Investigation of mechanical and micro structural properties of ST14 steel sheet joints by friction stir welding process

Abstract High strength and ductility are considered as the superior features of ST14 steel, which have resulted in the extensive usage of this material in the automotive and aerospace industries. Friction stir welding (FSW) is one of the new methods of solid-state welding with preferable mechanical properties for joining steel components. In this study, the mechanical and microstructural properties of 1.5 mm thick ST14 steel sheets in FSW process are investigated. The results revealed the highest tensile strength of 305 MPa for the welded specimen at the rotational speed of 800 rpm and linear speed of 80 mm/min. In addition, higher separation rate of the tungsten carbide particles from the tool as a result of higher heat input to the piece was realized from the metallographic test with the use of sample with rotational speed of 1000 rpm and linear speed of 50 mm/min. Moreover, regarding the results of micro hardness test, an increased hardness to 115\(\pm\)1 HV in the stirred zone (SZ) was acquired in this sample. Furthermore, the presence of the tungsten carbide particles were observed in this area.