Fig. 1. Microstructure of QP1180 steel

Fig. 2. Dimensions of tensile test sample

Fig. 3. Bulge test equipment and schematic. (a) MTS 866.72S metal sheet forming machine; (b) schematic of bulge test

Fig. 4. Microstructures of low-speed welding joint. (a) Macro appearance; (b) FZ; (c) CGHAZ; (d) FGHAZ; (e) ICHAZ; (f) SCHAZ; (g) local magnification of SCHAZ

Fig. 5. Microstructures of high-speed welding joint. (a) Macro appearance; (b) FZ; (c) CGHAZ; (d) FGHAZ; (e) ICHAZ; (f) SCHAZ; (g) local magnification of SCHAZ

Fig. 6. Microhardness profile of welding joints cross-section

Fig. 7. Samples after tensile test. (a) Low-speed welding joint samples; (b) high-speed welding joint samples

Fig. 8. LDH values of tested sheets at different weld line offsets

Fig. 9. Photos of low-speed welding sheets after cupping test at different weld line offsets. (a) 0 mm; (b) 10 mm; (c) 20 mm; (d) 30 mm

Fig. 10. Fracture position and hardness distribution of low-speed welding sheet at weld line offset of 0 mm

Fig. 11. Photos of high-speed welding sheets after cupping test at different weld line offsets. (a) 0 mm; (b) 10 mm; (c) 20 mm; (d) 30 mm

Fig. 12. Fracture morphology of low-speed welding sheet with 0 mm weld line offset. (a) Macro appearance; (b) middle part of the fracture; (c) bottom part of the fracture

Fig. 13. Fracture morphology of high-speed welding sheet with 0 mm weld line offset. (a) Macro appearance; (b) middle part of FZ; (c) bottom part of FZ; (d) HAZ