Both are nickel-based superalloys. Both handle service above 600 °C. Both resist severe chemical corrosion. But 625 is solid-solution strengthened (no heat treat needed); 718 is precipitation-hardened (stronger after age). Price per kg differs only 15-20%, but they have very different machining, welding, and service profiles. Picking wrong wastes significant money.
| Element | Inconel 625 | Inconel 718 |
|---|---|---|
| Nickel (base) | 58% min | 50-55% |
| Chromium | 20-23% | 17-21% |
| Molybdenum | 8-10% | 2.8-3.3% |
| Niobium | 3.15-4.15% | 4.75-5.5% |
| Iron | ≤5% | Balance (17% typical) |
| Titanium | ≤0.4% | 0.65-1.15% |
| Aluminum | ≤0.4% | 0.2-0.8% |
| Strengthening | Solid-solution (Mo + Nb) | Precipitation (γ" Ni₃Nb) |
| Heat treatment | Solution anneal only | Solution + aging required |
Key insight: 625 is ready-to-use off the bar (high strength from the Mo/Nb in solution). 718 requires heat treatment (solutionize + double age) to develop its strength through Ni₃Nb precipitation. This means different machining workflows.
| Property (at 20°C) | Inconel 625 | Inconel 718 (aged) |
|---|---|---|
| Tensile strength | 830 MPa | 1,300 MPa |
| Yield strength | 450 MPa | 1,100 MPa |
| Hardness | 180 HB | 36-44 HRC |
| Elongation | 30% | 15% |
| Density | 8.44 g/cm³ | 8.19 g/cm³ |
| Max service temp (structural) | 980 °C | 700 °C |
| Creep strength at 650°C | Good | Excellent (better) |
| Machinability rating | ~15% (of steel baseline) | ~12% |
| Weldability | Excellent | Fair (cracking risk) |
718 is nearly 2× stronger at room temperature. But 625 retains service strength to higher temperatures (980 °C vs 700 °C). The max service temperature is the dividing line for many applications.
Aerospace exhaust components, gas turbine cases, heat exchangers in petrochemical service. 718 degrades; 625 holds up.
Chemical process equipment, offshore oil and gas, subsea wellhead components. The high Mo content (8-10%) in 625 provides best-in-class chloride resistance. 718 with 3% Mo is less resistant.
625 welds readily with minimal cracking risk. Used for welded vessels, piping, and complex weldments. 718 has higher cracking sensitivity in the heat-affected zone.
625 retains ductility and toughness to -196 °C (liquid nitrogen). Used in LNG, aerospace cryogenic systems. 718 also works but 625 is more forgiving.
Gas turbine disks, compressor blades, engine shafts. 718 delivers 1,100+ MPa yield at 650 °C — better than any competing material in that temperature range.
Aircraft engine disks, turbocharger wheels, impellers. The combination of high strength + fatigue resistance + temperature capability is hard to beat.
High-temperature fasteners for engine and turbine applications. 718 holds clamping force at temperatures where stainless fasteners relax.
Tools in sour-service (H₂S) wells at elevated temperatures. 718 resists sulfide stress cracking. Industry-standard material for this service.
Both Inconel 625 and 718 are on the difficult end of CNC machining:
718 is slightly harder to machine than 625 (machinability rating 12% vs 15%) due to its higher strength. Aged 718 (after heat treat) is harder still — most shops rough machine in solution-annealed condition, heat treat, then finish grind.
Typical CNC rates for Inconel work: $150-250/hour (US) or $55-90/hour (China). At these rates, even small parts become expensive. A 2-inch Inconel bracket that would cost $20 in aluminum easily runs $200-400.
| Material form | Inconel 625 ($/kg) | Inconel 718 ($/kg) |
|---|---|---|
| Bar stock (small) | $80-110 | $95-130 |
| Sheet / plate | $90-130 | $110-150 |
| AMS-certified aerospace | $150-220 | $180-280 |
| Forged billet | $180-280 | $220-350 |
Typical lead time for sourced Inconel: 3-8 weeks depending on size and form. Common sizes stocked at specialty suppliers; rare sizes require forging.
For AMS-certified aerospace material, add 50-80% premium over commercial grades, plus additional lead time for certification documentation.
Email [email protected] with drawing and service conditions (temperature, environment, certification requirements). We'll source the right grade and quote both the machining cost and applicable heat treatment cycles.
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