Deep Hole Drilling Cutting Tool Materials
The cutting tool material determines the maximum cutting speed, tool life, and achievable surface finish in deep hole drilling. While tungsten carbide dominates the field, advanced materials like PCBN, PCD, and CVD diamond are used for specific applications.
This guide covers all cutting tool materials used in deep hole drilling, their properties, and how to select the right material for your application.
Tungsten Carbide (WC-Co)
Tungsten carbide is the standard cutting tool material for deep hole drilling. It accounts for over 95% of all deep hole drilling tools.
Composition
Tungsten carbide cutting edges consist of:
- Tungsten carbide (WC) particles — The hard, wear-resistant phase
- Cobalt (Co) binder — The metallic binder that holds carbide particles together
How Carbide Grade Affects Performance
| Property | Higher Cobalt → | Lower Cobalt → |
|---|---|---|
| Hardness | Decreases | Increases |
| Wear resistance | Decreases | Increases |
| Toughness | Increases | Decreases |
| Edge strength | Higher (resists chipping) | Lower (more brittle) |
| Heat resistance | Lower | Higher |
Carbide Grades by Application
| ISO Code | Cobalt % | WC Grain Size | Hardness (HV) | Application |
|---|---|---|---|---|
| K10–K15 | 3–5% | Coarse (2–5 µm) | 1,800–2,000 | Aluminum, non-ferrous, finishing |
| K20–K30 | 6–8% | Medium (1–2 µm) | 1,600–1,800 | General steel, cast iron |
| K30–K35 | 8–10% | Medium | 1,500–1,600 | Stainless steel, alloy steel |
| K35–K40 | 10–12% | Fine (0.5–1 µm) | 1,400–1,500 | Titanium, superalloys |
| K15–K20(G) | 4–6% | Ultra-fine (0.2–0.5 µm) | 1,900–2,100 | Hardened steel (HRC 45+) |
Selection rule: Choose the hardest grade that does not chip. If the edge chips, switch to a tougher grade (higher cobalt). If tool life is too short due to abrasive wear, switch to a harder grade (lower cobalt).
Micro-Grain and Ultra-Fine Carbide
Modern carbide grades with grain sizes below 1 micron offer a unique combination of high hardness and good toughness:
| Grain Class | Grain Size | Properties | Application |
|---|---|---|---|
| Medium | 1–5 µm | Standard, good all-round | General production |
| Fine | 0.5–1 µm | 10–20% harder than medium | Precision, wear resistance |
| Ultra-fine | 0.2–0.5 µm | Combines hardness + toughness | Small diameters, hardened materials |
| Nano | < 0.2 µm | Maximum hardness | High-speed finishing |
Coatings
Coatings extend tool life 2–5× by providing a hard, low-friction, thermally insulating layer on the carbide substrate.
PVD Coatings (Physical Vapor Deposition)
| Coating | Hardness | Max Temp | Best For |
|---|---|---|---|
| TiN (Titanium Nitride) | 2,300 HV | 500°C | General purpose (older coating) |
| TiCN (Titanium Carbonitride) | 3,000 HV | 400°C | Wear resistance on steel |
| TiAlN (Titanium Aluminum Nitride) | 3,300–3,500 HV | 800–900°C | Standard for steel, stainless |
| AlTiN (Aluminum Titanium Nitride) | 3,400–3,800 HV | 900–1,100°C | Hardened steel, superalloys |
| DLC (Diamond-Like Carbon) | 5,000–6,000 HV | 400°C | Aluminum, non-ferrous (anti-galling) |
CVD Coatings (Chemical Vapor Deposition)
| Coating | Hardness | Max Temp | Best For |
|---|---|---|---|
| CVD Diamond | 8,000–10,000 HV | 600°C | High-Si aluminum, composites |
| Al₂O₃ (Aluminum Oxide) | 2,100 HV | 1,000°C | High-speed cutting (not common on gun drills) |
Coating Selection
| Workpiece Material | Recommended Coating |
|---|---|
| Low-carbon steel | TiAlN |
| Alloy steel | TiAlN or AlTiN |
| Stainless steel | AlTiN (nano) |
| Titanium | AlTiN |
| Superalloys (Inconel) | AlTiN (nano) |
| Aluminum (wrought) | DLC or uncoated |
| Aluminum (high-Si cast) | CVD diamond |
| Cast iron | TiAlN or uncoated |
| Composites / CFRP | CVD diamond or DLC |
For detailed coating comparisons, see our gun drill coatings guide.
PCBN (Polycrystalline Cubic Boron Nitride)
PCBN is the second-hardest known material after diamond. It is used for machining hardened steels and superalloys.
| Property | Typical Value |
|---|---|
| Hardness | 4,000–5,000 HV |
| Max temperature | 1,200°C |
| Chemical stability | Excellent — inert with iron |
| Cost | 3–5× carbide |
| Typical application | Hardened steel (> HRC 50) |
PCBN Gun Drilling
PCBN-tipped gun drills have been developed for high-throughput drilling of nickel-based superalloys like Inconel 718. Studies have shown:
- Reduced cutting forces and torque compared to carbide
- Better hole straightness at high penetration rates
- Longer tool life at higher cutting speeds
Best for: High-volume production in hardened steels and superalloys where the additional tool cost is offset by productivity gains.
PCD (Polycrystalline Diamond)
PCD is the hardest cutting tool material, made by sintering diamond particles with a metallic binder.
| Property | Typical Value |
|---|---|
| Hardness | 7,500–10,000 HV |
| Max temperature | 600–700°C (inert atmosphere) |
| Chemical stability | Poor with iron (graphitizes above 600°C) |
| Cost | 5–10× carbide |
| Typical application | High-Si aluminum, composites |
Limitation: PCD cannot be used on ferrous materials because the high cutting temperature causes the diamond to graphitize (convert to graphite) in contact with iron.
Best for: High-volume production of aluminum-silicon alloys (engine blocks, transmission housings) and abrasive composites.
Material Selection Guide
| Condition | Recommended Material |
|---|---|
| General production, all methods | Tungsten carbide (K20–K30) |
| High-precision, small diameters | Ultra-fine carbide |
| Stainless steel, titanium | Fine-grain carbide + AlTiN coating |
| Superalloys (Inconel, Hastelloy) | PCBN or fine carbide + AlTiN |
| Hardened steel (> HRC 45) | Ultra-fine carbide + AlTiN, or PCBN |
| High-silicon aluminum (> 12% Si) | PCD or CVD diamond |
| Composites, carbon fiber | PCD or CVD diamond |
| Aluminum (standard) | DLC-coated carbide or uncoated |
| Cast iron | Carbide (K20–K30), TiAlN optional |
Material Cost vs. Performance
| Material | Relative Cost | Tool Life Multiplier (vs uncoated carbide) |
|---|---|---|
| Uncoated carbide | 1× (baseline) | 1× |
| TiAlN-coated carbide | 1.2–1.5× | 2–3× |
| AlTiN-coated carbide | 1.5–2× | 3–4× |
| DLC-coated carbide | 2–3× | 3–5× (aluminum only) |
| CVD diamond | 3–5× | 5–10× (abrasive materials) |
| PCBN | 3–5× | 3–6× (hardened materials) |
Summary
Tungsten carbide is the standard cutting tool material for deep hole drilling, with cobalt content and grain size selected to match the workpiece material. Coatings (TiAlN, AlTiN, DLC) extend tool life 2–5×. PCBN and PCD/diamond are specialized materials for hardened steels and abrasive non-ferrous materials respectively, where their higher cost is offset by productivity gains. The selection hierarchy: start with coated carbide for the specific material, then consider advanced materials if tool life is the limiting factor.
For coating details, see gun drill coatings guide. For tool wear analysis, see deep hole drilling tool wear analysis. For a complete overview, visit the tools and equipment guide.