High-temperature oxidation of pure Fe and the ferritic steel 2.25Cr1Mo

Abstract

The global pressure for recycling and ecological energy production increases steadily in combination with the demand of cost-effective application of materials. However, some severe corrosion problems, associated with the high internal/intergranular corrosion rates in boiler components need to be avoid. Some commercial boiler materials contain a Cr content of 0.55 (wt. (%)) - 2.25 (wt. (%)). This Cr concentration in the alloys is not sufficient for the formation of a complete dense Cr2O3 scale. Hence, high oxidation kinetics may result. In this study, pure Fe and the steel 2.25Cr1Mo were oxidized in laboratory air at 550 °C using a thermobalance system. The surface as well as the cross section of oxidized specimens were analysed using scanning electron microscopy in order to quantify several factors (e.g. surface finishing, cold working and grain size) on the overall oxidation kinetics. For alloys with low Cr content, a decreasing in the grain size leads to an acceleration of the oxidation rate by facilitating the oxygen diffusion along alloy grain boundaries leading to an inward oxide layer formation. The study of effects of surface finish and cold working yielded results revealing that the oxidation process is complex and comparison of results from different laboratories is difficult and should be done.

Keywords

• low-alloy steels
• effect of cold work
• effect of grain size
• high-temperature oxidation