PSI - Issue 41

6

Paolo Ferro et al. / Structural Integrity Procedia 00 (2022) 000–000

Paolo Ferro et al. / Procedia Structural Integrity 41 (2022) 430–438

435

Fig. 7. Microstructure of the joint after PWHT at 1050 °C (20 min)

Results of EDS line scan are summarized in Fig. 8. Fig. 8b also shows a comparison between the distribution of elements after PWHT at 980 °C and 1050 °C. It was found that Mo and Nb tend to segregate during solidification in the inter-dendritic zones (Fig. 8a) while Ni behaves the opposite. Cr, on the other hand, is homogeneously distributed. This alloy elements distribution doesn’t change significantly after the induction short-term PWHT at 980 °C, because of kinetics reasons. Conversely, the short-term PWHT at 1050 °C seems able to restore an almost uniform nominal chemical composition, as highlighted in Fig. 8c. Results of corrosion tests are summarized in Table 3, while Fig. 9 highlights the corrosive attack occurred in the inter-dendritic spaces of FZ.

Table 3. Corrosion rate as a function of specimen condition. Specimen condition

Corrosion rate [mm/year]

As-welded

0,89 0,48 0,41

980°C, 20 min 1050°C, 20 min

a