and K but also to improve the ‘metallurgical quality’ of the iron melt. It was found that the use of high purity cast iron makes it possible to cope with higher Px
levels or less powerful inoculation additions.
For high purity charges with extremely low levels of anti- nodularising elements, REE would not be needed to neu- tralize elements like Ti, Pb, As. However, many foundries still believe they need REE in their FeSiMg treatment alloy, regardless of how pure their charges are. REE continue to be important to assist nodular graphite formation, encouraging higher nodule count with smaller, more spherical nodules with less risk of carbide formation, but foundries may be using more than they really need.
Rare Earth Elements Contribution in the Nodulizing Treatment
Rare Earth Element and Magnesium Recovery in Ductile Iron Production
The primary iron batch was melted in a foundry coreless in- duction furnace (acidic refractory lining, 1000kg, 1000Hz) using selected steel scrap, a high purity recarburizer, and low Al-FeSi and FeMn as charge materials to generate a constant base iron. Two experimental Heats (A and B) were obtained by remelting this base iron in an acidic refractory lined, lab- oratory coreless induction furnace (100kg, 2400Hz). In each case, the base iron melt was heated up to 1,500 - 1,520˚C (2,732-2,768˚F), with corrective carbon raiser addition (gra- phitic material, 99.1%C, 0.06%S) and desulphurization us- ing calcium carbide in the melting furnace35 into the nodulizing ladle.
and then tapped
A Tundish Cover Mg-treatment technique was used along with a 2.5 wt-% Mg-bearing FeSi master alloy addition. Two Mg-FeSi alloys with similar chemical compositions (Si, Mg, Ca, residuals) were selected, with the REE level being the main difference (Table 2). The treatment alloy used (FeSiCaMgRE0.26) is usually considered as a “rare- earths free Mg-ferrosilicon” in the foundry industry. The small amount of total rare earth TRE=0.26% (0.15% Ce, 0.11%La, 0.008%Nd) is due to rare earths absorbed from the ferroalloy treatment vessel lining. No intentional rare
It was also found that the anti-nodularising action of residual elements up to a level corresponding to K = 2.0 could be counteracted by REE additions. Such additions could be beneficial for K < 1.2 and can be regarded as compulsory for K > 1.2. The presence of high purity pig iron in the charge is extremely beneficial, not only to control the complex fac- tors Px
earths are added to the MgFeSi alloy, but this pickup is inevitable since the predominant MgFeSi alloy produc- tion is with significant levels of total rare earths elements (TRE). The second alloy (FeSiCaMgRE 1.42) is a popular nodulizing agent in ductile iron production, in many cases it is representative of the upper limit of total rare earth levels in these alloys.
The specially designed test mould (Fig. 1) included a central downsprue, which supplied Mg-treated iron simultaneously to four separate reaction test chambers (one as an un-inocu- lated reference and three to test different alloys).36, 37
W3
chill wedge samples [ASTM A367-85 specification, 19.1 x 38.1 x 101.6 mm (0.75 x 1.50 x 4in) dimensions, CM = 3.5 mm/0.138in cooling modulus], plate samples (4.5 mm/0.18 in thickness) and round bar samples cooling (25 mm/1in di- ameter) were gated off the inoculation reaction chamber, to evaluate the structure characteristics after treating the ductile irons to the different inoculants. Different Ca-bearing FeSi alloys were used for inoculation (0.04 - 0.18 wt-% consump- tion, 20x80mesh size). The test castings all were poured at 1,450˚C/2,642˚F, all within 3 minutes after Mg-treatment in
Figure 1. In-mould inoculation pattern for four work positions [1 - Down sprue; 2 - Gate; 3 - Reaction chamber; 4 –Runner; 5 - Wedge sample; 6 - Cylindrical bar; 7- Flat plate].
Table 2. Mg Treatment Alloys [wt-%]
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International Journal of Metalcasting/Volume 8, Issue 2, 2014
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