The object of study are structural transformations, structural-phase state, damageability and properties of welded joints of steam pipelines made of 12Х1МФ and 15Х1М1Ф steels, as well as rotors made of 25Х2НМФА steel during their operation in creep and fatigue conditions.
The subject of study is the influence of physical and chemical processes on structural and phase transformations and the formation of defective structures in the metal of welded joints of steam pipelines, the relationship between the structure of welded joints of steam pipelines and rotors with their properties and damageability.
The dissertation is devoted to comprehensive studies of physicochemical processes that occur in the metal of welded joints of steam pipelines made of 12Х1МФ and 15Х1М1Ф steels and provide structural and phase changes. The above studies were carried out in relation to welded joints of steam pipelines and turbine rotors, which work for a long time under conditions of creep, as well as fatigue and increased work loads.
It was substantiated that structural and phase changes contribute to the damage of welded joints, which occurs by the mechanism of creep and fatigue. The study of the peculiarities of the passage of structural and phase transformations provided an opportunity to reduce their manifestation. This manifestation was reduced by obtaining the original structure of welded joints of steam pipes and rotors with improved qualitative characteristics of their structure. For this improvement, improved welding processes were used, the indicators of which are based on the results of welding heating simulation of the manufactured joints.
The dependence of the reliable operation of welded joints of steam pipelines and turbine rotors, as well as their resource, on the structural and phase state of the metal of the welded joints and the presence of damage in the form of creep pores and fatigue cracks was established.
The studies were carried out using modern methods of analyzing the structural phase state and determining the properties of welded joints, as well as using simulation of welding heating of manufactured joints.
The introduction substantiates the relevance of research tasks, shows the connection of work with scientific programs, plans, topics, sets the goal and main tasks of the research, gives the main research methods and scientific novelty, and formulates the practical significance of the obtained results.
In the first chapter, on the basis of domestic and foreign experience, the prospects of researching the structural-phase state of welded joints of steam pipelines made of heat-resistant steels, which are operated for more than 270,000 hours, are substantiated in conditions of creep and fatigue.
The second chapter provides a description of the methods, techniques, equipment and materials used in the research. A brief description of the improved welding technology and modeling of welding heating is given, the use of which ensured the production of welded joints of steam pipes and rotors with an improved structure. Optical and electron microscopy methods, as well as surface microprobe analysis, were used to study the structure of welded joints. In general, the obtained results of the structural analysis ensured the optimization of the conditions for obtaining higher-quality welded joints of steam pipes and rotors.
The third section is devoted to the study of the influence of the structural phase state and metal deformation of welded joints of steam pipelines that have been in operation for more than 270,000 hours in conditions of creep and fatigue, on their damage.
The fourth section contains the results of research on the relationship between the structural and phase state of long-term operated welded joints and their microdamage under creep and fatigue conditions. The proposed scale definitions of the residual service life of welded joints with the presence of damage to their metal.
The fifth chapter is devoted to the theoretical and practical substantiation of the reliability of work, as well as the determination of the residual resource of welded joints of steam pipes and rotors of TPP and NPP turbines operating for a long time under conditions of creep and fatigue.
Keywords: welded joints, steam pipelines, rotors, resource, damageability, structure, creep, fatigue, properties, carbides, austenite, martensite, bainite, reliability.
