An assessment of microstructure, hardness, tensile and impact strength of friction stir welded ferritic stainless steel joints

Microstructure and mechanical characterization of friction stir welded 409M ferritic stainless steel joint were carried out. Single pass welds free of volumetric defects were produced at a welding speed of 50 mm/min and rotation speed of 1000 rpm. Optical microscopy, microhardness testing, transverse tensile, impact and bend tests were performed. The coarse ferrite grains in the base material are changed to very fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. Tensile testing indicates overmatching of the weld metal relative to the base metal. The joints are also exhibited acceptable ductility and impact toughness.