Biocorrosion of AISI 4340 Steel
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Biocorrosion of AISI 4340 Steel Sabrina M. Rovetta1,2, Antonio J. Abdalla 2, Sonia Khouri1, Choyu Otani3 and Walter Miyakawa2 1 Vale do Paraíba University, Av. Shishima Hifumi,2911, São José dos Campos, SP, Brazil. 2 Photonics Division, Instituto de Estudos Avançados, Trevo Cel. Av. José A. A. Amarante, 1, São José dos Campos, SP, Brazil. 3 Physics Department, Instituto Tecnológico de Aeronáutica, Praça Mar. Eduardo Gomes, 50, São José dos Campos, SP, Brazil. ABSTRACT The objective of the present work is to evaluate the Penicillium candidum filamentous fungi biocorrosion effects on AISI 4340 steel. Small AISI 4340 steel blocks are exposed to a biocorrosion process inside glass tubes containing culture media (Sabouraud Dextrose HIMEDIA broth) inoculated with Penicillium candidum spores for 14 days, at 25ºC constant temperature. The surface microstructures are evaluated by scanning electron microscopy, atomic force microscopy, and the chemical composition by energy dispersive X-ray spectroscopy. Comparison of micrographies before and after biocorrosion shows that surface structures present morphological alterations, suggesting corrosion wear. Grain contours can no longer be visualized and oxygen content on the steel surface increases to 32% after biocorrosion. Besides, topographic parameters like root mean square roughness (Rms), arithmetic mean roughness (Ra) and mean roughness (Rz) increase 57%, 132%, and 71%, respectively, from their initial values. It is concluded that AISI 4340 steel is reasonably susceptible to corrosion. INTRODUCTION Metabolites produced throughout microorganisms life cycles can be highly aggressive, leading to materials biocorrosion. This deterioration process can act in several metals like aluminum and its alloys, iron, steel, copper, zinc and lead. In the course of time, major economic and structural damages have been generated, as corroded material restoration consumes approximately 20% of the worldwide produced steel. The multiphase AISI 4340 steel is an advanced and special metal widely used in aeronautics and aerospace industries. Although high technology has been employed in its development, surface properties like hardness, corrosion resistance, friction wear, and fatigue life can be still improved by means of thermochemical treatments. Laser carburizing [1] and plasma nitrocarburizing [2,3,4] surface treatments have been effective to this aim. In fact, increases in corrosion resistance and high surface hardness have been already reported [2,4]. However, microbial induced corrosion investigations in the multiphase AISI 4340 steel are not frequently found in the literature. In a biocorrosion process, metal deterioration occurs as a consequence of an active participation of the biofouling [5], which is formed by biofilms, microbial metabolites, and corrosion products. Actually, a consortium of microorganisms is generally involved in the overall process. However, the evaluation of corrosive effects owing to a single microorganism is equally important, and from the scientific point of view
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