For B2B buyers selecting tungsten carbide rods or inserts, the single most common mistake is assuming "higher grade number equals better performance." In the ISO classification system, lower K-numbers mean harder and more wear-resistant, while higher K-numbers mean tougher and more impact-resistant.
K10 and K20 are the two most widely used grades in the K-series (cast iron and non-ferrous metals). Here is the definitive breakdown of how they differ and when to use each.
The fundamental difference lies in the cobalt content and grain size. Cobalt acts as a metallic binder that provides shock absorption. Therefore:
Low Cobalt + Fine Grain (K10): Maximum hardness and edge sharpness, but lower resistance to mechanical shock.
Higher Cobalt + Medium Grain (K20): Slightly lower hardness, but significantly higher transverse rupture strength and impact resistance.
The table below highlights the typical property envelopes for both grades based on ISO 513 standards.
Property | K10 | K20 |
|---|---|---|
Cobalt Content | 5–6% | 6–8% |
Tungsten Carbide (WC) | ~94% | ~92–94% |
Grain Size | Fine (0.5–1.0 µm) | Medium (1.0–2.0 µm) |
Hardness (HRA) | 91.5–93.0 | 90.5–92.0 |
TRS (MPa) | 1,600–1,900 | 1,900–2,300 |
Density (g/cm³) | 14.8–15.0 | 14.6–14.9 |
Wear Resistance | Highest | Moderate |
Toughness | Low | Medium |
Data compiled from ISO 513 standards and material testing references.
K10 is engineered for pure abrasive wear and high-speed precision. Its fine grain structure allows for an exceptionally sharp cutting edge, resulting in excellent surface finishes.
Ideal Conditions: Continuous cutting, high-speed finishing, low mechanical shock.
Typical Applications: Finish turning and boring of grey cast iron (GG25), precision machining of aluminum and copper alloys, PCB micro-drills, woodworking tools for abrasive panels, and wear parts like nozzles and seal rings.
Equivalent Grades: YG6A / YG6X (China), C3 / C4 (ANSI).
K20 hits the sweet spot between hardness and toughness. It is the most widely used general-purpose carbide grade because it can absorb vibration and intermittent shock without fracturing.
Ideal Conditions: Semi-finishing, light interrupted cuts, moderate impact, general-purpose machining.
Typical Applications: General milling and drilling of cast iron, automotive aluminum alloys, fiberglass, stone, and wood. Also widely used for bushings, plungers, and drawing dies.
Equivalent Grades: YG6 / YG8 (China), C2 (ANSI), Sandvik H13A.
The most frequent grade selection error is specifying K10 for roughing operations involving interrupted cuts. Because K10 is highly brittle, using it for heavy milling or rough turning on uneven castings will cause immediate micro-chipping and tool failure.
⚠️ Procurement Rule: If your operation involves any interruption in the cut—such as milling with chip breakers, turning scale-encrusted castings, or drilling cross-holes—always step up to at least K20 or K30. The slight loss in wear resistance is vastly outweighed by the prevention of catastrophic tool breakage.
Quote based on drawings
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