The main purpose of the current study was to investigate the effects of the size of WC grains on the damage evolution of WC-Co junk mills.The finite element method (FEM) simulation results showed that the fine-grain (FG) tool retained its cutting edges radii longer than the coarse-grain (CG) tool.This event leads to the larger wear rate in the CG tool.Moreover,FEM analysis indicated that through increasing the feeding rate,the wear rate and the cutting forces increased as well.The observation of worn tool surface revealed that the formation of micro-pits,micro-cracks,scratching grooves and broken WC grains was among the common signs of the damage for both CG and FG tools.However,it was found that the defects are more intensive in the CG tool.This can be due to the lower boundary strength and less WC connectivity in the CG milling tool.The finer grains also decreased the mean free path in the Co binder and impeded the micro-cracks propagation in the material.