Character of transformations in Fe–Co system

The phase transformations of Fe–(35–65%)Co alloys and `Permendurʹ (48.4%Fe–49.8%Co–1.8wt.%V) have been studied. It was found that the B2 phase is formed solely during heat treatment in air atmosphere and in a thin surface layer, but not in the bulk and not in vacuum. At high temperatures, the Fe–Co alloys separate into the pure components, but also only in a thin surface layer. A `550°C anomalyʹ arises as a result of changes of magnetic configuration in the alloys. The causes and consequences of these transformations in Fe–Co alloys are analysed.