Fungi induced corrosion on nitrocarburized multiphase 4340 steel

Resumo

Corrosion on multiphase steels is strongly influenced by the iron content. On the other hand, thermochemical surface treatments like plasma nitrocarburizing have been successfully used to enhance resistance to salt-spray corrosion, but the literature about microbial induced corrosion is still scarce. The objective of this work was then to evaluate the biocorrosion induced by the Penicilium candidum fungus on plasma nitrocarburized multiphase 4340 steel, comparatively with the untreated steel. Small blocks of treated and untreated metals were evaluated by SEM, AFM, and EDS, before and after the biocorrosion process. It was observed that biocorrosion drastically affected the surface of the untreated 4340 steel while nitrocarburized samples preserved their original aspect. Only 7% of oxide content was detected in the nitrocarburized steel against 32% in the untreated metal. It was concluded that plasma nitrocarburing is effective to improve biocorrosion resistance of multiphase 4340 steel, and consequently, the treated steel may be a potential substitute for the AISI 304 in dairy and cheese industries.