Alloy 725
Also known as Inconel® 725, UNS N07725
Alloy 725 is an age-hardened nickel-chromium alloy with roughly twice the strength of Alloy 625, approved for sour service.
Alloy 725 (UNS N07725) is a Nickel-Chromium alloy with additions of Molybdenum, Niobium and Titanium, age-hardened to deliver approximately twice the strength of Alloy 625 in the annealed condition. The high strength is achieved through gamma-prime precipitation while maintaining the corrosion resistance characteristic of Alloy 625.
Approved under NACE MR0175 / ISO 15156 for sour oil and gas applications, ASTM B805 and API 6A CRA. Excellent resistance to stress corrosion cracking, non-magnetic. Supplied hot worked, annealed and age-hardened.
We stock bar in the UK and USA. Plate, tube and fittings are available on enquiry; forgings and castings to order.
- Approved under NACE MR0175 for highly corrosive sour oil and gas wells
- Excellent corrosion resistance in seawater and industrial acids
- Approximately twice the strength of Alloy 625 in the annealed condition
- Good ductility and toughness
- Excellent resistance to stress corrosion cracking
| Element | Min | Max |
|---|---|---|
| Nickel (Ni) | 55.0 | 59.0 |
| Chromium (Cr) | 19.0 | 22.5 |
| Molybdenum (Mo) | 7.0 | 9.5 |
| Niobium+Tantalum (Nb+Ta) | 2.75 | 4.00 |
| Titanium (Ti) | 1.00 | 1.70 |
| Iron (Fe) | Bal | |
| Aluminium (Al) | - | 0.35 |
| Manganese (Mn) | - | 0.35 |
| Silicon (Si) | - | 0.20 |
| Carbon (C) | - | 0.03 |
| Phosphorus (P) | - | 0.015 |
| Sulphur (S) | - | 0.010 |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 120 ksi | 827 N/mm² |
| Tensile strength (min) | 150 ksi | 1034 N/mm² |
| Elongation (5.65√S0 & 4D) | 20% | |
| Reduction of area | 35% | |
| Hardness (Rockwell C) | < 43 | |
| Impact strength (-60°C) long. | 40 ft.lb av (35 ft.lb min) | 54 J av (47 J min) |
| Property | Imperial | Metric |
|---|---|---|
| 0.2% Proof stress (min) | 120 ksi | 827 N/mm² |
| Tensile strength (min) | 150 ksi | 1034 N/mm² |
| Elongation (5.65√S0 & 4D) | 20% | |
| Reduction of area | 35% | |
| Hardness (Rockwell C) | < 43 | |
| Impact strength (-60°C) trans. | 37 ft.lb av (32 ft.lb min) | 50 J av (43 J min) |
| Property | Value |
|---|---|
| Density (kg/m³) | 8310 |
| Magnetic permeability (20°C) | < 1.001 |
| Young's modulus (kN/mm²) | 204 |
| Poisson's ratio | 0.31 |
| Electrical resistivity, 20°C (µΩ.m) | 1.144 |
| Thermal conductivity, 20°C (W/m.K) | 10.6 |
| Mean coefficient of thermal expansion, 20-100°C (m/m/K) | 13 x 10⁻⁶ |
| Specific heat, 20°C (J/kg.K) | 430 |
Equivalents & cross-references
Standard designations
- UNS
- N07725Unified Numbering System
- ASTM
- B805Rod and bar
- NACE
- MR0175 / ISO 15156Sour service
- API
- 6ACRACorrosion-resistant alloy
Alloy 725 is also designated UNS N07725, ASTM B805, NACE MR0175 / ISO 15156 and API 6ACRA.
Trade name equivalents
-
Inconel 725
Special Metals Corporation
Inconel 725 is a trade name of Special Metals Corporation for Alloy 725.
Common questions
What is the UNS number for Alloy 725?
Alloy 725 is a nickel-chromium alloy with molybdenum, niobium and titanium additions, covered by UNS N07725, ASTM B805 and API 6CRA, and listed in NACE MR0175/ISO 15156. It is supplied in the hot worked, annealed and age-hardened condition, developing extremely high strength through precipitation of gamma-prime phase.
What is Alloy 725 used for?
Alloy 725 is used where very high strength must be combined with severe corrosion resistance, most commonly downhole equipment for corrosive and sour oil and gas wells, hangers, connectors and valve stems, and fasteners for marine applications. It is also used in chemical process equipment and agitators. Langley Alloys stocks it as bar, with plate, tube and fittings available on enquiry, and forgings and castings to order.
What is the difference between Alloy 725 and Alloy 625?
Alloy 725 has very similar corrosion resistance to Alloy 625 but roughly twice the strength, achieved by age-hardening rather than cold working, so it keeps excellent ductility and toughness even in large or non-uniform sections that cannot be strengthened by cold working. Its 0.2% proof stress is 827 N/mm² against 415 N/mm² for annealed Alloy 625.
Is Alloy 725 suitable for sour wells?
Yes. Alloy 725's combination of alloying elements provides excellent resistance to conditions found in sour oil and gas wells containing carbon dioxide, chlorides and hydrogen sulphide, and it is approved under NACE MR0175 for such applications. Its high nickel content resists stress corrosion cracking, molybdenum resists reducing acids such as sulphuric and phosphoric, chromium resists oxidising environments such as nitric acid, and titanium inhibits intergranular corrosion.
What is the density of Alloy 725?
Alloy 725 has a density of approximately 8.30 g/cm³ (8300 kg/m³).
Is Alloy 725 magnetic?
No. Alloy 725 is non-magnetic, with a magnetic permeability below 1.001.
Datasheets
625 corrosion resistance, 718 strength
In this Technical Corner, metallurgist Rodney introduces Alloy 725: a rare, high-performance nickel alloy that marries the corrosion resistance of 625 with the strength of 718.
Precipitation-strengthened and reserved for the most demanding oil and gas, naval and chemical-processing applications, it can carry long lead times, so we hold it in stock for mission-critical projects.
Visit our YouTube channelAlloy 725 is supplied in the hot worked, annealed and age-hardened condition; bars are supplied with a standard peeled surface, with each complete batch ultrasonically tested and all bars visually inspected.
Tools for this grade
Sour-service screen (NACE MR0175)
Sour-Service Screen
Work out whether a service is sour from the H2S partial pressure, and see each alloy's NACE MR0175 / ISO 15156 status and hardness limit. A first-pass screen for oil & gas material selection - the full environmental envelope for a grade is set in ISO 15156-3 Annex A.
Candidate grade
| Grade | Family | NACE status | Hardness limit |
|---|
First-pass screen only. This shows whether the service is sour (from H2S partial pressure) and each material group's NACE MR0175 hardness limit and general suitability. It does not reproduce the full environmental windows (maximum H2S partial pressure, temperature, chloride, in-situ pH per grade) - those are in ISO 15156-3 Annex A and must be checked there for the specific grade, product form and condition. Qualification also depends on heat treatment, cold work and welding.
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