Enhanced corrosion resistance of K-TIG welded DH32 steel joints with a Ni interlayer: A comprehensive electrochemical and microstructural investigation

Welding technology is a critical pillar of modern manufacturing, particularly in shipbuilding and engineering under extreme environments. However, the corrosion resistance of weld seams limits their application in corrosive conditions. This issue is especially pronounced in keyhole tungsten inert gas (K-TIG) welding, where high heat input often leads to coarse grain structures and compositional segregation, resulting in reduced corrosion resistance. This study systematically investigates the effect of nickel (Ni) interlayers with varying thicknesses on the corrosion resistance of weld seams in K-TIG-welded DH32 steel and explores the underlying mechanisms. Electrochemical testing, including open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization, reveals that with increasing Ni content, the corrosion potential of the weld seam shifts significantly in the positive direction. The corrosion current density decreases to 4.56 μA/cm², while the charge transfer resistance increases nearly threefold to 1294.9 Ω⋅cm², indicating a substantial enhancement in corrosion resistance. Microstructural analysis demonstrates that the addition of Ni refines the weld seam grains, transforming the ferrite-pearlite structure into lath martensite and forming Ni-enriched grain boundaries, which improve the compactness and stability of the passive film. Corrosion product analysis shows that high-Ni welds form mixed oxides (NiFe₂O₄) with high stability and low ion migration rates. This dense protective layer significantly reduces the driving force for corrosion reactions. In conclusion, Ni microalloying improves the corrosion resistance of K-TIG weld seams by optimizing the microstructure, composition of corrosion products, and electrochemical performance.