Microstructural Evolution during Friction Stir Welding of Austenitic Stainless Steel AISI 316 to Low Carbon Steel St 37

The microstructural evolution of dissimilar joining of austenitic stainless steel AISI 316 and low carbon steel St37 by friction stir welding has been investigated. Friction stir welding was carried out using a rotational speed of 600 rpm and a linear speed of 50 mm/min. The microstructure was characterized using a scanning electron microscope and optical microscopy. Also, possible phase transformations were determined using X-ray diffraction technique & electron diffraction spectroscopy. The results of phase investigations showed that no carbides and brittle phases were detected at the joined boundary. Microstructural investigations showed that the highest decrease in grain size occurred in the stir zone of the austenitic stainless steel which was attributed to discontinuous dynamic recrystallization caused by severe deformation imposed at high temperatures in this region.