Carbide Grades Explained
Choosing the right grain size for your application — from roughing steel to finishing titanium.
The grade of a carbide tool determines its hardness, wear resistance, and toughness. Choosing the wrong grade leads to premature tool failure, poor surface finish, or chipping. Here's what you need to know.
What is Carbide Grade?
Carbide grade refers to the grain size of tungsten carbide particles in the tool material, measured in microns (µm). Smaller grains = harder and more wear-resistant but more brittle. Larger grains = tougher and more impact-resistant but wear faster.
Grade Comparison
| Grade | Grain Size | Hardness (HRA) | Best For | Price |
|---|---|---|---|---|
| Submicron | 0.2-0.5 µm | 92.5-93.5 | Finishing, hardened steel (HRC 55+) | $$$ |
| Ultrafine | 0.5-0.8 µm | 91.5-92.5 | General purpose, stainless steel | $$ |
| Fine | 0.8-1.5 µm | 90.5-91.5 | Steel roughing, cast iron | $ |
| Medium/Conventional | 1.5-5 µm | 89.5-90.5 | Heavy roughing, interrupted cuts | $ |
Which Grade for Your Material?
Steel (General)
For general steel machining up to 45 HRC, ultrafine grade (0.5-0.8 µm) offers the best balance of tool life and cost. For high-volume production, submicron grades will last longer but cost more per tool.
Hardened Steel (45-65 HRC)
Use submicron grade (0.2-0.5 µm) with TiSiN coating. The fine grain structure provides the edge strength needed to withstand high cutting temperatures without deformation.
Stainless Steel
Ultrafine grade with AlTiN coating is the standard choice. The sharp edge geometry possible with fine grain sizes helps reduce work hardening.
Aluminum
Standard fine or ultrafine grade, uncoated or DLC coated. Sharp cutting edges are critical — avoid submicron grades as they may chip under the high speeds used for aluminum.
Titanium & Superalloys
Submicron grade with TiSiN coating. These materials require maximum heat resistance and edge hardness. Expect shorter tool life regardless of grade choice.
How to Verify Grade Quality
When sourcing from manufacturers, request the following:
- Material test certificate (MTC) with grain size measurement
- Hardness test results (HRA should be ≥90.5 for quality tools)
- TRS (Transverse Rupture Strength) — higher is tougher
- Cobalt content percentage — affects hardness vs toughness balance