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Inconel 600 (UNS N06600/W.Nr. 2.4816) alloy is a standard engineering material for applications which require resistance to corrosion and heat. The alloy also has excellent mechanical properties and presents the desirable combination of high strength and good workability.
Inconel 600 is mainly composed of Ni and Cr, and its chemical composition also includes a small amount of Fe, C, Si, Mn, S and other elements. The specific chemical composition ratio is as follows:
Grade | C≤ | Mn≤ | Si≤ | S≤ | Cu≤ | Fe | Ni≥ | Cr |
Inconel 600 | 0.15 | 1.0 | 0.5 | 0.015 | 0.5 | 6.0-10.0 | 72.0 | 14.0-17.0 |
Property | Standard Material | Annealed Material |
Tensile Strength (min) | 550 MPa (80 ksi) | ≥ 550 MPa |
0.2% Yield Strength (min) | 240 MPa (35 ksi) | ≥ 240 MPa |
Elongation (min) | 30% | ≥ 30% |
Inconel600 | 0.2% Yield strength ［N/mm2］ | Tensile strength ［N/mm2］ | Elongation ［%］ | Hardness | |
≧240 | ≧550 | ≧30 | — | ||
≧380 | ≧760 | ≧30 | — | ||
Example | Hot rolled plate | 321 | 677 | 42 | HB 171 |
Cold rolled plate | 337 | 704 | 40 | HRB 84 | |
Cold working increases yield and tensile strength significantly while reducing elongation. For applications requiring higher mechanical properties, Inconel 600 can be cold worked below 649°C (1200°F), as it is not an age-hardenable alloy.
Inconel 600 has a density of 8.47 g/cm³, melting range of 1370–1425°C, thermal conductivity of 14.8 W/(m·K), and linear expansion coefficient of 13.3 × 10⁻⁶/K.
Property | Value |
Density | 8.47 g/cm³ |
Melting Range | 1370 – 1425°C |
Thermal Conductivity | 14.8 W/(m·K) at 100°C |
Linear Expansion Coefficient | 13.3 × 10⁻⁶/K (20–800°C mean) |
Electrical Resistivity | 1.03 μΩ·m at 20°C |
Modulus of Elasticity | 205 GPa at 20°C |
Inconel 600 resists corrosion through two complementary mechanisms: its 72% Ni content prevents chloride stress-corrosion cracking and alkaline attack, while its 14–17% Cr content enables protective Cr₂O₃ oxide scale formation that blocks further oxidation at high temperature.
Chromium-driven oxidation resistance: The 14–17% Cr content exceeds the critical threshold for continuous Cr₂O₃ film formation, providing oxidation protection up to 1095°C in air and oxidizing atmospheres.
Nickel-driven SCC immunity: At >72% Ni, the alloy sits above the 45% Ni threshold for chloride stress-corrosion cracking resistance, making it immune to Cl-SCC that attacks lower-nickel alloys like Incoloy 800H.
Acid and alkali resistance: Good resistance to organic acids (acetic, formic, stearic), moderate resistance to inorganic acids (sulfuric, phosphoric), and excellent resistance to dry chlorine and hydrogen chloride gas.
Alkaline corrosion resistance: The high nickel content provides outstanding resistance to caustic alkali solutions, including >50% NaOH at elevated temperatures — an environment where Incoloy 800H is attacked.
Carburization resistance: Nickel above 70% slows carbon ingress, giving Inconel 600 longer life in carburizing furnace retorts compared to lower-nickel alternatives.
Product | Standard | Show |
Inconel 600 Bar | ASTM B166 AMS 5665 Din 17752 |  |
Inconel 600 Sheet | ASTM B168 AMS 5540 Din 17750 |  |
Inconel 600 Plate | ASTM B168 AMS 5540 Din 17750 |  |
Inconel 600 Tube | ASTM B167 |  |
Inconel 600 Pipe | ASTM B167 |  |
Inconel 600 Fitting | ASTM B366 |  |
Inconel 600 Forging | ASTM B564 Din 17754 |  |
STANDARD | WERKSTOFF NR. | UNS | JIS | BS | GOST | AFNOR | EN |
Inconel 600 | 2.4816 | N06600 | NCF 600 | NA 13 | МНЖМц 28-2,5-1,5 | NC15FE11M | NiCr15Fe |
Inconel 600 resists high-temperature oxidation through a three-layer oxide scale system: an inner Cr₂O₃ barrier that blocks oxygen diffusion, an intermediate NiCr₂O₄ spinel that reinforces scale adhesion, and an outermost MnCr₂O₄ spinel that further stabilizes the protective film — but intergranular chromium depletion and scale spallation limit long-term performance above 900°C.
The oxidation resistance of Inconel 600 is not simply "because it contains chromium." The actual protection mechanism is a multi-layer oxide scale that evolves with temperature and time. Understanding this mechanism is essential for specifying Inconel 600 correctly in high-temperature service.
Temperature | Inner Layer | Intermediate Layer | Outermost Layer |
700°C | Cr₂O₃ (primary barrier) | NiCr₂O₄ spinel | Spinel (Fe,Cr,Ni) mixed |
800°C | Cr₂O₃ + NiCr₂O₄ | Fe₂O₃ begins forming | Cr₂O₃ spinel |
900°C | Cr₂O₃ (thickening) | (Fe,Cr,Mn)₂O₃ spinel | MnCr₂O₄ spinel (dominant) |
Step 1 — Cr₂O₃ film nucleation. When Inconel 600 is first exposed to high-temperature air, chromium at the surface reacts with oxygen to form Cr₂O₃ (chromia). Because the alloy contains 14–17% Cr — well above the ~13% threshold for continuous chromia coverage — this film forms rapidly and covers the entire surface. Cr₂O₃ is dense and adherent; it blocks further oxygen diffusion into the substrate.
Step 2 — NiCr₂O₄ spinel formation. As oxidation continues, nickel from the matrix diffuses outward through the Cr₂O₃ layer. At the scale surface, Ni reacts with Cr₂O₃ and oxygen to form NiCr₂O₄ spinel. This spinel has a very low Gibbs free energy of formation (negative ΔG°), making it thermodynamically stable at high temperature. It reinforces the scale by providing a harder, more cohesive outer crust.
Step 3 — MnCr₂O₄ spinel and scale maturation. Above ~850°C, manganese ions diffuse through the Cr₂O₃ channels and form MnCr₂O₄ spinel on the outermost surface. MnCr₂O₄ has even greater thermodynamic stability than NiCr₂O₄ (ΔG° = −1815 kJ/mol at 900°C vs. −1648 kJ/mol), and its formation further improves scale adhesion and thermal cycling resistance.
Step 4 — Intergranular oxidation threat. The critical long-term degradation mechanism is intergranular chromium depletion. At temperatures of 540–760°C, chromium carbides (Cr⁷C₃, Cr₂₃C₆) precipitate along grain boundaries, depleting the surrounding matrix of chromium. When the local Cr content drops below ~12%, the grain boundary zone cannot form protective Cr₂O₃, creating preferential oxidation pathways that penetrate 30–50 μm after 1000 hours at 700°C. This is the primary mechanism limiting very long-term service in the 540–760°C range.
Step 5 — Scale spallation under thermal cycling. Above ~800°C, the adhesion between the oxide scale and the substrate weakens as the scale thickens and thermal expansion mismatch grows. During cooling, differential contraction causes the scale to crack and spall. Each cycle exposes fresh metal, and the re-formation of Cr₂O₃ further depletes the chromium reservoir. After many cycles, the surface Cr content may fall below the threshold for continuous scale coverage, leading to catastrophic breakaway oxidation.
• Temperature limit: Continuous service up to 1100°C (short-term). Long-term load-bearing service best controlled below 1000°C.
• Avoid 540–760°C prolonged exposure: This range maximizes carbide precipitation and intergranular oxidation. If service in this range is unavoidable, specify solution-annealed material and schedule periodic inspections.
• Environmental controls: Avoid high-sulfur fuels (sulfur destroys Cr₂O₃ by forming low-melting-point sulfides). Halogens (Cl, F) also attack the scale. For sulfur/halogen service, consider Inconel 601 (higher Al content) or Inconel 625.
• Oxidation rate reference: In air at 1000°C, typical oxidation follows parabolic kinetics at ~0.1–0.5 mg/cm²·h after 100 hours — superior to 309 stainless steel but inferior to Al-containing alloys like Inconel 601.
Inconel 600 is specified for furnace tubes when the operating environment requires resistance to oxidation, carburization, chloride stress-corrosion cracking, or caustic attack at temperatures above 600°C — conditions where stainless steels and Incoloy 800H may fail prematurely.
Furnace tubes are among the most demanding applications for any alloy. They face simultaneous challenges: high temperature, thermal cycling, corrosive atmospheres, internal pressure, and long service-life requirements. Inconel 600 addresses these through its balanced Ni-Cr-Fe composition.
Key Furnace Tube Applications
Carburizing furnace retorts and muffles: Inconel 600's >72% Ni content slows carbon pickup compared to lower-nickel alloys, extending retort life in cyclic carburizing service where carbon ingress accelerates metal dusting and embrittlement.
Nitriding furnace components: High nickel content reduces nitrogen absorption rate. Inconel 600 muffles and baskets outlast stainless steel alternatives in ammonia-rich nitriding atmospheres.
Chemical process furnace tubing: Heat exchanger tubes and furnace coils handling hot process gas, hydrogen, steam, or acidic vapors benefit from Inconel 600's combined acid resistance and oxidation protection.
Steam generator tubing (nuclear): Inconel 600 was the original specification for pressurized water reactor (PWR) steam generator tubing, where chloride SCC immunity and resistance to caustic stress corrosion were critical. While later reactors shifted to Inconel 690 for even higher Cr content, Inconel 600 remains specified in many legacy units.
Thermal processing furnace fixtures: Baskets, trays, radiant tubes, and heat-treating fixtures that undergo thousands of heating-cooling cycles benefit from Inconel 600's scale adhesion and creep-rupture strength above 700°C.
Petrochemical heater tubes: In hydrocarbon processing environments where chloride SCC is the controlling failure mode, Inconel 600 tubes provide the SCC immunity that Incoloy 800H cannot match.
Design Factor | Inconel 600 Capability | Limitation to Watch |
Max continuous temperature | Up to 1100°C in air | Long-term >1000°C: creep dominates |
Creep-rupture strength | ~8 MPa at 815°C / 100k hr | Lower than Incoloy 800H (~14 MPa) |
Carburization resistance | Good (high Ni slows C ingress) | Not as good as Al-containing alloys |
Thermal cycling resistance | Moderate (scale adhesion decent) | Scale spallation above ~800°C cycling |
Chloride SCC immunity | Immune (>72% Ni) | N/A — this is Inconel 600's key advantage |
Caustic resistance | Excellent (to >50% NaOH) | Incoloy 800H is attacked in same conditions |
The critical trade-off in furnace tube selection is between creep-rupture strength and corrosion resistance. Inconel 600 wins on corrosion (SCC immunity, caustic resistance, carburization resistance) but has lower creep-rupture strength than Incoloy 800H at 815°C.
For applications where SCC or caustic attack is the primary failure mode, Inconel 600 is the correct choice even at a 30–40% cost premium. For applications where creep life is the controlling factor and the atmosphere is non-corrosive, Incoloy 800H may be more economical.
Inconel 600 serves six major industry sectors: chemical processing (corrosion resistance), thermal processing (oxidation resistance), nuclear power (SCC immunity), petrochemical (chloride resistance), aerospace (high-temperature strength), and waste/power generation (combined heat and corrosion resistance).
• Chemical & process industries: Heat exchangers, reaction vessels, and piping handling acids, alkalis, and chlorides where stainless steels fail by SCC.
• Thermal processing: Furnace retorts, muffles, radiant tubes, baskets, and fixtures for carburizing, nitriding, and annealing operations.
• Nuclear power: Steam generator tubing in PWR reactors, control rod drive mechanisms, and reactor vessel internals — leveraging chloride SCC immunity.
• Petrochemical processing: Cracking furnace tubes, reformer components, and flare stacks where chloride SCC, carburization, and oxidation are simultaneous threats.
• Aerospace: Jet engine exhaust components, combustion chamber liners, and turbine shroud rings operating above 700°C.
• Waste processing & power generation: Incinerator liners, waste-to-energy superheaters, and gasifier components exposed to hot corrosive gas streams.
Inconel 600 is the superior choice when chloride SCC immunity, caustic resistance, carburization/nitriding resistance, or temperatures above 900°C are required. Incoloy 800H wins when creep-rupture strength above 700°C, cost efficiency, or carburization resistance in moderate atmospheres is the priority. They are NOT direct substitutes.
Inconel 600 (UNS N06600) and Incoloy 800H (UNS N08810) are the two most commonly compared alloys for high-temperature service. The choice between them has direct consequences for safety, cost, and service life.
Element | Inconel 600 (N06600) | Incoloy 800H (N08810) |
Ni | ≥ 72.0% | 30.0 – 35.0% |
Cr | 14.0 – 17.0% | 19.0 – 23.0% |
Fe | 6.0 – 10.0% | ≥ 39.5% |
C | ≤ 0.15% | 0.05 – 0.10% |
Al + Ti | Not specified | 0.30 – 1.20% (combined) |
Property | Inconel 600 | Incoloy 800H |
Tensile Strength (RT, min) | 550 MPa (80 ksi) | 450 MPa (65 ksi) |
Yield Strength (RT, min) | 240 MPa (35 ksi) | 170 MPa (25 ksi) |
Elongation (min) | 30% | 30% |
Creep-Rupture @ 815°C / 100k hr | ~8 MPa | ~14 MPa |
Max useful long-term temp | ~1095°C | ~815°C |
Typical cost premium | Baseline (higher) | 30–40% lower |
Service Condition | Choose Inconel 600 | Choose Incoloy 800H |
Chloride SCC environment | Yes — immune (>72% Ni) | No — susceptible (30–35% Ni) |
Caustic >50% NaOH | Yes — qualified grade | No — attacked |
Carburizing furnace retorts | Yes — slow carbon ingress | Moderate — Al+Ti helps but Ni is lower |
Nitriding furnace muffles | Yes — slower nitrogen pickup | Acceptable but shorter life |
Creep-critical service >700°C | Lower creep strength | Superior creep-rupture (~14 MPa) |
Reformer / cracking tubes | If chloride SCC is present | Standard choice (creep + cost) |
Temperature >900°C | Yes — oxidation resistance extends | Marginal — limit ~815°C long-term |
Cost-controlled procurement | 30–40% premium | More economical |
The two grades are NOT direct substitutes. They fall under different ASME specifications (Inconel 600: SB-167/B168/B564; Incoloy 800H: SB-407/B408/B409/B564), different ASME Section IX P-Numbers (Inconel 600: P-No. 42; Incoloy 800H: P-No. 45), and require separate welding procedure qualifications. Swapping one for the other without engineering review can create code violations and safety hazards.
What is the maximum operating temperature of Inconel 600?
Inconel 600 can operate continuously up to 1095°C (2000°F) in oxidizing atmospheres, but long-term load-bearing service should be limited to below 1000°C for optimal creep life, and prolonged exposure in the 540–760°C range should be evaluated for intergranular oxidation risk.
Is Inconel 600 resistant to chloride stress-corrosion cracking?
Yes. Inconel 600 is immune to chloride stress-corrosion cracking because its nickel content exceeds the 72% threshold — well above the ~45% Ni minimum required for SCC immunity. This is its primary advantage over Incoloy 800H in chloride-containing environments.
Can Inconel 600 be used in carburizing furnace environments?
Yes, Inconel 600 is one of the best standard alloys for carburizing furnace retorts and muffles because its >72% Ni content slows carbon absorption compared to lower-nickel alternatives, though for the highest carburization resistance, Al-containing alloys (Inconel 601) or higher-Cr alloys (Inconel 690) may offer longer life.
Why does Inconel 600 have lower creep strength than Incoloy 800H at high temperature?
Inconel 600 has lower creep-rupture strength (~8 MPa at 815°C / 100,000 hr) compared to Incoloy 800H (~14 MPa) because Incoloy 800H's controlled carbon content (0.05–0.10%) and Al+Ti addition (0.30–1.20%) create stable carbide and intermetallic precipitates that pin grain boundaries and resist dislocation creep, while Inconel 600's simpler Ni-Cr matrix lacks these strengthening precipitates.
What filler metal should be used for welding Inconel 600?
ERNiCr-3 (Inconel 182 / AWS A5.11) is the standard matching filler metal for Inconel 600 welding, and it is also used for dissimilar joints to stainless steel to accommodate thermal expansion differences.
How should Inconel 600 furnace tubes be inspected for remaining life?
Inconel 600 furnace tube remaining life is assessed through periodic metallographic examination, wall thickness measurement, and creep strain monitoring — with replacement recommended when intergranular oxidation exceeds 50% of wall thickness or creep strain reaches 2%.
Stainless steel: 304, 316L, 316Ti, 317L, 310S, 2205, 2507, 254SMO, 904L, S31254, 17-4PH...
Monel alloy: Monel 400, Monel K500...
Hastelloy: C276, C22, B2, B3, C4, C200, C2000, G30...
Inconel: Inconel 600, Inconel 601, Inconel 625, lnocnel 718...
Incoloy: Incoloy 800, Incoloy 800H/800HT, Incoloy 825, Alloy 20, Alloy 31...
