Fig. 1. Dimensions of fatigue specimen

Fig. 2. Microstructure of DP980 steel

Fig. 3. Morphologies of welding joints under different heat inputs. (a) 80 J·mm^-1; (b) 100 J·mm^-1; (c) 133 J·mm^-1

Fig. 4. Microhardness profiles of DP980 welding joints under different heat inputs

Fig. 5. Typical tensile failure locations of DP980 welding joints and base material. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

Fig. 6. Relationship between total strain amplitude and 2N_f for base material and DP980 welding joints

Fig. 7. Microstructures of L2 sample. (a) Weld zone, supercritical HAZ, and intercritical HAZ; (b) subcritical HAZ

Fig. 8. Microstructures of subcritical HAZ under different heat inputs. (a) 80 J·mm^-1; (b) 100 J·mm^-1; (c) 133 J·mm^-1

Fig. 9. Variation of stress amplitudes of base material and DP980 welding joints under different strain amplitudes with numbers of cycles. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

Fig. 10. Stabilized hysteresis loops at half fatigue life

Fig. 11. Low-cycle fatigue specimens of base material and joints

Fig. 12. Fatigue fracture domains of L2 and L3 samples. (a) Subcritical HAZ near L2 fracture; (b) subcritical HAZ near L3 fracture

Fig. 13. Macroscopic fatigue fracture morphologies of base material and welding joints when Δε_t/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

Fig. 14. Microscopic fatigue fracture morphologies of base material and welding joints when Δε_t/2=0.3%. (a) Base material; (b) L1 sample; (c) L2 sample; (d) L3 sample

Fig. 15. Macroscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δε_t/2=0.25%; (b) Δε_t/2=0.3%; (c) Δε_t/2=0.4%; (d) Δε_t/2=0.5%

Fig. 16. Microscopic fatigue fracture morphologies of welding joints of L3 sample under different strain amplitudes. (a) Δε_t/2=0.25%; (b) Δε_t/2=0.3%; (c) Δε_t/2=0.4%; (d) Δε_t/2=0.5%