Graphite nodule and eutectic cell count in cast iron : Theoretical model based on weibull statistics and experimental verification

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 38; no. 2; pp. 385 - 395
• Main Authors: FRAS, E, WIENCEK, K, GORNY, M, LOPEZ, H. F
• Format: Journal Article
• Language: English
• Published: New York, NY Springer 01-02-2007; Springer Nature B.V
• Subjects: Applied sciences; Cells; Chemicals; Computer simulation; Exact sciences and technology; Metallurgy; Metals. Metallurgy; Random variables; Studies; Substrates; Theory; Experimental test; Theoretical model; Modeling; Eutectic; Cast iron
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-006-9045-x

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^sub nuc^ can be given in terms of the maximum undercooling, ΔT^sub m^, by N^sub nuc^ = N^sub s^ exp (-b/ΔT^sub m^7), where N^sub 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^sub V,n^ or euteetic cell density, N^sub V^, after solidification equals N^sub s^. In this work, measuremenls of N^sub V,n^ and N^sub V^ values were carried out on experimental nodular and flake graphite iron castings processed under various inoculation conditions. The volumetric nodule N^sub V,n^ or graphite euteclic cell N^sub V^ count was estimated from the area nodule count, N^sub A,n^, or eutectic cell count, N^sub A^, on polished cast iron surface sections by stereological means. In addition, maximum undercoolings, ΔT^sub m^, were measured using thermal analysis. The experimental outcome indicates that the N^sub V,n^ or N^sub V^ count can be properly described by the proposed expression N^sub V,n^ = N^sub V^ = N^sub s^ exp (-b/ΔT^sub m^). Moreover, the N^sub s^, and b values were experimentally determined. In particular, the proposed model suggests that the size distribution of nucleation sites is exponential in nature. [PUBLICATION ABSTRACT]