Inconel 718 vs 625
Both are nickel-chromium superalloys with a niobium addition, but they get their strength in different ways. 718 is precipitation hardened: a solution treatment and a two-step age raise its yield strength to about 1100 MPa (160 ksi), and it holds that strength to around 650 °C (1200 °F). 625 is solid-solution strengthened by about 9% molybdenum plus niobium and is used annealed, at about 520 MPa (75 ksi) yield. That same molybdenum makes 625 far more resistant to pitting, crevice corrosion and seawater.
The rule of thumb: 718 when strength carries the design, 625 when corrosion or fabrication does. Turbine disks, shafts, bolts and oilfield hardware are 718. Seawater and chemical-process parts, welded sheet assemblies, bellows and weld overlays are 625. Both are slow and expensive to machine.
| Property | Inconel 718 | Inconel 625 |
|---|---|---|
| UNS | N07718 | N06625 |
| Strengthening | Precipitation hardening (solution treat and age) | Solid solution; used annealed |
| Nickel / chromium / iron | 50-55% / 17-21% / balance, ~18% | 58% min / 20-23% / 5% max |
| Molybdenum / niobium | 2.8-3.3% / 4.75-5.5% | 8-10% / 3.15-4.15% |
| Tensile | ~1375 MPa (200 ksi), aged; 1240 MPa (180 ksi) min | ~930 MPa (135 ksi), annealed; 827 MPa (120 ksi) min |
| Yield | ~1100 MPa (160 ksi), aged; 1035 MPa (150 ksi) min | ~520 MPa (75 ksi), annealed; 414 MPa (60 ksi) min |
| Hardness | 36-44 HRC aged | ~175-220 HB annealed |
| Density | 8.19 g/cm³ | 8.44 g/cm³ |
| Useful temperature | Strength to ~650 °C (1200 °F) | Lower strength; oxidation resistant to ~980 °C (1800 °F) |
| Pitting and seawater resistance | Good | Excellent |
| Typical uses | Turbine disks and shafts, fasteners, springs, oilfield hangers and valve stems | Seawater and chemical-process parts, bellows, heat exchangers, weld overlay and filler |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
Need a Inconel 718 or Inconel 625 part made?
- Machine shops that work with nickel alloys · 84
- Forging companies that work with nickel alloys · 17
- 3D Printing companies that work with nickel alloys · 10
- All U.S. manufacturers working with nickel alloys · 189
- Find specialty alloy suppliers
Attach a drawing (PDF or STEP) or describe the part; a U.S. shop that fits quotes it.
Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | Inconel 718 | Inconel 625 |
|---|---|---|
| Machining | Very difficult aged at 36-44 HRC; rough soft, age, then finish | ✓ Difficult; gummy and work-hardens, but softer |
| Welding | Good for an age-hardened alloy; resists strain-age cracking, re-age after | ✓ Excellent; its filler is the standard for dissimilar and overlay welds |
| Forming | Fair in the solution-treated state; high springback | ✓ Good annealed; about 40% elongation |
| Strength | ✓ ~1100 MPa yield aged, held to ~650 °C | ~520 MPa yield annealed |
| Corrosion resistance | Good; below 625 in seawater and reducing acids | ✓ Excellent; pitting, crevice, seawater and many acids |
| Finishing | Used bare; pickle or passivate after machining | Used bare; pickle or passivate after machining |
| Material cost | ✓ Roughly 8-15x 304 per pound | Similar to or a little above 718 per pound |
| Availability | Bar, forgings, sheet and plate; the most widely used superalloy | Sheet, plate, bar, pipe and weld wire, widely stocked |
Choose Inconel 718 when
- Strength-critical parts from room temperature to about 650 °C: turbine disks, shafts, cases, bolts
- Springs, fasteners and studs that must stay tight in hot or corrosive service
- Oilfield hangers, valve stems and downhole tools, typically to API 6A718
- Parts that can be roughed in the solution-treated state, aged, then finish machined
Choose Inconel 625 when
- Seawater, brine and chemical-process service where pitting and crevice corrosion decide life
- Welded fabrications: ducting, bellows, expansion joints, sheet-metal assemblies
- Weld overlay, cladding and dissimilar-metal joints with ERNiCrMo-3 filler
- High-temperature oxidation with modest load: exhaust systems, flare tips, heat shields
Frequently asked questions
- What is the difference between Inconel 718 and 625?
- How they get their strength. 718 is age hardened by niobium-rich precipitates and reaches roughly twice the yield strength of 625. 625 relies on molybdenum and niobium in solid solution and stays annealed, and in exchange it is more corrosion resistant, easier to weld and easier to form.
- Is Inconel 718 stronger than 625?
- Yes. Aged 718 is about 1100 MPa (160 ksi) yield against about 520 MPa (75 ksi) for annealed 625, and it keeps most of that up to roughly 650 °C (1200 °F). Above about 700 °C the precipitates in 718 coarsen and it loses its edge.
- Which Inconel is more corrosion resistant?
- 625. Its 8-10% molybdenum gives excellent resistance to pitting, crevice corrosion and seawater, and to many acids. 718 resists corrosion well for a high-strength alloy, but 625 is the safer choice for warm seawater and aggressive chemical service.
- Is Inconel 718 or 625 harder to machine?
- Aged 718 is usually the harder job: at 36-44 HRC it is abrasive and runs hot, so many shops rough it solution treated, age it, then finish. 625 is softer but gummy and work-hardens quickly. Both need rigid setups, sharp carbide or ceramic tools, steady feeds and plenty of coolant, and both machine far slower than stainless.
