PSI - Issue 41

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

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

temperatures of 980 °C and 1050 °C. Corrosion tests on as welded and heat treated samples were performed according to Standard ASTM G28, Method A, which involves measuring the mass loss after 120 h in boiling ferric sulfate/sulfuric acid solutions. The mass loss was then used to determine the corrosion rate for each of the specimens. Optical and scanning electron microscope analyses were carried out on samples after standard metallographic preparation and chemical attack with 97 ml HCl, 2 ml H � SO � , 1 ml HNO � solution. For the sake of simplicity only SEM micrographs will be reported. 3. Results and discussion The macrograph of the welded joint is shown in Fig. 3. Three zones were analyzed, say, fusion zone (FZ) (a), Heat Affected Zone (HAZ) (b) and Parent Metal (PM) (c). To investigate the possible sensitization effect induced by welding, the equilibrium diagrams of the analyzed alloy are also reported in Fig. 4 [Lindwall et al., 2019].

a

Fig. 3. Macrograph of the welded joint.

a

b

Fig. 4. Calculated equilibrium phase fraction as a function of temperature for a reduced composition (solid lines, composition: 0.02 pct C, 20.7 pct Cr, 0.72 pct Fe, 3.75 pct Nb, 8.83 pct Mo) used for the DICTRA simulations and the full (nominal) composition (dashed lines); (b) Calculated isopleth for varying Nb compositions [Lindwall et al., 2019].

Fig. 5 shows the microstructure of the as-welded joint and EDS spectra of detected precipitates. Compared to parent metal, the HAZ is characterized, as expected, by a greater grain size while the FZ by dendritic structure.