Issue 50

L. Romanin et al., Frattura ed Integrità Strutturale, 50 (2019) 251-263; DOI: 10.3221/IGF-ESIS.50.21 255 alteration compared to arc welding. It is also noted that in the heat affected zone, grains boundaries are less evident than those in the parent material (PM). Figure 3: FZ shape (a) and microstructure (b) Figure 4: HAZ details Grain boundaries in the PM were carefully analyzed by SEM (Fig. 5). A dark precipitate (Label 1), of about 3 μm, and a series of lighter and smaller precipitates (Label 2) with dimensions in the order of 0.1 μm were detected (Fig. 5b). The dark precipitate contains mostly Titanium and Niobium (Fig. 5c) and is therefore classified, according to literature [30], as MC (TiC) carbide. The smaller precipitates (Label 2) are distributed along the grain boundaries and have a fine globular aspect. Moreover, they contain mostly molybdenum and chromium like the M 23 C 6 carbides in references [31,32]. Niobium carbides and Leave’s precipitates are also found in the PM as shown in Fig. 6 [30,33]. No other type of precipitate has been found in the parent material. By comparing the spectra coming from EDS measurements in the dendritic and interdendritic zones, Mo was found to segregate in the interdendritic space (label 10) (Fig. 7). For the sake of simplicity, spectra coming from points 8 and 9 of Fig. 7 are not reported in this work. Anyway, because of their content of nickel, molybdenum, niobium and chromium, they were classified as Leave’s phase [33,34].