In-situ study of the orientation dependent microstructure defect density and phase transformation in metastable austenitic TRIP/TWIP steel under compressive loadWednesday (28.09.2016) 09:30 - 09:45 Part of:
The metastable austenitic steel 16-7-6 CrMnNi is characterized by an excellent ductility and a high strain hardening rate. These properties are related to a low stacking fault energy of this steel (17 mJ/m²) . Consequently, the compressive deformation results in a high stacking fault density and in the formation of twins, hcp epsilon-martensite  and bcc alpha´-martensite. In this contribution, the interplay of these microstructure features and their dependence on the deformation direction are illustrated on the results of the in-situ synchrotron compression experiments, which were performed up to 9 % compression.
The synchrotron diffraction patterns were recorded in transmission diffraction geometry by using a 2D detector. This experimental setup allowed the data acquisition in a wide range of angles between the diffraction vector and the applied load, which is required for lattice strain and texture measurements. A short wavelength of the synchrotron radiation made the diffraction measurements over a broad range of the diffraction indices possible, which is required for the evaluation of the phenomena that are related to the crystal anisotropy of the lattice distortion caused by elastic deformation and by the formation of dislocations and stacking faults. The elastic lattice deformation was concluded from the shift of the diffraction lines, the dislocation density from the anisotropic line broadening and the stacking fault probability from both, the shift and broadening of the diffraction lines. Concurrently, the in-situ synchrotron diffraction experiments revealed the phase composition of the deformed steel, which was used to track the load-induced transformation of the metastable austenite to epsilon-martensite and alpha´-martensite.