Cemented carbide is a hard alloy formed from refractory metals such as tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC). The most common binder system used is cobalt.
Other possible binder systems include nickel, iron, and mixtures thereof. However, the use of such materials may compromise some desirable wear properties or ductility.
Hardness
A cemented carbide is a powder-metallurgical two-phase material made of a hard material phase (such as tungsten, cobalt or nickel) and a binder metal phase. It has a characteristic high tensile strength, hardness and ductility.
The properties of a Cemented Carbide Plates depend mainly on the binder content and the grain size of its particles, which are formed during sintering. The higher the binder content, the more difficult it is to form cracks within the cemented carbide. In addition, the grain size is also important as it determines how much impact force a cemented carbide can withstand without breaking.
In some applications, the combination of a high binder content and a coarse grain shape is crucial as it prevents crack formation in the binder matrix. Similarly, the presence of small amounts of vanadium or chromium carbide in the binder improves its toughness.
This is particularly true in situations where the cemented carbide is subjected to dynamic stress during machining. These are, for example, bending or cutting processes which place a large amount of strain on the binder, or where it is subjected to impact loads.
During these operations, cyclic thermal stresses are created in the surface of the cemented carbide, which causes its temperature to rise. This effect is dependent largely on the parameters of the grinding process, but is also controlled by the thermal conductivity of the cemented carbide itself and the workpiece as well as by the environment.
However, the degree of thermal degradation in cemented carbides can be controlled by coating them with thin films. Such films can either dissipate heat, distributing it across a larger area, or create a thermal barrier, preventing heat from entering the carbide.
The ability of a cemented carbide to resist corrosive influences can be increased, for example, by using a higher-binder grade or replacing a straight-grade WC-Co with a complex-grade, such as WC-Co-Ni-Cr, which contains a high proportion of tungsten trioxide (WO3). In these cases, a layer of WO3 develops on the surface of the cemented carbide which reduces its wear resistance and increases its toughness.
Wear Resistance
Wear resistance in terms of tensile strength is a key factor in determining the lifetime of cemented carbide nails. The toughness of the material is determined by the metal binder and the WC grain size. The higher the WC grain size, the lower the hardness of the carbide.
The high modulus of elasticity and the high hardness and toughness ensure that the material deforms only slightly when exposed to pressure. This combination of properties makes tungsten carbide an ideal material for applications where high strength, good toughness and excellent wear resistance are required.
Various grades with different compositions and a variety of other properties are available on the market. These vary in their WC grain size (a phase) and in the addition of other metal binders. These are also referred to as mixed carbides.
In general, a low WC grain size is better for applications that are not subject to severe corrosion conditions. However, a high WC grain size can provide a higher wear resistance and a better corrosion protection. This is why a lot of WC/W2C coatings with very fine WC grains have been developed in recent years.
A thin WC coating on steel can improve the corrosion and Wear and corrosion resistant tee of metal components, especially in applications with heavy abrasive wear. Depending on the WC grain size and the metal binder, this type of coating can also reduce the tendency to cracking and adhesion.
The abrasion resistance of a WC coating can be improved by the use of a special deposition technique, such as laser cladding. This method allows very local coating of highly complex and shaped parts.
For example, a laser clad coating of WC-Ni on 20CrMnTi alloy steel was found to have a much better wear resistance than a bare nickel plated steel. This is due to the fact that the WC/Ni coating presents a graded distribution of microhardness, which leads to a higher surface hardness.
The abrasion resistance of WC-Ni coatings can be further enhanced by the use of a high-temperature oxy-fuel thermal spraying process. Compared to traditional thermal spraying, this process has the advantage of not causing damage and is also very fast.
Tensile Strength
Among the most important characteristics of cemented carbide nails is their tensile strength. This is important because it determines how strong the material can be and how much pressure it can withstand.
The tensile strength of cemented carbide can vary significantly according to its WC grain size, metal binder content and other additives. It is the combination of these three parameters which determines the material’s specific properties.
For example, the hard WC phase provides hardness and heat resistance, while the metal binder contributes to toughness. This combination of different physical properties makes cemented carbide an ideal material for many applications in the mechanical engineering sector.
Another characteristic of this material is its high elasticity, which ensures that it deforms only slightly under pressure. This is important because it can prevent bursting or cracking.
As a result, cemented carbide is a good choice for forming and welding joints because it can resist high temperatures without deteriorating its properties. Moreover, it can also withstand extreme wear conditions and be used in various industries where abrasion is a factor.
A wide range of grades are available for a variety of uses. For example, they are used for machining and for high speed drill bits, which must be extremely abrasive-resistant and withstand very high temperatures.
In addition, there are grades which have a high cobalt content and are used for micro-drills which are thinner than a human hair and must be able to withstand high bending forces. Similarly, there are high-performance grades with coarse grain, which deflect cracks in the binder matrix.
These high-performance cemented carbide grades are very often used in forged hammers, which are required to work with great force. These hammers must withstand consistent impact stress, and they must not fail or break.
Therefore, it is important to select the right type of tungsten carbide. In order to achieve the optimum results, it is crucial to find a high-quality material with a stable grain size and a homogeneous structure.
During production, the raw material is subjected to extensive testing and quality control to ensure its qualified rate. This includes testing for the presence of porosity and inclusions. It is also important to check for defects in the surface of the material. These can cause micro-cracks and affect the material’s tensile strength.
Corrosion Resistance
As a result of their hardness and strength, cemented carbides offer excellent resistance to wear and corrosion. This is why they are a preferred choice in many industries, particularly when the conditions are harsh or corrosive.
The material properties of cemented carbide are primarily determined by the WC grain size and the metal binder content (a phase). The latter is usually made from cobalt, although titanium, tantalum or niobium carbides are also used as binding agents.
During sintering, the Tungsten carbide grains are effectively wetted and solidify into a hexagonal (lattice) structure. The binder metal, usually cobalt, forms the strongest bonds with the tungsten carbide.
These bondings not only allow the WC carbide grain to be wetted during sintering, but are also essential in terms of structural integrity. This is especially true for WC-Co grades, which are used in a variety of applications and are the most common type of cemented carbide.
Corrosion in corrosive environments can cause the molten cobalt binder to disintegrate and expose the underlying tungsten carbide matrix, resulting in a loss of structural integrity. This is referred to as “cobalt leaching”.
While pure WC-Co carbides have limited resistance to corrosion, WC-Ni and Co/Cr carbide grades are the better choice. These binders are resistant to pH 7 or lower, and can even be used in extremely corrosive environments.
In addition to WC-Co and WC-Ni cemented carbides, mixed TiC-Co or TiC-Ni grades are available for additional corrosion-resistant properties. However, these types of carbide tend to be more brittle than WC-Co or WC-Ni grade materials.
As the metal binder is usually made from cobalt, a high cobalt content in the WC carbide can improve transverse rupture strength significantly compared to the pure WC-Co grade. This is particularly important for hammers and other forging tools as the impact forces can be high.
Carbide containing a small amount of vanadium, chromium or tantalum-niobium can further increase the toughness and fracture strength of a carbide grade. These doping additives are typically added in small quantities to ensure that a fine-grain structure is achieved in the product.
