Microstructural characteristics and localized corrosion behavior of electron beam welded 9Ni steel joints

The mechanical properties and microzone corrosion resistance of electron beam welded 9Ni steel joints are investigated. The welded joint can be clearly divided into three distinct regions: the weld zone (WZ), heat-affected zone (HAZ), and base metal (BM), each exhibiting unique microstructural and electrochemical features. Microstructural analysis revealed that the WZ is predominantly composed of coarse lath martensite, resulting in the mechanically weakest region of the joint. Surface Volta potential mapping combined with electrochemical testing demonstrated a distinct potential hierarchy among the regions, following the order BM > WZ > HAZ. The HAZ exhibits the poorest corrosion resistance because of its fine-grained microstructure and high residual stresses, which not only increase its electrochemical activity but also produce significant galvanic force due to the potential difference with the adjacent BM and WZ.