Maksimenko A. Weldability of capacity microalloyed steels with С т = 350 … 460 МPа and hardening of welded joints with the accumulated fatigue damages

The thesis aims to gain knowledge about the features of the changes in the properties and structure of steel welded joints strength class C350-C460 influenced by TСW and external loading. The results of experimental studies have shown that steel S355J2 and 10Г2ФБ, strength class С350 and С460, respectively, have a good capacity for welding. Equal strength and high frueture toughness of welded joints of steel can be achieved in a wide range of welding conditions (10 Qw 50 kJ/cm), and their high resistance to the formation of cold cracking during welding without preheating in a situation where content of diffusion hydrogen in the weld metal does not exceed 5,0 ml/100g. The process of fatigue damage accumulation in metals НАZ steel 10Г2ФБ and its impact on the change in model samples as well as on mechanical properties of welded joints, structure and value of gradient of magnetic field, the last before the falure, in relation to the initial increase in 5 - 6 times, was considered. The technology of preventive repair, which is performed on the stage before the formation of fatigue cracks and make it possible to increase durability in the welds 1,45 - 2 times is proposed. The technologies of welding of steels strength grade С350-С460 are developed.