Abstract
A supplementary examination of the quenched structure of an Fe-9.70 wt%Al-1.46 wt%C alloy has been carried out by means of transmission electron microscopy and diffraction, in order to clarify whether the retained austenite is ordered in the Cu3Au type, as reported in the previous paper (Trans. JIM, 12 (1971), 386), or it is composed of the κ carbide and the disordered γ austenite, as suggested by Oshima and Wayman (Met. Trans., 3 (1972), 2163). It is again verified that the retained austenite is basically ordered in the Cu3Au type, and a peculiar shape, which has markedly been observed in fundamental spots from the retained austenite, is shown to be due to an accompaniment of diffuse satellites with the austenite reflection spots. The appearance of satellites suggests the existence of such a modulation as that carbon atoms are concentrated in distorted regions near the second type antiphase domain boundaries. Some of the concentrated regions with carbon atoms possibly form the perovskite-type κ carbide, as suggested, since superlattice reflections from the retained austenite exhibit two kinds of intensities. The c⁄a ratio of the tetragonal martensite in this alloy is determined to be 1.14 from a definite twinned diffraction pattern.
