13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- 2. Experimental procedures 2.1 Material The material used in this investigation was microalloyed steel specified by API 5L Grade X70 standards. The same was obtained by thermomechanical treatment by controlled rolling. The chemical composition obtained by optical spectrometry technique is shown in Table 1: Table 1. Chemical composition of API X 70 steel C Si Mn P Al Cu S 0.14 0.27 1.45 0.01 0.05 0.03 0.00076 Nb V Ti Cr Ni Mo 0.051 0.041 0.018 0.0005 0.001 0.0045 2.2 Procedures 2.2.1 Charpy impact testing Charpy impact testing specimens were removed from the orientation and dimensions according to ASTM E-23 [4], as can be seen in Fig. 1. The tests were carried out in a range of temperature variation at 27°C up to -196°C, the specimens were immersed in a cryogenic bath of nitrogen and anhydrous alcohol liquids for 10 minutes, after that the same were withdrawn of the mixture and positioned on the machine. To increase the accuracy of this procedure the hammer would only be released whether all process occurred within 8 seconds. 2.2.2 Microtexture Microtexture analyses were performed by EBSD technique. To carry out these measurements were used two samples from the fractured specimens in the L-T orientation by impact testing at -25 °C and 226J of absorbed energy in the ductile brittle transition temperature region. The surface specimens analyzed were carried out in the perpendicular region to the direction of fracture propagation and near the edges of the crack generated by crack divider-type delamination, as shown in Fig. 2a), another analysis was performed parallel to the direction of fracture propagation and near the edge separation caused by delamination, as shown in Fig. 2b). Samples were polished in the Figure 1. Schematic drawing of the orientation notch specimens
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