We stock six core nickel alloys - Alloy K-500, Alloy 625, Alloy 718, Alloy 725, Alloy 825 and Alloy 925 - covering solid-solution and precipitation-hardened grades for everything from broad general corrosion resistance to the most demanding sour downhole service. Choosing between them comes down to two questions: how much strength the application needs, and which corrosive environment the finished part has to survive.
Solid-solution and precipitation-hardened grades
Alloy 625 gets its strength from solid-solution effects: molybdenum and niobium dissolved into the nickel-chromium matrix, supplied hot worked and annealed rather than age-hardened. It gives excellent corrosion resistance across a very wide temperature range, from sub-zero to 980°C, which is why it covers such a broad spread of applications.
Alloy 718, Alloy 725, Alloy 925 and Alloy K-500 are all precipitation-hardened instead. Fine intermetallic precipitates form during ageing and pin the microstructure, giving each of these grades considerably higher strength than Alloy 625 for a similar base composition - Alloy 725, for example, reaches approximately twice the strength of Alloy 625 in the annealed condition.
Matching the alloy to the environment
Alloy 825 stands apart from the rest of the range for its resistance to both reducing and oxidising environments, including sulphuric and phosphoric acids, alongside strong resistance to pitting, crevice corrosion and stress corrosion cracking in chloride environments.
Alloy 925 and Alloy K-500 both target the most aggressive sour conditions. Alloy 925 is approved under NACE MR0175-3 / ISO 15156-3 for downhole environments containing chlorides, CO2 and H2S, with a proof stress of 758-965 N/mm2. Alloy K-500, a nickel-copper alloy refined by ESR, is listed under NACE MR0175 for sour-gas service and additionally resists seawater, hydrofluoric acid, sulphuric acid and alkalis.
Alloy 718 sits closer to Alloy 625 in its corrosion resistance but trades some of that temperature range - retaining strength and corrosion resistance from cryogenic temperatures up to around 750°C - for the higher strength that precipitation hardening provides.
What we stock
All six grades are stocked as round bar from 5/8" to 10" diameter (15.87-254mm) in the UK and USA. Plate, tube and fittings are available on enquiry across the range, with forgings and castings to order.
Choosing between the range
| Grade | Strengthening | Distinguishing resistance |
|---|---|---|
| Alloy 625 | Solid-solution | Broad resistance, sub-zero to 980°C |
| Alloy 718 | Precipitation-hardened | Cryogenic to ~750°C |
| Alloy 725 | Precipitation-hardened | ~2x strength of Alloy 625 (annealed) |
| Alloy 825 | n/a | Reducing and oxidising acids |
| Alloy 925 | Precipitation-hardened | Sour downhole (chlorides, CO2, H2S) |
| Alloy K-500 | Precipitation-hardened | Seawater, hydrofluoric acid, sulphuric acid, alkalis |
For how this stock range came together, see our article on the investment behind our extended nickel alloy range.