The carbon content in the edge zone of cementite-containing iron materials is reduced when heat treated in oxidizing atmospheres.
In this process, the carbon-content of cementite in the edge zone of the work piece is oxidized to form carbon monoxide. Since the carbon in the center of the work piece diffuses to the decarburized edge zone due to concentration equalization, marginal decarburization slowly proceeds to deeper cross-sections. Marginal decarburization can be avoided by heat treatment in neutral atmospheres or by packing the material to be annealed in cast ironchips.
The solidification of cast iron materials may result in the burning of carbon and thus to graphite-free solidification caused by the intensive oxidation of the edge zones of the casting due to excessive mold material humidity. A steel-like layer without incorporated graphite is formed.