Fig. 1. Schematic diagram of welding test device

Fig. 2. Gas protection device

Fig. 3. Forming of bead surface

Fig. 4. Cross sections of beads

Fig. 5. Weld widths and penetration depths under different gas protection modes

Fig. 6. Transient plume flow states under different gas protection modes. (a) Bead 1; (b) bead 2; (c) bead 3; (d) bead 4; (e) bead 5; (f) bead 6; (g) bead 7

Fig. 7. Forming of front and back beads under different welding process parameters. (a) 1#,front; (b) 1#, back; (c) 2#, front; (d) 2#, back; (e) 3#, front; (f) 3#, back; (g) 4#, front; (h) 4#, back

Fig. 8. Forming of front and back beads during 15 mm thick stainless steel butt welding. (a) Front; (b) back

Fig. 9. Morphologies of microstructures. (a) Base metal; (b) weld seam; (c) heat affected zone

Fig. 10. Impact absorption energy values of 5 mm×10 mm×55 mm sample at different positions

Fig. 11. Morphologies of weld impact fracture. (a) Macroscopic fracture; (b) dimple

Fig. 12. Hardness distribution curve