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Alloy 800 vs Alloy 800H vs Alloy 800HT: A Comprehensive Comparison
| MOQ: | 5Ton |
| Price: | Based on grade, size, surface, processing, quantity and current raw material market price. |
| Standard Packaging: | Standard seaworthy export packing with bundles, waterproof wrapping, pallets or wooden cases. |
| Delivery Period: | 7-15 |
| Payment Method: | L/C,D/A,T/T,D/P,Western Union |
| Supply Capacity: | Stock supply, regular production and custom manufacturing available. |
Shaanxi Shangyou Stainless Steel Co., Ltd. supplies the full Incoloy 800 series family — Alloy 800 (UNS N08800), Alloy 800H (UNS N08810), and Alloy 800HT (UNS N08811) — in plate, sheet, round bar, seamless pipe, and forging forms. These nickel-iron-chromium alloys share the same base chemistry (approx. 32% Ni, 21% Cr, balance Fe) but differ in critical composition and heat treatment parameters that determine their high-temperature performance.
The 800 series was originally developed as a lower-nickel, cost-effective alternative to Alloy 600 for high-temperature service. As applications demanded longer service life and higher operating temperatures, the family evolved: Alloy 800H introduced controlled carbon (0.05-0.10%) and a high-temperature solution anneal to optimize creep-rupture strength above 600°C. Alloy 800HT further tightened the aluminum and titanium content (Al+Ti min 0.85%) to deliver the highest creep strength in the family for service up to 900°C+. All three alloys are available with EN 10204 3.1 MTC, PMI testing, and full traceability.
| Property | Alloy 800 (UNS N08800) | Alloy 800H (UNS N08810) | Alloy 800HT (UNS N08811) |
|---|---|---|---|
| Carbon Content | 0.10% max (no min) | 0.05 – 0.10% | 0.06 – 0.10% |
| Aluminum + Titanium (Al+Ti) | 0.30 – 1.20% | 0.30 – 1.20% | 0.85 – 1.20% (min 0.85%) |
| Solution Anneal Temperature | 980 – 1,040°C | ≥ 1,121°C (2,050°F) | ≥ 1,149°C (2,100°F) |
| Grain Size (ASTM) | Not specified | 5 or coarser | 5 or coarser |
| Tensile Strength, Annealed | 520 MPa (75.8 ksi) min | 450 MPa (65 ksi) min | 450 MPa (65 ksi) min |
| Yield Strength (0.2%) | 150 MPa (22 ksi) min | 172 MPa (25 ksi) min | 172 MPa (25 ksi) min |
| Elongation | 20% min | 20% min | 20% min |
| Density | ~7.94 g/cm3 | ~7.94 g/cm3 | ~7.94 g/cm3 |
| Maximum Creep Service Temperature | ≤ 593°C (1,100°F) | 593 – 760°C (1,100–1,400°F) | 700 – 900°C+ |
| ASME Pressure Vessel Design | Not permitted above 538°C | Code-approved; higher allowable stresses above 593°C | Code-approved; highest allowable stresses |
| Element | Alloy 800 (UNS N08800) | Alloy 800H (UNS N08810) | Alloy 800HT (UNS N08811) |
|---|---|---|---|
| Nickel (Ni) | 30.0 – 35.0% | 30.0 – 35.0% | 30.0 – 35.0% |
| Chromium (Cr) | 19.0 – 23.0% | 19.0 – 23.0% | 19.0 – 23.0% |
| Iron (Fe) | 39.5% min (Balance) | 39.5% min (Balance) | 39.5% min (Balance) |
| Carbon (C) | 0.10% max | 0.05 – 0.10% | 0.06 – 0.10% |
| Aluminum (Al) | 0.15 – 0.60% | 0.15 – 0.60% | 0.25 – 0.60% |
| Titanium (Ti) | 0.15 – 0.60% | 0.15 – 0.60% | 0.25 – 0.60% |
| Aluminum + Titanium (Al+Ti) | 0.30 – 1.20% | 0.30 – 1.20% | 0.85 – 1.20% |
| Manganese (Mn) | 1.5% max | 1.5% max | 1.5% max |
| Silicon (Si) | 1.0% max | 1.0% max | 1.0% max |
| Copper (Cu) | 0.75% max | 0.75% max | 0.75% max |
| Sulfur (S) | 0.015% max | 0.015% max | 0.015% max |
The 800 series was developed to address rising nickel costs while maintaining high-temperature performance. Alloy 800 offered lower nickel content than Alloy 600 at reduced cost. However, as operating temperatures in industrial furnaces and petrochemical plants increased, the need for improved creep strength became critical.
Alloy 800 was the original baseline grade. It performs well at temperatures up to approximately 600°C where creep is not a primary design concern.
Alloy 800H was developed by controlling carbon content to a minimum of 0.05% and applying a high-temperature solution anneal at ≥ 1,121°C to produce a coarse grain structure (ASTM 5 or coarser). These modifications provide significantly higher creep-rupture strength, making it suitable for service above 600°C.
Alloy 800HT represents the premium grade. By raising the minimum Al+Ti content to 0.85% (with individual minimums of 0.25% for both Al and Ti) and applying an even higher solution anneal temperature (≥ 1,149°C), 800HT achieves the highest creep strength in the family.
- Controlled Carbon (0.05% min): Promotes M23C6 carbide precipitation at grain boundaries, which "pins" boundaries and slows grain-boundary sliding — the dominant creep mechanism above ~600°C.
- Coarse Grain (ASTM 5 or coarser): Larger grains mean fewer grain boundaries per unit volume. Coarse-grained 800H/HT show 2–4× longer creep-rupture life compared to fine-grained material.
- Elevated Al+Ti ≥0.85% (800HT only): During prolonged exposure at 650–850°C, 800HT precipitates fine, coherent γ' phase (Ni3(Al,Ti)), providing dispersion strengthening that gives approximately 15–25% higher 100,000-hour rupture strength than 800H at 750–850°C.
All three alloys offer good resistance to oxidation, carburization, and stress corrosion cracking, with distinctions emerging at elevated temperatures.
| Corrosion Type | Alloy 800 | Alloy 800H | Alloy 800HT |
|---|---|---|---|
| Oxidation Resistance | Good to ~982°C | Good to ~982°C | Superior above 900°C |
| Carburization Resistance | Good | Better | Superior |
| Chloride SCC Resistance | Good (Ni content) | Good | Good |
| Creep-Rupture Strength | Baseline | ~2–4× improvement | Additional 15–25% over 800H |
| Thermal Fatigue Resistance | Moderate | Good | Best (Al/Ti balance) |
Alloy 800's Strength: The high nickel content (30-35%) provides excellent resistance to chloride stress-corrosion cracking and sigma phase embrittlement. It also offers good aqueous corrosion resistance in many chemical environments.
Alloy 800H's Strength: The controlled carbon and coarse grain structure dramatically improve high-temperature creep and rupture properties compared to Alloy 800.
Alloy 800HT's Strength: The tighter Al+Ti control and higher solution annealing temperature ensure the highest creep-rupture performance and resistance to grain boundary degradation at the highest service temperatures.
| Grade | Recommended Service Temperature | Application Context |
|---|---|---|
| Alloy 800 | ≤ 593°C (1,100°F) | Non-creep applications; lower-stress service |
| Alloy 800H | 593 – 760°C (1,100–1,400°F) | Creep-limited service; steam/hydrocarbon reformers |
| Alloy 800HT | 700 – 900°C+; up to ~982°C | Highest creep applications; steam methane reformers, radiant coils |
ASME Design Temperature Limitations:
- Alloy 800 (N08800) is not permitted for creep-based pressure design above 538°C (1,000°F) in ASME Section VIII Div. 1.
- Alloy 800H/HT receive significantly higher allowable stress values above 593°C and are code-approved for pressure service.
| Application Area | Specific Use Cases |
|---|---|
| Chemical Processing | Heat exchangers, process piping, nitric acid service |
| Industrial Heating | Applications below 600°C; non-creep critical |
| Nuclear | Steam generator tubing (nuclear grade) |
| Cost-Sensitive Projects | Where service temperature does not justify 800H/HT premium |
| Aqueous Corrosion Service | Chemical plant environments not requiring high creep |
| Application Area | Specific Use Cases |
|---|---|
| Petrochemical | Steam/hydrocarbon reformers, ethylene furnace quench boilers |
| Power Generation | Superheater and reheater tubes; boiler feedwater heaters |
| Industrial Heating | Radiant tubes, muffles, retorts in heat treatment equipment |
| Creep-Limited Service | Temperatures 600-760°C with design life requirements |
| Replacement Tubes | Matching existing 800H installations |
| Application Area | Specific Use Cases |
|---|---|
| Steam Methane Reformers | Radiant coils at 850–982°C; hydrogen production |
| Ethylene Cracking | Pyrolysis tubing convection and radiant sections |
| Gas Turbine Exhaust | Recuperators and exhaust systems at 800–950°C |
| Thermal Cycling Service | Transfer-line exchangers; continuous annealing furnaces |
| Long Design Life (>30 years) | Applications requiring maximum creep resistance |
| Aspect | Alloy 800 | Alloy 800H | Alloy 800HT |
|---|---|---|---|
| Weldability | Excellent | Excellent | Excellent |
| Recommended Filler | ERNiCr-3 (Inconel 82) | ERNiCr-3 (Inconel 82) | ERNiCr-3 (Inconel 82) |
| Post-Weld Heat Treatment | Not required | Not generally required | Not generally required |
| PWHT for Heavy Sections | Optional | 620°C for >25mm thickness | 620°C for >25mm thickness |
| Grain Size Impact | — | Critical for creep properties | Critical for creep properties |
Important Welding Note: ERNiCr-3 (Inconel 82) is commonly specified for welding 800 series alloys — not matching 800H filler — because the higher nickel content (67%) provides superior creep ductility in the weld metal. This practice has been standard in the ethylene and styrene industries for 40+ years.
Choose Alloy 800 when:
- Service temperature is at or below 600°C
- Creep is not a design concern
- Cost optimization is a priority
- Application is not pressure vessel service above 538°C
Choose Alloy 800H when:
- Service temperature is 600–760°C with creep as design driver
- ASME pressure vessel code compliance above 593°C is required
- Design life under approximately 30 years
- Cost premium over 800 is acceptable
Choose Alloy 800HT when:
- Service temperature exceeds 700°C (1,300°F)
- Maximum creep-rupture strength is required
- Design life exceeds 200,000 hours (>30 years)
- Thermal cycling is present in the service environment
- Steam methane reformer or ethylene cracking service
- Service temperature reaches 900°C+
For a detailed quotation or material selection assistance, please provide:
Alloy Grade Under Consideration · Required Standard · Product Form · Dimensions · Quantity · Service Conditions (Temperature, Pressure, Medium) · Application · Destination Port
For high-temperature service, also provide:
Operating Temperature · Cyclic Heating Requirements · Atmosphere Conditions (Oxidizing/Reducing/Carburizing) · Design Life Requirements
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- Request Alloy Selection Support
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The alloys share the same base chemistry but differ in carbon content, Al+Ti control, and solution annealing temperature. Alloy 800H adds controlled carbon (0.05-0.10%) and coarse grain for creep strength above 600°C. Alloy 800HT further tightens Al+Ti (≥0.85%) for maximum creep resistance at the highest temperatures.
Alloy 800HT has the highest creep-rupture strength, offering approximately 15-25% higher 100,000-hour rupture strength than 800H at 750-850°C.
Alloy 800 is recommended for service ≤600°C. Alloy 800H is suitable for 593-760°C. Alloy 800HT is rated for 700-900°C+ service, including applications up to ~982°C.
Alloy 800 is UNS N08800; Alloy 800H is UNS N08810; Alloy 800HT is UNS N08811. European Werkstoff numbers are 1.4876, 1.4958, and 1.4959 respectively.
ASTM B409 (plate/sheet/strip), ASTM B407 (seamless pipe/tube), ASTM B408 (bar), and ASME SB-409 (pressure vessel plate) apply to all three grades.
No. All 800 series alloys are solid-solution strengthened and are not age-hardenable. The alloys are strengthened through carbon content control and grain size, not through precipitation hardening.
Alloy 800HT is the preferred choice for radiant coils in steam methane reformers operating at 850-982°C. For replacement tubes matching existing installations, 800H may be used.
Yes. Both 800H and 800HT are approved under ASME Section VIII Div. 1, with significantly higher allowable stress values above 593°C. Alloy 800 is not permitted for creep-based pressure design above 538°C.
ERNiCr-3 (Inconel 82) is commonly specified for welding 800H and 800HT, not matching 800H filler. The higher nickel content provides better creep ductility in the weld metal.
Please provide the operating temperature, design life, whether thermal cycling is involved, pressure requirements, and the chemical environment (oxidizing, reducing, or carburizing). Our team can provide expert guidance based on your specific service conditions.
