1. Introduction
Inconel 600, designated as UNS N06600 and W. Nr. 2.4816, is a nickel-chromium-iron alloy engineered for high performance in extreme temperature and corrosive environments.
As one of the earliest superalloys developed in the Inconel series, it has become a foundational material in aerospace, chemical processing, power generation, and marine industries.
Belonging to the austenitic nickel-based superalloy family, Inconel 600 exhibits exceptional resistance to oxidation, chloride-ion stress corrosion cracking, and thermal degradation.
It is widely used where conventional stainless steels or lower-nickel alloys fall short.
2. What is Inconel 600?
Inconel 600 (UNS N06600) is a versatile nickel-chromium-iron alloy engineered for service across a wide temperature range—from cryogenic conditions up to 2000°F (1093°C).
It offers excellent resistance to corrosion and high-temperature oxidation, making it a preferred material in demanding chemical and thermal environments.
Its high nickel content provides exceptional resistance to chloride-ion stress corrosion cracking, while also offering protection against a broad spectrum of organic and inorganic compounds.
The chromium content enhances resistance to oxidizing environments, both at elevated temperatures and in corrosive media, and also helps combat sulfur-containing compounds.
In high-temperature applications, Inconel 600 maintains structural integrity and resists oxidation and scaling up to 2000°F (1093°C).
It performs particularly well in conditions involving carburization or exposure to moderate-temperature sulfur environments.
However, it may be susceptible to sulfidation under more severe high-temperature conditions.
This alloy is non-magnetic and cannot be hardened by heat treatment, but it can be strengthened through cold working.
Inconel® 600 is also readily weldable and suitable for processing using conventional shop fabrication methods.
3. Chemical Composition of Inconel® 600
Inconel® 600 (UNS N06600) is a solid solution-strengthened nickel-chromium-iron alloy designed for superior resistance to a broad range of corrosive environments and elevated temperatures.
The carefully balanced chemical composition provides the foundation for its mechanical integrity, corrosion resistance, and high-temperature performance.
Nominal Chemical Composition (% by Weight)
| Element | Content (%wt) | Function / Role |
| Nickel (Ni) | 72.0 min | Provides primary corrosion resistance, ductility, and thermal stability. |
| Chromium (Cr) | 14.0 – 17.0 | Enhances resistance to oxidizing agents and high-temperature scaling. |
| Iron (Fe) | 6.0 – 10.0 | Balances cost and mechanical properties; enhances strength. |
| Manganese (Mn) | ≤ 1.0 | Improves hot working and deoxidation during melting. |
| Copper (Cu) | ≤ 0.5 | Aids corrosion resistance in certain reducing acids. |
| Silicon (Si) | ≤ 0.5 | Deoxidizer; enhances oxidation resistance but kept low to avoid brittleness. |
| Carbon (C) | ≤ 0.15 | Strengthens alloy through solid solution hardening but limited to minimize embrittlement. |
| Sulfur (S) | ≤ 0.015 | Impurity; controlled to enhance hot workability and weldability. |
4. Key Material Properties of Inconel 600
Inconel® 600 (UNS N06600) is engineered for mechanical integrity and chemical resistance under demanding thermal and corrosive conditions.
Mechanical Properties
| Property | Typical Value (at Room Temp) |
| Tensile Strength | 655 MPa (95,000 psi) |
| Yield Strength (0.2% offset) | 310 MPa (45,000 psi) |
| Elongation (% in 50 mm) | ≥ 30% |
| Hardness (Rockwell B) | 85–90 |
| Modulus of Elasticity | ~207 GPa (30 x 10³ ksi) |
| Impact Toughness (Charpy V-Notch, 20°C) | > 100 J (typical) |
Note: Values vary slightly depending on product form, thickness, and heat treatment. Cold working increases strength while reducing ductility.
Corrosion Resistance Properties
Inconel 600 resists a wide variety of corrosive environments due to its high nickel and chromium content:
- Chloride-ion SCC resistance: Nearly immune, even in hot and concentrated chloride solutions.
- Oxidation resistance: Effective up to 1093°C (2000°F) in air and combustion atmospheres.
- Carburization resistance: Maintains integrity in carbon-rich industrial atmospheres.
- Acid and base resistance: Stable in many acidic and alkaline environments (e.g., nitric, sulfuric, sodium hydroxide).
- Marine performance: Good resistance to seawater and brine, though not immune to crevice corrosion under stagnant conditions.
5. Physical Properties of Inconel® Alloy 600
Inconel® Alloy 600 (UNS N06600) exhibits a range of physical properties that contribute to its outstanding performance in extreme environments.
| Property | Typical Value |
| Density | 8.47 g/cm³ (0.306 lb/in³) |
| Melting Range | 1354 – 1413°C (2470 – 2575°F) |
| Thermal Conductivity | 14.8 W/m·K at 100°C |
| Specific Heat Capacity (Cp) | 0.444 J/g·K at 25°C |
| Electrical Resistivity | 103.4 µΩ·cm at 20°C |
| Coefficient of Thermal Expansion | 13.3 µm/m·°C (20–1000°C) |
| Modulus of Elasticity | 207 GPa (30 × 10³ ksi) |
| Magnetic Permeability (μ) | ~1.0006 (non-magnetic) |
| Poisson’s Ratio | 0.30 |
| Sound Velocity (longitudinal) | ~5,050 m/s (in solid) |
6. High-Temperature Performance of Inconel® Alloy 600
- Oxidation Resistance:
Resists oxidation and scaling at temperatures up to 2000°F (1093°C), maintaining surface integrity and mechanical properties. - Carburization Resistance:
Performs well in carburizing environments, limiting carbon absorption and preserving structural stability. - Sulfidation Behavior:
Offers moderate resistance to sulfidation at elevated temperatures but may degrade in highly sulfide-rich atmospheres above certain temperature thresholds. - Thermal Stability:
Maintains mechanical strength and toughness during prolonged exposure to high temperatures and thermal cycling. - Structural Integrity:
Resists grain growth and maintains microstructural stability, preventing brittleness or deformation in service. - Limitations:
Performance may decline in environments combining extreme heat with highly aggressive chemicals (e.g., high sulfur content), necessitating alternative alloys for such conditions.
7. Fabrication & Machinability of Inconel® Alloy 600
Inconel® Alloy 600 (UNS N06600) is engineered for high corrosion and temperature resistance, but it also offers excellent workability across a range of standard fabrication processes.
It can be hot-worked, cold-formed, welded, and machined using conventional techniques adapted to account for its strength, work-hardening behavior, and metallurgical stability.
Casting
While not as commonly cast as Inconel 718, Inconel 600 can be investment-cast into complex shapes (e.g., valve bodies) with tight tolerances (±0.1 mm).
Casting requires controlled cooling to avoid carbide precipitation, which can reduce ductility.
Hot Working
Inconel 600 is highly ductile when processed at elevated temperatures, making it well-suited to hot forming operations such as forging, extrusion, and rolling.
- Recommended Hot-Working Temperature Range:
870–1230°C (1600–2250°F) - Heavy Deformation (Forging, Extrusion):
1040–1230°C (1900–2250°F) - Light Working (Finish passes, minor shaping):
As low as 870°C (1600°F) - Avoid Working Range:
650–870°C (1200–1600°F) — due to reduced ductility and risk of microcracking.
For best results, hot-working should be followed by annealing and rapid quenching to restore corrosion resistance and relieve internal stresses.
Cold Forming
Inconel 600 can be cold-formed using practices similar to those for stainless steels and low-alloy materials.
It exhibits greater work hardening than mild steel, though it is more forgiving than Type 304 stainless steel.
- Techniques: Bending, drawing, stamping, swaging
- Considerations:
-
- Intermediate annealing may be necessary for complex or deep forming.
- Lubrication and rigid tooling help maintain dimensional accuracy.
Cold deformation increases strength and hardness but may reduce ductility—annealing may be required before or after fabrication depending on the application.
Welding
Inconel® Alloy 600 demonstrates excellent weldability across all major arc welding methods, and is widely used in pressure-containing and structural applications that require clean, defect-free joints.
- Applicable Welding Processes:
-
- GTAW (TIG)
- GMAW (MIG/MAG)
- SMAW (Stick/MMA)
- Plasma Arc
- Recommended Filler Metals:
-
- ERNiCr-3 (for TIG and MIG)
- ENiCrFe-3 (for SMAW)
- Post-Weld Heat Treatment (PWHT): Not typically required, though stress-relief may be applied for critical systems.
Surface Finishing Tip: After welding, brushing with a stainless steel wire brush removes heat tint, leaving a clean surface with no further need for pickling.
Machining
Inconel 600’s machining behavior is comparable to other high-nickel alloys. While machinability is slightly better than 304 stainless, it is still inferior to free-machining grades like 303.
Key Machining Characteristics:
- Best Machined Condition: Annealed
- Work-Hardening Tendency: High — tools must cut below the hardened surface
- Cutting Speeds: Low, with constant tool engagement
- Tools: Carbide or ceramic inserts recommended
- Coolant: High-pressure, water-based coolant required to maintain surface finish and extend tool life
| Machining Factor | Best Practice |
| Feed rate | Moderate to high (avoid rubbing) |
| Depth of cut | Sufficient to penetrate hardened surface |
| Tooling | Sharp carbide or ceramic inserts; avoid worn tools |
| Rigidity | Use of rigid machines and work-holding fixtures is essential |
| Lubrication | Flood coolant to minimize thermal buildup |
8. Applications of Inconel 600
Inconel® Alloy 600’s unique combination of high temperature strength, corrosion resistance, and fabrication versatility makes it indispensable in many demanding industrial sectors.
| Industry | Typical Components | Key Advantages |
| Oil & Gas | Valves, downhole tools, flanges | Corrosion resistance, high strength |
| Power Generation | Steam generators, superheaters, turbines | High-temp oxidation resistance, thermal stability |
| Chemical Processing | Heat exchangers, pressure vessels | Resistance to acids and organic chemicals |
| Aerospace | Combustion chambers, seals, fasteners | High temp strength, cyclic thermal resistance |
| Marine | Pumps, valves, subsea connectors | Chloride corrosion resistance, seawater durability |
| Cryogenic & Food | Storage vessels, processing equipment | Toughness, corrosion resistance |
9. Advantages and Limitations
Advantages of Inconel 600
- Outstanding High-Temperature Performance:
Maintains mechanical strength and oxidation resistance up to about 1,095°C, with excellent creep resistance and structural stability. - Excellent Corrosion Resistance:
Resistant to a wide range of corrosive environments including seawater, mild acids, and chloride-induced stress corrosion cracking. - Good Fabricability:
Easily weldable and formable using standard methods; machinable with appropriate tooling despite work hardening. - Non-Magnetic and Radiation Resistant:
Its austenitic structure ensures non-magnetic behavior and good performance in nuclear environments exposed to radiation.
Limitations of Inconel 600
- Limited Resistance to Strong Acids:
Vulnerable to concentrated hydrochloric and mixed acids, limiting use in highly aggressive chemical environments. - Strength Declines at Very High Temperatures:
Mechanical properties degrade above 815°C, restricting use in ultra-high-temperature applications like turbine blades. - Higher Cost:
More expensive than common stainless steels in terms of material and processing costs. - Heat Treatment Sensitivity:
Requires controlled annealing to prevent carbide precipitation that can reduce corrosion resistance.
10. Comparison with Other Alloys
| Property / Alloy | Inconel 600 | Inconel 625 | Stainless Steel 316 | Hastelloy C-276 |
| Composition | Ni-Cr-Fe (approx. 72% Ni) | Ni-Cr-Mo (higher Mo content) | Fe-Cr-Ni-Mo | Ni-Mo-Cr-Fe |
| Maximum Service Temp | Up to 1,095°C (2,000°F) | Up to 982°C (1,800°F) | Around 870°C (1,600°F) | Up to 1,093°C (2,000°F) |
| Corrosion Resistance | Excellent in mild acids & seawater; limited in strong acids | Superior in oxidizing & reducing environments; excellent pitting & crevice resistance | Good general corrosion resistance; poor in chloride environments | Outstanding resistance to oxidizing/reducing acids and chloride-induced corrosion |
| Mechanical Strength | Good high-temp strength | Higher strength due to solid solution strengthening | Moderate strength | High strength and toughness |
| Fabricability | Good weldability and machinability | Good weldability; more difficult machining | Excellent formability and machinability | Difficult to machine and weld |
| Cost | Moderate to high | Higher than Inconel 600 | Lower cost | High cost |
| Typical Applications | Heat exchangers, valves, nuclear reactors | Aerospace, chemical processing, marine | Food processing, medical, general industry | Chemical reactors, pollution control, extreme corrosive environments |
11. Standards & Certifications
| Standard | Description |
| UNS | N06600 |
| W. Nr. | 2.4816 |
| ASTM | B166 (Rod, bar), B167 (Tube), B168 (Sheet) |
| ASME | SB166, SB167, SB168 |
| AMS | 5540 (Sheet), 5665 (Bar/Forging) |
12. Conclusion
Inconel 600 remains a pillar of high-performance engineering, offering a unique blend of high-temperature stability, corrosion resistance, and fabricability.
Its ability to thrive in diverse extreme environments—from nuclear reactors to deep-sea oil wells—underscores its versatility.
While newer alloys excel in niche applications, Inconel 600’s balance of properties and proven track record ensure its continued relevance in critical industries.
As engineering demands evolve, its role as a reliable, multi-purpose superalloy will persist.
Related Articles: https://www.specialmetals.com/documents/technical-bulletins/inconel/inconel-alloy-600.pdf
FAQs
What is Nickel Alloy 600?
Nickel Alloy 600 (Inconel® 600) is a high-performance, non-magnetic alloy composed mainly of nickel, chromium, and iron.
It is engineered for use in extreme temperature and corrosive environments, especially in aerospace, chemical processing, and marine industries.
What is the maximum service temperature for Inconel 600?
Inconel 600 can operate continuously at temperatures up to 1,095°C in oxidizing environments, with short-term exposure to 1,200°C possible.
Is Inconel 600 magnetic?
No, its austenitic microstructure makes it non-magnetic, a critical property for components in magnetic resonance imaging (MRI) equipment or electromagnetic environments.
Can Inconel 600 be used in seawater applications?
Yes, its corrosion rate in seawater is <0.01 mm/year, making it suitable for marine hardware like pumps, valves, and heat exchangers.
How does Inconel 600 compare to Inconel 718?
Inconel 600 offers better oxidation resistance and is more cost-effective, while Inconel 718 provides higher strength at elevated temperatures (up to 980°C) due to its precipitation-hardening chemistry.
What causes embrittlement in Inconel 600?
Carbide precipitation at grain boundaries during improper heat treatment (e.g., slow cooling from 600–800°C) can cause embrittlement. This is avoided by annealing at 1,095°C followed by rapid cooling.
