الفهرس 
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Abstract
The present work is undertaken to study the influence of MgFeSi and Rre Earth (mischmetal) nodularizer both separately and in combination on the structure and the mechanism of formation of S.G.
The work has been done by quenching the melt from different temperatures between liquidus and solidus to solidus to retain the non-equal structure. The work showed that the graphite nucleation occurs on inclusions.
Also the influence of holding time on MgFeSi and mischmetal nodularizer both separately and in combination on the structure were studied. The work showed that the addition of small amount of mischmetal with MgFeSi exhibit better results as holding time increased tall a certain time.
At the same time, the effect of different section size and moudling material (i.e. bentonite, CO2process and chamotte) on the graphite nucleation were studied. The work showed that at a given cooling rate, a high nodule count in microstructure were observed. This is due to the reduction in the carbon diffusion behavior, which promoting the stable reaction of graphite formation. This promoting in accounts are due to the strong correlation between the percent of ferrite and the nodule count.
Some of the markedly results samples from different melts were subjected to austempering process to study the effect of some variables (i.e. tepering temperature, holding time) on microstructure of the given samples. This study shows that austemering temperature affect markedly both the formed bainite and the residual and austenite. At the same time increasing the holding time to a certain extent at the transformation temperature, increases the amount of retained austenite while hardness is reduced.