THE IMPORTANCE OF RARE EARTH CONTRIBUTION FROM NODULIZING ALLOYS AND THEIR SUBSEQUENT EFFECT ON THE INOCULATION OF DUCTILE IRON
Iulian Riposan, Mihai Chisamera, Valentin Uta and Stelian Stan POLITEHNICA University of Bucharest, Bucharest, Romania
Rodney Naro and David Williams ASI International Ltd., Cleveland, OH, USA
Copyright © 2014 American Foundry Society
A version of this paper was previously published in the 2013 Keith Millis Symposium Proceedings Abstract
The unique properties of rare earth elements (REE) have made them crucial to a number of emerging and growing technologies [medical diagnosis equipment, critical mil- itary-based technologies, catalysts, computers, magnets, hybrid cars, windmills etc.] increasing their demand, and strategic importance. Recently, increased demand has led to supply problems, with corresponding price fluctuations and difficulties in obtaining REE for use in the cast iron industry.
both un-inoculated and inoculated irons. A low content of REEres
Rare Earth and the World Crisis The term ‘rare earths’ was proposed in 1794.1
The anti-nodularising action of deleterious residual ele- ments up to a level corresponding to K = 2.0 (Thielman factor) can be counteracted by REE additions. In rela- tively high purity base iron in terms of anti-nodularising trace elements (K = 0.7 to 0.8) and 0.04 to 0.05% Mgres higher REEres
,
contents increased carbide tendency, for (0.005 to 0.01%) for K < 0.8 is practical and
Keywords: rare earth elements, anti-nodularising elements, ductile iron, Mg-treatment, inoculation, inoculant enhancer, in-mould, chill tendency, carbide, graphite
It was used
because when they were found they were thought to be pres- ent in the Earth’s crust in only small amounts, and ‘earths’ because as oxides they have an earthy appearance. Rare earth elements (REE) or rare earth metals (REM) are a set of seventeen chemical elements in the periodic table, specifi- cally the fifteen lanthanides (atomic numbers 57 through 71) plus scandium (sc) and yttrium (y) (atomic numbers 21 and 39). Scandium and yttrium are considered REE since they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties.2, 3
These elements share similar chemical properties, often mak- ing them interchangeable in their commercial applications ranging from use in catalysts and computers, to magnets, cell phones, hybrid cars, TVs, fluorescent light bulbs, generators used in wind turbines etc.4
They are essential to medical diag-
nosis equipment and critical military-based technologies such as precision-guided weapons and night-vision goggles.3, 5, 6
International Journal of Metalcasting/Volume 8, Issue 2, 2014
Despite their name, the REE are each more common in the Earth’s crust than silver, gold or platinum, while cerium [the 25th most abundant element at 68 parts per million, similar to Cu],2
yttrium, neodymium and lanthanum are more com- mon than lead.1
The more abundant REE are each similar in crustal concentration to commonplace industrial metals such as chromium, nickel, copper, zinc, molybdenum, tin, tungsten, or lead. Even the two least abundant REE (Tm, Lu) are nearly 200 times more common than gold. However, in contrast to ordinary base and precious metals, REE have very little tendency to become concentrated in exploitable ore deposits. Although relatively abundant in total quantity, they appear in low concentrations in the earth’s crust and extraction and processing is both difficult and costly.3
Con-
sequently most of the world’s supply of REE comes from only a handful of sources.7
Rare earth elements can be further divided into two sub- groups using their atomic weight: heavy rare earth elements (HREE) and light rare earth elements (lree). heavy rare earth elements (Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) are the more
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sufficient in a Ca-bearing FeSi alloy inoculated iron. The REE addition from a Ca,REE-FeSi alloy appears to be unnecessary, or even unacceptable, due to the risk of in- creased chill tendency.
The use of a proprietary oxy-sulphide inoculant enhancer, (CaSi-based blend with S, O, Al, Mg) led to a substantial in- crease in the potency of the Ca-bearing inoculants. It was ef- fective, when utilized in an in-mould inoculation of Mg-FeSi (0% REE or 0.26% REE) treatment, for K = 0.4 - 0.8. Avoid- ance of chill (free carbides), control of casting hardness and improved graphite quality parameters were observed with the proprietary oxy-sulphide inoculant.
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