A single phase metastable austenite was obtained in compositions of Fe-3-7Al-2wt.%C and Fe-7Al-1.8C by the rapid solidification technique. The lattice parameter of the austenite increased almost linearly with increasing Al content. As Mn was added to Fe-7Al-1.8C, the samples became ductile and at the same time, the lattice parameter increased.
With a control of ejection pressure, thick samples (70-80 m thick) showing coherent-κ carbide, were obtained. When the retained austenite was annealed isothermally at 500℃, 600℃ and 700℃, it decomposed into ferrite and κ-carbide or $Fe_3C$. This decomposition was observed to start at grain boundaries by scanning electron microscope. This sample still remained in the metastable austenite after quenching in liquid nitrogen. As the Al content increased, the microhardness increased almost linearly. The lattice parameter and identification of phase were studied by X-ray diffraction.
