of cold drawing, in order to elucidate the physical micromechanisms of fracture of pearlitic steels in hydrogen environments, taking into account the progressively anisotropic fracture behaviour as the strain hardening level produced by cold drawing increases. MATERIALS AND MICROSTRUCTURE The materials used in this work were high-strength steels taken from a real manufacturing process at EMESA TREFILERIA, S.A. Wires with different degrees of cold drawing were obtained by stopping the manufacturing chain and taking samples from the intermediate stages. The different steels were named with digits 0 to 6 which indicate the number of cold drawing steps undergone. Table 1 shows the chemical composition common to all steels, and Table 2 includes the diameter (Di), the yield strength (sY), the ultimate tensile stress (sR) and the fracture toughness (KIC). TABLE 1 CHEMICAL COMPOSITION (wt %) OF THE STEELS __________________________________________________________________________ C Mn Si P S Cr V Al __________________________________________________________________________ 0.80 0.69 0.23 0.012 0.009 0.265 0.060 0.004 __________________________________________________________________________ TABLE 2 DIAMETER REDUCTION AND MECHANICAL PROPERTIES OF THE STEELS _____________________________________________________________________________ Steel 0 1 2 3 4 5 6 _____________________________________________________________________________ Di (mm) 12.00 10.80 9.75 8.90 8.15 7.50 7.00 sY (GPa) 0.686 1.100 1.157 1.212 1.239 1.271 1.506 sR (GPa) 1.175 1.294 1.347 1.509 1.521 1.526 1.762 KIC (MPam1/2) 60.1 61.2 70.0 74.4 110.1 106.5 107.9 _____________________________________________________________________________ The microstructural evolution with cold drawing was studied in previous woks [5-8]. Attention was paid to the evolution with cold drawing of the two basic microstructural levels: the pearlite colonies (first level) and the pearlitic lamellae (second level). With regard to the first microstructural level, a progressive elongation and orientation of the pearlitic colonies in the cold drawing direction (wire axis) was observed [5,6]. In the matter of the second microstructural level, the analysis showed an increasing closeness of packing (with decrease of the interlamellar spacing) and a progressive orientation of the pearlitic lamellar microstructure in the cold drawing direction [7,8]. Therefore, both pearlite colonies and pearlitic lamellar microstructure tend to align to a direction quasi-parallel to the wire axis as cold drawing proceeds. Figures 1 and 2 (cf.[8]) show the pearlitic microstructure of steels 0 and 6 respectively, by means of micrographs corresponding to longitudinal metallographic sections of the wires (those sections containing the wire axis). It is seen that, while the microstructure of steel 0 (hot rolled bar which is not cold drawn at all) is randomly oriented, the microstructure of steel 6 (prestressing steel heavily cold drawn) is markedly oriented in the direction of the wire axis (or cold drawing direction) which corresponds to the vertical side of the
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