PSI - Issue 28

Jesús Toribio et al. / Procedia Structural Integrity 28 (2020) 2404–2409 Jesús Toribio / Procedia Structural Integrity 00 (2020) 000–000

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1. Introduction In cold drawn pearlitic steels for prestressed concrete, the manufacturing process by cold drawing generates an effect on material microstructure (Toribio, 2017a) Apart from the general trends of microstructural evolution in drawn pearlite (progressive orientation of pearlitic colonies and lamellae in the wire axis or cold drawing direction and decrease of interlamellar spacing), special features appear during cold drawing, so that the new concept of microstructural integrity could be introduced (Toribio, 2020a). Between the most relevant phenomena taking place during the cold drawing drawing process, it is worth to mention the appearance of the so-called pearlitic pseudocolony (Toribio, 2020b), a special pearlitic colony in which the lamellae are not oriented along the wire axis or cold drawing direction, thereby producing an anomalous (extremely high) pearlitic interlamellar spacing. These characteristics make it a weakest area or potential fracture initiation unit, i.e., a place able to produce fracture path deflection, as described by Toribio (2020b). 2. Pearlitic pseudocolonies affecting micro- and nanostructutral integrity of cold drawn pearlitic steels Fig. 1 shows a typical slender pearlitic pseudocolony and Fig. 2 offers a enlarged view at high magnification, showing evidence of cementite lamellae that are not properly oriented following a direction parallel to the wire (drawing) axis (they remain transverse to the wire), curling of cementite and anomalous ( extremely high when compared to the average) local interlamellar spacing, and even some evidence of local fracture of specific lamellae.

Fig. 1. Pearlitic pseudocolony in a heavily cold drawn pearlitic steel after six drawing steps (longitudinal section of the wire). The boundaries of the pseudocolony are marked in the micrograph through a white dashed line. The vertical side of the micrograph is parallel to the wire axis or cold drawing direction, while the horizontal side is associated with the radial direction of the wire.

Fig. 2. Enlarged view (x8000 magnification) of a pearlitic pseudocolony in a heavily cold drawn pearlitic steel after six drawing steps (longitudinal section of the wire). The vertical side of the micrograph is parallel to the wire axis or cold drawing direction, while the horizontal side is associated with the radial direction of the wire.