A study of the effect of dual shot peening on the surface integrity of carburized steel: combined experiments with dislocation density-based simulations

As a novel processing technology for high surface integrity, dual shot peening enables improvement in residual compressive stress, hardness gradient, and a reduction in surface roughness, thus effectively enhancing the fatigue resistance of mechanical components. The modelling and experiments on the dual shot peening of 18CrNiMo7-6 carburized gear steel have been conducted. A dual-shot peening finite element model based on the dislocation density constitutive equation that considers hardness gradient, residual stress, and surface roughness has been developed. Extensive peening tests and surface integrity characterisation using TEM and EBSD were conducted. The correlation between peening parameters and surface integrity and the underlying mechanism have been explored. The results from modelling and the experimental dual shot peening tests are in good agreement, with the maximum errors of residual stress and microhardness less than 15.1% and 7.4%, respectively. For an effective dual shot peening process, high-intensity peening with medium shots is recommended as the first step, and low-intensity peening as the second step. This process increases the surface residual compressive stress and hardness to -950 Mpa and 790 HV, respectively, while maintaining a reduced surface roughness.