First establish what the size describes
A WC powder measurement and the grain size in a sintered carbide part describe different stages of the material. Ask whether the quoted value refers to incoming powder or the finished microstructure, and record the measurement method with the number.
FSSS uses air permeability to estimate an average equivalent particle diameter from a powder's specific surface area. It does not provide a particle-size distribution. Sample preparation and agglomeration matter, and the method is not intended for mixtures of different powders or powders containing binders or lubricants. ASTM B330: public scope and significance
For finished WC-Co hardmetal, ISO 4499-2 describes metallographic grain-size measurement using optical or electron microscopy and linear-intercept analysis. That is a different measurement from a powder Fisher number. Specify which result you need instead of using the two interchangeably. ISO 4499-2: measurement of WC grain size
| Information on a quotation | Question it helps answer | What to confirm |
|---|---|---|
| Powder FSSS result | How does this incoming powder compare under the agreed test? | Method, sample preparation and reported units |
| Finished WC grain size | What microstructure was measured after processing? | Microscopy method, reporting basis and acceptance range |
| Grade designation and composition | Which supplier material is being offered? | Binder type, binder mass fraction and specified additions |
| Finished-material properties | How does the proposed grade compare with the current grade? | Test method, specimen basis and typical versus guaranteed values |
These are complementary records. A matching powder FSSS number alone does not establish that two finished grades are equivalent. Keep the powder acceptance test, finished microstructure and grade property requirements distinct in the purchase specification. The table organizes the questions to ask; it does not assign a grade to an application.
Use grain size together with binder and grade data
Grain size affects performance alongside binder content and the rest of the grade design. In its material guidance, Hyperion describes WC-Co families by both cobalt content and WC grain size, including ultrafine grades developed for a combination of hardness, wear resistance and toughness. This does not support a rule that every fine grade is too brittle or that every coarse grade has higher strength. Hyperion: WC-Co grades
CERATIZIT describes finer grains as favoring hardness and wear resistance, and coarser grains combined with more binder as favoring fracture toughness. It also distinguishes transverse rupture strength from that trend: defects, microstructure and surface condition affect strength. Use these tendencies to shortlist materials, then compare the named grades' test data. CERATIZIT: grain size, binder and mechanical properties
The same CERATIZIT guide calls 0.8-1.3 micrometers fine grain and 2.5-6.0 micrometers coarse grain. Those are the classification ranges in that manufacturer's guide, not FSSS acceptance limits for a powder purchase. Ask the supplier to define its own label and measured range.
Start the comparison with the failure you need to reduce
If a part gradually loses its working dimensions through abrasive wear, ask for a finer, more wear-resistant candidate and check that its fracture performance still meets the application. If breakage under impact is limiting service life, ask for a tougher candidate; a coarser grade with a suitable binder content may belong in that comparison.
If the evidence is mixed, record both wear and breakage rather than selecting from the application name alone. Give the supplier the current grade, drawing, mating material, loading, operating conditions and photographs of used parts. Keep geometry and operating conditions documented during a trial so a change in service life can be interpreted.
For a polished working surface, specify the required finish and inspection method on the drawing. Ask for evidence that the proposed grade and finishing process meet it; a grain-class label alone is not an acceptance test for the surface.
Qualify the powder and the resulting part
For powder procurement, agree on incoming measurements and the finished-material checks that will establish suitability after your processing. Record the qualified formulation and process with the results. A universal furnace temperature or additive percentage cannot be selected from the word fine or coarse.
Compare candidates on accepted output and service performance, including finishing, rejects, maintenance and replacement frequency. Once a trial succeeds, retain the supplier grade designation, material specification and acceptance criteria for repeat orders. See the FSSS measurement guide for powder testing and the cobalt-content guide for binder comparisons.