Inconel® 625 Grade 2 (Alloy 625, UNS N06625) is the solution-annealed condition of the nickel alloy, annealed at 2000°F (1093°C) versus 1600°F (871°C) for Grade 1. The higher anneal lowers yield strength to 40ksi (from 60/50ksi) but improves high-temperature stability. Its 8-10% molybdenum gives a PREN above 45 for outstanding corrosion resistance.
What is the difference between Grade 1 and Grade 2?
Inconel 625 (Alloy 625, UNS N06625, DIN 2.4856) can be supplied to ASTM B446 in two conditions. Grade 1 is annealed and is the most commonly stocked version; Grade 2 is solution annealed. The difference is the annealing temperature - a minimum of 1600°F (871°C) for Grade 1 and 2000°F (1093°C) for Grade 2. An optional stabilisation anneal at 1800°F (982°C) can be applied to Grade 2 to increase resistance to sensitisation at high service temperatures. Because Grade 2 uses the higher temperature, existing Grade 1 stock can be converted to Grade 2 with an additional heat treatment.
What are the mechanical properties?
The higher anneal temperature lowers Grade 2 properties slightly compared with Grade 1:
| Property | Grade 1 (annealed) | Grade 2 (solution annealed) |
|---|---|---|
| Anneal temperature (min) | 1600°F (871°C) | 2000°F (1093°C) |
| Yield strength | 60ksi (414MPa) to 4" bar; 50ksi (345MPa) to 10" | 40ksi (276MPa) all sizes |
| Tensile strength (min) | 120ksi (827MPa) to 4"; 110ksi (758MPa) to 10" | 100ksi (690MPa) |
We carry significant stock as solid bar from 5/8" (15.875mm) to 10" (254mm) diameter, certified to API 6A CRA, NACE MR0175 / ISO 15156-3 and AMS 5666.
What is Alloy 625's composition?
Alloy 625 gains strength from molybdenum and niobium added to a nickel-chromium base:
| Element | Range |
|---|---|
| Nickel | 58.0% min |
| Chromium | 20.0-23.0% |
| Molybdenum | 8.0-10.0% |
| Niobium + Tantalum | 3.15-4.15% |
Its very high molybdenum (8-10%) gives a PREN above 45, beyond all but the most highly alloyed grades. In fresh seawater there is virtually no attack, and it resists aggressive oxidising and non-oxidising acids - it is one of the few alloys suitable for handling or storing hydrochloric acid.
Why choose Alloy 625?
Developed in the early 1960s by International Nickel (INCO), Alloy 625 gains its strength from solid-solution effects, high, though not as high as Inconel 718. The Inconel trademark is now held by Special Metals Corporation. Its high nickel content (above 58%) makes it one of the more expensive nickel alloys, but it performs strongly above 800°C; Special Metals quote service from cryogenic up to 980°C, with properties falling off more from 650-700°C. For a close comparison, see Alloy 625 vs Alloy 725.
Where is Alloy 625 used?
Alloy 625's combination of high-temperature strength and corrosion resistance suits demanding service across several sectors:
- Oil & gas: downhole equipment for corrosive/sour service, wellhead components
- Marine & offshore: propellers & shafts, propulsion motors
- Chemical processing: chemical process equipment
- Energy & power: reactor core & control rod components