Improving the corrosion behaviour of powder metallurgical 316L alloy by prepassivation in 20% nitric acid

The electrochemical improvement of PM 316L stainless steels by pre-alloyed powder prepassivation in 20% nitric acid in comparison with as-received specimens has been studied in this work. For comparison purposes a simultaneous study was carried out on similar composition wrought AISI 316L steels. Corrosion resistance was studied using evolution of the corrosion potential vs. time, anodic polarisations curves and Zero Resistance Ammeter technique. Reductions of the corrosion rate (icorr) were observed in prepassivated specimens in neutral chloride media. Crevice resistance was higher for prepassivated specimens and for higher densities and annealing as post-heat treatments.

Research highlights
► Prepassivation treatment interestingly improves the corrosion resistance of PM 316L stainless steels.
► A higher crevice resistance is also observed for the prepassivated specimens as well as for the annealed samples with higher densities.
► Blocking oxygen reduction sites and decrease in the porosity by the prepassivation treatment were the main reason for decreasing in the OCP.
► Noticeably, after 72 h exposure to 6% ferric chloride solution, the prepassivated PM 316L sample shows greater corrosion resistance than the bulk 316L stainless steel.