affect significantly the microsegregation of substitutional elements, while it can certainly homogenize carbon distribu- tion. A full understanding of the above features would thus certainly need a simulation of the microstructure evolution during the eutectoid transformation accounting for carbon redistribution. Note that the maximum ferrite content in as- cast condition is 80% whereas nearly fully ferritic structures are obtained after heat treatment.
Conclusion
A series of cast irons with copper content varying from 0.11 to 0.95 wt. % have been cast and then austenitized and cooled at different rates. The observation of their microstruc- ture confirmed that low level addition of copper to cast irons containing 0.1-0.2 wt. % of manganese does not decrease the final ferrite amount significantly under both as-cast and heat-treated conditions. On the contrary, addition of copper at a level equal or higher than 0.6 wt. % leads to a marked decrease of the ferrite fraction at all cooling rates. Analyzing the thermal records confirmed previous results that copper addition decreases the temperature for the start of both the ferritic and pearlitic reactions, but this could not explain the dramatic change beyond 0.6 wt. % Cu added. Comparing the DTA records showed this decrease to be due to an effect of copper on the growth kinetics of ferrite which is tentatively related to the strong decrease of the carbon diffusion coef- ficient in ferrite when the temperature drops below the Curie temperature of that phase.
Acknowledgments
This work has been supported by the Diputación Foral de Bizkaia and the Science and Technology Department of the Spanish Government. The authors would like to thank Bet- saide, S.A.L., Fytasa, S.A. and TS Fundiciones, S.A. Found- ries for all the collaborating efforts made in order to elabo- rate the alloys and to obtain the samples.
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Ferrite (%) (a)
Figure 9. Evolution of the ferrite fraction versus Ttrans 58 (a) and Vtrans
Ferrite (%) (b)
(b) for as-cast and heat treated samples (Vcool = 34-60 K/min). International Journal of Metalcasting/Winter 10
Ttrans
(ºC)
Vtrans
(K/s)
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