Revisiting the influence of surface roughness on pitting behavior of AISI 321 stainless steel joints via statistical analysis

The effect of surface roughness on the pitting behavior of 321 stainless steel welded joints was investigated. The pitting resistance of different weld zones exhibited distinctly different responses: the electron beam fusion zone (EB-FZ) showed a continuous decrease in pitting potential with increasing roughness; the tungsten inert gas fusion zone (TIG-FZ) remained stable over a wide roughness range and declined only at extreme levels; while the base metal (BM) was nearly unaffected. Statistical analysis of pit size and density by the potentiostatic pulse technique (PPT), combined with quasi-in-situ characterization using scanning electron microscopy (SEM), revealed that roughness increases pit initiation density by introducing geometric defect sites, without altering the intrinsic pitting susceptibility of inclusions and Cr-depleted zone near the δ-ferrite. The pitting potential of each zone is determined by the more susceptible active site type—roughness-induced surface defects or inherent microstructural weaknesses. This competitive mechanism provides a new framework for understanding the divergent corrosion behavior of weldments under different surface finishes.