Potentiodynamic polarization behaviour of AISI type 316 stainless steel in NaCl solution

•The potentiodynamic polarization behaviour of type 316 SS in NaCl solution was investigated.•A cumulative anodic charge density, Qc, for pitting was defined.•The values of Qc of the stainless steel turned out to be independent on the scan rate.•The results suggested that the Qc be associated with the critical condition for the stable pitting of a material.

Potentiodynamic polarization behaviour of AISI type 316 SS in NaCl solution was investigated in terms of the potential scan rate effect. The critical pitting potential, Epit, of the stainless steel appeared to be strongly dependent on the potential scan rate. A cumulative anodic electric charge density of the steel was defined as the total charge density from the open circuit potential, Eocp, and calculated using the potentiodynamic polarization curves. It was found that, plotted as a function of the polarization time, the values of the cumulative charge density consisted of two lines with different slopes. It was confirmed that the deflection of the cumulative charge density vs. time plots corresponded to Epit and the values of the cumulative charge density at the deflection were little dependent on the applied scan rate. The cumulative charge density at the deflection was defined as a critical electric charge density for the stable pitting. Also, it was suggested that this electric charge density should be associated with the critical condition for the stable pitting and the critical electric charge for stable pitting should be a representative parameter for the pitting resistance of a material.