Local Corrosion Behavior of 316L Stainless Steel Studied by Scanning Electrochemical Microscope

The potentiodynamic polarization curve of 316L stainless steel in NaCl solution was obtained by electrochemical test, and the characteristic potential was determined. The local corrosion behavior of stainless steel at different characteristic potentials in NaCl solution was studied by scanning electrochemical microscope. The results show that after polarization at the open circuit potential (-0.1 V), no obvious electrochemical active point was found in the surface scan image, and the substrate background current changed little, indicating good stability of the passivation film. After polarization at the self corrosion potential (-51.2 mV), there was an electrochemical active point in the surface scan image, but the peak current decreased and the substrate background current was stable with a slight decrease, indicating the existence of self passivation behavior in stainless steel. After polarization at a typical passivation potential (100 mV), the surface underwent continuous initiation and passivation of metastable pitting; the background current of the substrate first decreased and then remained stable; the degree of surface self passivation was higher. After polarization at the pitting potential (568 mV), steady-state pitting pits appeared on the surface, and after polarization stopped, the pits were passivated; the substrate background current decreased compared to that before polarization, indicating an enhanced stability of the passivation film in the non-pit areas.