1989 Volume 53 Issue 1 Pages 63-70
The behavior or carbon deposition on Fe-Al alloys containing 0-5.7 mass%Al was studied by metallography and thermogravimetry to elucidate the effect of aluminum in iron on carbon deposition on the surface in carburizing gas. Like silicon, aluminum accelerates the deposition of filamentous carbon by promoting the decomposition of Fe3C. In a 20%CO-H2 mixture at 923 K, filamentous carbon deposited with laminar carbon from the early stage of the reaction since the induction period for the filamentous carbon to begin to deposit was shortened by aluminum. This may also cause the retardation of laminar carbon deposition. Therefore, the rate of carbon deposition of the alloys containing 0.8-2.0 mass%Al became smaller than that of iron. In a 10%CH4-H2 mixture at 1273 K, this phenomenon was not observed because of the deposition of filmy carbon instead of laminar carbon. However, carbon deposition on the alloys containing more than 2.7 mass%Al was depressed because Al2O3 formed on the surface. Al2O3 may have formed by the reaction with small amounts of oxidizing gas contained in the atmosphere as an impurity gas. The behavior of Al2O3 formation under the present conditions was discussed thermodynamically and kinetically.
