PSI - Issue 81

Jesús Toribio et al. / Procedia Structural Integrity 81 (2026) 18–22

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( elongated & oriented ) becomes the critical fracture unit and determines the size of the elongated and oriented cleavage facet characteristic of the anisotropic fracture behaviour ( exfoliation ) in heavily cold drawn steels. In the cold drawing process described in previous paragraphs the boundary of the non-existing austenitic grain plays the role of the firstly-written old text whose heritage remains in the material (more or less present) during drawing, but the rewriting almost (if not fully) deletes such a heritage or presence, creating a new text (which is really the old corrected, improved or modified), in the same manner as the cold drawn pearlitic steel wire is an improvement of the previously hot rolled bar but, in certain sense, the cold drawn wire is not a new material, but an improved version of the old one , conditioned by the circumstance of the manufacturing process by cold drawing. From the philosophical viewpoint, this is an orteguian approach in the sense proposed by the Spanish philosopher Ortega y Gasset. Furthermore, a quantitative analysis of the metallographs and the fractographs proves their similitude by considering the similar sizes of the elongated & oriented pearlite colony (EOPC) and the elongated & oriented cleavage facet (EOCF), as shown in Table 1 obtained by quantitative metallography as well as quantitative fractography, thereby demonstrating that both sizes (EOPCS and EOCFS), evaluated as the maximum length in the cold drawing or wire axis direction, are approximately the same for a given steel wire with certain cold drawing degree.

Table 1. Sizes of the elongated & oriented pearlitic colonies and the cleavage facets in the steels. Steel 4 5 6 EOPCS (  m) 28.9 36.5 42.2 EOCFS (  m) 30.5 34.3 41.4 EOPCS: elongated & oriented pearlitic colony size (maximum dimension in the wire axis direction). EOCFS: elongated & oriented cleavage facet size (maximum dimension in the wire axis direction). The steel number indicates the number of cold drawing steps undergone by the corresponding wire.

In the case of conventional cleavage taking place in an initially pearlitic eutectoid steel, the cleavage facet size is a strong function of the prior austenite grain size, although it is always somewhat less (Park and Bernstein, 1979). This size is the zone in which the pearlite colonies inside the same grain share a common crystallographic orientation of ferrite, following the research by Park and Bernstein (1979). It represents the critical fracture unit in randomly oriented pearlitic microstructures (i.e., in an isotropic pearlitic steel) and determines the intrinsic material toughness linked to its microstructure. 3. Conclusions In anisotropic materials such as the progressively cold drawn steel wires analyzed in this paper, there is an orientation during manufacturing by cold drawing of all microstructural units following a direction close to the wire axis or cold drawing direction: (i) the prior austenitic grain (zero, “virtual” or “palimpsestus” microstructural level); (ii) the pearlitic colony (first microstructural level); (iii) the pearlite lamellae (second microstructural level). The slender pearlite colony more than the prior austenite grain (that is also virtually cold drawn in the palimpsestus approach) could be taken as critical fracture unit in the drawn material and determines the size of the elongated and oriented cleavage facet characteristic of the anisotropic fracture (exfoliation) in heavily cold drawn steels because different pearlite colonies in the same grain follow distinct orientations paths along the manufacturing route. The aforesaid evolution of the material points defining the prior austenitic grain represents, from the continuum mechanics viewpoint, an updated lagrangian formulation in which material points evolve with cold drawing, in the same manner as material properties also evolve towards higher resistance with cold drawing, so that a new (improved) material – the cold drawn pearlitic steel wire – appears, but it is not really a new material, but the old one (hot rolled) with improved properties. It is a sort of palimpsestus approach , similar to rewriting over an old, previously written, table or re-building over and old city in ruins (or destroyed), i.e., both the prior (“ virtual” ) austenitic grain (i.e., the material points defining its boundary) and the material itself are metaphorically re-written, i.e., evolve with cold drawing and create the new material over the old ( it being paradoxically old and new ) in the same manner as the Catholic Rome appears (and develops in a complementary manner) over the ancient (purely roman) Rome , or the Baroque Rome does the same over the Rome of the Caesars. 4. Epilogue: A Tribute to the Japanese cities of Hiroshima and Nagasaki The atomic bombing of the Japanese cities of Hiroshima and Nagasaki was a sort of cruel re-writting (“ palimpsestus ”) of the mentioned cities. Fig. 2 shows the plant of the city of Hiroshima and the Gembaku Dome , the only surviving monument, a sort of “ memento ” of the city prior to the bombing.