The greater the elongation and cross-sectional shrinkage of metal materials, the better the plasticity of the material, that is, the material can withstand greater plastic deformation without damage. Generally, metal materials with an elongation greater than 5% are called plastic materials (such as low-carbon steel, etc.), while metal materials with an elongation less than 5% are called brittle materials (such as gray cast iron, etc.). Materials with good plasticity can produce plastic deformation in a larger macroscopic range, and at the same time, the metal material is strengthened by plastic deformation, thereby improving the strength of the material and ensuring the safe use of parts. In addition, materials with good plasticity can be smoothly processed by certain forming processes, such as stamping, cold bending, cold drawing, straightening, etc. Therefore, when selecting metal materials for mechanical parts, certain plasticity indicators must be met.