Effect of Ca and Ba Containing Ferrosilicon Inoculants on Microstructure and Tensile Properties of IS-210, and IS-1862 Cast Irons.

Abstract

Microstructural modification of cast iron alloys by inoculation is a well-known practice to improve their mechanical properties. In foundries, several inoculants have been used to refine grain structure, and to obtain uniform distribution of graphite flakes. Inoculation is one of the most critical steps in cast iron production. The effectiveness of inoculants depends on melt temperature, method of addition, type of inoculants, and holding time. In this paper, the effect of Ca-based and Ba-based inoculants on microstructure and tensile properties of grey cast iron IS-210 and spheroidal graphite iron IS-1862 is reported. Results showed both Ca and Ba based inoculants were effective in obtaining uniform distribution of flaky and nodular graphite in IS-210, and IS-1862 cast irons, respectively. However, the effect of Ca and Ba based inoculants on tensile strength of both grey cast iron and spheroidal graphite iron was marginal.

Full text

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Effect of Ca and Ba Containing Ferrosilicon Inoculants
on Microstructure and Tensile Properties of IS-210,
and IS-1862 Cast Irons
Dhruv Patel1,a), P.K.Nanavati2, C.M.Chug 3
1) Department of Metallurgy Engineering, Indus University-Ahmedabad, Gujarat
2) Department of Metallurgy engineering, Government Engineering college, Gandhinagar-Gujarat
3) General Manager of Jyoti CNC Automation PVT LTD-Rajkot,Gujarat
a)Corresponding author: dhruv7654@gmail.com
Abstract
Microstructural modification of cast iron alloys by
inoculation is a well-known practice to improve their
mechanical properties. In foundries, several inoculants have
been used to refine grain structure, and to obtain uniform
distribution of graphite flakes. Inoculation is one of the most
critical steps in cast iron production. The effectiveness of
inoculants depends on melt temperature, method of
addition, type of inoculants, and holding time. In this paper,
the effect of Ca-based and Ba-based inoculants on
microstructure and tensile properties of grey cast iron IS-
210 and spheroidal graphite iron IS-1862 is reported.
Results showed both Ca and Ba based inoculants were
effective in obtaining uniform distribution of flaky and
nodular graphite in IS-210, and IS-1862 cast irons,
respectively. However, the effect of Ca and Ba based
inoculants on tensile strength of both grey cast iron and
spheroidal graphite iron was marginal.
Key Words: Inoculation treatment, Grey cast iron, Spheroidal
graphite cast ion
1. INTRODUCTION
Cast iron is widely used as housing material in
manufacturing industries. The inoculation phenomenon in
cast iron was discovered in 1920 and patented by Meeh in
1924. During inoculation, elements such as Ba, Ca and Sr in
ferrosilicon are usually introduced to molten cast iron in a
ladle or in the stream of melt during pouring from the
furnace [1]. Ferrosilicon containing these elements is
regarded as a complex inoculant. The purpose of this study
was to evaluate the effectiveness of inoculation and to
discuss the inoculation mechanism in cast iron.
1.1 Methods of inoculation in cast iron
Methods of introducing inoculants for microstructural
modification and their importance in foundry technology are
documented extensively in the literature. Three most widely
used methods to introduce inoculants in the melt are: A)
Ladle inoculation, B) Late inoculation, and C) Mould
inoculation. These processes are summarized in Figure 1
and described below.
A. Ladle inoculation
Ladle inoculation is a common method of treating gray cast
iron. In this method, inoculants are added to the metal
stream as it flows from the transfer ladle into the pouring
ladle. The amount of inoculant needed in this treatment
varies between 0.15 and 0.4 wt.%, depending on the
potency of the inoculant. However, when graphite inoculant
is used then its amount is limited to about 0.1 to 0.2 wt. %.
The selected grade of inoculant for ladle inoculation is
added to the metal stream when tapping from furnace to
ladle, or ladle to ladle [5]. Following are guiding rules for
the use of inoculation:

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inoculate,
or a given cast iron, thinner section of a casting requires
greater amount of inoculation and vice-versa.
inoculant.
B. Late inoculation
Particular difficulties arise with the use of automatic
pouring furnaces where conventional ladle inoculation is not
possible. So in this case, the late stream inoculation
treatment is followed. Two types of late inoculation
treatments are practiced in the foundry. These are: a) Stream
inoculation, and b) Mould inoculation.
In stream inoculation process, the inoculant is added to the
stream of metal flowing from the pouring ladle into the
mould. It consists of two units: 1) A control unit, 2) A
dispensing unit linked together by a special cable and air
line assembly. The working principle of stream inoculation
process is shown in Fig. 2.
Fig.1: Various inoculation techniques practiced in grey and SG cast iron foundries
Fig. 2: (a) Schematic showing the principle of stream inoculation and (b) live image of stream inoculation.
B. Mould inoculation
In mould inoculation process, powdered inoculants are
placed either in the pouring bush; or at the bottom of the
sprue. Inoculants added in casting mould are generally in
the form of pieces or grains [2]. The schematic of mould
inoculation process is shown in Fig. 3.
Fig. 3: Principle of mould inoculation process.
Inoculant (POWDER form)

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Inoculation causes significant improvement in mechanical
properties due to microstructural changes in cast iron [2].
However, cost of some of these inoculants is high and there
is a demand in cast iron foundries to use low cost inoculants
with reduced fading effect. The fading effect of inoculants
depends on the mechanism of inoculation.
1.2 Mechanism of inoculation in cast iron
Inoculation is a way of controlling the microstructure and
properties of cast iron by minimizing undercooling and
increasing the number of graphite nucleation events during
solidification. Inoculants are added to molten cast iron (both
grey and SG cast irons) prior to casting, which provide
heterogeneous sites for nucleation of graphite instead of iron
carbide (cementite, Fe3C) during subsequent solidification
stage. The primary objective of nucleation is to prevent melt
undercooling to temperatures below the metastable eutectic,
where iron carbide phase is formed. The cast iron
solidification mechanism is prone to form chilled iron
structures when inoculation is inadequate. The effect of
inoculants on microstructure fades with time and hence it is
very important to precisely control the holding time between
inoculation and casting in sand mould. Both short and long
holding times between inoculation and casting adversely
affect the size and size distribution of graphite in casting.
Traditionally, inoculants have been based on graphite,
ferrosilicon or calcium silicide. The most popular inoculant
today is ferrosilicon containing small quantities of elements
such as Al, Ba, Ca, Sr and Zr.
1.3 Inoculation of ductile & grey cast iron
The primary objective of inoculation is to achieve a good
combination of mechanical properties and optimum
machinability. This is achieved by:
1) Control of graphite structure
2) Elimination or reduction of chill/carbide
3) Reduction of casting section sensitivity
Inoculation of grey cast iron
The effect of inoculation is to facilitate graphite formation
during the solidification via eutectic transformation. This is
achieved by decreasing the undercooling required for the
formation of cementite. In other words, inoculation provides
a way to avoid chilling effect in casting.
Inoculation changes the structure of cast iron by altering the
solidification process. Fe-C phase diagram is shown in Fig.
4. A look at the phase diagram and cooling curve during
solidification of a hypoeutectic grey cast iron, that is, iron
with a carbon equivalent below 4.3% helps in understanding
the effect of inoculation (Figs.5-9). The first metallic phase
to solidify in hypoeutectic grey cast iron is primary
austenite. As cooling continues, the remaining austenitic
phase grows and the melt gets enriched with dissolved
carbon. Eventually, this liquid reaches the eutectic
composition of 4.3% carbon equivalent, at which eutectic
solidification takes place under equilibrium conditions.
Equilibrium solidification does not occur under most
foundry conditions because of variations in chemistry,
pouring temperature, solidification rate, and casting
thickness. Consequently, the cast iron cools below the
eutectic temperature before the start of final solidification. If
the undercooling is slight, random graphite flakes form
uniformly in the iron matrix. This is known as Type A
graphite. As the undercooling increases, the graphite will
branch out, thus forming abnormal patterns. This is known
as Type B graphite. The rosette flake structure (type B) is
characterized by a pronounced radial growth pattern, with
the individual cell structures readily apparent. Ferrite is
often present in the center of the cells. Type B graphite is
encouraged by rapid solidification, as in thin sections, and
absence of inoculation of the metal.
Fig. 4: Iron Carbon equilibrium diagram[3].
The type C graphite (Kish graphite) is normally found in
hypereutectic irons, characterized by coarse plates in heavy
sections and star shapes or clusters in light sections. The
undercooled graphite structure (type D) is characterized by a
fine graphite pattern sharply delineating the primary
dendrites. Type D graphite is promoted by rapid
solidification in thin sections, absence of inoculation, low
sulphur content, high superheating temperatures, prolonged
holding times and high titanium content [4].Type E occurs
in low carbon cast irons. Graphite flakes have preferred
orientation and appear in a quasi-regular pattern. Different
types of graphite structure in grey cast iron are shown in
Fig. 10.

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Inoculation of spheroidal cast iron
The effect of inoculant in on the SG iron is improve the
nodule size and also improve the number of nodular,
increase some ferrite content. Show in fig.11
1.4 Fading effect of various inoculants
Inoculants lose their ability to reduce chill and nucleate
graphite if the metal is held for extended period before
casting. The fading characteristics of inoculation depend on
the type of inoculants. For example, Barium containing
inoculant produces a high initial number of nucleation sites
as compared to other inoculants, and consequently, it
maintains a high nucleation rate throughout the holding
period. Thus Ba containing inoculant offers an excellent
potential to be a very effective inoculant for ladle
treatments. Ba-containing inoculants are effective chill
reducers for both low and high sulphur grey irons as well as
ductile irons [4].
Fig. 5: Carbon equivalent diagram [3] Fig. 6: Eutectic transformations [3]
Fig. 7: Cooling curve [3] Fig. 8: Cooling curve-chill [3]
Fig. 9: Role of inoculation in grey cast iron and ductile (SG) cast iron.

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2. EXPERIMENTAL WORK
2.1 Grey cast iron
Sand mould bars were cast from FG260 grade of IS-210
grey cast iron. The chemical composition of the alloy (with
Ca-based and Ba-based inoculants) is shown in Table 1.
Casting process parameters for each experiment are shown
in Table 2. Sand mould test bars were cast with Ca-based
and Ba-based inoculants and without any inoculants. The
inoculant was added to the melt via ladle inoculation
treatment.
Tensile test bar of 1” gauge length was machined from the
casting and room temperature tensile test was performed at
0.1inch/minute strain rate per ASTM E8 standard. Brinell
hardness was measured on various samples per ASTM E10
TYPE A
Random flake graphite
In a uniform distribution
TYPE B
Rosette flake graphite
TYPE C
Kish graphite
(Hyper-eutectic compositions)
TYPE D Undercooled
Flake graphite
TYPE E Interdendritic
Flake graphite (Hypo-eutectic
compositions)
Optimum nodule shape
Improve nodule count
Increase Ferrite content
Fig. 10: Graphite distribution in grey cast iron [6]
Fig. 11: Graphite distribution in SG cast iron [3]

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Metallographic samples were prepared following standard
procedure consisting of mounting, grinding on different
grits of emery paper, polishing per ASTM E3 standard
specification. Samples were etched with 4% Nital for
estimation of pearlite.
Table 1: Chemical composition of grey cast iron
produced using Ca-based inoculants.
Sample
Result (Wt%)
C
Si
Mn
Mg
P
S
Mo
Cequivalent
GI-2
3.35
1.77
0.06
0.07
0.04
0.016
0.004
3.95
GI-3
3.47
1.01
0.87
0.07
0.194
0.053
0.107
3.87
GI-2: Ca-based inoculation
GI-3: Ba-based inoculation
Table 2: Casting process parameters for grey cast iron.
Experimental
number
Types of
inoculant
Temperature °c
Tapping
temp.
Pouring
temp.
GI-1
-
1450
1440
GI-2
Ca-based
inoculant
1450
1430
GI-3
Ba-based
inoculant
1450
1420
2.2 Ductile cast iron
Ductile iron casting was prepared from SG600/3 grade of
IS-1860. Chemical composition of SG cast iron is shown in
Table 3. Ductile iron casting was produced with Ba-based
inoculation and without inoculation. The inoculant was
added to the melt following mould inoculation treatment.
The casting process parameters are shown in Table 4.
Table 3: Chemical composition of SG cast iron produced
without inoculation and with Ba-based inoculant.
Sample
Result (Wt%)
C
Si
Mn
Mg
P
S
Mo
Cequivalent
SG-1
3.39
1.77
0.06
0.07
0.039
0.013
0.108
3.99
SG-2
3.58
2.35
0.43
0.05
0.034
0.022
0.003
4.37
SG-1: Without inoculation
SG-2: With Ca-based inoculation
Table 4: Casting process parameters for SG cast iron.
Experimental
number
Types of
inoculant
Temperature °c
Tapping
temp.
Pouring
temp.
SG-1
-
1510
1440
SG-2
Ba-based
inoculant
1510
1430
3. RESULTS AND DISCUSSION
3.1 Grey cast iron
Effect of inoculants on microstructure
Microstructure of samples from sample #GI-1, GI-2, and
GI-3 predominantly consisted of flaky graphite of Type I.
There was no noticeable difference in size, size distribution
and relation orientation of graphite in all three samples.
Therefore, it is concluded that both Ca and Ba based
inoculants had negligible effect on nucleation and growth of
graphite in grey cast iron. Microstructural examination
showed that the amount of ferrite formed in grey cast iron
without inoculation was greater than those formed due to
Ba-based and Ca-based inoculation (See Figs. 12-14).
Moreover in the cost factors Ca-based inoculants was very
higher amount of price compare to Ba-based inoculant.
Further, the amount of ferrite grey cast iron produced using
Ca-based inoculant was marginally greater than those
produced by Ba-based inoculants.
(a) (b)
Fig. 12: Microstructure of grey cast iron (FG260 grade)
without inoculant - a)etched sample and b)unetched
sample
(a) (b)
Fig. 13: Microstructure of grey cast iron (FG260 grade)
with Ca-based inoculant - a)etched sample and
b)unetched sample
(a) (b)

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Fig. 14: Microstructure of grey cast iron (FG260 grade)
with Ba-based inoculant - a)etched sample and
b)unetched sample
Table 5: Amount of ferrite and pearlite in grey cast iron
Sample ID
Amount of
Pearlite (%)
Amount of
Ferrite (%)
GI-1
92.19
7.81
GI-2
98.10
1.89
GI-3
98.28
1.72
Effect of inoculants on tensile and hardness
Inoculation had significant effect on tensile strength. Tensile
strength of grey without inoculation was lower than those
produced using Ca and Ba-based inoculants (See Fig. 14).
Further, Ba-based inoculants resulted in greater tensile
strength vis-à-vis Ca-based inoculant. This could be due to
the difference in chemical composition between two
materials. The grey cast iron produced using Ba-based
inoculants had higher carbon equivalent as compared to
those produced with Ca based inoculant. Tensile strength of
grey cast increases with the increase in carbon equivalent.
Hardness of grey cast iron without inoculation is lower than
those with inoculation. Further, hardness of sample #GI-3 is
greater than GI-2. This is due to higher carbon equivalent in
the latter (i.e. GI-3) as compared to the former (i.e. GI-2).
Fig. 14: Tensile strength of grey cast iron (a) without
inoculation, (b) with Ca-based inoculants, and (c) with
Ba-based inoculants.
Table -5: Hardness of grey cast iron without and with
inoculation.
Types of inoculant
Hardness (BHN)
Without inoculant
180
Ca-based inoculant
190
Ba-base inoculant
210
3.2 SG cast iron
Effect of inoculants on microstructure
Microstructural examination showed that the amount of
pearlite in SG600 cast iron (20.72%) without inoculation
was much lower as compared to those with Ba-based
inoculation (85.94%) and conversely, the amount ferrite in
sample SG-1 was (79.28%) much higher than those in
sample SG-2 (14.06%) (See Figs. 15-16. The effect of
inoculation on graphite size was significant. In general, Ba-
based inoculants resulted in refinement of graphite nodule
as compared to those without inoculation. Amount of ferrite
and pearlite in SG600 ductile cast iron is shown in Table 6.
(a) (b)
Fig. 15: Microstructure of grey cast iron SG600 cast iron
without inoculant - a)etched sample b)unetched sample.
Fig. 16: Microstructure of grey cast iron SG600 cast iron
with Ba-based inoculant - a)etched sample b)unetched
sample.
Table 6: Amount of ferrite and pearlite in SG600 cast
iron
Sample ID
Amount of
Pearlite (%)
Amount of
Ferrite (%)
SG-1
20.72
79.28
SG-2
85.94
14.06
Effect of inoculation on tensile properties and hardness
Tensile properties and hardness values of SG600 ductile
cast iron are shown in Table 7. The effect of Ba-based
inoculant on ultimate tensile strength was marginal;
however, it results in significant reduction in yield strength
and marginal decrease in elongation in SG-2 as compared to
SG-1. The decrease in yield strength and elongation in SG-2
vis-à-vis SG-1 is attributed to higher amount of pearlite in
the the former (i.e. SG-2) than in the latter (i.e. SG-1).

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Table 7: Tensile Properties and Hardness of SG cast
iron
Sample
ID
(UTS,
N/mm2)
YS at
0.2%
offset
(N/mm2)
Elongation
(%)
Hardness
(BHN)
SG-1
674.36
587.61
7.41
195
SG-2
689
489
6.38
263
UTS: Ultimate tensile strength
YS: Yield strength
Conclusion:-
The following main conclusions can be given from the
present investigation:
In this work the effect of inoculant on the grain size and
mechanical properties of FG 260 and SG600/3.
The result showed that increasing the ferrite content on grey
cast iron and increasing the pearlite content on ductile cast
iron. Moreover grain size would be increase.
Thus, hardness, tensile and elongation are depend on this
grain size. The new inoculant has proven successful in
improving casting performance and properties.
ACKNOWLEDGEMENT
The author is grateful to Mr. C.M. Chug, General Manager
at JYOTI CNC AUTOMATION, Rajkot, for his help and
support.
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