Tungsten Carbide
Properties
| State | Solid |
| Color | Gray-black metallic |
| Solubility | Insoluble in water and most acids; dissolves in HF/HNO3 mixtures |
| Melting Point | 2870 °C |
| Boiling Point | 6000 °C (approximate) |
About Tungsten Carbide
Tungsten carbide crystallizes in a simple hexagonal P-6m2 structure where W atoms sit on a hexagonal-close-packed sublattice and carbon fills half the trigonal-prismatic interstices, an arrangement that gives WC a Vickers hardness around 2400 HV — close enough to diamond that it scratches sapphire and cuts hardened steel that would dull tool steel in seconds. The melting point sits at 2870 °C, the density at 15.6 g/cm^3 (almost twice steel), and the elastic modulus at roughly 700 GPa, three times that of steel. The industrial form is almost never pure WC. Cemented carbide, the material in Sandvik Coromant inserts and Kennametal drill bits, is WC powder sintered with 6 to 12 wt% cobalt binder at around 1400 °C in a vacuum furnace, producing a composite tough enough to survive the impact loading of an interrupted cut. Global production exceeds 100,000 tonnes per year, with the cutting-tool industry consuming most of it. WC also shows up as armor-piercing penetrator cores in 7.62 mm and 30 mm ammunition, scratch-resistant wedding bands sold under the "tungsten ring" label (which are actually WC-cobalt), and as a non-noble-metal electrocatalyst whose surface electronic structure mimics platinum closely enough to evolve hydrogen at competitive overpotentials.
Where you'll encounter it
If you have ever changed an insert on a CNC lathe, the gold-coated triangular tip you bolted onto the toolholder is sintered WC-Co, usually with a TiAlN or AlCrN PVD coating laid down a few microns thick to extend tool life. Machinists track tool wear in minutes per edge per material — a coated WC insert holding 304 stainless might last 15 to 30 minutes of cutting time before the flank wear hits 0.3 mm and the edge needs to be indexed. In the mining and oil-and-gas world, tricone and PDC bits use WC studs hammered into the cone matrix to grind through abrasive sandstone formations at 1000 m depth. The hard-metal grinding shops that resharpen these tools are the source of the cobalt-pulmonary fibrosis cases ("hard-metal lung disease") that drove the OSHA PEL for cobalt down to 0.1 mg/m^3 — the WC dust by itself is far less harmful than the cobalt that comes off with it.
Common Uses
- Indexable inserts and end mills for CNC machining of steel, cast iron, titanium, and Inconel
- Tricone bit teeth and PDC bit gauge protection for mining and oil-and-gas drilling
- Armor-piercing penetrator cores in 7.62 mm, 12.7 mm, and 30 mm anti-armor ammunition
- Wear plates, valve seats, and pump nozzles in slurry-handling and abrasive-flow service
- Scratch-resistant jewelry rings sold as tungsten wedding bands (typically WC-Co composite)
- Non-platinum electrocatalyst studied for the hydrogen evolution reaction in alkaline electrolyzers
- Studded snow tires and ice-grip hiking and mountaineering boot soles
- Ballpoint pen tips precision-machined from sintered WC microspheres
Safety Information
GHS classification for cobalt-bonded cemented carbide: Skin sensitization Category 1, Carcinogen Category 1B (cobalt fraction), and Specific Target Organ Toxicity Repeated Exposure Category 1 for the respiratory tract. The OSHA PEL for cobalt as Co metal and dust is 0.1 mg/m^3 as an 8-hour TWA, with NIOSH recommending 0.05 mg/m^3. The signature occupational disease is hard-metal lung disease, a giant-cell interstitial pneumonitis caused by inhalation of WC-Co fines from grinding operations, with onset latencies of 5 to 20 years. Wet grinding with HEPA-filtered dust collection, P100-rated respirators for dry operations, and routine medical surveillance for grinders are the standard controls. The bulk solid is inert; the hazard is entirely with the dust.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.