Fatigue analysis of B780CF steel welded joint

The fatigue properties of the B780CF high strength steel plate in the original state (quenched and tempered state), annealed state (annealing alter tempering), and the annealing state of the welded joint (quenched and tempered plate alter annealing) were tested by the lifting method under the action of tension and compression, respectively. The fatigue limit of the B780CF original state, the annealed state and the welded joint annealed under the stress ratio of -1 are 400 MPa, 415 MPa and 360 MPa, respectively. The impact toughness of B780CF welded joints decreased sharply after welding and thermal annealing, and the grains in the thick zone of the heat affected zone were seriously coarsened. The softening zone existed in the transition zone and the smectite was precipitated along the grain boundary. Scanning electron microscopy observations show that high strength steel plate and welded joint fatigue source area are located in the surface of the sample, also in the defects and the tissue microstructure of the sample.