Evaluation of tensile strength and fatigue strength of SUS304 stainless steel friction welded joints

Friction welding of SUS304 stainless steel was carried out in order to examine the relationship between joint strength and deformation heat input in the upset stage or upset bum-off length. Joint strength was evaluated by tensile and fatigue testings. It was found that the deformation heat input in the upset stage or the upset bum-off length correlated well with joint strength. That is, when the deformation heat input in the upset stage and upset bum-off length exceed 120 J/s and 1.0 mm respectively, a stable tensile strength was obtained. The tensile strength of sound joints was lower than that of SUS304 base material, because the heat affected zone of joints was softened by the friction heat and the fracture of sound joints occurred in this softened area. Meanwhile, the fatigue strength of sound joints was higher than that of SUS304 base material. This is probably because the material near the weld interface was hardened due to the work hardening. Evaluating the fatigue limit obtained in the fatigue test revealed that when the deformation heat input in the upset stage and the upset bum-off length exceed a certain value, sound joints can be produced as well as good tensile strength.