Passivation and Chloride-Induced Depassivation of Additively Manufactured Duplex Stainless Steel Clads in Simulated Concrete Pore Solution

Abstract

The metallurgical and electrochemical behavior of additively manufactured super duplex stainless steel (SDSS) clads on carbon steel [low-carbon steel (LCS)] substrates are investigated in a simulated concrete pore solution. The SDSS clads were manufactured using laser powder bed fusion (LPBF). Passivation and chloride-induced depassivation of the clads were studied as a function of LPBF parameters. It was shown that additively manufactured clads significantly improved the passivation characteristics and increased the chloride thresholds of the LCS substrate. The clads showed a decreasing γ-austenite phase fraction and increasing δ-ferrite phase fraction with increasing scan speeds. Increasing the δ-ferrite phase fraction resulted in faster passive film formation but lower critical chloride thresholds for the clads. The clads produced with 100-, 600-, and 1,000-mm/s laser scan speeds showed critical chloride thresholds of 4, 2.5, and 1.5 M, respectively. The as-cast SDSS alloy did not show any signs of depassivation until 5 M Cl− concentration, whereas LCS substrates depassivated at 0.75 M Cl−. The study proved the concept of additively manufactured carbon steel rebars with stainless steel clads and is a first step toward producing such rebars.