PSI - Issue 68

Eduard Navalles et al. / Procedia Structural Integrity 68 (2025) 1105–1114 Eduard Navalles et al. / Structural Integrity Procedia 00 (2025) 000–000

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number of dimples, as well as some large flat facets. These facets are formed during the separation of the specimen once the SSRT was completed. Figure 5c shows a closer view of the dimples, some of which exhibit a quasi-brittle appearance to different extent. For example, Figure 5b shows smoother round dimples, indicating a higher ductility in that area and the sharper quasibrittleness appearance in Figure 5c could be indicating that the crack propagated through that side of the specimen. Figure 5d illustrates the banded structure of the ferritic-pearlitic specimen. As ferrite is the most ductile phase of the material, it is present in this fractography as the dimpled stripes, while the brittle stripes in the micrograph are the pearlite.

Figure 5. SEM images of ferritic-pearlitic carbon steel after SSRT test in argon inert environment, 200 bar pressure at room temperature.

The specimen subjected to hydrogen testing can be seen in Figure 6. In this case, the fractographic analysis show a clear quasi-cleavage brittle behaviour in most of the micrograph. In Figure 6a, a post-mortem ductile appearance with many dimples can be observed; this fracture surface was formed after the specimen was pulled apart, and it seems it seems to have similar behaviour than argon specimen fractography in Figure 5c.

Figure 6. SEM images of ferritic-pearlitic carbon steel after SSRT test in hydrogen gas environment, 200 bar pressure at room temperature.

Figure 7b, c and d display signs of brittle fracture features and may explain the reduction in ductility obtained from the SSRT tests in hydrogen. Small dimples are visible as well, which makes the fracture surface fall into denomination of quasi-brittle category. Figure 6b has the same banded structure as in Figure 6d, but with brittle dimples in the