Dilatometric Study of Phase Transformation and Thermal Expansion in T91 Steel

A comprehensive characterization of the kinetic aspects of diffusional α'-martensite-> α - ferrite+carbides -> γ vaustenite phase transformation that occurs during heating and that of γ ->α '-martensite displacive phase transformation, which occurs upon continuous cooling has been performed using high resolution dilatometry, under varying thermal history. The results of dilatometry are analysed in terms of an appropriate thermo-kinetic framework to obtain useful information about transformation temperatures, their dependence on thermal history, and apparent activation energies involved in effecting phase changes. In addition, the results of temperature variation of dilatational strain (ΔI_T/l₀) measured under slow heating scans, are used to obtain reliable estimates of thermal expansion in the temperature range, 300-1000°C.