Microstructural homogenization and enhanced corrosion resistance of austenite/duplex dissimilar oscillating laser welded joints via high temperature solution treatment

The corrosion property of dissimilar steel welded joints used in ocean industry was seriously compromised by heterogeneous microstructures and detrimental phase precipitation. In this study, the poor microstructure of dissimilar welded joints was homogenized and the corrosion behavior was enhanced via optimized high temperature solution treatment. The results demonstrated that the initial as-welded coarse and segregated microstructure was effectively homogenized and transformed into a homogeneous austenite matrix (83.7%) with finely distributed skeletal ferrite (11.8%) and minimal σ-phase (4.4%) after 1050 °C post-weld heat treatment(PWHT) for 2 h. In contrast, microstructural heterogeneity and elemental segregation were aggravated by lower PWHT temperatures. Electrochemical characterization revealed that the 1050 °C/2 h PWHT sample exhibited optimal corrosion resistance, evidenced by the highest charge transfer resistance (9.18 × 10⁶ Ω) and the lowest passive current density (4.52 × 10^–6 A/cm²), representing a 16.3% increase and an 21.3% reduction compared to the as-welded condition, respectively. Moreover, a better re-passivation capability, characterized by the most noble protection potential (Ecorr₂ ≈ 0.5 V) was demonstrated by this condition in cyclic voltammetry(CV) tests. The enhanced corrosion performance was attributed to the homogenized microstructure and the resultant continuous and stable Cr-rich passive film (primarily FeCr₂O₄ and Cr₂O₃), effectively suppressing pit initiation and accelerating re-passivation. This work provided valuable insights for optimizing heterogeneous microstructures to enhance the durability of dissimilar steel welded joints in corrosive environments.