Fig. 1. Ultra-NGLW joint with each thickness and its groove design. (a)(d) 70 mm; (b)(e) 50 mm; (c)(f) 20 mm

Fig. 2. Residual stress test. (a) μ-X360n test equipment; (b) schematic of test; (c) Debye ring

Fig. 3. Meshing and boundary conditions of numerical model. (a) Mesh generation; (b) boundary confinement condition; (c) heat-transfer boundary condition

Fig. 4. Comparison of different practical welding pools with their corresponding heat source models. (a) Laser bottoming welded pool; (b) laser filling welded pool

Fig. 5. Schematic for sampling micro-shear specimens

Fig. 6. Micro-shear test. (a) Schematic; (b) relationship between load and cutter displacement

Fig. 7. MAG welded joint of B950CF steel. (a) Macro-morphology; (b) metallographic structure

Fig. 8. Morphology of Ultra-NGLW joint. (a) Macro-morphology of joint weld; (b) microstructure of cover filling layer; (c) microstructure of 4th filling layer; (d) microstructure of 2nd filling layer; (e) microstructure of base material

Fig. 9. Results of micro-shear strength and microstructures of joint. (a) Micro-shear strength versus L; (b) microstructure of joint fusion line; (c) microstructure of HAZ; (d) microstructure of non-full phase-transformation zone

Fig. 10. Toughness obtained by micro-shear test and calculated tensile strength. (a) Micro-shear power; (b) tensile strength versus L

Fig. 11. Residual stress test points for Ultra-NGLW joint. (a)L1 test line;(b)L2, L3 and L3 test lines

Fig. 12. Test results of upper surface residual stress of Ultra-NGLW joint. (a) 20 mm joint; (b) 50 mm joint; (c) 70 mm joint

Fig. 13. Residual stress comparison of Ultra-NGLW joints with different thicknesses. (a) Transverse residual stress; (b) longitudinal residual stress

Fig. 14. Cross-sectional residual stress of 70 mm joint. (a) Numerical simulation result; (b) transverse residual stress; (c) longitudinal residual stress