Effect of oxide scale on carbon deposition on Fe-Ni alloys in carburizing gas
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INTRODUCTION
IN the processes using the pyrolysis reaction of CO or hydrocarbons, carbon deposition often occurs and causes operating problems. For example, sooting occurs during gas carburization of steels, m carbon deposits on the surface of cold-rolled steel sheet during annealing in nonoxidizing or carburizing atmosphere, (21 coking in pyrolysis furnaces where ethylene is produced by thermal cracking of hydrocarbons, and carbon attack of their components. [3~ The behavior of carbon deposition depends upon the material factors, such as alloying elements and surface conditions, as well as on environmental factors, such as flow rates and gas compositions. If the effects of these factors on the behavior of carbon deposition are elucidated, it is expected to prevent or retard the degradation caused by carbon deposition. We have systematically studied the effects of the above factors on carbon deposition. In previous articles, we reported the effects of alloying elements (chromium, t4'5] silicon, t4] nickel, [5] aluminum, [6'7] and titanium [8]) on carbon deposition on iron in a CO-H2 or CH4-H2 gas mixture for a better understanding of the behavior of carbon deposition on high-temperature steels in carbonaceous atmospheres and found the following facts. (1) Chromium and titanium retard carbon deposition by formation of protective carbides; (2) nickel reduces catalytic activity; (3) silicon and aluminum promote filamentous carbon deposition because of the acceleration of decomposition of Fe3C formed on the surface; and
S. ANDO, Assistant Professor, and H. KIMURA, Emeritus Professor, are with the Department of Metallurgical Engineering, College of Engineering, University of Osaka Prefecture, Mozu-Umemachi, Sakai, Osaka 591, Japan. Manuscript submitted January 22, 1990. METALLURGICAL TRANSACTIONS A
(4) aluminum (_--__2.7 mass pct AI) and titanium (_->0.67 mass pct Ti) retard carbon deposition by formation of A1203 and TiO2, respectively. From these results, the formation of stable noncatalytic compounds, such as carbides and oxides, on steels can be considered as one of the methods for retarding or preventing carbon deposition. Nickel is a primary alloying element in heat-resisting steels and is indispensable for the improvements of the mechanical properties of steels at elevated temperatures, t9] There are many reports on the oxidation behavior and the mechanism of oxidation o f Fe-Ni alloys in various oxidizing atmospheres, t~~ However, the influence of oxide scale on carbon deposition on the alloys in carburizing atmospheres has not yet been studied. Although we have already reported the behavior of carbon deposition on as-polished Fe-Ni alloys, tS] it is of considerable fundamental and technological importance to clarify the effect of oxide scale on carbon deposition on the alloys. The aim of the present work is to investigate the behavior of carbon deposition on preoxidized Fe-Ni alloys containing 0 to 57.0 mass pct Ni in 10 pct CH4-H2 mixture at 1203 K which is a usual carburizing temperature to elucidate t
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