Understanding Corrosion Morphology of Duplex Stainless Steel Wire in Chloride Electrolyte

Abstract

The corrosion morphology in grade 2205 duplex stainless steel wire was studied to understand the nature of pitting and the causes of the ferrite phase’s selective corrosion in acidic (pH 3) NaCl solutions at 60 °C. It is shown that the corrosion mechanism is always pitting, which either manifests lacy cover perforation or densely arrayed selective cavities developing selectively on the ferrite phase. Pits with a lacy metal cover form in concentrated chloride solutions, whereas the ferrite phase’s selective corrosion develops in diluted electrolytes, showing dependency on the chloride-ion concentration. The pit perforation is probabilistic and occurs on both austenite and ferrite grains. The lacy metal covers collapse in concentrated solutions but remain intact in diluted electrolytes. The collapse of the lacy metal cover happens due to hydrogen embrittlement. Pit evolution is deterministic and occurs selectively in the ferrite phase in light chloride solutions.

Understanding the Passive Behaviour of Low-Chromium High-Strength Hybrid Steel in Corrosive Environments

“…Micro-galvanic corrosion occurs when the corroding region is active while the remaining part is passive, driven by the oxidation power strength of the electrolyte (and polarization). Such a phenomenon is typical, for example, for duplex stainless steel 24 . In earlier work, it has been shown that the pitting corrosion of duplex stainless steel in diluted chloride solution is pitting, which selectively occurs in the ferrite phase 24,25 .…”

“…Such a phenomenon is typical, for example, for duplex stainless steel 24 . In earlier work, it has been shown that the pitting corrosion of duplex stainless steel in diluted chloride solution is pitting, which selectively occurs in the ferrite phase 24,25 . The corrosion concentrates more on the entire ferrite phase when the chloride concentration is increased due to more pit nuclei forming next to each other in the ferrite phase.…”

Duplex Steels Used in Building Structures and Their Resistance to Chloride Corrosion

“…The intensity of pitting corrosion increases with the temperature of the electrolyte. Mixing the solution equalizes the depolarizers' concentration at the metal surface, thereby slowing the progress of corrosion [41]. A permanent polarization of the cell, i.e., blocking the anode or cathode reaction, may stop the progress of pitting corrosion.…”

Stress Corrosion Cracking Mechanisms of UNS S32205 Duplex Stainless Steel in Carbonated Solution Induced by Chlorides

“…For this reason, the corrosion and SCC behavior of DSS have been widely studied in the literature. In the case of chloride electrolyte, the preferential phase to dissolve is the α-phase until a threshold chloride concentration is reached (0.1 M NaCl at pH 3 and 60 • C), promoting lacy cover pitting instead in both phases [7,8]. Another focus of previous studies was on the property mismatch between phases such as the mechanical phase, where the α-phase cannot develop as high tensile stresses as the γ-phase [9], and the electrochemical phase, where the α-phase has lower corrosion potential (E corr ) (higher corrosion susceptibility) [10], also leading to galvanic microcouples [11].…”