INCONEL Alloy 600, Alloy 601, Alloy 617, Alloy 625, Alloy 718
INCONEL ALLOY is renowned for its exceptional performance in extreme environments, particularly where high temperatures and corrosive conditions prevail. These nickel-chromium-based superalloys maintain their strength and resist oxidation and corrosion across a wide temperature range, making them indispensable in industries such as oil and gas, aerospace, chemical processing, and marine engineering.
Inconel 600/UNS N06600
Inconel 600 is a solid-solution strengthened alloy primarily composed of nickel and chromium. It offers outstanding resistance to oxidation and corrosion, making it suitable for chemical processing, aerospace, and nuclear engineering applications. The alloy’s versatility allows it to withstand various corrosive environments and high-temperature conditions.
Inconel 601/UNS N06601
Building upon the foundation of Inconel 600, Inconel 601 enhances oxidation resistance with the addition of aluminum. This modification forms a protective oxide layer, enabling the alloy to perform exceptionally well in high-temperature environments. Common applications include thermal processing equipment, heat-treating baskets, and components in pollution control systems.
Inconel 617/UNS N06617
Inconel 617 combines nickel, chromium, cobalt, and molybdenum to deliver a superior strength and oxidation resistance balance at elevated temperatures. Its high-temperature strength and corrosion resistance make it ideal for gas turbines, petrochemical processing, and heat exchangers.
Inconel 625/UNS N06625
Noted for its remarkable fatigue and thermal-fatigue strength, Inconel 625 is highly resistant to oxidation and corrosion. This alloy is widely used in aerospace, marine, and chemical processing industries, particularly in applications requiring high strength and resistance to aggressive environments.
Inconel 718/UNS N07718
Inconel 718 is a precipitation-hardenable nickel-chromium alloy containing significant amounts of iron, niobium, and molybdenum, along with lesser amounts of aluminum and titanium. It combines corrosion resistance and high strength with outstanding weldability, including resistance to post-weld cracking. The alloy has excellent creep-rupture strength at temperatures up to 1300°F (700°C), making it suitable for gas turbines, rocket motors, and nuclear reactors.
Chemical Composition (wt%) of Inconel Alloy
| Alloy | Ni | Cr | Fe | Mo | Co | Nb | Al | Ti | Mn | Si | C | Other |
| Inconel 600 | ≥72 | 14-17 | 6-10 | – | – | – | – | – | ≤1 | ≤0.5 | ≤0.15 | Cu ≤0.5, S ≤0.015 |
| Inconel 601 | 58-63 | 21-25 | Balance | – | – | – | 1.0-1.7 | – | ≤1 | ≤0.5 | ≤0.10 | S ≤0.015 |
| Inconel 617 | ≥44.5 | 20-24 | ≤3 | 8-10 | 10-15 | – | 0.8-1.5 | – | ≤0.5 | ≤0.5 | 0.05-0.15 | B ≤0.006, S ≤0.015 |
| Inconel 625 | ≥58 | 20-23 | ≤5 | 8-10 | ≤1 | 3.15-4.15 | ≤0.4 | ≤0.4 | ≤0.5 | ≤0.5 | ≤0.10 | P ≤0.015 |
| Inconel 718 | 50-55 | 17-21 | Balance | 2.8-3.3 | ≤1 | 4.75-5.5 | 0.2-0.8 | 0.65-1.15 | ≤0.35 | ≤0.35 | ≤0.08 | B ≤0.006, Cu ≤0.3 |
Mechanical Properties (Annealed Condition) of Inconel Alloy
| Alloy | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (Rockwell) |
| Inconel 600 | 550 (80 ksi) | 240 (35 ksi) | 30% | B80 |
| Inconel 601 | 550 (80 ksi) | 205 (30 ksi) | 30% | B88 |
| Inconel 617 | 750 (109 ksi) | 345 (50 ksi) | 35% | B95 |
| Inconel 625 | 760 (110 ksi) | 345 (50 ksi) | 30% | B95 |
| Inconel 718 | 1240 (180 ksi) | 1035 (150 ksi) | 12% | C35 |
Product Forms and ASTM Standards
| Alloy | Pipes & Tubes | Plates, Sheets & Strips | Bars & Rods | Forgings | Rings |
| Inconel 600 | ASTM B167 | ASTM B168 | ASTM B166 | ASTM B564 | Custom |
| Inconel 601 | ASTM B167 | ASTM B168 | ASTM B166 | ASTM B564 | Custom |
| Inconel 617 | ASTM B166 | ASTM B168 | ASTM B166 | ASTM B564 | Custom |
| Inconel 625 | ASTM B444, B705 | ASTM B443 | ASTM B446 | ASTM B564 | Custom |
| Inconel 718 | ASTM B983 | ASTM B670 | ASTM B637 | ASTM B637 | AMS 5662 |
Heat Treatment Process of Inconel Alloy
| Alloy | Solution Annealing Temperature | Cooling Method | Precipitation Hardening (if applicable) |
| Inconel 600 | 1010–1150°C (1850–2100°F) | Air cool | Not applicable |
| Inconel 601 | 1065–1180°C (1950–2150°F) | Air cool | Not applicable |
| Inconel 617 | 1120–1205°C (2050–2200°F) | Air cool | Not applicable |
| Inconel 625 | 980–1040°C (1800–1900°F) | Water quench | Not applicable |
| Inconel 718 | 980°C (1800°F) for 1 hr, then 720°C (1325°F) for 8 hrs | Air cool | Yes — age-hardened for high-strength |
Weldability of Inconel Alloy
| Alloy | Weldability Rating | Recommended Welding Process | Post-Weld Heat Treatment |
| Inconel 600 | Excellent | GTAW (TIG), GMAW (MIG), SMAW (Stick) | Not required |
| Inconel 601 | Good | GTAW, GMAW, SMAW | Not required |
| Inconel 617 | Good | GTAW, GMAW | Not required |
| Inconel 625 | Excellent | GTAW, GMAW, SMAW, PAW (Plasma) | Not required |
| Inconel 718 | Moderate (susceptible to cracking) | GTAW, Electron Beam, Laser | Solution annealing is recommended after welding |
Welding Note:
Inconel 625 and 718 show excellent weldability with minimal cracking.
Inconel 718 requires precise heat control to avoid micro-cracks due to its precipitation-hardened structure.
Corrosion Resistance Comparison
| Alloy | Oxidation Resistance | Sulfidation Resistance | Acid Resistance | Seawater Resistance |
| Inconel 600 | Excellent up to 1095°C (2000°F) | Moderate | Good (Nitric, Hydrochloric acids) | Moderate |
| Inconel 601 | Outstanding up to 1250°C (2280°F) | Excellent | Limited (resists some acids) | Limited |
| Inconel 617 | Outstanding up to 1100°C (2000°F) | Excellent | Moderate | Limited |
| Inconel 625 | Excellent up to 980°C (1800°F) | Good | Excellent (resists most acids) | Excellent |
| Inconel 718 | Good up to 650°C (1200°F) | Good | Good | Moderate |
Corrosion Resistance Highlights:
Inconel 625 excels in marine environments due to its molybdenum content, making it highly resistant to pitting and crevice corrosion.
Inconel 601 forms a tightly adherent oxide scale, making it ideal for high-temperature oxidation.
Inconel 718 trades some corrosion resistance for strength and creep resistance, especially in high-stress aerospace applications.
Industry-Specific Applications
| Alloy | Aerospace | Oil & Gas | Chemical Processing | Marine & Offshore | Power Generation |
| Inconel 600 | Jet engine components, exhaust liners | Furnace components, heat exchangers | Caustic alkali environments | Not ideal (limited seawater resistance) | Steam superheaters, nuclear reactor components |
| Inconel 601 | Afterburners, combustion cans | Reformer tubes, flare stacks | High-temp sulfur-bearing atmospheres | Not ideal | Gas turbines, heat treating equipment |
| Inconel 617 | Gas turbines, combustion liners | High-temp piping, flue gas systems | High-temperature chemical processing | Limited use | Heat exchangers, petrochemical plants |
| Inconel 625 | Rocket engine thrust chambers, heat shields | Sour gas pipelines, offshore platforms | Acid-resistant piping, scrubbers | Propeller blades, seawater components | Nuclear reactors, waste heat boilers |
| Inconel 718 | Turbine discs, jet engines, space shuttle components | Downhole tools, casing hangers | Acidic environments needing high-strength | Limited use | Gas turbines, cryogenic tanks |
Key Takeaways:
Inconel 625 shines in marine and chemical environments due to superior corrosion resistance.
Inconel 718 rules aerospace thanks to high strength and creep resistance — but is overkill for corrosion-heavy environments.
Inconel 601 is unbeatable for extreme heat environments like furnaces and gas turbines.
Cost Analysis
| Alloy | Raw Material Cost | Machinability | Welding Cost | Lifecycle Value |
| Inconel 600 | $$ (Moderate) | Fair (work hardens) | Moderate | High (long lifespan in heat/corrosion environments) |
| Inconel 601 | $$ (Moderate) | Fair (better than 600) | Moderate | Very High (superior oxidation resistance) |
| Inconel 617 | $$$ (High) | Difficult (high cobalt content) | High (special handling) | High (high-temp, long-life applications) |
| Inconel 625 | $$$ (High) | Difficult (gummy behavior) | Low (excellent weldability) | Excellent (seawater, acidic environments) |
| Inconel 718 | $$$$ (Very high) | Difficult (age-hardened) | High (crack-sensitive) | Excellent (aerospace, high-stress parts) |
Cost Tips:
Inconel 625 offers the best cost-to-performance ratio for corrosion-heavy environments.
Inconel 718 is costly but justified where strength and high-temp creep resistance are critical — especially in aerospace.
Inconel 601 wins for high-temperature applications thanks to its balance of cost, oxidation resistance, and machinability.
Material Selection Guidance (By Industry)
Aerospace
Inconel 718: Best for jet engines, turbine blades, and rocket motors due to high strength and creep resistance.
Inconel 625: Great for heat shields and exhaust ducts — corrosion-resistant and handles extreme temps.
Recommendation: Use 718 for load-bearing components and 625 for parts exposed to corrosive exhaust gases.
Oil & Gas
Inconel 625: Perfect for sour gas environments, offshore platforms, and heat exchangers — fights pitting, crevice corrosion, and chloride stress corrosion cracking.
Inconel 617: Great for flue gas systems and reformers — withstands high-temp gas exposure.
Recommendation: 625 for corrosion-critical parts, 617 for high-temp exposure.
Chemical Processing
Inconel 600: Handles caustic environments and alkaline conditions, ideal for heat exchangers and piping.
Inconel 625: Superior acid resistance — perfect for scrubbers, ducting, and reactors.
Recommendation: 600 for basic corrosion resistance, 625 for aggressive acids and seawater conditions.
Marine & Offshore
Inconel 625: Best choice for propellers, marine exhausts, and seawater piping — outstanding resistance to saltwater corrosion.
Recommendation: 625 all the way — few alloys can match its marine corrosion performance.
Power Generation
Inconel 601: Excellent for gas turbines, superheater tubing, heat-treating equipment — high temp, oxidation, and carburization resistance.
Inconel 625: Great for nuclear reactors, waste heat boilers, and steam superheaters.
Inconel 718: Ideal for gas turbines under high mechanical loads.
Recommendation: 601 for heat environments, 625 or 718 where strength and corrosion resistance are key.
What is the Best Alloy for the Job?
| Need | Best Alloy Choice |
| High-temperature oxidation resistance | Inconel 601 |
| Sour gas, marine, or chemical corrosion | Inconel 625 |
| High strength + high temp creep resistance | Inconel 718 |
| Heat exchangers and caustic alkali handling | Inconel 600 |
| High-temp gas and petrochemical environments | Inconel 617 |
Conclusion
Selecting the appropriate Inconel alloy depends on specific application requirements, including environmental conditions, mechanical stresses, and temperature ranges. Understanding the unique properties of each alloy enables engineers and material specialists to make informed decisions, ensuring reliability and longevity in critical components. For comprehensive technical data and guidance, consulting resources provided by Golden Sunbird Metals are highly recommended. Don’t hesitate to get in touch with us at [email protected].
