Fatigue behavior and surface damage localization in welded S460 steel after accelerated corrosion exposure

An experimental programme was undertaken to examine the fatigue response and visible damage location of welded S460 specimens following accelerated corrosion conditioning. Four initial surface states were considered: no corrosion exposure, 3 days of exposure, 6 days of exposure, and a combined 6-day plus 3-day intensified stage, designated 3D, 6D, and 6 + 3D/9D. Tension-tension fatigue loading was applied at R = 0.1. Selected welded regions were documented with an Olympus DSX1000 digital microscope after the assigned exposure and again following cyclic testing, with emphasis on visible surface alteration and fracture localization. Qualitative optical observations showed increasingly extensive visible surface alteration across the examined representative regions. The 3D specimen exhibited limited visible surface alteration, the 6D specimen showed more distinct corrosion-product regions and pit-like surface features, and the 6 + 3D/9D specimen showed the most extensive visible surface alteration among the four representative specimens. No quantitative surface-topography, pit-depth, roughness, or direct mass-loss measurements were performed on the welded fatigue specimens. The fitted S - N curves showed a non-monotonic ordering within the investigated dataset: the fitted curves for the 3D and 6D conditions were positioned above the uncorroded reference curve, followed by a lower fitted response for the 6 + 3D/9D condition. Because statistical differences among the condition-specific curves were not established, this ordering is interpreted only as a descriptive experimental trend. After fatigue testing, all representative specimens showed visible fracture localization near the weld toe and weld-adjacent region. Corrosion-related surface alteration was visible within the same welded region, but the qualitative optical observations do not establish the precise microscopic crack-initiation site or a causal contribution from an individual pit-like surface feature. The principal contribution is therefore the observation, in the four representative specimens, that visible fracture localization remained associated with the welded region across the investigated exposure conditions, while corrosion-related surface alteration developed within the same fatigue-critical area.