Effect of Friction Stir Welding on the Microstructure and Mechanical Properties of Super Duplex Stainless Steel

The aim of this study is to investigate the microstructure and mechanical properties of friction stir welded super duplex stainless steels. In this regard, UNS S32750 steel is joined by friction stir welding (FSW) method. The tool used in this research is made of WC with 16-mm shoulder diameter and 5-mm pin diameter. Microstructural investigations are carried out by optical microscope and scanning electron microscope. In addition, in order to evaluate the mechanical properties, microhardness and tensile test are utilized. The results show that grain refinement occurs in the stir zone (SZ) during the FSW process. Image analysis reveals that the volume fraction of ferrite in the SZ was about 60%. Microhardness test shows that the average hardness value of base metal is 285 Vickers, however, in the stir zone, the hardness value is increased up to 360 Vickers.