Relationships Between Corrosion Behavior of AISI 304 Stainless Steel in High-Temperature Pure Water and Its Oxide Film Structures

Abstract

Abstract Effects of dissolved oxygen (DO) concentration on corrosion rates of AISI 304 stainless steel (SS) in high-temperature pure water were examined at temperatures between 200 and 320 C using impedance analysis techniques. A significant reduction in the corrosion rate >260 C and independence of the corrosion rate on the DO concentration at 320 C were observed as unique phenomena. To understand them, the oxide film structures were examined by scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS), and electrical capacity measurements. The oxide films could be divided into outer and inner layers. The outer layer consists of two sublayers, a porous precipitation sublayer and a cracked inner sublayer which is hypothesized to be formed by the breakdown of the inner layer. The outer layer was characterized by a decrease of Cr content towards the outer surface of the oxide film. The inner layer was defined as a residual oxide in which no decrease of Cr content occurred. The inner oxide f...