Fig. 1 SEM image of γ/Laves eutectic structure and TiC in the welded DM

Fig. 2 Analysis of the lamellar-like Cr23C6 carbides at the grain boundary in the DM after PWHT at 650 °C: a SEM image, b TEM image and SAED pattern, c EDS spectrum

Fig. 3 SEM image of the Cr23C6 carbide and γ/Laves eutectic structure at the grain boundary

Fig. 4 SEM and TEM analysis of the precipitates in the DM after PWHT at 850 °C: a granular Cr23C6 carbides at the grain boundary, b magnification of the region in the red frame of a, c TEM image and SAED pattern of the needle-like Cr23C6 carbides

Fig. 5 SEM images of the microstructure in the DM after PWHT at 950 °C: a precipitates distribution, b granular Cr23C6 carbides at the grain boundary, c needle-like Cr23C6 carbides in the interdendritic region

Fig. 6 Electrochemical analysis: a Nyquist plots, b potentiodynamic polarization curves

Fig. 7 Morphology of needle-like Cr23C6 carbides at 850 °C for different holding times: a 2 h, b 4 h, c 6 h, d 8 h

Fig. 8 Linear relationship between the size (l?3 and w?3) of needle-like Cr23C6 carbides and the holding time t at 850 °C in the DM (ρ was the correlation coefficient, and through the analysis of variance, the F value can be obtained)

Fig. 9 Relationship between α (α = l?/w?) and the holding time t

Fig. 10 SEM images of the DM with PWHT at various temperatures for 4 h after the electrochemical corrosion: a 650 °C, b 750 °C, c 850 °C, d magnification of the region in the red frame of c