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The tested materials were structural austenitic CrNiNb steels with FCC structure. The working parts of standard cylindric samples were given square cross sections. After testing at different amplitudes of deformation, from the standard cylindrical samples washers were cut for TEM examinations. The slices for TEM were cut after rupture of cylindrical specimens' perpendicular to the fatigue load axis. Foils were prepared by standard method of electro polishing. TEM studies were performed with Zeiss EM-10CR microscope operating at 100kV. For the analysis of the obtained micrographs and diffraction patterns stereographic and trace analysis were conducted.After low-cycle fatigue tests, in the TEM samples, microcracks are formed in the places of stress concentration (caused by redistribution of stresses accumulated during fatigue tests). The nucleated microcracks are of different sizes. Here focus is made on microcracks with the lengths comparable with austenite grain diameter and less. Trajectories of microcracks in the samples of austenitic steels were studied by TEM methods after low-cycle fatigue tests. It is revealed that the direction of microcrack propagation changes at austenite grain boundaries as well as at substructure elements within the grain. At the same time, the microcrack remains parallel with one of the slip bands. Based on stereographic and trace analyses crystallographic planes of fracture and directions of microcrack propagation directions were determined. It is shown that the fracture plane is of {111} type, and propagation direction of <110> type. Analysis of the experimental data allowed making a conclusion regarding the reasons of microcrack propagation trajectory deviation within grain, and about crystallographic character of microcrack propagation direction along <110>.

The work deals with the transmission electron microscopy (TEM) study of thin films of chromium-nickel Х18Н10 steel. The films were prepared from bulk samples after low cycle fatigue (LCF) tests. Focus was made on the processes accompanying propagation of small microcracks. Particularly, the microstructure changes near the crack tip were analyzed in terms of accommodation processes taking place during crack propagation, such as formation of slip bands, twins etc. The authors conducted crystallographic analysis of the defects formed during crack propagation in correlation with the reasons of their initiation and homogenous length of the slip bands. Thus, the reasons of microcrack deviation from the initial direction were determined. The research has shown that the most convenient microstructure variables in the austenitic crystals of polycrystalline sample, affecting the microcrack deviation, are microstructure, crystallography and the homogenous length of slip bands.

This study deals with the possible reasons of nucleation and propagation of macrocracks, mesocracks, and microcracks in stainless austenitic steels after low-cycle fatigue tests at room temperature. It is shown that macrocracks in these steels are formed only after completion of 20-30% of cycles of total deformation. Statistical analysis showed that the average length of slip bands and that of microcomponents of a macrocrack are equal, and they are always parallel to each other, that indicates their crystallographic character. Macrocracks preferably propagate through the grains with no apparent signs of plastic deformation and through isolated mesocracks, but not through mesocracks and grain boundaries.

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