SURFACE-ROUGHNESS AND THE METASTABLE PITTING OF STAINLESS-STEEL IN CHLORIDE SOLUTIONS

The effects of surface roughness on metastable pitting susceptibility of type 304 (UNS S30400) stainless steel (SS) in chloride (Cl-) solution and the transition to stable pitting corrosion were investigated. A smoother surface finish reduced the frequency of metastable pitting because the number of metastable pit sites available was reduced. Once formed, however, a metastable pit had a greater probability of achieving stable pit growth ii the surface was smoother. Observations were rationalized qualitatively in terms of the geometry of the available metastable pit sites and their ability to establish a diffusion-controlled dissolution rate.