PSI - Issue 60

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

515

6

Figure 4 : SEM image indicating location of points corresponding to chemical composition measurements in Table 2. Table 2: Chemical composition at different regions in Fig. 4.

Elements (in wt.%)

Ni

Cr

Co

Mo

Fe

Al

Ti

Cracked region (Spectrum 5)

63.4

22.4

11.5

0.9

0.6

0.1

0.6

Interface between cracked and uncracked region (Spectrum 6)

59.5

19.7

12.7

5.4

0.3

0.6

0.2

Uncracked region (Spectrum 7)

55.4

22.7

12.2

6.8

0.1

0.9

0.4

These defects can be mitigated by eliminating the root causes of cracking. This would necessitate careful control of the hot working process, whereby dynamic recrystallization occurs in a more homogeneous manner, thereby preventing the formation of soft regions. From a process control perspective, the lower occurrence of cracking at a moderate strain rate of 5s -1 (Fig. 2 (b)) indicates that strain rate control could be an effective route toward crack mitigation. The manufacturing of products made of Ni-base superalloys is vulnerable to manufacturing-induced defects. One such defect, the development of transverse ‘fir - tree’ cracks on hot extruded tubes, was investigated as a case study. It was concluded that the cracks originated from unfavorable microstructural developments during the hot working process; evolution of a heterogeneously recrystallized microstructure created local soft regions, which coincided with the tensile stresses experienced by the material. In addition, a possible role of chemical heterogeneity was noted. It is concluded that mitigation of such defects would require careful selection of process control factors such 4. Conclusion