Advancing Iron's properties. (Cast Iron).
In their presentation "Static Mechanical Properties of Ferritic and Pearlitic Lightweight Ductile Iron Castings" (03-109), L. Dix, R. Ruxanda, J. Torrance, M. Fukumoto and D. Stefanescu, Univ. of Alabama-Tuscaloosa, discussed new data detailing the properties of thin-wall iron castings. With aluminum's infiltration of the iron casting market, iron foundries are left defenseless because they don't have the design data nor the casting expertise to produce thin-wall, lightweight iron components. This presentation was further discussion of work performed in the industry to further arm the iron foundries in their struggles against aluminum.
The conclusions drawn from this research include:
* the mechanical properties of fully-machined thin-wall (2.56 mm thick) ductile iron plates are equivalent or superior to regular section (12.7 mm) ductile iron as long as the surface finish is maintained at a high level;
* preliminary measurements on the influence of average surface roughness indicate that a roughness threshold exists, above which a noticeable decrease in both strength and elongation is recorded;
* surface roughness is greatly influenced by the metallostatic pressure and the pouring temperature of the casting. Higher metallostatic pressure and pouring temperature result in greater surface roughness;
* high nodule count associated with the increased cooling rates of thin-wall castings is a major factor in matrix evolution. Because of the high nodule count produced by rapid cooling, the ferrite content increases with lower thickness (faster cooling);
* the influence of cooling rate on the mechanical properties of ferritic iron was negligible. However, lower tensile strengths were recorded as the cooling rate increased for pearlitic ductile iron plates due to the higher ferrite content.
In their presentation "Carbidic Austempered Ductile Iron (CADI): The New Wear Material" (03-088), K. Hayrynen and K. Brandenberg, Applied Process Technologies Div., discussed a new family of cast iron with given amounts of carbides that are austempered to exhibit adequate toughness and excellent wear resistance. The abrasion resistance of the material is improved over that of ADI and increases with increasing carbide content. In a number of wear applications, CADI compares favorably with high chromium abrasion resistant irons in addition to providing improved toughness.
According to the presenters, the level of interest in CADI as well as the number of possible applications continues to grow. To date, most applications have been in the agricultural industry where components with as-cast carbides have been produced since the early '90s. The first reported application was a small agricultural tip for Carroll Ag that went into production in 1992.
In February 2000, John Deere announced the use of CADI elements in its revolutionary new rotary combine. One month later, the firm publicly announced the use of CADI in its Lazer Rip ripper points. According to the authors, these two events have accelerated ongoing efforts in the industry for both production and research of CADI.
In their presentation "Magnesium-Sulfur Relationships in Ductile and Compacted Graphite Irons as Influenced by Late Sulfur Additions" (03-093), R. Naro, ASI International, Ltd., M. Barstow, U.S. Pipe & Foundry Co., D. Kelley, Jencast, Inc., and C. Mihai and R. Iulian, Politehnica University of Bucharest, discussed the complex role of sulfur in magnesium treated iron and the results of tests to determine how the resultant cast iron is affected by the late sulfur additions.
At elevated levels, sulfur can act as a harmful element, resulting in magnesium neutralization and increased dross formation. But, sulfur is beneficial and essential at lower levels because it promotes suitable nuclei for graphite precipitation.
In the tests, production foundry experience showed that it was possible to use controlled sulfur additions during a post-inoculation procedure to produce compacted graphite iron with titanium additions. Controlled sulfur additions during post-inoculation of ductile iron also improved the nodule count with a lower risk of carbides due to the enhanced inoculant performance. By avoiding titanium additions, both compacted and ductile irons can be obtained from the same iron melt using a two-step treatment process of sulfur and magnesium.
The presenters also found that the initial sulfur level in the base iron is one of the prime factors that influences graphite shape and nodularity.
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|Date:||Jun 1, 2003|
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