Influence of corrosion on ultra-low cycle fatigue performance of steel butt-welded joints with various welding methods

Abstract

Preferential corrosion of welded joints in steel structures has been observed in a wide range of scenarios and should receive enough attention. The current work focuses on the corrosion and ultra-low cycle fatigue (ULCF) behavior of low-alloy steel weld joints. Firstly, 1600 h neutral salt spray (NSS) tests were conducted on welded joints made by different welding methods, and then topography scanning of corrosion pits was carried out. It was found that the welded region is more susceptible to corrosion. Dynamic polarization curves of the welded joints were measured, and the results show that the self-corrosion potential of the welded region is lower than that of the base metal (BM) region, while the corrosion current density is higher than that of the BM region. Subsequently, cyclic tests were carried out on the corroded weld joints. The results show that corrosion can cause a maximum reduction of 11.79% in yield load and 20.87% in ultimate load of the welded joints. Corrosion has slight influence on the energy dissipation capacity of welded joints, but the maximum reductions in ULCF life could reach 77.31% due to corrosion. Fractography analysis further shows that secondary cracks, map cracks, and intergranular brittle fracture, apart from more common fatigue fracture, ductile fracture, and quasi-cleavage fracture, appear on the fracture surfaces. Supplementary numerical simulation was conducted to enable a better understanding of the failure processes. In the simulation, a geometric modeling method using topography scanning data of corrosion surface was proposed. By using the proposed modeling approach, together with Chaboche cyclic plasticity constitutive model and cyclic void growth model (CVGM) for capturing fracture behavior, the predicted results show an acceptable agreement with the experimental ones.