Masayuki MORISHITA, Norio TAKAHASHI, Daisuke MIYAGI, Masanori NAKANO
Okayama University
Examination of Magnetic Properties of Several Magnetic
Materials at High Temperature
Abstract. In order to accurately design magnetic devices which are used at high temperature, it is necessary to understand the behaviour of several
magnetic materials at high temperature. In this paper, the magnetic properties of several magnetic materials until Curie temperature are measured. It
is shown that the change of iron loss of rolled steel (SPCC and SS400) with the temperature is more remarkable than that of electrical steel sheet.
Streszczenie. W pracy przedstawiono właściwości magnetyczne niektórych materiałów w wysokiej temperaturze. Zmiana strat blachy walcowanej
SPCC I SS400 jest znacznie większa niż ma to miejsce w przypadku blach elektrotechnicznych. (Badania właściwości magnetycznych
niektórych materiałów magnetycznych w wysokiej temperaturze)
Keywords: high temperature, comparison of magnetic properties, iron loss, specific permeability
Słowa kluczowe: właściwości magnetyczne, straty, wysoka temperature.
Introduction
If the magnetic fields in magnetic devices, which are
used at high temperature, are analyzed using the magnetic
properties at a room temperature (RM), the obtained results
are fairly different from an actual behaviour [1, 2]. In order
to accurately design magnetic devices which are used at
high temperature, it is necessary to understand the
behaviour of several magnetic materials at high
temperature. Although the change of magnetization of
magnetic material measured using a VSM is well reported
[3], the data of magnetic properties, such as B-H curves
and iron loss curves which are indispensable to the precise
magnetic field analysis at high temperature are not familiar.
We have already reported the measurement method of
magnetic properties at high temperature until about 800C
using a ring specimen and discussed the behaviour of the
magnetic properties of electrical steel sheets [4]. However,
it seems that there is no report about the comparison of
magnetic properties of several magnetic materials.
In this paper, the magnetic properties of several
magnetic materials up to 700C are measured using ring
specimens. The measured results are compared and some
features of each magnetic material at high temperature are
discussed.
Method of Measurement
Fig.1 shows the special frame for measuring magnetic
properties of ring specimens (outer diameter: 100mm, inner
diameter: 70mm, thickness: 0.1-1.0mm) at high
temperature. The frame is made of ceramics which can be
used until more than 1000C. The ring specimens are set
inside it. The cold rolled steel sheet (SPCC, thickness:
1mm), rolled steel for general structure (SS400, thickness:
0.6mm), 6.5%Si steel (thickness: 0.1mm) and non-oriented
electrical steel sheets (35A250, thickness: 0.35mm) are
used as specimens. Each sheet of SPCC, SS400, 6.5 % Si
steel and 35A250 is set in the ceramic frame. The B coil is
wound on the frame. The B coil is a polyester copper wire
(PEW) and its diameter is 1.0mm. The exciting coil is
wound 80 turns over the B coil and its diameter is 1.5mm.
The insulation between coils is kept using a special
insulating tape which can be used until about 1000C. Fig.2
shows the ring sample for the high temperature
measurement.
Fig.3 shows the measurement system. In order to
measure the magnetic field strength in the specimen, the
magnetizing current method was used. The flux density
waveform of measured with the B coil is controlled to be
sinusoid. The exciting frequency is 50Hz.
106
Heating Method
A furnace is used for heating. The air inside the furnace
is substituted by the nitrogen gas to avoid the oxidation of a
specimen. The exciting coil and B coil are connected to
outside through the hearth terminals of the lid of furnace. A
K type thermocouple was used for the measurement of the
temperature.
Air Gap Compensation
Two kinds of setting methods of B coil, one is wound
directly on the specimens, and the other is wound on the
frame, are examined [4]. It was found that the sectional
area of the B coil cannot be determined exactly, if the B coil
is wound directly on the specimens. This is, because the
insulating tapes are set between each specimens, and also
between specimens and B coil. Then, it was decided to
wound the B coil on the frame.
The air gap between the B coil and specimen is large,
because the B coil is wound on the ceramic frame. As the B
coil detects the flux which passes through the air gap
together with the flux inside the specimen, the
compensation of the flux which passes through air gap is
made by subtracting the flux in the air gap. The
relationships between the flux density Bmea measured by the
B coil, the flux density Bspe in the specimen, the area of the
specimen Sspe, the area of air gap Sair, the measured
magnetic field strength Hmea, the flux spe in the specimen,
are given by
(1)
(2)
 spe  Bmea S spe   0 H mea S air
Bspe 
 spe
S spe
where 0 is the permeability of vacuum. Bspe is obtained by
(2). The magnetic field strength H is calculated from the
ampere-turns and the mean magnetic path length. The
specific permeability and iron loss are calculated using the
obtained Bspe and H.
Measured Results and Discussion
Magnetic properties of the ring specimens of the cold
rolled steel sheet (SPCC), rolled steel for general structure
(SS400), 6.5% Si steel and the non-oriented electrical steel
sheet (35A250) are measured up to 700C.
Figs.4 and 5 show the comparison of B-H curves and
specific permeability s. There are some differences in the
change of specific permeability s with increase of
temperature. The permeability at low flux density is
increased with temperature and that at high flux density is
PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 No 9b/2011
5
19
B [T]
decreased with temperature. The permeability at high
temperature (700C) of SPCC and SS400 becomes
maximum at about 0.6T. On the contrary, those of electrical
steels (6.5%Si steel, 35A250) become maximum at about
0.3T.
56
56
124
64
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
RT
100℃
200℃
300℃
400℃
500℃
600℃
700℃
0
1000
2000
H [A/m]
3000
4000
106
(a)SPCC
124
2
RT
(a) Ceramic frame
exciting coil
100℃
1.5
B coil
B [T]
ceramic porcelain
200℃
300℃
1
400℃
500℃
0.5
600℃
700℃
0
0
specimen
heatproof insulation tape
2000
4000
H [A/m]
6000
8000
(b)SS400
(b) Cross section
B [T]
Fig.1. Special frame for measuring magnetic properties of ring
specimens.
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
RT
100℃
200℃
300℃
400℃
500℃
600℃
700℃
0
5000
H [A/m]
10000
(c)6.5% Si steel
2
Fig.2. Ring sample for measurement at high temperature.
B [T]
attenuator
computer
IEEE-488 bus (GP-IB)
A/D
converter
(ELK-7121)
(DL-750)
Fig.3. Measurement system.
signal
amplifier
(NF P-62A)
signal
amplifier
(NF P-62A)
200℃
300℃
1
400℃
500℃
0.5
(P4-2.8G+VEE)
(BIOMATION 2202A)
clock pulse
generator
sampling
pulse
100℃
1.5
matching
(NF-4520N) transformer
power
amplifier
shunt resistor
trigger pulse
sampling pulse
(ELK-7000-D-SP) (NF-3627)
D/A
filter
converter
RT
600℃
700℃
0
0
2000
4000
H [A/m]
6000
magnetizing
winding
B coil
(d)35A250
specimen
Fig.4. Comparison of B-H curves.
PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 No 9b/2011
107
25
14000
12000
200℃
8000
6000
300℃
400℃
RT
4000
RT
0
0.5
1
B m [T]
600℃
700℃
0
0.5
1
1.5
100℃
200℃
300℃
400℃
500℃
600℃
700℃
2
B m [T]
(a)SPCC
25
5000
700℃
3000
μs
200℃
300℃
2000
RT
600℃
0
0.5
1
1.5
2
600℃
0
700℃
0
RT
60000
100℃
50000
200℃
40000
300℃
400℃
RT
20000
500℃
RT
600℃
0
0
0.5
700℃
1
B m [T]
1
1.5
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2
1.5
RT
RT
100℃
200℃
300℃
400℃
500℃
600℃
700℃
700℃
0
700℃
0.5
2
1
1.5
2
B m [T]
(c)6.5% Si steel
(c)6.5% Si steel
2.5
40000
700℃
200℃
RT
20000
300℃
400℃
500℃
10000
RT
0
0.5
600℃
700℃
1.5
100℃
200℃
300℃
1.5
400℃
500℃
600℃
1
0.5
700℃
700℃
0
0
700℃
1
B m [T]
(d)35A250
W [W/kg]
100℃
RT
RT
2
RT
30000
0
0.5
700℃
(b)SS400
700℃
10000
700℃
B m [T]
(b)SS400
30000
10
5
B m [T]
70000
15
500℃
W [W/kg]
0
100℃
200℃
300℃
400℃
500℃
600℃
400℃
1000
RT
20
W [W/kg]
100℃
RT
RT
RT
4000
μs
10
2
(a)SPCC
μs
15
0
700℃
1.5
RT
5
500℃
600℃
700℃
0
W [W/kg]
μs
20
100℃
10000
2000
RT
RT
700℃
0.5
1
1.5
2
B m [T]
2
(d)35A250
Fig.6. Comparison of iron loss W.
Fig.5. Comparison of permeability s.
108
PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 No 9b/2011
9.0E+06
RT
Wh [W/kg]
8
RT
8.0E+06
100℃
7.0E+06
Conductivity.[S/m]
10
200℃
300℃
6
4
2
700℃
400℃
500℃
600℃
700℃
0.5
1
1.5
5.0E+06
4.0E+06
3.0E+06
2.0E+06
0.0E+00
2
0
B m [T]
200
400
600
Temp.[℃]
1.4
100000
RT
RT
1
0.8
0.6
0.4
0.2
700℃
100℃
200℃
300℃
400℃
500℃
600℃
700℃
0.25T(SPCC)
0.6T(SPCC)
0.8T(SPCC)
0.25T(35A250)
10000
0.6T(35A250)
0.8T(35A250)
μs
1.2
0.25T(6.5% Si steel)
0.6T(6.5% Si steel)
1000
0.8T(6.5% Si steel)
0.25T(SS400)
0
0
0.5
1
1.5
0.6T(SS400)
2
100
6
4
2
700℃
100℃
200℃
300℃
400℃
500℃
600℃
700℃
800
1.5T(6.5% Si steel)
1.5T(SS400)
0
1.5
1.5T(SPCC)
1.5T(35A250)
μs
We [W/kg]
600
10000
RT
RT
8
1000
100
2
0
200
400
600
800
Temp.[℃]
B m [T]
(b) Permeability s (Bm=1.5T)
(i)SPCC
1.0T(SPCC)
100
0.2
1.4T(SPCC)
RT
RT
1.65T(SPCC)
100℃
200℃
300℃
0.1
0.05
700℃
400℃
500℃
600℃
700℃
1.0T(35A250)
10
1.4T(35A250)
W [W/kg]
0.15
We [W/kg]
400
(a) Permeability s (Bm  0.8T)
10
1
200
Temp.[℃]
(ii)6.5% Si steel, (a) hysteresis loss
0.5
0.8T(SS400)
0
B m [T]
0
800
Fig.8. Change of conductivity with temperature.
(i)SPCC
Wh [W/kg]
6.0E+06
1.0E+06
0
0
SPCC
6.5% Si steel
1.65T(35A250)
1.0T(6.5% Si steel)
1
1.4T(6.5% Si steel)
1.65T(6.5% Si steel)
1.0T(SS400)
0.1
0
0
0.5
1
1.5
2
B m [T]
(ii)6.5% Si steel, (b) eddy current loss
Fig.7. Comparison of hysteresis loss Wh and eddy current loss We.
1.4T(SS400)
0
200
400
600
800
1.65T(SS400)
Temp.[℃]
(c)Iron loss W
Fig.9. Effect of temperature on specific permeability and iron loss.
Fig.6 shows the comparison of iron loss W. The iron
loss W of all specimens are decreased with temperature.
Especially, the decrease of iron loss W with increase of
temperature is remarkable in the case of SPCC.
PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 No 9b/2011
109
The iron losses W of SPCC and 6.5%Si steel are
separated into the hysteresis loss Wh and the eddy current
loss We by the two-frequency method using iron losses at
30Hz and 50Hz. Fig.7 shows the comparison of the
hysteresis loss and the eddy current loss. The hysteresis
loss Wh and the eddy current loss We of both specimens are
decreased with temperature. As the spontaneous
magnetization is decreased with the increase of
temperature from the weirs theory [5], the area of hysteresis
loop is decreased, then it can be considered that the
hysteresis loss Wh is reduced with the temperature.
The percentages of eddy current loss to the whole iron
loss of SPCC is larger than that of 6.5% Si steel. This is due
to the difference in the thicknesses of the specimen.
Moreover, the decrease of hysteresis loss Wh and eddy
current loss We of SPCC with increasing temperature is
remarkable in comparison with that of 6.5%Si steel. The
remarkable change of We of SPCC can be explained by the
large change of conductivity (about twice compared with
6.5%Si steel) with the temperature as shown in Fig.8, and
the larger eddy current loss compared with 6.5% delete Si
steel. The conductivities are measured using rectangular
specimens (width: 30mm, length: 100mm) by measuring the
voltage difference at two points when dc current is supplied.
1.0T(SPCC)
10
1.4T(SPCC)
1.6T(SPCC)
1.0T(6.5% Si steel)
Wh [W/kg]
1.4T(6.5% Si steel)
1.6T(6.5% Si steel)
1
Fig.9 shows the effect of temperature on the specific
permeability s and iron loss W. The permeability s at
0.25T is increased with temperature. The tendency similar
to the Hopkinson effect[5] is observed. The permeability of
SPCC is increased with temperature when the flux density
is 0.8T. On the contrary, those of electrical steels (6.5%Si
steel and 35A250) don’t change so much with the
temperature when the flux density is 0.8T.The
permeabilities of all the specimens are decreased with
temperature at Bm=1.5T as shown in Fig. 9(b). The iron
loss is always decreased with temperature as shown in Fig.
9(c).
Fig.10 shows that the hysteresis loss and the eddy
current loss are decreased with the temperature and the
percentage of eddy current loss to the whole iron loss of
SPCC is larger than that of 6.5% delete Si steel.
Conclusions
Magnetic properties of the ring specimens of the cold
rolled steel sheet (SPCC), rolled steel for general structure
(SS400), 6.5%Si steel and the non-oriented electrical steel
sheet (35A250) have been measured and compared. The
obtained results can be summarized as follows:
(1)The permeability at high temperature (700C) of SPCC
became the maximum at about 0.6T. On the contrary, those
of electrical steels (6.5%Si steel, 35A250) became the
maximum at about 0.3T.
(2)The iron losses W of all the specimens were decreased
with increasing temperature. Especially, decrease of iron
loss W with temperature was remarkable in the case of
SPCC.
REFERENCES
0.1
0
200
400
600
800
Temp.[℃]
(a) Hysteresis loss Wh
1.0T(SPCC)
10
1.4T(SPCC)
1.6T(SPCC)
We [W/kg]
1.0T(6.5% Si steel)
1.4T(6.5% Si steel)
1
1.6T(6.5% Si steel)
0.1
0.01
0
200
400
600
800
Temp.[℃]
(b)Eddy current loss We
Fig.10. Effect of temperature on hysteresis loss and eddy current
loss.
110
[1] Kagimoto H., Miyagi D., Takahashi N., Uchida N., Kawanaka
K., Effect of Temperature Dependence of Magnetic Properties
on Heating Characteristics of Induction Heater, IEEE Trans.
Magn., 46 (2010), No.8, 3018-3021
[2] Kurose H., Miyagi D., Takahashi N., Uchida N., and Kawanaka
K., 3-D Eddy Current Analysis of Induction Heating Apparatus
Considering Heat Emission, Heat Conduction, and
Temperature Dependence of Magnetic Characteristics, IEEE
Trans. Magn., 45 (2009), No. 3, 1847-1850
[3] Bozorth R . M . , F e r r o m a g n e t i s m , V a n N o s t r a n d D .
(1951)
[4] Takahashi N., Morishita M., Miyagi D., Nakano M.,
Examination of Magnetic Properties of Magnetic Materials at
High Temperature using a Ring Specimen, IEEE Trans. Magn.,
46 (2010), No. 2, 548-551
[5] Chikazumi S., and Graham C.D., Physics of Ferromagnetism,
Oxford University Press (1997)
Authors: Mr.Morishita Masayuki, Dr.Daisuke Miyagi, Mr.Masanori
Nakano, Prof.Norio Takahashi, Dept. Electrical and Electronic Eng.
Okayama
Univ.,
700-8530,
Japan,
E-mail:
morishita@3dlab.elec.okayama-u.ac.jp,
norio@.elec.okayamau.ac.jp;
PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 No 9b/2011