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Investigation of Destruction Mechanisms in Reactor Steels

#G-719


Investigation of Destruction Mechanisms in Reactor Steels and Alloys under Cycling Deformation

Tech Area / Field

  • FIR-MAT/Materials and Materials Conversion/Fission Reactors
  • MAT-ALL/High Performance Metals and Alloys/Materials

Status
8 Project completed

Registration date
10.05.2001

Completion date
03.08.2006

Senior Project Manager
Pradas-Poveda J I

Leading Institute
Georgian Technical University, Georgia, Tbilisi

Collaborators

  • Michigan Technological University / Department of Metallurgical and Materials Engineering, USA, MI, Houghton\nAustrian Academy of Science/University of Leoben/Institut fuer Metallphysic, Austria, Leoben\nKagawa University, Faculty of Engineering, Department of Advanced Materials Science, Japan, Takamatsu\nTohoku University, Japan, Sendai\nGeorgia Institute of Technology, USA, GA, Atlanta\nFraunhofer Institut Werkstoffmechanik, Germany, Freiburg

Project summary

A contemporary (modern) industry permanently raise demands for the quality of construction steels and alloys. These demands are even stricter for the steels used in nuclear power engineering. It is caused by the possible danger of failure, which can lead to ecological catastrophe like the Chernobil nuclear tragedy.
It was experimentally shown that in the reactors a 10-20Hz pulsation takes place. During the process of vibration, tensions rise up to 0,1 MPC. While starting or stoppage of the process, because of thermal tensions, strain in metal may reach 0,5%.
In addition the heat-producing parts of nuclear reactors (TBEA) and technological channels are irradiated. (These parts are produced of austenitic, stainless steels such as X18H10T, X18H12T, 0X18H12Б, 1X14H16Б in the USSR and 304, 316, 321, 347 in the USA). Because of irradiation steel becomes mere brittle, changes shape and causes failure. Consequently, these steels should be radiation and corrosion resistant and have sufficient mechanical and cyclic strength. Such steels should stand a drastic changes of temperature that is inevitable at the lannching of the nuclear racket engines. Thus, metter of failure can be irradiation and thermal and mechanical cycling.
Study of these problems is of international interest from the point of view of nuclear security and ecological catastrophe. Notwistandig the importance of the above prolem, still are not completely investigated the following problems:1) influence of irradiation on structure of steel, 2) changes in internal structure of steel under cyclic deformations, 3) influence of irradiation and alteration of internal structure of steel. Location, matters and mechanisms of nucleation of microcracks still remain the question. For the solution to these problems we are proposing the project in order to win the grant.
The purpose of the project is to study the above questions related with cyclic deformations of the steel and influence of gamma irradiation. The Cr-Ni based steels used in reactors, turbo generators, submarines and other areas of modern engineering will be studied. To accomplish a task we intend to investigate the changes in the internal structures of steels. These changes will be studied not only during the whole duration of cyclic treatment and - irradiation but also after destruction of specimens. First step of the study will be the investigation of the initial internal structure of the steels, then changes of the structure at the first stages of cycling tests and during failure of the samples. ( after irradiation by gamma quanta as well). Changes in thermal treatment and chemical composition are also supposed.
The final purpose of the projeckt is to obtain the model alloy, that will be radiation-resistant and resistant to cyclic deformations, but less expensive that the existant alloys.
In the course of Project implementation following results are expected:
1.the reasons will be determined for premature destruction and catastrophic degradation of the steel working parts subjected to plastic deformation and mechanical cycling;
2. the types and locations of structural changes in steels will be defined, which are responsible for the microcrack formation and destruction;
3. the influence of -irradiation on the structure mechanical properties and destruction of steels will be studied;
4.the sound scientific bases will be formed to explain and simulate processes that cause premature destruction of the working parts during cyclic deformation in the similar conditions.
5. the chemical composition of commonly used steels will be changed in order to increase their mechanical resistance;
6. the optimal parameters for the thermal treatment will be established and recommendations will be elaborated for the reactor and structural steel manufacturers to increase their lifetime and prevent catastrophic degradation
7.a new type of steel will be alloyed with the cyclic properties and radiation resistance.

We have 30-years experience in the field of scientific investigation of different types of construction steels and alloys, their structure, mechanical and thermal properties, cyclic behavior.
Besides, the well qualified personnel works at our Center for Structural Research. Their scientific articles were published in different journals and reported at various international conferences and symposiums. The Center is equipped with modern scientific instruments. All these forms the sound bases for the successful implementation of this Project.
The final goal of our Project is to clarify the reasons for microcrack formation and subsequent destruction of steels. Participation in this Project will provide to our scientists an opportunity to redirect their knowledge and skills to peaceful activities. It will promote the integration of our scientists into the International Scientific Community. The Project is aimed to support the fundamental and applied research, and also to develop the technology for civilian purposes. Application of the results of this Project can increase the safety of nuclear power stations and prevent the environment pollution. The developed technology can be reduced to practice at the local factory thus promoting its transition to a market-based economy. The developed technology and steels can be widely used for nuclear, space, architectural, consumer and different industrial applications. The Project is open for collaboration with other concerned scientists and organizations.
The Project will be carried out in close collaboration with foreign scientific institutions. Our collaborators using their own equipment will verify the results obtained at our Center. Joint workshops and scientific seminars are also planned


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