Is Inconel easy to machine?
Inconel-Chemical composition
| Inconel | Ni | Cr | Fe | Mo | Nb | Co | Mn | Cu | Al | Ti | Si | C | S | P | B |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 600 | 72 | 14.0-17.0 | 6.0-10.0 | 1 | 0.5 | 0.5 | 0.15 | 0.015 | |||||||
| 617 | 44.2-56.0 | 20.0-24.0 | 3 | 8.0-10.0 | 10.0-15.0 | 0.5 | 0.5 | 0.8-1.5 | 0.6 | 0.5 | 0.15 | 0.015 | 0.015 | 0.006 | |
| 625 | 58 | 20.0-23.0 | 5 | 8.0-10.0 | 3.15-4.15 | 1 | 0.5 | 0.4 | 0.4 | 0.5 | 0.1 | 0.015 | 0.015 | ||
| 690 | 59.5 | 30 | 9.2 | 0.35 | 0.01 | 0.02 | 0.35 | 0.019 | 0.003 | ||||||
| 718 | 50.0-55.0 | 17.0-21.0 | balance | 2.8-3.3 | 4.75-5.5 | 1 | 0.35 | 0.2-0.8 | 0.65-1.15 | 0.3 | 0.35 | 0.08 | 0.015 | 0.015 | 0.006 |
| X-750 | 70 | 14.0-17.0 | 5.0-9.0 | 0.7-1.2 | 1 | 1 | 0.5 | 0.4-1.0 | 2.25-2.75 | 0.5 | 0.08 | 0.01 |
Inconel 718 is a nickel-based alloy typically supplied in high-strength grades. Inconel is a trademark of Specialty Metals Corporation. It has been widely used to machine parts but is considered more challenging to machine. Part of the reason for this difficulty can be attributed to its high strength, which results in high cutting forces at the tool tip. This means more powerful equipment is needed to cope. However, Alloy 718 has several more specific "metallurgical" properties that make it more challenging to process.
First, it works hardens during machining, significantly increasing the strength of the surface metal.
Because nickel-based alloys such as Inconel 718 have relatively low thermal conductivity, heat can be generated at the tool tip during machining. This can cause excessive tool wear, shorten tool life or require slower machining speeds.
Finally, grades such as Inconel 718 benefit from precipitation strengthening, by forming very fine precipitates throughout the metal. However, these intermetallic particles are very hard and can cause abrasive wear on the tool.
Alloy 718 is available in different specifications, including higher strength variants, as well as specifications for the aerospace industry. In this case, AMS5662 Alloy 718 can be purchased, which is less strong because it has not undergone the final heat treatment that results in higher strength (and the formation of these abrasive intermetallic particles). This makes it easier to machine complex parts, but still requires a final heat treatment process, which can present challenges.
