What are the differences between Incoloy 800H and Incoloy 825 alloys?
The main difference lies in their corrosion resistance. Incoloy 825 exhibits superior corrosion resistance in aqueous environments due to the addition of molybdenum and copper, while Incoloy 800H is better suited for high-temperature applications due to its superior creep and fracture strength. Incoloy 825 enhances its corrosion resistance by adding elements such as molybdenum, copper, and titanium, which improve its performance in acidic, chlorine-rich, and reducing environments. Incoloy 800H is an improved version of Incoloy 800 with more strictly controlled carbon content, resulting in better high-temperature strength and creep resistance.
What is Alloy 825?
Incoloy 825 alloy (UNS N08825) is an austenitic nickel-iron-chromium alloy with added molybdenum, copper, and titanium. It was specifically developed to provide excellent corrosion resistance in both oxidizing and reducing environments. This nickel alloy exhibits excellent resistance to chloride stress corrosion cracking and pitting corrosion.
Both alloys belong to the nickel-iron-chromium family, but they solve different problems. Alloy 800H (UNS N08810) is a controlled-carbon, coarse-grain variant of Alloy 800 developed for creep resistance at elevated temperature. Alloy 825 (UNS N08825) is a fully stabilized nickel-iron-chromium alloy with molybdenum, copper and titanium added specifically for aqueous corrosion service. Choosing between them is a temperature-versus-media decision.
Incoloy 800H vs. Incoloy 825:Comparison of chemical composition
| Element (%) | Alloy 800H (UNS N08810, ASTM B409) | Alloy 825 (UNS N08825, ASTM B424) |
|---|---|---|
| Nickel (Ni) | 30.0 – 35.0 | 38.0 – 46.0 |
| Chromium (Cr) | 19.0 – 23.0 | 19.5 – 23.5 |
| Iron (Fe) | 39.5 min | 22.0 min |
| Molybdenum (Mo) | - | 2.5 – 3.5 |
| Copper (Cu) | 0.75 max | 1.5 – 3.0 |
| Titanium (Ti) | 0.15 – 0.60 | 0.6 – 1.2 |
| Aluminum (Al) | 0.15 – 0.60 | 0.2 max |
| Carbon (C) | 0.05 – 0.10 | 0.05 max |
| Manganese (Mn), max | 1.5 | 1.0 |
| Silicon (Si), max | 1.0 | 0.5 |
| Sulfur (S), max | 0.015 | 0.03 |
Density: 800H ≈ 7.94 g/cm³; 825 ≈ 8.14 g/cm³. Minimum tensile/yield (annealed plate): 800H 450/170 MPa; 825 585/240 MPa.
Why 800H Wins at High Temperature?
The key to 800H is not just carbon control - it is the heat-treatment route. Per ASTM B409, 800H is solution annealed at approximately 1149–1204 °C (2100–2200 °F) to produce a coarse grain structure (ASTM grain size 5 or coarser). Coarse grains reduce grain-boundary sliding and give markedly better creep and rupture strength than fine-grained Alloy 800. The controlled carbon range (0.05–0.10%) supports carbide distribution without sensitization problems.
- Design temperature: creep design is commonly based up to about 1000 °C (1832 °F).
- Oxidation: the chromium oxide scale gives useful resistance to roughly 1100 °C in low-stress oxidizing atmospheres.
- Weakness: limited resistance to aqueous reducing acids and chloride pitting - it is not an aqueous-corrosion alloy.
Why 825 Wins in Aggressive Aqueous Media?
Alloy 825 combines high nickel (38–46%), molybdenum (2.5–3.5%) and copper (1.5–3.0%) to resist both oxidizing and reducing aqueous media:
- Sulfuric and phosphoric acids: excellent resistance across practical concentrations and temperatures - the classic pickling-tank and fertilizer-plant alloy.
- Chloride environments: strong resistance to pitting, crevice corrosion and chloride stress-corrosion cracking (SCC).
- Sour service: listed in NACE MR0175 / ISO 15156-3 for H²S service.
- Limits: continuous service is typically capped near 540 °C (1000 °F); above that, strength drops and the alloy has no high-temperature creep advantage.
Comparison: Incoloy 800H vs Incoloy 825
| Feature | Alloy 800H (UNS N08810) | Alloy 825 (UNS N08825) |
|---|---|---|
| Primary strength | High-temperature creep and oxidation resistance | Aqueous corrosion resistance |
| Key alloying additions | Controlled C 0.05–0.10%; coarse-grain anneal | Mo 2.5–3.5%, Cu 1.5–3.0%, Ti 0.6–1.2% |
| Corrosion resistance | Good oxidation resistance; limited aqueous-acid resistance | Excellent in sulfuric/phosphoric acids, chlorides, SCC |
| Service temperature | Creep design to ~1000 °C; oxidation to ~1100 °C | Continuous ~540 °C max |
| Typical applications | Furnace components, radiant tubes, petrochemical cracking, heat-treatment fixtures | Chemical processing, pickling tanks, oil & gas, pollution control, marine |
| Plate standard | ASTM B409 / ASME SB409 | ASTM B424 / ASME SB424 |
Selection Guidance
Metal temperature above ~550 °C, oxidizing atmosphere, creep loading → Alloy 800H.
Wet media, acids, chlorides, sour service, temperature below ~540 °C → Alloy 825.
Ambiguous cases: request corrosion coupon testing and check the design code allowable stress at your operating temperature before deciding.
Why Choose Gnee Nickel Alloy (Supplier Example)?
✅ Large stock of Incoloy alloy tubes/bars/plates/fittings/coils, fast shipping.
✅ Factory direct sales, highly competitive prices, excellent value for money.
✅ Comprehensive quality assurance: Material Testing Certificate (MTC), chemical composition certificate, and mechanical property certificate.
✅ Value-added services: slitting, cutting, polishing, surface treatment.
✅ Worldwide shipping, secure and reliable packaging, and provision of export-required documents.
Gnee Steel is a supplier of incoloy 800H/825 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/825 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/825, 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.
