Solid State Phenomena Vol. 313

Abstract: To improve the structure of metal in welded butt joints of railway rails produced by flash-butt welding and increase the reliability of butt joints, it is advisable to carry out their induction heat treatment using high-frequency currents. Solving the problem of a uniform bulk heating of weld metal of railway rails in a narrow area during its heat treatment remains an urgent task. The work describes the principle of designing an inductor without magnetic cores for carrying out a uniform bulk heat treatment of welded butt joints of railway rails for realization of favorable phase transformations of metal and normalization of its structure. The principle is based on the physical laws of propagation of electromagnetic fields and electric currents in the inductor and a rail. Based on the carried out investigations, an inductor was designed that has a variable shape along the perimeter of a rail and a variable distance from it, as well as a partial splitting of the inductor busbar for current parallelization, which provides a uniform bulk heating of a rail butt joint. Splitting of the inductor busbar allowed adjusting the propagation of currents in the inductor and a rail in such a way as to avoid overheating of a rail in its particular areas without a significant increase in the distance between the inductor and a rail, and respectively without a significant increase in the reactive power of the “inductor-product” system. The carried out experiments on heating the welded butt joint of a rail by the designed inductor showed the indices of uniformity and rate of its bulk heating, which are acceptable for heat treatment of rails both on the surface as well as in the depth of a rail in a narrow heating zone with providing the required temperature levels.

Abstract: As intensive work is underway in leading material science centers in the USA, EU, Russia, and China, both to modernize existing titanium alloys and to create new ones, the E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine developed titanium alloys T110 (Ti-5.5Al-1.2Mo-1.2V-4Nb-2Fe-0.5Zr system) and T120 (Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr system), which according to their characteristics, belong to the group of modern two-phase high-alloyed alloys characterized by high strength and good ductility. With more and more attention is being paid to the expansion in the usage of welded structures and assemblies of high strength titanium alloys with UTS ≥ 1100 MPa, there’s urgent need in studying best ways to obtain welded joints from such alloys. The weldability of two-phase high-alloyed titanium alloys, the use of which can give big reduction in structural weight, is significantly worse than low-alloyed alloys, therefore for a new alloy it is necessary to ensure the possibility of obtaining welded joints with a strength of at least 90% compared to the strength of base material. The aim of this work is to study the influence of the welding thermal cycle and reducing of weld metal alloying degree on the structure and mechanical properties of welded joints of high-strength titanium alloy Ti-6.5Al-3Mo-2.5V-4Nb-1Cr-1Fe-2.5Zr with tensile strength more than 1200 MPa, as well as assessment of it welded joints properties in comparison with other high-strength titanium alloys.

Abstract: Extending the lifetime of energy facilities is extremely important today. This is especially true of nuclear power plants, the closure (or modernization) of which poses enormous financial and environmental problems. High-quality repair of reactors can significantly extend their service life. One of the critical parts is heat exchangers, the tubes of which quite often fail. Sealing, as a type of repair of heat exchanger tubes by the plugs, is promising provided that the joint quality is high. Practical experience in the use of welding to solve this problem has shown the need to search technological solutions associated with increasing the depth of penetration and reducing the area of thermal effect. The aim of the work was to develop a highly efficient technology for repair and extension of service life of heat exchangers of nuclear power plants based on the results of studying the technological features of laser welding of joints of dissimilar austenitic steels AISI 321 and AISI 316Ti in the vertical spatial position. Based on the results of the analysis of mechanical test data, visual and radiographic control, impermeability tests and metallographic studies of welded joints, the appropriate modes of laser welding of plugs have been determined. The principal causes of defects during laser welding of annular welded joints of dissimilar stainless steels are determined and techniques for their elimination and prevention of their formation are proposed. Based on the results of the research, technological recommendations for laser welding of plugs in the heat exchange tube of the collector are formulated, which significantly improves the technology of repair of steam generators of nuclear power plants and extends the service life of reactors.

Abstract: It was revealed that spatial position during laser welding of AISI 321 stainless steel influences the processes in the weld pool and the process of its crystallization. The geometry, structure, distribution of chemical elements depend on the cooling rate of the welded joint, which varies in different spatial positions during laser welding of stainless steel AISI 321. To achieve the lowest variance of results and the maximum values of mechanical characteristics of the welded joints of AISI 321 stainless steel it is recommended to produce laser welding in a vertical position.

Abstract: It has been established that the developed method of manufacturing workpieces for the sectors of the drums of X20CrMoWV3 steel reel’s and die cubes from X5CrNiMo steel using a solid start and exothermic flux significantly reduces the complexity of their manufacture. The cast reel’s drum sectors workpieces and die cubes, obtained by the electroslag remelting (ESR) method, had a smooth surface without corrugations, sinkers, and slag inclusions. Heat treatment provides the required mechanical properties and the absence of flocs in the cast electroslag metal. An effective way to increase the performance of electroslag processes is using the exothermic flux, which contain scale, ferroalloys, aluminum powder and standard flux (welding flux ISO 14174 – S F AF3, etc.) in quantities sufficient for the exothermic reactions to occur, which ensures the generation of additional heat in the starting period of electroslag processes and contributes to the accelerated induction of the slag bath of the required volume at the “solid” start both monofilar and bifilar schemes of conducting the process instead of the “liquid” start. Electroslag processes using an exothermic alloyed flux on a “hard” start allow to obtain (compared to existing methods of slag bath formation) an increasing in the output of a suitable metal 2...10 %; saving on melting 1 kg of standard flux 1.2...1.4 kW h; reducing of the starting time of the ESR process to 25 %.

Abstract: This paper presents the results of a study of the effect of preliminary heat treatment and ball milling of aluminum powder on the cold spraying process and the properties of the obtained coatings (porosity and microhardness). The ball milling of aluminum powder leads to an increase in specific surface area, a decrease in apparent density and a decrease in the value of the crystallite size, which indicates a decrease in grain size. It is shown that coatings deposited from ball milled powders have slightly higher coatings hardness averagely. The profilometry of aluminum coatings obtained under the same conditions from the initial and processed powders did not reveal significant changes in the form of coatings and their typical dimensions (width, thickness), which indicates the absence of significant changes in the deposition coefficient of the initial and processed aluminum powders. Ball milled powders on average correspond to slightly higher hardnesses of coatings.

Abstract: X-ray structural studies have shown that with the increase of the life of the pipes, the surface layers of the metal adsorb a significant amount of gases (hydrogen, oxygen and sulfur), especially this is strongly manifested in the field of corrosion defects (ulcers, pitting). Also, it was found that in the process of long-term operation, the metal of the pipe walls is heavily flooded, which directly leads to its brittle and, as a consequence, increased hardness and reduced ductility. Such studies are unique in the subject of corrosion-mechanical resistance of metal and its degradation during long-term operation in the presence of alternating loads and at the same time, the aggressive environments of oil and gas fields.

Abstract: Influence of the rate at which energy is applied to aluminum powder during its ball milling is investigated. Rolling granulation is a main process due to which treated particles achieve their unique morphology and microstructure. Drastic temperature rise at rapid ball milling leads to increase in plasticity and local melting of treated powder particles that result in their adherence to the surfaces of milling balls and mill cylinder walls. Mass of aluminum powder adhered to the ball surface is proportional to the total surface area of all balls loaded in mill.