Abstract:The effects of initial grain size and hot deformation parameters on hot deformation characteristics of high-quality GH4738 alloy under different small deformation conditions were analyzed. The microstructure evolution and softening mechanisms during hot working process and sub-solid solution treatment process were investigated by OM, EBSD and TEM analyses. The results indicate that the flow stress is increased with the increase in initial grain size, especially under the lower hot working temperature, and the increment is decreased with the increase in deformation temperature. The volume fraction of dynamic recrystallization in GH4738 alloy has a strong dependence on the initial grain size. Increasing the hot deformation temperature and engineering strain can promote the process of dynamic recrystallization of this alloy. The dynamic recrystallization mechanisms of GH4738 alloy are mainly based on the discontinuous dynamic recrystallization mechanism of nucleation of grain boundary bulging. In the meantime, during the process of dynamic recrystallization and grain growth, the grain boundary undergoes small planarization due to atomic migration, resulting in a quasi-right angle staged grain boundary. The static recrystallization occurs during the sub-solid solution treatment process, and the grains are refined to a great extent due to the incomplete re-dissolution strengthening γ' phase, which can promote the nucleation of static recrystallization.