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 α′- martensite 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.