Investigation on the nickel content design and the corrosion resistance of low alloy steel welded joint in tropical marine atmosphere environment

In this study, three kinds of welding materials (WMs) with different Ni contents were designed for low alloy steel welded joints made by CO₂ gas-shielded welding technique. The corrosion resistance of welded joint was studied through the atmosphere exposure test in Trat, Thailand. Results show that there was a hardening in the heat-affected zone after welding, and the average hardness slightly increased with the increase of Ni in WM. The electrochemical activity at the fusion line zone enhanced with the addition of Ni in WM, indicating a more obvious local galvanic corrosion effect there. Ni promoted the generation of NiFe₂O₄ and the transformation from γ-FeOOH to α-FeOOH, which increased the impedance modulus of the rust film on WM. More important, the corrosion performance assessment illustrated that the addition of Ni in WM hardly had an effect on the corrosion step values after half a year test, which confirmed that there is no need to add excessive content of Ni.