Tungsten carbide density, and a weight check for your piece

Density is weight divided by volume, given here in g/cm³ and in lb/in³ (1 g/cm³ = 0.036127 lb/in³). Tungsten carbide (WC) on its own is about 15.6 to 15.7 g/cm³, or 0.56 to 0.57 lb/in³: NTP lists 15.6, a 2022 study gives 15.64 as the theoretical value for binderless WC, and NIST gives a model-derived 15.68 at 25 °C.

Tools are cemented carbide: WC grains held in a cobalt binder and sintered, a heat treatment that turns pressed powder into a dense, nearly pore-free body. Cobalt is lighter, so each grade (a set cobalt content and grain size) reads lower.

Sources: NTP Report on Carcinogens, cobalt-tungsten carbide profile; OSTI 1922808 (2022 study); NIST ceramics data: WC; ITIA: Cemented carbides (2010).

A 12.7 by 12.7 by 4.76 mm carbide insert (an indexable cutting tip) weighs only about 11.4 g, so weigh inserts on a scale that reads to 0.01 g: an error of 0.1 g shifts that answer by almost 1%.

Rod: diameter and length

Volume is π × diameter² ÷ 4 × length. On a drill or an end mill (a milling cutter ground from carbide rod) it counts the air in the flutes as metal, so the reading comes out light.

Block or insert: length, width and thickness

Volume is length × width × thickness, for square blanks and flat square inserts. A round, triangular or holed insert reads light, so use the water test.

The water test

Weigh the piece dry. Hang it from the scale on a thin thread, fully under water and touching neither the bottom nor the sides of the cup, and weigh it again. Density = air weight ÷ (air weight − water weight), times the density of water. Shake off air bubbles first, since they make it read light.

USGS puts water at roughly 1 g/cm³, with 1.00000 at 4 °C and 0.99802 at 21 °C (70 °F), so taking 1 at room temperature reads about 0.2% high. A piece at 100 g in air and 93.4 g under water works out to 15.15, or 15.12 with the 21 °C value. ASTM B311-22, the ASTM test method for cemented carbide density, also uses water displacement.

Sources: USGS Water Science School: water density; ASTM B311-22; OSTI 2376169 (2023 study); ITIA: Cemented carbides (2010); ITIA: Recycling of tungsten, part 1 (2018).

Carbide is heavy because it is mostly tungsten: ITIA gives tungsten 19.25 g/cm³ and NIST 19.30. Carbon is only 6.13% of the weight of stoichiometric WC, the exact one-to-one compound.

The cobalt binder, 8.900 g/cm³ in NIST's table, pulls a grade down. Adding up the volume each part takes, with 15.64 for WC, predicts 15.21 g/cm³ at 3.7% cobalt and 14.96 at 6.0%; two commercial grades measured 15.17 and 14.91. At about 19% cobalt the sum gives 13.67, and 96.2% of that is 13.15, matching the 13.1 an ORNL study used for a part at 96.2% of full density.

Grades made for cutting steel can carry titanium or tantalum carbide beside the WC, and NTP's table of representative P grades runs from 8.5 to 13.4 g/cm³, so a light reading alone does not rule carbide out.

Sources: ITIA: tungsten properties; NIST X-ray attenuation tables, Table 1; OSTI 1922808 (2022 study); OSTI 2376169 (2023 study); OSTI 1981641 (2022 study); OSTI 1607097 (ORNL); Materials 2024 review (PMC11722073); NTP background document on hard metals (2010).

Steel pulls a reading down, and ITIA notes that carbide products are in many cases attached, brazed onto or cast into steel parts. A piece half carbide at 14.9 and half steel at 7.8 by volume reads about 11.35, right on lead.

• Steel shanks. Weigh the carbide alone where you can, or say in the form which part is steel.
• Braze. On brazed parts the solder has to come off before the carbide is processed, so mention any braze line.
• Holes. Some drills carry internal coolant channels. A rod measurement counts them as solid; the water test does not, once water fills them.
• Coatings. ITIA gives PVD coatings as 2 to 8 microns and CVD as 5 to 20. Even 20 microns on both faces of a 4.76 mm insert is under 1% of its thickness, so a coating barely moves the number.
• Porosity. Sintered carbide has residual porosity commonly below 0.02 vol%. A piece whose under-water weight keeps rising is soaking up water, and ASTM B311 says the water method then reads high and no longer applies.

A perfect reading still has limits, because two ingredients can offset each other. In ASTM's words, "Density alone cannot be used for evaluating a cemented carbide grade."

Sources: ITIA: Recycling of tungsten, part 1 (2018); ITIA: Cemented carbides (2010); MIT 3.11 metals table (1999); NIST X-ray attenuation tables, Table 1; Johns et al., coolant channels in drills (Leeds, 2014); ASTM B311-22; OSTI 2376169 (2023 study).

Use the band as a first sort, not a verdict. Between 13.1 and 15.2 g/cm³ the piece reads like cobalt-bonded carbide; from 8.5 to 13.4 it may still be a steel-cutting grade.

Near 7.8 it reads like steel, including high-speed steel (HSS; see carbide vs HSS), a tool steel that is mostly iron: ITIA's table gives M2 6.0% tungsten and 5.0% molybdenum, and T1 18.0% tungsten.

Above 16 points to tungsten heavy alloy, typically 16 to 18 g/cm³ sintered and up to 18.5, or to tungsten itself. Tantalum, 16.65 in NIST's table, lands there too; molybdenum, at 10.22, falls between nickel alloys and lead.

Whichever band your reading falls in, send the form with the reading, how you measured, and photos that show any shank or braze. We buy scrap carbide in any form, and exotic metals and alloys too. We pay the shipping from any US state, and in California, Arizona and Nevada we pick up in every city. See how selling to us works.

Sources: NTP background document on hard metals (2010); MIT 3.11 metals table (1999); ITIA: Tungsten in steel (2008); Materials 2020 (PMC7288021); ITIA Newsletter, December 2007; NIST X-ray attenuation tables, Table 1; Materials 2024 review (PMC11722073); OSTI 1607097 (ORNL).