Sintering Technology in the Production and Processing of Powder Metallurgical Parts

The sintering process in the production and processing of powder metallurgy parts is one of the most basic processes in powder metallurgy, playing a decisive role in the physical and mechanical properties of powder metallurgy parts.

Sintering is a high-temperature heat treatment that involves knowledge of sintering furnace, sintering atmosphere, selection and control of sintering conditions, etc. Therefore, sintering is a very complex process. At the same time, sintering is a special process with high energy consumption, high equipment investment, and insufficient measurement of product quality characteristics. Therefore, it is one of the most important links that affect the quality and cost of powder metallurgy parts. The sintering process is crucial and must be strictly controlled to ensure the quality of sintered parts. Therefore, operators need to receive specialized skill training to comprehensively understand and master the basic principles of sintering, sintering process (such as materials, temperature and time, sintering atmosphere, environment, etc.), the role of sintering atmosphere, and factors affecting the quality of sintered products, in order to proficiently master sintering operation skills and improve the ability to analyze problems.

How are powder metallurgy parts sintered? Sintering is the heat treatment of a powder or compact at a temperature below the melting point of the main component. The purpose is to create metallurgical bonding between powder particles, even if the mechanical bonding between powder particles transforms into grain boundary bonding between atoms.

The purpose of sintering powder metallurgy parts is to obtain compacts that, although they have the appearance and size of mechanical parts, their strength is very low and cannot meet the requirements of use. Before sintering, the compact is only a mixture of powder particle interfaces in contact, rather than a material that truly combines atoms. Therefore, it is necessary to sinter the compacts to become metallurgical materials, endowing powder metallurgy parts with the required mechanical and physical properties. The strength and elongation of iron powder compacts significantly increase after sintering. If sintered at 1200 ℃, the tensile strength can be increased from zero to 200MPa, and the elongation can be increased from zero to 8%.

Requirements for sintering of powder metallurgy mechanical parts:

1. Precision requirements for size and shape. The size, shape accuracy, and surface roughness of sintered parts must meet the design requirements. Sintering can cause shrinkage or expansion of the sintered body, and due to uneven density distribution of the compacts and uneven furnace temperature, the sintered body can also undergo deformation. Therefore, through sintering, the size and shape of the sintered product will change. This requires strict control of sintering conditions to ensure the dimensional and shape accuracy requirements of sintered products.

2. Requirements for density. During sintering, due to the sintering between powder particles and the shrinkage or expansion of the sintered product, the density, porosity, voids, and shape of the sintered product change. The relative density and porosity characterize the density of powder metallurgy parts. As a self-lubricating powder metallurgy oil bearing, there is also a requirement for connecting gaps.

3. Organizational requirements. Powder metallurgy parts, like other materials, depend on their internal performance based on their organizational structure. The factors that characterize the organizational structure of powder parts include grain size, phase structure, phase distribution, alloy composition distribution, as well as porosity, pore size, and pore shape. The formation and change of the organizational structure of powder metallurgy parts mainly occur during the sintering process.

4. Requirements for mechanical and physical properties. The final sintered parts need to achieve the required mechanical and physical properties. Mechanical properties include strength, hardness, elongation, and impact toughness; Physical properties include density, conductivity, thermal conductivity, and magnetism.

The sintering of powder metallurgy parts can be divided into solid phase sintering and liquid phase sintering. Solid phase sintering is simply the sintering of metallurgical bonding between powder metallurgy particles, while liquid phase sintering is the sintering of certain molecular particles in powder metallurgy that produce a liquid state at a temperature higher than the melting point. The sintering process of powder metallurgy compact parts can be divided into pre sintering grease removal, high-temperature sintering, and cooling.