Dissolution and repassivation kinetics of a 12.3Cr-2.6Mo-6.5Ni super martensitic stainless steel - A comparative study

In this investigation, the dissolution and repassivation kinetics of a super martensitic (SM) stainless steel (Fe-12.3Cr-6.5Ni-2.6Mo) have been characterized using the artificial pit technique. As a part of this study, a diffusion model has been developed and employed for calculation of the pit surface concentration of dissolved species during the potential step experiments. For concentrations close to the saturation level, the dissolution kinetics are adequately described by a Tafel slope of approximately 57 mV/dec and a current density of 0.5 mA/cm(2) at 2300 mV vs. saturated calomel electrode. However, repassivation of the active pit surface occurs when the concentration of the dissolved species drops below 30% of the saturation value. Based on a comparison with relevant literature data, the observed response of the SM stainless steel to localized corrosion is similar to that reported for other high alloyed steels. This result is expected if the dissolution and repassivation kinetics are controlled by the content of Cr, Ni, and Mo in the parent material. (C) 2002 The Electrochemical Society.