The 080A15 and 30CrMnMo steels were cut by precision sawing machine. The microscopic characteristic of the chip surface and the chip failure microscopic mechanism have been studied. The studies show that the formation of saw-tooth chip is mainly a function of the strength and thermal conductivity. For 080A15 steel, the strength is low and the thermal conductivity is high, the plastic work was absorbed continuously by the process of plastic deformation, and the heat was dissipated at any moment. The heat energy did not reach the critical value causing thermal softening. The chip is more prone to ductile fracture. For 30CrMnMo steel, the bonding ability is stronger among atoms, and thermal conductivity is smaller. The plastic deformation is extremely fast and the instantaneous temperature rise was very high because the heat energy reached the critical value causing thermal softening. Therefore, the chip is more prone to adiabatic shear failure to form the saw-tooth chip divided uniformly by adiabatic shear band. The research results help to provide the basis for selecting materials with different adiabatic shearing sensitivities in the process of high-speed cutting by studying the energy barrier on the influence of chip failure mechanism.