Study of Fracture Mechanisms at Cyclic Fatigue of Steels Used in Nuclear Reactors I

Abstract

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.

Study of Fracture Mechanisms at Cyclic Fatigue of Austenitic Steels Used in Nuclear Reactors

“…However, after strengthening of austenite, martensitic transformation becomes energetically more preferable, or deformation of austenite and martensitic transformation are taking place simultaneously (especially at high values of amplitudes of cyclic deformation) [4]. Consequently, the orientation of micro-cleavages should change while crossing the boundary.…”

“…Thus, it should be supposed that the mesocracks were formed near the border of plastic zone. In the majority of cases, the orientation of mesocrack coincides or is close to the main direction of macrocrack [4]. Analysis of different areas of the zone and measurements showed that the size of the plastic zone is related to that of macrocrack, and an increase in macrocrack size increases plastic zone size.…”

TEM Study of Microstructure Changes, Formation and Distribution of Slip Bands in Austenitic Steels after Low-Cycle Fatigue (LCF) Deformation - II

“…Thus, it is unambiguously known, where preferably the micro plastic deformation takes place and where the microcracks form in the sample. Also, on (or in) which slip bands, and in what conditions are formed the first microcracks, and what kind of correlation exists between the microstructure, slip bands and microcracks.The proposed research is dealing with the above problems and is, in fact, a continuation of a previous work [1].…”

“…During the low cycle fatigue (LCF) deformation slip bands appear on the polished surface of the samples. The authors of [1][2][3][4][5][6][7][8] have shown that at LCF of FCC structures deformation is realized via slip through almost all the 12 slip systems of {111} <110> type. According to [2,6] a transversal glide of dislocations takes place in the slip bands, and the authors of [3][4][5]7] propose that microcracks form exceptionally along {111} planes.…”

Introductory Chapter: Why Austenitic Stainless Steels are Continuously Interesting for Science?

“…The microcrack propagation process and its correlation with the steel microstructure are also quite disputable. Despite numerous experimental results on alteration of microcrack propagation direction, there is no convincing hypothesis explaining the real reasons for the process [19,20]. …”