Localized Corrosion Susceptibility of 434 Ferritic Stainless Steel in Acid Chloride Media

Abstract:

The pitting corrosion resilience and passivation behaviour of 434 ferritic stainless steel was studied in 1 M H₂SO₄ solution at 0% to 2% NaCl concentration by potentiostatic technique and optical illustration characterization. Data showed 434 steel underwent metastable pitting activity at the lowest metastable pitting potential and current by reason of the effect of SO₄^2- anions within the electrolyte. Addition and increase in Cl^- anion concentration decreased the potential while simultaneously increasing the current value at which metastable pitting occurs till 1% NaCl concentration. The presence of chlorides decreased the passivation range of the steel with regards to Cl^- anion concentration compared to the electrolyte without chlorides till 0.5% NaCl concentration. Beyond this concentration no further decrease in the steel’s passivation range was observed despite increase in chloride concentration. Beyond 1% NaCl concentration passivation of the steel completely collapsed signifying threshold chloride concentration for optimal steel utilization on astringent conditions. Potentiostatic data showed variation in chloride concentration from 0.25% to 1% had strong effect on the pitting resistance of 434 steel. Optical images of 434 steel morphology at 0%, 0.25% and 2% NaCl concentration in 1 M H₂SO₄ solution showed important details. At 0% and 0.25% NaCl concentration, corrosion pits were clearly visible though the dimension and depth of the pits from the electrolyte with 0.25% NaCl concentration were more defined and deeper. At 2% NaCl concentration, corrosion pits were larger and the surface morphology showed severe morphological deterioration by reason of the synergistic action of SO₄^2- and excess Cl^- anions.

• Periodical: Materials Science Forum (Volume 1059)
• Pages: 29-34
• DOI: https://doi.org/10.4028/p-36uwat
• Online since: April 2022
• Authors: Roland Tolulope Loto*
• Keywords: 434 Steel, Corrosion, H₂SO₄, HCl, Pitting

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