Strain controlled low cycle fatigue tests are performed at 300 °C under tension compression on an 18%Cr ferritic stainless steel using base metal and welded specimens. Changes in the microstructure and geometry of the weld bead have a negative impact on the specimens' lifetime. Digital image correlation is used to get information on strain gradient in specimens. Potential drop measurements as metallographic observations are used to monitor micro-cracking. The significance of the results is discussed using finite element computations of welded specimens and observations of fracture surfaces. A tentative rationale is proposed using an energy based micro-crack growth model.