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Incoloy 800HT (UNS N08811 / W.Nr. 1.4959) and Inconel 600 (UNS N06600 / W.Nr. 2.4816) are both workhorse high-temperature nickel-base alloys, yet they serve different design intents. Incoloy 800HT is a Fe–Ni–Cr alloy (~45% Fe) optimized for creep strength + carburization resistance at 760–982°C in furnace/reformer service, while Inconel 600 is a high-nickel (≥72% Ni) Cr–Fe alloy prized for chloride stress-corrosion cracking (SCC) resistance, cryogenic toughness, and oxidation to ~1095°C in non-carburizing air. Below is a rigorous, side-by-side comparison to help engineers and purchasers choose correctly and avoid over-specifying (cost) or under-specifying (risk).
1. Chemical Composition & Metallurgical Difference
|
Element |
Incoloy 800HT (N08811) |
Inconel 600 (N06600) |
|---|---|---|
|
Ni |
30.0 – 35.0% |
≥ 72.0% (72–78%) |
|
Cr |
19.0 – 23.0% |
14.0 – 17.0% |
|
Fe |
≥ 39.5% (Balance) |
6.0 – 10.0% |
|
C |
0.06 – 0.10% |
≤ 0.15% (typ. 0.03–0.08%) |
|
Al + Ti |
0.85 – 1.20% (γ′ former) |
— (not intentionally added) |
|
Heat Treatment |
Solution annealed ≥ 1149°C, grain size ≥ ASTM 5 |
Solution annealed 870–1090°C (typ. 980°C), often finer grain |
Key takeaway: 800HT's Fe content reduces cost but limits maximum use in veryhigh sulfur or extremelypure oxidizing atmospheres above ~980°C; Inconel 600's high Ni gives it superior resistance to chloride SCC and better toughness down to cryogenic temps but makes it more expensive and less creep-strong above 700°C than 800HT in pressurized service.
2. High-Temperature Mechanical & Creep Performance
|
Property / Behavior |
Incoloy 800HT (N08811) |
Inconel 600 (N06600) |
|---|---|---|
|
Room Temp. Rm / Rp0.2 |
≥ 450 MPa / ≥ 170 MPa |
≥ 550 MPa / ≥ 240 MPa |
|
100,000 h Creep-Rupture (704°C) |
~115–130 MPa |
Lower in this temp band (not optimized for creep) |
|
ASME Design Temp. (Pressure) |
To 982°C (1800°F) per Sect. I; creep-governed 760–982°C |
Typically to 649–871°C depending on code case; nota creep-strength alloy >700°C |
|
Best Creep Service Range |
760–982°C (reformer/cracker tubes) |
< 650–700°C for stress; >700°C used for oxidation-only (non-pressurized) |
|
Grain Boundary Control |
Coarse grain + γ′(Ni₃(Al,Ti)) → creep resistant |
Usually finer grain → better formability, fatigue in some cases |
➡️ Rule of thumb: For pressurizedhigh-temp process (reformer tubes, ethylene cracker radiant tubes) → 800HT. For non-pressurizedhigh-temp oxidation shielding, furnace muffles, or where SCC/cryogenic matters → often Inconel 600 (or 601 if oxidation >1095°C).
3. Corrosion / Environmental Resistance Comparison
|
Environment |
Incoloy 800HT |
Inconel 600 |
Comment |
|---|---|---|---|
|
High-Temp Oxidation (air/combustion gas, ≤870°C cont.) |
★★★★☆ Good (Cr₂O₃) |
★★★★☆ Good (Cr₂O₃); slightly better at very high T (>980°C) due to higher Ni |
Both acceptable |
|
Oxidation >980°C (intermittent) |
Usable to ~1100°C short term |
Better — Inconel 601 preferred if >1050°C continuous |
— |
|
Carburization / Metal Dusting (CO/CH₄, furnace atm.) |
★★★★☆ Very good (coarse grain + Al/Ti) |
★★ Moderate — less resistant than 800HT |
800HT preferred for cracker tubes |
|
Cl⁻ SCC (aqueous, ≤200°C) |
★★★★★ (30% Ni suffices) |
★★★★★ (≥72% Ni, best-in-class) |
Both excellent vs. 300-series SS |
|
Caustic (NaOH/KOH) |
Good to ~300°C |
Excellent (high Ni) |
600 often chosen for caustic evaporators |
|
Reducing Acids (H₂SO₄, HCl) |
✗ Poor |
✗ Poor (use C-276 / 825) |
Neither is acid-alloy |
|
Sulfidation (low O₂, high S, >650°C) |
Limited — check pS₂ |
Slightly better due to higher Ni but still limited |
May need Inconel 601/671 or higher Cr |
4. Fabricability, Welding & Typical Applications
Weldability: Both are weldable with GTAW/GMAW.
800HT → filler ERNiCr-3 (NiCr-3, AWS A5.14) recommended; post-weld solution anneal restores optimal creep properties in high-temp service.
Inconel 600 → filler ERNiCr-3 or ENiCrFe-2/-3; often used as-is (as-welded) for aqueous SCC service; annealed for high-temp.
Formability: Inconel 600 (finer grain, higher ductility) springs back more but forms well; 800HT is stiffer at room temp due to coarse grain.
Typical 800HT Apps: Ethylene cracker radiant tubes, SMR catalyst tubes, secondary reformer transitions, carburizing furnace mufflers (760–950°C, creep + carburization).
Typical Inconel 600 Apps: Furnace muffles & retorts (non-pressurized, oxidation only), thermocouple sheaths, nuclear steam generator tubing (SCC resistance), caustic evaporator tubing, aerospace ducting, cryogenic tanks.
5. Cost & Sourcing Consideration (Practical Note for Buyers)
Material Cost (relative index): Incoloy 800HT ≈ 60–75% of Inconel 600 base price (Fe replaces ~40% of Ni). Actual spread varies with LME Ni fluctuation.
When to save with 800HT: High-temp creep-pressureservice where Inconel 600 lacks sufficient creep-rupture strength → 800HT is both cheaper and technically superior.
When to pay for Inconel 600: Need chloride SCC + cryogenic toughness, or aqueous caustic service, or non-pressurized high-temp air-oxidation <980°C where creep is not design driver and you want easier forming/higher Ni for certain passivation needs.
Don't substitute blindly: Never replace 800HT with 600 in reformer/cracker tube service (>760°C pressurized carburizing) — creep life will be inadequate. Conversely, don't replace 600 SCC-critical nuclear secondary side or caustic service with 800HT unless verified — usually acceptable but 600 is the benchmark.
