MOSSBAUER STUDY OF THE KINETIC-BEHAVIOR OF ANOMALOUS AUSTENITE FORMATION IN FE-12CR-4NI STEEL

Mossbauer spectroscopy was used in order to get information about the anomalous austenite formation1 taking place between 450-600 degrees-C in steel containing 12%Cr and 4%Ni. Even below the equilibrium transition temperature (640-degrees-C) of alpha-->gamma transformation a monotonic increase of the relative spectral area of the line belonging to austenite was observed in the Mossbauer spectra of the steel isothermally aged at 550-degrees-C with increasing ageing time. At the same time, the Cr content of the ferrite phase decreases. Time dependence of the quantity of austenite formed during the isothermal ageing follows the Avrami-kinetics with an exponent n=0.3.