Shot Peening Principle
Shot peening process is the high-speed movement of the projectile flow to the surface of the process of continuous jet. The jet of the projectile is hammered like a small hammer to the metal surface. This results in a very strong plastic deformation of the metal surface layer, i.e., a cold hardening layer, which is referred to as a surface strengthening layer. From the stress state, the reinforcement layer to form a higher residual stress; from the group structure only, the reinforcement layer to form a very high density (> 10 ?? 1 / cm?) Dislocations, and in the subsequent Stress or temperature (or both) under the effect of dislocation gradually arranged rules, the formation of polygonal, which gradually strengthen the layer to form a more sub-grain (sub-structure).
The compressive stress state and the group structure, which are different from the heart (matrix) in the shot peening layer, are the two main factors that improve the room temperature and high temperature fatigue strength of the parts and improve the stress corrosion resistance.
It is true that the compressive stress in the reinforcement layer and the structure of the group are not fixed, and the residual stress of the part is subjected to alternating stress at room temperature or high temperature for a long time. In general, the residual stress will gradually relax, Will gradually grow up, or even the occurrence of recrystallization process. In general, the rate of disappearance of residual stress and the rate of growth of subgrains depend on the level and temperature of the applied alternating stress. The higher the stress and the temperature, the greater the rate of change between the two. Therefore, the shot peening parts after a period of use, in order to restore its shot peening effect, often need to re-shot peening, and then put into use.