Tungsten Carbide Button Optimization Method
There are three optimization methods of tungsten carbide button: the optimization method of graded structure, the optimization method of microelement, the optimization method of the button shape.
Structure
The optimization of graded structure: The principle of preparation of the graded structure tungsten carbide is to use the tungsten carbide with lower carbon content, obtain the η phase tungsten carbide by vacuum sintering, and treat it in the carburizing atmosphere in order to change the distribution of the Co binder phase which makes the different parts of button distributed with different Co contents. In order to form the graded tungsten, the amount of carbon contained in the sintered part needs to be 0.1%-0.4% lower than the theoretical value. It also needs to increase appropriately the carburization temperature which facilitates the migration of the liquid phase Co into the sintered body. For sintered bodies of different particle sizes, different carburizing times should be selected accordingly.
Optimization method
The optimization method of microelement: A small amount of TaC is added during the preparation of tungsten carbide, which is to improve the composition of the binder phase and the microstructure of grain boundary and improve the wear resistance, thermal shock resistance and thermal plasticity resistance to some extent. But it will increase the cost to some degrees. If Tac is added excessively, the intensity of the product will decrease. An experiment shows that when Ta and Mo are added appropriately as additive to the WC-Co tungsten carbide, the tungsten carbide with high fracture toughness can be obtained without decreasing its hardness. The alloy is in a liquid phase at a relatively low temperature, and the early appearance of the liquid phase causes the dissolution and precipitation of the solid phase particles and the formation of the skeleton to occur in advance. Therefore, the sintering process is so complete that it effectively increases the densifying speed of the button and improve its performance.
The optimization method of the button shape: with the popularization of long-hole drilling and oil field boring, relevant equipment has a higher requirement for the properties of button. Most of button shapes are blunt-nosed shape and bullet shape. In daily process of production and applications, it is found that the conventional blunt-nosed buttons are easily passivated. Under the condition of being subjected to a large impact force they are easily broken due to insufficient strength of the base body, the thinness of the crown and the small radius. The tungsten carbide button has the advantages of blunt-nosed button and bullet button. Its head is composed of the spherical part and approximate cone. According to the law of spherical shape and wedge stress distribution, the spherical part is applied to spherical rock breaking and the approximate cone is applied to wedge rock breaking.