Incoloy 800H vs. Incoloy 800HT: What Are the Real Differences?
In the world of high-temperature superalloys, the Incoloy 800 series-specifically Incoloy 800H (UNS N08810) and Incoloy 800HT (UNS N08811)-are industry standards for heat-resistant applications. While they share the same base of Nickel, Chromium, and Iron, subtle variations in their chemistry and processing lead to significant differences in long-term performance.
1. Chemical Composition: The "Al + Ti" Factor
The most critical difference lies in the precise control of alloying elements, particularly Carbon, Aluminum, and Titanium.
Incoloy 800H: Maintains a carbon content of 0.05–0.10%. It is a solution-heat-treated version of the basic Alloy 800.
Incoloy 800HT: Further refines the 800H chemistry. It requires a combined Aluminum + Titanium (Al + Ti) content of 0.85% to 1.20%.
Comparison Table: Chemical Requirements
| Element | Incoloy 800H (UNS N08810) | Incoloy 800HT (UNS N08811) |
| Nickel (Ni) | 30.0 - 35.0% | 30.0 - 35.0% |
| Chromium (Cr) | 19.0 - 23.0% | 19.0 - 23.0% |
| Carbon (C) | 0.05 - 0.10% | 0.06 - 0.10% |
| Al + Ti | 0.30 - 1.20% | 0.85 - 1.20% |
| Heat Treatment | Solution Annealed | High-Temp Solution Annealed |
Note: The stricter control of Al and Ti in 800HT ensures superior creep rupture strength.
2. Heat Treatment Processes
Both alloys are designed for service at temperatures where creep and rupture are the primary failure mechanisms. However, their annealing temperatures differ:
800H: Typically heat-treated between 1100°C and 1180°C.
800HT: Requires a higher solution annealing temperature, usually between 1150°C and 1200°C.
This higher-temperature treatment for 800HT ensures a larger grain size (ASTM 5 or coarser), which is essential for maximizing creep resistance at temperatures above 700°C.
3. Performance Showdown: Which is Better?
While both alloys offer excellent resistance to oxidation, sulfidation, and carburization, Incoloy 800HT takes the lead in extreme environments.
Higher Creep Rupture Strength: Due to the optimized Al+Ti content, 800HT has significantly higher design stress levels than 800H at temperatures above 1100°F (600°C).
Oxidation Resistance: 800HT provides slightly better long-term surface stability in oxidizing atmospheres.
Thermal Expansion: Both alloys have similar coefficients, but 800HT remains more stable under continuous high-heat cycles.
4. Typical Applications
Where should you use these alloys?
Incoloy 800H: Ideal for heat-treating equipment, chemical and petrochemical piping, and components exposed to temperatures up to 1500°F (815°C).
Incoloy 800HT: The preferred choice for extreme high-temperature service (above 700°C/1290°F) in power plants, industrial furnace components, and steam generator tubing in nuclear power.
Summary: Which Alloy to Choose?
If your application involves temperatures below 700°C, Incoloy 800H is often sufficient and more cost-effective. However, if your equipment must endure sustained high temperatures with high mechanical stress, Incoloy 800HT is the superior investment due to its enhanced creep resistance and longevity.
Why Source Incoloy 800H/800HT from Gnee Steel?
As a leading supplier of nickel-based alloys, we ensure:
Strict Compliance: All 800H/800HT materials meet ASTM B407, B408, and B409 standards.
Verified Chemistry: Precise control of Al, Ti, and Carbon levels confirmed by third-party Lab testing.
Custom Forms: Available in seamless pipes, plates, round bars, and custom forgings.