A study on pitting initiation mechanism of super-austenitic stainless steel weld in chloride environment

There has been controversy over the localized corrosion mechanism of super-austenitic stainless steel weld due mainly to the lack of effective evaluation technique for identification of corrosion nucleation site in weld. For this reason, an electrochemical polarization method followed by an observation of microstructure using the back-scattered electron mode in field emission-scanning electron microscopy is used. To clarify the localized corrosion mechanism, energy dispersive spectroscopy line profile analyzed by transmission electron microscopy is additionally utilized. It clearly reveals that the selective corrosion is preferentially initiated around the sigma-phase precipitated in the interdendritic region in weld. The local depletion of Cr and Mo around the sigma-phase can be partly replenished by the diffusion of the elements into the depleted area during the subsequent heat treatment at 1180 degrees C.