Influence of microstructure on the microbial corrosion behaviour of stainless steels

Abstract

Several stainless steels (Types UNS S30300, S30400, S30403, S31600, S31603 and S42000) with different microstructural characteristics have been used to study the influence of heat treatments on microbiologically influenced corrosion (MIC). Biocorrosion and accelerated electrochemical testing was performed in various microbiological media. Two species of sulphate-reducing bacteria (SRB) have been used in order to ascertain the influence of microstructure. The morphology of corrosion pits produced in both chloride and chloride plus sulphide -SRB metabolites- was inspected by optical and scanning electron microscopy (SEM) complemented with energy-dispersive X-ray (EDX) analysis. Results have shown different behaviours regarding corrosion resistance in each case studied. Sensitized austenitic stainless steels were more affected by the presence of aggressive anions and pitting potential (Ep) values were more cathodic than those of as-received state. A corrosion enhancement is produced by the synergistic action of biogenic sulphides and chloride anions. Pitting corrosion in martensitic stainless steel Type UNS S42000 was found in a biocorrosion test. The pitting morphology is correlated to the chemical composition, the microstructure and the electrolyte.