Cutting materials for machining and how to choose the right tool grade

In machining, cutting materials are the substances that form and support the cutting edge. The choice affects tool life, surface finish, cycle time and process reliability, but it is rarely a simple case of “harder is better.” High-speed steel, cemented carbide, cermet, ceramic, cubic boron nitride and polycrystalline diamond each fit a different set of workpiece and process conditions. A sound selection starts with the workpiece material, then checks cutting speed, interrupted cuts, machine rigidity, coolant strategy, tolerance, surface finish and total tool cost. This guide reviews the main cutting materials and gives a practical framework for choosing a tool grade.

For more machining context across tooling, inserts and process selection, see the Cutting & Tooling section on Mechmeld.

What cutting materials actually do in machining

A cutting material must hold a sharp, stable edge while exposed to high contact pressure, heat, abrasion, adhesion and chemical wear. In turning, milling, drilling and grooving, the cutting edge is not only removing metal. It is working in a small, severe contact zone where temperature and stress can change quickly.

That is why tool material selection is always a compromise between hardness and toughness. A very hard material can resist abrasive wear and keep its geometry at high cutting speeds, but it may fracture when the setup has vibration, scale, interrupted engagement or weak workholding. A tougher material can absorb shock, but it may wear faster at high temperature. Good machining decisions balance these two requirements instead of maximizing one property in isolation.

ISO 513:2012 is the key international standard used to classify and apply hard cutting materials for chip-removal machining with defined cutting edges. In practical tool catalogs, the familiar application groups P, M, K, N, S and H help connect cutting materials and grades to steel, stainless steel, cast iron, non-ferrous metals, heat-resistant superalloys and hardened materials.

The main cutting material families

High-speed steel

High-speed steel, usually shortened to HSS, remains useful where toughness, edge formability and low tooling cost matter more than maximum cutting speed. It is common in drills, taps, reamers, broaches, saws and custom form tools. HSS can take a relatively sharp edge and tolerates less rigid machines better than more brittle tool materials.

The main limitation is hot hardness. At higher speeds and temperatures, HSS loses wear resistance faster than carbide or ceramic materials. In production machining, HSS is usually selected for flexibility, complex tool shapes, small batch work or operations where carbide would be too brittle or uneconomical.

Cemented carbide

Cemented carbide is the default cutting material for a large share of modern metalworking. It is typically based on tungsten carbide particles bonded with cobalt, with grade chemistry, grain size and binder content adjusted to achieve different combinations of hardness and toughness. Carbide is used in indexable inserts, solid end mills, drills, burrs and wear parts.

Its strength is balance. Carbide can run much faster than HSS, handle a wide range of steels and cast irons, and still survive moderate interruptions when the grade and edge preparation are correct. Tougher carbide grades are used for roughing, interrupted cuts and unstable setups. Harder, more wear-resistant grades are used for finishing, high-speed cutting and stable processes.

Carbide performance is also closely linked to coatings. PVD and CVD coatings can reduce friction, add hot hardness, improve crater-wear resistance and protect the substrate. The coating does not replace the substrate decision; it refines it.

Cermet

Cermet combines ceramic and metallic characteristics. In cutting tools, cermets are often used where wear resistance, low adhesion and fine surface finish are more important than impact resistance. They are especially associated with finishing and light-to-medium machining of steels and some stainless steels.

Cermet can be a strong option when built-up edge is hurting finish or dimensional consistency. However, it is usually less tolerant of heavy interruption, chatter and rough scale than a tougher carbide grade. In simple terms, cermet rewards stable finishing conditions and punishes poor rigidity.

Ceramic cutting materials

Ceramic cutting materials include alumina-based ceramics, silicon nitride ceramics, SiAlON ceramics and whisker-reinforced ceramics. Their key value is hot hardness. They can operate at high cutting temperatures and high surface speeds in selected materials, particularly cast iron and nickel-based heat-resistant superalloys.

The tradeoff is fracture toughness. Ceramics generally need stable machines, strong clamping, suitable edge preparation and consistent engagement. They are often used dry because thermal shock from inconsistent coolant can be damaging in some ceramic applications. For continuous high-speed cuts, ceramics can remove material very quickly. For unstable cuts with heavy impact, carbide is often the safer choice.

Cubic boron nitride

Cubic boron nitride, or CBN, is a superhard cutting material used mainly for hard turning and difficult ferrous applications. Polycrystalline CBN tools are produced by sintering CBN particles with binders. They are valued for hot hardness and chemical stability in hardened steels, hard cast irons and some superalloy applications.

CBN is commonly considered when a shop wants to replace or reduce grinding in hardened components, such as bearing steels, tool steels or hardened shafts. It is not a universal roughing tool. CBN grades are expensive, and they need the right edge preparation, depth of cut and machine stability to justify their cost.

Polycrystalline diamond

Polycrystalline diamond, or PCD, is used where abrasion resistance and edge life are critical in non-ferrous and non-metallic materials. Typical applications include high-silicon aluminum, copper alloys, brass, graphite, carbon-fiber composites, glass-fiber composites and some plastics.

PCD is generally not the right choice for cutting ferrous steels at high temperature because diamond is carbon-based and can suffer rapid chemical wear in contact with iron under cutting conditions. In the correct non-ferrous application, however, PCD can deliver excellent surface finish and long tool life.

Quick comparison of common cutting materials

Cutting material	Primary strength	Typical use	Main limitation
HSS	Toughness and easy tool forming	Drills, taps, reamers, form tools and low-volume work	Lower speed capability than carbide
Cemented carbide	Balanced hardness, toughness and productivity	General turning, milling, drilling and grooving	Grade and coating must match the operation
Cermet	Wear resistance and surface finish	Stable finishing in steels and selected stainless steels	Less tolerant of shock and chatter
Ceramic	High hot hardness and high-speed capability	Cast iron and nickel-based heat-resistant alloys	Brittleness and sensitivity to unstable conditions
CBN	Superhard performance in hard ferrous materials	Hard turning, hard cast iron and selected superalloys	High cost and strict process requirements
PCD	Extreme abrasion resistance in non-ferrous materials	Aluminum, copper alloys, graphite and composites	Unsuitable for most hot ferrous cutting

Match the cutting material to the workpiece first

The workpiece material should be the first filter. A steel shaft, stainless valve body, gray iron casting, aluminum housing, Inconel component and 60 HRC bearing race do not fail cutting tools in the same way. Some generate continuous chips and heat. Some work-harden. Some are abrasive. Some create notch wear, chemical wear or built-up edge.

The ISO application groups are useful because they remind buyers and process engineers that the tool material must match the material being cut: See also: CNC Machining.

• P for steel: often machined with coated carbide, with cermet useful in stable finishing and CBN used only in specific hardened conditions.
• M for stainless steel: requires attention to work hardening, edge strength, heat and chip control; sharp PVD-coated carbide is often useful.
• K for cast iron: abrasive wear is important; carbide, ceramics and CBN can all be relevant depending on stability and speed.
• N for non-ferrous metals: sharp carbide and PCD are common, especially for aluminum, copper alloys and abrasive non-metallic materials.
• S for heat-resistant superalloys and titanium: heat, notch wear and chemical interaction drive grade choice; carbide and selected ceramics are common depending on the operation.
• H for hardened materials: CBN, ceramic and hard carbide grades may be used, depending on hardness, tolerance and interruption.

This classification is not a substitute for a toolmaker’s data sheet, but it prevents one of the most common mistakes: choosing a tool because it worked in another shop without checking whether the workpiece failure mode is the same.

Coatings, edge preparation and geometry are part of the material decision

In production machining, the cutting material is rarely selected on its own. The same carbide substrate can behave very differently with a sharp edge, a honed edge, a reinforced land, a PVD coating or a CVD coating. Coatings and geometry turn a raw material choice into a usable cutting edge.

PVD and CVD coatings

PVD coatings are often associated with thinner coatings and sharper cutting edges. They can be useful in applications that need lower cutting forces, sharper geometry or better performance on stainless steel and sticky materials. CVD coatings are generally thicker and can provide strong wear and heat resistance in many steel and cast iron operations, especially where the edge is stable enough to support them.

Kennametal’s technical guidance on solid carbide end mills emphasizes that coating selection depends on workpiece material, tool geometry, feed rate, spindle speed, application and coolant use. That principle applies beyond one brand: a coating is not a universal upgrade if the cutting data and process conditions do not let it work in its intended temperature and load range.

Edge preparation

A sharp edge lowers cutting force and can improve finish, but it is also more fragile. A honed or chamfered edge improves strength, but it increases cutting force and may require higher feed or more stable engagement. This matters especially for CBN, ceramic and hard carbide tools, where edge strength can determine whether the tool wears predictably or chips immediately.

For finishing aluminum with PCD, a very sharp polished edge may be desirable. For hard turning with CBN, a controlled hone or T-land may be necessary. For rough milling steel with carbide, the edge must survive entry and exit shock. In every case, edge preparation should match the operation, not just the material label.

A practical selection framework

When the catalog offers several cutting materials for the same workpiece, use a staged decision process:

1. Identify the workpiece group and condition. Confirm alloy family, hardness, heat treatment, scale, casting skin, inclusions and whether the material work-hardens.
2. Define the operation. Roughing, semi-finishing, finishing, grooving, threading, drilling and milling place different loads on the edge.
3. Check process stability. Long overhangs, weak fixturing, interrupted cuts and older machines favor tougher materials and more conservative grades.
4. Choose the speed range. If the machine cannot reach or hold the required speed, a high-speed ceramic or CBN strategy may not deliver its value.
5. Decide coolant strategy. Some materials and coatings benefit from coolant; some ceramic and high-temperature applications may be better run dry or with consistent coolant delivery.
6. Calculate total cost, not insert price. Tool cost per edge matters, but so do cycle time, scrap risk, downtime, finish consistency and secondary operations.

For example, a stable finish pass on hardened steel may justify CBN because it can hold size and reduce grinding. A rough interrupted cut on the same part may still need carbide. A high-silicon aluminum housing may justify PCD for finish and tool life, while a prototype batch may be more economical with sharp uncoated or coated carbide.

Cost, supply and sustainability considerations

Tool material selection is also affected by supply risk and material recovery. The U.S. Geological Survey describes tungsten’s largest use as tungsten carbide in cemented carbides, and its 2025 final critical minerals list includes tungsten and cobalt. That matters because cemented carbide supply chains depend on materials that are economically important and potentially exposed to supply disruption.

This does not mean carbide should be avoided. It means shops should manage carbide as a valuable industrial material. Insert recycling, tool-life tracking, correct grade selection and avoiding premature tool changes can reduce waste. In high-volume manufacturing, a slightly more expensive grade that runs predictably may reduce total cost by lowering scrap, tool inventory and unplanned downtime.

Superhard materials also require economic discipline. PCD and CBN can look expensive on a per-edge basis, but they may be justified if they remove grinding, stabilize finish, reduce tool changes or allow much higher throughput. They are poor choices when the machine, fixture or operation cannot support them.

Common mistakes when choosing cutting materials

• Choosing the hardest material by default. Hardness helps with wear, but low toughness can cause chipping in interrupted or unstable cuts.
• Ignoring the workpiece condition. Annealed steel, hardened steel and scaled forging stock can require different tool materials even when the alloy name is similar.
• Copying cutting data from a different setup. A grade that works in a rigid turning center may fail in a long-overhang boring operation.
• Treating coatings as a cure-all. Coatings help when the substrate, geometry, speed and heat conditions are suitable.
• Using PCD on the wrong materials. PCD is excellent for many non-ferrous and abrasive materials but is generally unsuitable for hot ferrous cutting.
• Underestimating edge preparation. Many tool failures blamed on “bad material” are actually edge-strength or geometry problems.

Frequently asked questions

What is the most common cutting material in CNC machining?

Cemented carbide is the most common choice across modern CNC turning, milling and drilling because it offers a strong balance of hardness, toughness, productivity and availability. HSS, ceramic, CBN and PCD remain important, but they are more application-specific.

When should a shop choose HSS instead of carbide?

HSS is useful for low-volume work, custom tools, complex forms, tapping, reaming and unstable setups where toughness and low cost matter more than cutting speed. Carbide is usually preferred when productivity, wear resistance and higher cutting speed are required.

Is ceramic better than carbide?

Ceramic is not universally better. It can outperform carbide in stable, high-speed applications such as cast iron or selected nickel-based superalloy machining. Carbide is usually better where impact, vibration, interruptions or process uncertainty are present.

What is the difference between CBN and PCD?

CBN is mainly used for hard ferrous materials such as hardened steels and hard cast irons. PCD is mainly used for non-ferrous and abrasive materials such as aluminum, graphite and composites. Both are superhard cutting materials, but they solve different machining problems.

How should cutting materials be tested in production?

Test one variable at a time: tool material, grade, coating, edge preparation, speed, feed or coolant. Track tool life, wear pattern, part finish, dimensional drift and scrap. A reliable tool is not only the one that lasts longest, but the one that fails predictably and supports the required part quality.