Deep Hole Drilling Superalloys: Inconel, Hastelloy, and Waspaloy

Deep Hole Drilling Superalloys

Nickel-based superalloys — Inconel 718, Hastelloy, Waspaloy, and others — are the most difficult materials for deep hole drilling. They combine extreme work hardening, high cutting temperatures, abrasive carbides, and chemical reactivity in a material that aerospace and power generation applications cannot avoid.

This guide covers the parameters, tooling, and strategies needed for deep hole drilling in superalloys.

Superalloy Material Properties

Property	Inconel 718	Comparison to Steel
Thermal conductivity	11 W/m·K	4–5× lower than steel
Work hardening rate	Extreme (2–3× stainless steel)	Much higher
Abrasive carbides	Present (MC and M₆C carbides)	Not present in standard steel
Hardness	35–45 HRC (aged)	Higher than most steels
Tensile strength	1,200–1,400 MPa	2× typical steel

Key Challenges

Extreme work hardening — Superalloys work-harden aggressively. The surface can reach 60+ HRC at the cutting zone. Once hardened, it is nearly impossible to cut.
Abrasive wear — Carbide particles in the alloy matrix act as abrasives, wearing the cutting edge rapidly.
Heat concentration — Low thermal conductivity means the tool absorbs most of the cutting heat.
Chemical reactivity — The material reacts with the cobalt binder in carbide at cutting temperatures.
Chip control — Chips can be tough and difficult to break.

Cutting Parameters

Gun Drilling — Inconel 718 (Annealed)

Diameter	Speed (m/min)	Feed (mm/rev)	Coolant Pressure (bar)
3–6 mm	10–15	0.005–0.010	120–140
6–12 mm	12–18	0.008–0.015	100–120
12–20 mm	12–18	0.012–0.020	70–100
20–30 mm	10–15	0.015–0.025	60–80

BTA Drilling — Inconel 718 (Annealed)

Diameter	Speed (m/min)	Feed (mm/rev)	Coolant Pressure (bar)
20–40 mm	12–18	0.06–0.12	50–60
40–65 mm	10–15	0.10–0.18	40–55
65–100 mm	10–15	0.12–0.20	35–50

Tool Life Expectations

Tool Type	Expected Life (Inconel 718)
Gun drill (carbide)	100–300 linear inches between regrinds
BTA head (brazed)	50–200 holes between regrinds
BTA/DTS insert	30–100 holes per edge

Accept shorter tool life as normal for superalloy drilling. Do not push tools beyond early wear signs — the cost of a broken tool in an Inconel part far exceeds the cost of a regrind.

Tool Selection

Carbide Grade

Recommendation	Grade	Cobalt	Grain Size
Best	K40/K40-KF	10–12%	Fine (0.5–1 µm)
Alternative	K35 with AlTiN	8–10%	Ultra-fine

Coating

Coating	Performance on Superalloys
AlTiN nano (best)	Excellent — withstands temperatures up to 1,100°C
TiAlN (good)	Acceptable — for moderate parameters
AlCrN/AlTiCrN	Emerging — excellent oxidation resistance

Tool Geometry

Feature	Recommended
Nose grind (gun drill)	Facet grind with reinforced corner
Insert geometry (BTA/DTS)	TXN or TPMX with positive rake
Edge preparation	Sharp edge, very light hone (< 0.02 mm)
Chip breaker	Aggressive — must break tough chips

Coolant Strategy

Parameter	Recommended
Coolant type	Neat oil, heavy EP additives (chlorine, sulfur)
Coolant pressure	Maximum available — 50%+ above steel standards
Coolant volume	Maximum — both pressure and flow are critical
Coolant temperature	25–30°C — chiller required for any production volume
Filtration	5–10 micron — abrasive carbides accelerate wear

Chip Control

Chip shape in superalloys tends to be tougher and harder to break than in steel or stainless:

Chip Type	Implication	Action
Short, well-broken chips	Ideal — indicates good parameters	Maintain
Long, coiled chips	Feed too low or chip breaker inadequate	Increase feed; check insert geometry
Burned / discolored chips	Heat too high	Reduce speed; increase coolant
Ribbon chips	Very high ductility	Consider different insert grade or chip breaker

Depth Ratio Adjustments

Superalloys require the most aggressive depth ratio reductions:

Depth Ratio	Speed Reduction	Feed Reduction	Coolant Increase
< 15:1	None	None	Standard
15:1–30:1	15%	10%	15%
30:1–45:1	25%	20%	25%
45:1–60:1	35%	30%	35%
> 60:1	Not recommended for most superalloys	—	—

Common Problems

Problem	Cause	Solution
Rapid tool wear (flank wear)	Abrasive carbides in alloy	Reduce speed; use AlTiN coating; check coolant filtration
Notch wear at depth-of-cut line	Hard surface layer from previous pass	Increase feed; use edge-prep tool
Built-up edge	Material welding to carbide	Increase speed; check coolant EP additives
Chatter / vibration	High cutting forces	Increase feed; ensure rigid setup
Chip packing	Tough chips difficult to break	Increase feed; change insert geometry
Tool breakage	Heat weakens edge; work hardening	Reduce speed; never let tool dwell
Scrap from work hardening	Tool stop in cut	Never stop feed while tool is engaged
Poor hole straightness	High cutting forces cause deflection	Add whip guides; use contra-rotation

Critical Rules for Superalloy Drilling

Never let the tool dwell in the cut — Even a 1-second hesitation work-hardens the surface. Once hard, the tool will fail on re-entry.
Maintain steady feed — The feed must be continuous and uninterrupted. Use torque monitoring with automatic feed-stop to prevent stall.
Accept short tool life — 100–300 linear inches between regrinds is normal. Do not push beyond the first sign of wear.
Use maximum coolant — Both pressure and flow must be at the maximum the system can deliver.
Check the first 5 holes carefully — If tool wear is acceptable after 5 holes, the parameters are correct. If not, adjust before production.

Summary

Deep hole drilling in superalloys requires the most conservative parameters of any material group: speeds of 10–18 m/min, moderate feeds with aggressive chip breaking, maximum coolant delivery, and AlTiN-coated carbide tools. Never stop the feed while the tool is in the cut — work hardening occurs instantly. Accept tool life of 100–300 linear inches as normal. The cost of regrinding is far less than the cost of a broken tool in an expensive Inconel part.

For tool materials, see cutting tool materials guide. For troubleshooting, see deep hole drilling troubleshooting. For a complete overview, visit the materials-specific drilling guide.