parameters on un-etched samples and then etched with Nital to determine free carbides percentages.
Cooling rate and Mg-treated iron melt conditions [lower or higher TRE content in nodularized iron, un-inoculated and inoculated irons] were found to be the most important fac- tors on carbide sensitivity. In general, an inverse relation- ship exists between the amount of free carbides and distance from the apex of the chill wedge (Figs. 4 and 5).
In the relatively high purity base iron, in terms of anti-nod- ularising trace elements (K < 0.8) and a relatively high Mg level (0.06%Mgres
TRE content after Mg-treatment in- creased the chill (carbides) tendency of un-inoculated irons as the TRE content increased. When the level of REE ex- ceeded 0.02%REEres
and 0.045-0.05%Mgres after nodulizing
treatment, free carbides presence charac- terized the entire wedge sample section, with no inoculation and with a visible end effect. As expected, inoculation de- creased carbide-forming tendency. This was very evident at distances of more than 20 mm/0.79in from the apex, cor- responding to more than 10mm/0.39in wall thickness casting, respectively.
For this good quality base iron, the rare earths addition from the Ca,REE-FeSi alloy for a Mg,REE-FeSi treated iron appears to be unnecessary, or even un- acceptable, due to the risk of increased chill tendency, inclusively for less than 0.01%REEres content in Mg-treated irons. Supplementary additions of rare earth in Ca-FeSi alloy do not appear to improve its inoculation power indepen- dently of residual rare earth content as a nodulizing treatment contribution. With- out the role to neutralize the anti-nodula- rising elements in these irons, rare earths addition could become excessive.
(a)
after Mg-treatment in castings) the
Ca-FeSi inoculated irons, at a normal addition level of in- oculant for an in-mould treatment technique (0.18 wt-% al- loy), are noticeably less sensitive to chill formation, for both rare earth contents in the iron than without inoculation, but at lower inoculation capacity in higher TRE content irons in these experimental conditions (Heat A). The role of Ca- bearing FeSi alloy as a universal inoculant in ductile irons was shown.
ficient to obtain a low chill tendency with a conventional in-
It was also found that a low level of rare earths (0.005 - 0.01%TREres
) in a relatively pure ductile iron (K < 0.8) is suf-
Figure 4. Macrostructure of W3
wedge samples [ASTM A367] at different total
rare earth (TRE) contribution of nodulizing treatment and applied in-mould inoculation.
(b)
ductile irons [a - Heat A; b - Heat B] [UI – uninoculated; Ca - 0.18wt-%Ca-FeSi; Ca,RE – 0.04wt-% Ca,RE-FeSi; Ca + En – 0.04wt-% [75% Ca-FeSi +25% Enhancer].
Figure 5. Influence of the distance from the apex [W3 International Journal of Metalcasting/Volume 8, Issue 2, 2014 71
wedge samples, ASTM A367] on the carbides amount, in tested
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