Poznyakov V. Weldability of high-strength steels in repair of long - term in-service structures.

The thesis is devoted to the study of effect of residual stresses on the structure and properties of welded joints of high-strength steels and development on this basis of scientific fundamentals of creation of repair-welding technologies for restoration of metal structures to improve their service life and reliability. It was defined that main factors which determine behavior of metal under influence of thermodeformational welding cycles at the repair of metal structures are level of residual stresses and dislocation structure. The pecularities of effect of residual stresses on the change of mechanical properties of welded joints performed under the conditions of rigid fixture and their resistance to brittle, delayed and fatigue fracture were revealed. The conceptions of kinetics of welding stresses in materials with complex structure transformations were developed, which showed that level of residual stresses can be controlled changing the parameters of thermal cycle of welding. The quantitative correlation between residual stresses, diffusion hydrogen content in the deposited metal and resistance to the cold cracks initiation in welded joints of high strength steels with different equivalent of carbon was established. The method of control of stress-strain state of rigid fixtured welded joints by optimizing the technique and technology and compulsory plastic welds deformation was suggested. The technologies of repair welding for restoration of integrity of sub-assemblies and their 1.5 - 2.0 times improvement of their reliable service life were developed and realized.