PSI - Issue 33

Jesús Toribio et al. / Procedia Structural Integrity 33 (2021) 1197–1202 Jesús Toribio / Procedia Structural Integrity 00 (2021) 000–000

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2. Scientific bases: notch-induced fracture and structural integrity of cold drawn pearlitic steels

The scientific bases of this interdisciplinary paper are established on the basis of notch-induced fracture and structural integrity of cold drawn pearlitic steel, a material of the highest interest in engineering, as stated by Borchers and Kircheim (2016). The microstructural evolution of pearlitic microstructures during cold drawing has been extensively studied in the past, from the classical studies performed by Embury and Fisher (1966) and Langford (1977) about drawing and deformation of pearlite, to the review of data on the interlamellar spacing published by Ridley (1984) or the study performed by Zelin (2002) of microstructure evolution in pearlitic steels during wire drawing. Specific analyses by Toribio and Ovejero (1997, 1998a, 1998b, 1998c) demonstrate the progressive slenderizing and orientation (in 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 Previous research by Toribio and Ayaso (2020) on fracture of notched samples (Fig. 1) of progressively cold drawn pearlitic steels of very different geometries (very distinct degree of constraint) demonstrated the necessity of both microstructural orientation and triaxiality level to obtain fracture path deflection, cf. Figs. 2-6 showing the fracture profile for notched samples of cold drawn pearlitic steel wires. It is seen that notched samples of the most heavily cold drawn pearlitic steel wires behave in anisotropic manner, exhibiting crack path deflection and mixed mode propagation created by delamination cracks, it being consistent with the research by Tanaka et al. (2016).

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Fig. 1. Notched samples of cold drawn pearlitic steels with very different geometries.

Fig. 2. Fracture profile (notched sample 4A: 4 drawing steps & geometry A).