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What it is made ofHow is tungsten carbide made? From ore to sintered part
Tungsten carbide is made from ore by chemistry and then powder metallurgy: the ore becomes ammonium paratungstate (APT), then oxide, tungsten powder and carbide powder, which is milled with cobalt, pressed, sintered solid and ground with diamond. Worn carbide can go back into that chain, and we buy carbide in any form.
The tungsten carbide manufacturing process, step by step
A finished carbide part sits at the end of eleven steps, each explained in the sections below.
| # | Step | What happens |
|---|---|---|
| 1 | Concentrate the ore | Scheelite or wolframite is crushed, ground and concentrated |
| 2 | Make APT | Caustic soda or hydrochloric acid gives ammonium tungstate, then APT |
| 3 | Heat to oxide | APT decomposes to yellow WO3 or blue oxide |
| 4 | Reduce | Hydrogen turns the oxide into tungsten powder |
| 5 | Carburize | Tungsten powder and carbon black at 1,300 to 2,200 °C in hydrogen make tungsten carbide (WC) powder |
| 6 | Wet mill | WC, cobalt and inhibitors milled in solvent, plus a pressing binder |
| 7 | Dry | The slurry is dried, for example by spray drying |
| 8 | Shape | Pressing, extrusion or injection molding |
| 9 | Dewax or presinter | The binder comes out; some parts are presintered at 500 to 800 °C before machining |
| 10 | Sinter | 1,350 to 1,550 °C, in vacuum or hydrogen or by sinter-HIP; the part shrinks |
| 11 | Grind | Diamond grinding, wet or dry; some parts are coated |
Sources: USGS Open-File Report 2005-1028 (tungsten, 2005); Shen et al., JOM 2018 (wolframite conversion); ITIA: tungsten intermediates and their properties; NTP Report on Carcinogens background document: cobalt-tungsten carbide (2009/2010); ITIA: Cemented carbides, a success story (2010 newsletter).
From tungsten ore to APT
Only two of the more than 20 tungsten minerals matter commercially. Scheelite, sometimes called white ore, is calcium tungstate (CaWO4); wolframite, or black ore, is an iron and manganese tungstate, (Fe,Mn)WO4.
Most ore concentrate is processed chemically into ammonium paratungstate (APT), the main tungsten raw material traded on the market, usually by way of ammonium tungstate, which is made by treating the concentrate with caustic soda or hydrochloric acid. APT is a white crystallised powder whose trace elements usually sit in the low parts-per-million range, and ITIA says tungsten powder purity depends mainly on the APT it came from.
Sources: USGS Open-File Report 2005-1028 (tungsten, 2005); Shen et al., JOM 2018 (wolframite conversion); ITIA: tungsten intermediates and their properties.
Tungsten oxide, hydrogen reduction and carburizing
Heating APT under oxidising conditions gives yellow tungsten trioxide (WO3); slightly reducing conditions give tungsten blue oxide, which USGS calls the most common starting material for tungsten powder.
Hydrogen reduces the oxide to metal powder, in pusher furnaces where the powder rides through in boats, or in rotary furnaces at 700 to 1,000 °C. Changing only the reduction conditions can give any average particle size from 0.1 to 100 µm.
To carburize, the tungsten powder is mixed with carbon black and heated at 1,300 to 2,200 °C in hydrogen, which gives the tungsten carbide powder the later steps use. A grade's grain size starts here: ITIA says WC grain size follows the tungsten powder size and the carburizing temperature, and the hotter the furnace, the coarser the carbide. Stoichiometric WC is 6.13% carbon by weight.
Sources: ITIA: tungsten intermediates and their properties; USGS Open-File Report 2005-1028 (tungsten, 2005).
Wet milling with cobalt and grain growth inhibitors
Cemented carbide is hard carbide grains, mainly WC, held in a tough metal binder, most commonly cobalt. The powders are ball milled or attritor milled together; NTP describes milling in heptane or a similar solvent, with paraffin or polyethylene glycol (PEG) added as a pressing binder.
The recipe of a grade is fixed at the mill. Commercial grades generally run from 3% to 16% cobalt, and a 1999 thesis calls it common industrial practice to add a little carbon soot or tungsten powder during milling to reach the binder composition wanted.
Grain growth inhibitors go in too: carbides such as VC, Cr3C2, NbC and TaC that keep WC grains from growing too far during sintering. A 2012 paper calls vanadium carbide and chromium carbide by far the most effective, and says industry widely uses inhibitors for ultrafine WC-Co.
The slurry is then dried before pressing; a 2007 US study cited by NTP sampled the air at powder mixing, spray drying, screening and pressing.
Sources: ITIA: Cemented carbides, a success story (2010 newsletter); LLNL manuscript on WC-Co binders, 2018 (OSTI); NTP Report on Carcinogens background document: cobalt-tungsten carbide (2009/2010); University of Cape Town MSc thesis on WC-Co sintering (1999); Materials Science (Medziagotyra) 18(1), 2012: grain growth inhibitors; Int. J. Refractory Metals and Hard Materials, 2022 manuscript (OSTI).
Pressing, extrusion and injection molding
The shaping method follows the part. Inserts and mills, made in large lots with fairly simple shapes, are die pressed to final shape, and large parts such as rolls, hobs and anvils are mainly cold isostatically pressed as a block, then machined. Cylindrical parts and parts with a large length-to-diameter ratio are extruded, with waxes added so the mix flows through the die, and rods can then be ground into drills and end mills.
Small, complex parts are made by powder injection molding (PIM), in which feedstock of powder and a removable binder is molded, debound and sintered.
A pressed, unsintered part is called green. Held together by paraffin or a similar agent, it is soft enough for lathes and milling machines, and some parts are presintered at 500 to 800 °C first to strengthen the porous body.
Sources: ITIA: Cemented carbides, a success story (2010 newsletter); NTP Report on Carcinogens background document: cobalt-tungsten carbide (2009/2010); ITIA: Recycling of tungsten products, part 1 (2018); Journal of Metals, Materials and Minerals 17(1), 2007: injection moulding WC-Co.
Sintering: vacuum, sinter-HIP and shrinkage
Sintering is the heat treatment that turns the green part into solid carbide, and NTP notes the material is sometimes called sintered carbide. NTP gives 1,350 to 1,550 °C; a 1999 thesis puts the low end with high-cobalt grades and the high end with low-cobalt grades, usually in vacuum.
NTP says sintering also removes the paraffin or other temporary binder. One 2017 lab schedule, for WC-Co with an added (Ti,Zr)C carbide, dewaxed green parts at 450 °C for 2 hours under argon and hydrogen, then sintered them in vacuum at 1,410 °C for 1 hour.
The furnace stays below the melting point of both ingredients. A 2022 paper describes WC-Co as liquid-phase sintered at 1,370 to 1,425 °C, below the melting points of both WC (about 2,800 °C) and pure cobalt (1,495 °C).
ITIA wrote in 2010 that sintering is done in vacuum or under hydrogen, and that pressure-aided sintering (sinter-HIP) had become standard for defect-free, high-strength material. A 2020 paper describes the cycle ending with gas pressure raised up to 10 MPa to remove the last porosity, and says that step proves insufficient, especially for grades with less than 10 wt% cobalt.
The result is dense, with residual porosity commonly below 0.02 vol%. ITIA gives a "lateral shrinkage between 17 and 24%" as the pores close. At 20%, a green blank 15 mm across comes out at 12 mm, so it is pressed larger than the finished size.
Sources: NTP Report on Carcinogens background document: cobalt-tungsten carbide (2009/2010); NTP Report on Carcinogens profile: cobalt-tungsten carbide; University of Cape Town MSc thesis on WC-Co sintering (1999); Materials (Basel) 2017, 10(1):57: WC-Co sintering study; Materials (Basel) 2022, 15(3):1187; ITIA: Cemented carbides, a success story (2010 newsletter); Annales de Chimie, Science des Materiaux 44(4), 2020.
Diamond grinding and finishing
Sintered parts are typically finished by wet or dry grinding. An end mill shrinks a great deal in the furnace, and its final shape is formed by post-sinter grinding with diamond tools. ITIA notes that the better the milling, granulation, pressing and sintering, the less must be ground away.
Some parts are then coated, with titanium nitride for example. The grinding sludge left behind is what ITIA counts as soft scrap; the toxicity page covers the dust.
Sources: NTP Report on Carcinogens background document: cobalt-tungsten carbide (2009/2010); ITIA: Cemented carbides, a success story (2010 newsletter); ITIA: Recycling of tungsten products, part 2 (2019).
The recycling loop: zinc process and chemical routes
Used carbide re-enters this chain at two points: the zinc process returns it as ready-to-press powder before step 8, and chemical recycling returns it as APT at step 2.
In the zinc process, hard scrap is sorted by grade, cleaned of braze, crushed and immersed in molten zinc under argon. The zinc reacts with the binder and bloats the pieces; once it is vacuum-distilled off, the porous material is milled, screened and carbon-adjusted, ready to press. ITIA says the powder keeps the scrap's composition, and USGS says the process "is not a purification process", so oil, solder and coatings must come off first.
Chemical recycling takes almost any carbide scrap, including soft scrap. Usually the scrap is oxidized and leached with sodium hydroxide into sodium tungstate, a cobalt-bearing sludge is filtered out, and the purified solution becomes virgin-quality APT. ITIA (2019) puts hard scrap in Europe and the US at about a third zinc and two-thirds chemical.
A 2005 USGS report cites ITIA statistics that in 2001 an estimated 70% of the APT made by reporting companies in Europe, Japan and the United States came from scrap, and ITIA says cutting inserts are recycled at above 95% in industrial settings.
A worn insert or a drum of grinding sludge still holds the WC and cobalt from all eleven steps. Send photos, what form it is in and about how much it weighs through the quote form; we pay the shipping from anywhere in the US, or pick up in every city in California, Arizona and Nevada. See selling tungsten carbide.
Sources: USGS Open-File Report 2005-1028 (tungsten, 2005); USGS Open-File Report 01-349 (2001); ITIA: Recycling of tungsten products, part 2 (2019); ITIA: supply and circularity.
Questions people ask
What is sintered carbide?
Another name for cemented carbide: tungsten carbide grains bound with a metal, usually cobalt, and made solid by sintering pressed powder.
Is tungsten carbide melted and cast like steel?
Cemented carbide is not. It is pressed from powder and sintered below the melting point of WC. Fused (cast) tungsten carbide is a different product: tungsten and WC are melted together, cast and quenched into hard particles for hardfacing.
Can carbide be machined before it is sintered?
Yes. A green part is soft enough to turn or mill, and some are presintered first for strength. Once sintered, it is ground with diamond tools.
Can old carbide be made into new carbide?
Yes. The zinc process turns clean, sorted hard scrap back into powder of the same composition, and chemical recycling turns almost any carbide scrap back into APT. We buy worn and broken carbide in any form through the quote form.
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.