Hastelloy, Stellite, Monel, and Waspaloy are not as common as Inconel 718, but when a job comes in requiring one of them, the parameters that work for standard steel will not work at all. These materials combine work-hardening, abrasiveness, and low thermal conductivity in ways that punish mistakes.
Here is what I have learned about drilling each one.
Common Characteristics of Exotic Alloys
All four of these materials share properties that make deep hole drilling difficult:
- Machinability rating: 5-20% of mild steel (100% baseline)
- Low thermal conductivity: Heat stays at the cutting edge instead of being carried away by chips
- Work-hardening: The material gets harder as you cut it. Any dwell or rubbing makes the problem worse
- Abrasiveness: Carbide tool wear is significantly faster than in steel
| Material | Type | Typical Hardness | Machinability Rating |
|---|---|---|---|
| Hastelloy X | Nickel-based | 32-40 HRC | 9-10% |
| Waspaloy | Nickel-based | 38-44 HRC | 9-15% |
| Monel 400 | Nickel-copper | 20-30 HRC | 20-30% |
| Stellite 6 | Cobalt-based | 32-36 HRC | 18% |
| Inconel 718 (reference) | Nickel-based | 36-42 HRC | 10% |
The machinability rating tells you that these materials will cut at 5-20% of the speed of mild steel and with significantly shorter tool life.
Cutting Parameters for Exotic Alloys
| Parameter | Hastelloy X | Waspaloy | Monel 400 | Stellite 6 |
|---|---|---|---|---|
| Cutting speed | 20-25 m/min | 15-20 m/min | 25-35 m/min | 15-25 m/min |
| Feed (6mm drill) | 0.05-0.08 mm/rev | 0.04-0.07 mm/rev | 0.06-0.10 mm/rev | 0.04-0.07 mm/rev |
| Feed (12mm drill) | 0.08-0.12 mm/rev | 0.07-0.10 mm/rev | 0.10-0.15 mm/rev | 0.07-0.10 mm/rev |
| Feed (20mm drill) | 0.10-0.15 mm/rev | 0.08-0.12 mm/rev | 0.12-0.18 mm/rev | 0.08-0.12 mm/rev |
| Coolant pressure (min) | 1000 psi | 1200 psi | 800 psi | 1000 psi |
Monel is the most forgiving of the four — its lower hardness allows higher cutting speeds and feed rates. Waspaloy at 44 HRC is the least forgiving.
I cover the general approach to difficult materials in Deep Hole Drilling Difficult Materials.
Hastelloy X
Hastelloy X is a nickel-based superalloy used in gas turbine combustion zones, ductwork, and chemical processing equipment. It retains strength at high temperatures and resists oxidation.
The main challenge in drilling Hastelloy X is its work-hardening rate. If the cutting edge dwells or rubs, the surface work-hardens instantly and the next pass has to cut through a harder layer.
Key recommendations:
- Keep feed rate above 0.05 mm/rev for drills under 10mm. Below this, the edge rubs rather than cuts.
- Use AlCrN-coated carbide. TiAlN will work but tool life is 20-30% shorter.
- Coolant pressure at the tool tip should be 1000 psi minimum. Chip evacuation is critical — Hastelloy chips are tough and do not break easily.
- Never peck. Continuous feed only.
Waspaloy
Waspaloy is a precipitation-hardened nickel-based superalloy used in turbine discs and shafts. At 38-44 HRC, it is harder than most other nickel alloys.
Waspaloy is the most abrasive of the four materials listed here. Tool wear in Waspaloy is primarily by flank wear and notch wear at the depth-of-cut line.
Key recommendations:
- Reduce cutting speed to 15-20 m/min. Higher speeds accelerate edge wear dramatically.
- Use AlCrN coating. The higher oxidation resistance matters at the elevated edge temperatures generated when cutting Waspaloy.
- Expect tool life of 50-80% of Inconel 718 in similar operations.
- Monitor the cutting edge condition closely. A chipped edge will fail rapidly in Waspaloy.
Monel 400
Monel 400 is a nickel-copper alloy known for corrosion resistance. It is used in marine engineering, chemical processing, and oil and gas components.
Monel is the most machinable of the four — its lower hardness (20-30 HRC) allows higher speeds and feeds. But it has a tendency to produce built-up edge, which degrades surface finish and can cause dimensional issues.
Key recommendations:
- Standard carbide grades work well. DLC coating helps prevent BUE.
- Cutting speed of 25-35 m/min is acceptable.
- Feed rates can be 20-30% higher than for Hastelloy at the same diameter.
- Coolant pressure of 800 psi is adequate for most diameters.
- Monitor for BUE. If surface finish degrades, check the cutting edge for built-up material.
I cover BUE in Built-Up Edge Gun Drilling.
Stellite 6
Stellite 6 is a cobalt-based alloy designed for wear resistance at high temperatures. It is used for valve seats, pump components, and cutting tools themselves.
Stellite is different from the nickel-based alloys — its cobalt matrix with high carbide content makes it extremely abrasive. Tool wear in Stellite is primarily by abrasion rather than adhesion or work-hardening.
Key recommendations:
- Use the most abrasion-resistant carbide grade available. Submicron carbide with AlCrN coating.
- Keep cutting speed at 15-25 m/min. Higher speeds do not improve productivity because tool wear accelerates faster than material removal rate.
- Feed rate should be high enough to keep the cutting edge below the work-hardened layer. Do not reduce feed below 0.04 mm/rev for small diameters.
- Expect shorter tool life than in nickel-based alloys. Plan for more frequent tool changes.
Common Mistakes When Drilling Exotic Alloys
| Mistake | Consequence |
|---|---|
| Using standard steel parameters | Rapid tool failure, scrapped parts |
| Running coolant pressure too low | Chip packing, drill breakage |
| Peck drilling | Work-hardening at each dwell point |
| Dull tool detection too late | Work-hardening from rubbing edge |
| Wrong coating selection | 50%+ reduction in tool life |
The most expensive mistake is treating these materials like steel. Every parameter — speed, feed, pressure, coating — must be adjusted for the specific alloy.
Tooling and Coating Summary
| Alloy | Preferred Coating | Carbide Grade | Expected Tool Life (relative) |
|---|---|---|---|
| Hastelloy X | AlCrN | Submicron | 60-80% of Inconel 718 |
| Waspaloy | AlCrN | Submicron | 50-70% of Inconel 718 |
| Monel 400 | DLC or AlCrN | Standard | 120-150% of Inconel 718 |
| Stellite 6 | AlCrN | Submicron, wear-resistant | 40-60% of Inconel 718 |
I cover coating selection in Gun Drill Coatings.
Key Takeaways
- Hastelloy, Stellite, Monel, and Waspaloy each need different parameters. Do not assume one setting works for all.
- Hastelloy work-hardens rapidly. Keep feed above 0.05 mm/rev and never peck.
- Waspaloy is the most abrasive. Use AlCrN coating and expect shorter tool life.
- Monel is the most forgiving but watch for BUE. DLC coating helps.
- Stellite is cobalt-based and extremely abrasive. Use the hardest carbide grade available.
- Coolant pressure of 1000 psi or more is required for all four materials. Chip evacuation is the limiting factor.
- Standard steel parameters will fail immediately. Reduce speed by 60-80% from steel values and use appropriate coatings.