The so-called cemented carbide is to heat the powder compact to a certain temperature (sintering temperature) and hold it for a certain time (holding time), and then cool it down to obtain the material with the required properties. This heat treatment process is called sintering.
Sintering turns the porous powder compact into a product with a certain structure and properties. Although the properties of the product are related to many process elements before sintering, in many cases, the sintering process has serious effects on the structure and properties of the final product. is a decisive influence. The sintering process of cemented carbide is relatively complicated, but these basic knowledge must be controlled. Classification of sintering process There are many classification methods of sintering process. According to the number of components of sintered products, it can be divided into unit system sintering and multi-component sintering. For example, tungsten and molybdenum bar sintering belongs to unit system sintering, and cemented carbide winding belongs to multi-component sintering. . According to the state of the phase in the components during sintering, it is divided into solid phase sintering and liquid phase sintering. For example, the sintering process of tungsten and molybdenum does not show liquid phase, which belongs to solid phase sintering. Liquid phase sintering. According to the process characteristics, it can be divided into hydrogen sintering, vacuum sintering, activation sintering, hot isostatic pressing sintering, etc. Many sintering methods can be used for cemented carbide sintering. In addition, it can also be divided according to the name of the sintered material, such as cemented carbide sintering, molybdenum plug sintering. From the perspective of learning the nature of the sintering process, it is reasonable to divide the sintering process into two categories: solid-phase sintering and liquid-phase sintering, but in production, it is mostly classified according to the sintering process characteristics. The fundamental change in the sintering process After the cemented carbide compact is sintered, the most easily observed change is that the volume shrinkage of the compact becomes smaller, the strength increases sharply, the porosity of the compact is generally 50%, and the sintered product is close to The theoretical density, the porosity should generally be less than 0.2%, and the change in the strength of the compact is even greater. The strength of the compact before sintering is so low that it cannot be measured by ordinary methods, and the compact only accepts the strength necessary for transfer during the production process. However, after sintering, the product can reach the strength value required to meet various harsh working conditions. Obviously, the improvement of the strength of the product is much larger than the improvement of the density. The sudden change of product strength and other physical and mechanical energy indicates that the compact has undergone qualitative changes during the sintering process. In the pressing process, although the contact surface of the powder body can be increased due to the action of external force, the surface atoms and molecules in the particles are still disordered, and even there is internal stress, and the joint force between the particles is very weak, but after sintering the particles The surface contact state has undergone a qualitative change, which is due to the chemical reaction of the powder contacting surface atoms and molecules, as well as physical and chemical changes such as diffusion, movement, grain growth, etc., which make the contact between particles tight, the internal stress is eliminated, and the product constitutes a product. Strong overall, so that its performance is greatly improved.
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