2003 Keith Millis Symposium
on Ductile Cast Iron

INTRODUCTION
In October of 2003, the third Keith Millis Symposium on Ductile Cast Iron (co-sponsored by the DIS and AFS) was held at Hilton Head Island, SC. Foundry experts from North America, Europe and Asia gathered to discuss the latest technology, processing and marketing information on ductile cast iron.

This article provides a summary of several presentations that were made at this conference. The complete articles are available in the Conference Proceedings.

CONFERENCE SUMMARY
The conference opened with a keynote address from Dr. Karl Rundman, retired Michigan Technological University. The story of the physical metallurgy of ductile cast iron was described as one of cooperating with or attempting to fool mother nature.

A. Alagarsamy of Citation Corp suggested that scrap rates could be significantly reduced by employing a disciplined approach to understanding the nature of defects and the mechanism of defect formation as well as controlling key process variables. Casting defect codes from The International Atlas of Casting Defects Handbook were shown. It was contended that the use of these codes would enable foundry personnel to share and use data from one foundry to another, thus, disseminating the knowledge for solving casting defect problems.

The current state of worldwide standards for ductile iron were discussed by several members of the SAE Division 9 Iron and Steel Casting Standards Committee. Reviewing and updating these standards to keep them current in terms of materials properties is an on-going activity. It was emphasized that such activities are necessary for design engineers to consider ductile iron for applications.

C. Labrecque of Rio Tinto Iron & Titanium demonstrated that high purity pig iron generated the least amount of slag during the production of ductile iron when compared to other charge materials like ductile iron returns and steel scrap. The amounts of slag generated by the different charge materials expressed as the percentage of liquid bath weight are listed in Table 1.

Table 1: % Weight of Slag Formed

Note: Corrected results are for a charge made of 100% of the material listed.

P. Scarber of the University of Alabama-Birmingham demonstrated the use of real time x-ray technology in the production of ductile cast iron. The flow of iron into the mold under different conditions was shown and correlations were made between the flow characteristics and the formation of defects.

T. Skaland of ELKEM Foundry Products compared Lanthanum and Cerium bearing treatment alloys. Experimental results revealed that La-bearing MgFeSi alloys when used in the ladle treatment process have advantages over using Ce-bearing alloys. Such advantages include: increased nodule counts (2 – 3 times), improved nodularity (10-20%), reduction of pearlite content of up to 50%, substantial lowering of the chilling tendency and the elimination of shrinkage porosity in a hot spot crossbar. The use of a 0.5% La-bearing alloy was found to minimize or eliminate the need for post inoculation, thus, providing a cost effective alternative for ladle treatment.

L. Bjφrkegren of the Swedish Foundry Association described the challenges with machining Grade 500-7 ductile iron with a hardness range of HBW 170-230. A new alloy with a higher Si content was designed in order to narrow the hardness range to HBW 185-215, thus minimizing some of the machinability variations with the wider hardness range of conventional Grade 500-7 iron. Cost reductions of 10% for machining in addition to time reductions of 5-20% have been realized. A new designation of SS 0725 is recognized for this material in Sweden while the new ISO standard will refer to the material as GJS 500-10.

K. Hayrynen of Applied Process Technologies Division discussed the state of the ADI industry in 2003. The historical growth rates of ADI suggest that North American ADI production could approach 200,000 tons per year by the end of this decade and exceed 300,000 tons per year by 2020 as shown in Figure 1.

Figure 1: Estimated Worldwide ADI Production

T. Tackaberry of Foseco described direct pouring on automatic horizontal molding machines using a specially designed insulating sleeve containing a reticulated ceramic foam filter. Users of this system were found to experience the production savings of high-volume molding, yield improvements, increased pattern productivity and reduced cleaning expenses. Overall increases in productivity and improved foundry profitability are also realized.

K. Taylor of Foseco presented a series of casting production case studies that illustrated how yield, quality and productivity were improved in leading European foundries. The use of ceramic foam filters was highlighted, not as an emergency solution only, but as a means of improving the quality of castings as a whole. In the broader global context, the use of ceramic foam filtration is now a state-of-the art technique, which supports the manufacture of high quality automotive and engineering components at optimum cost.

I. Riposan of Politehnica University of Bucharest discussed the use of cooling and contraction curves to identify the influence of inoculants on the shrinkage behavior of hypereutectic ductile irons in green sand molds. Analysis was completed on several inoculated ductile irons. By using this method of analysis, a Ca-Ce-S-O-FeSi alloy was demonstrated to be a powerful inoculant without promoting shrinkage in ductile iron.

N Downes of Dana de Venezuela proposed ten steps for improving casting yield in ductile iron foundries. In the past, conventional attempts at reducing costs have focused on scrap reduction. While the importance of scrap reduction was recognized, it was suggested that yield improvement can be a more significant cost reduction tool. The ten steps highlighted included: use of ceramic foam filters, use of stable raw materials, use of trapezoidal gate cross-sections, optimizing pour times and pouring sequence, optimum gating/runner modulus to control temperature loss, use of risers to compensate expansion, placing risers at optimum locations, use of a riser for more than one casting (if feasible), use of top risers and use of hot risers.

W. Bauer of the Austrian Foundry Research Institute discussed the bending fatigue behavior of ductile iron with as-cast surfaces. In general, the bending fatigue behavior of as-cast surfaces does not necessarily correlate with tensile strength, as is the case with machined specimens. It was found to depend more on the frequency and size of the defect as well as on the intensity and uniformity of blast cleaning (i.e. level of residual compressive surface stresses), than on matrix structure or grade of ductile iron. The following ranges were determined for the bending fatigue limit with as-cast surfaces. (See Table 2.)

Table 2: Bending Fatigue Limit Ranges (50% failure probability)

R. Griffin of the University of Alabama presented results from a study on understanding ductile iron machinability. The effects of strength, hardness, matrix structure and minor alloy concentrations in both drilling and turning operations were investigated for varying amounts of Cu and Sn. The data suggests that at a given strength, tin would provide better machinability compare to copper, however, additional research is necessary to confirm these initial findings.

R. Voigt of Penn State University showed that the complex interaction between the matrix and the graphite in cast irons influences the deformation and fracture events taking place at a microstructural level ahead of and beneath the cutting tool during machining. The goal of on-going research on machinability of ductile iron at PSU is to gain insight into lot-to-lot variations in machinability of production ductile irons and to identify production practices for insuring consistent high machinability. Machining video clips can be accessed and viewed at the following website: www.ie.psu.edu/mcg/default.htm.

D. Gamble of St. Gobain Advanced Ceramics presented work on the effects of inclusion particles on the microstructure of unalloyed austempered ductile irons. Within the colony of a eutectic cell, inclusions that were deficient in Mg were surrounded by a ferrite ring while Mg-enriched inclusions were surrounded by acicular ferrite. Manganese segregation in the intercellular regions was determined to affect the ability to form acicular ferrite near inclusions with formation only occurring near Mg-deficient inclusions.

H. Roedter of Rio Tinto Iron & Titanium reviewed the development history of the ductile iron wind power industry in Europe, which has accelerated, beginning in the 1990’s. Ferritic ductile iron (EN-GJS-400-18 LT) is the grade of choice for such applications. It is expected that the North American market for wind energy power plants will follow the same trend as the European market during the 2000-2010 decade.

J. Fourmann of Pechiney discussed the benefits of using Lanthanum to minimize the appearance of micro shrinkage in ductile iron. When La additions are made, an equiaxed solidification behavior is favored. This results in a reduction in the thickness of the columnar solidification zone which leaves larger free flowing passages for the remaining molten iron to travel and, thus, feed those casting areas in need of liquid iron.

ADDITIONAL INFORMATION
The proceedings from the 2003 Keith Millis Symposium on Ductile Cast Iron are available for purchase. Contact the American Foundry Society at www.afsinc.org.

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