1b shows 88 eutectic cells after a solidification time of 85 s (after the recalescence temperature). In turn, this indicates that after reaching Tm there is no nucleation of new cells. On the contrary, it is likely to have a small process of coagu- lation or coalescence of eutectic cells.
photo shows 94 eutectic cells after a solidification time of 31 s, (near the temperature, Tm
We agree with the reviewer that in the final solidification stage segregation can play a role on nucleation. This phe- nomenon of secondary nucleation of small cells 14 or nod- ules is an interesting one. The proposed model also can be used to explain this phenomenon. Secondary nucleation oc- curs when a second undercooling maximum, ∆Tm,s
arises at result, new small cells are formed (see Fig.IIc,d). sites become active in the lm
the end of solidification that exceeds the initial maximum un- dercooling, ∆Tm
( see Fig. IIb). In this case new nucleation to lm,s
Accordingly, we agree with the reviewer with regards to the possible role of segregation on the nucleation of new cells during solidification.
Reviewer: The model of the authors is based on undercool- ing and related to cooling curves (e.g. Fig. 2b and page 3). The authors do not specify whether the undercooling is valid in a small microscopic volume or if it is the average value as measured in a larger CUP. Probably, it is the second one since only this can be measured. However, in a CUP, nodule count or eutectic cell count differs largely from the mold wall till the thermal center. This raises the question: are av-
(a) range ( see Fig.2a ). As a
Authors: In a given casting, M is constant and does not change during solidification. Yet, what can change during heating is the material mold ability to absorb heat. The cell or nodule count are measured in small volumes close to the thermocouple (Fig.IId) used to measure the temperature and local cooling rates.
Reviewer: In Fig. 6 a different behavior between gray and ductile iron is noticed. This is a very important finding. However, it is explained by the fact that the nucleation co- efficient b (Table 2) varies differently with CE (+ for gray and–for ductile iron). Consequently, the simulation result is based on adjusting parameters in order to reproduce the ex- perimental findings.
(c)
) while the micrograph in Fig.
erage grain counts predicted or actual grain counts in small microscopic areas? The authors should specify this.
Authors: The cell or nodule counts were measured in small volumes close to the location of the thermocouple used for temperature measurements (see Fig.IId).
Reviewer: The authors introduce the casting modulus M. M changes during solidification as the cooling effect of the mold wall varies during heating of the sand. More- over, M represents the casting ( Vc and Fc are the volume and surface area of the casting). I do not think that it has sense to predict an average grain count for a casting nod- ule count is needed in critical areas. Consequently, cast- ing modulus is not needed but local cooling conditions within a casting.
(b) (d)
Fig.II. (a) Size distribution for graphite nucleation sites, (b) cooling curve T(l) when secondary nucleation occurs (c), undercooling range for secondary nucleation and (d), secondary cells near a thermocouple location.
60 International Journal of Metalcasting/Summer 10
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