Torsion plastometer trials to investigate the effect of non-proportional loading paths in caliber rolling on damage and performance of metal parts

Abstract

AbstractThe non-proportional loading path describes a strain-dependent development of stress triaxiality and Lode parameter during metal forming processes. Existing studies suggest a strong dependence of damage evolution on the non-proportional loading path. This work focuses on investigating the influence of non-proportional loading paths observed in hot caliber rolling of the case-hardening steel 16MnCrS5 using laboratory scale experiments. The applied torsion plastometer is highly flexible as it can apply combined loading types (tension, compression and torsion) on notched round specimen and enables deformation at elevated temperature. In this study, two characteristic non-proportional loading paths in caliber rolling and the maximal achievable non-proportional loading path variation were recreated in the torsion plastometer based on both FE simulations and experiments. After deformation, the specimen were further analyzed using Scanning Electron Microscopy (SEM) to quantify the damage. The results indicate an influence of the non-proportional loading path on damage evolution. Furthermore, fatigue tests were employed to characterize the fatigue performance of the deformed specimens. In the torsion plastometer trials carried out no clear correlation of performance and damage was observed. This is most likely due to differences in residual dislocation density after static recrystallization and deviations in the microstructure after hot working. Thus, the superposition of microstructure evolution and damage needs to be considered carefully when testing at elevated temperature.