Investigation of cathodic potential induced stress corrosion cracking of marine carbon steel and its weldments in seawater

• Investigated the influence of cathodic protection potentials on stress corrosion cracking (SCC) in S420 steel welded joint structures. • Explored the dynamic evolution of SCC dominant mechanisms (anodic dissolution vs. hydrogen embrittlement) across distinct potential regimes. • Revealed SCC susceptibility variations among weld zones (BM, HAZ, WM) and their linkage to microstructural mechanisms. This study systematically investigates the electrochemical characteristics and stress corrosion cracking (SCC) susceptibility of distinct microstructural zones (base metal (BM), heat-affected zone (HAZ), and weld metal (WM)) in S420 steel welded joints under cathodic polarization potentials through combined electrochemical characterization and slow strain rate tensile (SSRT) testing. Results demonstrate that HAZ exhibits the highest corrosion current density among the three zones, indicating enhanced anodic dissolution and consequent SCC promotion. All zones display similar electrochemical responses to potential variations, with charge transfer resistance initially increasing then decreasing as polarization potential shifts negatively, peaking at -850 mV where anodic reactions dominate. SCC susceptibility progressively intensifies with cathodic polarization, transitioning from mixed anodic dissolution/weak hydrogen embrittlement (HE) at -750 mV to HE-dominated failure at -950 mV. The superior SCC susceptibility of HAZ is attributed to its coarser grain structure and abundant pearlite bands, yielding a hydrogen embrittlement susceptibility coefficient of 39.1 % at -850 mV - significantly higher than WM (19.3 %) and BM (16.0 %).