Materials Science and Engineering, A173 ( 1993 ) 115-118 115 Microstructure vs. casting processes in the Fe-Si-Ca-A1 system F. Margarido Dept. Eng. Materials, IST/UTL, 1096 Lisboa Codex (Portugal) J. P. Martins Dept. Eng. Quimica, FEUP, R. dos Bragas, 4000 Porto (Portugal) A. Gonqalves Dept. Quimica, ICEN, Estrada Nac. 10, 2685 Sacavdm (Portugal) M. O. Figueiredo Centro de Cristalografia e Mineralogia, HCT, Alameda D. Afonso Henriques, 41-4oE, 1000 Lisboa (Portugal) Abstract A quaternary phase isostructural with a-Fel_ xSi 2 and named "caalsifer" for its chemical constitution was earlier detected in industrial ferrosilicon alloys (Margarido and Figueiredo, 1988). With the aim of ascertaining the possible domain for such a non-equilibrium compound and contributing to the understanding of microstructure and phase solidification in casting processes of ferrosilicon alloys, a systematic study of phase formation within the quaternary Fe-Si-A1-Ca system was undertaken. Results are presented of laboratory experiments using both arc and induction fusion furnavces with water-cooled copper crucibles, and compositions close to that assumed for caaisifer. The obtained materials were chemically and composifionally characterized through scanning electron microscopy and X-ray diffraction. A relation is tentatively established between microstructure plus phase assemblage on the one hand, and cooling rate on the other. 1. Introduction Silicon extraction and refining deals with ferro- silicon alloys containing phases that fall within the quaternary system Fe-Si-Ca-AI, which furthermore covers materials with technological applications such as the compound FeSi2, occurring under two structural forms a and t3 with distinct magnetic and transport properties [ 1]. Beyond binary and ternary equilibrium compounds produced in laboratory experiments within partial phase diagrams [2], a non-equilibrium quaternary phase, named "caalsifer" because of its constitution, was described in industrial alloys [3] and later on related to the kinetics of the hydrometallurgical silicon refining process [4]. With the purpose of ascertaining the possible domain for such non-equilibrium compound and con- tributing to the understanding of microstructure and phase solidification in casting processes of ferrosilicon alloys, a systematic study of phase formation within the quaternary Fe-Si-A1-Ca system was undertaken. 2. Experimental methodology The starting materials were powders (industrial ferrosilicon alloy and calcium disilicide) and small frag- ments of aluminium metal and common iron, mixed together in the right proportions and pressed into pellets. Bulk compositions of synthesized samples are listed in Table 1. They lie in the region of the FeSi-Si partial phase diagram reproduced in Fig. 1, which covers the chemical domain of the quaternary phase caalsifer. Single-phase compositions corresponding to e-FeSi and a-Fel_ xSi2 were also synthesized. Two types of fusion furnaces, arc and induction, with water-cooled copper crucibles were used in order to achieve different fusion and solidification regimes. A full description of these furnaces may be found else- where [5, 6]. Before each fusion run and to prevent oxidation, the quartz vessel enveloping the crucible was evacuated three times to less than 1 Pa before the pressure of the inert gas was adjusted. Because the starting materials are non-conductive, a preliminary 0921-5093/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved