PSI - Issue 22

L. Sena et al. / Procedia Structural Integrity 22 (2019) 171–180 177 Lígia T. Silva, Bruno Mendes, Carlos Oliveira, Cristina Reis, Paula Silva; José Silva / First International Symposium on Risk and Safety of Complex Structures and Components (2019), Porto, Portugal In SEM observations, corrosion occurs more mainly in the matrix region, the lighter part is decreasing, other phases appear in white and dark gray, and the sharp grain outline around the phases as the concentration increases (Figure 5). Corrosion then happens in the intergranular mode, which causes loss of mechanical properties, leading to fractures when subject to mechanical stresses, corrosion under fracturing stress (GENTIL, 1996). Graphitization is explained as a rigorous matrix attack, the anodic region, whiles the inert cathode region and optimum electron conducting is found in graphite, enabling the development of effective galvanic cells. This destructive mechanism causes the oxidation of iron that goes into solution according to reaction 1 (GENTIL, 1996). Fe→Fe 2+ + 2e - (1)

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(c) Fig. 5. SEM images of Gray Cast Iron samples after immersion in phosphoric acid at 298.15 K over a period of 86,400 s (a) 1%; (b) 2%; (c) 3%.