Metallurgical investigation of direct drive friction welded joint for austenitic stainless steel (AISI 316)

The present study investigates the metallurgical behavior of direct-drive friction-welded (DDFW) joints for high Cr, Ni, and Mo steel (AISI 316). Macro-microscopic, microhardness, and X-ray diffraction (XRD) were conducted. The results for the macroscopic view showed that the narrow welding center did not exceed 600 µm and there were no macro cracks or defects, indicating a uniform structure. The microstructure exhibited a significant welded joint interface with microcavities and a grain refinement of 10 µm, about three times smaller than the grain size of AISI 316, due to the creation of a highly plastically deformed zone (HPDZ), while the thermo-mechanically affected zone (TMAZ) formed in the neighboring area with a grain growth of about 100 µm, relatively enlarged three times compared to AISI 316 and time time related HPDZ. Thus, the high level of microhardness was investigated at the welding center and low values in the neighboring area were caused by the formation of the HPDZ and TMAZ, respectively. XRD also illustrated the concentration of gamma iron at the 111 level due to the grain refinement resulting from high plastic deformation.