PSI - Issue 26

Jesús Toribio et al. / Procedia Structural Integrity 26 (2020) 360–367 Toribio / Structural Integrity Procedia 00 (2019) 000 – 000

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3

Fig. 3 plots the stress-strain curves for the progressively cold-drawn pearlitic steels form A0 (hot rolled steels, not cold drawn at all) to the commercial prestressing steel wire A6 (heavily cold drawn pearlitic steel that has undergone 6 drawing steps). Both the yield strength  Y and the ultimate tensile strength  max increase with the drawing degree.

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. 3. Stress-strain curves of the progressively drawn pearlitic A0 to A6 (from 0 to 6 cold drawing steps).

A key issue in cold drawn pearlitic steels is the relationship between microstructure and strength (Toribio, 2004a), i.e., the effect of microstructural evolution on the (macroscopic) mechanical properties (Toribio et al., 2014), since the final aim of the manufacture process by cold drawing is the improvement of mechanical properties (increase of strength) by a strain hardening mechanism. 3. Microstructure evolution during cold drawing The microstructural evolution of pearlitic microstructures during cold drawing has been studied in the past, from the classical studies by Embury and Fisher (1966) and Langford (1977) about drawing and deformation of pearlite, to the review by Ridley (1984) or the analyses performed by Toribio and Ovejero (1997, 1998a, 1998b, 1998c). A recent systematic compendium about microstructural evolution in cold drawn pearltic steel was published by Toribio et al. (2016). Results demonstrate the progressive slenderizing and orientation (along the wire axis or cold drawing direction) of the pearlitic colonies (first microstructural level), as well as increasing orientation and 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 wires becomes progressively oriented as the cold-drawing degree increases. Figs. 4 shows the microstructures of hot rolled and cold drawn pearlitic steels.

Fig. 4. Microstructures of the hot rolled bar (left) and the cold drawn wire (right) in longitudinal sections. The 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 (wires).