It is a work restricted by many factors to select suitable materials from all kinds of materials. The commonly used materials of mechanical parts are steel, cast iron, non-ferrous metals and non-metals. The grades, properties and heat treatment knowledge of commonly used materials can be consulted in the mechanical design manual. It is an important link to select materials in mechanical design. With the continuous development of material science, the requirements of mechanical manufacturing industry for parts are improving. Therefore, when selecting materials, designers should fully understand the properties and applicable conditions of the materials, and consider the requirements of the use, process and economy of the parts. The following are the general principles for the selection of metallic materials (mainly iron and steel) Give a brief introduction.

The principle of selecting mechanical parts materials is that the required materials should meet the requirements of parts, have good process and economy and so on.

It should be considered that the materials used can be easily manufactured from blank to finished products. For example, the parts with complex structure and large size are difficult to forge and can be cast or welded. Their materials must have good casting or welding properties.

According to the selected process, the processing possibility of the material to the process should be considered. For casting, we should consider the liquid fluidity of the material, the possibility of shrinkage and segregation, etc. For welding, we should consider the weldability of the material and the tendency to produce cracks, etc. For forging, we should consider the elongation, thermal brittleness and deformation ability of the material, etc. For parts that need heat treatment, we should consider the hardenability of the material, the tendency of quenching deformation, etc.