Research Methods and Design Basis for Cogging Process of Large-Scale GH4738 Superalloy

Abstract:

The distribution and evolution of the internal grain structure of large-scale GH4738 alloy during the complex continuous deformation cogging process, based on the process sequentiality and organizational heredity, were investigated by employing a finite element model combined with secondary development methods, providing a general approach for process design and outcome prediction. Finite element simulation calculations were conducted based on the actual billet preparation process of GH4738 superalloy with Ф660 mm grade, comparing the simulation results with the grain size at corresponding positions of the actual billets to verify the reliability and accuracy of the established model. Utilizing this model, typical upsetting and cogging processes were analyzed, and the effects of process parameters on the microstructural evolution of the billet during multiple deformation passes were discussed, along with methods for process formulation. Results show that during the upsetting process, as the upsetting speed increases, the deformation temperature decreases, the reduction amount decreases, and the degree of dynamic recrystallization within the billet decreases. In the cogging process, as the upsetting speed decreases, the cogging temperature increases, the feed amount decreases, and the degree of dynamic recrystallization within the billet increases. Furthermore, based on the specific analysis, it is recommended to control the upsetting speed during the upsetting process between 5 and 12 mm/s; the initial upsetting temperature should be 1160 °C; the single-pass reduction amount should be controlled between 25% and 35%. The cogging process is more complex than the upsetting process. Taking into account the factors such as grain refinement within the billet, surface temperature drop during the cogging process, and the occurrence of the "concave center" phenomenon, the upsetting speed is controlled between 60 and 90 mm/s; the second cogging temperature is chosen between 1120 and 1130 °C; the feed amount is controlled between 200 and 350 mm.