PSI - Issue 26

Jesús Toribio et al. / Procedia Structural Integrity 26 (2020) 368–375 Toribio / Structural Integrity Procedia 00 (2019) 000 – 000

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8. Hydrogen-assisted cracking paths (HACP): HELP versus HEDE. 8.1. Randomly oriented pearlite with microstructural isotropy in hot rolled or slightly cold drawn pearlitic steels: Hydrogen-Enhanced Localized Plasticity (HELP) A fracto-metallographic analysis was performed on the fractured specimens to elucidate the HACP. Fig. 10 shows the HACP in a hot rolled pearlitic steel bar (not cold drawn at all) with microstructural isotropy, showing that cementite lamella are broken as the crack progresses by TTS driven by the hydrogen environment. It is a kind of micro-damage caused by plasticity at the finest microscopic level, and thus a mechanism of hydrogen-assisted localized plasticity (HELP) could be operative in this case, resembling MSST.

Fig. 10. Hydrogen-assisted cracking paths (HACP) in hot rolled pearlitic steel (not cold drawn at all) with microstructural isotropy.

8.2. Oriented pearlite with microstructural anisotropy in moderately and heavily cold drawn pearlitic steels: Hydrogen-Enhanced Delamination (HEDE) Fig. 11 shows the HACP in a heavily cold drawn pearlitic steel wire with microstructural anisotropy, showing delamination fracture as the crack progresses by EOTTS driven by the hydrogen environment. It is a kind of micro damage caused by splitting or exfoliation at the finest microscopic level, and thus a mechanism of hydrogen-assisted delamination (HEDE) could be operative in this case, resembling DWST.

Fig. 11. Hydrogen-assisted cracking paths (HACP) in heavily cold-drawn pearlitic steel with microstructural anisotropy.

9. Resembling Mantegna’s Dead Christ Perspective (MDCP) Heavily cold-drawn pearlitic steels exhibit in their HACP evidence of strongly anisotropic behavior with a marked deflection/deviation angle of 90º. This resembles Mantegna’s Dead Christ Perspective (MDCP) painting with is relevant and innovative change of point of view in the descriptio n of the Dead Christ (90º rotated from the traditional perspectives) with his body axis perpendicular to the canvas ( foreshortening perspective ), see Fig. 12.