Summary
Rare earth elements are important and critical to hundreds of high-tech applications, essential to medical diagnosis equip- ment and almost all military systems. Their unique proper- ties have made them crucial to a number of emerging and growing technologies, increasing their demand and strategic importance, and, consequently, the price. The REE produc- tion process is complex and expensive, inclusively due to the toxic byproducts (radioactive U, Th). The emission caps on about 15 pollutants will apply to all industry players in- cluding miners and smelters of RE alloys, so new rules are expected to raise global prices.
Light REE, mainly including La, Ce, Pr and Nd are gener- ally used for metallurgical applications. Despite that these elements are generally more abundant and less valuable than the heavier REE, they are more attractive for other high-tech applications, and less available for cast iron use in graphite morphology control. Generally, REE are employed in duc- tile iron to accomplish the following: (a) neutralize tramp elements like Ti, Pb, Bi, As etc; (b) assist in nodulizing or provide a supplementary effect to Mg to make the graph- ite shape more spheroidal, ie, to improve the roundness or spherical shape; (c) assist in nucleating graphite.
It was found that the anti-nodularising action of residual ele- ments up to a level corresponding to Thielman’s factor K = 2.0 could be counteracted by REE additions: such addi- tions could be beneficial for K < 1.2 and can be regarded as compulsory for K > 1.2. The recovery level of Mg and TRE is clearly different in the final castings. Recoveries of TRE were typically double those of Mg, while Cerium recoveries were double those of La.
In relatively high purity base iron in terms of anti-nodula-
rising trace elements (K = 0.7-0.8) and 0.04-0.05%Mgres in castings, the TRE content after Mg-treatment increased
Mg-treated iron, the rare earths addition from the Ca,REE-FeSi alloy appears to be unnecessary, or even unacceptable, due to the risk of increased chill tendency.
the carbides tendency as the TRE content increased, in both un-and inoculated irons. For K < 0.8 base iron and > 0.005%REEres
Ca-FeSi inoculated irons are noticeably less sensitive to chill formation, independently of REE content in the final iron. It was found that a low content of REE (0.005 - 0.01%TREres
)
in a relatively pure ductile iron (K < 0.8) is practical and sufficient to obtain a low chill tendency and good quality graphite phase in terms of nodularity and nodule count in a Ca-FeSi inoculated ductile iron.
The use of the proprietary inoculant OS-IE enhancer, incor- porating potent oxy-sulphide nuclei-forming elements, led to significantly increasing the conventional Ca-FeSi inoculant effectiveness. It was found that the overall level of Ca-FeSi inoculant could be reduced by 77.7% by using a combination of 75% Ca-FeSi + 25% OS-IE Enhancer. The combination re- sulted in decreased carbide sensitivity, with similar or slightly better graphite parameters as compared to using just Ca-75Fe- Si or compared to an equivalent addition of a REE-bearing, Ca-FeSi alloy. It should be noted that the 75% Ca-FeSi and the OS-IE were added as separate additions to the test casting reaction chamber and not mixed or pre-blended.
This OS-IE alloy, used as a solo inoculant addition, was also very effective, when utilized in an in-mould application of REE free Mg-FeSi treated ductile iron, at low levels of anti- nodularising elements (K = 0.4). Similar behavior was also identified in low sulphur grey cast irons.36
A 0.03 wt-% ad-
dition of the complex OS-IE inoculant produced results at least comparable with additions of 0.20 wt-% to 0.30 wt-% Ca-FeSi75. The high inoculation efficiency of this complex alloy could be an alternative solution to REE presence in treatment alloys in ductile iron castings production.
Acknowledgement
The Romanian authors would like to recognize and thank Dr. Rod Naro, ASI International Ltd, for partially supplying funding for the experiments and the resulting presentation at the 2013 Keith Millis Symposium.
REFERENCES 1. Rare Earth Elements.
http://www.resources.nsw.gov.au/__data/assets/pdf_ file/0016/238201/RareEarth.pdf
Figure 11. Comparison of a 7.5 gram complex inoculant tablet to 75 grams of foundry-grade FeSi75, shown in a ratio of 1 to 10 reflecting the performance of 0.03wt-% Complex Alloy to 0.3wt-% FeSi75. Complex Alloy (OS- IE) Tablet inoculant dimensions are 19 mm diameter and 11.6 mm high.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
2. Rare earth element,
www.wikipedia.org. 3. Hurst, C., “China’s Ace in the Hole: Rare Earth Elements,” Joint Forces Quarterly, Issue 59, 4th Quarter, pp. 121-126 (2010).
http://www.ndu.edu/ press/lib/images/jfq-59/JFQ59_121-126_Hurst.pdf.
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