The influence of alloying elements on the corrosion behaviour of ferritic steels in simulated combustion atmospheres

摘要

The low-chromium steels (Cr content 0.7-1.4 wt.%) are usually being used in low temperature boiler applications where the environments are not so aggressive as in waste-fire boilers. To improve their mechanical properties and corrosion resistance several alloying elements have been used. In the present study the new low-chromium steels modified with Si, Ni and Ce have been investigated. These steels were compared with the common boiler steel -2.25Cr1M. The multi-sample exposure tests were made in moist air (8% O{sub}2+ 15% H{sub}2O) with and without 200 ppm SO{sub}2 or 2000 ppm HCl addition at the isothermal temperature of 500 ℃. Corrosion products were analysed by Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM/EDS) and XRD techniques. The results of the study show that addition of Ni and Si to the steels studied could improve their corrosion resistance, but only in moist air atmospheres. In SO{sub}2-containing atmospheres the corrosion resistance seems to remain the same, when in HCl-containing atmospheres Ni and Si additions seem to have a negative effect on the corrosion behaviour. As could by seen from SEM analysis, the scales formed, on the steels with above elements, are more adherent to the metallic core. The cerium was added to the studied materials mainly to improve their mechanical properties. This alloying element seems to increase the corrosion rate of materials, especially in atmospheres containing Cl.