yield varies by spec)
Yield Strength (Rp0.2): 170 - 240 MPa (min)
Elongation (A): 30% min

Room temperature properties are similar to standard 800. The critical properties are elevated temperature strength and creep data.

Physical Properties

Density: 7.94 g/cm³
Melting Range: 1350 - 1400 °C
Primary Service Range: 600°C - 950°C (1110°F - 1740°F) for maximum benefit of enhanced creep strength.

Optimized for long-term exposure in this high-temperature window.

Key Performance Attributes

• Excellent and Predictable Creep & Stress-Rupture Properties• Excellent resistance to oxidation, carburization, and sulfidation.• Good resistance to chloride stress corrosion cracking.• Good weldability and fabricability.

The benchmark alloy for high-temperature, pressurized components like reformer and cracking furnace tubes.

Mandatory Thermal-Mechanical Processing

Material must be annealed at a minimum of 1121°C (2050°F) to achieve an ASTM grain size of 5 or coarser (typically ASTM 3-5).

This controlled coarse grain structure is essential to develop the specified high-temperature creep strength. It is a mandatory requirement per ASTM B407/409.

Key Standards (Plate)

Primary Plate Spec: ASTM B409 / ASME SB-409
Mandatory Supplementary Spec: ASTM B407 (Covers grain size and heat treatment requirements for UNS N08810 & N08811)

Purchasing to ASTM B409 alone is insufficient. Orders must specify compliance with ASTM B407 to guarantee the high-temperature properties.

Typical Applications

• Petrochemical: Steam Methane Reformer (SMR) & Ethylene Cracking Furnace Tubes and Header Piping• Power Generation: Heat Exchanger Tubesheets, Superheater Supports
• Industrial Heating: Radiant Tubes, Retorts, Muffles for Heat Treating Furnaces
• Nuclear: High-Temperature Gas-Cooled Reactor (HTGR) Components

The dominant material for pressurized high-temperature tubing and critical fittings in the petrochemical industry.