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What a magnet really tells you about a piece of carbide
By Carbide Buyers USA · Updated
Is tungsten carbide magnetic? Most of the carbide you will hold is tungsten carbide grains held together by cobalt, and cobalt is a magnetic metal, so many pieces do respond to a magnet. Steel responds too, so treat the magnet as a first sort, then check the weight and send us photos of anything you are unsure about.
Most of the pull comes from the cobalt glue
A piece of carbide is two materials, not one. ITIA, the tungsten industry association, describes a typical grade as tungsten carbide grains about 1 to 2 microns across, held in a tough cobalt alloy matrix: the carbide brings the hardness, the cobalt the toughness. A common recipe is 90% tungsten carbide and 10% cobalt, which ITIA calls a straight grade, and an NTP report puts commercial grades at generally 3% to 16% cobalt.
That cobalt is the binder, the metal that glues the grains into a solid part, and a national laboratory paper calls it the most common one. Cobalt is also a magnetic metal. The US Geological Survey (USGS) describes it as ferromagnetic, meaning a magnet attracts it, and the Cobalt Institute counts strong magnetic properties among its traits.
The pull carries through into finished carbide. Researchers at Oak Ridge National Laboratory (ORNL) measured a tungsten carbide-cobalt (WC-Co) part with about 19% cobalt by weight at a magnetic saturation of 0.5 T (tesla), and wrote that the figure is similar to WC-Co of similar cobalt content and grain size.
So a carbide drill that clings to your magnet has not been shown to be steel. No source we use says how hard a given insert ought to pull, so we do not give you a pull to expect.
Sources: ITIA, Cemented carbides (June 2010 newsletter excerpt); ITIA, Applications and markets; NTP, Report on Carcinogens background document for hard metals (2010); LLNL manuscript on cemented tungsten carbide binders (2018); USGS Circular 1196-M (2004); Cobalt Institute, About cobalt; ORNL manuscript on binder-jet WC-Co (2019).
Nickel, iron and mixed binders muddy the reading
Not every grade is glued with cobalt alone. A 2023 paper notes the binder can also be nickel, iron or another transition metal. ITIA says nickel, nickel-chromium and iron-nickel-cobalt binders have widened where carbide is used, and that for wear parts, where WC-Co is the usual choice, CoNiCr, NiCr, FeNiCo and pure nickel binders are considered when corrosion matters. So the odd die or seal ring in your box may carry a nickel-based binder.
A 2024 paper in a chemistry journal notes that replacing cobalt with nickel tends toward a tougher, less hard grade, and replacing it with iron tends the other way. Recycling researchers (Zeiler and colleagues, 2021) say alternative-binder grades, and parts built from two or more grades, pose a new problem in scrap identification.
We have found no source we trust on how strongly a nickel-bound grade reacts to a magnet, so we will not guess. A weak pull, or none at all, does not prove a piece is not carbide. Weigh it before you set it aside.
Sources: Journal article manuscript on cemented tungsten carbides (2023); ITIA, Cemented carbides (June 2010 newsletter excerpt); Eclética Química review of cemented carbides (2024); Zeiler et al., tungsten recycling review (2021, ITIA-hosted open access copy).
A magnet test for carbide, piece by piece
Here is what the magnet can and cannot tell you about the things that usually end up in a scrap box.
| In your box | What it is made of | What the magnet tells you |
|---|---|---|
| Solid carbide drill or end mill | Carbide rod ground into the tool (ITIA), so carbide from tip to shank | A pull is normal for a cobalt grade and does not mean steel |
| Brazed lathe tool, carbide-tipped saw | Carbide tips brazed onto a steel part (ITIA; a university machining lecture) | The steel body grabs the magnet whatever the tip is |
| HSS drill, tap or bimetal saw blade | High-speed steel (HSS), a tool steel with 1.5% to 20% tungsten (ITIA) | It pulls, because it is steel |
| Wear part built for corrosive service | May use a nickel-based binder (ITIA) | No source we found says; never discard it on a weak pull |
| Grinding sludge, sweepings, powder | What ITIA calls soft scrap | Bag it before you test it (see the handling notes below) |
Steel pulls on a magnet; that is close to the definition. Arizona's scrap metal law describes ferrous metals as "those metals that will attract a magnet". Shape will not rescue you either: ITIA says about 95% of HSS goes into machining tools such as drills, taps, milling cutters, gear cutters, saw blades and knives, and lists fine-grained carbide for round tools such as drills, threaders, reamers and routers. ITIA also notes that some bimetal blades have HSS teeth, not carbide ones.
Scrap sorters treat the magnet as one test among several. USGS describes a first sort by shape, object recognition, color and weight, followed if needed by tests such as response to a magnet or the spark pattern a piece throws on an abrasive wheel. For carbide, leave the wheel out of it.
Sources: Arizona Revised Statutes 44-1641; ITIA, Tungsten in steel (December 2008 newsletter excerpt); ITIA, Cemented carbides (June 2010 newsletter excerpt); ITIA, recycling newsletter excerpt (May 2018); ITIA, recycling newsletter excerpt (August 2019); King Saud University, fundamentals of metal cutting lecture (2010 textbook material); USGS Circular 1196-M (2004).
Density settles what the magnet leaves open
Density, the weight of a piece for its size, answers the question the magnet cannot. NTP lists tungsten carbide itself at 15.6 grams per cubic centimetre (g/cm3), and a NIST database gives a model value of 15.68. Real grades come in a little lighter because cobalt, at about 8.9 g/cm3, is lighter than the carbide:
- 15.17 g/cm3 for a commercial grade with 3.7% cobalt, and 14.91 for one with 6.0% (2023 paper).
- 14.0 to 14.3 g/cm3 for four commercial grades with 10% to 12% cobalt (2022 study).
- 13.1 g/cm3, the figure ORNL used for its part with about 19% cobalt.
NIST lists pure iron at 7.874 g/cm3. Divide 14.91 by 7.874 and you get about 1.9, so a 6% cobalt piece weighs close to twice as much as an iron piece of the same size.
Two cautions. NTP's table of representative steel-cutting P grades, which carry other carbides as well, runs from 8.5 to 13.4 g/cm3, so a lighter reading does not rule carbide out. And tungsten heavy alloy, typically 16 to 18 g/cm3 when sintered, is heavier than carbide; it is a different metal, and we buy it too. Our guide on how to identify carbide walks through measuring density at home with a cup of water.
Sources: NTP, Report on Carcinogens profile: cobalt-tungsten carbide; NIST ceramics data portal, tungsten carbide (Reeber and Wang, 1999); Journal article manuscript on cemented tungsten carbides (2023); Study of four commercial WC-Co grades (2022); ORNL manuscript on binder-jet WC-Co (2019); NIST X-ray mass attenuation tables, Table 1; NTP, Report on Carcinogens background document for hard metals (2010); Tungsten heavy alloy machining study (Materials, 2020).
Handling sludge and fines while you sort
Keep every check non-destructive: no grinding, filing or spark wheel. NTP says dusts holding both cobalt and tungsten carbide can come from sharpening or grinding hard-metal products, and it lists cobalt-tungsten carbide powders and hard metals as reasonably anticipated to be a human carcinogen.
The limit is small next to what grinding can release. IARC (2006) found that sharpening and maintaining hard-metal tools can put cobalt into the air at several hundred micrograms per cubic metre. NIOSH recommends no more than 0.05 mg/m3 as cobalt, which is 50 micrograms, averaged over a 10-hour shift, for carbide with more than 2% cobalt. A spark test is grinding, so it makes that kind of dust.
Solid pieces are a different case: IARC says exposure while using hard-metal tools is much lower than during their manufacture. The fines need more care. ATSDR says skin contact with cobalt particles may cause irritation and discoloration, so wear gloves. If you try a magnet on grinding sludge, slip it into a zip bag first, so the fines come away with the bag instead of your fingers.
Sources: NTP, Report on Carcinogens profile: cobalt-tungsten carbide; IARC Monographs Volume 86 (2006); ATSDR ToxFAQs: cobalt.
Sell us the box, sorted or not
You do not have to settle every piece with a magnet first. We buy scrap carbide in any form, and all exotic metals and alloys as well, so a box holding a bit of both is still one we want to hear about.
Use the quote form: what form the carbide is in, about how much it weighs, a few photos, and which pieces grabbed the magnet. Email help@carbidebuyersusa.com works as well, or ring us on (877) 899-5778.
From any state, you can send the box by carrier and we cover the shipping cost. We also drive out and collect in every city in California, Arizona, Utah and Nevada. We pay cash where state law allows it.
Common questions
Is carbide magnetic or not, in one line?
Often it is, because most grades use cobalt as the binder and cobalt is a magnetic metal. Grades bound with nickel or other metals may behave differently, and steel pulls too, so the magnet alone never settles the question.
My brazed lathe tool grabs the magnet. Where is the carbide?
In the tip. The carbide is brazed onto a steel body, and that steel grabs a magnet on its own, so the pull tells you nothing about the tip. Send brazed tools as they are; we buy brazed tools and saw tips.
If a piece ignores the magnet, should I throw it out?
No. A grade with a nickel-based binder may not act like a cobalt grade, and some carbide comes from parts built for corrosive service. Check its weight for its size, keep it with the rest, and mention it on the quote form.
Is a magnet test for carbide enough to price a lot?
No. We quote every lot from its photos, the form it is in and about how much it weighs, and we never print a price, because every lot is different. The magnet is only a way for you to get a rough sort done first.
More for sellers
How to identify carbide
Telling carbide from steel and HSS in a toolbox
Learn more
Sorting carbide scrap
What to keep together, what to separate, and why
Learn more
Saw tips and brazed tools
Carbide-tipped saw blades, saw tips and brazed tools
Learn more
Tungsten and heavy alloy
Pure tungsten and tungsten heavy alloy
Learn more
High-speed steel (HSS)
HSS drills, taps, end mills and tool bits
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.