Effect of High Temperature on the Corrosion Behavior and Passive Film Composition of 316L Stainless Steel in Concentrated NaOH Solution

Abstract Corrosion resistance to high temperature concentrated alkali solutions (>20 wt.%) is very important for 316L austenitic stainless steel (316L SS). Herein, the effect of high temperature (130℃) on the corrosion behavior and passive film composition of 316L SS in 50 wt.% NaOH solution was investigated by electrochemical methods, XPS, and AES. The results indicated that the corrosion resistance of passive films was significantly affected by temperature. When the temperature was increased from 40°C to 130°C, the passive current density increased by two orders of magnitude, and the number of film defects were also significantly increased. AES results showed that as the temperature increased from 40°C to 130°C, the passive film shifted from selective dissolution of Fe to dissolution of both Fe and Cr. The composition of the passive film shifted from being Cr-rich to Ni-rich. The outer layer of passive film on 316L SS was mainly composed of Cr2O3, Cr(OH)3, FeCr2O4, NiO, Fe3O4, FeO, Fe2O3, and FeOOH at 40℃, and was converted to Fe3O4, FeO, Fe2O3, FeOOH, Ni(OH)2, and NiFe2O4 at 130℃. Additionally, Ni oxides and hydroxides exhibited excellent stability in the high-temperature concentrated NaOH solution.