Effect of Silicon on the Cast Macrostructure of Fe-Si Alloys
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Effect of Silicon on the Cast Macrostructure of Fe-Si Alloys H. J. A. García1, M. H. Cruz1, A. A. Balandra1, F. G. González1, Y Houbaert2 1
Departamento de Ingenieria Metalurgica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria Coyoacan 04510, México D.F. Email: [email protected] 2 Departamento de Ciencia e Ingenieria de Materiales, Universidad de Gante, Gante Belgica ABSTRACT In this work was studied the effect of silicon content from 0.5 to 3 wt.% Si on the macrostructure of casting ingots. Fe-Si alloys with low contents of impurities were produced in electric induction furnace under inert atmosphere. Castings of 12.5 cm thick, 25 cm long and 30 cm high were obtained of each alloy poured into metallic mould. The ingots obtained were sectioned in slices of 12 cm wide, 25 cm high and 2 cm thick, the central slice of each ingot was prepared metallographically to reveal the macrostructure of the six cast alloys. The results indicate that alloys with low silicon levels (0.5 and 1.0% Si) and with small solidification intervals have relatively fine equiaxed grains, while alloys with higher silicon content and a higher solidification intervals present predominantly columnar grains. These macrostructures are not the usually structures linked to short and long freezing range. Another important result is the absence of dendritic structure usually present in cast alloys. Keywords: Grain size, Hardness, Magnetic properties, Casting, Directional solidification. INTRODUCTION Iron-silicon steels with a high Si content are an important material to develop superior magnetic properties and to be applied in magnetic devices due to its high permeability, high electrical resistivity and near zero magnetostriction, which low core loss and low device noise >1, 2@. However the workability of these materials is hard during the rolling processes because its embrittlement at room temperature linked to the formation of intermetallic phases like B2 and DO3 >3@. Several methods have been developed in order to avoid this problem such as: rapid quenching >4@ and hot dipping diffusion >5@. However the most practical is the casting process followed by hot or cold rolling. Directional solidification of grain improves the ductility of this material because large amount of low energy grain boundaries with strong resistance to intergranular fracture are formed. Therefore columnar grain with high grain ratio long/width (L/W) is preferred >6, 7@. In this paper Fe-0.5 to 3 wt% Si were produced in metallic moulds in order to determinate the relationship of the macrostructure as a function of the silicon amount, also its grain ratio (L/W) and the hardness of the alloys were evaluated, because these characteristics are important to improve the workability of Fe-Si steels.
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EXPERIMENTAL DETAILS Iron was melted in an electric induction furnace under inert atmosphere of argon gas, silicon adjustments were made with ferrosilicon (FeSi 75). Steel ingots were obtained in metallic moulds with a total weight of 100 Kg i
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