Cemented Carbide Grades Explained: Grain Size, Cobalt Content, and HRA Hardness
A practical guide to how WC grain size and cobalt binder content set the hardness-toughness balance of cemented carbide, and how to read HRA values.
What cemented carbide is made of
Cemented carbide (hardmetal) is a powder-metallurgy composite: hard tungsten carbide (WC) grains bonded by a ductile cobalt binder. The WC phase contributes extreme hardness — up to about 2,200 HV in the pure phase — while cobalt gives the material the toughness that lets a tool survive impact.
Almost every grade decision comes down to two levers: WC grain size and cobalt content. Working hardness for industrial parts typically falls between 85 and 93.5 HRA on the Rockwell A scale.
Grain size: the Hall-Petch lever
Finer WC grains raise hardness and wear resistance; coarser grains improve toughness. The industry groups grain sizes roughly as follows:
- Nano and ultrafine (below ~0.5 µm): highest hardness, used for micro-drilling and precision wear parts
- Fine and submicron (0.5–1.5 µm): high hardness with good strength, typical for cutting tools
- Medium (1–5 µm): balanced wear and toughness for general engineering parts
- Coarse (above 5 µm): maximum toughness for mining and impact tools
Cobalt content: the toughness lever
Cobalt content typically ranges from about 3% to 20% by weight. More binder means a tougher, more impact-resistant part at lower hardness; less binder pushes hardness and wear resistance up. Mining inserts and HPGR studs sit toward the tougher end; precision balls and seal rings toward the harder end.
Grade names such as YG6, YG8, or YG10 group binder contents (6%, 8%, 10% Co respectively) and remain a common shorthand between Chinese suppliers and international buyers.
Reading HRA values in quotations
When a quotation lists hardness as, for example, 88.5 HRA with 8% cobalt and a 1.2 µm grain size, the three numbers should be internally consistent. If hardness looks high for the cobalt content, ask which grain size class and which test method the value is based on — consistency here predicts how repeatable the grade will be across production lots.
- Ask for hardness together with density and cobalt content, not hardness alone
- Request the reference grain-size class for the grade being quoted
- For critical parts, agree the inspection sampling plan before the first production lot
Summary
Grain size sets hardness; cobalt sets toughness. Buyers who specify the pair — plus an HRA acceptance band — give the supplier an unambiguous target and make incoming inspection straightforward.