PSI - Issue 60

Mantosh Mandal et al. / Procedia Structural Integrity 60 (2024) 510–516 Mantosh Mandal/ Structural Integrity Procedia 00 (2019) 000 – 000

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compression) during extrusion. Thus, the hot compression tests are qualitatively similar to the hot extrusion process. To maintain the similitude, the compression experiments were performed at two different strain rates (5s -1 and 20s -1 ), which correspond to typical strain rates encountered in the hot extrusion process. The compressed specimens were used to analyze the likely causes of defects. The midsection of the compressed specimens was polished using standard metallographic procedure, followed by electrochemical etching (10% oxalic acid solution, 6V, 10s). The etched specimens were examined using an optical microscope. Important features were examined at higher magnifications using scanning electron microscopy (SEM).

Figure 1 : Circumferential cracks observed in hot-extruded tubes

4. Results and Discussions The physical simulation of hot extrusion through hot compression led to the generation of cracks on the curved surface of the compressed cylinders. The cracks were well developed upon compression at the higher strain rate of 20s -1 (Fig. 2 (a)). On the other hand, compression at the lower strain rate of 5s -1 led only to an early stage of crack initiation, as shown in Fig. 2 (b). Therefore, further investigations were conducted on the cylinder compressed at 20s -1 . The polished midsection of this specimen revealed the generation of radial cracks from the curved surface. These cracks, shown in Fig. 2 (c), are analogous to the cracks on the curved surface of tubes (Fig. 1). Upon microscopic evaluation, the cracks appeared to propagate inward along the grain boundaries (Fig. 2 (d)).