The hot deformation behavior of as-cast AISI M2high-speed steel containing mischmetal(RE)has been investigated on a Gleeble-3500simulator in the temperature range of 1 000-1 150℃and strain rate range of 0.01-10 s-1 at true strain of 1.0.The mechanical behavior has been characterized using stress-strain curve analysis,kinetic analysis,processing maps,etc.Metallographic investigation was performed to evaluate the mechanism of flow instability.The results show that the deformation activation energy decreases with increasing deformation temperature; the efficiency of power dissipation increases with decreasing strain rate and increasing temperature;flow instability is observed at low-to-medium temperature and higher strain rate region when the strain is smaller,but extends to lower strain rate and high temperature regions with the increment of strain,in which it is manifested as flow localization near the grain boundary.Hot deformation equations and processing maps are obtained.The optimal processing window is suggested and the deformation mechanism is dynamic recrystallization(DRX). The hot deformation behavior of as-cast AISI M2high-speed steel containing mischmetal (RE) has been investigated on a Gleeble-3500 simulator in the temperature range of 1000-1 150 ° C and strain rate range of 0.01-10 s-1 at true strain of 1.0. The mechanical behavior has been characterized using stress-strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the mechanism of flow instability. The results show that the deformation activation energy decreases with increasing deformation temperature ; the efficiency of power dissipation increases with decreasing strain rate and increasing temperature; flow instability is observed at low-to-medium temperature and higher strain rate region when the strain is smaller, but extends to lower strain rate and high temperature regions with the increment of strain, in which it is manifested as flow localization near the grain boundary. Hot deformation equations and processing maps are obtained al processing window is suggested and the deformation mechanism is dynamic recrystallization (DRX).