Choosing between Inconel 718 and Inconel 625 is one of the most common material selection decisions in high-performance engineering. Both are nickel-chromium superalloys with excellent high-temperature and corrosion-resistant properties, but they achieve their performance through fundamentally different strengthening mechanisms—leading to distinct advantages in different applications.
Strengthening Mechanism
Inconel 718 is a precipitation-hardened alloy, strengthened by gamma-prime and gamma-double-prime phases formed during aging heat treatment. This produces very high mechanical strength—tensile up to 180+ ksi—but the strengthening precipitates begin to dissolve above approximately 1,300°F, limiting its high-temperature capability.
Inconel 625 is solid-solution strengthened by its high molybdenum (8-10%) and niobium (3.15-4.15%) content. While its maximum tensile strength is lower (120-150 ksi), it maintains useful properties over a broader temperature range and offers superior corrosion resistance in aggressive chemical environments.
Property Comparison
| Property | Inconel 718 | Inconel 625 |
|---|---|---|
| UNS Number | N07718 | N06625 |
| Tensile Strength | 180+ ksi (aged) | 120-150 ksi |
| Yield Strength | 150+ ksi (aged) | 60-100 ksi |
| Max Service Temp | ~1,300°F (704°C) | ~1,800°F (982°C) |
| Strengthening | Precipitation hardening | Solid solution |
| Weldability | Good (age-hardenable weld) | Excellent |
| Chloride Resistance | Good | Excellent |
| Cost (relative) | Moderate | Higher (Mo content) |
When to Choose Inconel 718
Select Inconel 718 when your application requires maximum mechanical strength at temperatures up to 1,300°F. Typical applications include gas turbine discs and shafts, aerospace structural fasteners, compressor blades, nuclear reactor springs, and any component where high fatigue strength under cyclic loading is the primary design requirement.
When to Choose Inconel 625
Select Inconel 625 when corrosion resistance is the dominant concern, particularly in chloride-bearing environments, seawater, or reducing acid conditions. Typical applications include subsea oil and gas equipment, chemical processing vessels and piping, marine propulsion components, flue gas desulfurization systems, and aerospace exhaust components exposed to combustion products.
ForceBeyond Can Help
ForceBeyond manufactures components in both Inconel 718 and Inconel 625 through casting, forging, and CNC machining. Our metallurgical team can help you select the optimal alloy and manufacturing process for your specific application requirements. Contact us for expert guidance and a free quotation.