Study of microstructure effects and corrosion resistance of dissimilar joints of stainless steel 304 to carbon steel St37 by friction stir welding

In this study, plates of 304 stainless steel and st37 steel were welded together by friction stir welding which has been set at a welding speed of 50 and 100 mm/min and tool rotational speed of 400, 600 and 800 rpm in order to study the effect of parameter variations on micro structure and corrosion resistance. Samples were cut from the cross section of the joint and metallographic imaging was performed after etching. For the corrosion resistance evaluation, samples were immersed in Ferric Chloride and acetic acid 2M and then were studied by macroscopic imaging and stereograms also Tafel polarization and electrochemical impedance spectroscopy (EIS) tests have been performed in 3.5% NaCl solution in order to verify weight loss results. The results showed that the corrosion rate of the St37 base metal is more than other parts of the joint. On the other hand, all parts of stainless steel 304 was galvanically protected. The best corrosion resistance among all the weld areas were determined for the weld at the tools rotational speed of 800 rpm due to minimum grain growth by heating.