Influence of Heat Treatment Temperature on Crevice and Pitting Corrosion of UNS S32205 Duplex Stainless Steel

Abstract

Duplex stainless steels (DSSs) have outstanding mechanical properties and corrosion resistance. However, operating conditions and/or inadequate heat treatments can induce precipitation of deleterious phases or change the proportion of ferrite (α) and austenite (γ) phases. This study evaluates the impact of ageing at 850 and 950 °C and solubilization at 1000 and 1150 °C treatments on pitting and crevice corrosion of DSS UNS S32205. Cyclic polarization tests revealed that samples with a more balanced α/γ ratio (≈50/50), that is, the base material (BM) and that solubilized at 1000 °C, exhibited the lowest corrosion rate (0.044–0.074 μm/year) and better repassivation capacity (E_R ≈ 0.96 V). Conversely, the 1150 °C treatment led to reduced corrosion resistance (0.158 ± 0.009 μm/year) and is associated with a reduction in the %Cr in α. Pitting is present in the aged conditions only. Moreover, the BM and 1000 °C samples showed the lowest crevice corrosion susceptibility, presenting the lowest volume loss (1 × 10⁶ μm³ cm⁻²) and current densities (≈1000 μA cm⁻²), followed by samples treated at 1150, 950, and 850 °C. Therefore, the results show that ageing treatments make UNS S32205 susceptible to pitting and crevice corrosion, which is related to the deleterious phase fraction and the α/γ ratio imbalance.