Oxidation pretreatment to reduce corrosion of 20%Cr-25%Ni-Nb stainless steel. II. Surface morphology and oxide characterization

Abstract

Improved corrosion behavior of 20%Cr-25%Ni-Nb steel resulting from a low pressure oxidation pretreatment in CO2 has been related to changes in elemental composition and distribution in the oxide scale. Auger electron spectroscopy, secondary ion mass spectroscopy, electron microprobe, and X-ray diffraction techniques have been used to investigate the properties of the oxide scale formed on both untreated and pretreated specimens when oxidized at 823 K and 923 K in a CO₂-1%CO atmosphere. A sputter ion plating technique has been used to separate the oxide from the metal and the incorporation of chromium and silicon at the metal-oxide interface has been investigated at grain centers and grain boundaries by depth profiling. The improvement in oxide adhesion and oxidation rates, using data from Parts I and II of this study, is assessed in terms of oxide formation by solid-state displacement reactions.