MIC of stainless steels: A technical review on the influence of microstructure

Microbiologically influenced corrosion (MIC) attacks various types of material. Among these can be found stainless steels. The case histories published usually make some reference to the appearance of this type of corrosion in welded zones, which usually take the shape of pitting. This is what leads us to believe that there is a correlation between the susceptibility to this type of corrosion and to the microstructural state in which stainless steels are found. There is relatively little information available on the subject of austenitic stainless steels. It seems that, in this latter case, there is some correlation between the MIC and the sensitization state of the steel, or more exactly, with the chromium depleted zones which may exist, whether carbide precipitations are produced at the grain boundaries or in the austenite-ferrite interphase. In the case of ferritic or martensitic stainless steels, there is even less information available. There does seem to be some relation with the microstructural state; carbide stability may play a role in this. In such a case, the as-received annealed state behaves better in terms of corrosion than the quench and tempered states, especially if carried out at low temperatures. In any case, it seems that more research must be done on the subject so that the microstructural state of the materials that undergo MIC is determined in a more precise and quantative way.