Journal of Mine ra ls & Materials Characteri za ti o n & Engineering, V ol. 10, No.3, pp. 257-266, 2011
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257
Effect of Silicon Content and Shake-Out Time on Hardness and Grain Size
Properties of GL 250 Cast Iron
P. Atanda 1, G. Oluwadare 2 and O. Oluwole *3
1Materials Science and Engineering Dept.,Obafemi Awolowo University, Nigeria
2Industrial Chemistry Department,Bells University, Nigeria.
3Mechanical Engineering Dpartment,University of Ibadan, Nigeria
*Corresponding Author:
ABSTRACT
The properties of cast iron grade GL 250 are dependent on the microstructures developed during
casting. These microstructures are in turn dependent on the composition of the alloy, type of
mould and other numerous casting practice variables such as shake-out time, pouring
temperature, mould ambient conditions and inoculating technique.
In this work, the effect of silicon content and shake-out time on the grain size (GS) and hardness
properties of GL 250 cast iron was studied using a pouring temperature of 14000C and sand
mould casting. Using charge materials consisting of pig iron and other additives, GL 250
castings containing silicon contents of 1.7, 2.1 and 2.7% were casted using a constant pouring
temperature of 14000C, molding sand of specified properties and ambient mould temperature of
320C.
Results showed that type A flake type was obtained at 30mins shakeout time for all samples for
the C.I composition under study. Increasing shake-out time decreased hardness and increased
carbide grain size. Increasing silicon content was observed to increase grain size and reduce
free graphite but with resultant decrease in hardness. Two mathematical relationships were
derived. One related grain-size to silicon content and shakeout time while the second related
Brinnel Hardness to Silicon content and shake-out time. They are: Grain Size=0.40
Si+0.17Shake-out Time-0.15 and BHN=-60.53Si-7.15Shake-out Time+329.35 at 14000C pouring
temperature in a molding sand of specified properties and sand mould ambient temperature of
320C.
Keywords: Shake-out time; Silicon content; Hardness; Grain-Size; GL 250 C.I

258 P. Atanda, G. Oluwadare and O. Oluwole Vol.10, No.3
1. INTRODUCTION
Cast irons are widely used today in every sphere of life. Cast iron is an iron alloy characterized
by its relatively high carbon content (usually 2% to 4%).When molten cast iron solidifies some
of the carbon pr ecipi tates as gr aphite, f or ming tiny , irregular flak es with in the crystal stru cture of
the metal (Walton,1958). While the graphite enhances the desirable properties of cast iron, the
flakes disrupt the crystal structure and precipitate cracks, leading to cast iron's characteristic
brittleness. White cast iron, gray cast iron and ductile iron are still massively in use today. In
nodular cast iron the disadvantage opened up by free flakes in the cast matrix have been
overcome, the free flakes having been nodularized with magnesium, or cerium and recent
developments show that cheaper nodularization could be made with a combination of
magnesium and calcium [1,2]. Gray iron is the most widely used, with annual production several
times total of all other cast metals. It has excellent machinability, good wear resistance, and high
vibration absorption [3]. Gray iron is valued particularly for its ability to be cast into complex
shapes at relatively low cost. Thus, its application includes: sanitary wares, household
appliances, rolling mill and general machinery parts, ingot moulds, cylinder blocks and heads for
I.C. engines, frames for electric motors, machine tool structures, etc. [4]GL 250 grade of cast
iron (or ASTM A-247 or DIN 1671) is a grade of grey iron with type A4-A7 graphite flakes
having uniform distribution and apparent random orientation [5]. Mould material, inoculation,
and shake-out time are some of the casting variables that affect the grain size of the as cast
product. This work focused on the effect of shake-out time on hardness and grain size properties
of GL 250 cast iron.
2. MATERIALS AND METHODS
2.1 Materials
2.1.1 Charge composition for GL 250 cast iron
The GL 250 Cast iron was cast from starting materials with composition as shown below in
Table 1.
Melting was done using a coreless induction furnace of 250kg capacity and power rating of
250kw/1000Hz. After melting the spectrometric analysis of the melt was obtained and is
presented in Table 2.
2.1.2 Innoculant
Ferrosilicon was used as innoculant; introduced into the melt just before tapping of the liquid
metal. 100g innoculant was used for every 250kg ladle.

Vol.10, No.3 Effect of Silicon Content and Shake-Out Time 259
259
Table 1: Material Charge Composition
Material Composition
C Si Mn P S Cu Sn
Pig iron 4.0 2.2 0.8 0.9 0.8 - -
Cropped Ends
From rolling
mill
0.23 0.2 0.5 - - 0.3 -
Foundry
Returns 2.9 2.9 0.9 - - 0.3 0.04
Carburizer 99.3 0.1 - - - - -
Ferrosilicon 0.1 75.0 - - - - -
Ferro-
manganese 0.1 - 75.0 - - - -
Copper - - - - - 99.1 -
Tin - - - - - - 99.1
Table 2: Spectrometric Analysis of As-Cast GL250 Cast Iron
Composition
C Si Mn P S Cu Sn
3.3 2.1 0.68 0.09 0.09 0.25 0.05
2.1.3 Moulding sand
Moulding sand used comprised of Nigerian moulding sand mixtures ( 70% Igbokoda and 30%
Basita sands). The moulding sand was subjected to standard tests: Sand finess number (AFS),
Permeability, Mould Strength, Moisture Content, Clay Content, Shatter Index and Sand Strength
Tests. The results are presented in Table 3 .
2.2 Method
2.2.1 Casting
Five sand moulds of auto flywheels were made using a Peugeot 504 auto flywheel, giving the
flywheel some rapping for ease of removal from the moulds. The charge materials were then
input into a 250kg capacity coreless induction furnace for melting. Just before tapping,
ferrosilicon was added as innoculant. Innoculation is believed to have important effect on the
formation of graphite nuclei during solidification, thus influencing the resulting structure and

260 P. Atanda, G. Oluwadare and O. Oluwole Vol.10, No.3
strength of casting[4,6]. The metal was poured into the five moulds and left for 12 mins, 30
mins, 1hr, 5hrs and 10hrs before shake-out. This procedure was repeated for melts having silicon
contents of 1.7%, and 2.7%. Pouring temperature was fixed at 14000C. Specimens from the
castings were then prepared for microstructureobservation.
Table 3: Results of Tests on Moulding Sand
AFS
Permeab
ility
Mould
Strength
(N/m2)
Moisture
Content
(%)
Clay
Content
Shatter
Index
Sand Strength (KN/m2)
Green
comp Green Shear Dry
Comp
Dry
Shear
62 125 80 3.0 1.5 85 112 38 660 370
2.2.2 Metallographic examination
Specimens were prepared for metallographic examination by using standard grinding and
polishing methods [7-12]. Polished and etched samples were observed under an optical
microscope with camera attachment at X100 magnification to assess the microstructure
developed in the casting with varying shake-out times; the type of carbides and graphite flakes
formed and the grain size of the carbides.
Photomicrographs of the observed microstructures were taken. The linear intercept method for
grain size measurement was employed. Flake type was obtained using AFA and ASTM graphite
flakes classification [13].
2.2.3 Hardness measurement
Brinnel hardness tests were carried out on samples of the castings.
3. RESULTS AND DISCUSSION
3.1 Results
Optical micrographs of Cast Iron containing 1.7% , 2.1% and 2.7% Si for shake-out times of 12
mins, 30 mins, 1hr, 5 and 10 hrs are presented in Figure1. It was observed that there was less free
graphite with increasing silicon content. Grain size was observed to increase as well with
increasing silicon content.

Vol.10, No.3 Effect of Silicon Content and Shake-Out Time 261
261
A(Type B graphite)
F(Type A graphite) K(Type B graphite)
B(Type A graphite)
G(Type A graphite)
L(Type A graphite)
C(Type D graphite)
H(Type C graphite)
M(Type C graphite)
D(Type D graphite)
I(Type C graphite)
N(Type C graphite)
E(Type E graphite) J(Type E graphite)
O(Type D graphite)
Fig.1: Optical micrographs of GL 250 cast in sand mould. Pouring Temperature-14000C X100
A-E-Cast Iron containing1.7% Si. (A=12mins,B=30mins,C=1hr,D=5hrs,E=10hrs)
F-J-Cast iron containing 2.1%Si (F=12,G=30mins,H=1hr,I=5hrs,J=10hrs)
K-O -Cast iron containing 2.7%Si (K=12,L=30mins,M=1hr,N=5hrs,O=10hrs)

262 P. Atanda, G. Oluwadare and O. Oluwole Vol.10, No.3
Figures 2 and 3 present the plots of shake-out time on grain size and hardness respectively with
varying silicon content of the cast iron. It was observed that grain size increased with increasing
shake-out time. Hardness decreased with in c r e a sing shake-out time. Increasing silicon content of
the cast iron was observed to increase grain size of carbide while decreasing hardness. The
values of variation of grain size and hardness with shake-out time for 1.7%, 2.1% and 2.7% Si
content Cast iron are presented in Tables 4-6 respectively.
Fig.2: Plot of effect of shake-out time on grain size
Fig.3:Plot of effect of shake-out time on hardness
Table 4: Effect of Shake-out Time on Hardness and Grain-size for Casting with 1.7 Wt% Si
Content
Shake-out Time
(Hrs) Grain-size(mm) BHN
0.2 0.20 268
0.5 0.45 220
1.0 1.05 196
5.0 1.66 178
10.0 2.14 152

Vol.10, No.3 Effect of Silicon Content and Shake-Out Time 263
263
Table 5: Effect of Shake-out Time on Hardness and Grain-size for Casting with 2.1 Wt% Si
Content
Shake-out Time
(Hrs) Grain-size(mm)BHN
0.2 0.30 211
0.5 0.66 190
1.0 1.23 183
5.0 1.81 161
10.0 2.22 145
Table 6: Effect of Shake-out Time on Hardness and Grain-size for Casting with 2.7 Wt% Si
Content
Shake-out Time
(Hrs) Grain-size(mm)BHN
0.2 0.56 190
0.5 1.00 168
1.0 1.48 135
5.0 2.01 112
10.0 2.43 106
3.2 Discussion
3.2.1 Variation of grain-size with shake-out time
Observations from Figs.1 and 2 showed that the finest microstructures are obtained in short
shake-out time [14,15]. For the different values of silicon addition to melt, it was observed that at
30mins shake-out time, type A flakes were obtained for all the materials. At all the other
shakeout times, flake types were of other grades than A. As shakeout time progressively
increased for the varying percentages of silicon addition, grain size increased and consequently
the pearlite-ferrite distribution (Figs. 1B-E, G-J and L-O). Therefore choice of appropriate
shake-out time is critical in developing the right microstructure for different applications to
which GL 250 Cast Iron is made use. For example, auto brake-drum applications requiring type
A graphite must have controlled shake-out time. Gray iron composition must be strictly
controlled for different applications desired. For example the brake drum needs a Nickel addition
of about 1.25% and chromium of 0.5% [13].
3.2.2 Variation of grain-size with silicon content

264 P. Atanda, G. Oluwadare and O. Oluwole Vol.10, No.3
Grain size was observed to increase with increasing silicon content of melt. Grain size in Fig. 1B
was smaller than Fig.1G which was also smaller than Fig.1 L . The same was observed in Figs.
1 C, H and M. Grain size of 1 D< 1I<1N and Grain size of 1E<1J<1O. These are also observed
in Fig.2.
3.2.3 Variation of hardness with shake-out time
The hardness property of the casting was observed to follow an inverse relationship with increase
in shake-out time (Fig.3). With increasing silicon content of casting, hardness was observed to
decrease as well (Fig. 3)
3.2.4 Variation of hardness with shake-out time and silicon content
From Tables 4, 5 and 6 it was observed that increase in grain-size led to a decrease in hardness of
the casting for all the values of silicon content used in the casting. It was also observed that
hardness decreased with increasing silicon content of the cast iron.
3.2.5 Derivation of equation relating shake-out time to silicon content, grain-size and
hardness properties of GL 250 cast iron using moulding sand and pouring temperature of
14000C.
The parameters varied; shake-out time and silicon content and the measured properties; grain
size and hardness were linked up with shake-out time in two predictive equations by using
multiple regression analysis. Microsoft excel was used in the regression analysis. Placing Grain-
size and Brinnel Hardness as unknowns, with two known values-silicon content, and shake-out
time two equations were obtained as given:
Grain Size=0.40 Si+0.17Shake-out Time-0.15
BHN=-60.53Si-7.15Shake-out Time+329.35
With these equations, shake-out time could be determined with preset Grain size or Brinnel
Hardness. Combining both equations give:
Shake-outTime=6.85Grain-size-0.017Si+0.045BHN-13.19
4. CONCLUSION
In this work, the effect of silicon content and shake-out time on the grain size(GS) and hardness
properties of GL 250 cast iron was studied.

Vol.10, No.3 Effect of Silicon Content and Shake-Out Time 265
265
The results showed that increasing shake-out time decreased hardness and increased carbide
grain size. Increasing silicon content was observed to increase grain size and reduce free graphite
but with resultant decrease in hardness. Thus, grain size of carbide and hardness are both
dependent on silicon content of the melt. Therefore, a particular shake-out time and silicon
content can be chosen that will give desired carbide grain size and hardness for specified
application material. However, graphite flake type A was obtained at 30 mins shakeout time for
all samples. Two mathematical relationships were derived. One related grain-size to silicon
content and shakeout time while the second related Brinnel Hardness to Silicon content and
shake-out time at a pouring temperature of 14000C using moulding sand of specified properties.
They are:
Grain Size=0.40 Si+0.17Shake-out Time-0.15 and BHN=-60.53Si-7.15Shake-out Time+329.35
Shake-out time can be predicted using this equation if the specified pouring temperature and
moulding sand properties are adhered to. Otherwise, any change in mould propertries will affect
cooling rate, hence carbide grain-size. It is necessary for foundries to determine applicable
relationship for their operating conditions. Combining both equations give: Shake-
outTime=6.85Grain-size-0.017Si+0.045BHN-13.19
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