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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This paper offers a macro- and micro-approach to the problem of hydrogen embrittlement (HE), hydrogen degradation (HD) or hydrogen assisted cracking (HAC) of cold-drawn eutectoid pearlitic steels used in wire form in prestressed concrete. An analysis is provided of the hydrogen-assisted micro-damage (HAMD) at the finest microscopic level, together with the elucidation of hydrogen-assisted cracking paths (HACP), especially in oriented pearlitic microstructures after heavy cold drawing. 2. Progressive (multi-step) cold drawing of pearlitic steels Manufacture of commercial prestressing steels is made by progressive (multi-step) cold drawing of a previously hot-rolled bar with pearlitic microstructure. Fig. 1a shows two views of the real cold drawing chain in the factory and Fig. 1b offers a typical drawing process with six passes through the corresponding dies and their associated diameter reductions in the steel wire.

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Fig. 1. Manufacture of commercial prestressing steel wires by multi-pass cold drawing: (a) two photographs of a real ( in situ ) drawing procedure in the factory; (b) scheme of a typical drawing process with six passes and progressive diameter reduction. 3. Pearlite microstructure changes during cold drawing The pearlite microstructural changes during cold drawing (at the two levels of pearlitic colonies and lamellae) were studied by Toribio and Ovejero (1997, 1998a, 1998b, 1998c), showing the following trends: (i) slenderizing of the colonies (Toribio and Ovejero, 1997); (ii) decrease of interlamellar spacing (Toribio and Ovejero, 1998a); (iii) orientation in the direction of cold drawing (wire axis) of both the colonies (Toribio and Ovejero, 1998b) and the lamellae (Toribio and Ovejero, 1998c). This evolution is shown in Fig. 2 for different drawing degrees.