Seawater corrosion fatigue properties and fracture characteristics of EH36 steel welded joints

Taking welded joints of EH36 steel as the research object, corrosion fatigue life and fracture mechanism of welded joints under different stress ranges in seawater environment of South China Sea were studied. According to DNV-RP-C203 standard, actual seawater environment corrosion fatigue test results were corrected, and the corrected equation of S-N curve was lg N=15.414-4.005lg Δσ. The S-N curve showed that fatigue life of welded joints of EH36 steel in actual seawater decreased significantly with the increase of fatigue stress range, whose corrosion fatigue performance was superior to that of welded joints in simulated seawater environment under DNV-RP-C203 standard. Scanning electron microscope was used to observe corrosion fatigue fracture surface of welded joints, and source area of corrosion fatigue cracks mainly occurred near the surface of welded joints. The reason was that there was a significant stress concentration around the corrosion pit on the surface of welded joints, which resulted in crack initiation. The crack propagation area was relatively flat macroscopically, and a number of tearing edges generated from crack source area on the surface of welded joints converged into a tearing edge in this area. Obvious fatigue steps and secondary cracks appeared in the microcosmic crack growth zone, and crack growth mode was mainly transgranular. The main morpholgy of instantaneous fracture area of corrosion fatigue was dimple, and fracture form was plastic fracture.Highlights: Based on fatigue life prediction theory of group method, S-N curve of welded joints of EH36 steel in seawater environment of South China Sea was drawn. Combined with microscopic analysis method, microscopic characteristics of corrosion fatigue fracture surface of welded joints were studied, and corrosion fatigue mechanism of EH36 steel welded joints in actual seawater free corrosion environment was revealed.