The article presents today's possibilities of modifying the fatigue strength of welded joints made in steel S700MC using the high frequency impact treatment (HiFIT). Research-related fatigue tests involved MAG-welded butt joints, T-joints with two-sided fillet welds as well as joints with a longitudinal rib and a girth fillet weld. The tests required the adjustment of appropriate parameters of the HiFIT and the performance of the above-named treatment in relation to the half of previously made

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... oints. The article presents results of fatigue tests of joints after welding and after the HiFIT. The research also included the development of fatigue characteristics and the calculation of fatigue categories FAT, constituting the basis for the design of structures exposed to fatigue (in accordance with European standards). The results obtained in the tests unequivocally demonstrated the possibility of increasing the fatigue strength of welded joints made in steel S700MC by applying the HiFIT, with the level of fatigue strength modification depending on the type of a joint.