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How to tell if something is carbide, one piece at a time
By Carbide Buyers USA · Updated
If you are working out how to identify carbide in a drawer of old tooling, start with weight for size, because carbide is far heavier than steel. Shape, colour and a magnet help you sort, none of it needs a grinder, and anything that still has you guessing can go to us as photos with a quote request.
Pick it up first: carbide is heavier than it looks
Density is weight divided by size, and you can measure it at home. Carbide sits far above steel and below pure tungsten. Figures are in grams per cubic centimetre (g/cm3).
| Material | g/cm3 | Where the figure comes from |
|---|---|---|
| Tungsten carbide itself | about 15.6 to 15.7 | NTP table; NIST model value |
| Fine-grain carbide, 2% to 6% cobalt (lab samples) | 15.2 to 14.8 | 2024 paper's table |
| Commercial grades, 3.7% and 6.0% cobalt | 15.17 and 14.91 | 2023 paper |
| Commercial grades, 10% to 12% cobalt | 14.0 to 14.3 | 2022 study of four grades |
| Carbide part, about 19% cobalt | 13.1 | ORNL |
| Steel-cutting P grades with other carbides | 8.5 to 13.4 | NTP table (representative values) |
| Pure tungsten | 19.25 to 19.30 | ITIA; NIST |
| Tungsten heavy alloy, sintered | 16 to 18 (typical) | 2020 paper |
| Cobalt | 8.90 to 8.92 | NIST; NTP |
| Pure iron | 7.874 | NIST |
| 1020 and 4340 steel | 7.8 | MIT course table (1999) |
Our arithmetic: 14.91 divided by 7.874 is about 1.9, so a 6% cobalt carbide piece weighs close to twice an iron piece of the same size. No source we use gives a density for high-speed steel, so the table has no row for it and we do not guess one.
Sources: NTP, Report on Carcinogens profile: cobalt-tungsten carbide; NIST ceramics data portal, tungsten carbide (Reeber and Wang, 1999); Review of WC-Co processing and properties (Materials, 2024); Journal article manuscript on cemented tungsten carbides (2023); Study of four commercial WC-Co grades (2022); ORNL manuscript on binder-jet WC-Co (2019); NTP, Report on Carcinogens background document for hard metals (2010); ITIA, Properties and intermediates; NIST X-ray mass attenuation tables, Table 1; Tungsten heavy alloy machining study (Materials, 2020); MIT 3.11 metals properties table (1999); ITIA, Tungsten in steel (December 2008 newsletter excerpt).
Measuring density with a kitchen scale and a cup of water
You need a scale that reads in grams, a cup of water and thin thread.
- Weigh the dry piece and note the number.
- Set the cup of water on the scale and zero it.
- Hang the piece on the thread, fully under water, touching neither side nor bottom. The reading is the water it pushed aside, which is its volume in cubic centimetres, near enough.
- Divide the dry weight by that reading.
Example: a 150.0 g piece that pushes aside 10.2 g of water works out at about 14.7 g/cm3, right in the carbide rows. A 150 g steel piece at 7.8 g/cm3 would push aside about 19.2 g.
Why near enough: a USGS table gives water at 1.00000 g/cm3 at 4 degrees C and 0.99802 at 21 degrees C (70 degrees F), so calling it 1 is about 0.2% off. ASTM B311, the standard density method for cemented carbides, rests on the same water displacement idea.
The limits: a 10 g insert pushes aside only about 0.7 g, too little for a scale that reads whole grams, so test your largest piece. ASTM warns that a piece which gains weight under water has surface-connected porosity and reads high, and that density alone cannot evaluate a grade. A good reading says probably carbide, not which grade.
Sources: USGS Water Science School, water density; ASTM B311-22, density of PM materials and cemented carbides; MIT 3.11 metals properties table (1999).
Colour, coatings and box labels: useful hints, weak proof
Bare tungsten carbide is gray, as NTP's property table lists it. Plenty of tools are coated: ITIA's 2010 newsletter puts the coated share at more than 80% of turning inserts and about 70% of milling inserts. TiN is gold, and a university coating lab lists TiCN as copper, TiAlN as lilac-black, AlTiN as black and CrN as silver. Those are one lab's colours, so read them as typical, not as a rule. A coating says a tool was coated, not what is under it.
Box labels help more, with two limits. ISO 513:2012 marks hard cutting materials by what they cut, with letters and colours such as P blue for steel, M yellow for stainless and K red for cast iron. But it covers ceramics, diamond and boron nitride as well as hardmetals, and its HT class is cermet, an uncoated carbide based mainly on TiC or TiN. NTP adds that ISO application codes are guidance only, set at each maker's discretion. Keep inserts in their boxes where you can, and photograph the label for us.
Sources: NTP, Report on Carcinogens background document for hard metals (2010); ITIA, Cemented carbides (June 2010 newsletter excerpt); TalTech thin coatings lab, PVD coatings; ISO 513:2012 preview.
The magnet: a clue with two blind spots
Cobalt, the usual binder, is ferromagnetic according to USGS, so a lot of carbide reacts to a magnet. Steel does as well, and ITIA describes grades bound with nickel, nickel-chromium or iron-nickel-cobalt. Those are the two blind spots: a pull does not prove a piece is steel, and a weak pull does not rule carbide out.
It is still handy for spotting the steel parts of a tool, such as a shank or holder. The full story is in our guide is tungsten carbide magnetic.
Sources: USGS Circular 1196-M (2004); ITIA, Cemented carbides (June 2010 newsletter excerpt).
Look-alikes: high-speed steel, heavy alloy and ceramic
High-speed steel and carbide drill bits
High-speed steel (HSS) is the look-alike you will meet most. ITIA says it carries 1.5% to 20% tungsten, hardens up to HRC 63 to 68, and about 95% of it becomes machining tools: drills, taps, milling cutters, gear cutters, saw blades and knives. Shape will not separate it from carbide, and HSS has no row in the table above; what the table does show is that a reading near 14 to 15 belongs with the carbide grades, far above plain steel.
ITIA notes that carbide rod is ground into drills and end mills, so a solid carbide drill is carbide from tip to shank. A drill with a carbide tip brazed to a steel body is part of each; a university machining lecture describes tips fixed to a shank by brazing. ITIA also says some bimetal saw blades have HSS teeth.
Tungsten heavy alloy
A 2021 paper describes the classic heavy alloys as tungsten with nickel and iron or nickel and copper, 80% to 98% tungsten, and a 2020 paper puts sintered pieces at 16 to 18 g/cm3: heavier than carbide. Bag it separately; we buy tungsten and heavy alloy too.
Ceramic and cermet inserts
The same lecture names carbide, ceramic and diamond tools all made as inserts, and ISO 513 classes cermets alongside hardmetals. ITIA says alumina and silicon carbide behave brittle under load, while carbide keeps considerable toughness because it is partly metallic. None of our sources gives a density for these inserts, so lean on the label, keep anything marked ceramic or cermet apart, and say so on the form.
Sources: ITIA, Tungsten in steel (December 2008 newsletter excerpt); ITIA, recycling newsletter excerpt (May 2018); King Saud University, fundamentals of metal cutting lecture (2010 textbook material); NTP, Report on Carcinogens background document for hard metals (2010); Tungsten heavy alloy review (Materials, 2021); Tungsten heavy alloy machining study (Materials, 2020); ISO 513:2012 preview; ITIA, Cemented carbides (June 2010 newsletter excerpt).
Never grind, spark or snap a piece to check it
USGS lists the spark pattern from an abrasive wheel as one way sorters tell alloys apart. Do not use it on carbide. NTP says dusts containing cobalt and tungsten carbide come from sharpening or grinding hard-metal products, and that cobalt-tungsten carbide causes hard-metal disease, a giant-cell interstitial pneumonia that can develop into lung fibrosis and is not seen with cobalt alone. NIOSH recommends no more than 0.05 mg/m3 of cobalt, averaged over 10 hours, for cemented tungsten carbide with more than 2% cobalt.
Breaking a piece open adds nothing a scale cannot tell you. ASTM B406 describes most commercial cemented carbides as brittle, with negligible ductility: they break rather than bend, so a hammer only gives you broken pieces to bag.
Sludge, sweepings and powder are what ITIA calls soft scrap. Keep them in a lidded pail and wear gloves (ATSDR says skin contact with cobalt particles may cause irritation and discoloration); see grindings, sludge and powder.
Sources: USGS Circular 1196-M (2004); NTP, Report on Carcinogens profile: cobalt-tungsten carbide; ASTM B406-96(R21), transverse rupture strength of cemented carbides; ITIA, recycling newsletter excerpt (August 2019); ATSDR ToxFAQs: cobalt.
Still guessing? Let us look at it
Sorting to the last piece is not your job. We buy scrap carbide in any form, mixed lots included, plus exotic metals and alloys, so pieces you could not place are still worth a photo.
On the quote form, give the form, a rough weight and what your checks showed, with photos of the pieces and any labels. Or email help@carbidebuyersusa.com, or call (877) 899-5778.
From anywhere in the US you can ship your carbide to us and we pay the shipping; anywhere in California, Arizona, Utah or Nevada we can pick it up instead (how selling works). We pay cash where state law allows.
Common questions
How do I identify carbide drill bits in a mixed drawer?
Weigh each bit against a plain steel piece of about the same size: a solid carbide bit comes out close to twice as heavy. A carbide-tipped bit has a steel body that grabs a magnet. A bit that weighs like steel may be high-speed steel, so photograph it and let us look. We buy end mills and drills and brazed tools.
My piece came out lighter than the table. Is it steel?
Not necessarily. Steel-cutting grades with other carbides weigh less than straight grades, and small pieces measure badly. Retest your largest piece, then send photos.
Does a gold insert mean it is carbide?
It means the insert has a coating, often titanium nitride (TiN), which is gold. Coated carbide inserts are very common, but the colour is not proof of what is underneath. Check weight for size.
Can I send pieces I could not identify?
Yes. Bag them separately, note them on the quote form and add photos. Unknown pieces get looked at like everything else: from your photos, their form and a rough weight.
More for sellers
Is tungsten carbide magnetic?
What a magnet can and cannot tell you
Learn more
Sorting carbide scrap
What to keep together, what to separate, and why
Learn more
End mills, drills and reamers
Solid carbide end mills, drills, reamers and burs
Learn more
Used inserts
Used indexable inserts, coated or not, chipped or worn
Learn more
High-speed steel (HSS)
HSS drills, taps, end mills and tool bits
Learn more
Tungsten and heavy alloy
Pure tungsten and tungsten heavy alloy
Learn moreReady to sell your carbide?
Send a few photos and a rough weight. From any state, you ship it and we cover the shipping; in California, Arizona, Utah and Nevada, we drive out to you.