Magnesium recoveries generally ranged from 39% to 40% during ladle treatment and 30% to 33% in the final castings. Conversely, TRE recoveries ranged from 75% to 90% after Mg treatment and 66% to 90% in the test castings. Cerium recovery rate was greater for Heat B (the 0.26% TRE alloy) compared to Heat A (the 1.42% TRE alloy) while La recoveries for both heats showed little variation (51% to 55% after Mg-treatment and 44% to 47% in the sample castings).
Structure Characteristics
The level of trace elements in the final chemistry of Heats A and B were well within the range of typical ductile iron pro- duction. The cumulative influence of the chemical compo- sition of the Mg-treated irons as they affect pearlite content (factor Px
, Equation 1) and anti-nodularising effect (factor K, Equation 2), according to Thielman’s factors30 trated by Figure 3.38
, are illus- It could be concluded that the content
= 2.3 - 2.5 indicates a pearlite forming tendency for conventional solidification conditions. There is practically no difference in the two heats even though there were differ- ent rare earth levels in the treatment alloys.
Figure 4 compares the macrostructure of W3 wedge sam-
ples of Heats A and B, at both high and low residual REE levels after Mg-treatment, and for different in-mould in- oculation variants (Table 3). Two commonly used post- inoculants were evaluated. The analysis and addition level are shown below: • Standard
Ca-bearing, 75% FeSi • High performance TRE inoculant: (73.80%Si,
0.87%Ca. 0.83% Al) at 0.18 wt-% consumption level.
(73.52%Si,
1.02%Ca. 0.77% Al, 1.86% TRE) at 0.04 wt-% consumption level.
The above inoculants were added to the in-mould reaction chamber. Another inoculation variant consisted of adding a proprietary oxy-sulphide inoculant enhancer alloy [(OS-IE) based on a proprietary blend of CaSi, aluminum and oxy- sulphide elements].39
the reaction chamber with 75% Ca-bearing FeSi at the rate shown below: • Standard
Ca-bearing, 75% FeSi
0.87%Ca, 0.83% Al) at 0.03 wt-% consumption level,
• Inoculant Enhancer (OS-IE): (37.3%Si, 34.4% oxy-sulphide forming elements) at 0.01 wt-% con- sumption level.
The RE-bearing Ca,FeSi alloy (considered a more potent, proprietary inoculant) and the standard Ca-bearing 75% FeSi inoculant with the inoculant enhancer (added as a
70 factors of experimental Mg-treated irons. Figure 3. Pearlite (Px International Journal of Metalcasting/Volume 8, Issue 2, 2014 ) and Antinodularising (K) Thielman’s (73.80%Si,
The wedge test samples were used to evaluate the influence of the cooling rate on the percentage of free carbides and the characteristics of the graphite phase in different inoculated irons. These samples were polished to determine graphite
of anti-nodularising elements in Mg-treated irons is low enough (K < 1.0), so the rare earths role, to counteract these elements is not necessary. On the other hand, the pearlite factor Px
Metallographic analysis of chill test samples is a realistic method to evaluate the chill sensitivity of ductile irons. There is difficulty in visually separating the white, mottled areas and the free carbide areas in these irons since the white colour of the carbides is very similar to the silver colour of the carbide-free fracture. For this reason, the effects of in- oculation were also analyzed by comparing the microstruc- tures of alloys treated with varying amounts of REEs.
separate addition to the chamber) were both used at a total level of 0.04% wt-% (a reduction in total inoculant addi- tion of 77.7%).
The oxy-sulphide inoculant enhancing (OS-IE) alloy is a ferrosilicon-free inoculant alloy containing approximately 16% calcium and suitable amounts of sulphur and oxygen and other graphitizing elements. This new alloy has demonstrated remarkable abilities to reduce shrinkage, improve inocula- tion (reduced chill, elimination of carbides), improve nodule counts and nodule shape, and improve mechanical properties (elongation, impact properties, yield and tensile strength). While this alloy can be used as a solo inoculant addition, it also can be used as an inoculant enhancer. It can be added as a separate addition with standard calcium-bearing foundry fer- rosilicon (but not mixed with 75% FeSi) to yield outstanding results, equaling or exceeding results shown with a 75% FeSi based, rare earth oxy-sulphide inoculant. 28
The inoculant enhancer was added to
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