Effect of the temperature on the passivity of the modified martensitic stainless steels

Abstract

The limits and nature of the passive behavior exhibited by modified martensitic stainless steels (MMSS) is studied in brine solutions at different temperatures using electrochemical methods and the point defect model (PDM), in an environment at pH is 3 and temperatures up to 150°C, using autoclaves with CO2 gas up to 2.8 MPa. The results show that passivity on the MMSS is characterized by the metal cation vacancy diffusivity (D) which indicates that the passivity up to temperatures of 75°C is more stable than at higher temperatures up to 150°C. The value of D is used to describe the transition between the passive layers at the threshold temperature of 75°C; at which exhibits the largest stability. MMSS specimens passivated at 75°C exhibit higher passivity stability in experiments performed at 25°C, when compared the pre passivation, suggesting that the change experienced at 75°C is at least partially irreversible.