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

Abstract

The presented work deals with the possible reasons of nucleation and propagation of macro-, meso-, and microcracks after low-cycle fatigue (LCF) tests of stainless, austenitic steels at room temperature. This research will also support the solution of some important problems of steel modeling and their application to EURATOM, FUSION, TACIS, PHARE, CORDIS, PERFECT, AMES, FP 7, and GEN IV programs. The scanning electron microscopic (SEM), X-ray, and transmission electron microscopic (TEM) examinations and statistical analysis of the samples which undergone the low-cycle fatigue (LCF) showed that the average length of slip bands and micro-components of macrocrack are equal, and they are always parallel to each other, indicating their crystallographic character. The microcracks in these samples, caused by the residual stresses after the LCF, were studied in the TEM samples after their preparation to reveal the features of microcrack initiation and nucleation. It was shown that microcracks propagate along slip bands and change their propagation direction at the boundaries of grains and subgrains. This confirms that microcracks, as well as micro-components of mesocrack, are crystallographic. Mathematical calculations of elastic-plastic model are also performed which showed that the length of plastic zone, according to our assessments, is equal to 110-120 d, where d is a width of crack opening.

High Temperature Fatigue Behaviour of Austenitic Stainless Steel : Microstructural Evolution during Dwell-Fatigue and Thermomechanical Fatigue

“…Regions where numerous dislocations move on adjacent slip planes are called slip bands and these are associated with regions of intense plastic shear deformation separated by regions of almost no shear [49,52,53]. Evidence of slip planes and slip bands are commonly found when investigating the microstructural features of high temperature fatigued austenitic stainless steels [54][55][56]. Wavy slip originates from multiple screw dislocations changing from one plane to another, called cross-slip.…”