Mechanisms of intergranular corrosion and self-healing in high temperature aged lean duplex stainless steel 2404

This study investigated the intergranular corrosion mechanism of lean duplex stainless steel 2404 after long-term aging at 700 and 800 °C using electrochemical methods, thermodynamic calculations, and kinetic models. At 700 °C, σ phase growth significantly increases the degree of sensitization (DOS) and decreases the breakdown potential (E_b). At 800 °C, a self-healing process at the ferrite/σ interface helps recover Cr and Mo depleted regions, reducing DOS after 72 h of aging and stabilizing E_b after 24 h at higher electrode potentials. However, the corrosion process is intensified at the σ/austenite interface, compromising intergranular corrosion resistance during prolonged aging. The findings show that complete recovery of corrosion resistance via self-healing is not achieved when high fractions of σ phase are formed. In addition, DICTRA calculations effectively evaluate corrosion resistance degradation from σ phase growth, providing deeper insights into the intergranular corrosion mechanism.