Corrosion of Fe–9Cr–(Mn, Si) alloys in CO2–H2O–SO2 gases. (September 2015) - Yu, Chun
Highlights: SO2 suppresses carburisation of all investigated alloys in CO2 –H2 O gas. SO2 improves the corrosion resistance of Fe9Cr by partially forming Cr2 O3 scale. SO2 improves SiO2 layer formation on Fe9Cr0.5Si with higher corrosion resistance. Predominance phase diagrams are used to discuss oxides and sulphides formation. Abstract: Model alloys, Fe–9Cr, Fe–9Cr–2Mn and Fe–9Cr–0.5Si (wt%) were exposed to Ar–20%CO2 –20%H2 O–(0, 0.1, 0.5 and 1.0%)SO2 gases at 650 °C. In the absence of SO2, all alloys grew thick iron-rich oxide scales. Adding SO2 led to partial passivation by chromia formation on Fe–9Cr and Fe–9Cr–0.5Si, but not the Fe–9Cr–2Mn. Alloy carburisation was extensive in sulphur-free gas, but substantially suppressed by SO2 . Internal sulphidation and oxidation were also observed. A silica layer formed beneath the chromia scale on Fe–9Cr–0.5Si in SO2 -bearing gas, but not in sulphur-free gas. Reaction morphologies are discussed in terms of oxide grain boundary diffusion, as affected by sulphur uptake.