Shot peening is a widely used method to improve the fatigue strength of automobile gears by mechanical means to produce compression deformation on the surface of automobile gears and produce deformation modification layer on the surface, so as to improve the surface strength. Shot peening causes great plastic deformation in the strengthening layer of the tooth surface, the residual austenite on the surface of the tooth surface transforms into martensite, and the induced transformed martensite has directionality and is arranged in parallel bundles along the slip line. The dislocation density of the original martensite increases and the structure is refined. Shot peening improves the surface microhardness of the automobile gear and the residual compressive stress under tens of microns of the tooth surface, The bending fatigue strength limit and service life of automobile gears can be greatly improved. Shot peening makes the following main changes in the surface integrity of automobile gears, namely:
① Introduce residual compressive stress field;
② Deformation refinement of microstructure;
③ Change of surface hardness;
④ Change of surface roughness;
Among them, ① ② ③ the first four surface changes can improve the fatigue life of automobile gears, while the increase of surface roughness caused by shot peening may reduce the fatigue performance of materials and worsen the noise of automobile gears, which is not conducive to the vibration and noise characteristics of automobile. The influence of shot peening on the surface integrity of gear is improved by controlling the process parameters such as shot peening intensity and shot diameter and adopting composite shot peening. The key to control the surface integrity of automotive gear shot peening is mainly reflected in the control of the residual stress distribution and surface roughness of the tooth surface, so as to avoid the improper shot peening of “under spraying” and “over spraying”.