Corrosion behavior of a 2304 lean duplex stainless steel cold-rolled and short-term annealed at different temperatures

ABSTRACT

This study examined the effects of cold working and subsequent annealing treatment for a short time on the corrosion behavior of a lean duplex stainless steel (LDSS). The as-received sample was solution treated at 1100 °C for 1800 s and cold rolled. The cold deformation (75%) was followed by isochronic annealing at 900, 950, 1000, 1050 and 1100 °C for 180 s. The microstructural changes were evaluated by scanning electron microscopy (SEM) and Vickers hardness, while corrosion behavior was investigated by cyclic potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution at 22 ± 2 °C. After cyclic polarization, pits morphology was characterized by SEM. Cold rolling lowered lamellar spacing between the phases and increased hardness. Hardness at temperatures higher than 950 °C was equal to the 2304 LDSS solution treated. Although grain refinement is observed due to recrystallization, the corrosion resistance was not significantly improved. The highest pitting potential and charge transfer resistance were obtained after annealing at 1000 °C for 180 s. The pit distribution indicates that the corrosion behavior of the phases changed during the cold rolling and annealing treatment, and pitting was initiated preferentially in the α/γ boundaries and inside the α domains.

Keywords
lean duplex stainless steel; pitting corrosion; short-term annealing