Cemented Carbide Property Facts

1. Wear resistance

The most important characteristic of Cemented Carbide is its wear resistance. This combination of properties is related to surface phenomena. When two surfaces slide against each other, material will be removed from both of them. At a low load, this loss of material will take place through the loss of single grains or parts of single grains. This process is generally referred to as attrition. At higher load, the loss of material takes place by clusters of grains becoming detached. This process is known as abrasion. Both these processes, leading to loss of surface material, contribute to wear. In practice, the material loss is often also affected by the local environment, particularly if corrosion or oxidation is encountered. The nature of wear is very complex and the wear rate depends on many variables.

2. Toughness

When components in tools like carbide rolls are exposed to external loads, static or dynamic, mechanical stresses occur within the material. The mechanical strength and deformability of the material are therefore important. In many cases, particularly in carbide rolls, when dealing with shock loading, both these characteristics must be considered at the same time. This forms the background to the term “toughness” which can be defined as “the ability to resist fracture”, for example, a complete separation into at least two parts.

Different Cemented Carbides show large differences in toughness. The Palmqvist method is commonly used for determining the toughness of Cemented Carbides. The results of toughness tests show that this property increases with increasing binder content, and with increased WC grain size.

3. Hardness

The hardness, being of a high order, requires for accurate measurement some specialization in both equipment and specimen preparation. Hardness is normally determined using the Vickers indentation method according to EN 23 878 (ISO 3878). This method allows a range of loads but HV30 is preferred. The force of a 30 kg weight, 294 N, is used to create a measurable indentation with minimal cracking at the corners. For the hardest grades, the size of the impression and cracking contribute to reduced precision and accuracy.

4. Transverse rupture strength

Transverse rupture strength (TRS) or bending strength testing is the simplest and most common way of determining the mechanical strength of Cemented Carbide used in cemented components and tools. Owning to lack of ductility in carbide, tensile strength is difficult to measure with any degree of accuracy.

Transverse rupture is a more convenient and consistent basis of comparison and is calculated from the ultimate loading applied at the centre of a specimen supported between two fulcrum edge. The figures tend to vary inversely with hardness and range from about 180 tons /sq. in. for the soft tougher grade down to about 80 tons /sq. in. for the very hard cutting grades.

5. Modulus of Elasticity

Cemented carbide is generally regarded as a non-ductile material. Young’s modulus of elasticity is some two to three times that of steel. This property means extremely high deflection, and is used in solid carbide tooling, bars, precision spindles and other components where rigidity must be maintained under heavy loading. It is a feature which must also be taken into consideration designing combined steel and carbide parts where the relative sections of the two materials must be such as to equate, at least, the defection throughout the stress pattern.

6. Thermal properties

As tungsten carbide has a very low linear expansion coefficient, WC-Co Cemented Carbides have values of approximately half that of ferritic and martensitic steels while the ratio to austenitic steels is about 1:3.

If titanium carbide is included, the values will be slightly higher than for straight WC-Co Cemented Carbides. This values optimizes the resistance for carbide components or carbide tools like Carbide Rotary Cutters.

The thermal conductivity of WC-Co Cemented Carbides is approximately twice that of unalloyed steels and one third of that of copper. The tungsten carbide grain size has a minor effect but the presence of g- phase decreases the thermal conductivity considerably. This value optimizes the resistance for carbide components or carbide tools like Carbide Rotary Cutters too.

7. Corrosion Resistance

Cemented carbide is generally accepted as having a high resistance to corrosive fluids and atmospheres. It is vulnerable to certain concentrated acids which can attack the cobalt. It may also be subject to certain concentrated acids which can attack the cobalt.

Corrosion of Cemented Carbide leads generally to a surface depletion of the binder phase and, thus, the surface region will remain only as a carbide skeleton. The bonds between adjacent carbide grains are rather weak and the deterioration rate will increase accordingly. At low binder phase contents, the carbide skeleton is more developed and, accordingly, such grades exhibit a somewhat higher combined wear and corrosion resistance than corresponding grades with higher binder phase contents.