Abstract
The most commonly used inoculants for producing grey iron are ferrosilicon based, but also there are reports indicating that silicon carbide can act as inoculant. There are few published studies of fading and nucleation sites of graphite when silicon carbide is used as inoculant, thus the understanding of the inoculation effect of silicon carbide is incomplete. To study these two aspects, fading and graphite nucleation sites, an ASTM class 35B grey iron inoculated with silicon carbide was produced and characterized. The results were compared with an ASTM class 35B grey iron inoculated with a ferrosilicon base inoculant and without inoculation. It was found that the effect of the silicon carbide was comparable to the ferrosilicon base inoculant and fading was similar. In addition, the graphite nucleation sites in the grey iron inoculated with silicon carbide were irregular shaped manganese sulfides larger than the nuclei in the grey iron inoculated with ferrosilicon, which suggest a similar nucleation mechanism for both inoculants.
Highlights
Grey iron is widely used due to its good mechanical properties, thermal conductivity, damping capacity, castability and low cost
Edalati et al studied the effect of silicon carbide as inoculant and as silicon carrier in grey iron poured at different temperatures, the results showed that using SiC as inoculant increased the liquid and eutectic temperatures, type A graphite and eutectic cell count and decreases undercooling and chill depth [12,13]
Fading and graphite nucleation sites have been studied widely for grey iron inoculated with ferrosilicon base inoculants, there are few published reports of these topics for materials inoculated with silicon carbide which limits the understanding of its inoculation effect
Summary
Grey iron is widely used due to its good mechanical properties, thermal conductivity, damping capacity, castability and low cost. Inoculation provides sites for heterogeneous nucleation, which increases the amount of eutectic cells leading to a finer microstructure It decreases undercooling, making the solidification temperature closer to a stable equilibrium, which favors the precipitation of graphite instead of carbides [3]. Benecke reported that using silicon carbide to produce cast iron has positive effects increasing the eutectic cells counting, the tensile strength-hardness relationship, machinability and microstructural homogeneity of the casting [15]. Another important consideration when producing grey iron is fading, which consists of the loss of the inoculation effect with time, which increases undercooling during solidification, favors the formation of carbides instead of graphite, increases hardness and decreases tensile strength. Fading and graphite nucleation sites have been studied widely for grey iron inoculated with ferrosilicon base inoculants, there are few published reports of these topics for materials inoculated with silicon carbide which limits the understanding of its inoculation effect
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