Inconel 625 and 718 are both nickel-based superalloys, but they are built for different jobs: 625 for corrosion resistance and fabricability, 718 for high strength through age hardening.
| Property | Inconel 625 | Inconel 718 |
|---|---|---|
| UNS number | N06625 | N07718 |
| Strengthening | Solid solution (Mo, Nb); not age-hardenable | Precipitation hardening (Nb, Ti, Al) |
| Bar standard | ASTM B446 | ASTM B637 (AMS 5662 / 5663) |
| Min tensile | 827 MPa (B446 Grade 1) | 1240 MPa (solution treated and aged) |
| Min yield | 414 MPa | 1030 MPa |
| Min elongation | 30% | 12% |
| Corrosion resistance | Excellent in seawater, pitting and crevice corrosion | Good, lower pitting resistance than 625 |
| Useful temperature | Oxidation resistance to about 980°C | High strength to about 650–700°C |
Inconel 718 is roughly one and a half times stronger than 625 in the specified condition because it is age-hardened. Inconel 625 relies on molybdenum and niobium for strength and is chosen mainly for its outstanding resistance to seawater, pitting, crevice corrosion and a wide range of chemicals.
Inconel 625 is supplied annealed (B446 Grade 1) or solution annealed (Grade 2) and is not hardened by aging. Inconel 718 is machined in the solution-treated condition and then given a double-age treatment to reach full strength. Because of this, 718 parts are often ordered solution treated, machined, then aged.
Both alloys work-harden, so use sharp carbide tooling, positive feeds and good coolant. 718 is known for resistance to strain-age cracking, which makes it more weldable than most age-hardened nickel alloys. 625 welds readily with matching filler.
Choose Inconel 625 for subsea and seawater hardware, chemical process equipment and exhaust or ducting where corrosion resistance and fabrication matter most. Choose Inconel 718 for turbine components, downhole oilfield tools, fasteners and shafts where strength is the driver.
If your project requires NACE MR0175 / ISO 15156 compliance, state the required condition and hardness limits in your enquiry so we can quote the correct material.
