Incoloy 800, Incoloy 800H, and Incoloy 800HT—three remarkable nickel-based alloys with distinct properties and applications:

Incoloy 800 Series: High-Temperature Alloys

1. Introduction:

The Incoloy 800 series of alloys, developed by the Special Metals Corporation, represents a lineage of nickel-iron-chromium alloys designed for high-temperature strength and exceptional resistance to oxidation, carburization, and other forms of high-temperature corrosion. These alloys have evolved over time, each building upon the strengths of its predecessor. Let’s delve into their characteristics, techniques, and industrial applications.

2. Characteristics:

Incoloy 800 (UNS N08800):

Composition: Primarily composed of nickel (30-35%), chromium (19-23%), and iron (39.5% minimum).

Strength at High Temperatures: Maintains excellent strength even in elevated temperature environments.

Oxidation Resistance: Resists oxidation, making it suitable for furnace components, petrochemical furnace cracker tubes, and electrical heating element sheathing.

Weldability and Formability: Easily formed, welded, and machined.

Historical Context: Introduced in the 1950s as a heat- and corrosion-resistant alloy with relatively low nickel content due to nickel’s strategic status at the time.

Incoloy 800H (UNS N08810):

Higher Carbon Content: Alloy 800H contains higher carbon levels, enhancing creep and rupture properties.

Dual-Certified Alloy: Often offered as a dual-certified alloy, meeting the chemical composition requirements of both Incoloy 800 and 800H.

Applications: Used in power generation, chemical processing, and aerospace industries.

Incoloy 800HT (UNS N08811):

Further Carbon Restriction: The carbon content in Incoloy 800HT is even more restricted (0.06-0.10%).

Aluminum and Titanium Additions: Aluminum (0.15-0.60%) and titanium enhance high-temperature properties.

Applications: Widely employed in heat-treating operations, radiant tubes, and chemical processing equipment.

3. Techniques:

Solution Annealing: Common heat treatment method for Incoloy 800 series alloys.

Age Hardening: Precipitation hardening process for achieving higher strength.

Fabrication Ease: These alloys are readily machined, formed, and welded.

4. Industries and Applications:

Chemical Processing: Reactor vessels, heat exchangers, and corrosive environments.

Aerospace: Components in aircraft and gas turbine engines.

Power Generation: Gas turbine parts, heat exchangers, and more.

Cryogenic Tankage: Suitable for storage tanks.

Other Fields: Jet-engine igniters, fasteners, instrumentation, and pollution control systems.

In summary, the Incoloy 800 series alloys continue to set the industry standard for high-temperature applications, combining strength, corrosion resistance, and versatility.