Cemented carbide plays a vital role in button bits, but its failure modes often lead to performance degradation or even failure of the button bit. To improve the service life of button bits, it’s essential to grasp the intricacies of potential failure modes and implement effective measures to address them.
Abrasive wear
In the absence of other failure mechanisms playing an important role, the service life of drill bit depends on the carbide wear. The service life can be improved by appropriately increasing the wear resistance of the carbide button, and the wear resistance of gauge button should be higher than that of middle button. For example, reducing the cobalt content and refining the WC grain.
Thermal fatigue
When thermal fatigue plays a major role, several or even hundreds of cracks can be seen on the surface of the button. Reducing the contact time between the button and the rock, can minimize thermal fatigue damage. Therefore, the drilling method has a great influence on the generation of thermal fatigue cracks. In the case of improper drilling methods, it can be seen that in some parts of the carbide, there are very severe thermal cracking cracks, while in other parts there is nothing. The main factors influencing the formation of thermal fatigue cracks are the button layout angle of the carbide button, the design of drill bit, and especially the drilling method. From the carbide material, thermal fatigue cracking can be reduced by lowering its coefficient of thermal expansion. Since the thermal expansion coefficient of cobalt is about three times that of WC, reducing the cobalt content of the carbide can reduce the coefficient of thermal expansion and increase the grain size of the carbide to improve the thermal conductivity. At the same time, the non-uniform structure of WC grains is used to ensure the reasonable matching of thermal fatigue resistance, wear resistance, and toughness. If the thermal fatigue effect cannot be eliminated due to other factors, drill bit design can be adjusted to reduce the exposed area of a button to reduce the adverse effect. Reduce the rate and magnitude of temperature change in the drill bit and reduce the occurrence of thermal fatigue cracking through enhanced cooling measures.
Flaking
The flaking of cemented carbide particles is mainly caused by insufficient bonding force between cemented carbide and binder. To solve this problem, we can take the following measures:
Enhance the interface bonding strength between cemented carbide and the binder by refining the surface condition of cemented carbide particles through advanced surface treatment technologies. This approach aims to elevate the bonding force between the particles and the binder, thereby minimizing the likelihood of flaking.
Optimize the preparation process of cemented carbide: by optimizing the preparation process, it is possible to enhance the distribution, size, and shape of cemented carbide particles, resulting in improved overall performance and wear resistance while minimizing particle spalling. For instance, improving the alloy’s toughness and minimizing structural imperfections such as pores, graphite inclusions, and eta phases can be instrumental in this improvement. It means increasing the cobalt content of the alloy while refining the WC grains.
Internal cracks
To some extent, all buttons have internal cracks. Under normal conditions, these cracks are small and infrequent. However, if the operating conditions are harsh and the impact and shear stress on the carbide button are large, these small cracks will cause crack fracture due to stress concentration, thus causing early failure of drill bit. Therefore, manufacturers can use materials with better toughness for carbides, and the better the toughness of the material, the smaller the sensitivity of crack fracture.
Fracture of non-exposed parts
During the processing of the drill bit, the smoothness of button after grinding should be ensured, and there should be no out of round and no grinding cracks. At the same time, the button hole of the drill bit must also be round, without taper, and the bottom of button hole must have a proper support shape that conforms to the bottom surface of the button. Choosing the right amount of button diameter and hole diameter fit when cold pressing or hot inserting teeth is also an important factor.
Shear fracture
The button must be rounded off during processing. Choose a suitable drill bit structure form so that drill bit can bear a smaller load.
Surface cracks
Generally, surface cracking can be suppressed by increasing the surface hardness of the carbide. The surface of carbide should reduce the cobalt content to increase the hardness, which can effectively reduce the cracks caused by wear, thermal fatigue, and shear stress. At the same time, it is also necessary to improve the toughness of the heart of carbide to delay the expansion of the surface cracks that have been generated, and the formation of small cracks is more stable and less likely to expand if the alloy toughness is better. From the point of view of carbide the functional gradient material should be used to ensure that the functional gradient material ensures the hard skin of carbide soft heart nature.
Dealing with the failure modes of button bit carbide requires approaches from many aspects. At the same time, we should also pay attention to the development and application of new cemented carbide materials to provide more possibilities for improving the service life of button bits. In the future, with the continuous advancement of technology and the growing demand for applications, we are confident that addressing the failure issues with button-bit carbide will lead to a more effective solution, offering a robust guarantee for the advancement of associated industries.
