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The paper presents the transmission electron microscopy (TEM) investigations of the structure and phase composition of the heat-affected zone (HAZ) in welded joint modified by four types of welding, namely: electrode welding and electropercussive welding both with and without the introduction of artificial flaws. Artificial flows are aluminum pieces. TEM investigations are carried out within HAZ between the deposited and base metal at 1 mm distance to the latter. The type 0.09C-2Mn-1Si-Fe steel is used as weld material. It is shown that the welding process has an effect on the material morphology, phase composition, faulted structure and its parameters. Long-range stresses are divided into plastic and elastic components. It is demonstrated that the type of welding does not change the structural quality of welded joint represented by perlite and ferrite as contrasted with their volume fraction. According to observations, any type of welding with the introduction of artificial flaws results in the destruction of perlite. Polarization of the dislocation structure occurs. The amplitude of mean internal stresses does not practically depend on the welding type. It is shown that the introduction of artificial flaws both during electrode and electropercussive welding reduce the quantitative parameters of the faulted structure.