STRUCTURE AND DECOMPOSITION OF A13-TYPE PHASE IN RAPIDLY SOLIDIFIED HIGH-CARBON CR-SI IRON ALLOY

A high-carbon iron alloy containing chromium and silicon was rapidly solidified into a ribbon. The structure consisted of a single phase which was confirmed to be A13-type structure, psi phase, from X-ray diffraction and transmission electron microscopy. The pair distribution functions showed that the psi phase is of looser atom packing compared with austenite (gamma), epsilon, and chi phases and rather close to an iron-base amorphous phase in regard to local atom arrangement. Decomposition of the psi phase took place in two stages: the decomposition of the psi phase to ferrite (and/or MS-I) plus MS-II phase at 700 to 800 K and the transformation of the MS-II phase to M7C3 carbide around 1000 K. Thus, it was found that the psi phase structure had an atom configuration close to an iron-base amorphous phase, and the decomposition behavior was also similar to that of the amorphous phase.