Role of Chemical Driving Force in Martensitic Transformations of High-Purity Fe-Cr-Ni Alloys

The main objective of the present work is to point out the respective roles of chemical driving force and stacking fault energy (SFE) in the occurrence of martensitic transformations in high-purity Fe-Cr-Ni alloys. For this purpose, the transmission electron microscope (TEM), X-ray diffractometer, thermal differential microanalyzer (TDA), and tension test were employed to report M _s temperatures, austenite stacking fault energies, and driving forces for the concerned alloys. It was observed that the martensitic transformations in the studied alloys occur through the γ → ε → α′ steps. As a remarkable result, it was shown that a low SFE, if necessary to ε-phase nucleation, is not a sufficient condition for nucleation of α′ phase. In fact, the formation of stable α′ nuclei from α′ embryos occur if the required chemical driving force is provided. Also, an equation was proposed for the kinetics of spontaneous martensitic transformation as a function of driving force.