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Graphite Morphology Control in Cast Iron

Published online by Cambridge University Press:  21 February 2011

S. V. Subramanian ,
D. A. R. Kay  and
G. R. Purdy
S. V. Subramanian
Affiliation:
Department of Metallurgy and Materials ScienceMcMaster University Hamilton, Ontario
D. A. R. Kay
Affiliation:
Department of Metallurgy and Materials ScienceMcMaster University Hamilton, Ontario
G. R. Purdy
Affiliation:
Department of Metallurgy and Materials ScienceMcMaster University Hamilton, Ontario
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Abstract

Graphite morphology in cast iron is analyzed in terms of the growth kinetics of graphite crystals in liquid iron. At small driving forces, i.e., low supersaturation or small kinetic undercooling, graphite growth is characterized by faceted growth, resulting in flake, compacted and spherulitic graphite morphologies. However, at large driving forces, there is a transition from facted to non-faceted growth, resulting in a dendritic growth morphology.

Flake morphology is rationalized in terms of impurity dependent crystal growth mechanisms, whereas a spherulitic morphology is attributed to a defect controlled spiral growth mechanism. Compacted graphite morphology is considered as a transition between flake and spherulitic morphology.

A thermodynamic approach is used to inter-relate the residual concentrations of impurities of technological interest, i.e. S and 0, as a function of the residual concentration of the reactive elements, Mg, Ca, and Ce in a typical cast iron melt at 1500'C and atmospheric pressure. Such a diagram that quantitatively relates graphite morphology in thick cast iron sections to soluble concentrations of impurities is referred to as a graphite morphology control diagram.

In thin section castings that freeze at faster cooling rates and large kinetic undercoolings, the basal spiral growth mechanism dominates over the impurity controlled prism growth mechanism, leading to deviations from predictions based simply on the graphite morphology control diagram. In the ase of compacted graphite, where growth on both the prism and basal faces is involved, the degree of nodularity increases with the cooling rate, giving rise to section sensitivity.

At large undercoolings, the prevention of the nucleation and growth of cementite is an essential feature of graphite morphology control. It is estimated that the mobility of the cementite interface exceeds that of the prism interface in flake graphite growth by an order of magnitude and that of the basal interface in spherulitic graphite growth by three orders of magnitude. In practice, the driving force for graphite growth is raised selectively through the addition of graphite stabilizing elements, such as silicon, which raise the temperature of the graphite eutectic and depress the temperature of the carbide eutectic. Kinetic growth undercooling can be decreased by increasing the number of heterogeneous nuclei for graphite growth through inoculation. The application of the above concepts for the control of graphite morphology in shaped automotive castings is discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 34: Symposium – Physical Metallurgy of Cast Iron , 1984 , 47
Copyright
Copyright © Materials Research Society 1985

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References

REFERENCES

1. Minkoff, I., “Graphite Crystallization”, Chapter 1 in “Preparation and Properties of Solid State Materials”, Vol.4 (Marcel Dekker, Inc., New York, NY 1979), pp. 1–46.Google Scholar
2. Hillert, M., ASM Symposium on Cast Iron, Detroit (1964), Ed. Merchant, H. D., Gordon and Breach, New York, NY, pp. 101–127.Google Scholar
3. Brigham, R., Purdy, G.R. and Kirkaldy, J.S., Int. Conf. Crystal Growth, Boston, MA, June 1966, pp. 161–169.Google Scholar
4. Morrogh, H. and Williams, W.J., J.I.S.I. (March 1947), pp. 321–371.Google Scholar
5. Scheil, E. and Schobel, J.D., Giesserei, Techn. Wiss. Bieh. (1963), p. 203.Google Scholar
6. Wetterfall, S.E., Fredriksson, H. and Hillert, M., J.I.S.I. (May 1972), ASM Source Book on “Ductile Iron”, pp. 162–171.Google Scholar
7. Jackson, K.A., “Current Concepts in Crystal Growth from the Melt”, Chapter 2 in “Progress in Solid State Chemistry”, Vol.4, Ed. Reiss (Pergamon Press, New York, NY).10.1016/0079-6786(67)90005-2CrossRefGoogle Scholar
8. Minkoff, I. and Nixon, W.C., J. Appl. Phys., 37 (1966), p. 4848.10.1063/1.1708149CrossRefGoogle Scholar
9. Weeks, J.D. and Gilmner, G.H., Adv. Chem. Phys. 40 (1979), pp. 167–227.Google Scholar
10. Gilmer, G.H., Proceedings of Symposium on “Modeling of Casting and Welding Processes”, Ed. Brody, H.D. and Apelian, D. (AIME Publications, July 1981), pp. 385–401.Google Scholar
11. Kerr, J.A. and Trotman-Dickenson, A.F., Handbook of Chemistry and Physics, 62nd Edition,Ed. R.C. Weast and M.J. Astle (1981–1982).Google Scholar
12. Chernov, A.A., “Stability of Faceted Shapes”, J. of Crystal Growth, Vols. 24–25 (1974), pp. 11–31.10.1016/0022-0248(74)90277-2CrossRefGoogle Scholar
13. Vahed, A. and Kay, D.A.R., Met. Trans. B, (1976), pp. 375–383.Google Scholar
14. Ghosh, D.S. and Kay, D.A.R., Proceedings of the 12th Rare Earth Research Conference, Vail, Colorado, Ed. C.E. Lundin, Vol. II, p. 1083–1092.Google Scholar
15. Gschneidner, K.A., Kippenham, N. and McMasters, O.J.: Report No. IS-RIC-6, Rare Earth Information Center, Ames, Iowa.Google Scholar
16. Kumar, R.V., Ph.D. Thesis, McMaster University (1984).Google Scholar
17. Dwivedi, R.K., Ph.D. Thesis, McMaster University (1982).Google Scholar
18. Subramanian, S.V., Ghosh, D.S., Purdy, G.R., Kay, D.A.R. and Gray, J.M., “Process for the Production of Vermicular Cast Iron”, U.S. Patent No. 4, 227,924 (1980).Google Scholar
19. Subramanian, S.V., Ghosh, D.S., Kay, D.A.R. and Purdy, G.R., Iron and Steelmaker (March 1980), Vol.7, No. 3, p. 18.Google Scholar
20. Hillert, M. and Rao, V.V. Subba, “The Solidification of Metals”, ISI Publ. No. 110 (1968), pp. 204–211.Google Scholar
21. Carlherg, T. and Fredrikason, H., Proceedings of Int. Conf. on “Solidification and Casting of Metals” (Sheffield, July 1977).Google Scholar
22. Loper, C.R., Hleine, R.W. and Chaudhari, M.D., The Metallurgy of Cast Iron, Ed. Lux, B., Minkoff, I. and Mollard, F. (Georgi Publishing Co., Switzerland 1975), p. 644.Google Scholar
23. Oldfield, W. and Humphreys, J.G., B.C.I.R.A.J I., 10 (May 1962), pp. 315–325.Google Scholar
24. Oldfield, W., B.C.I.R.A.I. (1962), 10, p. 17–27.Google Scholar
25. Oldfield, W., ASM Seminar on “Recent Research on Cast Iron”, Ed. Merchant, I.D., Gordon, and Breach, (New York, NY 1968), pp. 347–362.Google Scholar