Study of the influence of grain size on the total magn etic losses in [620333]

Study of the influence of grain size on the total magn etic losses in
silicon steel

STOIAN Elena Valentina1,a, BRATU Vasile2,b,
ANGHELINA Florina Violeta 3,c*, PETRE Ivona4,d, FLUIERARU Petre
Cristian5,e, NEGREA Alexis6,f

1,2,3,4,5,6 Valahia University of Targoviste, Faculty of Materials Engineering and Mechanics,
Department of Materials Engineering, Mechatronics and Robotics,
Aleea Sinaia Street, Targoviste, Romania
a [anonimizat], b [anonimizat] , c* [anonimizat] d
[anonimizat], e [anonimizat], f [anonimizat]

Keywords : non oriented electrical steel, roll, magnetic loss, grain size, cold rolled strip

Abstract. The purpose of this work was to study microstructural changes of the bands investigated
during processing occurring siliceous strips with non- oriented grains , and the study the influence of
grain size on the total magnetic losses at 1.0 T and 1.5 T.
There have been studies 10 rolls intended to be processed into quality electrical steel M400-50A
(according to EN 100027-1) rolls who underwent conventional lamination technology. For the 10 rolls were made measurements of magnetic characteristics at the induction J = 1 500 mT and at a
frequency f = 50 Hz and after that, we made correlati ons between the specific losses, and grain size.
Materials were analyzed by metallographic micros cope Neophet 32 and the magnetic characteristics
was made with Epstein frame according IEC 6040/4-2, with an exiting current frequency of 50Hz at
1.5T and 1.0T induction after aging treatment of 225
0C for 24 hours. Sample for light microscopy
observation were prepared by polishing and etching in 5% Nital.
Subsequently, the microscopic analysis was performed on a band in which the non-oriented grain
silicon steel which have 1.224%Si , wich was decarburized and annealed, so obtaining the different
values of microstructures with different grains size.
Introduction
In cold rolling , the properties of products obtained from hot rolling , eg. mechanical and
technical characteristics, are changed by compress ion between rollers without previous heating of
the input.
Non/oriented electrical sheets are sheets tailor ed to produce specific properties and are
produced from Fe-Si or Fe-Si-Al alloys. Non-oriented electrical steel sheets are incorporated into a
wide range of equipment, from the simplest dome stic appliances to hybrid and pure electric
vehicles.
Cold rolled products are mainly strips and sheets with a high quality surface finish and precise
metallurgical properties for use in high specification products.
In 1996 the production of cold rolled strip (sheets and plates) was about 39.6 million tons. [1].
The main producing countries were Germany with about 10.6 million tons, France with 6.3 million
tons , Italy with 4.3 , UK with 4.0 million tons and Belgium with 3.8 million tons.
Cold rolled strip industry in the EU is concen trated and fragmented. The largest 10 companies
account for 50 % of production while another 140 companies account for the remaining 50 %. Most
large companies are located in Germany, which dominates the market with about 57 % of EU
production (2.57 million tons in 2012), while the re maining companies are classified as small and
medium sized enterprises. [2]
In 2012 , Germany produced about 45 % of the total cold rolled strip, with 1.9 million tonnes,
followed by Italy and France each with a production of 0.9 million tons.

Total production of cold rolled flat products in 2010 was 39.7 million tonnes , represented by
15 EU member states. Production of stainless and electrical sheet mean 2.3 and respectively 1.13
million tons , representing 6.4 % and 3.2 % of the total. [3, 4 , 5]
able 1
Production of cold rolled
sheet and strip [ 1000 t ]
Austria 1289
Belgium 3852
Denmark 0
Finland 890
France 6296
Germany 10615
Greece 380
Ireland 0
Italy 4271
Luxembourg 336
Netherlands 2088
Portugal 202
Sweden 1174
Spain 3093
UK 4026
3%
10%
0%
2%
16%
29% 1%0%11%1%5%1%3%8%10%Austria
Belgium
Denmark
Finland
France
Germany
Greece
Ireland
Italy
Luxembourg
Netherlands
Portugal
Sweden
Spain
UK

Fig.1 Production of cold rolled sheet and strip
[1000t]

Non-oriented electrical steel cold rolled electr ical steel have approximately equal magnetic
properties in all directions tape (isotropic mate rials) and are used for electrical motors and
generators , small transformers and other equipment .[4, 5 ,6 , 13]
Electrical steel is the most important soft magne tic material currently used. Its use as an alloy
to improve magnetic properties was patented by Sir Robert Hadfield at the end of the century XIX.
[10, 12, 13, 14]
The continuous development of the industry producing electricity required for steel
manufacture with superior properties in order to d ecrease power dissipation as heat in electric
devices to reduce the physical size of the equipment and also to improve their performance.
Most of the electrical energy produced in the en tire world is consumed in electrical motors
[10,11,13,16,17,20], which are rotating machines th at employ nonoriented electrical steels as soft
magnetic materials.
Results and discussions
From to brand of steel 5542 are obtained 5 types of electrical steel sheet. They are: M330-35A,
M330-50A, M350-50A, M400-50A and M400-65A.
From a sample of 40 rolls we analyzed 10 rolls intended to be processed into quality electrical
steel M 400-50A (according to EN 100027-1).
So for mark M 400-50A we have a non-oriented electrical steel magnetic strip with specific
losses at 1,5T maximum of 400 [W/kg] at 50 [Hz] , a nominal thickness of 0,50 mm .
According to the process flow of cold rolling , to obtain the electrical cold rolled strip, the flow
of cold rolling need of hot rolled strip ( SRH ).[15,18,19]
The study of metallographic structure is important because it gives information on how to
develop on heat treatments, mechanical and thermo, putting into evidence the defects (microporosity, nonmetallic inclusions).
The resultant magnetic proprietes were measur ed via Epstein testing according IEC 60404-2,
with an exciting current frequency of 50 [Hz] at 1, 5 T and 1,0 T induction after aging treatment of

2250C for 24 hours. Samples for light microscopy observation, were prepared by polishing and
etching in 5% Nital.
Microstructural analysis
Microstructural analysis of electrical cold roll ed strip was made for one chemical compositions
of electrical steel, namely for example strip A, chemical composition was, according to Table 2:
Table 2
Chemical composition of the strip A
C Mn Si S P Al
0.024 0.216 1.224 0.004 0.071 0.23

The cold rolling hot rolled strip suffer 4-5 high passes each pass deformation of 20-25% and a
total degree of reduction of 80%. For strip A, rolling finish temperature was 9230C.
The strips were subjected to an annealing treatm ent duplex. Thus, the strips were subjected to
recrystallization heat treatment followed by a decarburization treatment.This treatment helps to
increase non-oriented grains.[7, 8, 9]
Decarburization treatment was conducted at 8300C temperature, and the recrystallization at
9400C .
Magnetic loss includes hysteresis losses and eddy current losses. They are determined with
Epstein frame, at certain induction and frequency. For lot analised frequency measurements were
performed at the induction J = 1500 mT and frequency f = 50 Hz .
In Table 3 are shown the characteristics of th e non-oriented electrical steel sheet, which has
represented the base of research .
Table 3
The characteristics of the non-oriented electrical steel sheet analysed

According to table 3, we find that the magnetic losses specific to 1.0 T are located around 2
[W/kg] , with a maximum value of 2.11 [W/kg] and a minimum value of 1.85 [W/kg]. Loss
magnetic at 1.5 T for non-oriented electrical steel silicon are located close range of 4 [W/kg] with a
maximum value of 4.66 [W/kg] and a minimum value of 4.13 [W/kg] .
In terms of standards, we found that all rolls analyzed have noticeable loss in accordance with
EN 10027-1 falling , namely for lot M 400A -50A magnetic loss of around 4.00 [W/kg] .
Following decarburization and annealing heat tr eatments for band A, the grain size ranges
around 50 µm. Under the same conditions of heat tr eatment for decarburization and annealing (the
line speed of treatment is 32 [m/min] and the temperature of decarburization and annealing are
8300C respectively 940°C) for the other bands were obtained grain sizes much finer, by
approximately 27 µm.
This difference is reflected later in grain values total magnetic losses. Thus, band A, the total
magnetic losses are 4.16 [W/kg] for the tape while the finer particle size of the magnetic losses, are
4.66 [W/ kg]. No.of roll Grain
size
[µm] Magnetic
loss at 1.0TMagnetic
loss at 1.5THmax
[A/m]Jmax
[mT]Hc
[A/m]
55447 27 2.11 4.66 1142 ,8 1500 ,49 6,669
56161 30 2.1 4.61 1149 ,6 1500 ,59 5,668
56162 31 1.91 4.2 1241 ,8 1500 ,19 6,653
56160 33 1.92 4.28 1242,2 1500,6 95,539
56147 46.5 1.89 4.24 1312 ,3 1500 ,29 5,649
55409 47 1.88 4.24 1344 ,7 1500 ,27 5,009
56158 45 1.85 4.20 1221 ,9 1500 ,77 6,837
56159 46 1.86 4.13 1408 ,7 1500 ,27 6,357
55408 47.5 1.87 4.16 1142 ,0 1500 ,67 7,423
56152 48.5 2.01 4.16 1257 ,1 1500 ,37 8,337

It is noted that the carbon content after de carburization and annealing is around 0.003 % .
Subsequently, the microscopic analysis was pe rformed and a band in which the non-oriented
grain silicon steel, wich was decarburized and an nealed conditions, obtaining the following values
of microstructures with different grain size, shown in figures 2-6:

Fig.2 Band thickness 0.5mm
(Grain size: 48.5 µm;Total loss at 1.5T = 4.16
[W/kg];Attack: Nital 5%; Magnification: x 200)

Fig.3 Band thickness 0.5mm
(Grain size: 45 µm,Total loss at 1.5T =
4.20[W/kg],Attack: Nital 5%, Magnification: x
200)

The microstructure of Figure 2 was obtained after a holding time of 619 seconds, yielding a
grain size of 48.5µm and total loss at 1.5 T of 4.16 [W/kg].
The microstructure of Figure 3, was obtained after a holding time only 578 seconds , and the
particle size was fine , resulting in a size of grai n of 45 micrometres and the value of the total loss at
1.5 T being 4.20 [W/kg].
The treatment line speed was between 28 [m/min ] (see figure2) and 30 [m/min] (see figure 3).

Fig. 4 Band thickness : 0.5mm
(Grain size: 33 µm;Total loss at 1.5T=4.28
[W/k g];Attack: Nital 5%;Ma gnification: x 200)

Fig. 5 Band thickness: 0.5mm
(Grain size: 30 µm;Total loss at 1.5T =4.61
[W/kg];Attack: Nital 5%; Magnification: x 200x)

Fig. 6 Band thickness : 0.5mm
(Grain size: 29 µm;Total loss at 1.5T =4.66
[W/kg];Attack: Nital 5%;Magnification: x
200)

The microstructure of figure 4 has been obtaine d after a holding time of 542 seconds, the line
speed of treatment is 32 [m/min] obtaining a size of grain of 33 µm, and the total loss at 1.5 T being
4.28 [W/kg] .

For the microstructure 5, are the same as the conditions for maintaining only that, there was
obtained a grain size of 30 micrometres and the valu e of the total loss at 1.5 T being 4.61 [W/kg ].
Microstructure of figure 6 was obtained after a holding time of 510 seconds, the treatment line
speed was 34 m / min . Obtained a grain size of 29 micrometres and the total loss at 1.5 T were 4.66
[W/kg ].
For all 10 types of strip, thickness was 0.5 mm, measurements were made of the grain size
and the magnetic losses, specifice at 1.5T and 1.0T respectively, and the results are presented in
Table 3.
Based on the results summarized in Table 3 in terms of grain size bands analyzed and loss
magnetic at 1.0T and 1.5T , I could draw graphs on the influence of grain size on the total magnetic
losses, the 1.0T ( see figure 7) and 1.5T (see figure 8 ).
y = 2,2495e-0,0037x
R2 = 0,88
1,81,922,12,2
25 30 35 40 45 50 55
Grain size [µm]P 1 T [W/kg]

Fig. 7 The influence of grain size on the total
magnetic losses at 1.0T y = 5,2325e-0,0039x
R2 = 0,7911
4,14,24,34,44,54,64,7
25 30 35 40 45 50 55
Grain size [µm]P 1,5T [W /kg]

Fig.8 The influence of grain size on the total
magnetic losses at 1.5T

Increasing the grain size is desirable for non-orie nted electrical steel st rips electro. Magnetite
total losses are much lower since the grain size is larger. For lot examined, a size of grain of 27 µm
afforded the total magnetic losses at 1.0T and 1.5 T, 2.11[W/kg] respectively 4.66 [W/kg].

Conclusions
After analyzing silicon steel non-oriented el ectrical steel annealed and decarburized
treatmnets, hold time treatment varied between 510-619 seconds, and the line speed was between 28-34 [m /minutes].
For group analyzed magnetic losses decreases with increasing grain size. Thus loss magnetic
lowest are 2.01 to 1.0 T [W/kg] and the 1.5T to 4.16 [W/kg].
Also Loss magnetic 1.0 T and 1.5T increase with increasing concentration of carbon to silicon
steel non-oriented electrical steel analyzed.
Total magnetic losses are even lower since the grain size is larger. For lot examined, a size of
grain of 27 µm it led to obtaining the total magnetic losses at 1.0 T is 2.11 [W/kg] and at 1.5 T
respectively 4.66 [W/kg ].
For a larger grain size of 48.5 µm magnetic losses to 1.5 T and 1.0 T decreased values
2.01 [W/kg] respectively 4,16 [W/kg], according table 3. For the correlation coefficients were
obtained significant values, namely R
1T = 0.88 and R 1.5T = 0.79.
Since in both cases were obtained correlation coef ficients wich tends to value one , we can say
that between the two variables (size of grain and magnetic losses total at 1.0 T and 1.5 T,
respectively) there is a linear relationship of positive slope or directly proportional.
References
[1] Rehman S, Solar radiation over Saudi Arabia and comparisons with empirical models, Energy
1998; 23(12), pp. 1077 – 1082.

[2] I. Petryshynetsa, F. Kovaca , V. Stoykaa and J. Borutab, Influence of Microstructure Evolution
on the Coercive Forces in Low Silicon Non-Orient ed Steels, 14th Czech and Slovak Conference on
Magnetism, Košice, Slovakia, July 6–9, 2010, Vol. 118 (2010) Acta Physica Polonica a No. 5.
[3] Lyudkovsky, G. Effect of Antimony on Recryst alization Behaviour and Magnetic Properties of
a Nonoriented Silicon Steel,Metallurgical and Materials Transaction A, Vol. 15, No.2, February
1984.
[4] J. Hunady , M. Cernik , E. J. Hilinski , M. Predmersky , A. Magurova, Influence of Chemistry
and Hot Rolling Conditions on High Permeability Non-Grain Oriented Silicon Steel, Journal of
Metals, Materials and Minerals. Vol.15 No.2 pp.17-23, 2005.
[5] Darja Steiner Petrovic, Non-oriented el ectrical steel sheets, ISSN 1580-2949 MTAEC9,
44(6)317(2010).
[6] T. Shimazu, M. Shiozaki, K.J. Kawasaki, J. Magn. Magn. Mater. 133, 147 1994.
[7] R.H. Heyer, D.E. McCabe, J.A. Elias, Flat Rolled Products, Interscience New York 1962, p. 29.
[8] F.E. Werner, R.I. Jaffee, J. Mat. Eng. Perf. 1 (1992) 227.
[9] M.F. de Campos et al. The optimum grain size for minimizing energy losses in iron, Journal of
Magnetism and Magnetic Materials 301 (2006) 94–99.
[10] C.O. Rus ănescu, M. Rus ănescu, F.V.Anghelina – Variation of mechanical properties with
temperature for an ecomaterial; Optoelectronics and advanced materials – rapid communications,
Vol. 7, No. 11-12, 2013, p. 947-951.
[11] E. Cazimirovici, ș.a., Machinery and processes in steel, Didactic and Pedagogic Publishing,
Bucharest 1974.
[12] A. Nanu, Materials technology, Didactic and Pedagogic Publishing, Bucharest, 1977.
[13] C.O. Rus ănescu, C. Jinescu, G. Paraschiv, St. Biris, M. Rus ănescu, O. Ghermec -Influence of
the Nb, V and Mo Elements on the Ecological Micro-alloyed Steel Properties, Revista de
chimie 66, no. 5 (2015): 754-757, ISSN: 0034-7752.
[14] Nicolae C ănănău, Victor Petrescu, Plastic deformation technology, Macarie Publisher,
Târgoviște, 2002.
[15] Erdemir România SRL/ Working procedure for cold rolling .
[16] C.O. Rus ănescu, M. Rus ănescu, T. Iord ănescu, F. V. Anghelina – Mathematical relation ships
between alloying elements and technological deformab ility indexes, Journal of optoelectronics and
advanced materials, Vol. 15, No. 7-8, 2013, p. 718-723.
[17] F.V.Anghelina, V. Bratu, I. N. Popescu, Estimating the stacking faults of high alloyed
steels, pp. 7 – 11, The Scientific Bulletin of Valahia University, Materials Science and Mechanics, Nr. 8 (year 11), ISSN 1844-1076, 2013.
[18] C. O. Rus ănescu, M. Rus ănescu, F. V. Anghelina, V. Bratu – The influence of the micro-
alloying elements on physical and structural characteristics of the some steel destined for
manufacturing the oil pipes, Romanian Reports in Physics, Vol. 68, No. 1, P. 278–293, 2016,
ISSN: 1221-1451 ; eISSN: 1841-8759.
[19] F.V.Anghelina, Correlation Between Primary Recrystallization Texture And Goss Texture For
The Electrotechnical Steel, Magazine JOSA-Journal of Science and Arts, Nr. 1 /2014, ISSN 1844-
9581, Ed. Bibliotheca,Targoviste.
[20] C. O. Rus ănescu, M. Rus ănescu – The influence of the residual copper on the pipes steel hot
plasticity according to environmental requirements, Journal of Mining and Metallurgy, Section B:
Metallurgy; J. Min. Metall. Sect. B-Metall . 49 (3) B (2013) 353 – 356 ; ISSN: 1450-5339.