Mechanical and microstructural characterization of ST 37 butt joints by friction stir

The aim of this research is to investigate mechanical and microstructure characteristic of ST 37 Friction Stir Welded (FSW) butt joints. The rolled plate of ST 37 steel was used as the base material. Tungsten carbide (20 mm on diameter) was used as the tool. The FSW process was conducted on a CNC milling machine. FSW joints were produced at 1500 and 2000 rpm of rotational speeds variation and the transverse speed is constan at 40 mm/min. Furthermore, the influence of rotational speed on the microstructure and mechanical properties of the joints were investigated based on parameters mentioned above. The tensile test was done based on JISZ 2241 standard. Microhardness was investigated based on ASTM E 384. Joint microstructure was also analyzed by optic microscopy. As a result, FSW joint at 2000 rpm tool rotation shows higher tensile strength, yield strength and percentage of elongation in compare to 1500 rpm rotaton speed. In addition, its tensile strength is about 5 % lower than Base Material (BM) which its ductility decreases up to 30 %