PSI - Issue 81

Jesús Toribio et al. / Procedia Structural Integrity 81 (2026) 558–561

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2. Cold drawing of pearlitic steels Manufacturing of prestressing steel wires is made by multi-step cold drawing to increase the yield strength and the ultimate tensile strength (UTS) by activating a strain hardening mechanism. Fig. 1 shows the stress-strain curves of progressively cold drawn pearlitic steels wires from A0 (hot rolled material) to commercial prestressing steel wire (six steps of cold drawing).

2.0

1.5

1.0

0.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 A6 A5 A4 A3 A2 A1 A0  (GPa)  0.5

Fig. 1. Stress-strain curves of progressively drawn pearlitic steels A0-A6 (from 0 to 6 drawing steps).

3. Microstructural evolution with cold drawing Progressive cold drawing of pearlitic steel affects the microstructural arrangement in the form of slenderizing of the colonies, decrease of interlamellar spacing and orientation in the direction of cold drawing (wire axis) of both colonies and lamellae (Toribio and Ovejero, 1997, 1998a, 1998b, 1998c), i.e., inducing microstructural anisotropy. 4. Notch-induced anisotropic fracture behavior Notched specimens are optimal to establish fracture criteria in structural materials and to study hydrogen embrittlement (HE) processes (Toribio and Ayaso, 2004). In the matter of notch-induced anisotropic fracture behavior , research work was performed by Toribio and Ayaso (2002a, 2002b, 2003, 2009). The present paper revisits the results using very different notch geometries (Fig. 2) to achieve very different triaxiality (constraint) levels.

A

B

C

D

Fig. 2. Notched samples of cold drawn pearlitic steels with very different geometries.

The dimensions of the notched geometries used in the analysis (Fig. 2) were as follows: Geometry A : R/D = 0.03, C/D = 0.10 Geometry B : R/D = 0.05, C/D = 0.30 Geometry C : R/D = 0.40, C/D = 0.10 Geometry D : R/D = 0.40, C/D = 0.30

where R and C are respectively the notch radius and the notch depth, and D the diameter of the specimen. Samples were named with a number indicating the cold drawing steps undergone by the steel wire and a letter indicating the geometry (cf. Fig. 2). 5. Fractographic analysis This section offers a macro-and micro-approach to the fractographic analysis, covering both the macro-fracture path and the microscopic fracture modes to correlate, in the sense of materials science and engineering, the microstructure of the material and its macroscopic fracture behaviour. Figs. 3-5 shows the 3D fracture paths (or 3D fracture profiles ) in notched specimens A, B and C (Toribio and Ayaso, 2002a), frequently with a deflection angle close to 90ª (markedly anisotropic behaviour). Such a step exhibits a non-conventional