Papers by Keyword: Austenite Ferrite Phase Transformation

Abstract: Austenite/ferrite phase transformations in Fe-xCu-10Ni alloys, 0<x<15 (mass%), are studied under two different cooling conditions, ice-brined quenching or slow cooling in the dilatometer. The influence of copper addition and cooling rate on the microstructure of the alloys is studied. Metallographic examinations of quenched samples show that metastable transformations occur during cooling. As for Fe-Ni alloys, it is impossible to stabilize the high temperature phase (γ_FeNi) in the Fe-Ni-Cu alloys. Dilatometry measurements of the γ → α transformation temperature with a cooling rate of 2°C/min also indicate a metastable phase formation despite the low cooling rate. For all alloys, a mixture of massive and lath ferrite is observed, one being predominant depending on the cooling conditions and composition. It is shown that the cooling rate has nearly no influence on the microstructure of alloys with a small amount of Cu unlike the alloys containing more Cu. In all alloys containing Cu, nanometric γ_Cu precipitates, much finer in the quenched samples, are detected in the ferrite grains.

Abstract: Dilatometer is often used for in situ measurement of phase transformation by monitoring the length change during heating or cooling cycle. However, the inevitable temperature gradient across the specimen length during inductive heating, introduces uncertainty in temperature measurements and hence the associated phase transformation kinetics. Due to this uncertainty, it is more meaningful to interpret the transformation kinetics from dilatometry in terms transformation ranges instead of unique values of fraction transformed. In the present work, a probabilistic approach has been used to predict the fraction transformed ranges, arising due to the temperature gradient during dilatometry. The approach has been validated for Fe-5.93 at.% Ni undergoing austenite to ferrite phase transformation at various constant cooling rates.