The α-σ Transformation of Iron-Chromium Alloy

Abstract

The transformation from α phase to σ phase of an iron-chromium alloy which contains nearly an equal content of both the components proceeds autocatalytically such as the tin pest. The transformation rate is very slow, and we observed the σ phase grow in the form of hexagon. The transformation rate which was measured dilatometrically is greatest near 740°. Young’s modulus of the σ phase which had been obtained when the transformation took place above 770° at room temperature was found to differ markedly from that of the σ phase which had been obtained below 730°. We assume that two kinds of σ phase exist. We observed strain lines in the σ phase which had been obtained above 770°, but not in the σ phase which had been obtained below 730°.