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Superalloy that can serve above 800 °C is urgently needed for the development of high-performance aero-engine turbine disk. Increasing the content of γ′ phase could significantly improve high temperature machinal properties, and GH4151 alloy is the typical representative of superalloys with more γ′ phase, and its γ′ phase content is about 55 wt.%. Besides, GH4151 alloy could serve at 800 ℃ and presents a broad application prospect. However, the higher content of γ′ phase also increases the difficulty of deformation. Cogging process of the homogenized ingot is an important part in preparation of turbine discs. However, there is still a lack of systematic research on the hot deformation behavior of homogenized GH4151 alloy. Therefore, the deformation behavior of homogenized GH4151 alloy was studied by isothermal hot compression test and hot processing maps were established based on flow curves. In addition, FESEM and coupled EBSD/EDS methods were utilized to analyze deformed microstructure. Based on the results of hot processing map, the domains with good workability are 1060 ~ 1090 ℃,0.1 ~ 0.2 s-1 and 1060 ~ 1070 ℃,0.1 ~1 s-1. A large amount of primary γ′ phase (γ′Ⅰ) in initial structure hinders the movement of dislocations to promote recrystallization, and pins the grain boundaries to refine the grains. An increasing deformation strain contributes to a larger instability domain. The main form of GH4151 alloy deformation instability is that the tensile stress at the bulging zone of deformed sample induces cracking of grain boundary and γ/γ′Ⅰ phase boundary. Increasing deformation temperature and deformation rate will promote cracking.