Effects of Cold Work and 475°C Aging on Corrosion Behavior of Duplex Stainless Steel

Abstract

The effects of cold working and 475°C aging on corrosion behavior of the active and pitting region of duplex stainless steel have been studied in sulfuric acid and chloride media. The main results obtained were summarized as follows:
In a 5% H₂SO₄ solution at boiling or 60°C, the corrosion loss and the critical current density for passivation of duplex stainless steels increased with the progress of aging and the increase in α content. The anodic current maximum in the active region was separated into two peaks with the progress of aging. This separation was observed obviously with specimens containing large amount of α, aging for long time and undergoing large degree of working, and that was attributable to the decrease in corrosion resistance of α. In case of a 5% H₂SO₄ solution containing NaCl, the separation of the anodic current maximum in the active region was not clear, however, preferential dissolution phase of specimens in active region was the same as that in the solution free from NaCl.
In 3% NaCl solution at 30 and 70°C, it was found that pitting potential had a tendency to become less noble with the progress of aging, and by preworking before aging for specimens containing large amount of α. When unworked specimens were subjected to aging, pitts produced with anodic poralization occurred in α and grew preferentially in α.