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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Fig. 2. Microstructures of the hot rolled bar (left) and the cold drawn wire (right) in longitudinal sections. Vertical side of the micrograph is always parallel to the wire axis or drawing direction, whereas horizontal side is associated with the radial direction of the cylinders. 4. Experimental programme Slow strain rate tests were performed on transversely precracked axially-loaded steel wires immersed in aqueous solution of 1g/l Ca(OH) 2 plus 0.1g/l NaCl (pH=12.5). The experimental device consisted of a potentiostat and a three-electrode assembly: metallic sample (working electrode), platinum counter-electrode and saturated calomel electrode (reference). Tests were performed at constant electrochemical potential of – 1200 mV SCE. 5. Consequences of cold drawing on crack paths Fig. 3 shows the evolution of crack paths with cold drawing under HAC conditions, where a progressive change in the macroscopic topography as the cold drawing increases was observed in all fracture surfaces. For the most heavily drawn steels (4 to 6) the crack deflection takes place suddenly after the fatigue precrack and the deviation angle is close to 90º (propagation step or perpe ndicular deflection/deviation).

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Fig. 3. Evolution of hydrogen-assisted crack paths (HACP): (a) general appearance of the fracture surfaces; (b) geometric parameters describing the HACP; (c) evolution of fracture profiles; f: fatigue crack growth; I: mode I cracking; II: mixed mode cracking; F: final fracture by cleavage.