Brno University of Technology
Czech Foundrymen Society – CFS
International PhD Foundry Conference
3rd June 2009
THE IMPACT OF ELECTROMAGNETIC
FIELD ON THE MORPHOLOGY OF
GRAPHITE IN GREY CAST IRON
Wojciech Sebzda, Marcin Stawarz, Tomasz Wróbel, Jan Szajnar
Silesian University of Technology,Institute of Engineering
Materials and Biomaterials, Foundry Department
Casting in electromagnetic field is a very complex process, which depends on many factors among others magnetic induction
B, current density J, field frequency f, current intensity I, as well as the casted alloy type. First studies on the application of
stirring of liquid metal at the time of its solidification in order to improve the castings quality were carried out by Russ
Electroofen in 1939 and concerned the casting of non-ferrous metals and their alloys .
The forced convection of metal caused by the electromagnetic field affects the casting structure in diversified ways, i.e.
minimization of gas porosity,
minimization of gravity segregation,
increase of equiaxed crystals zone in the intersection of the ingot,
improvement of uniformity of heat abstraction (fig. 1),
increase of uniformity and intensity of cooling.
Bz=0mT 1 Bz=40mT 1
200 3 200 3
1 23 1 23
0 40 80 120 160 200 0 40 80 120 160 200
Time, s Time, s
Fig. 1. Casting process temperature change graph
a) without electromagnetic field, b) with the use of electromagnetic field 
2. Domain of study
The objective of the study was to determine the influence of electromagnetic field and the cooling rate on the changes in the
morphology of graphite in grey cast iron. The domain of study included casting samples (diameter 20 mm and height of 200
mm) from grey iron EN-GJL-200 (tab.1). The research stand (fig. 2) was equipped with a inductor enabling the stirring of
melted solidifying metal in the mould with the use of electromagnetic field.
Chemical analysis [%]
C Si Mn P S Cr Ni Mo Cu Al Ti Fe
3,890 1,920 0,350 0,372 0,054 0,433 0,020 0,074 0,057 0,101 0,017 91,700
Tab.1.Chemical analysis of the EN-GJL-200 grey cast iron
The study examined two types of rotary electromagnetic field i.e. unidirectional rotary field (WPM) and a reversion rotary field
with a pause between the change of the rotation direction (IRPM) .
Fig. 2. Research stand scheme: 1 – electromagnetic field inductor, 2 - mould,
3 - transformer, A - amperometer, MWE – multivibrator
In order to diversify the cooling rate of the liquid metal, moulds were made from material of different thermal conductivity
λ where used in the study:
graphite λ=90 [W/(mK)],
sand surrounded with resin λ=1,5 [W/(mK)],
insulation material SIBRAL SI-R30 λ=0,35 [W/(mK)].
In order to take into consideration the value of the thermal conductivity λ, the thickness of the mould wall g and the size of
the ingot r, a q factor was introduced to simplify the heat factor in the casting-mould assembly :
r ⎡m⋅ K ⎤
g ⋅λ ⎢ W ⎥
Further samples where cut out from the casting specimen at the height of 100mm from ground. The next step was to perform
a quality analysis of the influence of electromagnetic stirring of solidifying metal in the mould on graphite morphology. For
the reasons of the required abrasion resistance of the studied iron, such conditions of solidification were searched, that would
ensure obtaining the flake graphite of type IA5 according to the PN-EN ISO 945 standard .
The experiment design included following castings for every mould material type:
model (without electromagnetic field),
rotating field (intensity 10 [A]),
impulsive rotary electromagnetic field (frequency 0,5 [Hz], intensity 10[A]),
impulsive rotary electromagnetic field (frequency 1 [Hz], intensity 10[A]).
The samples were analyzed in three fields presented on the figure 3.
Fig. 3. Measurement areas scheme on the intersection of analyzed casting (with description)
The metallographic studies were carried out on the metallographic microscope Nikon OPTIPHOT. On the basis of the
metallographic analysis the graphite morphology was specified (shape and arrangement) on the grounds of .
Additionally a analysis of the temperature change in the range of pouring temperature – liqidus temperature, for every type
of mould material. This analysis allowed to determine the cooling rate of the mould materials.
3. Analysis of study results
On the basis of metallographic analysis we can notice, that the best graphite shape and distribution from the point of view of
the required criteria of grey iron structure evaluation was obtained in the mould made of sand surrounded in resin (fig. 4÷6).
The graphite morphology in this case was defined as 95%IA+5%VA. The sand surrounded in resin mould allowed to obtain
a cooling rate of 11 [°C/s].
Whereas the worst effects where acquired in the samples poured into graphite moulds, where the fast heat abstraction i.e.
about 20[°C/s], concluded hard spots in the outer ingot zone. The graphite distribution and shape in grey iron was defined as
95%IIC + 5%IC (fig. 7).
The SIBRAL mould allowed to considerably elongate the solidification time (cooling rate 2[°C/s]) what resulted in receiving
a graphite distribution and shape of 95%IA + 5%IVA (fig. 8). On the figures 9÷11 show the metallographic structures of grey
iron casted in the mould made of surrounded sand under the rotating electromagnetic field, adequately in the 1 (side of the
specimen), 2 (half radius of the specimen), 3 (center of the specimen) area of measurement.
Based on the study results, a beneficial effect of the forced convection generated by the unidirectional rotating
electromagnetic field was concluded. The use of electromagnetic stirring on the liquid metal allows to homogenize and reduce
the size of graphite flakes.
Fig. 4. Microstructure of gray cast iron EN GJL-200 Fig. 6. Microstructure of gray cast iron EN GJL-200
cast in the shell mould (II):measuring area 1 cast in the shell mould (II):measuring area 3
Microstructure of gray cast iron EN GJL-200 cast in Fig. 7. Microstructure of gray cast iron EN GJL-200
the shell mould (II):measuring area 1 cast in the graphite mould (I):measuring area 3
Fig. 8. Microstructure of gray cast iron EN GJL-200 Fig. 10. Microstructure of gray cast iron EN GJL-200
cast in the SIBRAL mould (III):measuring area 3 cast in the shell mould under WPM(V):measuring
Fig. 9. Microstructure of gray cast iron EN GJL-200 Fig. 11. Microstructure of gray cast iron EN GJL-200
cast in the shell mould under WPM(V):measuring cast in the shell mould under WPM(V):measuring
area 3 area 1
On the present stage of research, two conclusions can be presented. The main influence on receiving the required
graphite morphology has the cooling rate. The cooling rate should be on the level of about 11 [°C/s], in order to obtain such
values of the interfacial distance of the examined irregular eutectic, what will cause the value of λm being slightly higher then
the value of λ (fig. 12). The cooling rate should not be to high, because as shown in the study casting into graphite moulds
caused a very high cooling rate of about 20[°C/s] what concluded in receiving short irregularly distributed graphite flakes.
Additionally the ingot casted into graphite mould revealed hard spots. In the case of SIBRAL mould the effect was to big and
concluded in receiving a large difference between the values of λm and λ (λm >> λ), what caused forming of long graphite
flakes (fig. 8).
The analysis of the study results allowed to conclude that the speed of solidification should oscillate around the value
obtained in the surrounded sand mould. It was found that the forming of graphite in the structure of grey cast iron can be put
into practice with the use of electromagnetic field, however it is only possible at the required thermal conditions in the
arrangement casting – mould.
Fig.12. Scheme of the Fe-Cgr irregular eutectic microstructure and liquid with the characteristic distances: λm – distance after
which the wall phase starts branching, λ - distance typical for a regular eutectic after which the wall phase stops growing .
Scientific work financed from the resources on science in years 2008 – 2009 as a research project N R07 0002 04.
 Asai S.: Recent development and prospect of electromagnetic processing of materials, Science and Technology of
Advanced Materials, 1, 2000, s. 191 – 196.
 Ren Z., Dong H., Dent K., Jiang G.: Infuence of High Frequency Electromagnetic Field on the Initial Solidification
during Electromagnetic Continuous Casting, ISIJ International, Vol. 41(2001), No. 9, pp.981-985.
 Polish Standard PN-EN ISO 945: Cast Iron – characteristics of graphite. (in Polish)
 Podrzucki C.: Grey Iron vol.2. ZG STOP, Kraków 1991 (in Polish).
 Stawarz M., Szajnar J.: Electromagnetic stirring influence on graphite morphology of gray cast iron Archives of
Foundry, No. 22 , vol. 6, 2006, 463.
 Li Qiushu, Liu Liqiang, Li Renxing, Hou Xu, Zhai Qijie: Effect of pulse magnetic field on graphite morphology and
solidification of gray cast iron PROCEEDINGS vol.1, 66th World Foundry Congress Istanbul 2004. pp. 147-156.
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