| Abstract: | Corrosion performance of duplex steels in caustic solutions The corrosion performance of stainless ferritic-austenitic steels (DIN 1.4362, DIN 1.4462, Uranus 50 and Ferralium 255) was investigated in boiling sodium hydroxide solutions. It was found that these steels are corrosion resistant in NaOH solutions up to 30 mass-% with corrosion rates lower than 0.01 mm/a. The mass loss rate increases with increasing NaOH concentration, reaching a maximum in 60 mass-% NaOH solution. Small flow rates (e.g. 0.08 m/s; rotating disc) increase the corrosion rate by a factor of 6 with respect to stagnant conditions. However, further increase of flow rate yields no additional enhancement of the corrosion rate up to 1 m/s. Under conditions of free corrosion no stress corrosion cracking was observed at constant deflected samples or at tensile probes tested to failure under CERT-conditions in boiling 20–70% NaOH solutions. The corrosion attack is uniform in NaOH solutions up to 30 mass-%. In more concentrated NaOH solutions the dissolution rate of the austenitic phase is slightly higher than the ferritic phase. The corrosion products contain more nickel than the base material. |
