Pitting Corrosion Studies on Solution-Annealed Borated Type 304L Stainless Steel Using Electrochemical Noise Technique

The pitting corrosion resistance of Type 304L (UNS S30403) stainless steel (SS) with (1.2 wt%) and without boron in as-received and solution-annealed (1,423 K for 2 h and 4 h) conditions was evaluated using the electrochemical noise (EN) technique in neutral 0.5 M sodium chloride (NaCl) solution for 72 h at the corrosion potential (E_corr). EN data were analyzed using visual records, statistical parameters, spectral analysis, and shot-noise parameters. Weibull and Gumbell plots were prepared to study the distribution of pitting and passivation events and metastable pit radii, respectively. Current transient analysis showed the maximum number of pit nucleation and metastable pitting events in an as-received specimen, which decreased gradually with solution annealing. Pit radii calculated using Gumbell distribution showed the lowest metastable pit radii in solution-annealed specimens compared to as-received specimens. Therefore, EN analysis of the data revealed the improvement in pitting corrosion resistance of solution-annealed specimens. Pits were found to be growing around the boride particles in the matrix because of the Cr depletion around these particles. Large boride particles dissolved to smaller ones because of solution annealing; therefore, the homogenized surface resulted in the improvement in the pitting corrosion of the solution-annealed specimens at 1,423 K/4 h.