Laser-welded structures are often subjected to dynamic service loads ranging from cyclic fluctuations to completely random ones. The laser-welded lap joints suffer from defects resulting in notch effects, surface cracks, residual strains and stresses. The fatigue strength of the laser-welded lap joints is reduced significantly because of the presence of these defects, and the size of the welded joints is small. Therefore, the mechanical strength of laser-welded structures must be defined in terms of the fatigue strength and residual stress of the obtained joints or assemblies. To analyze the above-discussed effects, this paper proposed two approaches: numerical and experimental methods. The originality of the work is to weld the rolled sheet in three directions (0°, 45°, 90°). The residual stresses before and after low cyclic tensile tests of assemblies obtained from overlapped thin DP600 steel sheets were calculated by ABAQUS. The obtained results were compared to the experimental data by neutron diffraction. The presented results in terms of residual stresses curves, spatial distributions of residual stresses obtained at the end of laser welding and low-cycle fatigue. It showed the relaxation effect of residual stresses and the direction effect of welding. These results have been explained by several factors.