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

1. Introduction

High-strength cold drawn pearlitic steels are materials of the highest interest in structural engineering since they are components of prestressed concrete structures. This paper reviews previous research by the author in the matter of notch-induced anisotropic fracture of progressively cold drawn pearlitic steels and the associated crack path deflection and mixed-mode stress state.

2. Microstructural evolution with cold drawing

Manufacture of commercial prestressing steel wires is made by progressive repetitive (multi-step) cold drawing of a previously hot rolled pearlitic steel bar to produce a heavily cold drawn pearlitic steel wire with a really very high strength (yield stress and UTS) after activating a strain hardening mechanism in the material to improve its classical mechanical properties. Fig. 1 shows a schematic presentation of the cold drawing process with multiple passes.

Fig. 1. Schematic presentation of the cold drawing process with multiple passes through the dies.

There are important classical papers studying pearlitic microstructures and their evolution during cold drawing. The oldest are those by Embury and Fisher (1966) and Langford (1977) about drawing and deformation of pearlite, and the review of data on the interlamellar spacing published by Ridley (1984). During the 90s, specific papers were published by Toribio and Ovejero (1997, 1998a, 1998b, 1998c) demonstrating the progressive slenderizing and orientation/alignment (along the wire axis or cold drawing direction) of the pearlitic colonies (first microstructural level), as well as increasing orientation/alignment (again along the wire axis or cold drawing direction) together with densification of the ferrite/cementite lamellae (second microstructural level) linked with a decrease of pearlite (ferrite/cementite) interlamellar spacing. Thus the microstructure of the cold drawn pearlitic steel wire becomes progressively oriented and aligned as the cold-drawing degree increases, as shown in Fig. 2. Toribio et al. (2016) published a recent paper with detailed information on drawing-induced microstructural evolution pearlitic steel.

Fig. 2. Microstructures of progressively cold drawn pearlitic steels (in longitudinal sections) for steels that have undergone 0 (left) 3 (middle) and 6 (right) steps of cold drawing. Vertical side of the micrograph is always parallel to the wire axis or drawing direction.