Effects of Chromium and Silicon on Carbon Deposition on Iron in CH₄-H₂ Mixture at 1273 K

Abstract

The carbon deposition on iron, Fe-Cr, Fe-Si and Fe-Cr-Si alloys has been studied by means of metallography and thermogravimetry, in order to elucidate the effects of chromium and silicon on the carbon deposttion behavior on iron and to get a better understanding on the mechanism of the carbon deposition.
Chromium retards the carbon deposition by forming the carbide, (Fe,Cr)₃C, more stable than Fe₃C, whereas silicon accelerates the deposition of filamentous carbon, and in particular on an Fe-3.0 mass%Si alloy only deposition of filamentous carbon is observed. This behavior on the Fe-Si alloys is probably ascribed to the effect of silicon on the stability of Fe₃C and the diffusion rate of carbon atoms.
The carbon deposition behavior on Fe-Cr-Si alloys containing 0.8-1.5 mass%Cr changes according to the proportion of chromium to silicon; at Cr%≥Si% only filmy carbon deposits, while at Cr%<Si% only filamentous carbon does. Silicon in high chromium alloys containing ca. 12 mass%Cr has an effect to refine and disperse carbides, and further addition of silicon may result in the deposition of filamentous carbon.
The deposition behavior of filamentous carbon on all these alloys can be explained by the mechanism of formation and decomposition of Fe₃C.