Analysis of structural factor influence on local internal stresses and zones of deformation localization in upper and lower bainite structures in welded joints of low-alloy steel at wet underwater welding was performed. It is established that when welding joints under the water and applying an external electromagnetic field in the metal of the heat-affected zone (HAZ), a finer-grained substructure is formed with a general decrease in the dislocations density and with their uniform distribution. Estimates of the local internal stresses level considering the dislocation density distribution in the structural zones of their localization show that their maximum level is formed in the metal of the HAZ overheating region at welding without the external electromagnetic field along the upper bainite laths boundaries. The upper bainite structure is characterized by forming localized deformation zones, where the most significant dislocation density gradients are observed. This can lower the crack resistance of welded joints. Low values of local internal stresses are characteristic of welded joints obtained in the modes applying an external electromagnetic field. This is facilitated by the overall decrease in the dislocation density and their uniform distribution in the lower bainite structural components, which provides high crack resistance of welded joints.

The aquatic environment will negatively affect the processes that occur during the formation of a welded joint and leads to a deterioration in its properties. The welding conditions do not allow the use of traditional methods to improve the quality of the weld metal - preheating or subsequent heat treatment. One of the possible effective ways to solve this problem when welding with flux-cored wire is the use of external electromagnetic exposure. Generation of axial alternating control magnetic fields in the welding zone allows controlling the hydrodynamics of the molten weld pool. Because of the interaction of an external electromagnetic field with an electric field of the arc, ponderomotive forces appear in the weld pool, which leads to mixing of the liquid metal. Changing the direction of electromagnetic induction with a given frequency and interval, you can periodically change the direction of flow in the weld pool. Intensive reverse mixing of the melt occurs, during which the hydrogen accumulated in front of the crystallization front as a result of concentration compaction is removed from it, the melt temperature in the central and peripheral areas of the pool is averaged, which slightly reduces the crystallization rate of the weld pool, thereby increasing its degassing time. As a result, it was possible to significantly reduce the porosity of the weld metal (more than 8 times) and reduce the hydrogen content (more than 2.5 times). Metallographic studies showed a significant refinement of the structure both weld metal and the heat-affected zone (2 and 1.3 times, respectively), its homogenization and a decrease in the degree of defectiveness. Thus, the investigations showed that the external electromagnetic effect on the liquid metal pool in the process of wet welding underwater is a useful tool that allows you to control the processes that occur during the crystallization stage of the weld pool and significantly increase the ductility of the weld metal (more than 1.5 times).