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Inconel Grades and Nickel Superalloys for CNC Machining
Eleven grades buyers send most often, with the designations a shop needs, the spec that usually goes with them and how hard each one is on the machine.
Grade designations and common bar specs
Trade names (Inconel, Incoloy, Monel, Hastelloy, Waspaloy) belong to their producers. Shops buy to the UNS number and the spec, so that is what to write on the drawing. The specs listed are common bar and rod callouts; plate, sheet, tube and forgings have their own.
| Grade | UNS | W.Nr (EN) | Common bar spec | Strengthening |
|---|---|---|---|---|
| Inconel 600 | N06600 | 2.4816 | ASTM B166, AMS 5665 | Solid solution |
| Inconel 601 | N06601 | 2.4851 | ASTM B166 | Solid solution |
| Inconel 625 | N06625 | 2.4856 | ASTM B446, AMS 5666 | Solid solution |
| Inconel 718 | N07718 | 2.4668 | ASTM B637, AMS 5662 / 5663 | Age-hardenable |
| Inconel X-750 | N07750 | 2.4669 | ASTM B637, AMS 5667 | Age-hardenable |
| Incoloy 825 | N08825 | 2.4858 | ASTM B425 | Solid solution |
| Hastelloy C-276 | N10276 | 2.4819 | ASTM B574 | Solid solution |
| Hastelloy X | N06002 | 2.4665 | AMS 5754 | Solid solution |
| Monel 400 | N04400 | 2.4360 | ASTM B164 | Solid solution |
| Monel K-500 | N05500 | 2.4375 | ASTM B865 | Age-hardenable |
| Waspaloy | N07001 | 2.4654 | AMS 5706 / 5707 | Age-hardenable |
Spec numbers are a starting reference, not a substitute for the drawing. The Unified Numbering System is maintained by ASTM and SAE. Terms like AMS, PMI and aging are explained in the glossary.
What each grade is chosen for
Buyers rarely pick a nickel alloy for one property. These are the usual reasons each grade ends up on a drawing.
Inconel 600 / 601
Oxidation resistance at furnace temperatures. 601 adds aluminum for better scaling resistance. Fixtures, baskets, muffles.
Inconel 625
Corrosion resistance plus strength without heat treatment. Marine, exhaust, chemical process and weld overlay work.
Inconel 718
High strength up to roughly 650 to 700°C after aging. Turbine discs, shafts, aerospace fasteners.
Inconel X-750
Age-hardened strength with good relaxation resistance. Springs, seals, bolts and gas turbine parts.
Incoloy 825
Resistance to sulfuric and phosphoric acids and chloride stress corrosion cracking. Downhole and process piping.
Hastelloy C-276 / X
C-276 for severe chemical corrosion, X for oxidation resistance in combustor and furnace hardware.
Monel 400 / K-500
Seawater and hydrofluoric acid resistance. K-500 adds age-hardened strength for pump shafts and fasteners.
Waspaloy
Strength at higher temperatures than 718. Turbine discs, rings, shafts and high-temperature bolting.
Inconel, Monel, Hastelloy or Incoloy: how to choose · Inconel 625 vs 718
How each grade machines
Ordered roughly from easiest to hardest on tools. Typical tolerances on functional features; the shop that quotes you confirms what it can hold on your geometry.
| Grade | Machining notes | Typical tolerance |
|---|---|---|
| Monel 400 | The easiest in this list. Gummy rather than hard, so sharp positive tools and steady feed matter more than tool grade. | ±0.02 mm is routine |
| Inconel 600 / 601 | Annealed and relatively soft. Work hardening is the main problem, not tool wear. | ±0.05 mm is a safer target on large fixtures |
| Incoloy 825 | Iron-bearing and a little kinder to tools than 625. Similar strategy. | ±0.02 to ±0.05 mm |
| Inconel 625 | High strength without aging. Tough on tools, very prone to work hardening. | ±0.02 to ±0.05 mm |
| Hastelloy C-276 / X | Comparable to 625 or harder on tools. High molybdenum content makes chips tough and stringy. | ±0.02 to ±0.05 mm |
| Monel K-500 | Machine before aging where possible. Aged K-500 cuts noticeably harder than 400. | ±0.02 mm |
| Inconel 718 / X-750 | Rough in the solution-treated condition, age, then finish. Aged material is the main tool-wear driver. | ±0.02 to ±0.05 mm |
| Waspaloy | Among the hardest to machine in this list once aged. Expect slow speeds, frequent tool changes and EDM for fine features. | ±0.02 to ±0.05 mm |
Choosing a grade
If the drawing already names a grade and spec, keep it. These notes are for buyers still deciding, or checking whether an alternative is worth asking about.
- Temperature firstAbove about 650°C under load, age-hardenable grades (718, X-750, Waspaloy) are usually in play. Below that, corrosion often decides instead.
- Then the mediumSeawater points to Monel or 625. Sour gas and chlorides point to 825 or 625 (see NACE MR0175 / ISO 15156). Strong reducing acids point to C-276. Monel vs Inconel
- Welding on the part625 and C-276 weld readily. 718 welds but needs the aging response planned. Welding Inconel
- Stock availability625, 718 and 825 bar is easier to source in common sizes than X-750 or Waspaloy, which can add weeks of material lead time on a prototype.
- PaperworkAerospace grades usually come with an AMS spec and full traceability. Ask for mill certs and PMI on the RFQ. Mill certs and PMI
Questions about nickel alloy grades
Is Inconel 625 or 718 easier to machine?
625 in the annealed condition and 718 in the solution-treated condition machine at a similar level of difficulty. Aged 718 is harder on tools than 625, which is why shops often finish 718 after aging only on the features that need it.
Can I substitute Hastelloy C-276 for Inconel 625?
Sometimes, in corrosion service, but it is an engineering decision for the part owner, not the shop. The two alloys differ in molybdenum and tungsten content and in spec coverage. Put the grade your drawing calls for on the RFQ and ask about alternatives separately.
What does the UNS number tell a shop?
The UNS number fixes the chemistry range, so it removes ambiguity between trade names. It does not fix the condition, testing or product form. The ASTM or AMS spec on the drawing does that, which is why both belong on the RFQ.
Which nickel alloys can shops in your network quote?
Inconel 625, 718 and 825 most often, plus 600 and 601. For Hastelloy, Monel, X-750 or Waspaloy, name the grade and spec on the RFQ and we only match shops that already run that alloy.