Inoculation is a metallurgical treatment that improves the nucleation ability of atoms in liquid cast iron. This is a critical step in the production of high quality ductile cast irons that are free from chill and carbides.
Ce-bearing FeSi inoculant shows a better performance than Ca, Ba-FeSi inoculant for most of the solidification conditions (casting cooling modulus and wall thickness). This is important for the production of thin wall castings.
The inoculant based on the Zr-Mn alloy has a positive effect on the graphitization of grey cast iron. It can eliminate white mouth, reduce the hardness of castings, prevent the occurrence of nitrogen pores, and promote the growth of the graphite core during annealing. It is also effective in reducing the content of ferrite in the matrix and improving the strength and toughness of cast iron.
EDXA analysis confirmed the role of complex (Mn,X)S compounds in graphite nucleation. The presence of these compounds is independent of iron melt chemistry, inoculant type and addition rate. The nucleation effect of Ce-bearing FeSi inoculant is stronger than that of Ca,Ba-FeSi at the used addition rates.
The critical conditions, mainly expressed by low sulphur content (
Inoculation of ductile cast iron is generally carried out at several stages during production. However, it is most effective just before or during pouring. Careful inoculation offers two main advantages – it makes the casting free from carbides and it makes heat treatment unnecessary.
A special inoculant alloy containing barium and zirconium has been developed. It is characterized by particularly good suppression of the precipitation of carbide and by a preparation process which can be industrially performed with favorable costs.
The alloy is suitable for treating molten synthetic metal in induction furnaces and for the non desulphurized melt from cupola furnaces with initial S
The inoculant alloy according to the invention has excellent nucleating properties and suppresses the precipitation of iron carbide, which has an adverse effect on the quality of cast iron. In contrast to hitherto known inoculant alloys based on ferrosilicon, the alloy according to the invention does not have an undue concentration of calcium or aluminum.
Inoculation is a vital process used by ductile and grey cast iron manufacturers worldwide including India to avoid metallurgical defects such as white fracture. Inoculation is a process that increases the number of graphite nuclei in the melt and minimizes undercooling below the metastable eutectic temperature, favoring formation of spheroidal graphite rather than cementite.
The inoculant has a high nucleation rate immediately after adding to the melting process, and the nucleation rate decreases more slowly than traditional inoculants. It eliminates cementite very successfully in both grey and nodular cast iron, and can also reduce casting inclination to cause shrinkage cavities.
The critical solidification conditions characterized by low sulphur content, high control factor, a high Mn/S ratio and residual aluminium content in the base iron melt resulted in undercooled graphite morphologies and free carbides formation in un-inoculated cast irons. A strong chill tendency, evaluated by Relative Clear Chill (RTC) values, was also observed for these cast irons.
Inoculation with the rare earth ferro silicon inoculant – Cheegoole -Ferro Silicon Barium enables to significantly reduce the chill phenomena and the sensitivity of cast irons to free carbides formation, without decreasing the eutectic cell size. This was proven by structural analysis of W2 and W3 wedge castings in terms of the solidification cooling modulus and wall thickness variations, with or without inoculation of the base iron with Ca-FeSi inoculant at two addition rates. The results show that the graphitizing efficiency of Ca,Ba- and Ce,Ca-FeSi inoculant increases with increasing inoculant addition rate. At the same time, RTC values were less negative for inoculated cast irons compared to un-inoculated ones.
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