Alloy 725 INCONEL® 725 – UNS N07725 / ASTM B805, B564
Alloy 725 INCONEL® 725
Alloy 725 INCONEL® 725 is a nickel-chromium-molybdenum-niobium alloy designed to offer high corrosion resistance and age-hardening properties, providing exceptional mechanical strength. Its corrosion resistance equals that of INCONEL® 625, but precipitation hardening enables mechanical strength nearly double that of the annealed version of INCONEL® 625.
Unlike other cold-worked strengthened alloys, INCONEL® 725 maintains excellent ductility and toughness, making it ideal for components subjected to high stress and extreme corrosive environments. The alloy is particularly suitable for acidic environments containing hydrogen sulfide (H₂S), chlorides and carbon dioxide, such as those typical of natural gas wells and offshore applications.
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Reference standards:
- ASTM B805 (bars and wire)
- ASTM B564 (flanges and forgings)
- ASME Code Case 2217 (bars and forgings for high-pressure applications)
Chemical composition (%)
| Element | Content (%) |
|---|---|
| Nickel (Ni) | 55.0 – 59.0 |
| Chromium (Cr) | 19.0 – 22.5 |
| Molybdenum (Mo) | 7.0 – 9.5 |
| Niobium (Nb) | 2.75 – 4.0 |
| Titanium (Ti) | 1.0 – 1.7 |
| Aluminium (Al) | 0.35 max |
| Iron (Fe) | Balance |
| Carbon (C) | 0.03 max |
| Manganese (Mn) | 0.35 max |
| Silicon (Si) | 0.20 max |
| Phosphorus (P) | 0.015 max |
| Sulphur (S) | 0.010 max |
Mechanical properties
| Temperature (°C) | Tensile strength (MPa) | Yield strength (MPa) | Elongation (%) |
|---|---|---|---|
| 20 | 1254 | 892 | 32 |
| 300 | 1189 | 826 | 30 |
| 600 | 1099 | 782 | 32 |
| 900 | 1075 | 807 | 31 |
Heat treatments
- Solution treatment: 1040°C with air cooling to maintain optimal structure.
- Ageing: 730°C for 8 hours, controlled cooling to 620°C for 8 hours, followed by air cooling.
- Hot forming: Working temperature between 900 and 1120°C, with gradual cooling to avoid duplex grain structures.
Available forms
INCONEL® Alloy 725 is available in the following forms:
Industrial applications
Thanks to its unique combination of mechanical strength and corrosion resistance, INCONEL® 725 is used in:
- Aerospace and Defence: Structural components for extreme environments.
- Power Generation: Heat exchange systems in high-temperature plants.
- Chemical and Pharmaceutical Industry: Components for reactors, piping and tanks in acidic environments.
- Motorsport: High-performance engine parts exposed to corrosive gases.
- Nuclear: Structural materials for aggressive radioactive environments.
- Oil & Gas: Instrumentation for high-pressure and high-temperature wells, resistance to sulphide stress corrosion and chloride stress corrosion cracking.
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