The resulting microstructure, phase decomposition and mechanical property changes occurring during the heat treatment of some rapidly solidified Fe-Ni-Al-C alloys have been investigated by a combination of X-ray diffractometry, optical and scanning electron microscopic studies. The rapidly solidified microstructures have been compared with those of the same alloys prepared by the conventional quenching technique. 1-roll melt spinning method has been used as a rapid solidification process technique to prepare rupidly solidified alloys with the norminal content ranging from 0.1 to 2.0 C wt.%, 3 to Alwt.% and 5 to 40 Ni wt.%.
Retained austenite (r), ferrite (α) and martensite (α') phases have been found in the rapidly solidified Fe-Ni-Al-C alloys. The relative amount of each phase depended on the processes as well as the compositions. In many occasions when the supersaturated austenite was formed in the rapid solidification stage direct from the melt, an early phase decomposition accompanying the sideband phenomena seems to be tied to the early stage of the decomposition of austenite into K-carbide of $L'l_2$ type structure. The wavelength of the modulated structure decreases with increasing cooling rate. The austenitic alloy decomposes into perovskite K-phase and/or cementite ($Fe_3C$) during heat treatment at temperature 823K.
The mean austenite lattice parameter in these alloys increases linearly with the carbon content. The Vickers hardness number of rapidly-solidified alloys increases with increasing carbon content and decreases with increasing nickel content. The lowest DPN was obtained at 225 in the carbon-free alloy in series of Fe-38Ni-8Al-C, and the highest DPN was obtained at 795 in the Fe-5Ni-8Al-2C alloy. The ultimate tensile strength (UTS) increases with increasing carbon and aluminum content and the highest value was obtained at about 1380MPa in Fe-25Ni-9Al-2C alloy. Elongation increases with decreasing carbon and aluminum contents. The highest elongation was obtained at about 12% in Fe-10Ni-7Al-1.6C alloy.