PSI - Issue 71

Ninad Vasant Pawar et al. / Procedia Structural Integrity 71 (2025) 134–141

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Fig. 3 Circumferential view of fractured zone in failed cone

Fig. 4 Representative images of fractured surface showing different fracture features and zones.

3.4. Scanning Electron Microscopy of fractured surface The fractured surface, starting from the groove till the face, was analyzed on broken flanges at multiple locations. As mentioned in earlier sections, the centers of arches were selected to analyze fracture origins. Representative SEM micrographs are shown in fig. 5 and 6. Fig. 5 shows a representative overall fractured area divided into 3 zones, numbered 1 to 3, in the yellow box. The magnified SEM images are included in Fig. 6 each from three identified zones. Fig. 6(b) shows area near groove surface. It shows stable crack growth. Decohesion of carbides in fig. 6(d) and 6(e) is evident. The projected features are flattened due to surface rubbing with their fractured counterparts. The edge of the groove (top area of fig. 6(a) and 6(b)) can be seen flattened from consequential contact with rollers in the later stage of fracture as the flange area was moving away with the propagating fracture. Fig. 6(c) and 6(d) show intergranular fracture with some transgranular fracture. Surface rubbing is also evident from the rubbing marks observed in 6(d). The grain surface of the zone shows carbides embedded as well as separated from the grain boundary surface. Zone 3, which is shown in fig. 6(e) and 6(f), shows predominantly intergranular fractures, indicating unstable crack growth (Miller et al. 2022). Fig. 6(g) shows one of the un-damaged regions. The initiation can be seen taking place on the groove surface with evident ratchet like features aligned in fracture propagation direction. The micro-surface features observed in fig.6(h) highlight the difference in crack growth in initiation zone as compared to intermediate and fast fracture zone of fig. 6(d) and fig.6(f). Typical fatigue striations were not observed given the nature and heat treatment condition of SAE 52100.