Phase Equilibria of the Fe-Si-Cr-Al Quaternary System at 800 °C

The isothermal sections of the Fe-Si-Cr-Al quaternary system at 800 °C with the Fe composition being fixed at 67 at.% and 50 at.% were determined experimentally using optical microscopy, scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, and x-ray diffractometry. Two three-phase regions (BCC-A2 + σ + D03, FeSi + Fe5Si3 + D03) were found in the isothermal sections at 67 at.% Fe. Phase microstructures of Fe-corner in the quaternary Fe-Si-Cr-Al system were investigated, especially the multiphase regions containing bcc disordered phase and bcc ordered phases. D03 occupies almost half of the isothermal section and could maintain equilibrium with all phases (BCC-A2, σ, Fe5Si3, FeSi) in the isothermal section. One four-phase region (BCC-A2 + σ + Cr3Si + D03) and five three-phase regions (Cr3Si + D03 + BCC-A2, Cr3Si + σ + BCC-A2, Cr3Si + D03 + σ, Cr3Si + Fe5Si3 + D03, FeSi + Fe5Si3 + D03) were found in the isothermal section at 50 at.% Fe.