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#089 Fundamentals of Steel Materials for Dies (8) Cemented Carbides Used in Dies

Category : Die Materials
August 5, 2011

Cemented carbides used in press dies are alloys of tungsten carbide (WC) and cobalt (Co). The main constituent of the material is tungsten carbide, and cobalt has the role of a binder (adhesive material). The amount of cobalt is in the range of 5 to 25%.

The hardness of cemented carbide decreases as the amount of cobalt increases.
This material has been stipulated into the types of V10, V20, V30, V40, V50, and V60 in the standard 019 of the Japan Cemented Carbide Tool Manufacturer's Association.
V10 has about 5% cobalt, V30 has about 12%, and V60 about 25%.
The hardness is 89 HRA or more in the case of V10, 87 HRA or more in the case of V30, and 78 HRA or more in the case of V60. By the way, 85 HRA is converted to 67 HRC.

Apart from the amount of cobalt, the hardness is also related to the size of WC particles. The hardness increases as the particle size becomes smaller. The particle size of ordinary cemented carbide is about 2.5 to 1.5 μm. Ultra fine particles have diameters in the range of 0.7 to 0.5 μm.
When the material has ultra fine particles, it is possible to enhance the properties of both wear resistance and brittleness.
Cemented carbide is a hard material but is also brittle. The material property is selected considering the balance between hardness and brittleness according to the intended application. V30 and V40 are about the standard for press dies.

In the case of blanking dies and punches, V30 is used for punches and V40 is used for dies. For bending and drawing, a slightly harder V30 and V20 are used giving priority to wear resistance. A softer V50 and V60 are used in compression forming in order to prevent breakage.
Even if the selection of the material is appropriate, if the surface roughness is bad, it may not be possible to satisfy the expected life even in the case of cemented carbide. Reducing the surface roughness by lapping is a very frequently used countermeasure in the case of cutting blades. However, when machining copper, nickel, and pure iron, the wear of cemented carbide may be fast. The reason for this is that the affinity between the cobalt present in cemented carbide and copper or nickel causes the wearing of the cemented carbide to progress faster.
Although cemented carbide appears to be hard and versatile, caution should be exercised because it may not meet the expectations depending on how it is used.

Although the standards of the Japan Cemented Carbide Tool Manufacturer's Association were used for the above explanations, the code used can be different for different manufacturers. Use the standards of JCCMA to compare and slelct the appropriate material.

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