Graphite Nodule and Eutectic Cell Count in Cast Iron: Theoretical Model Based on Weibull Statistics and Experimental Verification

Abstract

In this work, a model is proposed for heterogeneous nucleation on substrates whose size distribution can be described by the Weibull statistics. It is found that the nuclei density, N nuc can be given in terms of the maximum undercooling, DT m , by N nuc = N s exp (-b/DT m ), where N s is the density of nucleation sites in the melt and b is the nucleation coefficient (b > 0). When nucleation occurs on all possible substrates, the graphite nodule density, N V,n , or eutectic cell density, N V , after solidification equals N s . In this work, measurements of N V,n and N V values were carried out on experimental nodular and flake graphite iron castings processed under various inoculation conditions. The volumetric nodule N V,n or graphite eutectic cell N V count was estimated from the area nodule count, N A,n , or eutectic cell count, N A , on polished cast iron surface sections by stereological means. In addition, maximum undercoolings, DT m , were measured using thermal analysis. The experimental outcome indicates that the N V,n or N V count can be properly described by the proposed expression N V,n = N V = N s exp (-b/DT m ). Moreover, the N s and b values were experimentally determined. In particular, the proposed model suggests that the size distribution of nucleation sites is exponential in nature.

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Foundry and Development of Ductile Iron Crankshaft

“…Production process, at the same CE, pouring temperature and other conditions, different sources of charge (pig iron factory conversion or join rescaling etc. ), the shrinkage of scrap vary widely, sometimes shrinkage reject rate below 1%, sometimes up to 30% [11].…”

The Effect of Carbon on the Transition from Graphite to Cementite Eutectic in Cast Iron

“…During the nucleation stage, various graphite nucleating particles (substrates) of different sizes are found to be present in the Fe-melts. [18][19][20] A more detailed analysis [21] shows that the various nucleation sites can be described by a unimodal size distribution function K(l), where l is the nucleation site size. Accordingly, this function can be used to establish the graphite nucleation potential of an undercooled melt during solidification.…”