Freiberg for the hot rolled TRIP steel samples. For the metallographic sample preparation we would like to thank Mrs. Dipl.-Ing. A. Mueller, Mrs. K. Becker; for the conventional preparation of TEM samples and the FIB preparation of TEM samples on Infineon, Dresden we would like to thank Mrs. Dipl.-Ing. A. Leuteritz.Microstructure defects control the TRIP effect and/or the TWIP effect and contribute significantly to the absorption of deformation energy in plastically deformed austenitic CrMnNi steels. In this study, the propagation and interaction of dislocations, stacking faults and twins connected with the formation of Lomer-Cottrell locks, stacking fault tetrahedra, dislocation clusters, deformation bands, microtwins with high-energy incoherent twin boundaries and the nucleation of a 0martensite in the areas of the high local lattice strain due to the fluctuation of the stacking fault density and the lattice shearing, were analysed in the CrMnNi TRIP steel after different deformation extents via transmission electron microscope with high resolution and via scanning electron microscope. ADVANCED ENGINEERING MATERIALS 2013, 15, No. 7
The microstructure development in CrMnNi TRIP steel during the onset of the plastic deformation was investigated with the aid of in‐situ X‐ray diffraction experiments. The analysis of the shift and broadening of the X‐ray diffraction lines allowed the elastic and the plastic components of the lattice deformation to be separated from each other. This separation made possible to follow the formation of the microstructure features like stacking faults, deformation bands and local lattice rotations that were afterwards confirmed by X‐ray diffraction with high resolution, scanning electron microscopy and transmission electron microscopy.
Formation of microstructure defects at the phase boundaries in TRIP steels was investigated with the aid of microstructure analysis on a TRIP steel crystal, which was grown by the Bridgman technique. The microstructure studies comprised scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and transmission electron microscopy with high resolution (HRTEM). Initial XRD measurements revealed that the crystals under study consist of austenite and ferrite with extremely strong preferred orientations. Subsequent XRD pole figure measurements and EBSD scans have shown that the orientation relationship between austenite and ferrite can be described by the Nishiyama-Wassermann model. For a detailed description of the microstructure of the Bridgman crystal, the orientation distribution of crystallites within the individual phases was investigated using the XRD reciprocal space mapping and the rocking curve measurements. These experiments have shown that the density of microstructure defects is much lower in ferrite than in austenite. The direct information about the defect structures at the phase boundaries between austenite and ferrite was obtained from the TEM micrographs, which revealed complicated micro-twin structures at the boundaries between the neighbouring phases. HRTEM discovered very narrow stripes of ferrite embedded in austenite that were regarded as a source of the microstructure defects in austenite.
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