The choice of tool material for deep hole drilling is not about which is "best" — it is about which is best for the specific application. Carbide is the default choice for most deep hole drilling because it offers the best balance of wear resistance, toughness, and cost. But HSS has applications where its toughness and lower cost make it the correct choice — low-speed drilling, small batches, and difficult materials where carbide is too brittle. Cermet fills a niche for finishing operations and small diameters where surface finish and wear resistance at moderate speeds are the priorities. Understanding the strengths and limitations of each material is essential for selecting the right tool.
Material Properties
| Property | HSS (M42) | Carbide (Micro-grain) | Carbide (Ultra-fine) | Cermet | Ceramic | PCD |
|---|
| Hardness (HV) | 900–1000 | 1500–1800 | 1800–2000 | 1600–2000 | 2000–3000 | 6000–8000 |
| Transverse rupture strength (MPa) | 3000–5000 | 2500–3500 | 3000–4000 | 1500–2500 | 500–1000 | 1000–1500 |
| Fracture toughness (MPa·√m) | 15–25 | 8–12 | 10–14 | 5–8 | 3–5 | 5–8 |
| Thermal conductivity (W/m·K) | 20–30 | 80–120 | 60–100 | 20–40 | 30–50 | 500–600 |
| Coefficient of thermal expansion (×10⁻⁶/K) | 11–13 | 5–6 | 5–6 | 7–8 | 7–9 | 3–5 |
| Maximum operating temperature (°C) | 550–600 | 800–1000 | 800–1000 | 900–1100 | 1200–2000 | 600–700 |
| Minimum practical edge radius (µm) | 5–10 | 5–15 | 3–8 | 5–10 | 10–20 | 5–15 |
Application Range by Material
| Application | HSS | Carbide — Micro-grain | Carbide — Ultra-fine | Cermet | Ceramic | PCD |
|---|
| Low-carbon steel | Acceptable | Excellent | Excellent | Good | Not recommended | Not recommended |
| Medium-carbon steel | Acceptable | Excellent | Excellent | Good | Not recommended | Not recommended |
| Alloy steel — annealed | Acceptable | Excellent | Excellent | Good | Not recommended | Not recommended |
| Alloy steel — hardened | Not recommended | Good | Good | Not recommended | Acceptable | Not recommended |
| Stainless steel | Good | Good | Excellent | Good | Not recommended | Not recommended |
| Cast iron | Good | Excellent | Excellent | Excellent | Good | Acceptable |
| Aluminum | Acceptable | Excellent | Excellent | Not recommended | Not recommended | Excellent |
| Superalloys (Inconel) | Good | Good | Excellent | Not recommended | Not recommended | Not recommended |
| Titanium | Good | Good | Excellent | Acceptable | Not recommended | Not recommended |
| Abrasive composites | Not recommended | Acceptable | Good | Not recommended | Not recommended | Excellent |
| Hardened materials (> 50 HRC) | Not recommended | Acceptable | Good | Not recommended | Acceptable | Not recommended |
HSS for Deep Hole Drilling
HSS Grades
| Grade | Hardness (HRC) | Toughness | Wear Resistance | Typical Application | Notes |
|---|
| M2 (standard) | 63–65 | Good | Moderate | General purpose — short runs — small diameters | Most common HSS grade — good balance of properties |
| M42 (cobalt HSS) | 66–69 | Moderate | Good | Difficult materials — higher speed — better wear resistance | 8% cobalt improves hot hardness — best HSS for deep hole drilling |
| T15 (high vanadium) | 64–66 | Moderate | Very good | Abrasive materials — long runs — better wear than M42 | High vanadium content increases wear resistance — more expensive |
| PM (powder metallurgy) grades | 66–69 | Good | Excellent | Premium applications — combines wear resistance with toughness | Higher cost — best wear resistance of any HSS — used in premium gun drills |
| ASP (ASP 2030, 2052) | 66–69 | Good | Excellent | Premium deep hole drilling — long life between regrinds | PM grade — consistent properties — excellent for small diameter drills |
HSS Application Guidelines
| Parameter | HSS Recommendation | Notes |
|---|
| Cutting speed — steel | 15–40 m/min | Depends on grade — M42 can run 25–40 m/min — M2 runs 15–25 m/min |
| Cutting speed — stainless | 10–25 m/min | Lower speed needed — work-hardening limits speed |
| Cutting speed — aluminum | 30–80 m/min | Higher speed possible — but HSS cannot match carbide speeds |
| Feed rate | 0.02–0.08 mm/rev | Lower than carbide — HSS edge is less wear-resistant at high feed |
| Tool life between regrinds | 5–50 m of drilling | Depends on material and speed — much shorter than carbide |
| Regrinds possible | 10–25 (depending on diameter) | HSS is easy to regrind — no special grinding wheels needed |
| Cost per drill | Low — 1/3 to 1/2 of carbide | Lower initial cost — but shorter tool life may offset |
Carbide for Deep Hole Drilling
Carbide Grades
| Classification | Grain Size (µm) | Hardness (HV) | Toughness | ISO Application Range | Best For |
|---|
| Coarse grain | 2–5 | 1200–1500 | Very good | K30–K40 | Heavy interrupted cuts — cast iron roughing — low-speed applications |
| Medium grain | 1–2 | 1400–1600 | Good | K20 — P20–P30 | General purpose — standard deep hole drilling — steels and cast iron |
| Micro-grain | 0.5–1.0 | 1500–1800 | Good | K10–K20 — P10–P20 | Most gun drills and BTA heads — good wear resistance and toughness |
| Sub-micro grain | 0.3–0.5 | 1700–2000 | Moderate–Good | K05–K15 — M10–M20 | Premium gun drills — stainless steel — superalloys — titanium |
| Ultra-fine grain | 0.1–0.3 | 1900–2200 | Moderate | K01–K10 | High-precision — small diameters — abrasive materials — finishing |
Carbide Application Guidelines
| Parameter | Carbide Recommendation | Notes |
|---|
| Cutting speed — steel | 60–120 m/min | 3–5× HSS speed — major advantage of carbide |
| Cutting speed — stainless | 40–80 m/min | 2–3× HSS speed — work-hardening still limits speed |
| Cutting speed — aluminum | 100–200 m/min | High speed possible — excellent for production |
| Cutting speed — cast iron | 60–120 m/min | Excellent performance — long tool life |
| Feed rate | 0.03–0.15 mm/rev | Higher than HSS — carbide edge can handle higher feed |
| Tool life between regrinds | 50–500+ m of drilling | 3–10× HSS tool life — wear resistance is the primary advantage |
| Regrinds possible | 3–15 (depending on diameter) | Requires diamond grinding wheels — fewer regrinds than HSS |
| Cost per drill | Moderate–High | 2–3× HSS cost — but lower cost per hole due to longer life |
Cermet for Deep Hole Drilling
Cermet Compositions
| Composition | Hardness (HV) | Toughness | Wear Resistance | Best For | Limitations |
|---|
| TiC-based (titanium carbide + Ni/Mo binder) | 1600–1800 | Low–Moderate | Good — adhesive and abrasive wear | Finishing — steels — cast iron — surface finish | Low toughness — not for interrupted cuts |
| TiCN-based (titanium carbonitride) | 1700–2000 | Moderate | Very good — chemical stability | Semi-finishing — steels — stainless — nodular iron | Not for heavy roughing — edge sensitive |
| TiN-based (titanium nitride) | 1500–1800 | Low–Moderate | Good — low friction | Non-ferrous materials — finishing | Limited application range |
| Multi-component (TiCN + TaC + WC) | 1800–2200 | Moderate | Excellent — wide application range | General purpose cermet — wider application | Higher cost than simple cermets |
Cermet Application Guidelines
| Parameter | Cermet Recommendation | Notes |
|---|
| Cutting speed — steel | 80–200 m/min | Higher than carbide — excellent wear resistance at high speed |
| Cutting speed — stainless | 60–120 m/min | Good performance — better surface finish than carbide |
| Cutting speed — cast iron | 80–200 m/min | Excellent — best surface finish of any tool material for cast iron |
| Feed rate | 0.02–0.08 mm/rev | Lower than carbide — cermet edge is more sensitive to feed |
| Tool life between regrinds | 30–200 m of drilling | Good — but less than carbide in roughing applications |
| Edge toughness | Low–Moderate | Not for interrupted cuts — not for entry impact — use with stable conditions |
| Cost per drill | High — comparable to premium carbide | Higher initial cost — but may be justified by surface finish and speed |
Coating Options
| Coating | HSS | Carbide | Cermet | Benefits | Limitations |
|---|
| TiN (titanium nitride) | Good — 2–3× life improvement | Good — 2–3× life improvement | Good | Lowers friction — reduces BUE — general purpose | Moderate wear resistance — lower hardness than other coatings |
| TiAlN (titanium aluminum nitride) | Not recommended (deposition temp too high for HSS) | Excellent — 3–5× life improvement | Good | High hardness — high temperature stability — excellent for steel | Higher cost — not for HSS |
| AlTiN (aluminum titanium nitride) | Not recommended | Excellent — 3–6× life improvement | Good | Highest hot hardness — best for high-speed machining | Higher cost — requires high deposition temperature |
| TiCN (titanium carbonitride) | Good — 2–4× life improvement | Good — 2–4× life improvement | Good | Low friction — good wear resistance | Lower temperature stability than TiAlN |
| DLC (diamond-like carbon) | Good — for aluminum | Good — for aluminum | Not recommended | Lowest friction — excellent for aluminum — non-stick | Not for steel (chemical reaction) — limited wear resistance |
| CVD diamond | Not applicable | Excellent — for abrasive materials | Not applicable | Highest wear resistance — for composites — ceramics — graphite | Not for ferrous materials — high cost — thick coating |
Selection Decision Criteria
Decision Matrix
| Application Condition | Recommended Tool Material | Reason |
|---|
| Low production volume — < 100 holes/month | HSS (M42) | Lower tool cost — acceptable tool life — no justification for higher-cost carbide |
| High production volume — > 1000 holes/month | Carbide (micro-grain or ultra-fine) | Lower cost per hole — longer tool life — less downtime for tool changes |
| Small diameter — < 3 mm | HSS (PM grade) or carbide (ultra-fine) | HSS for toughness in small diameters — carbide for wear resistance if stable |
| Large diameter — > 50 mm | Carbide (micro-grain) | Carbide provides required wear resistance at economical cost per hole |
| Low-speed machine — < 3000 RPM | HSS (M42) | Carbide cannot utilize its speed advantage — HSS is more economical |
| High-speed machine — > 5000 RPM | Carbide (micro-grain or ultra-fine) | Carbide can utilize high speed — HSS would wear too rapidly |
| Stainless steel — 304/316 | Carbide (ultra-fine) or HSS (M42) | Ultra-fine carbide for production — HSS for low volume or unstable conditions |
| Superalloy — Inconel | Carbide (ultra-fine) — or HSS (M42) for low speed | Ultra-fine carbide at moderate speed — HSS at low speed where carbide may chip |
| Cast iron — gray | Carbide (medium grain) | Long tool life — low cost per hole — carbide is optimal |
| Aluminum — wrought | Carbide (micro-grain — polished) | High speed capability — long tool life — polished to prevent built-up edge |
| Titanium | Carbide (ultra-fine) or HSS (M42) | Ultra-fine carbide for best tool life — HSS for low-speed operations |
| Surface finish critical — Ra < 0.8 µm | Cermet (TiCN-based) | Best surface finish — excellent for finishing passes |
| Interrupted cut — cross holes | HSS or tough carbide grade | Toughness required — HSS for maximum toughness — carbide K30–K40 for better wear |
| Abrasive material — composites | Carbide with CVD diamond coating — or PCD | Maximum wear resistance — carbide alone wears too rapidly |
FAQ
For most deep hole drilling applications, micro-grain or ultra-fine grain tungsten carbide is the best tool material. Carbide offers the best combination of: wear resistance (3–10× longer tool life than HSS — carbide maintains its cutting edge geometry for significantly more drilling length — less frequent tool changes — more consistent hole quality over the tool's life). Speed capability (carbide can run at 3–5× the cutting speed of HSS — for a 20 mm diameter drill, carbide can run at 80–120 m/min (1300–1900 RPM) vs HSS at 20–40 m/min (300–650 RPM) — the higher speed directly translates to faster drilling cycles and higher productivity). Toughness (modern micro-grain and ultra-fine grain carbide grades have good toughness — sufficient for most deep hole drilling applications — they can handle the interrupted cutting and entry impacts common in BTA drilling). Cost per hole (although the initial tool cost is higher (2–3× HSS), the longer tool life and higher speed capability result in lower cost per hole for production volumes above approximately 100 holes per month). Specific exceptions: HSS is better for low-speed applications (where the machine cannot utilize carbide's speed advantage — the lower tool cost of HSS is more economical), small batch sizes (where the setup time for optimizing carbide parameters is not justified), and applications requiring maximum toughness (interrupted cuts, unstable conditions, small diameter drills under 3 mm where carbide is too brittle). Cermet is better for finishing operations where surface finish is the primary requirement (cermet provides the best surface finish of any tool material in steel and cast iron). For the vast majority of deep hole drilling operations — steels, stainless steels, cast iron, aluminum — carbide is the optimal choice.
When should I choose HSS over carbide for deep hole drilling?
Choose HSS over carbide for deep hole drilling when: the machine cannot run at carbide-appropriate speeds (the machine's maximum spindle speed limits the cutting speed to below 40–50 m/min for the drill diameter — at low speeds, carbide's wear resistance advantage is not fully utilized — HSS provides acceptable tool life at lower cost). The operation requires maximum edge toughness (small diameter drills under 3 mm — the carbide edge may chip under the entry impact or in materials with hard inclusions — HSS is more forgiving of impact and vibration). The operation involves interrupted cuts (drilling through cross holes, keyways, or other interruptions — carbide edges can chip at the interruption — HSS can survive interruptions that would chip carbide). Production volume is low (fewer than 50–100 holes per month — the lower initial cost of HSS is more economical — the higher cost of carbide may not be recovered through longer tool life at low volumes). The material is difficult to machine with carbide (some titanium alloys and superalloys at low speeds — HSS (M42 or PM grades) can provide better tool life than carbide at low cutting speeds where carbide may chip). Regrinding facilities are limited to conventional grinding wheels (HSS can be reground with aluminum oxide wheels — carbide requires diamond wheels — if the shop does not have diamond grinding capability, HSS is the practical choice). In all these cases, HSS provides adequate performance at lower tool cost — but at lower productivity (slower cutting speeds) and shorter tool life between regrinds. The decision should be based on total cost per hole — not just the initial tool cost.
Cermet tools offer several advantages for deep hole drilling in specific applications: superior surface finish — cermet produces the best surface finish of any tool material for steel and cast iron — the low friction and chemical stability of the cermet cutting edge produces Ra values 30–50% lower than carbide under the same conditions — this is the primary reason to choose cermet for finishing operations. High temperature wear resistance — cermet maintains its hardness at high cutting temperatures (up to 900–1100°C) — better than carbide under high-speed continuous cutting — this allows higher cutting speeds (80–200 m/min for steel) while maintaining tool life. Chemical stability — cermet has excellent chemical stability — it does not react with steel at high temperatures — no diffusion wear (the primary wear mechanism in carbide at high speeds in steel). This makes cermet particularly effective for machining steel at high speeds. Low tendency to built-up edge — cermet has low affinity for workpiece materials — BUE formation is minimal — the cutting edge stays clean — contributing to consistent surface finish and hole quality. The limitations of cermet: lower toughness than carbide (cermet is more brittle — cannot handle interrupted cuts, entry impacts, or vibration — requires stable cutting conditions). Lower thermal conductivity (20–40 W/m·K vs 80–120 for carbide) — heat concentrates at the cutting edge — coolant is essential. Higher cost (cermet is typically 1.5–2.5× the cost of equivalent carbide tools). For deep hole drilling, cermet is most often used for: finishing passes in BTA drilling where surface finish is critical, small-diameter holes (< 10 mm) in steel where surface finish and hole quality requirements are high, and high-speed finishing in cast iron (where cermet provides excellent surface finish and tool life). Cermet is not recommended for: roughing passes, interrupted cuts, hard materials (> 45 HRC), or unstable setups.
Can HSS, carbide, and cermet be coated for deep hole drilling?
Yes — all three tool materials can be coated for deep hole drilling, but the coating options and benefits differ: HSS can be coated with TiN, TiCN, and DLC coatings — coating deposition temperatures for these coatings are below the HSS tempering temperature (550°C) — so HSS hardness is not affected. TiN coating on HSS typically improves tool life by 2–3× in deep hole drilling by reducing friction and built-up edge. TiAlN and AlTiN coatings cannot be used on HSS because the deposition temperature (600–800°C) exceeds the HSS tempering temperature — the HSS would soften during coating. Carbide can be coated with all common coatings — TiN, TiCN, TiAlN, AlTiN, and DLC. CVD diamond coating is also available for carbide (but not for HSS or cermet). The best coating for carbide depends on the application: TiAlN or AlTiN for steel and stainless steel (high hot hardness — excellent for the cutting temperatures in deep hole drilling) — TiCN for general purpose (low friction — good wear resistance) — DLC for aluminum (non-stick — prevents built-up edge) — CVD diamond for abrasive composites (maximum wear resistance). The typical tool life improvement from coating carbide in deep hole drilling is 2–5× over uncoated carbide. Cermet can be coated with TiN, TiCN, TiAlN, and AlTiN — but the improvement is typically smaller than for carbide (15–50% life improvement vs 100–400% for carbide) because cermet already has high chemical stability and wear resistance — the coating provides less additional benefit. CVD diamond coating is not available for cermet. For all three materials: the coating must be compatible with the coolant chemistry (some coatings degrade in high-pH coolants — check compatibility). The coating must be properly applied (correct thickness, adhesion, and edge coverage) — a poorly applied coating can reduce tool life by flaking off and exposing the substrate. The most important factor: coating is not a substitute for the correct tool material selection — it is a performance enhancer for the correct base material.
Tool material affects cost per hole through three factors: tool cost (initial cost of the tool — HSS is lowest — carbide is moderate — cermet is highest — but the initial cost is only part of the equation). Tool life (the number of holes the tool can drill before needing replacement or regrind — carbide typically provides 3–10× the tool life of HSS — cermet provides 1–3× the tool life of carbide in finishing operations). Regrind cost (the cost to regrind the tool — HSS is cheapest to regrind (aluminum oxide wheel — low wheel cost — fast grinding) — carbide is moderate (diamond wheel — longer grinding time) — cermet is most expensive (diamond wheel — slow stock removal — careful setup). Example cost per hole calculation for a 20 mm gun drill drilling medium-carbon steel: HSS (M42) — tool cost $50 — regrinds possible 15 — cost per regrind $10 — tool life between regrinds 30 m — total holes per drill 450 — cost per hole $0.18 (excluding labor and overhead). Carbide (micro-grain) — tool cost $120 — regrinds possible 8 — cost per regrind $25 — tool life between regrinds 150 m — total holes per drill 1,200 — cost per hole $0.12 (excluding labor and overhead). Carbide (coated) — tool cost $150 — regrinds possible 6 — cost per regrind $30 — tool life between regrinds 300 m — total holes per drill 1,800 — cost per hole $0.10 (excluding labor and overhead). In this example, carbide has a lower cost per hole despite the higher initial tool cost — because the longer tool life more than compensates. The additional benefit of carbide is the higher cutting speed capability — faster drilling cycles reduce labor and machine cost per hole — further widening the cost advantage. HSS remains competitive in low-volume applications where the lower initial tool cost and the ability to use less expensive grinding equipment offset the shorter tool life.
The choice between HSS, carbide, and cermet for deep hole drilling depends on the specific application requirements: carbide is the default choice for most deep hole drilling — offering the best combination of wear resistance, toughness, and cost per hole. Choose HSS for low-speed applications, small diameters, interrupted cuts, and low production volumes where the lower tool cost and higher toughness are advantageous. Choose cermet for finishing operations where surface finish is the primary requirement. Coat each material with the appropriate coating for additional performance — TiAlN for carbide in steel — DLC for carbide in aluminum — TiN for HSS. Select the tool material based on cost per hole — not initial tool cost — and match the tool material to the cutting speed capability of the machine. This article reflects industry practice as of 2026.
