Modeling Microstructure Evolution in the Delta Process Forging of Superalloy IN718 Turbine Discs

摘要

The microstructure development in the Delta Process (DP) forging of Superalloy IN718 turbine discs were predicted using the combined approach of axisymmetric finite element simulation and modeling for the dynamic recrystallization and grain growth. In order to establish the deformation constitutive equation and dynamic recrystallization models for the DP process of Superalloy IN718, the isothermal compression tests were carried out in the temperature range 950 to 1010 °C and strain rates range 0.001 to 0.1s~(-1). Moreover, the isothermal heat treatment tests after hot deformation were conducted in the temperature range 950 to 1040°C to generate the grain growth model. The experimental results indicated the existence of the δ phase could make the activation energy of deformation increase. Furthermore, the existence of the δ phase could stimulate the occurrence of dynamic recrystallization, and the grain growth was restrained due to the pinning effect of δ phase. The predicted grain size and its distribution in the DP forging of Superalloy IN718 turbine discs were compared with the actual microstructures deformed by the hot die forging. It was found that the forging with uniform fine grains could be obtained by the application of DP process to the forging of the turbine disk, in which the alloy was pre-precipitated δ phase after the baiting in the original process.