Effect of Mo species on metastable pitting of Fe18Cr alloys—A current transient analysis

The analysis of current transients occurring on Mo containing ferritic Fe–18Cr steels in chloride containing electrolyte in absence or presence of MoO42- molybdate anions as external inhibitor reveals insight into the role of Mo-species in metastable pitting events, consisting of pit initiation, pit propagation including some metal dissolution, and pit repassivation. A mathematical method on the basis of statistical distribution functions was developed in order to meet the requirements of a systematic data analysis which allows to compare different systems of alloys and electrolytes. The results clearly indicate the beneficial effect of alloyed Mo as well as MoO42- in the electrolyte in inhibiting (metastable) pitting corrosion. However, the mechanism of inhibition is unlike for alloyed Mo and MoO42- added into the electrolyte.