Impact wear behaviors of Hadfield manganese steel at different impact angles were investigated. The results of impact wear tests show that there exists a critical impact load for Hadfield steel. The wear rate suddenly turns down after some impact cycles when the impact load is greater than the critical load. The critical impact load is smaller than 8.2 J in this research because the nano-sized austenitic grains embedded in amorphous delay the crack propagation in subsurface. From high resolution transmission electron microscope (HRTEM) examination of subsurface microstructure, it is found that a large amount of nano-sized grains embedded in bulk amorphous matrix are fully developed and no martensitic transformation occurs during the impact wear process. The analytical results of worn surface morphology and debris indicate that the initiation of crack, propagation and spalling are restricted in the amorphous phase, resulting in the size distribution of debris in nano-sizes, which is the reason why the wear rate of Hadfield steel is greatly decreased at high impact load.