Welding of dissimilar materials is frequently accompanied by structural and technological difficulties and not always successful. The knowledge resulting from dissimilar welding experiments can be used to further identify directions and suitable technological parameters for optimal results. This paper report on the difficulties encountered on friction welding of nodular cast irons with low alloyed steels, due in principle to the low deformation capacity and the microstructural differences. It was shown through experiments that low friction times and high axial pressure leads to a significant plastifiation of the cast iron, while the low alloyed steel remains practically undeformed. The early (premature) plastifiation of the cast iron leads to a radial expulsion of the base structure associated with a continuous transport of the graphite nodules in the joint plan. As a result, a new graphite film forms which hinders a metallic contact between the parts and a welded joint. Qualitative and quantitative electron microscopy observations reveal carbon and alloying elements diffusion phenomena on the interface of the dissimilar materials to be joined.