This study conducted axial force fatigue tests on φ4 mm round bar specimens and plate bending fatigue tests on out of plane gusset welded joints t o clarify the effect of improving fatigue crack initiation life at the heat affected zone (HAZ) for fatigue crack intiation resistant steel. As a result, the effectiveness of fatigue strength improvement at the HAZ was clarified. The results of plate bending fatigue tests on out of plane gusset welded joints also showed that the fatigue initiation life improved an d the fatigue limit improved for fatigue crack initiation resistant steel compared with conventional steel.
