Cutting Tools Reference Library · Coatings & Tool Materials
Drill Bit Materials & Coatings
How the substrate (HSS, cobalt M35/M42, carbide) and the finish (bright, black oxide, TiN, TiCN, TiAlN/AlTiN) change what a drill can do — and why both are filters within a length series rather than categories.
Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.
What it is
Every drill has a substrate — the steel or carbide the tool is made of — and usually a finish or coating on its surface. The substrate decides toughness, hot hardness and price. The coating changes friction, wear resistance and heat behavior at the cutting edge. Neither one is a product category: a cobalt TiAlN jobber drill is first a jobber drill, then cobalt, then TiAlN.
How to identify
Shank markings and packaging are the reliable source: "HSS," "M2," "M35," "M42," "Co 5%," "Co 8%" or "Carbide." Carbide is noticeably heavier than steel and is usually a solid, uniform gray; carbide drills are rarely sold in fractional hardware-store indexes. Coating color is a hint only — gold usually means TiN, violet-gray or near-black can be TiAlN or AlTiN, and a dull black is usually black oxide — but many coatings look alike and some brands tint their products.
Materials and finishes compared
| Material or finish | What it is | Where it fits | Watch out for |
|---|---|---|---|
| HSS (M1, M2, M7) | General-purpose high-speed steel | Mild steel, aluminum, wood, plastics, general maintenance | Loses hardness if overheated; lowest cost |
| Cobalt HSS — M35 | HSS with about 5% cobalt | Stainless steel, tougher alloys, higher heat | Slightly less tough than plain HSS |
| Cobalt HSS — M42 | HSS with about 8% cobalt | Harder and heat-resistant alloys | More brittle than M35; avoid flexing in hand drills |
| Solid carbide | Tungsten carbide in a cobalt binder | CNC production, high speeds, abrasive materials | Brittle; needs rigid setups and low runout |
| Bright (uncoated) | Ground finish, no coating | Aluminum and non-ferrous, where coatings can promote buildup | No added wear protection |
| Black oxide | Conversion surface treatment, not a hard coating | General steel drilling; holds lubricant and resists rust | Adds little wear resistance |
| TiN | Gold-colored PVD hard coating | General-purpose wear resistance on HSS and cobalt | Benefit is lost on regrind at the point, though margins keep it |
| TiCN | Harder carbonitride variant of TiN | Abrasive materials, cast iron | Not usually preferred for hot, dry cutting |
| TiAlN / AlTiN | Aluminum-rich PVD coating that resists heat | High speed, dry or minimal-coolant cutting, steels and stainless | Often not the best choice in aluminum |
Key points
- Pick the substrate for the material and the machine first, then the coating. A coating cannot make up for the wrong substrate or a flexible setup.
- Cobalt is an alloy throughout the tool, not a coating — a resharpened cobalt drill is still cobalt. A resharpened TiN drill has lost the coating where it was ground.
- Carbide gives its advantage only on rigid machines with good spindle runout and coolant. In hand drills it often chips or breaks.
- For aluminum and other gummy non-ferrous metals, bright or specially coated tools are common; confirm with the manufacturer's application chart.
- Catalog filters should include: material, coating/finish, point angle and shank type — applied inside each length series.
Common mistakes
- Treating "titanium" drills as solid titanium. The word refers to a titanium-nitride or similar coating.
- Assuming black oxide is a premium wear coating.
- Recommending carbide to a customer drilling by hand.
- Matching a replacement by color instead of the marked material and coating.
Governing standards: ASTM A600 (high-speed tool steels); ISO 513 (classification of hard cutting materials). Coating performance is manufacturer-specific — use the maker's data.
Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.