· KAIPU Engineering · material-comparison · 6 min read
YG6X vs YG8 Tungsten Carbide: Which Grade for Your Industrial Blade?
YG6X and YG8 are the two most-specified Chinese GB standard tungsten carbide grades for industrial knives. The 2 % cobalt difference looks small but it changes the wear-toughness trade, the impact resistance, and the substrate fit. Here is the engineering comparison.
Tungsten carbide is a powder-metallurgy composite of tungsten carbide (WC) grains in a cobalt (Co) binder. The single biggest material lever is the cobalt content: more Co = tougher, less wear; less Co = harder, more wear, more brittle. YG6X (6 % Co, fine grain) and YG8 (8 % Co, medium grain) are the two most-specified Chinese GB standard carbide grades for industrial knives. They sit in the same K-series (machining of cast iron, non-ferrous metals, non-metallic materials) but in different ISO 513 sub-classes: K10/K20 for YG6X, K20/K30 for YG8.
TL;DR: YG6X is harder and more wear-resistant, used where the cut is clean and the substrate is abrasive but not impact-loaded. YG8 is tougher and more impact-resistant, used where the cut includes contamination, variable feed, or occasional metal debris. For most paper, film and polymer slitters, YG6X. For granulator rotors, recycling and shear blades — YG8 or higher-Co grades.
The two grades in plain terms
| Property | YG6X (K10/K20) | YG8 (K20/K30) |
|---|---|---|
| Cobalt content | 6 % | 8 % |
| WC grain size | 0.8–1.2 µm (fine) | 1.2–2.0 µm (medium) |
| Density | 14.85–15.05 g/cm³ | 14.65–14.85 g/cm³ |
| Hardness | HRA 91.5–92.5 (~ HRC 80–81) | HRA 90.0–91.0 (~ HRC 78–79) |
| Transverse rupture strength | 1,800–2,000 MPa | 2,100–2,400 MPa |
| Compressive strength | 4,200–4,500 MPa | 4,000–4,300 MPa |
| Fracture toughness K_IC | 9–11 MPa·√m | 12–15 MPa·√m |
| Thermal conductivity | 80 W/m·K | 75 W/m·K |
| ISO 513 classification | K05–K20 | K20–K30 |
| Primary application | Wear parts, slitters, granulator bed knives | Impact-loaded parts, granulator rotors, shear blades |
The 2 % Co change does three things at once: drops hardness by ~ 1.5 HRA points, raises transverse rupture strength by 15–20 %, and roughly doubles the fracture toughness. In the field that translates to “YG6X will wear longer; YG8 will survive more impact events.”
Substrate-by-substrate recommendation
| Substrate / application | Recommended grade | Why |
|---|---|---|
| Paper slitter, top blade | YG6X | Wear life, clean cut, low impact |
| Tissue slitter | YG6X | Wear, tight burr control |
| Film slitter (PE, PP, PET) | YG6X | Wear, edge geometry control |
| Foil slitter (Al) | YG6X | Abrasive on long runs |
| Plastic granulator bed knife | YG6X | Wear on abrasive filled polymers |
| Plastic granulator rotor knife | YG8 or YG10X | Impact from contamination, metal debris |
| Recycling / shredder rotor | YG10X / YG15 | High impact, contamination |
| Corrugated slitter | YG6X | Abrasive liners, low impact |
| Corrugated scorer | YG6X | Abrasive, controlled cut |
| Stainless plate shear (≤ 4 mm) | YG8 or carbide insert | Impact, work hardening |
| Carbon steel plate shear (≤ 6 mm) | YG8 or carbide insert | Impact, ductile substrate |
| Food cutting (frozen meat, fish) | YG6X (low-Co) | Corrosion resistance, wear |
| Wood chipper | YG8 / YG10X | Impact, occasional metal |
The rule of thumb: if the line has contamination risk or impact events, move to ≥ 8 % Co (YG8 or higher). If the line is clean and wear-dominated, stay at 6 % Co (YG6X) for the longest life.
Grain size matters as much as cobalt
The “X” in YG6X (and in grades like YG10X) denotes a fine grain carbide — typically 0.8–1.2 µm WC grain vs 1.5–3.0 µm for the non-X grades. Fine grain delivers:
- 1.0–1.5 HRA points higher hardness at the same Co content.
- Better edge retention on a thin knife (carbide grains do not pull out at the edge).
- Tougher response to impact because the crack has to navigate a finer path.
For thin slitter blades (< 3 mm section) the X-grade is non-negotiable. For thick granulator rotors (15–25 mm) the grain size is less critical and the non-X YG8 is acceptable.
When the grade above or below is the right answer
- YG6 (no X): 6 % Co, coarse grain (1.5–2.5 µm). Cheaper; used for non-precision wear parts. Avoid for slitters.
- YG6X: the workhorse for slitting knives. 6 % Co + fine grain = best wear-to-toughness balance for clean cuts.
- YG8: general-purpose impact grade for granulator bed knives and rotor knives. The default carbide grade in most Chinese granulator-knife shops.
- YG10X, YG10: 10 % Co, fine or medium grain. For higher-impact granulator rotors, recycling rotors, shear blades. Toughness up, wear down by ~ 15 %.
- YG15, YG20: 15–20 % Co. For the most extreme impact (mining, primary shredders, hammer mills). Wear life half of YG6X, but survives blows that would shatter a YG6X blade.
- YG4C, YG6A: sub-grain ormium (TaC, NbC) additions for hot hardness and crater wear. Used in high-temperature cutting; rare in industrial knife applications.
Common field failures
- YG6X on a contaminated granulator rotor. Chipped edges after 1–2 weeks. Move to YG8 or YG10X.
- YG8 on a precision slitter. Edge pulls out faster than YG6X; burr grows. Move to YG6X with a 10 µm hone.
- Re-grinding on a standard abrasive wheel. Causes micro-cracking that explodes on the next impact. Diamond wheels only, with a controlled infeed (0.001–0.002 mm/pass) and flood coolant.
- Edge prep too sharp. Carbide micro-chips above 0.05 mm edge radius on impact substrates. Hone to 0.1–0.2 mm for granulator rotors.
- Mismatched hardness between bed and rotor knives. Bed knife harder than rotor accelerates rotor wear. Match or have the rotor 0.5–1.0 HRA softer.
- Brazing stress. Brazed carbide tips on a steel body can crack at the braze joint. Mechanical clamping or diffusion bonding is preferred for high-impact applications.
Edge prep and grinding
Carbide regrinding is a controlled process:
- Wheel: diamond, resin-bonded, 100–120 grit for roughing, 200–400 grit for finishing.
- Wheel speed: 25–30 m/s surface speed.
- Infeed: 0.002–0.005 mm/pass for roughing, 0.001 mm/pass for finishing.
- Coolant: flood, water-soluble, 5–8 % concentration.
- Spark-out: 2–3 passes at final depth to relieve grinding stress.
- Edge hone: 0.05–0.10 mm radius for slitters, 0.10–0.20 mm for granulator bed knives, 0.20–0.30 mm for granulator rotors.
If your regrind shop cannot meet these parameters, send the knife back to the OEM. A bad re-grind will cut carbide life in half.
Sourcing and certification
For a critical carbide blade, request:
- Mill certificate with Co content, WC grain size, hardness (HRA) andTRS.
- ISO 513 classification stamped on the blade.
- Magnetic particle or dye-penetrant test report for brazed joints.
- For medical / food-contact: cobalt-leaching test per regional regulation. [MISSING SPECIFICATION — confirm regional cobalt-migration limit]
If your drawing specifies a single carbide grade (e.g. “YG6X”), your supplier should be able to back it with a traceability document. If the supplier pushes a “K20 equivalent”, ask for the actual grade and Co content — “K20” is a class, not a material.
Cost model
For a 250 mm OD carbide slitter on a 1,200 m/min film line:
| Item | YG6X | YG8 |
|---|---|---|
| Initial knife cost | 100 % | 95 % |
| Regrinds per year | 0.5 | 0.8 |
| Service life on abrasive substrate | 100 % | 80 % |
| Annual edge cost | 100 + 0.5 × 60 = 130 % | 95 + 0.8 × 60 = 143 % |
| Annualised per hour of cut | 130 / (life) | 143 / (0.8 × life) = 1.79× baseline |
| Per-hour comparison | 1.0 (cheaper on clean cut) | 1.43× (more expensive) |
On a clean film line, YG6X is cheaper per hour. On a contaminated line where YG8 would survive 1.5× longer than YG6X, the cost equation flips.
The engineering recommendation
For an industrial machine knife, pick the carbide grade by impact, not by substrate. If the line is clean (paper, film, foil, neat polymer), YG6X. If the line has any contamination risk (recycling, granulator, metalwork), start at YG8 and move up. The wear difference is 20 %; the impact difference is 2×. Get the impact right first, then optimise wear.
For a copy of the full five-factor selection method, see The KAIPU 5-Factor Blade Selection Framework. For a coating comparison to extend carbide life further, see Coating Comparison Table. For a runnable carbide grade cross-reference, see Material Grade Converter.
For a written YG6X / YG8 quotation, send the part drawing, the substrate and the impact profile to engineering@kaipu-industrial.com or use the request-a-quote form. Specification, FOB quote and lead time within one business day.
About the author
KAIPU Engineering is the technical team at KAIPU Industrial Blades, in operation since 1998. ISO 9001:2015 certified. Ships to converters, recyclers and OEMs across four continents.