Mechanism of Sigma-Phase Formation in the Fe-V System

The phase transformations in the Fe-rich part of the Fe-V system were studied by x-ray diffraction and electron microscopy. The results demonstrate that the σ phase exists in the range 650–1219°C and is formed directly from a solid solution of V in α-Fe, with no B2 ordering. Below 650°C, the solid solution phase-separates, and strongly Fe-enriched grains are formed. The Fe-V phase diagram inferred from these results is presented.