Kurtosis as a Decisive Topographic Parameter for Pitting Attack of AISI 304L Stainless Steel

The effects of the centerline average (R_a), kurtosis (Rku), and Cr concentration at the surface on the pitting corrosion resistance of AISI 304L stainless steel were studied based on the modification of the corroding surface by mechanical polishing and electropolishing routes. The values of E_P − E_corr, E_P − E_rp, and i_P were devised as the quantitative measures of pitting resistance, where E_P is the pitting potential, E_rp is the repassivation potential, E_corr is the corrosion potential, and i_P is the passive current density. Preliminary, the improved resistance against pitting corrosion was associated with the reduced R_a and the elevated Cr concentration on the surface. However, more intense analysis revealed that the samples with Rku < ~3 (platykurtic distribution) exhibited a good resistance to pitting attack, irrespective of the values of R_a and Cr content. Accordingly, the importance of the Rku as a decisive topographic parameter for pitting attack was established.