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Effect of grain size, deformation, aging and anisotropy on hysteresis loss of electrical steels
Journal of Magnetism and Magnetic Materials 215}216 (2000) 97}99
E!ect of grain size, deformation, aging and anisotropy on hysteresis loss of electrical steels F.J.G. Landgraf *, M. Emura , J.C. Teixeira , M.F. de Campos Technological Research Institute (IPT), Av. Prof. Almeida Prado 532 CEP Sao Paulo, 05508-901, Brazil Depto. Met. Mat., EP Universidade de SaJ o Paulo, Sao Paulo, 05508-900, Brazil
Abstract The investigation of the e!ect of cold deformation, anisotropy, aging and grain size on the shape of the hysteresis curve of non-oriented electrical steels shows that most of the hysteresis energy is dissipated in the high-induction region (above the maximum permeability induction). It indicates that more attention should be given to the energy dissipation mechanisms in that region, such as the domain annihilation and nucleation. 2000 Elsevier Science B.V. All rights reserved. Keywords: Electrical steel; Losses separation; Grain size; Deformation; Aging; Anisotropy
The separation of total magnetic losses in its hysteresis, classical and anomalous losses components o!ered important clues to the development of electrical steels processing. A quantitative description of the e!ect of microstructural parameters is still needed, and also a better understanding of which mechanisms, besides domain wall movement, should be used to understand it. Two methods of separating the hysteresis loss into components that could di!erentiate the e!ect of texture from the other parameters have been proposed recently, one suitable for grain oriented steels [1], other using the Preisach modeling coe$cients [2]. This paper intends to apply a third approach [3] to analyze the e!ects of dislocation density and residual stresses, texture and second phase, comparing them to the already described e!ect of grain size. The method is based on the simpli"ed hypothesis that the maximum permeability region of the magnetization curve separates the realm of domain wall movement and the domain rotation as the predominant (but not exclusive) mechanisms of magnetization change. Grain size and second phases are the most important variables to control the &low induction region', below the
* Corresponding author. Technological Research Institute, IPT Av. Prof. Almeida Prado 532 CEP 05508-901, Sa o Paulo, Brazil. Tel.: #55-11-37674211; fax: #55-11-37674037. E-mail address: [email protected] (F.J.G. Landgraf ).
&knee' of the curve, whereas crystallographic texture controls the domain rotation at the &high induction region' above the knee. However, if domain wall movement must be the main energy dissipation mechanism below the knee of the curve, reversible domain rotation is not dissipative, whereas other energy dissipation mechanisms must account for the losses at the &high induction' region. Bertotti [4] assumes that domain annihilation and domain nucleation are the main dissipation mechanisms above the knee. The objective of this paper is not to identify the operating mechanisms, but to o!er a quantitative estimation of the phenomena. The method assumes that the fraction of the hysteresis loop area that lies inside the maximum permeability induction values must be the region of the domain wall movement pre-eminence, while the area outside those lines must be the regions where other mechanisms, more sensitive to crystallographic texture or other sources of anisotropy, predominate. All data came from quasi-static hysteresis measurements taken from Epstein samples. Di!erent experiments were used to gather data for this investigation. The e!ect of dislocation density and residual stresses is based on commercially available fully processed 2% silicon steel samples that were subjected to cold rolling with di!erent amounts of elongation, from 0% to 8%. To evaluate the e!ect of texture, samples were taken at di!erent directions from a 2% silicon steel that showed the normal high induction permeability anisotropy, as it is
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 0 7 6 - 7
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F.J.G. Landgraf et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 97}99
Fig. 1. E!ect of di!erent variables on the low- and high-induction components of hysteresis loss, measured as energy loss per cycle: (a) sample orientation to the rolling direction, on 2% Si steel; (b) amount of plastic deformation, on 2% Si steel, RD sample (c) annealed versus aged condition of lamination steel and (d) grain size of 0.5% Si steel, RD.
Fig. 2. E!ect of the same variables as in Fig. 1, on the shape of quasi-static hysteresis curves.
F.J.G. Landgraf et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 97}99
conceivable that all other variables are probably constant. The e!ect of second phases is evaluated on lowcarbon steel samples that showed signi"cant magnetic aging when subjected to the standard 225C 24 h accelerated magnetic aging procedure. The e!ect of grain size is based on semi-processed 0.5% Si steel samples with different amounts of temper rolling, that after annealing reached di!erent grain sizes, as previously described in Ref. [3]. Fig. 1 shows the e!ect of texture (a), deformation (b), aging (c) and grain size (d) on the low-induction and high-induction energy dissipation. The loss anisotropy shows an interesting behavior: the high-induction loss goes through a maximum around 453, while the lowinduction loss steadily increases. In both cases, the e!ect of texture (anisotropy) and deformation, the high-induction loss is the larger component. In the case of grain size and second phase, the loss increase is lead mainly by the low-induction component. Fig. 2 shows how the hysteresis curve is changed by those variables. The growth of a second phase (as in aging) or the decrease in grain size show changes in the domain wall movement region (coercive force) and in the domain annihilation region (lower branch of second
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quadrant) with little change in the domain nucleation region (upper branch). In the case of the e!ect of texture and deformation, a larger amount of domain rotation can explain the decrease in remanence and high-induction permeability but should not be used for the large increase in high-induction loss seen in Figs. 1c and d. Unfortunately, very little has been published on the energy loss mechanisms in the high-induction region. The authors wish to thank FAPESP (Proc. 97/4877-0) for the research Grant.
References [1] N. Morito, M. Komatsubara, Y. Shimizu, Kawasaki Steel Tech. Report 39, 1998, p. 3. [2] L.R. DupreH , G. BaH n, M.V. Rauch, J.A.A. Melkebeek, J. Magn. Magn. Mater. 195 (1999) 233. [3] F.J.G. Landgraf, M. Emura, J.C. Teixeira, M.F. de Campos, C.S. Muranaka, J. Magn. Magn. Mater. 196}197 (1999) 380. [4] G. Bertotti, Hysteresis in Magnetism, Academic Press, New York, 1998, p. 320.
E!ect of grain size, deformation, aging and anisotropy on hysteresis loss of electrical steels F.J.G. Landgraf *, M. Emura , J.C. Teixeira , M.F. de Campos Technological Research Institute (IPT), Av. Prof. Almeida Prado 532 CEP Sao Paulo, 05508-901, Brazil Depto. Met. Mat., EP Universidade de SaJ o Paulo, Sao Paulo, 05508-900, Brazil
Abstract The investigation of the e!ect of cold deformation, anisotropy, aging and grain size on the shape of the hysteresis curve of non-oriented electrical steels shows that most of the hysteresis energy is dissipated in the high-induction region (above the maximum permeability induction). It indicates that more attention should be given to the energy dissipation mechanisms in that region, such as the domain annihilation and nucleation. 2000 Elsevier Science B.V. All rights reserved. Keywords: Electrical steel; Losses separation; Grain size; Deformation; Aging; Anisotropy
The separation of total magnetic losses in its hysteresis, classical and anomalous losses components o!ered important clues to the development of electrical steels processing. A quantitative description of the e!ect of microstructural parameters is still needed, and also a better understanding of which mechanisms, besides domain wall movement, should be used to understand it. Two methods of separating the hysteresis loss into components that could di!erentiate the e!ect of texture from the other parameters have been proposed recently, one suitable for grain oriented steels [1], other using the Preisach modeling coe$cients [2]. This paper intends to apply a third approach [3] to analyze the e!ects of dislocation density and residual stresses, texture and second phase, comparing them to the already described e!ect of grain size. The method is based on the simpli"ed hypothesis that the maximum permeability region of the magnetization curve separates the realm of domain wall movement and the domain rotation as the predominant (but not exclusive) mechanisms of magnetization change. Grain size and second phases are the most important variables to control the &low induction region', below the
* Corresponding author. Technological Research Institute, IPT Av. Prof. Almeida Prado 532 CEP 05508-901, Sa o Paulo, Brazil. Tel.: #55-11-37674211; fax: #55-11-37674037. E-mail address: [email protected] (F.J.G. Landgraf ).
&knee' of the curve, whereas crystallographic texture controls the domain rotation at the &high induction region' above the knee. However, if domain wall movement must be the main energy dissipation mechanism below the knee of the curve, reversible domain rotation is not dissipative, whereas other energy dissipation mechanisms must account for the losses at the &high induction' region. Bertotti [4] assumes that domain annihilation and domain nucleation are the main dissipation mechanisms above the knee. The objective of this paper is not to identify the operating mechanisms, but to o!er a quantitative estimation of the phenomena. The method assumes that the fraction of the hysteresis loop area that lies inside the maximum permeability induction values must be the region of the domain wall movement pre-eminence, while the area outside those lines must be the regions where other mechanisms, more sensitive to crystallographic texture or other sources of anisotropy, predominate. All data came from quasi-static hysteresis measurements taken from Epstein samples. Di!erent experiments were used to gather data for this investigation. The e!ect of dislocation density and residual stresses is based on commercially available fully processed 2% silicon steel samples that were subjected to cold rolling with di!erent amounts of elongation, from 0% to 8%. To evaluate the e!ect of texture, samples were taken at di!erent directions from a 2% silicon steel that showed the normal high induction permeability anisotropy, as it is
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 0 7 6 - 7
98
F.J.G. Landgraf et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 97}99
Fig. 1. E!ect of di!erent variables on the low- and high-induction components of hysteresis loss, measured as energy loss per cycle: (a) sample orientation to the rolling direction, on 2% Si steel; (b) amount of plastic deformation, on 2% Si steel, RD sample (c) annealed versus aged condition of lamination steel and (d) grain size of 0.5% Si steel, RD.
Fig. 2. E!ect of the same variables as in Fig. 1, on the shape of quasi-static hysteresis curves.
F.J.G. Landgraf et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 97}99
conceivable that all other variables are probably constant. The e!ect of second phases is evaluated on lowcarbon steel samples that showed signi"cant magnetic aging when subjected to the standard 225C 24 h accelerated magnetic aging procedure. The e!ect of grain size is based on semi-processed 0.5% Si steel samples with different amounts of temper rolling, that after annealing reached di!erent grain sizes, as previously described in Ref. [3]. Fig. 1 shows the e!ect of texture (a), deformation (b), aging (c) and grain size (d) on the low-induction and high-induction energy dissipation. The loss anisotropy shows an interesting behavior: the high-induction loss goes through a maximum around 453, while the lowinduction loss steadily increases. In both cases, the e!ect of texture (anisotropy) and deformation, the high-induction loss is the larger component. In the case of grain size and second phase, the loss increase is lead mainly by the low-induction component. Fig. 2 shows how the hysteresis curve is changed by those variables. The growth of a second phase (as in aging) or the decrease in grain size show changes in the domain wall movement region (coercive force) and in the domain annihilation region (lower branch of second
99
quadrant) with little change in the domain nucleation region (upper branch). In the case of the e!ect of texture and deformation, a larger amount of domain rotation can explain the decrease in remanence and high-induction permeability but should not be used for the large increase in high-induction loss seen in Figs. 1c and d. Unfortunately, very little has been published on the energy loss mechanisms in the high-induction region. The authors wish to thank FAPESP (Proc. 97/4877-0) for the research Grant.
References [1] N. Morito, M. Komatsubara, Y. Shimizu, Kawasaki Steel Tech. Report 39, 1998, p. 3. [2] L.R. DupreH , G. BaH n, M.V. Rauch, J.A.A. Melkebeek, J. Magn. Magn. Mater. 195 (1999) 233. [3] F.J.G. Landgraf, M. Emura, J.C. Teixeira, M.F. de Campos, C.S. Muranaka, J. Magn. Magn. Mater. 196}197 (1999) 380. [4] G. Bertotti, Hysteresis in Magnetism, Academic Press, New York, 1998, p. 320.