Introduction
When planning a successful metal cutting process, the choice of cutting tool material is an important consideration.
A basic understanding of each cutting tool material and its properties is essential for making the right choice. Considerations include the workpiece material to be machined, the type and shape of the part, machining conditions, and the required surface quality level.
This section presents information about each cutting tool material, its advantages, and best-use recommendations.
Cutting tool materials exist in many combinations of hardness, toughness, and wear resistance, and they are divided into many materials with specific properties. In general, cutting tool materials that perform successfully within their field of application should have the following properties:
- Sufficient hardness with resistance to flank wear and deformation
- High enough toughness to resist catastrophic failure
- Non-reactive with the workpiece material
- Chemical stability, with resistance to oxidation and diffusion wear
- Thermal fatigue resistance
Coated Carbide Cutting Tool Materials
- Coating – CVD
- Coating – PVD
- Carbide
What are coated carbide cutting tool materials?
Currently, coated carbides account for 80–90% of all cutting inserts. Their success as a cutting tool material can be attributed to the unique combination of wear resistance and toughness, along with the ability to be manufactured in complex shapes.Coated carbide is a combination of carbide and coating. Together they form materials tailored for specific applications.
Coated carbides are the first choice for a wide range of applications.
Coating – CVD
Definition and properties
CVD stands for Chemical Vapor Deposition. CVD coatings are formed through chemical reactions at high temperatures between 700–1050 °C.CVD coatings offer high wear resistance and excellent adhesion to the carbide substrate.
The first CVD-coated carbide introduced to the market was a single-layer titanium carbide (TiC) coating. Later, aluminum oxide (Al2O3) coatings and titanium nitride (TiN) coatings were introduced. Today, titanium carbonitride coatings (MT-Ti(C,N) or MT-TiCN, also called MT-CVD) are widely used because they bond well with carbides and other coatings, greatly improving material performance.
Modern CVD coatings typically combine MT-Ti(C,N), Al2O3, and TiN. Continuous improvements in adhesion, toughness, and wear resistance have been achieved through microstructure optimization and advanced post-treatment technologies, significantly enhancing coating performance. See Inveio™ technology.
MT-Ti(C,N) – High hardness provides very high resistance to abrasive wear, reducing flank wear.
CVD-Al2O3 – Chemically inert with low thermal conductivity, offering high resistance to crater wear. It also serves as a thermal barrier to improve resistance to plastic deformation.
CVD-TiN – Improves wear resistance and is used for wear detection.
Post-treatment – Improves cutting edge strength and reduces the tendency for chip adhesion.
Applications
CVD-coated grades are the first choice in a wide variety of applications where wear resistance is critical. These include general turning and boring of steel (where thick CVD coatings provide crater wear resistance), general turning of stainless steels, and milling grades for ISO P, ISO M, and ISO K materials. For drilling, CVD grades are typically applied to peripheral inserts.Coating – PVD
Definition and properties
Physical Vapor Deposition (PVD) coatings are formed at relatively low temperatures (400–600 °C). The process involves metal atoms or molecules reacting with nitrogen and other elements to form hard nitride coatings on the cutting tool surface.The high hardness of PVD coatings increases wear resistance. Residual compressive stresses further enhance cutting edge strength and resistance to comb cracks. See Zertivo™ technology.
The main PVD coating components are described below. Modern coatings consist of these components arranged in specific sequences, including multilayer composite coatings. These multilayers consist of many nanometer-thick layers, providing higher hardness.
PVD-TiN – Titanium nitride was the first PVD coating on the market. It offers good all-around performance and is golden yellow in color.
PVD-Ti(C,N) – Titanium carbonitride is harder than titanium nitride (TiN), improving resistance to flank wear.
PVD-(Ti,Al)N – Titanium aluminum nitride combines high hardness and oxidation resistance, improving overall wear resistance.
PVD oxide coatings – Used for their chemical inertness and strong resistance to crater wear.
Applications
PVD-coated grades are recommended for applications requiring both cutting edge strength and sharp edges, as well as when machining sticky materials. These applications are very broad, including all solid end mills and solid drills, as well as most grades used for grooving, threading, and milling. PVD-coated grades are also widely used for finishing operations and as central inserts in drilling.Carbide
Definition and properties
Carbide is a powder-metallurgical material; this composite consists of tungsten carbide (WC) grains and a cobalt (Co) metal binder. Carbides for metal cutting applications contain more than 80% hard-phase tungsten carbide. Other important components often added include cubic carbonitrides, especially in gradient-sintered grades. Carbides are formed into blanks by powder pressing or injection molding, followed by sintering to full density.Tungsten carbide grain size is one of the most important parameters for adjusting the hardness/strength balance of a grade; for a given binder content, finer grains result in higher hardness.
The cobalt binder content and composition are used to control toughness and resistance to plastic deformation. At equal tungsten carbide grain sizes, higher binder content improves toughness but increases susceptibility to plastic deformation wear. Too little binder leads to brittleness.
Cubic carbonitrides, also called the γ phase, are often added to improve hot hardness and form cobalt-enriched zones (gradient sintering).
Gradient sintering perfectly combines higher resistance to plastic deformation with higher cutting edge strength. Cubic carbonitrides enrich the cutting edge for high hot hardness, while cobalt-rich structures away from the edge better resist crack propagation and chip hammering.
Applications
Medium-grain to coarse-grain tungsten carbide
Medium- to coarse-grain tungsten carbide provides the best balance of hot hardness and strength. These materials, combined with CVD or PVD coatings, are used in grades suitable for all applications.
Fine-grain or ultrafine-grain tungsten carbide
Fine- or ultrafine-grain tungsten carbide is typically used with PVD coatings to ensure sharp edges with high strength. They also have excellent resistance to thermal and mechanical cycling loads. Typical applications include solid carbide drills, solid carbide end mills, parting and grooving inserts, milling, and finishing grades.
Gradient-sintered carbides
The superior properties of gradient-sintered carbides, in combination with CVD coatings, are successfully applied in turning of steels and stainless steels, as well as in many parting and grooving grades.
Uncoated carbide
What is uncoated carbide?
Uncoated carbides account for a very small share of the total cutting tool category. These grades are either pure tungsten carbide/cobalt composites or contain large amounts of cubic carbonitrides.Applications
Typical applications for these materials include machining HRSA (heat-resistant superalloys), titanium alloys, and low-speed turning of hardened materials.Uncoated carbides wear faster but in a controlled manner, with a self-sharpening effect.
Cermet Cutting Tools
What is cermet?
Cermet is a carbide mainly based on titanium. The name “cermet” is derived from a combination of “ceramic” and “metal.” Traditional cermets are composites of titanium carbide (TiC) and nickel. Modern cermets are nickel-free and consist mainly of titanium carbonitride Ti(C,N), with additions of (Ti,Nb,W)(C,N) and other hard phases, combined with a cobalt-based binder.Ti(C,N) increases wear resistance, other hard phases improve plastic deformation resistance, and cobalt controls toughness.
Compared with carbide, cermet has higher wear resistance and lower tendency for adhesion. On the other hand, it has lower compressive strength and poorer thermal shock resistance. Cermets can also be PVD-coated to further improve wear resistance.
Applications
Cermets are frequently used in machining sticky materials where built-up edge is a problem. Their excellent self-sharpening ability helps maintain low cutting forces even after long cutting times. In finishing operations, this ensures long tool life, close tolerances, and shiny surfaces.Typical applications include finishing of stainless steels, ductile irons, low-carbon steels, and other ferrous materials.
Tips:
- Use low feed and small depth of cut
- Replace inserts when flank wear reaches 0.3 mm
- If thermal cracks and edge chipping occur, stop using coolant.
Ceramics
What are ceramics?
All ceramic cutting tool materials have excellent wear resistance at high cutting speeds.There is a wide range of ceramic grades available for different applications.
Oxide ceramics are alumina (Al2O3)-based ceramics, with zirconia (ZrO2) added to suppress cracking. These materials are highly chemically stable but lack thermal shock resistance.
(1) Mixed ceramics are reinforced with carbide or carbonitride (TiC, Ti(C,N)) particles, improving strength and thermal conductivity.
(2) Whisker-reinforced ceramics contain silicon carbide whiskers (SiCw), which significantly increase strength and enable use with coolant. Whisker-reinforced ceramics are ideal for machining nickel-based superalloys.
(3) Silicon nitride ceramics (Si3N4) consist of elongated grains that form a self-reinforcing structure with high strength. Silicon nitride is very successful for machining grey cast iron but limited in other materials due to poor chemical stability.
Sialon ceramics combine the strength of self-reinforced silicon nitride with the chemical stability of alumina-based ceramics, making them ideal for machining HRSA.
(1) Mixed ceramics
(2) Whisker-reinforced ceramics
(3) Silicon nitride ceramics
Applications
Ceramic grades can be used for a wide range of applications and materials, most commonly for high-speed turning, but also for grooving and milling. Correctly applying the unique properties of each ceramic grade ensures high productivity. Knowledge of when and how to use ceramics is a key success factor.Limitations of ceramics include lower thermal shock resistance and fracture toughness.
Cubic Boron Nitride
What is cubic boron nitride?
Cubic boron nitride (CBN) is a cutting tool material with excellent hot hardness, suitable for very high cutting speeds. It also provides good strength and thermal shock resistance.Modern CBN grades typically contain 40–65% CBN with a ceramic binder. The chemically wear-resistant ceramic binder improves crater wear resistance. Another type of CBN contains 85% to nearly 100% CBN, usually with a metallic binder for improved toughness.
CBN is brazed onto carbide substrates to form inserts. Safe-Lok™ technology greatly enhances bonding strength of CBN tips to negative inserts.
Applications
CBN grades are mainly used for finish turning of hardened steels above 45 HRc. For steels harder than 55 HRc, CBN is the only cutting tool that can replace traditional grinding methods. In softer steels below 45 HRc with higher ferrite content, CBN wear resistance is negatively affected.CBN can also be used for high-speed roughing of grey cast irons in turning and milling operations.
Polycrystalline Diamond
What is polycrystalline diamond?
PCD is a composite of diamond particles sintered with a metallic binder. Diamond is the hardest of all materials, and thus the most wear resistant. As a cutting tool material, PCD offers excellent wear resistance, but lacks chemical stability at high temperatures and dissolves in iron.Applications
PCD tools are limited to cutting non-ferrous materials such as high-silicon aluminum alloys, metal-matrix composites (MMC), and carbon-fiber-reinforced plastics (CFRP). With abundant coolant flow, PCD tools can also be used for ultra-finishing of titanium alloys.The choice of cutting tool material determines not only tool life but also machining performance, productivity, and cost-efficiency. By understanding the properties, strengths, and limitations of each material—from coated carbides and ceramics to CBN and PCD—manufacturers can make informed decisions that optimize cutting processes and achieve superior results across a wide range of applications.
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