Inconel 625 · UNS N06625 · W. Nr. 2.4856 · GH3625 · NiCr22Mo9Nb
Inconel 625 (N06625): composition, properties, fittings and flanges
Inconel 625 (UNS N06625, W. Nr. 2.4856, Chinese grade GH3625) is a niobium-stabilised Ni-Cr-Mo alloy with a minimum of 58 % nickel, 20-23 % chromium, 8-10 % molybdenum and 3.15-4.15 % niobium plus tantalum. Its strength comes from the solid-solution effect of molybdenum and niobium rather than from a precipitation-hardening…
- UNS
- N06625
- W. Nr.
- 2.4856
- Density
- 8.44 g/cm³ (0.305 lb/in³)
- Key strength
- 827 MPa / 120 ksi
Identification and standards
| Short form | Inconel 625 · UNS N06625 · W. Nr. 2.4856 · GH3625 · NiCr22Mo9Nb |
|---|---|
| Classification | Solid-solution strengthened nickel-chromium-molybdenum-niobium alloy |
| UNS | N06625 |
| Werkstoff number | 2.4856 |
| Material family | Inconel Alloys |
Chemical composition
| Element | Composition (wt %) | Why it is there |
|---|---|---|
| Nickel (Ni) | 58.0 min | Matrix - provides chloride SCC immunity |
| Chromium (Cr) | 20.0 - 23.0 | Oxidising acid and high-temperature oxidation resistance |
| Molybdenum (Mo) | 8.0 - 10.0 | Pitting and crevice corrosion resistance |
| Niobium + Tantalum (Nb+Ta) | 3.15 - 4.15 | Solid-solution strengthening, stabilises against sensitisation |
| Iron (Fe) | 5.0 max | - |
| Cobalt (Co) | 1.0 max | Restricted for some nuclear applications |
| Manganese (Mn) | 0.50 max | Deoxidiser |
| Silicon (Si) | 0.50 max | - |
| Aluminium (Al) | 0.40 max | - |
| Titanium (Ti) | 0.40 max | - |
| Carbon (C) | 0.10 max | - |
| Phosphorus (P) | 0.015 max | - |
| Sulphur (S) | 0.015 max | - |
Note Single figures are maximum limits unless shown as a range. Always confirm against the heat-specific EN 10204 3.1 certificate supplied with your order.
Mechanical properties
| Tensile strength, min (annealed plate, ASTM B443) | 827 MPa / 120 ksi |
|---|---|
| 0.2 % yield strength, min | 414 MPa / 60 ksi |
| Elongation in 2 in (50 mm), min | 30 % |
| Typical hardness, annealed | 170 - 220 HB |
| Typical impact energy at room temperature | 100 - 160 J |
| Service temperature range in air | -196 °C to 980 °C |
Warning Values depend on product form, section thickness and heat treatment. Larger sections generally achieve lower strength than thin product; always design against the applicable code allowable stress rather than these figures.
Physical properties
| Density | 8.44 g/cm³ (0.305 lb/in³) |
|---|---|
| Melting range | 1290 - 1350 °C (2350 - 2460 °F) |
| Modulus of elasticity | 207 GPa (30 x 10⁶ psi) |
| Thermal conductivity at 20 °C | 9.8 W/m·K |
| Mean coefficient of thermal expansion, 20-100 °C | 12.8 µm/m·°C |
| Electrical resistivity at 20 °C | 1.29 µΩ·m |
| Magnetic behaviour | Essentially non-magnetic when annealed |
Specifications by product form
| Bar / rod | ASTM B446 / ASME SB-446 (Grade 1 and Grade 2), AMS 5666 |
|---|---|
| Plate / sheet / strip | ASTM B443 / ASME SB-443, AMS 5599 |
| Seamless pipe & tube | ASTM B444 / B444M, ASTM B163 (condenser tube) |
| Welded pipe & tube | ASTM B705 / B704 |
| Forgings & flanges | ASTM B564 / ASME SB-564 (UNS N06625) |
| Butt weld fittings | ASTM B366 (WP625, Grade 1 and Grade 2) |
| Welding consumables | ERNiCrMo-3 wire (AWS A5.14), ENiCrMo-3 electrode (AWS A5.11) |
| UNS / EN / China | UNS N06625 · EN NiCr22Mo9Nb · W. Nr. 2.4856 · GB GH3625 |
Product forms available
Hangbo supplies this grade in the following forms. Sizes outside the listed range can often be produced to order.
- Seamless and welded pipe & tube to ASME B36.19M / B36.10M schedules
- Forged rings, discs and step forgings
- Butt weld elbows, tees, reducers, caps and stub ends to ASME B16.9
- Forged flanges to ASME B16.5 Class 150 - 2500 and B16.47 Series A/B
Typical applications
- Seawater cooling, ballast and firewater piping on ships and offshore platforms
- Subsea manifolds, risers, flowlines and wellhead components (API 6A / NACE MR0175)
- Flare stacks, scrubber internals and flue gas desulphurisation ducting
- Chemical process piping carrying mixed oxidising and reducing acids
- Aerospace engine bleed air ducts, thrust reverser assemblies and exhaust systems
- Nuclear waste handling and spent fuel pool equipment
- Hydraulic and instrumentation tubing where chloride stress corrosion cracking must be eliminated
Welding, forming and machining
- Welding
- Excellent weldability by GTAW, GMAW, SMAW and SAW with ERNiCrMo-3 filler. No preheat required; keep interpass temperature below 150 °C. Because there is no precipitation-hardening response, no post-weld ageing is needed to develop strength - unlike Inconel 718.
- Hot forming
- Hot work between 1150 °C and 950 °C, finishing not below 1010 °C to avoid grain-refinement gradients; water quench or rapid air cool after solution annealing at 1090-1200 °C.
- Machining
- Work hardens rapidly. Use carbide tooling, positive rake, low cutting speed (20-35 m/min), heavy constant feed, and never allow the tool to dwell or rub.
- Pickling
- Remove oxide by shot blasting then pickling in HF-HNO₃; avoid sulphur-bearing lubricants, which can cause embrittlement above 550 °C.
Buy Inconel 625 from Hangbo
Material is supplied with full heat-number traceability, solution annealing or ageing performed under calibrated furnace control, and an EN 10204 3.1 certificate covering chemical analysis, mechanical properties, heat treatment records and the agreed NDT scope. Positive material identification and third party inspection and test reports from SGS are available for critical service.
Inconel 625 frequently asked questions
What is the difference between Inconel 625 Grade 1 and Grade 2?
Grade 1 is annealed at a higher temperature, typically around 1093 °C, giving a coarser grain with higher creep and fatigue strength for service above 600 °C. Grade 2 is annealed at around 982 °C, giving a finer grain with better low-temperature tensile strength and fatigue life. Both meet the same minimum chemistry.
Is Inconel 625 suitable for seawater?
Yes. Chromium, molybdenum and niobium together give a pitting resistance equivalent number above 45, making the alloy resistant to chloride pitting and crevice attack in natural seawater, and unaffected by marine biofouling. It is the standard upgrade path where 316L or even duplex 2205 has failed.
Can Inconel 625 be used in sour (H2S) service?
Yes. Annealed Inconel 625 is listed in NACE MR0175 / ISO 15156 and is commonly supplied to API 6A requirements. Cold worked or surface hardened material must be evaluated case by case.
Which standards cover Inconel 625 flanges and fittings?
Forged flanges are produced to ASTM B564 UNS N06625 in ASME B16.5 dimensions (NPS ½ to 24) or ASME B16.47 (NPS 26 to 60). Butt weld fittings are produced to ASTM B366 WP625 in ASME B16.9 dimensions, or MSS SP-43 for light wall Schedule 5S / 10S fittings.
What welding filler metal should be used for Inconel 625?
Use over-matched ERNiCrMo-3 wire for GTAW/GMAW and ENiCrMo-3 electrodes for SMAW. Dissimilar joints to carbon steel are normally made with the same nickel filler to limit the effect of dilution.
Does Inconel 625 need a post-weld heat treatment?
Because it is strengthened by solid solution rather than precipitation, no post-weld ageing is required. Stress relieving at 815-870 °C may be applied for dimensional stability, and stabilising treatments above 1000 °C are only used when sensitisation control is critical.