Structure and mechanical properties of welded joints of high strength steels at the hybrid laser-arc welding

Purpose.Nowadays the production of critical welded structures of high-strength steels more and more new technologies are used hybrid laser-arc welding, which increase the productivity of the process and provide the strength and plasticity of welded joints. The aim of this study was to investigate the features of phase and structural changes in the metal of welded joints of high-strength steel obtained by hybrid laser-arc welding and evaluate the effect of one of the main technological parameters -welding speed on a formed structure and mechanical properties of welded joints. Methodology.Studies were carried out on welded joints of high-strength steel 14HGN2MDAFB. Welds were obtained in conditions of diverse speeds (72-110 m / h) of the hybrid laser arc welding. The structural changes were studied using a complex technique of research, which includes optical metallography, analytical scanning and transmission electron microscopy. Findings. On the basis of information obtained at different structural levels (from grain to dislocation) the analytical assessment of the impact of the structural parameters on the mechanical properties and fracture toughness of welds are made. Originality. Optimal technological modes of the hybrid laser-arc welding of high strength steel 14HGN2MDAFB providing, in terms of formed structure, high mechanical properties and fracture toughness of metal welded connections have been established. Practical value. The presented results showed the prospect of the development of technological modes of the hybrid laser-arc and solutions of objectives of formation of the most favourable structure of welded joints of highstrength steel to provide the necessary complex mechanical properties and fracture toughness of welds.