PSI - Issue 79

Giuseppe Macoretta et al. / Procedia Structural Integrity 79 (2026) 508–516

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3.4. Fractographic analysis

Fractographic analysis confirmed the evidence of the tensile SSRT, as shown in Fig. 7 and Fig. 8. The H-free material featured a ductile fracture and presented a marked necking, Fig. 7a). As shown in Fig. 7d), the fracture is quite planar and angled by 70° with respect to specimen loading direction, which is aligned with the sheet rolling direction. The SEM investigation confirmed this evidence. Fig. 8 a) shows the typical features of a ductile fracture surface, with marked microvoid coalescence phenomena, which were observed on the whole fracture surface of the H-free material. In the case of the H-charged specimens, while the H content increases, the necking decreases and the fracture becomes almost orthogonal to the specimen loading direction, as shown in Fig. 7e) and f). In the case of the specimen featuring an H content of 2.1 ppmw, Fig. 7c), the fracture surface presented wide shiny areas, planar and orthogonal to the loading direction. Examination of those regions by SEM, as shown in Fig. 8b), revealed an extended intergranular fracture, pointing out that a HE occurred. Specimens featuring an H concentration of 0.7 ppmw presented a surface fracture characterized by a ductile fracture Fig. 7b) and e), similar to what has been observed for the H-free material.

Fig. 7. Fracture surfaces observed via stereomicroscope in direction orthogonal (a-c) and parallel (d-e) to the specimen loading axis. H-free specimen (a and d), specimen with a H concentration of 0.7 ppmw (b and e), specimen with a H concentration of 2.1 ppmw (c and f).