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Efeito da Pre Inoculação com SiC

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1" (25mm) wide plates with the following thickness: 0.039" (1 mm), 0.059" (1.5
mm), 0.079" (2 mm), and 0.118" (3 mm).
Tapping and Pouring. The liquid iron was tapped into the flow-through chamber containing FeSiMg-masteralloy and
FeSi75 inoculant and then teemed into the ladle. Average time of treatment was 31 seconds. Then treated iron was poured
into three experimental molds. Average pouring time of the first mold was approximately 4 sec.; average time of pouring all
three experimental molds was 21.5 sec.
Chemical Composition of Base and Treated (Ductile) Irons. The carbon, silicon, and carbon equivalent values, obtained
from a thermal analysis system, allowed adjusting chemical composition of base iron before tapping, if necessary.
Simultaneously with pouring, thermal analysis system sample and right after treatment, chill buttons were poured to evaluate
the chemical composition of base and treated (ductile) irons via spectrometer. The magnesium recovery (Mgr) was calculated
using the following equation [5]:
(0.76 x ∆S + Mg2) x 100 Mgr =
Mg1
, %
where:
∆S –difference between the sulfur content in the base iron and the treated metal, wt. %; Mg1 – total magnesium additions,
wt. %; Mg2 -residual magnesium content, wt. %.
The carbon equivalent (CE) was calculated using the equation [6]:
 CE = C+ 0.31Si , %
where:
C– residual carbon content, wt. %; Si– residual silicon content, wt. %.
Cooling curves of base iron obtained from the thermal analysis system used to study solidification behavior of base
irons pre-inoculated with FeSi75 or SiC.
Castability of Ductile Iron Thin Wall Plates. As soon as experimental molds were shaken out, the castability of thin wall
ductile iron plates was studied using a ruler with metric and inch scales. The distance from the ingate up to furthest end of
each solidified plate was considered as the castability/fluidity criterion.
Chill Tendency in Ductile Iron Thin Wall Plates. The thin wall plates at each level were separated from the riser and
marked according to level and experimental tree identification. The plates, taken from the middle level of each experimental
tree, were broken in the middle of the plates to study chill depth on the fractures. The chill area of each plate, usually located
at the edges of the fracture, was measured with a rule as a length of chill from the edge toward the center, and calculated in
percentage as a ratio of the chill to the whole fracture length.
Microstructure Analysis. The same plates that were taken for chill tendency evaluation were used for microstructural analysis.
Plates taken from the middle level of each experimental tree were stacked together, in sequence, according to their thickness
(from thinnest to thickest). This set of plates, representing each experimental tree, was then mounted in bakelite pre-molds,
polished and marked for identification number.
AFS Transactions 01-064 (Page 5 of 15)
The microstructure analysis was conducted utilizing both optical microscope and an imaging system. The first stage
of this evaluation was to determinate graphite morphology at magnification X200 on an unetched surface using the image
analysis system. The periphery and center of each plate were studied, evaluating the following parameters: area of graphite,
nodule count, and nodularity.
The second stage comprised of evaluation of metallic matrix at magnification X200 using optical microscope.
Before this evaluation, all mounted sets were etched for 3 seconds, using 4% Nital as an etching reagent. On this stage, the
ferrite/pearlite ratio and iron carbides percentage were evaluated at the periphery and the center of each sample.
RESULTS AND DISCUSSIONS
Residual Magnesium and Magnesium Recovery. Average values of residual magnesium and calculated magnesium
recoveries are given in Figure 5. As can be seen, the highest residual magnesium (0.039%) was obtained in heats using SiC
and standard additions of FeSiMg-master alloy, while in experimental heats using FeSi75 pre-inoculant and standard
additions of FeSiMg-masteralloy residual magnesium averaged 0.032%. Even using 11% less FeSiMg-masteralloy added
(1.6%), the iron pre-inoculated with SiC still contained 4.1% higher ( 0.033%) residual magnesium than in heats with FeSi75
and standard additions of FeSiMg-masteralloy. In heats pre-inoculated with SiC and treated with 1.4% FeSiMg-masteralloy
(reduced by 22%), residual magnesium content was 0.029%.
Magnesium recovery in experimental heats using SiC pre-inoculant and standard FeSiMg-masteralloy additions was
the highest (61.7%) over all experimental heats. When the SiC pre-inoculant and reduced additions of 1.6% and 1.4% of
FeSiMg-masteralloy were applied, the magnesium recovery observed still higher (58% for both cases) than in those heats
using FeSi75 and standard FeSiMg-masteralloy additions, where magnesium recovery was less (55.3%). Obtained data
obviously demonstrated that pre-inoculation with SiC improves magnesium recovery.
A
B
Figure 2. Core boxes (A) and cores (B) used for production of experimental molds.
AFS Transactions 01-064 (Page 6 of 15)
Figure 3. Experimental mold for pouring thin wall ductile iron plates.
Figure 4. Experimental thin wall ductile iron casting with the gating system.
AFS Transactions 01-064 (Page 7 of 15)
A
0
0.01
0.02
0.03
0.04
0.05
R
e
si
d
u
a
l M
g
, 
%
1 2 3 4
50
55
60
65
M
a
g
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e
si
u
m
 r
e
co
ve
ry
, 
%
B
1 2 3 4
Figure 5. Average residual magnesium (A) and magnesium recovery (B) in thin wall ductile iron plates pre-inoculated
with SiC and FeSi75: 1- pre-inoculated with FeSi75 and treated with standard FeSiMg (1.8% / 4.5 lb.) additions;
2- pre-inoculated with SiC and treated with standard FeSiMg (1.8% / 4.5 lb.) additions;
3- pre-inoculated with SiC and treated with reduced FeSiMg (1.6% / 4.0 lb.) additions;
4- pre-inoculated with SiC and treated with reduced FeSiMg (1.4% / 3.5 lb.) additions.
In fact, when iron was pre-inoculated with SiC, magnesium recovery was 61.7%, and 55.3% when iron was pre-inoculated
with FeSi75 with the same amount of FeSiMg-masteralloy.
Castability Evaluation. The average results of castability in thin wall ductile iron using FeSi75 and SiC, and treated with
standard and reduced additions of FeSiMg-master alloy, are shown in Figure 6. As can be seen, experimental ductile iron
plates with 0.059" (1.5mm), 0.079" (2mm), and 0.118" (3mm) thickness were completely filled in all tests. Thereby the main
emphasis of this evaluation was to evaluate castability of 0.039" (1mm) plates. Better castability was found in those heats
using SiC with both reduced FeSiMg-masteralloy additions 1.6% (4.0 lb.) and 1.4% (3.5 lb.), and also in heats using FeSi75
with standard FeSiMg-masteralloy additions 1.8% (4.5lb.). Lower castability was found in the heats using SiC pre-inoculant
with the standard additions of FeSiMg-masteralloy 1.8% (residual magnesium content was 0.039%).
Chill Tendency Evaluation. The average results of the chill depth in fracture of thin wall ductile iron plates, pre-inoculated
with FeSi75 and SiC, and treated with standard and reduced additions of FeSiMg-masteralloy are shown in Figure 7. It was
found that all 1mm plates had white fracture, which was evidence of complete chill, regardless of materials used in the
furnace, final chemistries, pouring temperatures, or amount of FeSiMg-masteralloy additions used. Similar to the castability
results, the chill depth in 1.5-mm plates (varied from 52% to 76%), 2-mm plates (varied from 40% to 48%), and 3-mm plates
(varied from 20% to 32%), was the lowest when SiC was added in the furnace with lower 1.6%, or 1.4% FeSiMg additions,
or when FeSi75 was used with the standard FeSiMg additions. Those heats, where SiC used in the furnace with the standard
1.8 % (4.5 lb.) additions of FeSiMg-masteralloy, resulted in higher residual magnesium, tended to also have higher
concentration of iron carbides: chill depth was subsequently in 1.5-mm plates-76%, in 2-mm plates-52%,