Inconel 718 (UNS N07718) is, by a wide margin, the most widely used nickel-based superalloy in industry. Precipitation-hardened primarily through niobium and titanium additions that form strengthening gamma-double-prime and gamma-prime phases, it delivers an unusually strong combination of high yield and tensile strength, good fatigue and creep-rupture resistance, and useful strength from cryogenic temperatures up to roughly 1300°F/704°C. That combination, together with relatively good weldability and forgeability for a superalloy, is why 718 dominates rotating and static gas-turbine hardware — discs, shafts, casings, blades, and fasteners in jet engines, industrial gas turbines, and turbochargers — as well as high-strength aerospace fastener and structural applications outside the hot section.

Chemically, 718 is a nickel-chromium-iron alloy with a substantial iron content compared to most other nickel superalloys, plus a niobium-plus-tantalum addition in the 4.75-5.5% range that is the defining precipitation-hardening element, supported by titanium, aluminum, and molybdenum. This page covers standard Inconel 718 in its conventional solution-treated-and-aged (STA) condition. Two closely related process/temper variants — Inconel 718 DA (Direct-Aged) and Inconel 718 OP (Overaged) — share this same base chemistry but are heat-treated differently to shift hardness, strength, and machinability; see those pages for variant-specific machining data.

Inconel 718 carries the classic difficulties of the nickel-superalloy family, and because it is the grade most shops encounter most often, its behavior is the benchmark against which other HRSA materials are usually judged. Low thermal conductivity is the first obstacle: heat generated in the cut does not flow into the chip and workpiece the way it would in steel, so it concentrates at the tool-chip interface and accelerates crater wear, edge deformation, and thermal cracking.

Rapid work hardening is the second major factor. The same gamma-double-prime and gamma-prime precipitates that give 718 its strength also make the surface harden aggressively under cutting stress — any rubbing, hesitation, or dull edge burnishes a hardened skin into the surface that is tougher to remove than the parent material. Consistent, adequate feed per tooth/revolution is essential so the edge is always cutting beneath the previous pass's affected layer rather than skating across it.

Unlike steel, 718 does not soften appreciably at elevated cutting temperatures, so the edge stays under heavy mechanical load even as heat builds up, which drives notch wear and chipping if speeds are pushed too high. The alloy's chemical affinity for common tool materials also promotes galling and built-up edge, tearing the finished surface and accelerating tool failure. Rigid, vibration-free setups, sharp positive-rake carbide with a wear-resistant coating, moderate-to-low cutting speeds, and generous coolant delivery are the standard countermeasures.