Study on the effect of pre-stress unloading time on surface integrity in PSHG process

Abstract

Pre-stress hardening grinding (PSHG) is a complex process that combines pre-stress grinding and grinding hardening. Pre-stress, as input stress, has been working throughout the grinding process. Since the grinding heat generates on the surface of material, unloading the pre-stress at different time nodes will affect the phase change after the grinding process. In this paper, the effect between pre-stress unloading time and the grinding hardening is further studied. In order to study the effect of pre-stress unloading time, experiment and simulation are used for analysis and to optimize grinding hardening layer in the PSHG process. After the PSHG experiment, the microstructure of the grinding-hardened surface is observed and investigated by scanning electron microscopy (SEM). And the SEM images are binarized to obtain the martensite content on the hardened surface. It is showed that as the pre-stressed unloading time increases, the martensite content increases. Then, a simulation model is established based on the heat conduction equation, initial boundary conditions, and latent heat of phase change. According to the simulation results, three time nodes are selected to study the unloading pre-stress. The pre-stress unloading time affects the mechanical thermal stress of the material surface layer, but has little effect on the inner layer. In the simulation, the influence of the pre-stress unloading time on the mechanical-thermal stress of the surface is compared. Finally, the effects of pre-stress unloading time on the phase transition and phase transition stress are discussed.