PSI- Issue 9

Jesús Toribio / Procedia Structural Integrity 9 (2018) 311–316

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Author name / Structural Integrity Procedia 00 (2018) 000–000

and lamellae orientation and alignment induced by cold drawing) to produce fracture path deflection and propagation in the drawing direction, because it is seen that it only appears in notched samples A and B (minimum notch radius; maximum stress triaxiality) and in notched sample C in the case of heavily drawn steels, and it never appears in notched samples D (minimum stress triaxiality). The fractographic appearance of the deflected fracture path resembles enlarged and oriented cleavage and caused by special pearlitic pseudocolonies (enlarged and oriented colonies in which the lamellae are not fully oriented, thereby generating an anomalous and very high local interlamelar spacing, making them special microscopic units with minimum local resistance) as suggested by Toribio et al. (1997) and Toribio and Ayaso (2002b).

Fig. 5. Microstructure, fracture profile and appearance of the crack path deflection; specimen 5B (5 drawing steps; notch B).

Fig. 6. Microstructure, fracture profile and appearance of the crack path deflection; specimen 6B (6 drawing steps; notch B).

The afore-said a nisotropic fracture behavior associated with crack path deflection shows that the progressively drawn steel exhibit strength anisotropy in the presence on notches, the deflection being enhanced by the constraint (triaxialty) level in the samples generated by the notch geometry. This is fully consistent with the marked strength anisotropy and crack path deflection in cracked specimens of cold drawn pearlitic steel studied by Toribio and Toledano (2000), Toribio (2002b, 2004), Toribio and Valiente (2004 and 2006) and Toribio et al. (2013).

5. Hydrogen effects on anisotropic fracture behavior and crack path deflection

When hydrogen is present a new circumstance affects material behavior, promoting crack path deviation, in addition to the inherent microstructural anisotropy created by cold drawing, as shown in the studies of hydrogen assisted micro-damage and anisotropic fracture in progressively cold drawn pearlitic steel wires performed by Toribio (1999, 2008), Toribio and Ovejero (1999, 2000, 2001, 2007), Toribio and Vergara (2013) and Toribio et al. (2016, 2017a, 2017b). Fig. 7 shows the fracture surfaces in the case of a low constraint notched specimen (notch D).