Investigations on grain size characteristics in microstructure during grinding of maraging steel 3J33

Abstract

Due to the nonlinear and tight coupling of the process parameters in grinding, the surface integrity of the parts is influenced by multiple factors. At present, most studies have macroscopically analyzed the effect of grinding force and heat caused by grinding parameters on surface morphology and mechanical property, while the investigation of dynamic evolution in the material microstructure during grinding and its influencing mechanism on the surface integrity is not yet fully understood. In this study, a novel microscopic grain size model comprehensively considering grinding temperature, heating rate and strain is proposed to investigate the phase transformation, surface hardness and roughness of maraging steel 3J33. The key factors affecting the change of the grain size are deeply studied and the model coefficients are calibrated by heat treatment and grinding experiments at first. Then the relationship between grain size and phase transformation is revealed based on the proposed model and the sensitivity of grain size to different process parameters is quantitatively analyzed. The surface integrity of the workpiece, such as hardness and roughness, is further investigated by comparing the variation of the grain size and phase transformation before and after the grinding process. The theoretical and experimental results show that large cutting depth and low workpiece speed are more beneficial to reduce the grain size. The phase transformation is strongly correlated with grain size and higher wheel speed is supposed to restrain the phase transformation of the material. Based on this analysis, the guideline of process optimization is provided for the grinding of maraging steel to obtain better surface integrity.