Role of welding-induced microstructural heterogeneity in the corrosion of low-Cr ferritic stainless steel welded joints in simulated coal leachate

The corrosion behavior of T4003 low-chromium (Cr) ferritic stainless steel welded joints was investigated in a simulated coal leachate solution containing sulfite ions (0.01 mol/L NaHSO 3 , pH 4.5, 45 °C). Welding induced pronounced microstructural heterogeneity, with the high-temperature heat-affected zone (HTHAZ) exhibiting severe grain coarsening and an increased KAM value. As a result, localized corrosion preferentially initiated in the HAZs, particularly in the HTHAZ, where deeper pits and higher pit depth-to-width ratios were observed. XPS and electrochemical analyses revealed a reduced Cr 2 O 3 content, enrichment of FeSO 4 and FeS, and a decreased resistance of the passive film in the HAZs, indicating defect accumulation and instability of both the passive film and the corrosion product layer. These results demonstrate that preferential corrosion of the heat-affected zones is controlled by the synergistic interaction between welding-induced microstructural degradation and sulfite-assisted chemical attack.