The electrochemical behavior and oxide film structure of the weld of 316L/52M/A508 dissimilar metal welded joints were investigated via scanning electron microscopy (SEM), potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and X‐ray photoelectron spectroscopy (XPS). The electrochemical measurements revealed that the weld materials could be arranged in descending order of protectiveness of the oxide film formed on their surface; that is, Alloy52Mw > Alloy52Mb > C52M > C308. The results of EIS and XPS analyses showed that the oxide films formed on these materials were duplex‐structured; this duplex structure consisted of a Cr‐rich (in 52M nickel‐based weld materials) or Cr/Fe‐rich (in C308 stainless steel weld materials) inner layer and a Ni/Fe‐rich (in 52M nickel‐based weld materials) or Fe‐rich (in 308 stainless steel weld materials) porous outer layer.

The effects of temperature on the electrochemical behavior and oxide film property of Alloy 800 in hydrogenated high temperature water are studied using potentiodynamic polarization curves, electrochemical impedance spectra (EIS), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The corrosion resistance of Alloy 800 passes through a local minimum at 250 °C. The kinetic controlling step of the growth of oxide films at 200–300 °C changes from the diffusion of ions in aqueous phase to the growth of Cr‐rich barrier layer. A modified model is proposed to explain the effect of temperature on the property of the oxide films on Alloy 800 in hydrogenated high temperature water.