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

Abstract

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 highpurity 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 c fi e fi a¢ steps. As a remarkable result, it was shown that a low SFE, if necessary to ephase nucleation, is not a sufficient condition for nucleation of a¢ phase. In fact, the formation of stable a¢ nuclei from a¢ 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.

Microstructural investigation on deformation behavior of high purity Fe–Cr–Ni austenitic alloys during tensile testing at different temperatures

“…7a, the yield strength of the 20/12 and 16/12 alloys is not affected considerably by decrease in the deformation temperature, being consistent with the previous studies [12,13,16,30]. The increase in the yield strength of the 20/10 alloy is related to the formation of spontaneous α 0 -martensite at low temperatures [7]. In contrast, tensile strength and elongation of the alloys are highly dependent on the deformation temperature.…”

“…It has been shown that the deformation-induced martensitic transformations in the Fe-Cr-Ni austenitic alloys occur most probably through the γ-ε-α 0 steps [7].…”

“…In a recent study on spontaneous martensitic transformation in high purity Fe-Cr-Ni alloys [7], it was shown that a low SFE, if necessary to ε phase nucleation, is not a sufficient condition for nucleation of α 0 phase. In fact, the formation of stable α 0 nuclei from α 0 embryos occurs if the required chemical driving force is provided.…”

A microstructural investigation on deformation mechanisms of Fe–18Cr–12Mn–0.05C metastable austenitic steels containing different amounts of nitrogen

“…6b, the volume fraction of e-and a 0 -martensite phases are both increased with increasing tensile strain, however, the formation of e-martensite is predominant in this steel. This is in contrary to many previous studies in Cr-Ni austenitic steels in which the content of a 0 -martensite phase is increased in the expense of the e-martensite during deformation [49]. Therefore, the deformation path of c ?…”

Neutron Diffraction and Diffraction Contrast Imaging for Mapping the TRIP Effect under Load Path Change

“…The preferred deformation mechanisms in austenitic stainless steels strongly depend on the stacking fault energy (SFE) [1][2][3]. When the SFE is sufficiently low, the transformation induced plasticity (TRIP) effect occurs upon deformation [4].…”