Thermal reactive deposition coating of chromium carbide on die steel in a fluidized bed furnace

The application of thermal reactive deposition (TRD) and diffusion technique to form a carbide layer for enhancing the tool life is of increasing importance in surface modification of steel. This study focused on investigating the influences of the amount of addition on the formation rate of the chromium carbide layers by three different alloy powders, namely, pure chromium, 71Cr-29Fe-0.03C, and 66Cr-26Fe-7.7C containing carbide-forming elements. Three kinds of tool steel (AISI M2, H13 and modified D2) were treated between the temperature of 950-1050 degrees C in a fluidized bed furnace where a special feeder was designed and used for continuous feeding of the activator. The carbide layers were evaluated based on microstructure, thickness, hardness, X-ray diffraction and chemical composition distribution analysis. The results indicated that the formation of carbide layers was not only influenced by the purity of chromium powder but also by the amount of the carbon dissolved in the matrix of the steels at the TRD processing temperature, rather than the nominal carbon content of the steels. (C) 1998 Elsevier Science S.A.