<p>This article aims to use a combination of numerical simulation and experimental methods to study the microstructural evolution of high-speed cutting of nickel-based superalloys GH4169 under high temperature and high strain rate conditions. The formation mechanism of serrated chips is analyzed through chip and metallographic images obtained from cutting experiments, with a focus on exploring the influence of dislocation density and grain size evolution on serrated chip formation. The findings reveal that a cross-scale simulation framework, encompassing dislocation evolution information, integrating 3D-DDD with the finite element method (FEM), can be employed to study the stress, strain, cutting force and temperature during machining processes. This framework can capture the deformation behaviour of the microstructure under cutting conditions, including the evolution of grain size and dislocation density. It has been established that the majority of grain refinement takes place within the initial deformation zones. The degree of grain refinement on the machined surface is relatively weak. As cutting progresses, the average grain size of the chips is significantly smaller than that of the machined surface, and the grain refinement in the chip shear zone is most obvious. At the same time, thermal softening occurs due to the temperature rise, and plastic deformation and the accumulation of dislocations in the shear band cause cracks and voids, which accelerates the generation of serrated chips.</p>