Evaluating the fatigue property of S355J2W steel butt-welded joint: Multiple notch effects

Abstract

The fatigue fracture mechanisms and the fatigue property evaluations of S355J2W steel butt-welded joints relieved welding residual stresses with and without welding reinforcement were systematically investigated by microstructure characterization and fatigue tests. Experimental results show that the complex evolution of microstructure at welded joint results in the notable degradation of mechanical properties. The fatigue performance of the as-welded specimen with welding reinforcement is significantly poorer than that of the smooth-welded specimen without welding reinforcement. Stress concentration under the fish-scale pattern at the weld toe caused by geometric dimension change is the major reason for the fatigue fracture of the as-welded specimen. By comparison, the cementite segregation at grain boundary in the partial recrystallization zone of the heat affected zone caused by the sharp change of microstructure should be responsible for the fatigue fracture of the smooth-welded specimen. The fatigue notch coefficient (Kf=1.89) calculated by the effective notch stress method is consistent with that (Kf=1.9) measured by the fatigue tests, which shows that the effective notch stress method can well evaluate the multiple notch effect under the coupling of the weld toe and the fish-scale pattern. Furthermore, the fatigue risk factor (Rf) model was employed to evaluate the fatigue performance of welded joint, and the intuitive Rf curves show that the fatigue fracture occurs at the fatigue life exceeding 2 × 106 cycles, i.e., Rfmax exceeds 0.7.