PSI - Issue 37

Jesús Toribio et al. / Procedia Structural Integrity 37 (2022) 1007–1012 Jesús Toribio / Procedia Structural Integrity 00 (2021) 000 – 000

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3.3. Curvature induced fracture It is a type of punctual micro-damage that is observed within the lamellae of a colony, which appear curved due to its accommodation during the drawing process. Most of the lamellae that make up the pearlite colonies bend when subjected to the stresses of the manufacturing process, the curvatures being more noticeable the more the orientation of the lamellae differs in relation to that of the longitudinal axis of the considered wire , Fig. 5 (a). The micro-damage can evolve along the wire drawing in the following ways: – Deforming in the direction of the wire drawing (longitudinal axis of the wire), increasing its width, Fig. 5 (b) – Fragmented pearlitic, sometimes constricted in different directions, as highlighted in Fig. 5 (c).

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Fig. 5. Evolution of the micro-damage called curvature induced fracture of cementite lamellae during the cold drawing process

3.4. Micro-decolonization Micro-decolonization is a micro-defect that occurs during wire drawing as a consequence of non-accommodation between colonies, Fig. 6 (a). This micro damage is specific to colony boundaries. Said micro defect begins with the generation of gaps in the border between two colonies, the lamellae that make up both border colonies seem to separate, forming gaps between them. It can be seen from the first step of the wire drawing process. Throughout the drawing process this type of micro damage may evolve, like leopard skin, towards an intracolonial or intercolonial tear along the boundaries between colonies, the intercolonial tear being the most feasible evolution in the material, Fig. 6 (b). This micro-damage generates large discontinuities within the pearlitic lamellar microstructure, Fig. 6 (c).

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Fig. 6. Evolution from micro-decolonization to intercolonial tearing during the drawing process.