Microstructure changes, mechanism of microcrack nucleation, their growth, and reasons of fracture of martensitic steels at low cycle fatigue used in reactors of nuclear power stations

none2This project deals with one of the main problems of solid state physics, the reasons and mechanism of premature fatigue failure and degradation. To solve this problem the study of martensitic steels used in nuclear reactors and turbo generators is supposed. Consequently, the aim of the project is to reveal the steel with the best mechanical and cyclic properties and radiation hardness; with the minimum content of alloying elements such as Ni and Mo. Since 60-70s of twentieth century the martensitic and ferrite-martensitic steels are used in steam–boilers and turbo generators of nuclear power plants. Later this material was considered a building material for the first walls of fast nuclear reactors. Because of their radiation hardness, several grades of the steels were designed in the USA, Europe, Japan and former soviet union. During performance the steels undergo different thermal, radiation and mechanical cyclic impacts that cause degradation and premature damage, leading to failures and ecological catastrophes. Therefore, the main tasks to be solved within the proposed project is to investigate: a. location of internal stresses peculiar to martensitic structure, b. physics of nucleation and crystallography of ultra-microcraks’ growth, characteristics of structural changes facilitating formation of cracks and degradation of the materials; c. relation between the sizes of initiated microcracks, plastic zones, martensitic crystals and former austenite grains; d. the influence of amplitude and frequency of fatigue deformation and anisotropy of the material on the processes of microcrack nucleation and propagation. As the factors, listed above, predetermine the reliability and service life of nuclear power generating machines, clearing of these questions is both of scientific and commercial importance. In addition, the solution of the above tasks will provide a deeper understanding of physical aspects of degradation and damage of martensitic steels and other materials used in nuclear power stations, and contributes to physics of fracture and degradation of materials, that in turn will support design of other innovative, advanced materials with significant market potential. Besides, the acquired results may be used for improvement of the available software such as “PROMETEI” and “PERFECT” which are currently intensively developing. The acquired results will supplement the knowledge accumulatd within such international programs as EURATOM, FUSION, TACIS, PHARE etc. Conduction of the above research is provided by the necessity to improve the materials and ways of their fabrication. The proposed project will facilitate to approach these goals with the least expenses and enables improved performance, enhanced safety, and reduced overall system costs.noneEterashvili T.; Ferretti E.Eterashvili T.; Ferretti E