Abstract
Investigations were performed on the capacity of the alloying element iron to suppress transpassive dissolution of stainless materials. It was earlier observed that due to this property stainless steels and other ferrous stainless alloys are resistant to transpassive dissolution in near-neutral, strongly oxidizing environments, as in chlorine dioxide bleached pulp washers, whereas non-ferrous stainless materials are susceptible and may suffer general corrosion thinning.
Electrochemically controlled experiments were performed in solutions of different buffers at pH 1.0 to 4.4. At pH-values below about 2, ferrous and non-ferrous stainless materials essentially exhibited the same transpassive behaviour which was regarded to be determined by the element chromium. In less acid solutions a passivation reaction in the transpassive potential range induced by iron was detected for the ferrous alloys. This reaction becomes more pronounced with increasing solution pH and iron content. It is concluded that this iron-induced passivation makes stainless steels or other ferrous stainless alloys resistant to transpassive dissolution in strongly oxidizing less acid or near neutral environments whereas non-ferous stainless alloys are susceptible because their transpassive behaviour is governed by the element chromium in these media.
