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Selecting the appropriate cutting tool material is a critical factor in machining and metalworking, directly impacting productivity, surface quality, tool life, and overall manufacturing cost. This guide provides a clear comparison of cermet inserts, carbide tools, cubic boron nitride (CBN), and polycrystalline diamond (PCD), highlighting their material characteristics, typical applications, and economic considerations. With a deeper understanding of these cutting tool materials, manufacturers can make more precise and cost-effective tooling decisions for different machining operations.
In modern machining, selecting the right cutting tool material can significantly influence machining efficiency, surface quality, tool life, and overall production cost. The comparison of cermet inserts vs. carbide vs. CBN vs. PCD is therefore essential for machinists, manufacturing engineers, and procurement professionals alike.
Each cutting tool material delivers a distinct combination of hardness, toughness, wear resistance, and thermal stability, making it suitable for specific machining conditions and workpiece materials. This article explores the core characteristics, strengths, and limitations of cermet, carbide, cubic boron nitride (CBN), and polycrystalline diamond (PCD), helping you make confident and technically sound tooling decisions.
The term cermet is derived from “ceramic” and “metal,” reflecting its hybrid composition. Cermet inserts are typically manufactured from fine particles of titanium carbide (TiC) or titanium carbonitride (TiCN), bonded with a nickel- or cobalt-based metallic binder. This structure delivers a unique balance between ceramic hardness and metallic toughness, positioning cermet as an intermediate material between carbide and advanced ceramics.
Cermet inserts are especially valued for their thermal stability, chemical inertness, and ability to maintain a sharp cutting edge under stable machining conditions.
Advantages:
· Higher wear resistance than conventional carbide
· Excellent thermal and chemical stability
· Capable of producing superior surface finishes
· Reduced built-up edge when machining steel
Disadvantages:
· Lower fracture toughness compared to carbide
· More brittle, making them less suitable for interrupted cuts
· More limited grade selection and availability than carbide
Cermet inserts are commonly used in:
· Finishing and semi-finishing of carbon steel and alloy steel
· High-speed machining under stable cutting conditions
· Applications where surface finish quality is a critical requirement
Carbide inserts, commonly referred to as cemented carbide, are manufactured from tungsten carbide (WC) grains sintered together with a cobalt (Co) metallic binder. This microstructure provides an effective balance between hardness and toughness, allowing carbide tools to withstand a wide variety of cutting forces, temperatures, and machining conditions.
Thanks to continuous developments in grain size control, binder composition, and advanced coatings, carbide inserts remain one of the most adaptable and widely used cutting tool materials in modern manufacturing.
Advantages:
· Well-balanced combination of hardness and toughness
· Extensive range of grades optimized for different materials and cutting conditions
· Reliable wear resistance under both continuous and interrupted cuts
· Cost-effective solution for most general machining operations
Disadvantages:
· Lower hot hardness and oxidation resistance compared to ceramics and superhard materials
· Performance may be limited at very high cutting speeds
· Often requires PVD or CVD coatings to enhance wear resistance and tool life
Carbide inserts are extensively applied in:
· General-purpose machining of steel, stainless steel, cast iron, and non-ferrous metals
· Turning, milling, and drilling operations across multiple industries
· Roughing and semi-finishing operations where durability and versatility are required
Cubic boron nitride (CBN) is a synthetic superhard material, second only to diamond in terms of hardness. It is produced by converting hexagonal boron nitride into a cubic crystal structure under high temperature and high pressure. This unique structure gives CBN exceptional hardness and thermal stability.
Advantages:
· Extremely high hardness and wear resistance
· Excellent thermal stability at elevated cutting temperatures
· Outstanding performance when machining hardened steels
· Good chemical stability when cutting ferrous materials
Disadvantages:
· Higher cost compared with carbide and cermet
· Brittle nature requires stable cutting conditions and careful application
· Limited effectiveness and cost efficiency when machining softer materials
CBN is particularly suitable for:
· Machining hardened steels above 45 HRC
· High-speed machining of cast iron
· Finishing operations with tight dimensional tolerances
Polycrystalline cubic boron nitride (PCBN) is a composite form of CBN in which CBN particles are sintered together using ceramic or metallic binders. Compared with pure CBN, PCBN provides improved toughness, making it more suitable for interrupted cutting operations and a wider range of machining applications.
Polycrystalline diamond (PCD) is composed of diamond particles sintered together under high pressure and temperature, typically using a cobalt metallic binder. This manufacturing process produces an extremely hard cutting tool material with outstanding wear resistance and edge retention.
Advantages:
· Exceptional hardness and wear resistance
· Excellent thermal conductivity
· Capable of producing superior surface finishes
· Very long tool life in suitable applications
Disadvantages:
· Relatively high cost compared to carbide-based tools
· Chemical reactivity with ferrous materials at elevated temperatures
· Brittle nature requires stable machining conditions and careful application
PCD cutting tools are best suited for:
· Machining non-ferrous metals such as aluminum, copper, and brass
· Cutting highly abrasive materials, including fiberglass and carbon fiber composites
· Ultra-precision machining operations where surface quality is critical
When comparing cermet inserts vs. carbide vs. CBN vs. PCD, hardness is one of the most important reference factors. Based on relative material hardness, the ranking from lowest to highest is as follows:
· Carbide
· Cermet
· CBN
· PCD
While PCD offers the highest hardness, it is not universally applicable. Its chemical reactivity with ferrous materials limits its use in steel machining, meaning the hardest material is not always the most suitable choice.
The cost of cutting tool materials differs significantly depending on raw materials, manufacturing complexity, and performance capabilities. From the least expensive to the most expensive, the general cost ranking is:
· Carbide
· Cermet
· CBN
· PCD
Although CBN and PCD tools have higher initial costs, they can deliver superior performance and extended tool life in suitable applications, which may offset the higher investment over time.
· Cermet inserts: Best suited for finishing operations on steel and cast iron, delivering excellent surface quality under stable cutting conditions.
· Carbide: A versatile and reliable option for a wide range of materials and machining operations.
· CBN: Ideal for high-speed machining of hardened steels and cast irons.
· PCD: Provides unmatched performance when cutting non-ferrous and highly abrasive materials.
Is CBN harder than carbide?
Yes. CBN is significantly harder than carbide. On the Knoop hardness scale, CBN typically measures around 4000–5000 KHN, whereas carbide generally falls in the range of 1000–2000 KHN.
What are CBN inserts used for?
CBN inserts are mainly used for machining hardened steels above 45 HRC, cast irons, and other hard materials. They are especially effective in high-speed machining and finishing operations where tight tolerances are required.
Will a CBN wheel sharpen carbide?
Yes. CBN grinding wheels can effectively sharpen carbide tools. Due to its extreme hardness, CBN is well suited for grinding and sharpening carbide cutting tools, producing a precise and durable cutting edge.
What is the difference between PCD and CBN?
The key differences between PCD and CBN include:
· Hardness: PCD is harder than CBN
· Chemical stability: CBN is more stable when machining ferrous materials
· Applications: PCD is best suited for non-ferrous and abrasive materials, while CBN is preferred for hardened steels and cast irons
Why is CBN better for machining steel than PCD?
CBN performs better in steel machining due to its chemical stability at high temperatures. PCD tends to react with iron under high heat, leading to rapid tool wear, whereas CBN remains stable, enabling efficient machining of hardened steels and cast irons.
Is CBN harder than diamond?
No. Diamond, including PCD, is the hardest known material. CBN is the second-hardest material and offers advantages over diamond in specific applications, particularly when machining ferrous materials.
Why is CBN so expensive?
The high cost of CBN is mainly due to:
· A complex manufacturing process involving extremely high temperatures and pressures
· The need for synthetic production because of limited natural availability
· Specialized equipment and technical expertise required for production
· Strong industrial demand driven by its unique performance characteristics
When comparing cermet inserts vs. carbide vs. CBN vs. PCD, a clear understanding of the detailed composition and physicochemical characteristics of each material is essential. These fundamental properties directly explain their performance differences across various machining applications.
· Hard phase: Typically 70–85% by volume, consisting of titanium carbide (TiC), titanium carbonitride (TiCN), or titanium nitride (TiN)
· Binder phase: Usually 15–30% by volume, composed of nickel, molybdenum, and/or cobalt
· Density: 5.6–7.4 g/cm³, depending on composition
· Hardness: 1500–2200 HV (Vickers hardness)
· Thermal conductivity: 15–40 W/m·K
· Coefficient of thermal expansion: 7.0–8.5 × 10⁻⁶/K
· Transverse rupture strength: 1200–2500 MPa
· Young’s modulus: 400–450 GPa
Cermet materials combine the high hardness and wear resistance of ceramic phases with the toughness provided by metallic binders. The titanium-based hard phase delivers excellent hardness and abrasion resistance, while the metallic binder improves toughness and resistance to thermal shock.
· Hard phase: Typically 70–97% by volume, consisting of tungsten carbide (WC)
· Binder phase: Usually 3–30% by volume, primarily cobalt (Co)
· Density: 11.0–15.0 g/cm³, depending on cobalt content
· Hardness: 1000–1800 HV, inversely related to cobalt content
· Thermal conductivity: 50–100 W/m·K
· Coefficient of thermal expansion: 4.9–7.1 × 10⁻⁶/K
· Transverse rupture strength: 1500–3000 MPa
· Young’s modulus: 450–650 GPa
Carbide inserts provide a well-balanced combination of hardness and toughness. Tungsten carbide contributes hardness and wear resistance, while the cobalt binder enhances toughness and impact resistance. These properties can be tailored by adjusting carbide grain size and cobalt content.
· CBN crystals: 50–95% by volume
· Binder phase: 5–50% by volume, typically ceramic (e.g., TiN, AlN) or metallic (e.g., Co, Ni, Al)
· Density: 3.4–4.3 g/cm³
· Hardness: 4000–5500 HV
· Thermal conductivity: 100–200 W/m·K
· Coefficient of thermal expansion: 4.6–4.9 × 10⁻⁶/K
· Transverse rupture strength: 500–800 MPa
· Young’s modulus: 680–720 GPa
CBN is a synthetic superhard material with a cubic crystal structure similar to diamond. It exhibits exceptional hardness, high thermal stability, and strong chemical inertness, particularly when machining ferrous materials. Its relatively high thermal conductivity enables efficient heat dissipation during cutting.
· Diamond crystals: 90–95% by volume
· Binder phase: 5–10% by volume, typically cobalt
· Density: 3.5–4.0 g/cm³
· Hardness: 8000–10000 HV
· Thermal conductivity: 500–2000 W/m·K
· Coefficient of thermal expansion: 2.0–4.8 × 10⁻⁶/K
· Transverse rupture strength: 1200–1700 MPa
· Young’s modulus: 776–925 GPa
PCD consists of diamond particles sintered together with a metallic binder, usually cobalt. It offers extremely high hardness and wear resistance, along with outstanding thermal conductivity. However, PCD exhibits chemical reactivity with iron at elevated temperatures, which limits its suitability for machining ferrous materials.
When evaluating cermet inserts vs. carbide vs. CBN vs. PCD, several key physicochemical differences become evident:
· Hardness:
PCD > CBN > Cermet > Carbide
Higher hardness generally correlates with improved wear resistance and longer tool life in abrasive applications.
· Thermal conductivity:
PCD > CBN > Carbide > Cermet
Higher thermal conductivity enhances heat dissipation during machining, potentially allowing higher cutting speeds.
· Density:
Carbide > Cermet > PCD > CBN
Lower-density materials such as CBN and PCD can be advantageous for high-speed rotating tools by reducing centrifugal forces.
· Thermal expansion:
Cermet > Carbide > CBN > PCD
Lower thermal expansion coefficients provide better dimensional stability under temperature fluctuations.
· Transverse rupture strength:
Carbide > Cermet > PCD > CBN
Higher transverse rupture strength indicates better resistance to chipping and fracture, which is particularly important in interrupted cutting operations.
Understanding these detailed compositions and physicochemical characteristics is essential when selecting the most suitable cutting tool material for specific machining applications. The choice between cermet inserts vs. carbide vs. CBN vs. PCD should always be based on careful consideration of these properties in relation to the workpiece material, machining conditions, and desired performance outcomes.
In the comparison of cermet inserts vs. carbide vs. CBN vs. PCD, there is no universal solution that fits every machining scenario. The optimal choice depends on multiple factors, including:
· Workpiece material
· Machining operation (roughing, finishing, high-speed machining)
· Required surface finish
· Tool life expectations
· Budget constraints
A clear understanding of the individual properties, advantages, and limitations of each cutting tool material enables more informed and effective decision-making. While advanced materials such as CBN and PCD deliver superior performance in specific and demanding applications, traditional materials like carbide and cermet inserts continue to play a vital role in modern machining due to their versatility and cost efficiency.
As machining technologies and materials continue to evolve, staying knowledgeable about cutting tool materials remains essential for maintaining competitiveness. Whether machining conventional steels or more specialized materials, selecting the right cutting tool material is key to achieving optimal performance, consistency, and productivity.
