Effect of C-Si synergy on microstructural evolution and low-temperature toughness of GMAW weld metal in seawater corrosion-resistant steel

This study investigates the synergistic effect of C-Si on the microstructural evolution and low-temperature toughness of gas metal arc welding (GMAW) weld metal for seawater corrosion-resistant steel. Two weld metals with different C-Si contents (0.064 wt.%C-0.52 wt.%Si and 0.095 wt.%C-0.74 wt.%Si) were produced and characterized using multi-scale microstructural techniques to evaluate phase constitution, grain boundary characteristics, dislocation density, crystallographic texture, and mechanical properties. The results show that increasing C-Si content significantly modifies the weld metal microstructure. The microstructure mainly consists of acicular ferrite (AF), proeutectoid ferrite (PF), and granular bainite (GB), accompanied by martensite-austenite (M-A) constituents. Higher C-Si levels promote the formation of GB and irregular lath-like M-A constituents while reducing the PF fraction. Meanwhile, the fraction of high-angle grain boundaries decreases by 11.8%, and the dislocation density increases from 1.7 × 10 9 cm -2 to 1.6 × 10 10 cm -2 , accompanied by stronger crystallographic texture. These microstructural changes slightly increase the yield strength but reduce the average impact energy at 0 °C from 68 J to 35 J, indicating deteriorated low-temperature toughness. Fracture analysis reveals smaller plastic fracture zone (PFZ) and shear zone (SZ) regions and multiple secondary cracks in the high C-Si weld metal, suggesting reduced energy consumption during crack propagation. Mechanistic analysis indicates that the synergistic action of C stabilizing austenite and Si suppressing carbide precipitation promotes M-A formation, reduces high-angle grain boundaries, and enhances texture intensity, thereby facilitating crack propagation and deteriorating low-temperature toughness. These findings provide guidance for the compositional design of welding consumables for seawater corrosion-resistant steels.