Start with the grade and the working conditions
A cobalt percentage alone does not specify a cemented carbide. The hard carbide phase supplies hardness, while the metallic binder contributes toughness. Binder content and carbide grain size both influence the resulting properties. Suppliers generally state binder content as a mass fraction; confirm that basis before comparing percentages. CERATIZIT: cemented carbide
For a replacement part, collect the current grade designation, drawing, operating conditions and evidence of how it wears or breaks. Ask the supplier to compare candidate grades against that starting point. A chipped edge is evidence to investigate, rather than a measurement of how many percentage points of cobalt to add.
What published grade data actually show
These examples come from General Carbide's grade specification chart, marked November 2025. They are that manufacturer's finished-material data, not NOC powder specifications or guaranteed results from a particular powder recipe. The chart reports average transverse rupture strength in psi. General Carbide: grade specifications, page 1
| Manufacturer grade | Grain class | Cobalt, wt% | Hardness, HRA | Average TRS, psi |
|---|---|---|---|---|
| GC-012F | Ultrafine | 12 | 92.2–93.7 | 475,000 |
| GC-206 | Fine | 6 | 91.2–92.7 | 480,000 |
| GC-315 | Medium | 15 | 87.8–90.3 | 520,000 |
| GC-320 | Medium | 20 | 85.1–86.8 | 470,000 |
Read each row as one named grade. GC-012F demonstrates that an ultrafine grade with more than 10 wt% cobalt is a published commercial material. Among the two medium-grain examples, the 20 wt% grade has lower listed hardness and lower average bending strength than the 15 wt% grade. These observations do not isolate cobalt as the only changing variable and should not be interpolated into a universal property calculator.
Keep strength and toughness separate
Transverse rupture strength (TRS) is a bending-test result. Fracture toughness, often reported as KIC, describes resistance to crack extension; it is a different property. A higher TRS number alone does not establish better impact performance in your part.
Hyperion explains that defects and specimen volume affect measured strength, and that different specimen geometries can produce different TRS results. Compare the test method, specimen geometry, units and reporting basis before ranking grades. Do not assume that strength rises indefinitely with cobalt content. Hyperion: mechanical strength
Ask for hardness, fracture-toughness and strength data relevant to the proposed grade and service conditions. For powder purchases, also agree how the supplier's reported grain size relates to the finished microstructure. An FSSS powder measurement is not a direct measurement of the grains in a sintered part.
Corrosion and magnetism need their own specification
For wet service, provide the fluid composition, concentration and operating temperature. Hyperion's corrosion discussion identifies pH, temperature and dissolved salts as relevant variables, and describes specially alloyed nickel-binder grades for corrosion resistance. Its laboratory comparisons do not turn a single pH value into an approval for every process fluid. Hyperion: corrosion resistance
If low magnetic response is required, specify the acceptance criterion and request a grade qualified for it. CERATIZIT identifies particular nickel-bound grades, including CTS17R NM, as non-magnetic for magnet-powder compaction. That is a grade-specific claim; the word “nickel” alone is not a magnetic specification. CERATIZIT: e-mobility applications
Make the trial answer the purchase question
Shortlist named grades with the supplier, keep the comparison conditions documented, and judge them against agreed wear, breakage, dimensional and service-life criteria. Include machining, rejects, maintenance and downtime when comparing cost. Select the composition that passes the application trial, then record its grade designation, material requirements and acceptance checks so the next order asks for the same result.