Fig. 1 Groove detail (all dimensions in millimeters).

Fig. 2 a Schematic of the Charpy impact specimens: extracted positions and notch locations; schematic of the tensile b and side bend c specimens (all dimensions in millimeters).

Fig. 3 Cross-sectioning observations of the joints.

Fig. 4 Statistical results of the cross-sectional porosity of the welds at different depths.

Fig. 5 Effect of water depth on the main element contents in WM: a carbon and oxygen, b alloying elements.

Fig. 6 Product of weld metal carbon and oxygen contents as a function of water depth.

Fig. 7 Typical optical images of columnar microstructures in WM of A a, I b, J c, K d welds.

Fig. 8 a HAZ containing three different regions, and HAZ microstructures of the DH36 b, d, f and X65 c, e, g weld joints. Green, red, and blue marked squares denote the region of CGHAZ, FGHAZ, and ICHAZ, respectively.

Fig. 9 Typical crack morphology in CGHAZ a, WM b.

Fig. 10 Hardness distribution of the joints welded at different water depths.

Fig. 11 Average hardness values in WM of the DH36 joints welded at different water depths.

Fig. 12 Charpy impact-absorbed energy of the DH36 joints welded at different water depths.

Fig. 13 Typical pore morphology in DH36 Charpy impact samples after fracture: a 25 m, b 45 m.

Fig. 14 Fracture morphology of the weld metal for the impact specimens that were welded at 2 m a, 11 m b, 25 m c, 45 m d depth.