Guides / Process

Heat Treatment Sequencing for Inconel 718: Before or After Machining

August 22, 2026

Inconel 718 is not delivered ready to machine at full strength and stay that way. It is age-hardenable, which means its final mechanical properties depend on a heat treatment step that happens somewhere in the process, and where that step falls relative to machining changes both the cost and the outcome.

Solution annealed versus aged, in plain terms

718 starts life, after mill processing, in a condition called solution annealed. In that state the alloying elements are dissolved fairly evenly through the metal’s structure, and the material is relatively soft and machinable compared with what it becomes later. Aging is a separate heat treatment cycle, run at a lower temperature over several hours, that causes fine particles to precipitate out of that structure. Those precipitates are what give 718 its high strength, which is why the process is called precipitation hardening. A part in the aged condition is significantly harder and tougher to cut than the same part in the solution-annealed condition, even though the geometry has not changed at all.

This is different from a general heat treatment note on a drawing. Specifying “718” without a condition leaves open whether the buyer expects the part machined before or after aging, and a shop that assumes the wrong one can end up quoting the wrong process entirely.

Why many shops rough soft and finish hard

A common sequence is to rough the part in the solution-annealed condition, when the material cuts closer to how a tough stainless would, send it out for aging, then finish the critical features once the part is at full hardness. Roughing soft removes the bulk of the material with less tool wear and faster cycle times than roughing the same shape after aging would take. Finishing after aging matters for a different reason: aging can cause a small amount of dimensional movement in the part, and finishing critical features after that movement has already happened means the final dimensions are cut on the material in its actual final condition, not on a prediction of where it will land after the heat treatment cycle.

For a part with light material removal and no especially tight tolerances, machining entirely in one condition, either fully before or fully after aging, can be simpler and is sometimes the more practical choice. The rough-then-age-then-finish sequence earns its extra complexity mainly on parts with substantial stock removal or tolerances tight enough that post-aging movement would matter.

The tradeoffs

Aging is a genuine outside-processing step, not a note on a traveler. It usually means the part leaves the machine shop, goes to a heat treatment vendor, and comes back, which adds real lead time and a second setup on the machine for finishing. Skipping it, or aging before any roughing happens, avoids that extra step but creates its own problems. A part machined entirely at full aged hardness is a tougher, slower, more tool-intensive job from the first cut, since none of the material removal benefits from the softer solution-annealed condition. A part machined complete and only aged afterward with no finish pass risks being left slightly out of tolerance by whatever dimensional movement the aging cycle causes, on features where that movement matters.

There is no single right answer independent of the part. A simple bracket with generous tolerances may not justify the extra step and lead time of rough-then-age-then-finish. A part with tight fits and substantial material removal usually does.

What to put on the RFQ or drawing

State the required final condition explicitly rather than leaving it implied. “Solution treated and aged” to a named specification, or a specific aging schedule if your application requires one, tells the shop exactly what strength level the part needs to reach and lets it plan the machining sequence around that requirement instead of guessing. If a particular hardness range or mechanical property is required by your application, state that too, since different aging cycles on 718 can land at different strength levels. A drawing that just says “Inconel 718” with no condition called out is one of the most common gaps between what a buyer expects and what a shop quotes. For why 718 stops near 650°C and what follows above it, see high temperature nickel alloys.

Frequently asked questions

Keep reading

• How to Turn Inconel 718: Insert Grades, Cutting Speeds and Chip Control
• Machining 3D Printed Inconel 718: Supports, HIP and Finish Stock