Inconel® 718 is difficult to machine because it is high strength and work-hardens as it is cut, generating high cutting forces. Its low thermal conductivity traps heat at the tool tip, and the hard intermetallic particles from precipitation strengthening cause abrasive tool wear. Together these demand robust machines, controlled speeds and frequent tooling changes.
What makes Inconel 718 hard to machine?
Inconel 718 is a high-strength nickel alloy, so machining generates high cutting forces at the tool tip and needs robust equipment. For a fuller overview of the grade, see what is Inconel 718? Three metallurgical characteristics add to the challenge:
- Work-hardening. The surface hardens as it is cut, raising its strength appreciably.
- Low thermal conductivity. Heat builds up at the tool tip instead of leaving with the chip, causing excessive tool wear, shorter tool life or slower speeds.
- Hard intermetallic particles. The fine precipitates that give 718 its strength are very hard and abrade the tooling.
Can it be machined in a softer condition?
Alloy 718 is made in several specifications, including a higher-strength variant and aerospace grades. As AMS5662 it is supplied at lower strength, before the final heat treatment that forms the abrasive intermetallic particles, so complex parts can be machined more easily. The final heat treatment is still required afterwards and brings its own challenges. Our own machining and processing team handles grades like this in-house.
What does Langley Alloys stock?
We stock nickel alloy 718 as round bar from 1/2" to 10" diameter (12.7 to 254mm). For a related machinability topic, see Sanmac® stainless steels engineered for machinability.