Abstract: Shot peening can improve the fatigue resistance of CP800 complex phase steel. Different levels of shot peening strength, namely, low (0.15 mmA), medium (0.3 mmA) and high (0.5 mmA), were used to treat the surface of CP800 complex phase steel following 5% prestretch deformation. The surface morphology and residual stress of the material after shot peening were studied, and the fatigue fracture was analyzed following a tensile-compression fatigue test. The results showed that CP800 complex phase steel with a 2 mm plate thickness was more suitable for low shot peening strength, and its fatigue life was approximately three times that of the unshot peening sample. The increase in fatigue life was attributed to the plastic deformation of the surface layer and increase in dislocation density. Residual compressive stress could also inhibit crack initiation. The surface roughness of the material increased after shot peening, and high shot peening intensity could easily increase the number of surface defects. In particular, under high shot peening strength, there would be more delamination damage on the surface of the sample, which negatively affected its fatigue properties.

Key words: shot peening, CP800 complex phase steel, fatigue resistance, residual compressive stress