Abstract
A number of applications may require cast iron. Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases may be manufactured by using grey cast iron while bearing surfaces with white cast iron. Thus, understanding the solidification behaviour of eutectic cast iron becomes an essential task, with certain points to be accomplished. Transient directional solidification may provide particular advantages in order to deal with these items, such as the large variation of growth rate (V) and cooling rate (T) values, which may allow a variety of microstructures and morphologies to be studied. The aim of this work is to examine the macrostructure regions, scale of the dendritic microstructure, proportions of the formed phases and hardness of samples obtained by transient directional solidification of a eutectic cast iron (Fe-3.5wt%C-2.5wt%Si). It was shown that a CET criterion should be based on a critical V value at the solidification front of about 0.6 mm/s. The effects of the formed phases, their proportions and λ2 on hardness of the cast alloy are assessed.
Highlights
Cast iron is a binary iron-carbon of multicomponent FeC-X alloy that is rich in carbon and exhibit a considerable amount of eutectic in the solid state
The thermal readings have been used to provide a plot of position from the metal/mold interface and the corresponding time of the eutectic front passing by each thermocouple
The reason why the eutectic front displaced faster in the case of bottom part in steel is probably due to the higher thermal conductivity of this material compared with graphite
Summary
Cast iron is a binary iron-carbon of multicomponent FeC-X alloy that is rich in carbon and exhibit a considerable amount of eutectic in the solid state. According to the metastable phase diagram, Fe-Fe3C, the white eutectic or austenitic (γ), iron carbide Fe3C may form. Considering the stable diagram iron-graphite (a significant amount of Si is required in this case), the gray eutectic, austenite-graphite (Gr) may grow. Depending on the equivalent carbon, the primary phase can be either austenite for hypoeutectic cast iron or graphite for hypereutectic cast iron. More attention from investigators has been given to the eutectic cell count and morphology. This is probably because dendrites are not readily discernible in the structure. A lot of research have been done on the relationships between dendritic growth and the solidification thermal parameters (G, V and Ṫ) for light alloys[2,3,4,5]
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