C-C INTERACTION IN IRON-BASE AUSTENITE AND INTERPRETATION OF MOSSBAUER-SPECTRA

Interaction between the carbon atoms in FeC austenite was studied usin g the experimental data; of Mossbauer spectroscopy giving the abundanc es of the iron sites with different carbon neighbourhoods and Monte Ca rlo computer simulation with CC pair interaction parameters which coul d result in carbon distribution satisfying the experimental data. The values of the carbon activity in FeC austenite were also derived from CC interaction parameters and compared with the experimental data avai lable, which, in turn, allowed one to test the existing interpretation s of the Mossbauer spectra of FeC austenite. It was shown that the con centration dependence of the carbon activity at different temperatures can be successfully described only by taking into account CC interact ions in several coordination spheres: a weak repulsion in the first co ordination sphere and a stronger one in the second sphere. This corres ponds to the interpretation of Mossbauer spectra as consisting of the component of ''pure'' iron atoms, Fe-0, iron atoms with one carbon ato m as a nearest neighbour, Fe-1, and iron atoms with paired carbon atom s in the neighbouring interstitial sites, Fe-2-90'. It is shown that s uperstructures like Fe4C1-x and Fe8C1-x proposed in some Mossbauer stu dies of FeC austenite could exist only at those combinations of C-C in teraction parameters in the first, second and third coordination spher es which are not consistent with the values of the carbon activity. Co pyright (C) 1996 Acta Metallurgica Inc.