Oxidation of stainless steel under dry and aqueous conditions: Oxidation behaviour and composition

Abstract

The oxidation of austenitic stainless steel (316Ti) under dry oxidation and under pressurized aqueous conditions, both at ∼300°C, was studied by applying XPS, depth profiling and x-ray diffraction. After dry oxidation a relatively smooth surface was found, depleted of chromium, nickel and molybdenum and leaving behind nearly exclusively iron oxides. In the oxide layer chromium oxides were detected, followed by metallic nickel and molybdenum. The growth of the whole oxide layer follows a logarithmic growth law. Under aqueous conditions a rougher surface was found, with oxide layers being a factor of ≥10 thicker than under dry oxidation conditions. A greater variety of the oxides were found, e.g. chromium and nickel oxides and hydroxides are present in considerable amounts already at the sample surfaces. Again, molybdenum is first detected in the oxide layer. During the first 60 days of steel oxidation in pressurized water, the oxide layer formation follows a parabolic growth law.