KINETICS OF ALPHA-GAMMA PHASE-TRANSITION OF FE-12CR-4NI ALLOY AGED BETWEEN 600-650 DEGREES-C

Using Mossbauer spectroscopy and X-ray diffraction as analytical tools , an ''anomalous'' alpha-gamma phase transformation observed previousl y in steels was studied It was shown in this work that this phase tran sformation is a feature of the Fe-12Cr-4Ni ternary alloy, and the agei ng-time dependence of the gamma-phase formation follows Avrami kinetic s representing a diffusion controlled process. The activation energy o f the process was also determined The equillibrium composition of the samples could be interpreted in terms of calculated phase diagrams of the Fe-Cr-Ni system. On the basis of the hyperfine-field distributions derived from the spectra it was shown that two processes take place i n the ferromagnetic alpha-phase during the ageing at diffrent rates in which the slower one is in accordance with a decrease of the chromium concentration in the alpha-phase owing to the gamma-phase formation.