What is a tungsten carbide drill bit?
A tungsten carbide drill bit is made of cemented carbide: hard grains of tungsten carbide (WC) held together by a tough metal binder such as cobalt, nickel or iron. In the two grades the International Tungsten Industry Association (ITIA) pictures, the WC grains are 1 to 2 microns across; the WC supplies the hardness and the cobalt the toughness.
Commercial grades generally carry 3% to 16% cobalt. Grain size and cobalt content are the two main settings: at the same 12% cobalt, a finer grain gives a harder but less tough carbide. Fine-grained carbide is used for drills and other round tools (see grades and binders).
Carbide can reach 92 HRA, which a University of Pennsylvania lecture puts at about 80 HRC, and carbide tools are chosen for rapid hole drilling because they are harder and outlast high-speed steel (HSS). The same lecture names the cost: poor toughness and a high price. More in carbide vs HSS.
Sources: ITIA, Cemented carbides (Newsletter June 2010); ITIA, Applications and markets; NTP, Cobalt-tungsten carbide background document (2010); ITIA, Properties of intermediates; University of Pennsylvania, Speeds and Feeds lecture; Drilling Al6061-T651 with carbide, Materials 2021.
Solid carbide, carbide tipped and indexable-insert drills
All three cut with carbide; they differ in how much of the tool is carbide and how it is held.
| Type | How it is built | What is carbide |
|---|---|---|
| Solid carbide | Ground from a carbide rod | The whole drill |
| Carbide tipped | A carbide tip joined to a steel body, for example by brazing | The tip only |
| Indexable insert | Carbide inserts screwed onto a steel body | The inserts, which come off whole |
Solid carbide drill bits are ground from a carbide rod. At the small end, ITIA describes printed circuit board drills down to 150 µm (about 0.006 inch) across, run at up to 300,000 rpm, that need a hard, ultrafine-grain carbide with an elastic modulus of 660 GPa.
Carbide tipped drill bits join a carbide cutting piece to a steel body by brazing or welding. In one brazing study the steel expanded 11.6 millionths per °C and the carbide 5.7, about half as much, so the two shrink unevenly as the joint cools. The stress left behind can crack the cutting edge early under steady or repeated loads.
Indexable-insert drills carry carbide inserts on a steel body. ITIA says insert tooling is built for quick and easy insert change and that inserts are typically above 80% tungsten.
Sources: ITIA, Recycling of tungsten (Newsletter May 2018); ITIA, Cemented carbides (Newsletter June 2010); Steel-to-carbide brazing study, Materials 2019; Residual stress in brazed carbide tools, Materials Science Forum 2000 (OSTI).
Masonry and rock drill bits
Carbide drills stone too: a US National Toxicology Program report lists masonry drills and rock drilling bits among its uses. In mining, many carbide bits may be shrunk into one steel part to make a drill head, and roller cone rock bits carry carbide buttons and inserts. Sandia describes the PDC cutter on oil and gas bits as a synthetic diamond table bonded to a tungsten carbide disc, which is brazed onto the bit body.
In NIOSH roof-bolter tests with 1 inch and 1-3/8 inch tungsten carbide spade bits, an excessively worn bit missed its targeted bite depth and raised respirable dust by as much as 61.5%.
Sources: NTP, Cobalt-tungsten carbide background document (2010); ITIA, Recycling of tungsten (Newsletter May 2018); Sandia National Laboratories, SAND2024-13076; NIOSH roof-bolter drilling study, 2022.
Coatings and through-coolant drills
A coating is a hard layer only microns thick: ITIA gives 5 to 20 µm for CVD and 2 to 8 µm for PVD.
CVD (chemical vapor deposition) heats the carbide to 800 to 1150 °C in its thermally activated form, and a 2023 paper says CVD at 1100 °C lowers tool strength. PVD (physical vapor deposition) runs at about 200 to 500 °C, and ITIA says the keenest edges come from PVD coatings. Common coatings include TiN (the gold one), TiCN, TiAlN, AlCrN and diamond; on abrasive high-silicon (hypereutectic) aluminum alloys, the 2023 paper says variations of conventional coatings do not improve tool life, but diamond coatings do. See the coatings page.
Through-coolant drills have internal helical channels that carry high-pressure coolant to the cutting edge, taking heat away and helping clear chips; that has been shown to raise tool life and improve finish. The hottest point of the tool/chip interface may reach 600 to 1000 °C, and carbide oxidizes in dry, high speed cutting. Even so, in studies of drilling aluminum alloys, carbide tools gave better finish and longer life, especially when cutting dry.
Sources: ITIA, Cemented carbides (Newsletter June 2010); Review of cutting tool coatings, Materials 2022; End mill coating paper, 2023 (OSTI); University of Leeds, through-coolant drill study (WCCM 2014); Oxidation of WC carbides, Frontiers in Materials 2021; Drilling Al6061-T651 with carbide, Materials 2021.
What wears a carbide drill out
Carbide cutting tools, drills among them, wear in a few distinct ways, each with its own mark.
- Flank wear is a worn land rubbed into the edge by the newly cut surface. It is mostly abrasion and is the normal wear of a well-run tool; as it grows, finish and size drift.
- Crater wear is a hollow in the tool face where the chip slides. The face runs hotter, so this wear is mostly chemical, such as diffusion wear. It goes with ductile work, while flank wear goes with brittle cast iron and bronze.
- Chipping and cracking. Apart from deformation, edge wear generally comes from cracking and microchipping; thermal cracks across the edge come from thermal shock.
- Built-up edge (BUE) is work material stuck to the tool, common in aluminum alloys. Its broken fragments scrape the tool face as the chip passes.
- Margin wear is wear on the narrow lands along the flutes, and it can limit how many regrinds a drill will take.
Wear runs in three phases: a fast break-in, a long steady stretch, then accelerated wear. Noise while drilling is one sign a tool is done.
Sources: AAST course IM212, Tool Wear and Tool Life; Wear of carbide turning Ti6Al4V, Materials 2019; University of Mons, ESAFORM 2018 paper; Drilling Al6061-T651 with carbide, Materials 2021; Abeni et al., Procedia CIRP 2025; University of North Texas thesis, 2008.
How tool wear is measured
Tool life is usually judged by flank wear, the width of the worn land (VB for its average), because crater wear is harder to measure. Tool life is typically the time to reach a set flank wear width, though crater depth can be used too.
The limits most often quoted come from ISO 3685:1993, the tool-life test for turning, as reported by a paper that cites it: an average flank wear VBB of 0.3 mm (about 0.012 inch), or a maximum VBBmax of 0.6 mm (about 0.024 inch) where wear is uneven. A milling study following ISO 8688 stopped at 0.3 mm average or 0.5 mm maximum. These are test limits for turning and milling, not a drilling rule.
Speed shortens that life. In one coated carbide turning test on AISI 1045 steel with a 0.3 mm limit, estimated tool life fell from 34.1 minutes at 300 m/min to 15.1 minutes at 400 m/min.
Sources: AAST course IM212, Tool Wear and Tool Life; Karandikar, Abbas and Schmitz, Precision Engineering 2013; University of Mons, Materials Science Forum vol. 986 (cites ISO 3685:1993); Coated carbide milling of AISI 4340, Materials 2022 (cites ISO 8688); Abeni et al., Procedia CIRP 2025.
Regrinding a carbide drill, and when it is scrap
Regrind a carbide drill at a set flank wear limit, before it breaks down. A tool-wear course says to regrind when average flank wear reaches a set allowable value; once wear enters the rapid third phase, regrinding is uneconomical.
A regrind is not always as good as new. In a test cited by a 2008 thesis, two identical solid carbide TiAlN-coated drills made 730 holes in 1038 steel, then went to two sources to be stripped, reground and recoated. The one from source A, the original supplier, failed from chatter after 463 holes; both drills reground at source B (one used, one new) made 560 holes before the test ran out of material. Margin wear was the worry, because it "might limit the number of regrinds that can be performed before a drill must be discarded".
NTP says sharpening or grinding hard-metal tools can make dust holding both cobalt and tungsten carbide. Read is tungsten carbide toxic? before you grind carbide yourself.
A drill past its last regrind still has value: the USGS Minerals Yearbook 2021 says tungsten-bearing scrap was used in place of other tungsten materials in cemented carbides, and ITIA traces the tungsten from a scrapped carbide drill into a counterweight. Brazed tools need their solder removed before processing, so tell us whether your drills are solid or tipped.
Worn and broken drills still hold their tungsten. Send photos and a rough weight through the quote form: we pay cash where state law allows, pay the shipping from anywhere in the US, and pick up in every city in California, Arizona and Nevada. Selling tungsten carbide sets out both routes.
Sources: AAST course IM212, Tool Wear and Tool Life; University of North Texas thesis, 2008; NTP, Report on Carcinogens profile: cobalt-tungsten carbide; USGS Minerals Yearbook 2021, Tungsten; ITIA Newsletter, May 2018; ITIA, Recycling of tungsten (Newsletter May 2018).
Questions people ask
Are solid carbide drill bits better than carbide tipped drill bits?
Neither wins everywhere. A solid carbide drill is carbide from point to shank, so it has no braze joint to crack. A carbide tipped drill keeps carbide only at the cutting end of a steel body, which uses less carbide but leaves brazing stress in the joint.
Can you sharpen a tungsten carbide drill bit?
Yes. Carbide drills are reground, and coated ones can be stripped and recoated. Regrind when flank wear reaches a set limit; once a drill is in its rapid-wear phase, a regrind stops paying for itself.
Do you buy used carbide drill bits?
Yes. We buy scrap carbide in any form, including worn, chipped and broken drills, solid or tipped. Send photos through the quote form, email help@carbidebuyerus.com, or call us.
Have tungsten carbide to sell?
Tell us what form it is in and about how much it weighs, and add a few photos. Ship it from any state and we pay the shipping, or we pick up anywhere in California, Arizona and Nevada.