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Inconel 718 (UNS N07718) achieves 1379 MPa tensile strength through precipitation hardening with gamma prime/double prime phases — approximately 2x stronger than Inconel 625. However, 718 is limited to 700°C service temperature before its strengthening precipitates become unstable. Inconel 625 (UNS N06625) provides 827 MPa tensile strength with solid-solution strengthening, enabling use up to 982°C with superior corrosion resistance in chloride and marine environments.
| Property | Inconel 718 | Inconel 625 |
|---|---|---|
| UNS | N07718 | N06625 |
| W.Nr. | 2.4668 | 2.4856 |
| Strengthening Mechanism | Precipitation hardened (γ′/γ″) | Solid-solution strengthened |
| Tensile Strength (RT) | 1379 MPa (200 ksi) age-hardened | 827 MPa (120 ksi) |
| Yield Strength (RT) | 1034 MPa (150 ksi) age-hardened | 414 MPa (60 ksi) |
| Yield Strength (650°C) | ~800–1000 MPa | ~255 MPa (37 ksi) |
| Yield Strength (700°C) | ~800 MPa | ~240 MPa (34.8 ksi) |
| Elongation | 12% min. | 30% min. |
| Max Service Temperature | 700°C (1300°F) | 982°C (1800°F) |
| Density | 8.19 g/cm³ | 8.44 g/cm³ |
| Corrosion Resistance | Very good | Excellent — superior to 718 |
| Weldability | Good | Excellent |
| Hardness (aged) | 36–44 HRC | 95 HRB max. |
Maximum mechanical strength is critical and service temperature stays below 700°C. Applications: gas turbine discs, aerospace structural bolts, nuclear reactor internals, high-pressure oil & gas equipment. At 1034 MPa yield strength (age-hardened), 718 delivers performance that 625 cannot match structurally.
Corrosion resistance is the primary concern, operating temperature exceeds 700°C, or the application is in aggressive marine or chemical environments. 625 provides excellent weldability and retains useful properties up to 982°C where 718's precipitates would coarsen and weaken.
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