Fatigue properties of laser-arc hybrid welded Q345E steel T-joints

To investigate the feasibility of laser-arc hybrid welding in bogie structures, the hybrid welding of 20mm-thick Q345E steel T-joints was carried out. The fatigue properties were assessed using both the single-point method and the staircase method. The findings reveal that, at the specified 5 million cycles, the median fatigue strength of the hybrid-welded T-joint stands at 148.3 MPa. Furthermore, the conditional fatigue strength at 2 million cycles is 181.5 MPa, representing a remarkable 39.6% increase compared to the corresponding arc-welded T-joint. Analysis of the fatigue crack morphology indicates that the fatigue crack originates at the root weld toe, with the instantaneous fracture region displaying a ductile fracture mode. The enhanced fatigue properties of the hybrid-welded T-joint can be attributed to the reduced stress concentration factor at the root weld toe and the finer weld microstructure composed of the intragranular ferrite. This prevents premature fatigue crack initiation and hinders fatigue crack propagation.