PSI - Issue 41

Paolo Ferro et al. / Procedia Structural Integrity 41 (2022) 430–438 Paolo Ferro et al. / Structural Integrity Procedia 00 (2019) 000–000

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Precipitates are also identified by EDS, in all the three zones, as carbides enriched in Mo/Nb (light colored precipitates) or oxides (dark colored precipitates).

Fig. 5. Microstructure of the as-welded joint.

The microstructure of the welded joint after the annealing heat treatment at 980 °C is shown in Fig. 6. It didn’t change significantly compared to that of the as-welded joints. However, carbides morphology in HAZ now appears as a grain boundary narrow film. EDS analysis (not reported here) reviled that such secondary precipitate was a Mo and Nb rich phase.

Fig. 6. Microstructure of the joint after PWHT at 980 °C (20 min).

Finally, Fig. 7 shows the microstructure of the joint after short PWHT at 1050 °C. Here, secondary phases in HAZ became equiaxed and resulted, according to EDS investigations, more enriched in Nb and Mo.