Study on the grain refinement mechanism of the machined surface of Inconel 718

In machining processes, the high temperature and stress can lead to plastic deformations of the workpiece material. Thermomechanical loading has a significant impact on the microstructure of the machined surface, including grain deformation, recrystallization, and refinement. Among these factors, grain refinement plays a crucial role in determining the mechanical properties of the materials. To investigate the mechanism of grain refinement on the machined surface of Inconel 718 at different cutting speeds, the experiments and finite element simulations were conducted. The microstructural characteristics were quantitative analyzed, including grain size, grain boundary distribution characteristics, average orientation (KAM), and geometrically necessary dislocation (GND) density distribution. The mapping relationship between the multi-physical fields (equivalent plastic strain, temperature) during cutting and the microstructural evolution of Inconel 718 was established. The research indicated that the increasing the cutting speed leads to a higher degree of grain refinement. At a cutting speed of 450 m/min, the maximum grain refinement is achieved with an approximately grain size of 2.48 mu m. The contribution from plastic deformation (dynamic recuperation) gradually increases while high temperature remains dominant as factors influencing grain refinement. Conversely, the equivalent plastic strain becomes the primary factor contributing to grain refinement, with a gradual increase in the proportion due to dynamic recrystallization at cutting speeds of 250 m/min and 350 m/min.