Issue 50

Ch. Apostolopoulos et alii, Frattura ed Integrità Strutturale, 50 (2019) 548-559; DOI: 10.3221/IGF-ESIS.50.46 557 Figs.12 and 13 present a SEM and an EDX analysis of a longitudinal cut in the fracture region in a noncorroded specimen after tensile test (B450c). According to these findings, the area depicted is rich in MnS and FeS compounds, phenomenon which gradually leads to a local decomposition, and inevitably to the failure of the material. Figure 12 : SEM analysis of the fracture region in a noncorroded specimen after tensile test (B450c). 2 4 6 8 10 12 14 keV 0.0 0.2 0.4 0.6 0.8 1.0 cps/eV Fe-KA Mn-KA S-KA Fe Fe Mn Mn S 1.00 * Scan Figure 13 : EDX analysis of the fracture region in a reference specimen after tensile test (B450c). It is very likely that the adsorption of Cl- ions in and around the strained regions of a MnS–Fe interface triggers the anodic dissolution of Fe2+ ions. It is important to reemphasize here that Cl- ions are not involved in redox reactions but catalyze the anodic processes by adsorbing on the surfaces around the MnS inclusions and by chasing away the conduction electrons of the strained matrix, which results in the anodic dissolution of iron from these regions as depicted in Fig.14 [27]. Figure 14 : Corrosion mechanisms surrounding a MnS inclusion: refer to Avci et al.[27] for details.