oculation using a Ca-FeSi alloy.38 prietary inoculating enhancer39
In these irons, using the pro- increased the Ca-bearing FeSi
alloy inoculation efficiency, as the Ca-FeSi + Enhancer inocu- lation variant led to the lowest chill sensitiveness, compared to Ca-FeSi variant, but with a 77.7% lower alloy consumption in the reaction chamber. This combination of additions (at a 0.04 wt-% alloy addition), 0.03% Ca-FeSi + 0.01% OS-IE was more effective than in the REE-bearing Ca-FeSi inoculation.
It is presumed that adopting a late addition of TRE, via in- oculation, in place of adding TRE elements with Mg in a MgFeSi alloy could change the target values for these ele- ments: The TRE content should be a fraction of that in a conventional nodulizing treatment in order to avoid the risk of promoting carbides due to excessive TRE content.
As Figure 4 shows, it appears that the tested ductile irons are also differentiated by the sensitiveness to form the spe- cific porous area, located in the thermal centre of the wedge samples, which is typical for the ductile iron solidification pattern. Generally, for the same base chemical composition, including residual magnesium, and residuals content (Table 3), the different levels of residual rare earth elements led to different porous area size it is at higher values for Heat A samples (0.023-0.024wt-%REEres ples (0.0056-0.0064wt-%REEres
) compared to Heat B sam- ). The smallest porous area
size appears to characterize the Ca-FeSi + OS-IE Enhancer inoculation, which was Heat B with the lowest residual con- tent of rare earth elements.
Figure 6 illustrates several selected graphite phase parameters, and Figure 7 the graphite aspect in the analyzed wedge samples, on the centerline area and at different distance from the apex, for inoculation variants shown macro-structurally in Figure 4.
The structure variation on the centerline direction from the apex up to the base of wedge sample was evaluated in three points (center and 1.0 mm/0.04 in. distance left to right), for each considered distance from the apex, the averages of the structure parameters were determined.
The graphite characteristics were evaluated with Automatic Image Analysis [analySIS® FIVE Digital Imaging Solutions software], which evaluated the following parameters [5µm trap size, 100x magnification, 3 fields analyzed (minimum 500 nodules)]:
Graphite Nodularity (NG) = 100 [ΣAnodules + 0.5 x ΣAintermediates
where: ΣAnodules
] / ΣAall particles means the sum of areas of all of graphite particles
considered to be nodules. Sphericity Shape Factor (SSF) = 4πAG Roundness Shape Factor (RSF) = 4ΑG / πLG
/ PG 2 2 72 Eqn. 4 Eqn. 5 Eqn. 3
where: Anodules
is the area of particles classified as nodules;
Aintermediates Aall particles
graphite particle in question. The graphite nodules were defined by using the ISO 16112/2005 statement, that is, the nodules which have the Roundness Shape Factor RSF = 0.625 - 1.0. The intermediate particles were defined by RSF = 0.525 – 0.625.
graphite particle in question; PG ite particle in question. LG
Graphite phase characteristics are affected by: • the solidification cooling rate (higher distance from the apex of wedge castings, lower cooling rate),
• residual rare earth content (Heat A –higher content versus Heat B-lower content),
• post-treatment application (un-inoculated versus inoculated ductile irons),
• inoculant type.
B). These irons are also characterized by higher graphite nodularity and higher graphite nodule count (Fig. 6), for both un-inoculated and inoculated conditions, compared to 0.02%REEres
irons.
Graphite nodularity (Figs. 6c and 6d) and sphericity shape factor (Figs. 6e and 6f) are less affected by cooling rate in lower REE content irons, where the two considered graph- ite parameters are visible at higher levels; the difference between un-inoculated and inoculated irons is at a reduced level in these irons (see Figures 6c-6f).
The highest nodule count was recorded at the highest cool- ing rate (see Figure 6h, 1.6mm/0.06in from the apex), in low rare earth content irons (Heat B), especially in inoculated irons. At distances greater than 10 mm/0.39 in. from the apex (more than 5mm/0.02 in. wall thickness in the wedge sample), the nodule count appears to have only a limited de- pendence on the wall thickness, but is favorably influenced by inoculation.
Inoculant type has a complex influence on the graphite phase parameters. Generally, standard Ca-bearing FeSi alloys ap- pear to act as a good inoculant, for a 0.18 wt% consumption in an in-mould technique treatment, for both levels of rare earth content in the Mg-treated ductile irons.
The use of the proprietary inoculant enhancer39 signifi-
cantly increased the effectiveness of the Ca-FeSi conven- tional inoculant, as only a 0.04 wt-% alloy addition in the in-mould treatment [75%Ca-FeSi + 25% Enhancer] was
International Journal of Metalcasting/Volume 8, Issue 2, 2014
As expected, the greater the distance from the apex, larger graphite amounts were observed for all of the tested irons, and especially more for inoculated irons (Figures 6a and 6b). Generally, more graphite was observed with the lower rare earth contents after Mg-treatment (<0.01%REEres
, Heat
– area of particles classified as intermediates; – area of all graphite particles; AG
– area of the – perimeter of the graph- – maximum axis length of the
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