Issue 35

X.C. Arnoult et alii, Frattura ed Integrità Strutturale, 35 (2016) 509-522; DOI: 10.3221/IGF-ESIS.35.57 511 parts by the center. Guo 2002 [1] observed a similar phenomenon on CT specimens fabricated from API X70 steel. As Guo et al, Yan et al observed small delamination cracks close and parallel to the main delamination cracks. Figure 2 : SEM picture of a fracture observed on a 200°C-tempered tensile specimen [6]. Figure 3 : SEM picture of fracture of 600°C tempered tensile specimen [6]. Tankoua et al [10] studied the influence of test temperature on the fracture surface of Arcelor pipeline steel. Specimen orientations were 0° and 90° according to the rolling direction. For both orientations, the authors observed three fracture modes in competition on notch tensile specimen. At 20°C, 100°C and -196°C the ductile fracture, ductile fracture with central delamination cracks and cleavage fracture were observed, respectively. This indicates a ductile-brittle-transition- temperature in the fracture behavior of this steel. In the case of -196°C, the cleavage fracture mode was accompanied by a small number of micro delamination cracks. Baldi and Buzzichelli [23] found central delamination cracks on a well- developed ductile fracture surface. In the last decade, irradiated 08Ch18N10T specimens (chemically equivalent to A321) originating from the reactor vessel of the decommissioned VVER-440-Type 230 nuclear power plant located in Greifswald in northern Germany was evaluated by Hojna et al. [16, 17]. The authors observe a complex fracture surface after a tensile test at room temperature: ductile fracture zone and many different types of secondary cracks, among which delamination cracks were present [17].