“What grade should I use?” is the most common question our application desk gets — and the honest answer is: it depends on how the part fails. Tungsten carbide isn't one material; it's a family tuned along two axes. Understand those axes and grade selection stops being guesswork.
The two levers
Cemented carbide is hard tungsten-carbide (WC) grains held together by a metallic binder, almost always cobalt (Co). Two variables do most of the work:
- Grain size — how large the WC particles are, from sub-micron (<0.5 µm) to coarse (>2.5 µm).
- Binder content — how much cobalt, typically 6% to 12% by weight.
Everything else — hardness, toughness, transverse rupture strength, wear life — flows from where you land on these two axes.
The fundamental trade-off
Finer grains and lower cobalt make the material harder and more wear-resistant, but more brittle. Coarser grains and higher cobalt make it tougher and more impact-resistant, but softer and quicker to wear. You are almost always trading hardness against toughness. The skill is knowing which one your application actually needs.
| Lever | Toward hardness / wear life | Toward toughness / impact |
|---|---|---|
| Grain size | Fine / sub-micron | Coarse |
| Cobalt binder | Low (≈ 6%) | High (≈ 10–12%) |
| Best against | Abrasion, high-speed wear | Impact, interrupted cuts, shock |
| Typical use | Finishing inserts, seal faces | Rock drilling, broaches, dies |
Start from the failure mode
Before choosing a grade, characterise how parts fail today:
- Flank and face wearing smooth, edges rounding → abrasion-dominated. Move harder: finer grain, lower cobalt.
- Edges chipping or corners fracturing → impact/shock-dominated. Move tougher: coarser grain, more cobalt.
- Both at once → you're in the compromise zone, where grain and coating strategy matter. Worth an engineering conversation.
Worked examples
- Mining button bits hammering granite: impact rules. A tough, coarser grade around 10–12% Co survives where a hard finishing grade would shatter.
- A precision seal ring running against a mating face: abrasion rules. A fine-grain, ~6% Co grade holds flatness and finish far longer.
- A general turning insert: a balanced medium grain at ~8% Co is the versatile middle ground.
The point isn't to memorise grades — it's to describe your failure mode accurately. Do that, and any good application engineer can put the right microstructure in your hand.
Written by Alok Kanani — Chief Executive Officer, Carbide India. General guidance, not a substitute for application-specific engineering advice.