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Magnetic properties and recrystallization texture of phosphorus-added non-oriented electrical steel sheets
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613 www.elsevier.com/locate/jmmm
Magnetic properties and recrystallization texture of phosphorus-added non-oriented electrical steel sheets I. Tanaka, H. Yashiki Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, 660-0891 Amagasaki, Japan Available online 20 March 2006
Abstract The effect of phosphorus on magnetic properties and recrystallization texture has been investigated in non-oriented electrical steel sheets to develop low core loss and high permeability core materials. Specimens with different phosphorus contents were cold-rolled to various thicknesses, i.e. with various cold-rolling reductions, and annealed for recrystallization and grain growth. Although magnetic induction of the steel with low phosphorus content dramatically dropped with reducing thickness, i.e. with increasing in cold-rolling reduction, that of the steel with high phosphorus content only slightly decreased. The most effective way to reduce core loss was to reduce thickness of electrical steel sheets. Therefore, phosphorus-added thin gauge non-oriented electrical steel sheets have achieved low core loss and high permeability. The typical magnetic properties of phosphorus-added non-oriented electrical steel sheets 0:27 mm in sheet thickness were 16:6 W=kg in W 10=400 and 1:73 T in B50 . These excellent magnetic properties were due to the recrystallization texture control. f1 1 1gh1 1 2i component in recrystallization texture was suppressed by the phosphorus segregation at initial grain boundaries. Accordingly, phosphorus would greatly contribute to the improvement of magnetic properties. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 81.40.Ef Keywords: Core loss; Magnetic induction; Texture; Phosphorus; Non-oriented electrical steel
1. Introduction Recently, there has been a great demand for reducing core loss, especially high-frequency core loss, in nonoriented electrical steel sheets from the viewpoint of energy conservation. The most effective solution to reduce highfrequency core loss is to reduce thickness of electrical steel sheets, so that thin gauge non-oriented electrical steel sheets of 0:35 mm and less in thickness have been used for high-efficiency motors. However, low core loss is incompatible with high permeability in conventional nonoriented electrical steel sheets, since magnetic induction of these sheets dramatically drops with increasing in coldrolling reduction due to the recrystallization texture change. In this study, the effect of phosphorus on magnetic properties and recrystallization texture has been investi-
Corresponding author. Tel.: +81 6 6489 5721; fax: +81 6 6489 5790.
E-mail address: [email protected] (I. Tanaka). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.155
gated in non-oriented electrical steel sheets to develop low core loss and high permeability core materials. 2. Experimental Main chemical composition of steels used in the present study on a mass% basis was as follows: 0.002% C, 2.0% Si, 0.3% Al, 0.01% P (0.01P steel) or 0.1% P (0.1P steel), the balance Fe. Hot-rolled bands with these different phosphorus contents were annealed at 800 C for 10 h in an Ar atmosphere. Both steels had almost the same grain diameter after the hot-rolled band annealing. These specimens were cold-rolled to 0.27, 0.35, 0:5 mm thick sheets, and then they were annealed at 1000 C for 30 s in an Ar atmosphere for recrystallization and grain growth. Magnetic measurements were carried out for annealed sheets by a 30 mm 100 mm single strip tester in rolling and transverse directions, and then the measured values were averaged to parallelize with Epstein method. The orientation distribution functions (ODFs) of annealed sheets were
ARTICLE IN PRESS I. Tanaka, H. Yashiki / Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613
e612
calculated from three incomplete pole figures (f2 0 0g, f1 1 0g and f2 1 1g) measured at the mid-planes using an X-ray diffraction method.
0
ψ1
90
0
ψ1
90
0 6 5
3. Results and discussion
4
Φ
The effect of cold-rolling reduction and thickness on magnetic properties is shown in Fig. 1. Core loss of both steels decreased with reducing thickness and magnetic induction also decreased with increasing cold-rolling reduction. However, magnetic induction rose with phosphorus addition. Furthermore, magnetic induction of 0:1 P steel only slightly decreased with increasing cold-rolling reduction. The result would mean that phosphorus-added thin gauge non-oriented electrical steel sheets have achieved low core loss and high permeability. The typical magnetic properties of 0:1 P steel of 0:27 mm in sheet thickness were 16:6 W=kg in W 10=400 and 1:73 T in B50 . Phosphorus significantly increases the resistivity of BCC iron. However, the increase of resistivity with 0.1% phosphorus addition is approximately 1 108 Om. Hence, the beneficial effect of phosphorus on core loss presented in Fig. 1 would be attributed to the decrease in hysteresis loss due to the texture improvement mentioned below as well as the eddy current loss. Recrystallization textures of 0:27 mm thick steels after annealing at 1000 C for 30 s are presented in Fig. 2. f1 1 1gh1 1 2i intensity of 0.1P steel was lower than that of 0.01P steel. f111gh112i component deteriorates magnetic
35
Cold-rolling reduction (%) 77 84 87
Core Loss, W10/400 /W kg-1
30 25 20 15
Magnetic Induction, B50 /T
1.74 1.73 1.72 1.71
Open:0.01P
1.70
Solid:0.1P
1.69 0.6
0.5
0.4 Thickness, t/mm
0.3
0.2
Fig. 1. Effect of cold-rolling reduction and thickness on magnetic properties.
3 2 1 90 (A)
0
(B)
(×random)
Fig. 2. c2 ¼ 45 ODF of (A) 0.01P and (B) 0.1P steels at the mid-plane of 0:27 mm thick sheets after annealing at 1000 C for 30 s.
properties, especially magnetic induction, of electrical steel sheets. Therefore, this texture change is likely to have caused the increase in the magnetic induction with phosphorus addition shown in Fig. 1. It is well known that phosphorus is one of the typical elements which segregate to grain boundaries [1]. This would imply that the texture change shown in Fig. 2 is due to the phosphorus segregation at initial grain boundaries (IGBs). To verify this idea, the effect of the phosphorus segregation at IGBs on recrystallization texture was investigated in 0.1P steel. The hot-rolled band of 0.1P steel was annealed at 825 C for 10 h in an Ar atmosphere, again annealed at 900 C for 2 min in a salt bath, and air-cooled to eliminate the grain boundary segregation of phosphorus. Additionally, some specimens were annealed at 700 C for 100 h in an Ar atmosphere and then quenched into water to promote the grain boundary segregation of phosphorus. Hereinafter, this heat treatment was called as segregation treatment (ST). Grain diameters have not changed during ST. Consequently, specimens with and without ST had the same phosphorus content and initial grain diameter, but the different state of the phosphorus segregation at IGBs. These specimens were cold-rolled to 0.27 mm thick sheets, and then they are annealed at 1000 C for 30 s in an Ar atmosphere. Textures were determined in the same way described above. Recrystallization textures of steels with and without ST after annealing at 1000 C for 30 s are presented in Fig. 3. f1 1 1gh1 1 2i intensity of the steel with ST was much lower than that of the steel without ST. Recrystallization texture without ST was found to be fairly close to that of 0.01P steel shown in Fig. 2. This would mean that recrystallization texture is hardly affected only by phosphorus addition, but the phosphorus segregation at IGBs is responsible for the suppression of f1 1 1gh1 1 2i component. It has been reported that f1 1 1gh1 1 2i component develops and consequently magnetic induction decreases with increasing in phosphorus content [2]. These results are obtained through the experiment without a hot-rolled band annealing. Initial grain diameters decrease with increasing in phosphorus content [2]. Hence, it would seem that the development of f1 1 1gh1 1 2i component with increasing in
ARTICLE IN PRESS I. Tanaka, H. Yashiki / Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613 ψ1
0
ψ1
90
0
90
0 6 5 4 Φ
3 2 1
90
(A)
0
(B)
(×random)
Fig. 3. c2 ¼ 45 ODF of 0.1P steel (A) without and (B) with ST at the mid-plane of 0.27 mm thick sheets after annealing at 1000 C for 30 s.
phosphorus content results from the decrease in initial grain diameters. In the case where steels have the same initial grain diameter and the phosphorus segregation at IGBs is sufficiently promoted, phosphorus would contribute to the suppression of f1 1 1gh1 1 2i component in the similar way to antimony [3]. Accordingly, phosphorus would greatly contribute to the improvement of magnetic properties of non-oriented electrical steel sheets. 4. Conclusion The effect of phosphorus on magnetic properties and recrystallization texture has been investigated. The following results were obtained.
e613
(1) Magnetic induction rises with phosphorus addition, and moreover, magnetic induction of the steel with high phosphorus content only slightly decreases with increasing cold-rolling reduction. (2) In recrystallization textures, f1 1 1gh1 1 2i intensity of the steel with high phosphorus content is lower than that of the steel with low phosphorus content. These textures correspond to the magnetic induction change with phosphorus addition. (3) Recrystallization texture of the high phosphorus content steel without segregation treatment is fairly close to that of the steel with low phosphorus content. Therefore, the phosphorus segregation at initial grain boundaries is responsible for the recrystallization texture control.
References [1] H. Kimura, Trans. Jpn. Inst. Met. 29 (1988) 521–539. [2] J.T. Park, J.S. Woo, S.K. Chang, J. Magn. Magn. Mater. 182 (1998) 381–388. [3] H. Shimanaka, T. Irie, K. Matsumura, H. Nakamura, J. Magn. Magn. Mater. 19 (1980) 63–64.
Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613 www.elsevier.com/locate/jmmm
Magnetic properties and recrystallization texture of phosphorus-added non-oriented electrical steel sheets I. Tanaka, H. Yashiki Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., 1-8 Fuso-cho, 660-0891 Amagasaki, Japan Available online 20 March 2006
Abstract The effect of phosphorus on magnetic properties and recrystallization texture has been investigated in non-oriented electrical steel sheets to develop low core loss and high permeability core materials. Specimens with different phosphorus contents were cold-rolled to various thicknesses, i.e. with various cold-rolling reductions, and annealed for recrystallization and grain growth. Although magnetic induction of the steel with low phosphorus content dramatically dropped with reducing thickness, i.e. with increasing in cold-rolling reduction, that of the steel with high phosphorus content only slightly decreased. The most effective way to reduce core loss was to reduce thickness of electrical steel sheets. Therefore, phosphorus-added thin gauge non-oriented electrical steel sheets have achieved low core loss and high permeability. The typical magnetic properties of phosphorus-added non-oriented electrical steel sheets 0:27 mm in sheet thickness were 16:6 W=kg in W 10=400 and 1:73 T in B50 . These excellent magnetic properties were due to the recrystallization texture control. f1 1 1gh1 1 2i component in recrystallization texture was suppressed by the phosphorus segregation at initial grain boundaries. Accordingly, phosphorus would greatly contribute to the improvement of magnetic properties. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 81.40.Ef Keywords: Core loss; Magnetic induction; Texture; Phosphorus; Non-oriented electrical steel
1. Introduction Recently, there has been a great demand for reducing core loss, especially high-frequency core loss, in nonoriented electrical steel sheets from the viewpoint of energy conservation. The most effective solution to reduce highfrequency core loss is to reduce thickness of electrical steel sheets, so that thin gauge non-oriented electrical steel sheets of 0:35 mm and less in thickness have been used for high-efficiency motors. However, low core loss is incompatible with high permeability in conventional nonoriented electrical steel sheets, since magnetic induction of these sheets dramatically drops with increasing in coldrolling reduction due to the recrystallization texture change. In this study, the effect of phosphorus on magnetic properties and recrystallization texture has been investi-
Corresponding author. Tel.: +81 6 6489 5721; fax: +81 6 6489 5790.
E-mail address: [email protected] (I. Tanaka). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.02.155
gated in non-oriented electrical steel sheets to develop low core loss and high permeability core materials. 2. Experimental Main chemical composition of steels used in the present study on a mass% basis was as follows: 0.002% C, 2.0% Si, 0.3% Al, 0.01% P (0.01P steel) or 0.1% P (0.1P steel), the balance Fe. Hot-rolled bands with these different phosphorus contents were annealed at 800 C for 10 h in an Ar atmosphere. Both steels had almost the same grain diameter after the hot-rolled band annealing. These specimens were cold-rolled to 0.27, 0.35, 0:5 mm thick sheets, and then they were annealed at 1000 C for 30 s in an Ar atmosphere for recrystallization and grain growth. Magnetic measurements were carried out for annealed sheets by a 30 mm 100 mm single strip tester in rolling and transverse directions, and then the measured values were averaged to parallelize with Epstein method. The orientation distribution functions (ODFs) of annealed sheets were
ARTICLE IN PRESS I. Tanaka, H. Yashiki / Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613
e612
calculated from three incomplete pole figures (f2 0 0g, f1 1 0g and f2 1 1g) measured at the mid-planes using an X-ray diffraction method.
0
ψ1
90
0
ψ1
90
0 6 5
3. Results and discussion
4
Φ
The effect of cold-rolling reduction and thickness on magnetic properties is shown in Fig. 1. Core loss of both steels decreased with reducing thickness and magnetic induction also decreased with increasing cold-rolling reduction. However, magnetic induction rose with phosphorus addition. Furthermore, magnetic induction of 0:1 P steel only slightly decreased with increasing cold-rolling reduction. The result would mean that phosphorus-added thin gauge non-oriented electrical steel sheets have achieved low core loss and high permeability. The typical magnetic properties of 0:1 P steel of 0:27 mm in sheet thickness were 16:6 W=kg in W 10=400 and 1:73 T in B50 . Phosphorus significantly increases the resistivity of BCC iron. However, the increase of resistivity with 0.1% phosphorus addition is approximately 1 108 Om. Hence, the beneficial effect of phosphorus on core loss presented in Fig. 1 would be attributed to the decrease in hysteresis loss due to the texture improvement mentioned below as well as the eddy current loss. Recrystallization textures of 0:27 mm thick steels after annealing at 1000 C for 30 s are presented in Fig. 2. f1 1 1gh1 1 2i intensity of 0.1P steel was lower than that of 0.01P steel. f111gh112i component deteriorates magnetic
35
Cold-rolling reduction (%) 77 84 87
Core Loss, W10/400 /W kg-1
30 25 20 15
Magnetic Induction, B50 /T
1.74 1.73 1.72 1.71
Open:0.01P
1.70
Solid:0.1P
1.69 0.6
0.5
0.4 Thickness, t/mm
0.3
0.2
Fig. 1. Effect of cold-rolling reduction and thickness on magnetic properties.
3 2 1 90 (A)
0
(B)
(×random)
Fig. 2. c2 ¼ 45 ODF of (A) 0.01P and (B) 0.1P steels at the mid-plane of 0:27 mm thick sheets after annealing at 1000 C for 30 s.
properties, especially magnetic induction, of electrical steel sheets. Therefore, this texture change is likely to have caused the increase in the magnetic induction with phosphorus addition shown in Fig. 1. It is well known that phosphorus is one of the typical elements which segregate to grain boundaries [1]. This would imply that the texture change shown in Fig. 2 is due to the phosphorus segregation at initial grain boundaries (IGBs). To verify this idea, the effect of the phosphorus segregation at IGBs on recrystallization texture was investigated in 0.1P steel. The hot-rolled band of 0.1P steel was annealed at 825 C for 10 h in an Ar atmosphere, again annealed at 900 C for 2 min in a salt bath, and air-cooled to eliminate the grain boundary segregation of phosphorus. Additionally, some specimens were annealed at 700 C for 100 h in an Ar atmosphere and then quenched into water to promote the grain boundary segregation of phosphorus. Hereinafter, this heat treatment was called as segregation treatment (ST). Grain diameters have not changed during ST. Consequently, specimens with and without ST had the same phosphorus content and initial grain diameter, but the different state of the phosphorus segregation at IGBs. These specimens were cold-rolled to 0.27 mm thick sheets, and then they are annealed at 1000 C for 30 s in an Ar atmosphere. Textures were determined in the same way described above. Recrystallization textures of steels with and without ST after annealing at 1000 C for 30 s are presented in Fig. 3. f1 1 1gh1 1 2i intensity of the steel with ST was much lower than that of the steel without ST. Recrystallization texture without ST was found to be fairly close to that of 0.01P steel shown in Fig. 2. This would mean that recrystallization texture is hardly affected only by phosphorus addition, but the phosphorus segregation at IGBs is responsible for the suppression of f1 1 1gh1 1 2i component. It has been reported that f1 1 1gh1 1 2i component develops and consequently magnetic induction decreases with increasing in phosphorus content [2]. These results are obtained through the experiment without a hot-rolled band annealing. Initial grain diameters decrease with increasing in phosphorus content [2]. Hence, it would seem that the development of f1 1 1gh1 1 2i component with increasing in
ARTICLE IN PRESS I. Tanaka, H. Yashiki / Journal of Magnetism and Magnetic Materials 304 (2006) e611–e613 ψ1
0
ψ1
90
0
90
0 6 5 4 Φ
3 2 1
90
(A)
0
(B)
(×random)
Fig. 3. c2 ¼ 45 ODF of 0.1P steel (A) without and (B) with ST at the mid-plane of 0.27 mm thick sheets after annealing at 1000 C for 30 s.
phosphorus content results from the decrease in initial grain diameters. In the case where steels have the same initial grain diameter and the phosphorus segregation at IGBs is sufficiently promoted, phosphorus would contribute to the suppression of f1 1 1gh1 1 2i component in the similar way to antimony [3]. Accordingly, phosphorus would greatly contribute to the improvement of magnetic properties of non-oriented electrical steel sheets. 4. Conclusion The effect of phosphorus on magnetic properties and recrystallization texture has been investigated. The following results were obtained.
e613
(1) Magnetic induction rises with phosphorus addition, and moreover, magnetic induction of the steel with high phosphorus content only slightly decreases with increasing cold-rolling reduction. (2) In recrystallization textures, f1 1 1gh1 1 2i intensity of the steel with high phosphorus content is lower than that of the steel with low phosphorus content. These textures correspond to the magnetic induction change with phosphorus addition. (3) Recrystallization texture of the high phosphorus content steel without segregation treatment is fairly close to that of the steel with low phosphorus content. Therefore, the phosphorus segregation at initial grain boundaries is responsible for the recrystallization texture control.
References [1] H. Kimura, Trans. Jpn. Inst. Met. 29 (1988) 521–539. [2] J.T. Park, J.S. Woo, S.K. Chang, J. Magn. Magn. Mater. 182 (1998) 381–388. [3] H. Shimanaka, T. Irie, K. Matsumura, H. Nakamura, J. Magn. Magn. Mater. 19 (1980) 63–64.