An Intensive Study on Effect of Tool Traverse Speed on Formation of Stir Zone Microstructure and Mechanical Properties of Friction Stir Welded HSLA Steel Joints

This study examined the impact of tool traverse speed (WS) on the generation of heat and plastic swirl during Friction Stir Welding (FSW) of DMR249A steel. In this experiment, lanthanated tungsten tools were used to weld 5 mm thick steel plates. The tool traverse speeds ranged from 20 mm/min to 40 mm/min, with a constant tool rotation speed of 600 rpm and a 2.5 mm/min tool plunge rate and axial force of 15 kN. Optical Microscopy (OM), scanning electron microscopy (SEM), SEM with Energy Dispersive Spectroscopy (EDS), and Electron Backscattered Diffraction Analysis (EBSD) were employed to analyze the microstructural properties of the weld samples. Of the five tool traverse speed, it is found that the welding pace of 30 mm/min resulted a defect-free sound weld with good strength and acceptable impact toughness properties. Due to the production of finer grains in the weld nugget region during the stirring action of the spinning tool, the tensile strength of the stir zone is higher (overmatched) than that of the parent metal. Because of the small dispersion of tool material in the stir zone, the joints' ductility and impact toughness were reduced as compared to the DMR249A HSLA steel.