Superalloys are nickel, iron-nickel, and cobalt-based alloys built to survive where ordinary metals fail — extreme heat, aggressive chemicals, and sustained stress. They're also slow to machine, expensive to buy, and frequently over-specified. This page helps you pick the right one and machine it without burning through tooling budgets.
Start here. Most superalloy jobs fall into one of these scenarios.
| Your Situation | Use This | Cost vs Steel |
|---|---|---|
| Aerospace turbine / engine component (high temp + high strength) | Inconel 718 | 8–12x |
| Aerospace / marine exhaust, seawater fasteners (corrosion + heat 600–900°C) | Inconel 625 | 8–15x |
| Chemical processing, pickling equipment, flue gas scrubbers (worst-case corrosion) | Hastelloy C-276 | 10–15x |
| Gas turbine combustion chamber (1000°C+ sustained) | Hastelloy X | 10–15x |
| Offshore / marine valve, pump shaft, heat exchanger (saltwater + moderate heat) | Monel 400 | 5–8x |
| Gas turbine disks, high-stress rotating parts (600–750°C) | Waspaloy | 12–18x |
| High-temp springs, fasteners, bellows | Inconel X-750 | 8–12x |
| Just need corrosion resistance, no extreme heat | Don't use superalloys | — |
| Prototype / first article, not sure which alloy | Inconel 718 | Start here, then optimize |
| Alloy | Density (g/cm³) |
Tensile (MPa) |
Max Service Temp |
Machinability (1–10) |
Cost Level | Typical Use |
|---|---|---|---|---|---|---|
| Inconel 718 | 8.19 | 1240–1400 | 700°C | 8/10 | High | Turbine discs, engine mounts, aerospace structural |
| Inconel 625 | 8.44 | 750–900 | 980°C | 7/10 | High | Exhaust systems, seawater components, chemical |
| Hastelloy C-276 | 8.89 | 690–760 | 1090°C | 9/10 | Very high | Chemical processing, scrubbers, pharmaceutical |
| Hastelloy X | 8.22 | 655–780 | 1200°C | 8/10 | High | Combustion chambers, furnace components |
| Monel 400 | 8.80 | 480–580 | 500°C | 6/10 | Medium-high | Valves, pumps, heat exchangers, marine |
| Waspaloy | 8.19 | 1200–1380 | 750°C | 9/10 | Very high | Gas turbine disks, high-stress rotating parts |
These rules apply across all nickel-based superalloys. Specific alloys have nuances (covered in the deep-dives below), but the fundamentals don't change.
| Rule | Detail |
|---|---|
| Low SFM — no exceptions | 30–60 m/min for milling, 15–35 m/min for drilling. Turning: 20–50 m/min. Going faster doesn't cut faster — it burns the tool without removing more material. The work-hardened zone just gets deeper. |
| Flood coolant is mandatory | Superalloys have thermal conductivity 3–5x lower than steel. Heat concentrates at the cutting edge. Without high-volume flood coolant (8–15 L/min at the tool), tool life drops to single-digit minutes. Use water-soluble coolant with 8–12% concentration. |
| Positive rake, sharp edge | Use inserts with positive rake geometry (5–10°) and a sharp hone. Ground inserts outperform pressed inserts. Ceramic or CBN inserts can work on some alloys at higher speeds, but carbide with proper geometry is the safe default. |
| Chip control is critical | Superalloy chips are tough and stringy. They don't break easily. Use chipbreaker geometry on inserts, program peck cycles for drilling, and keep tool engagement consistent. Re-cutting chips destroys surface finish and tool life. |
| Never dwell | A rotating tool touching a superalloy surface without cutting causes instant work hardening. The next pass hits a hardened zone and the tool fails. Keep the tool moving — every rotation must be removing material. |
| Minimize radial engagement | For milling, keep radial depth of cut below 30–40% of tool diameter when possible. Full-width slotting generates maximum heat. If you must slot, reduce axial depth to compensate. |
| Replace tools early | On superalloys, a worn tool doesn't just produce a bad surface — it work-hardens the part surface and makes subsequent operations fail. Replace inserts at the first sign of flank wear (0.2–0.3mm). The cost of a new insert is always less than a scrapped part. |
Inconel 718 accounts for roughly 50% of all superalloy machining by volume. It's the default choice for aerospace structural components, turbine discs, and engine mounts. The combination of high strength (1240 MPa tensile in aged condition), good creep resistance up to 700°C, and relative machinability (relative being the key word) makes it the first superalloy most shops encounter.
Inconel 718 is supplied in different conditions, and the condition dramatically affects machinability. Always check the material cert before programming.
| Condition | Hardness | Tensile (MPa) | Machinability | Notes |
|---|---|---|---|---|
| Annealed (solution treated) | 30–36 HRC | 900–1000 | Manageable | Best condition for roughing. Machine all features before age hardening when possible. |
| Solution + Aged (precipitation hardened) | 40–47 HRC | 1240–1400 | Difficult | Final condition for service. Tools wear 2–3x faster than annealed. |
| Overaged | 35–40 HRC | 1050–1150 | Moderate | Slightly easier to machine than peak-aged. Used when toughness is prioritized over maximum strength. |
| Operation | Speed (m/min) | Feed | Doc | Tool / Notes |
|---|---|---|---|---|
| Roughing (end mill) | 30–45 | 0.08–0.15 mm/tooth | 1–3 mm | Coated carbide (TiAlN or AlTiN). 4–6 flute for finishing, 2–3 flute for roughing. |
| Finishing (end mill) | 40–60 | 0.05–0.10 mm/tooth | 0.1–0.3 mm | Fresh insert, radial DOC <30% dia. Trochoidal milling extends tool life significantly. |
| Drilling (φ6–12mm) | 15–25 | 0.05–0.10 mm/rev | — | Peck cycle (0.5–1.0mm peck depth). Through-coolant drills preferred. Carbide or cobalt HSS. |
| Tapping | 5–10 | — | — | Thread forming taps (no cutting action) if possible. Spiral flute taps with TiN coating. Use thread lubricant. |
| Turning (OD rough) | 25–40 | 0.15–0.30 mm/rev | 1–3 mm | CNMG or DNMG inserts, positive rake. Ceramic inserts (SiC whisker) can run at 150–200 m/min for finishing. |
| Turning (OD finish) | 30–50 | 0.10–0.15 mm/rev | 0.1–0.5 mm | Fresh insert edge, light DOC. Ceramic or CBN for production. |
Inconel 718 bar stock in China runs roughly 150–350 CNY/kg ($20–50/kg) depending on size, quantity, and whether it's annealed or aged. Forged billets and aerospace-certified material (with full material cert to AMS 5662/5663) cost 30–50% more. Minimum order from most Chinese suppliers is 10–50kg. Smaller cuts are available from metal distributors but carry a premium.
Lead time for standard sizes (20–100mm round bar) is typically 3–7 days in the Dongguan/Shenzhen area. Non-standard sizes, forgings, or aerospace-certified material can take 2–6 weeks.
Hastelloy C-276 exists for one reason: when every other metal has failed. It resists pitting, crevice corrosion, and stress corrosion cracking in the most aggressive chemical environments — oxidizing and reducing acids, chlorides, sulfur compounds, and seawater at elevated temperatures. If your part sits in hydrochloric acid, mixed acid waste, or offshore processing equipment, C-276 is probably on the drawing.
| Condition | Inconel 625 | Hastelloy C-276 | Why C-276 |
|---|---|---|---|
| Hydrochloric acid (HCl) at elevated temp | Fails | Resists | C-276 has ~16% Mo, which provides HCl resistance. Inconel 625 has only 8–10%. |
| Wet chlorine / chlorine dioxide | Marginal | Excellent | Low carbon (<0.01%) prevents carbide precipitation in the heat-affected zone. |
| Sour gas (H2S) service | OK | Better | Superior resistance to sulfide stress corrosion cracking. |
| Pharmaceutical / biotech (cleanliness) | Good | Best | Low carbon + high Mo = minimal leaching and contamination risk. |
| Flue gas desulfurization | Fails | Standard choice | Mixed acidic/chloride environment is exactly what C-276 was designed for. |
| Seawater at ambient temp | Fine | Overkill | Inconel 625 or even super duplex stainless handles this at lower cost. |
| Aerospace structural (high strength) | Moderate | Not ideal | C-276 is softer (690 MPa) than Inconel 718 (1240 MPa). Use Inconel for strength. |
C-276 is one of the hardest-to-machine nickel alloys. The high molybdenum (16%) and tungsten (3.5%) content make it abrasive, and the material work-hardens aggressively. Expect tool life to be 50–70% of what you get on Inconel 718 under similar conditions.
| Operation | Speed (m/min) | Feed | Notes |
|---|---|---|---|
| Roughing (end mill) | 20–35 | 0.06–0.12 mm/tooth | TiAlN coated carbide. Lower speeds than Inconel 718. Expect shorter tool life. |
| Finishing (end mill) | 25–45 | 0.04–0.08 mm/tooth | Fresh insert mandatory. Any wear = surface work hardening. |
| Drilling | 10–20 | 0.04–0.08 mm/rev | Peck cycle every 0.5mm. Through-coolant drill. Carbide only — HSS has no chance. |
| Turning | 15–30 | 0.10–0.20 mm/rev | Positive rake ceramic inserts for finishing (if experience allows). Carbide for roughing. |
Hastelloy C-276 is expensive. Raw material runs 300–600 CNY/kg ($40–85/kg) in China, roughly 2–3x the cost of Inconel 718. The price premium reflects the high molybdenum content (Mo is costly) and the relatively low production volumes. ASTM B574 (plate/sheet) and B575 (strip) certified material costs more. Lead time for common bar sizes (10–80mm) is 1–2 weeks from Chinese suppliers. Aerospace or NACE-certified material may need 4–8 weeks.
Superalloys are expensive and not always easy to source. Here's a practical comparison for procurement planning.
| Alloy | Material Cost (CNY/kg, approx) | Cost vs Carbon Steel | Typical Lead Time (China) | Min Order (bar stock) | Availability |
|---|---|---|---|---|---|
| Inconel 718 | 150–350 | 8–12x | 3–7 days | 10–50 kg | Good — most widely stocked superalloy |
| Inconel 625 | 200–450 | 10–15x | 5–10 days | 10–50 kg | Good |
| Hastelloy C-276 | 300–600 | 15–20x | 1–3 weeks | 10–30 kg | Moderate — not always in stock locally |
| Hastelloy X | 250–500 | 12–18x | 2–4 weeks | 20–50 kg | Moderate — specialty item |
| Monel 400 | 120–280 | 5–8x | 3–7 days | 10–50 kg | Good |
| Waspaloy | 400–800 | 20–30x | 3–6 weeks | 20–50 kg | Limited — usually requires mill order |
| Procurement Tip | Detail |
|---|---|
| Buy oversize, machine down | Superalloy bar is available in standard diameters (20, 25, 30, 40, 50, 60, 80, 100mm). If your part needs 37mm, buy 40mm and machine down. Custom diameters require mill runs and long lead times. |
| Verify material before cutting | PMI (Positive Material Identification) testing takes 5 minutes with a handheld XRF gun. Run it on every superalloy blank — material mix-ups on expensive parts are catastrophic. |
| Stock for recurring jobs | If you have a repeat superalloy part, buy enough bar for 6–12 months. Material prices fluctuate and lead times are unpredictable. Holding a few hundred kg of Inconel 718 is cheap insurance against delivery delays. |
| Consider alternative suppliers | Chinese suppliers: ATI (Allvac), BaoSteel, CISRI, and various specialty metal traders. Western suppliers: Haynes International (Hastelloy), Special Metals (Inconel). Chinese material is typically 30–50% cheaper but verify quality carefully. |
Superalloy mistakes are expensive — both in scrapped parts and wasted tooling. Here's what goes wrong most often.
| Mistake | What Happens | Correct Approach |
|---|---|---|
| Specifying superalloy when stainless steel suffices | 5–15x material cost, 3–5x machining cost, no performance benefit for the application | Run the actual temperature, corrosion, and stress numbers. 316L, 904L, or super duplex stainless handles many "superalloy" applications at a fraction of the cost. |
| Running cutting speeds too high | Tool burns out in minutes, work-hardened surface layer, scrapped part | Start at the low end of recommended SFM. You can always increase speed. You can't un-burn a tool or un-harden a surface. |
| Dwelling or rubbing with the tool | Instant work hardening at the contact point. Every subsequent operation at that location fails. | Keep the tool engaged and cutting at all times. Program continuous toolpaths. If you must retract, do it clear of the work surface. |
| Not using flood coolant | Tool life drops from 20–30 minutes to 2–5 minutes. Surface finish degrades. Dimensional accuracy suffers from thermal expansion. | High-volume flood coolant (8–15 L/min) directed at the cutting zone. Check coolant concentration regularly. |
| Using dull tools on superalloys | A worn insert doesn't just cut poorly — it work-hardens the surface, which kills the next tool. Cascading failure mode. | Replace inserts at 0.2–0.3mm flank wear. Keep a log of cutting time per insert edge. When in doubt, change it out. |
| Full-width slotting in superalloys | Maximum heat generation, poor chip evacuation, rapid tool failure | Use ramp or helical entry instead of plunging. Keep radial engagement under 40% of tool diameter. If slotting is unavoidable, reduce axial DOC significantly. |
| Not checking material cert | Wrong alloy, wrong heat treatment condition, or uncertified material delivered. Aerospace parts get rejected at inspection. | Require material cert with every order. Run PMI testing on received blanks. Verify the spec number matches the drawing. |
| Machining aged Inconel 718 when annealed was acceptable | 2–3x longer cycle time, 2–3x more tool wear, higher risk of surface defects | Confirm with the customer whether pre-age machining is acceptable. If so, machine in annealed condition and leave stock for post-heat-treatment grinding. |
| Ignoring work-hardened surface layer | Drills wander, taps break, finishing passes produce chatter and poor surface finish | After roughing, take a light spring pass (0.05–0.10mm) with a fresh tool to remove the work-hardened layer before finishing or drilling. |
| Underestimating lead time for material | Project delayed 2–6 weeks waiting for specialty alloy. Customer unhappy. | Check material availability BEFORE quoting delivery. For Waspaloy, Hastelloy C-276 in non-standard sizes, or any certified aerospace material, add 3–6 weeks for procurement. |