Interface Controlled Materials (RUEHLE:INTERFACE CONT.MAT O-BK) || Growth Kinetics of Iron Carbide Layers during Gas Carburization

✍ Scribed by Rühle, M.; Gleiter, H.

• Publisher: Wiley-VCH Verlag GmbH & Co. KGaA
• Year: 2005
• Weight: 227 KB
• Category: Article
• ISBN: 352760622X
• DOI: 10.1002/352760622x.ch5

✦ Synopsis

The growth kinetics of carbide layers on iron surfaces has been studied by gas carburization in CO-H 2 -H 2 O-H 2 S gas mixtures at 500°C. Small additions of H 2 S have been added to the atmosphere to prevent graphite formation and carbide decomposition (metal dusting). The carburization was performed with CO-H 2 -H 2 O-H 2 S mixtures at carbon activities in the range 12 < a C < 4600. At a C ≤ 100 only cementite (Fe 3 C) is formed, at higher carbon activities an outer layer of Hägg carbide (Fe 5 C 2 ) grows on the inner layer of cementite.

Parabolic rate constants have been determined for the growth of cementite and of Hägg carbide. From the dependence of the rate constant on carbon activity the self diffusion coefficient D C * for carbon in both carbides has been derived.