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Metal Casting Technologies : March 2007
TECHNICAL FEATURE 22 www.metals.rala.com.au more attention to melt preparation. In particular work on the use of recarburisers has shown that foundries can improve the metallurgical condition of melts in terms of control of Carbon Equivalent and nucleation potential if graphitic carburizers with high degrees of crystallinity are used in place of amorphous carbons . Pre-conditioning has proved its effectiveness in the production of ductile irons [20,21,24]. For example it is reported  that with pre-conditioning the spread of hardness and % elongation values were 150-190Hb and 18-24% respectively compared to values of 160- 240Hb and 10-24% without pre-conditioning. Also in producing ferritic ductile irons pre- conditioning with very small additions of Cerium (20-60ppm) and Bismuth (10-20ppm) has been recommended to ensure sufficiently high nodule numbers. With the increasing interest in reducing wall thicknesses in iron castings and in producing Compacted Graphite Irons (CGI) without the use of Ti, pre-conditioning of melts, computer aided thermal analysis, and improved Mg & inoculation treatments will remain the key areas for future developments. For example, attention has been drawn to the care needed in inoculating CGI  where inoculation must prevent eutectic carbides without promoting the formation of graphite nodules. This work has also shown that with correct pre-conditioning, if a suitable inoculant material is used in place of steel as the cover in sandwich ladle treatment, then it is possible to produce satisfactory CGI structures without any post-inoculation. It has also been found that CGI can be successfully produced without Ti by using fed wire treatment with Ce bearing MgFeSi . In spite of many advances in the understanding and technology of inoculation treatments, some foundries still do not pay sufficient attention to the correct use of inoculants. For example, putting the inoculant at the bottom of a slag covered ladle (instead of adding it to the pouring stream during filling of a clean properly maintained ladle) and then wondering why there are problems with carbides and inclusions. The "do's and don'ts" of inoculation practice are well documented [e.g. 27]. Foundries with inoculation problems should revisit these and also seek the detailed technical advice readily available from the major ferroalloy and inoculant suppliers to make sure that they are using the best inoculant for the job, and using it in the correct way. ● References 1. H.T. Angus, "Cast Iron: Physical and Engineering Properties". 2nd edition, Butterworths, London, U.K. (1976). 2. J.T.H. Pearce and J.J. Dudley. "Foundry Metallurgy". Chapter 3 in "Fundamentals of Foundry Technology". Edited by P.D. Webster. Portcullis Press, Redhill, U.K. (1980). 3. R. Elliot. "Cast Iron Technology". Butterworths, London, U.K. (1988). 4. H.W. Lownie. "Barium inoculants resist fading". Foundry 1963, vol. 91, 66-68. 5. A. Moore. "Some factors influencing inoculation and inoculant fade in flake and nodular graphite irons". Transactions of the American Foundrymen's Society, 1973, vol. 81, 268-277. 6. V.H. Patterson and M.J. Lalich. "Fifty years of progress in cast iron inoculation". Transactions of the American Foundrymen's Society 1978, vol.70, 33-42. 7. A.G. Fuller. "Fading of inoculants". Proceedings of "Modern inoculating practices for gray and ductile iron", Rosemount, Illinois, February 1979, AFS/ CMI, Session 8, 141-183. 8. J.V. Dawson. "The stimulating effect of strontium on ferrosilicon and other silicon containing inoculants". Modern Castings 1966, vol. 49, 171-177. 9. J.V. Dawson and S. Maitra. "Recent research on the inoculation of cast iron". British Foundryman 1967, vol. 60, 117-127 10. R.A. Clark and T.K. McCluhan. "American experience with a new strontium inoculant in gray iron". Modern Casting 1966, vol. 49, 88-94. 11. T. Skaland. "Inoculation of ductile iron and the mechanisms of graphite nucleation". Proceedings of Best Practices in the Production, Processing and Thermal Treatment of Castings, 10 -12 October, 1995, Raffles City Convention Centre, Singapore. 23/1-23/30. 12. C.R. Loper Jr. "Inoculation of cast iron: a summary of current understanding". Proceedings of the 6th Asian Foundry Congress, 23-26 January, 1999, Calcutta, India, 145-152. 13. J.C. Morrison. "What's in a name -- Nickel and Ductile Iron". Foundryman 1998, vol.91, 228-232. 14. W. Hauke. "Production of SG Iron with the pure magnesium converter". Foundryman 2000, vol.93, 406-409. 15. S. Hasse and W. Hauke. "Procedure for the production of ductile iron". Giesserei-Praxis Special Supplement, October 2002, Berlin, Germany, 23pp. 16. Y.S. Lerner. "Overview of ductile iron treatment methods" Foundry Trade Journal 2003, vol.177, Part 1 September, p19-22; Part 2 October, p25-27. 17. K. Deelokcharoen. "Magnesium treatment of ductile iron". Proceedings of the Third Thai Foundry Conference, 23 November 2006, Thai Foundrymen's Society, Bangkok, Thailand, pp.4/1-21. 18. R.D. Forrest. "The progress and industrial acceptance of the covered ladle for ductile iron production". British Foundryman 1982, vol.75, 41-51. 19. K.J. Best. "Oxygen and Sulphur -- metallurgical partners in cast iron melts". Foundry Trade Journal 2004, vol.178, 299-301. 20. C.R. Loper Jr. "The pre-conditioning of cast iron melts and its use in safety components production". Foundry (India) 2006, vol.18, 45-50. 21. C.R. Loper Jr. "Preconditioning effect from crystalline recarburisers and their use in safety cast components production". Foundry Trade Journal 2006, vol.180, 139-142. 22. A. Jentsch. "Influence of recarburisers in the microstructure and properties of cast components: cost analysis". Foundry Trade Journal 2006, vol.180, 262-266. 23. R. Sillen. "Adjusting cast iron melts using Active Carbon Equivalent". Foundry (India) 2002, vol.14, 15-17. 24. R.D. Forrest and J.D. Mullins. "Achieving and maintaining optimum ductile iron metal quality". Foundry (India) 2003, vol.15, 51-58. 25. C.M. Ecob and C. Hartung. "An alternative route for the production of compacted graphite irons". Proceedings of the Eighth Asian Foundry Congress 17-20 October 2003, Bangkok, Thailand, pp.146-159. 26. M.J. Fallon. "Experiments on the treatment of compacted graphite iron". Foundry Trade Journal 2004, vol.178, 34-38. 27. "Ladle-inoculation practice". BCIRA Broadsheet 184.