Effect of the structure on the mechanical properties and cracking resistance of welded joints of low-alloyed high-strength steels

Abstract

Low-alloyed high-strength steels are widely used for the manufacture of welded metal structures in various branches of modern industry, including construction, agricultural, transport, engineering and defence. To produce joints of these metals mechanized or automatic welding in shielding gases are mostly used. Nowadays, such progressive technologies as laser and hybrid laser-arc welding implement, which allows obtaining welded joints at increased speed with much smaller dimensions of welds and heat-affected zones, to improve the quality of high-strength steel joints and the to raise productivity of their manufacture. In this work, we studied the influence of the structural-phase composition and specific parameters of the structure, which are formed in the weld metal and the heat-affected zone, on the strength and crack resistance of welded joints of low-alloyed high-strength steels. The structure and phase composition of welded joints of high-strength steels was investigated depending on the technological parameters of arc, laser and hybrid laser-arc welding. It is shown how the microstructure affects the operation properties of welded joints. The relationship between the phase composition, the parameters of the grain and fine structure of the metal (substructures, dislocation densities, sizes and distribution of carbides in the structural components of bainite, martensite, etc.) of welded joints, their mechanical properties, fracture toughness and the level of local internal stresses in various structural components is investigated. The most influencing structural factors shown to be the dispersion of the bainitic structure and substructure, the uniform distribution of the density of dislocations, and the absence of extended dislocation clusters − zones of nucleation and propagation of cracks.