Residual stresses play an important role in the mechanical behavior of steels and welded structures. To examine the effect of residual stresses on tensile behavior and fatigue, residual stresses in the specimens were generated by welding. Experimental stress-strain curves of the specimens with/without residual stresses were obtained and compared to simulated curves obtained by the finite element analysis. The two results are in a good agreement. Finally, to study the relaxation of the residual stresses during fatigue crack propagation, we carried out fatigue crack propagation analysis by a 3-D cohesive zone model. Initial welding residual stresses decrease as the number of cycles increases.