Inconel 625: properties, composition, uses and standards
Inconel 625 is a nickel–chromium–molybdenum alloy with niobium, chosen for seawater, high strength and high temperature in one alloy. UNS N06625, W.Nr 2.4856, PREN ≈ 51, density 8.44 g/cm³.
What is Inconel 625?
Inconel 625 is a nickel–chromium–molybdenum alloy with niobium. Engineers choose it for seawater, high strength and high temperature in one alloy. It is also known as Alloy 625, UNS N06625, W.Nr 2.4856, Nicrofer 6020.
- UNS
- N06625
- W.Nr
- 2.4856
- EN
- NiCr22Mo9Nb
- BS
- NA 21
- JIS
- NCF 625
- Trade names
- Inconel 625 · Nicrofer 6020
- Density
- 8.44 g/cm³
- Melting range
- 1290 – 1350 °C
- Magnetic
- Non-magnetic
- PREN (approx.)
- ≈ 51
Chemical composition and what each element does
| Element | Weight % |
|---|---|
| Nickel | 58.0 min |
| Chromium | 20.0 – 23.0 |
| Molybdenum | 8.0 – 10.0 |
| Niobium + Tantalum | 3.15 – 4.15 |
| Iron | 5.0 max |
| Carbon | 0.10 max |
| Manganese | 0.50 max |
| Silicon | 0.50 max |
| Titanium | 0.40 max |
| Aluminium | 0.40 max |
Per ASTM B443 for UNS N06625.
About 9% molybdenum gives PREN above 50 — seawater pitting is rarely a concern.
Niobium strengthens the matrix without heat treatment: yield about 414 MPa annealed.
High nickel makes it virtually immune to chloride stress-corrosion cracking.
Keeps useful strength and oxidation resistance at high temperature.
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength | 827 MPa · 120 ksi |
| Yield strength 0.2% | 414 MPa · 60 ksi |
| Elongation | 30% |
Grade 1 annealed plate, minimum values. Values for pipe, bar and forgings differ slightly — see the product standard.
Where Inconel 625 is used
- Offshore & subsea. Risers, flowlines and clad pipe. Industry →
- Aerospace. Ducting, exhaust and bellows. Industry →
- Chemical. Mixed-acid and chloride service. Industry →
- Flue-gas desulphurisation. Scrubber and stack linings. Industry →
- Marine. Propeller blades and seawater parts. Industry →
Welding 625
The matching filler is ERNiCrMo-3 (AWS A5.14). ENiCrMo-3 electrode.
Keep heat input moderate and interpass temperature low, clean joints thoroughly, and pickle or passivate after welding where the service is corrosive.
Inconel 625 compared with similar grades
| Grade | PREN | Choose it for |
|---|---|---|
| Inconel 625 | ≈ 51 | Seawater, high strength and high temperature in one alloy |
| Inconel 825 | ≈ 31 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| Super Duplex 2507 | ≈ 42 | Seawater and high-chloride service where strength also matters |
| Hastelloy C276 | ≈ 68 | The most aggressive mixed acids, wet chlorine and hypochlorite |
Inconel 625 standards by product
Buying Inconel 625: what to specify
- The product standard and the UNS or designation — for example ASTM B443 UNS N06625.
- Size, thickness or schedule, and quantity in pieces and kg or metres.
- Heat-treatment condition where the standard offers a choice.
- Certificate: EN 10204 3.1 as standard, 3.2 if a third party must witness.
- NACE MR0175 / ISO 15156 compliance if the service contains H₂S.