Single pit initiation on 316L austenitic stainless steel using scanning electrochemical microscopy

Scanning electrochemical microscopy was used to locally release a controlled amount of chloride ions close to a 316L austenitic stainless steel (SS) substrate in sulphuric acid medium to generate a single pit. Then, usual electrochemical techniques were applied for studying the early stages of pit initiation and propagation. The amount of chloride ions needed to reach the requisite threshold concentration for pit initiation was determined. It was found to be higher for SS than for pure iron. The amount of dissolved cations was also determined as a function of the substrate potential. Different pit shapes and depths were observed depending on the potential applied to the substrate. Following the pit repassivation, it was observed that a part of the dissolved products precipitated at the bottom of the pit.

► Scanning electrochemical microscopy was used to locally release a controlled amount of chloride ions close to a 316L austenitic stainless steel (SS) substrate in sulphuric.
► A special attention has been paid to study the influence of the potential of the steel on the pit initiation and propagation.
► Contrary to observation on pure iron, a significant amount of chloride ions was needed to initiate pitting on SS.
► With potential ennoblement within the passive layer, pits were smaller but deeper in contrast with pits generated in traditional cells at neutral pH.