When selecting nickel-based superalloys, machinability is a critical factor, directly impacting manufacturing costs, delivery times, tool life, and overall project efficiency. Among the most commonly used grades, Inconel 625 and Inconel 718 are often compared due to their excellent high-temperature strength and corrosion resistance-but they exhibit significant differences in machinability.
What is Inconel 625 (UNS N06625)?
Inconel 625 is a solid-solution strengthened nickel-chromium-molybdenum alloy with added niobium.
It does not rely on precipitation hardening, therefore it has better machinability compared to many age-hardened superalloys. It is suitable for oil and gas pipelines, chemical equipment, marine components, and heat exchangers.
What is Inconel 718 (UNS N07718)?
Inconel 718 is a precipitation-hardened nickel-based superalloy, primarily strengthened by the γ'' and γ' phases formed after aging treatment. This structure gives it extremely high strength, but also makes it more difficult to machine. It is suitable for aerospace components, gas turbines, high-strength fasteners, and nuclear equipment.
inconel 625 vs 718：Chemical Composition Comparison (Typical, %)
| Element | Inconel 625 | Inconel 718 |
|---|---|---|
| Ni | ≥ 58.0 | 50.0 – 55.0 |
| Cr | 20.0 – 23.0 | 17.0 – 21.0 |
| Mo | 8.0 – 10.0 | 2.8 – 3.3 |
| Nb + Ta | 3.15 – 4.15 | 4.75 – 5.5 |
| Fe | ≤ 5.0 | Balance |
| C | ≤ 0.10 | ≤ 0.08 |
inconel 625 vs 718：Mechanical Properties (Room Temperature)
| Property | Inconel 625 | Inconel 718 |
|---|---|---|
| Tensile Strength | ≥ 827 MPa | ≥ 1240 MPa (aged) |
| Yield Strength (0.2%) | ≥ 414 MPa | ≥ 1030 MPa |
| Elongation | ≥ 30% | ≥ 12% |
| Hardness | ≤ 220 HB | 330–420 HB (aged) |
inconel 625 vs 718：machinability
Compared to Inconel 718, Inconel 625 is generally easier to machine because 718 exhibits a higher degree of work hardening, making it more difficult to cut, especially after hardening heat treatment (e.g., in the condition conforming to AMS 5663). While 625 is still very tough, it does not harden as quickly as 718, resulting in more stable tool life. In contrast, 718 requires very specialized machining techniques, lower cutting speeds, and is typically machined in the softer solution-treated condition (conforming to AMS 5662) to cope with its extremely high hardness and high strength at elevated temperatures.
(AISI B1112 free-cutting steel = 100)
| Alloy | Relative Machinability |
|---|---|
| Inconel 625 | ~ 30 |
| Inconel 718 (Solution Annealed) | ~ 25 |
| Inconel 718 (Aged) | ~ 20 |
Is Inconel 625 easier to machine than Inconel 718?
Yes. Inconel 625 generally offers better machinability because it is solid-solution strengthened and does not require aging treatment, resulting in lower hardness and reduced tool wear.
Why is Inconel 718 so difficult to machine?
Inconel 718 work-hardens rapidly, has very high cutting forces, and retains strength at high temperatures, leading to severe tool wear and poor chip control.
Can Inconel 718 be machined before heat treatment?
Yes. Machining Inconel 718 in the solution-annealed condition is strongly recommended to reduce tool wear and improve dimensional control.
Although both Inconel 625 and Inconel 718 are high-performance nickel alloys, machinability is a decisive factor. From a manufacturing and cost-effectiveness perspective, Inconel 625 offers distinct advantages, while Inconel 718 excels in applications requiring high strength and heavy loads.
Purchasing Recommendation: Selecting the appropriate alloy in advance helps reduce production risks, shorten delivery times, and improve overall project success.
To better serve international buyers, GNEE offers flexible payment methods, including T/T (30% down payment, 70% before shipment), sight letter of credit (L/C), and DP/DA payment options for long-term partners; uses seaworthy wooden crates or pallets for packaging, providing moisture-proof, rust-proof, and edge protection measures, while clearly marking the heat number and dimensions on the plates; guarantees efficient delivery, with in-stock Inconel 625 plates shipped within 7-10 days and custom sizes within 15-25 days; provides complete factory test certificates (MTC 3.1), and boasts extensive global export experience covering the Middle East, Europe, the United States, and Southeast Asia.
