Nucleation and grains density in grey cast iron—A theoretical model and experimental verification

The present work is based on a heat balance during the solidification of cast iron. Accordingly, an analytical expression was derived to relate the chilling tendency (CT) of cast iron to nucleation and growth processes associated with the eutectic graphite and cementite constituents. A relationship is found between the CT and factors such as the physicochemical state of liquid, the distribution of nucleation sites, and the density of nucleation sites for eutectic cells. In particular, it is found that the CT can be related to the critical casting modulus (M cr ), enabling determinations of minimum wall thickness for chilled castings or chill widths in wedge-shaped castings. Finally, the present work provides a rational for the effect of technological factors such as the chemistry of the melt, inoculation practice, holding temperature, and time on the resultant CT and chill of the cast iron.

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“…[18] Similarly, from Eq. [11], the expression for the CT can be simplified as [19] where N t is the cell count at T ϭ T c .…”

Section: Discussionmentioning

confidence: 99%

“…A simple model for heterogeneous nucleation has already been proposed. [18] Since each graphite nucleus gives rise to a single graphite eutectic cell, the density of eutectic cells (N) can be described by [19] [12]…”

Section: Discussionmentioning

confidence: 99%

The transition from gray to white cast iron during solidification: Part I. Theoretical background

Fraś

Górny

López

2005

Metall Mater Trans A

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“…2(c)). When all the C n molecules and sites of sizes lϾl m become nuclei at DT m , the density of graphite nuclei can be described by a previously developed heterogeneous nucleation model 4,5) where N s and b, are the nucleation coefficients for flake graphite or nodular cast iron and DT m is the maximum degree of undercooling at the onset of eutectic solidification, (see Fig. 2(e)).…”

Section: Discussionmentioning

confidence: 99%

“…In liquid melts, C n molecules and particles-nucleation sites of various size can be characterised 4,5) by a unimodal size distribution function, (L(l) (Fig. 2(d).…”

Section: Discussionmentioning

confidence: 99%

“…Hence, cast iron melts can be considered as a liquid containing carbon dispersed as a graphite suspension, with particle sizes ranging 1,3) from 1 nm to 1 000 nm. Since the iron melt already contains a distribution of graphite particles, some of them become active nuclei 4,5) as soon as the temperature falls below the graphite liquidus temperature, T gr . 6,7) Moreover, in liquid cast iron nucleation particle substrates (for graphite) of various sizes exist.…”

Section: Introductionmentioning

confidence: 99%

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Eutectic Cell and Nodule Count in Cast Iron: Part I. Theoretical Background

2007

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In this work, heat balance is incorporated in developing expressions of general validity for the solidification of hypo-eutectic flake graphite cast iron, as well as eutectic and slightly hyper-eutectic nodular iron. These expressions incorporate the active nucleation and growth processes that occur in flake and nodular graphite. The derived analytical equations describe the eutectic cell N and nodule count N n as a function of the solidification parameters and melt chemistry. From this analysis, eutectic cell or nodule counts can be predicted based on experimental data related to cooling rates and chemical composition. In particular, it has been found that the quality of the liquid cast iron is closely tied to its intrinsic nucleation properties (N s and b coefficients in the nucleation equation, N nuc ϭN s exp(Ϫb/DT m )), or directly to the graphite nuclei density, N nuc . Moreover, the outcome of the present work is used in providing a rational for the effect of technological factors such as the material mold ability to absorb heat, the casting modulus, pouring temperature, chemistry, inoculation practice, holding temperatures and times on the resultant cell count or nodule count in cast iron.KEY WORDS: gray cast iron; nodular cast iron; eutectic cell count; nodule count. 259

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The transition from gray to white cast iron during solidification: Part II. Experimental verification

Fraś

Górny

López

2005

Metall Mater Trans A

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In this work, an experimental verification for the transition theory from gray to white cast iron solidification is presented. Experimental tests have been implemented using plate-and wedge-shaped castings of various sizes. The experiments included inoculated and noninoculated cast irons of different chemical compositions and time-temperature histories of the inoculation effects. In addition, thermalanalysis tests were employed to determine the degree of undercooling of graphite eutectic (⌬T m ). This included microstructural evaluations in order to establish the eutectic-cell densities. This procedure enabled the calculation of the theoretical chill width (w), as well as the chilling tendency (CT) of cast iron. It was found that the predictions of the theoretical analysis are in good agreement with the experimental outcome for the chill exhibited in wedge-and plate-shaped castings.

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Nucleation and grains density in grey cast iron—A theoretical model and experimental verification

Cited by 8 publications

References 4 publications

The transition from gray to white cast iron during solidification: Part I. Theoretical background

The transition from gray to white cast iron during solidification: Part I. Theoretical background

Eutectic Cell and Nodule Count in Cast Iron: Part I. Theoretical Background

The transition from gray to white cast iron during solidification: Part II. Experimental verification

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