The Behavior Of Grain Evolution And Its Numerical Simulation During Isothermal Forging Of GH4698 Turbine Disk

Turbine disk is one of the key parts of aero engine. Because of poor service environment, the performance requirements of turbine disk is very strict. The superalloy used for the manufacture of turbine disk usually has characteristics such as high alloying degree and complex microstructure, so it is difficult to be formed due to the the crack and the narrow forging temperature window in deformation process. In addition, due to the increasing size of the turbine disc, it is easy to cause the defects such as coarse grain and mixed grain in the process of manufacturing, which can affect the performance of the turbine disc. Thus, obtain the hot deformation behavior of superalloy and therefore obtain the influence law of hot working parameters on the grain structure is an important theoretical support to solve the problem of turbine disc manufacturing.In this paper, the GH4698 wrought superalloy was chosen as the research object. By isothermal hot compression experiments in Gleeble thermal simulation test machine, the high temperature deformation behavior of the alloy at the temperature of 900~1200°C and the strain rate of 0.001~1s-1 were studied; The grain evolution of a turbine disk in the isothermal forging process was simulated by using finite element software DEFORM. The deformation condition of the grain refinement of the turbine disk was obtained. The main contributions given in this dissertation are as follows:(1) with the increase and the decrease of deformation temperature and strain rate, the flow stress decreases significantly; When the deformation temperature is lower than 1000°C, the surface of the deformed specimen is cracked.(2) The peak stress prediction model and the constitutive model considering strain compensation of GH4698 alloy were obtained; The dynamic recrystallization kinetics law was defined, and the dynamic recrystallization grain size model was established. Based on the dynamic material model, the processing map was established, and a reasonable hot working region was obtained.(3) The results of finite element analysis of DEFORM show that if the GH4698 turbine disk was made by isothermal forging process, fine grain microstructure can be obtained in most region of the turbine disk under the condition of forging temperature 1050°C and deformation rate 5mm/s.