PSI - Issue 5

Jesús Toribio et al. / Procedia Structural Integrity 5 (2017) 1446–1453 Jesús Toribio / Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 3. Hydrogen-assisted micro-damage (HAMD): tearing topography surface (TTS).

Fig. 4. Transition from TTS to quasi-MVC (left) and Transition from quasi-MVC to cleavage (right), cf. Toribio (2012).

The extension of the TTS zone is an indicator of the HAMD, and therefore allows the clarification of the fact that the main mechanism of hydrogen transport in pearlitic steel takes place by diffusion, as demonstrated in earlier research works by Toribio (1992c, 1993, 1996), it being mainly driven by the gradient of hydrostatic stress, as formulated in the stress-assisted hydrogen-diffusion models proposed by Toribio and Kharin (1997, 2000). In the case of cold-drawn pearlitic steels, the afore-said microstructural orientation (at the two basic microstructural levels of pearlitic colonies and ferrite/cementite lamellae) makes the HAMD process develop by a HDT that evolves as a function of the cold drawing degree: HDT (i) , where i is the number of drawing steps undergone by each steel. For heavily drawn steels ( ≥ 4), the HDT develops in the form of a sort of enlarged an oriented TTS (EOTTS), the enlargement and orientation being parallel to the wire axis or cold drawing direction, as analyzed by