PSI - Issue 3

6

Author name / Structural Integrity Procedia 00 (2017) 000–000

Jesús Toribio et al. / Procedia Structural Integrity 3 (2017) 3–10

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6. Microstructure and fracture performance In the matter of the relationship between microstructure and fracture performance of cold drawn pearlitic steel in the presence of notches , large research work was performed by Toribio and Ayaso (2001, 2002a, 2002b, 2003, 2004) on notched samples of progressively cold-drawn pearlitic steels with very different notch geometries (Fig. 8) and thus very distinct stress triaxiality (constraint) were analyzed with regard to their role in fracture behavior. The main conclusion of these studies is the anisotropic fracture behavior of cold-drawn pearlitic steel in the presence of notches, although it was proved the necessity of both triaxiality (constraint) and microstructural orientation (induced by cold drawing) to produce fracture path deflection and propagation in the drawing direction, as shown in Fig. 9 in which it is seen that it only appears in notched samples A and B (minimum notch radius; maximum stress triaxiality) and in notched sample C in the case of heavily drawn steels, and never appears in notched samples D (minimum stress triaxiality), the fractographic appearance of the propagation step resembling enlarged and oriented cleavage and caused by the pearlitic pseudocolonies, as suggested by Toribio et al. (1997) and Toribio and Ayaso (2002b).

A

B

C

D

Fig. 8. Geometries of the notched samples of cold-drawn pearlitic steels with very different triaxiality.

Fig. 9. Fracture paths in notched samples 4A (4 drawing steps; notch A), 4B (4 drawing steps; notch B), 6C (6 drawing steps; notch C), and micrograph of the fracture propagation step parallel to the wire axis or cold drawing direction, resembling enlarged and oriented cleavage .