The dissolution kinetics of FeC in ferrite.

The rate of dissolution of spheroidized FeC in ferrite in both high purity and commercial purity plain carbon eutectoid steels has been investigated. The experiments consisted of equilibrating wire specimens of spheroidized eutectoid steels at 650°C or 700°C and then jumping the temperature (in 2 to 7 m-sec) 4 to 32 C deg above the equilibration temperature. After heating, the specimens were maintained constant at the new temperature, and the dissolution of FeC was followed by observing the changes in electrical resistivity. The data are correlated to changes in the average carbon concentration in ferrite and are compared to the predictions of a generalized phenomenological model. Two important facts have been determined. First, the FeC ferrite interfaces are not in a state of local equilibrium during dissolution; the deviations from equilibrium in all cases were large. Second, the kinetics of dissolution are first order and the log of the reaction rate constants are a linear function of (1/ T), where T is the absolute temperature. These results lead to the conclusion that under the present experimental conditions, the dissolution of FeC in ferrite is controlled entirely by an interfacial reaction. A rather detailed description of the experimental procedure is included in this paper because the technique is new, and it is broadly applicable in the study of many metallurgical phenomena. [ABSTRACT FROM AUTHOR]