Chervyakov M. High-temperature deformation and fracture of welded joints from austenitic steels and nickel alloys

Object of research - polycrystalline plates of nickel alloys, processes of structuring, formation of hot cracks in welded joints during fusion welding. The purpose is to study the peculiarities of the mechanism of localization of plastic deformations and appropriateness of fracture of metal polycrystals in welded joints on macro- and mesolevels and to develop, on this basis, the criteria for assessing boundary conditions of metal during the welding process, including ways to increase the resistance of welded joints to formation of cracks. Methods: generally accepted world-wide techniques for investigating the tendency of austenitic materials to form hot cracks, light, transmissions, electron microscopy, scanning electron microscopy, statistical analysis. A complex approach is proposed and implemented to assess the tendency to form hot fissures during fusion welding, which includes experimental studies and simulation of the stress-strain state of welded joints at various scale levels. The developed mathematical model allowed to obtain new data on thermodeformation processes on macro- and mesolevels during fusion welding. The method of numerical investigation of the influence of technological parameters of the welding mode on the formation of a stress-strain state during welding of polycrystalline materials, taking into account their grain structure, is proposed. The criteria for evaluating the technological strength are substantiated, thus the dependence of the probability of the formation of hot cracks on both the chemical composition and structure of the metal as well as the welding modes is established. Optimization of the welding technology should be done taking into account the values of deformations and stresses by controlling the thermal cycles of welding, which will ensure the stability of the material against the formation of hot cracks. On the basis of the established regularities of the processes of deformation and fracture of materials on macro- and mesorelines, further experimental and computational methods for assessing the crack-resistance of materials with a stable austenitic structure were developed and the principles of developing welding technology for modern structural materials with high strength of welded joints were formulated.