What is the Difference Between Incoloy 800H and 825?
What is the Difference Between Incoloy 800H and 825?
Incoloy 800H exhibits excellent high-temperature strength and oxidation resistance, making it suitable for furnace components; while Incoloy 825 offers superior overall corrosion resistance, particularly in acidic (sulfuric acid, phosphoric acid) and chloride-rich marine/chemical environments, thanks to its added molybdenum and copper elements, but it is also more expensive. The main difference between the two is that 825 has greater resistance to pitting corrosion, crevice corrosion, and reducing acids, making it more suitable for complex chemical processing applications, while 800H is primarily used in applications requiring high temperature resistance and high strength.
What is the heat treatment process for Incoloy 800 alloy?
The chemical composition of INCOLOY 800HT alloy falls within the composition range of 800H alloy, but with certain restrictions, and requires heat treatment at a minimum temperature of 2100°F (1149°C). Its carbon content is 0.06% to 0.10% (compared to 0.05% to 0.10% for 800H alloy), and its aluminum + titanium content is 0.85% to 1.20% (compared to 0.30% to 1.20% for 800H alloy).
Chemical composition of Incoloy 800H and Incoloy 825 alloys
| Element | Incoloy 800H (UNS N08810) | Incoloy 825 (UNS N08825) |
|---|---|---|
| Nickel (Ni) | 30.0 – 35.0 % | 38.0 – 46.0 % |
| Chromium (Cr) | 19.0 – 23.0 % | 19.5 – 23.5 % |
| Iron (Fe) | ≥ 39.5 % | ≥ 22.0 % |
| Carbon (C) | 0.05 – 0.10 % | ≤ 0.05 % |
| Aluminum (Al) | 0.15 – 0.60 % | ≤ 0.2 % |
| Titanium (Ti) | 0.15 – 0.60 % | 0.6 – 1.2 % |
| Molybdenum (Mo) | – | 2.5 – 3.5 % |
| Copper (Cu) | ≤ 0.75 % | 1.5 – 3.0 % |
| Manganese (Mn) | ≤ 1.5 % | ≤ 1.0 % |
| Silicon (Si) | ≤ 1.0 % | ≤ 0.5 % |
| Sulfur (S) | ≤ 0.015 % | ≤ 0.03 % |
| Phosphorus (P) | ≤ 0.045 % | ≤ 0.03 % |
| Al + Ti | 0.30 – 1.20 % | – |
Mechanical properties of Incoloy 800H and Incoloy 825 alloys
| Property | Incoloy 800H (Annealed) | Incoloy 825 (Annealed) |
|---|---|---|
| Tensile Strength (MPa, min) | 450 – 585 | 586 – 724 |
| Yield Strength (0.2% Offset, MPa, min) | 170 – 310 | 241 – 345 |
| Elongation (% in 50 mm, min) | 30 | 30 |
| Hardness (Rockwell B) | 79 – 95 HRB | 88 HRB |
| Hardness (Brinell HB) | 120 – 190 HB | 146 – 217 HB |
| Density (g/cm³) | 7.94 | 8.14 |
| Melting Range (°C) | 1350 – 1400 | 1370 – 1400 |
| Modulus of Elasticity (GPa) | 200 | 196 |
| Maximum Service Temperature (Continuous, in Air) | ~1150°C | ~540°C |
| Thermal Conductivity (W/m·K, at 20°C) | 11.8 | 11.1 |
| Coefficient of Thermal Expansion (×10⁻⁶/K, 20–100°C) | 14.4 | 14.0 |
| Creep Resistance | Very Good (high temperature) | Good (moderate temperature) |
| Oxidation Resistance | Very Good | Good |
| Corrosion Resistance | Good (oxidizing atmospheres) | Excellent (acids, chlorides, seawater) |
| Impact Toughness (Charpy V-Notch, J) | Good | Good |
| Fatigue Strength | Good | Good |
How do the corrosion resistance properties of Incoloy 800H and Incoloy 825 compare?
While both Incoloy 800H and 825 exhibit excellent corrosion resistance, they perform differently in various environments due to their differing compositions. Understanding these differences is crucial for selecting the appropriate alloy for a specific application:
1. General Corrosion Resistance: Incoloy 825 generally offers superior overall corrosion resistance compared to Incoloy 800H. This is due to its higher nickel content (approximately 42% compared to 800H's approximately 32%) and the addition of molybdenum (3%), which enhances its resistance to a wide range of corrosive media.
2. Pitting and Crevice Corrosion: Incoloy 825 exhibits better resistance to pitting and crevice corrosion, particularly in chloride-containing environments. The presence of molybdenum in 825 significantly improves its resistance to these forms of localized corrosion.
3. Stress Corrosion Cracking (SCC): Both alloys have good resistance to stress corrosion cracking, but Incoloy 825 generally performs better in chloride-containing environments due to its higher nickel content.
4. Sulfuric Acid Environments: Incoloy 825 demonstrates excellent resistance to sulfuric acid corrosion at various concentrations and temperatures, making it a preferred choice for chemical processing applications involving sulfuric acid.
5. Oxidizing Environments: Incoloy 800H excels in high-temperature, highly oxidizing environments due to its ability to form a stable chromium oxide layer. This makes it particularly suitable for high-temperature applications in oxidizing atmospheres.
6. Reducing Environments: Incoloy 825 generally exhibits better resistance to reducing acids and other reducing environments compared to Incoloy 800H.
7. Seawater and Marine Environments: Incoloy 825 has excellent corrosion resistance to seawater and marine atmospheres, making it a preferred choice for offshore and coastal applications. 8. High-Temperature Corrosion: Although both alloys perform well at high temperatures, Incoloy 800H maintains its corrosion resistance at even higher temperatures (up to 1100°C) compared to Incoloy 825 (typically used at temperatures up to 540°C). It's worth noting that while Incoloy 825 exhibits excellent overall corrosion resistance in many environments, Incoloy 800H is generally the better choice for applications requiring superior high-temperature strength and oxidation resistance. The choice between these two alloys depends on the specific environmental conditions, temperature requirements, and the mechanical properties needed for the application.
How to Choose:
Choose 800H/HT: Suitable for applications where the main challenge is extreme high temperature and corrosive media are limited, to save costs.
Choose 825: Suitable for handling corrosive chemicals, chlorides, or marine environments where there is a risk of pitting and acid corrosion.
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Gnee Steel also supplies custom incoloy 800H products in various sizes and specifications. Please send us your drawings for a quote!
Gnee Steel is a supplier of incoloy 800H alloy, offering a wide range of products including: seamless pipe (sizes: 4-219 mm; thickness: 0.5-20 mm); welded pipe (sizes: 5.0-1219.2 mm; thickness: 0.5-20 mm); plates (thickness: 0.1 to 100 mm; width: 10-2500 mm); strips; alloy round bars (diameter: 3-800 mm); flat bars (thickness: 2-100 mm; width: 10-500 mm); hexagonal bars (size: 2-100 mm); wire rods; and extruded profiles. We collaborate with steel mills to provide our customers with incoloy 800H alloy products that meet or exceed numerous leading industry standards, including ASTM, ASME, SAE, AMS, ISO, DIN, EN, and BS standards.
Gnee Steel stocks and sells incoloy 800H, pipes, plates, strips, round bars, flat bars, forged billets, hexagonal steel, wire rods, and extruded profiles. Please feel free to contact us at ss@gneesteel.com for a quote.
