Inconel 718 is not a hard steel that happens to be inconvenient. It is a material that punishes whatever tries to cut it, and shops that mill it watch their most expensive carbide wear out in hours. The reason is not hardness on its own. It is how the alloy behaves under a cutting edge, and understanding that explains why a completely different process owns this work.
Why the cutter loses
Nickel superalloys like Inconel hold their strength at very high temperature. That property is the entire reason they are worth using in a turbine, and it is the same property that kills tooling: the heat of the cut does not soften the material, so it concentrates in the cutting edge instead. Add the alloy's tendency to work harden as you deform it and you get accelerated wear, chatter and poor finishes, in that order.
The alloys that behave this way
- Inconel 625 and 718, nickel-chromium, common in aerospace and energy.
- Hastelloy C-22 and C-276, for extreme chemical and thermal resistance.
- Stellite, cobalt-based, used at wear points.
- Titanium Ti-6Al-4V, high strength at low density.
- Tool steels hardened past HRC 50.
What they share is not a hardness number. It is that they all defeat a physical cutting edge, which is why the process that wins here does not use one.
The process that never learns how hard the material is
Wire EDM does not cut with a tool. It cuts with controlled electrical discharges across a wire that never touches the part. The only property the process cares about is whether the material conducts electricity, not how hard it is or how well it holds strength at temperature. Hardened Inconel cuts the same way soft aluminum does. No tool wear, no mechanical force, no thermal distortion.
What that changes on a real part
Parts that took days of CAM programming and consumed expensive tooling come off a wire EDM in hours, with no residual stress and no change to the material's microstructure. For small-run turbine components, high-temperature seals or tooling in special alloys, that difference frequently decides whether the part is viable at all rather than merely cheaper.
The honest limit
EDM does not replace milling, and any shop that tells you otherwise is selling. For bulk material removal, large flat faces or open geometry in soft material, the mill is still faster and cheaper by a wide margin. EDM wins specifically when the material is hard or refractory, the geometry is fine, or the part cannot tolerate contact force. Knowing which case you are in is half the job, and it is the half that should happen before the PO, not after the first bad part. We walk through that decision in CNC versus wire EDM.
Can any alloy be cut by EDM?
Any material that conducts electricity, regardless of hardness: nickel superalloys, titanium, carbide, hardened steels. Non-conductive materials such as pure ceramics and unfilled plastics cannot be cut by EDM.
Does EDM change the properties of Inconel?
Not significantly. With no mechanical contact and none of the sustained heat of milling, the part comes out without residual stress and without changes to the material microstructure.
Do you run production quantities in these alloys, or only prototypes?
Both. We work from a single piece up to small production runs, quoted on material, geometry, tolerance and quantity.
Why is Inconel so hard to machine if it is not the hardest material?
Because it retains strength at cutting temperature instead of softening, so heat concentrates in the tool edge, and because it work hardens as it deforms. Hardness alone does not predict machinability.