Fig. 3.. Optical microstructure of the specimen annealed at 350 °C for 7 days (analogous to Fig. 2): (a) Panoramic image of the whole sample area (10 × 6 mm2) (RD-TD plane); (b) - (d) magnified images of several outlined areas in (a) revealing a more uniform grain size distribution than that in Fig. 2, which is taken as an indication for the absence of AGG at 350 °C.