DISCUSSION Form the observation of the fractographs corresponding to HDT(0) (Figure 5) and HDT(6) (Figure 6), the following statements may be drawn: • All the HDT modes for different degrees of cold drawing are associated to the same HAC mechanism (cathodic potentials and decrease of stress intensity factor). • A generic HDT(i) exhibits an apparent deformation (in the fractograph) which is an increasing function of the degree of cold drawing (represented by the superindex i which indicates the number of cold drawing steps undergone by the steel). • Such a deformation seems to be oriented in the direction of the larger size of the fractograph, i.e., in a direction quasi-parallel to the wire axis or cold drawing direction. Thus the question arises about whether or not a geometric relationship does exist between the HDT modes so that one can be virtually obtained by deformed a previous one (associated with a lower degree of cold drawing). This virtual transformation is sketched in Figure 7, in which the initial fractograph HDT(0) (or pure TTS) in the hot rolled bar is virtually oriented in the direction of HAC in the cold drawn material and deformed by transformations in the radial, hoop and axial directions. The parameters of the geometric transformations are obtained by the hypothesis of conservation of volume in the Plasticity theory and represent the virtual deformation which should be applied to the HDT(i) to obtain other HDT(j) (j > i). Figure 8 shows the results of this virtual deformation process to obtain HDT(6) from HDT(4), where it is seen that this virtual topography really resembles the real one shown in Figure 6, which confirms that the micromechanism of fracture is similar in both cases. Figure 7: Virtual deformation of the fractograph. Figure 8: Virtual HDT(6) by deformation of HDT(4).
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