Thermodynamic modeling of chemical conversions in the surface layer of tools in hot pressing

Depending on the phase and chemical composition of the surface layer of the tool, chemical and phase conversions take place when in contact with the hot blank and the lubricant which to a large degree determine the durability of the die and the mold. The thermodynamic analysis of the interaction of the carbides with the iron oxide Fe/sub 2/O/sub 3/ and the lubricant showed that the chemical and phase transformations were based mainly on two processes: a) the reduction of the iron oxide by carbon with the formation of cementite; b) the interaction of the carbon with the carbides of the coating in the reducing atmosphere of the thermal decomposition products of the lubricant. The performed thermodynamic calculations have shown that the following investigated carbides possess the highest thermodynamic stability under the given operating conditions: TiC, V/sub 4/C/sub 3/, Cr/sub 3/C/sub 2/, MnC/sub 2/, Fe/sub 3/C, NbC, Mo/sub 2/C, and WC.