Polycrystalline cubic boron nitride (PCBN) cutting tools have become the standard for machining hardened ferrous metals and cast iron where carbide and ceramic tools fall short. Within the PCBN category, the CBN content percentage — the proportion of CBN crystals in the composite — is the primary factor that determines a tool's toughness, wear resistance, thermal conductivity, and suitability for specific cutting conditions.
Selecting the correct CBN content grade is not simply a matter of choosing the hardest available option. A grade optimized for continuous high-speed finishing may fail catastrophically in an interrupted cutting application, while a tough grade suited for roughing may wear too quickly in a precision finishing operation. This guide explains how CBN content affects tool behavior and provides practical selection criteria to match the right grade to your workpiece material and machining conditions.
PCBN is a composite material consisting of CBN crystals bonded together by a ceramic or metallic binder. The ratio of CBN crystals to binder fundamentally governs the tool's mechanical and thermal properties:
| CBN Content | Primary Characteristics | Suitable Materials | Typical Applications |
|
40% – 60% (Low content) |
Maximum toughness; high impact resistance; resistant to chipping | Hardened steel, alloy steel, tool steel, die steel (HRC 45–65) | Interrupted cutting, gears, bearings, die components |
|
60% – 75% (Medium content) |
Balanced toughness and wear resistance; supports higher cutting speeds | Hardened steel, tool steel, high-speed steel | Continuous cutting, finishing, semi-finishing |
|
75% – 90% (High content) |
High hardness; excellent wear resistance; long tool life | High-hardness hardened steel, chilled cast iron, powder metallurgy materials | High-speed finishing, mirror finishing |
|
90% – 95%+ (Ultra-high content) |
Maximum wear resistance; superior thermal conductivity; lower toughness | Gray cast iron, high-chromium cast iron, hard alloy spray coatings | Continuous cutting, high-volume production, high-precision machining |
Low-content grades contain a higher proportion of binder material, which gives them the highest toughness among PCBN grades. This makes them the preferred choice for operations subject to cutting impact and vibration.
Key advantages:
● Highest binder content provides maximum toughness
● Withstands significant cutting impact without failure
● Resistant to chipping and edge fracture
Suitable workpiece materials:
● Hardened gears (various grades)
● 42CrMo hardened components
● GCr15 bearing steel
● SKD11, SKH9, and similar die steels
● Workpieces with interrupted cutting surfaces
Industry applications: Automotive gears, bearing manufacturing, die and mold production
This is the most commonly used general-purpose grade, offering a practical balance between the toughness of low-content grades and the wear resistance of high-content grades.
Key characteristics:
● Significantly improved wear resistance over low-content grades
● Retains good toughness for moderate cutting conditions
● Supports higher cutting speeds than low-content alternatives
Suitable workpiece materials:
● Hardened steel HRC 58–64
● Cr12MoV
● D2 tool steel
● High-speed steel
Applications: Shaft components, die components, hydraulic parts, continuous finishing operations
High-content grades are designed for high-efficiency machining where wear resistance and thermal management are the dominant requirements. They are not suitable for severe interrupted cutting due to their reduced toughness.
Key characteristics:
● Extremely high wear resistance
● Excellent thermal conductivity for heat dissipation
● Long tool life in stable cutting conditions
● Not recommended for severe interrupted cutting
Suitable workpiece materials:
● Hardened steel above HRC 60
● Chilled cast iron
● Powder metallurgy high-speed steel
Applications: Precision bearings, wind turbine gears, aerospace components
Ultra-high content grades maximize the proportion of CBN crystals, approaching the theoretical hardness limit of the material. They excel in continuous cutting of abrasive materials but have the lowest toughness.
Key characteristics:
● Highest CBN crystal ratio
● Best thermal conductivity for heat management
● Hardness approaching the theoretical maximum
● Relatively lower impact resistance
Suitable materials:
● Gray cast iron
● High-chromium cast iron
● Laser cladding layers
● Thermal spray coatings
Use the following reference to match common workpiece materials to recommended CBN content ranges:
| Workpiece Material | Recommended CBN Content | Recommended Grade Type |
|---|---|---|
| GCr15 bearing steel (HRC 60) | 50% – 70% | Low to medium content |
| 42CrMo hardened components | 45% – 65% | Low content |
| Cr12MoV | 55% – 75% | Medium content |
| SKD11 | 60% – 75% | Medium content |
| SKH9 high-speed steel | 60% – 80% | Medium to high content |
| Chilled cast iron | 80% – 95% | High to ultra-high content |
| Gray cast iron | 90%+ | Ultra-high content |
| Powder metallurgy high-speed steel | 75% – 90% | High content |
The following principles provide a practical framework for CBN grade selection:
Low CBN content (40% – 60%): Prioritize toughness. Suitable for interrupted cutting and impact-heavy conditions such as hardened steel, gears, and bearing components.
Medium CBN content (60% – 75%): Balanced overall performance. The mainstream choice for hardened steel, die steel, and high-speed steel machining.
High CBN content (75% – 95%): Prioritize wear resistance and thermal conductivity. Suitable for continuous high-speed finishing, high-hardness materials, and cast iron, but requires stable cutting conditions.
For PCBN insert substrates, CBN content in the range of 60% – 95% currently represents the mainstream market offering. Within this range, approximately 60% – 70% is well-suited for hardened steel finishing, while 80% – 90% and above is better matched to cast iron, powder metallurgy, and high-wear-resistance materials in high-efficiency continuous cutting applications.
We supply PCBN inserts across the full spectrum of CBN content grades — from tough 40%-60% grades for interrupted cutting of hardened steel to ultra-high 90%+ grades for continuous high-speed machining of cast iron and spray-coated surfaces. Our technical team can analyze your workpiece material, hardness, and cutting conditions to recommend the CBN grade, edge preparation, and insert geometry that will deliver the best balance of tool life, productivity, and part quality for your operation.
Contact us with your application details — including workpiece material, hardness, cutting mode (continuous or interrupted), and surface finish targets — and we will provide a tailored PCBN insert recommendation.
CBN content is the fundamental variable that determines how a PCBN tool will perform in a given application. Understanding the trade-off between toughness and wear resistance — and how it shifts across the 40% to 95% content range — enables engineers to make informed selections that match the tool to the workpiece and cutting conditions.
Low-content grades win in toughness-critical applications. Medium-content grades provide the versatility that most general-purpose hardened steel machining demands. High-content grades deliver the wear resistance and thermal performance needed for high-speed continuous cutting of the hardest materials. By applying the selection principles outlined in this guide, manufacturers can optimize tool life, reduce cost per part, and achieve consistent machining results across diverse ferrous metal applications.
For hardened steel (HRC 45-65), the recommended CBN content depends on cutting conditions. For interrupted cutting or impact-prone operations, use 40%-60% CBN for maximum toughness. For continuous finishing of HRC 58-64 steel, 60%-75% CBN is the most common general-purpose grade. For high-speed continuous cutting of HRC 60+ steel, 75%-90% CBN provides superior wear resistance and longer tool life.
Low CBN content (40%-60%) has higher binder content, providing maximum toughness and resistance to chipping under impact. High CBN content (75%-95%) has more CBN crystals, delivering superior hardness, wear resistance, and thermal conductivity, but with reduced toughness. Medium grades (60%-75%) balance both properties for general-purpose applications.
High CBN content grades (75%-90%) are generally not recommended for severe interrupted cutting due to their lower toughness and reduced resistance to impact loads. For interrupted cutting of hardened steel, lower CBN content grades (40%-60%) are preferred because their higher binder content provides better resistance to chipping and fracture.
For gray cast iron and high-chromium cast iron, ultra-high CBN content grades (90%-95%+) are recommended. These grades provide the maximum wear resistance and thermal conductivity needed for efficient continuous cutting of abrasive cast iron materials.
CBN crystals have higher thermal conductivity than the ceramic or metallic binders used in PCBN composites. As CBN content increases, the proportion of high-conductivity crystals increases, improving the tool's ability to dissipate heat from the cutting zone. This is why high-content grades perform better in high-speed applications where thermal management is critical.
