Date of Award
Doctor of Philosophy (PhD)
Professor J.S. Kirkaldy
A thermodynamically self consistent phase diagram together with T₀ line for iron-rich Fe-Mn system has been evaluated using the experimental tie-line information from this study and other sources and thermodynamic data from the literature.
The competing morphologies resulting from the decomposition of Fe-Mn austenite due to variation in composition and cooling rate are equiaxed, ragged ferrite and lath morphology. The former two may result via a massive mode, whereas the last one may be due to a martensitic reaction. The massive mode of decomposition has been observed in the two phase field of this system.
The solute drag theory for massive transformation due to Hillert and Sundman has been further developed for the low velocity branch. Our theory predicts a C-shaped TTT curve and an optimum in the rate of entropy production with respect to a structure parameter related to defect density.
Isothermal transformation tests have yielded a C-shaped TTT curve for Fe-3.1%Mn alloy. The transformation behaviour has been explained as controlled by trace interstitial impurities (C and N) diffusion above the nose and by the massive mode at lower temperatures.
Srivastava, Kamalesh Kumar, "Thermodynamics and Kinetics of Austenite Decomposition in the Iron-rich Iron-Manganese System" (1980). Open Access Dissertations and Theses. Paper 587.