Ceramic inserts are excellent tools for achieving mirror-like surface finishes in turning operations. Let us first define what cermet (ceramic-metal composite) materials are.

Literally, the term refers to a combination of metallic and ceramic materials. The ASTM defines it as a heterogeneous composite material consisting of a metal or alloy and one or more ceramic phases, with the ceramic phase accounting for approximately 15% to 85% of the total volume.

They are produced by mixing metal carbide powders (such as WC, TiC, etc.) with binders (such as Co, Ni, etc.), followed by pressure forming and sintering.

I. Characteristics of Cermets

1. High hardness: Titanium carbonitride (TiCN)-based cermets possess higher hardness than tungsten carbide (WC)-based cemented carbides. Consequently, they are generally suitable for machining materials such as cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, and titanium alloys.

2. Excellent wear resistance and crater wear resistance: They exhibit very low wear rates during high-speed steel cutting operations.

3. High heat resistance: Cutting tools made from these materials can operate at temperatures between 1100°C and 1300°C. They support cutting speeds comparable to or exceeding those of WC-based carbides, reaching 200–400 m/min.

4. High oxidation resistance: The TiO2 formed upon the oxidation of TiC acts as a lubricant; thus, the oxidation level of Ti(C,N)-based cermets is approximately 10% lower than that of WC-based cemented carbides.

5. Good chemical stability: During cutting, TiCN-based cermet tools form thin films of Mo2O3, nickel molybdate, and TiO2 at the tool-chip interface. Even at temperatures of 700–900°C, adhesion is minimal and built-up edge (BUE) formation is unlikely. This helps improve workpiece surface quality, enabling the achievement of a mirror-like finish.

This characteristic makes them highly suitable for dry cutting, which helps reduce production costs.

2. Selecting the Right Cermet Inserts

Typical Cermet Materials

When formulating machining processes, it is essential to make the right choice between cemented carbide inserts and cermet inserts.

Unlike coated cemented carbide, cermet is not suitable for roughing operations. When large chips are generated, significant fluctuations in shearing action and cutting resistance occur; this continuous impact can lead to dimensional inaccuracies and, ultimately, tool breakage.

Furthermore, during operations involving large depths of cut, the impact of large chip coils against the tool flank exacerbates notch wear, thereby damaging the cermet tool. Such severe notch wear is particularly likely to occur when machining difficult-to-cut materials (such as nickel-, iron-, and cobalt-based heat-resistant alloys).

Consequently, cermet tools are generally unsuitable for machining difficult-to-cut materials. For this reason, coated cemented carbide tools are a better choice than cermet tools for both roughing and the machining of difficult-to-cut materials.

The figure above compares the tool life and material removal volume of cemented carbide, coated cemented carbide, and cermet when turning carbon steel. It is evident that high-speed cutting offers superior cost-efficiency due to the higher volume of material removed. Like CVD-coated cemented carbide tools, cermet tools are highly cost-effective options for high-speed cutting.

Examples of Tool Grades

Common examples include Seco’s TP1020 and TP1030; Sandvik Coromant’s CT5015 and GC1525; Kennametal’s KT5020; and Iscar’s IC20N and IC520N.

Can you recall which brands the following grades belong to—NX2525, NX3035, NS730, GT720, TN60, CT3000, CN1000, TT9080, TC430, and PV3010—and have you ever used them?