~ Pergamon 0008-4433(95)00011-9 Canadian Metallurgical Quarterh', Voh 34, No. 3, pp. 25%263,1995 Copyrigh~ ~ 1995 CanadianInstitute of Mining and Metallurgy Printedin GreatBritain. All rights reserved 0008 4433/95 $9.50+0.00 THE ROLE OF SPECIAL GRAIN BOUNDARIES DURING THE GRAIN GROWTH IN Fe 3%Si K. T. LEE and J. A. SZPUNAR Department of Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada, H3A 2A7 ( Receired 2 Auqust 1994: in rerisedJbrm 13 Oclober 1994) Abstract An experimental study of the role of coincidence site lattice (CSL) boundaries in the process of grain growth in grain oriented Fe 3%Si has provided important information about the development of texture. Specimens obtained after decarburization were annealed at temperatures both lower and higher than the temperature of secondary recrystallization. The textures of these specimens were analyzed and the frequency of CSL boundaries from all grains was calculated. In addition, the frequency of CSL boundaries with respect to the {110} <001) grains was calculated for the investigated specimens. By comparing the distribution of CSL boundaries obtained for Goss grains and the distribution of CSL boundaries from all grains, it was possible to predict which CSL boundaries affect the Goss grain growth during secondary recrystallization. Our analysis indicates that Goss grains having a high amount ofi25 CSL boundaries before the secondary recrystallization have a lower number of these boundaries during grain growth. Analysis of other types of grain boundaries indicate that development of the { 110} <001 > texture in silicon steel is not influenced by the total number of CSL boundaries, but rather by the frequency of specific CSL boundaries such as the 525 CSL boundaries. In the investigated specimens, the Goss grains have a size advantage over other grains, which can be considered another important factor in the preferred growth of Goss grains. R~sum~--Une 6tude exp6rimentale du r61e des joints CSL dans le processus de croissance des grains dans du Fe 3%Si nous a apport6 des informations importantes 5. propos du dgveloppement 5. des temp6ratures tout ',i la lois plus basses et plus dlevdes que la temp6rature de recristallation secondaire. Nous avons analys6 la texture de ces specimens et nous avons calcul6 la fr6quencie des joints CSL ~, partir de tousles grains. En plus, nous avons calcul6 la fr6quence des joints CSL par rapport aux grains { 100} <001 >, pour les sp6cimens 6tudi6s. On a pu pr6dire quels joints CSL affectent la croissance des grains de Goss pendant le recristallation secondaire et comparant la distribution des joints CSL obtenus pour les grains de Goss et la distribution des joints CSL de tousles grains. Nos analyses indiquent que les grains de Goss ayant une plus grande quantit6 de joints •5 CSL avant la recristallisation secondaire, ont moins de ces joints pendant la croissances des grains. L'analyse d'autres types de grains montre que le d6veloppement des textures {100} <001 ) darts l'acier au silicium n'est pas influenc6 par le nombre total de joints CSL mais plut6t par la fr~quence specifique des joints CSL comme les joints 25 CSL. Pour les sp6cimens 6tudi6s, les grains de Goss, par leur taille, ont un avantage par rapport aux autres grains, ce qui peut 6tre consid6r6 comme un autre facteur important de croissance pr&6rentielle des grains de Goss. 1. INTRODUCTION Fe-3%Si with a sharp {100} <001) texture has been widely used to build high power transformers. This texture, also called the Goss texture [1], is developed during secondary recrys- tallization. In this process, a few grains having {100} <001) orientation grow very large at the expense of the surrounding grains. In order for secondary recrystallization to occur, the growth of other primary grains must be restrained. For this purpose a variety of precipitates such as manganese sulphide and aluminium nitride have been used [2~4]. Recent studies indicate that the character of grain boundaries influences the Goss texture development during the initial stage of secondary recrystallization and the coincidence site lattice (CSL) bound- aries play a special role [5 7]. These CSL boundaries, especially low-Y boundaries, have low energy: therefore, they are less often occupied by precipitates and are mobile while other gen- eral boundaries are inhibited, Until now it has not been clearly understood what role the CSL boundaries play and why Goss grains grow while other grains do not during the initial stage of secondary recrystallization. This paper reports new experimental data, which provide additional arguments in discussing the role of CSL boundaries. The experiments were carried out on decarburized silicon steel specimens that were annealed at temperatures both below and above the temperature of secondary recrystallization, An etch- pit method [8] was used to identify the orientation of each grain and the grain misorientation of each grain boundary. The frequency of CSL boundaries from all grains and the frequency of CSL boundaries between {100} <001) grains and neigh- bouring grains were obtained. This data was used to analyze the effect of CSL boundaries on Goss texture development. 257
Transcript
~ Pergamon
0008-4433(95)00011-9
Canadian Metallurgical Quarterh', Voh 34, No. 3, pp. 25%263, 1995 Copyrigh~ ~ 1995 Canadian Institute of Mining and Metallurgy
Printed in Great Britain. All rights reserved 0008 4433/95 $9.50+0.00
THE ROLE OF SPECIAL G R A I N B O U N D A R I E S D U R I N G THE G R A I N G R O W T H IN Fe 3%Si
K. T. LEE and J. A. SZPUNAR Department of Metallurgical Engineering, McGill University, 3450 University Street, Montreal,
Quebec, Canada, H3A 2A7
( Receired 2 Auqust 1994: in rerisedJbrm 13 Oclober 1994)
Abstract An experimental study of the role of coincidence site lattice (CSL) boundaries in the process of grain growth in grain oriented Fe 3%Si has provided important information about the development of texture. Specimens obtained after decarburization were annealed at temperatures both lower and higher than the temperature of secondary recrystallization. The textures of these specimens were analyzed and the frequency of CSL boundaries from all grains was calculated. In addition, the frequency of CSL boundaries with respect to the {110} <001) grains was calculated for the investigated specimens. By comparing the distribution of CSL boundaries obtained for Goss grains and the distribution of CSL boundaries from all grains, it was possible to predict which CSL boundaries affect the Goss grain growth during secondary recrystallization.
Our analysis indicates that Goss grains having a high amount ofi25 CSL boundaries before the secondary recrystallization have a lower number of these boundaries during grain growth. Analysis of other types of grain boundaries indicate that development of the { 110} <001 > texture in silicon steel is not influenced by the total number of CSL boundaries, but rather by the frequency of specific CSL boundaries such as the 525 CSL boundaries. In the investigated specimens, the Goss grains have a size advantage over other grains, which can be considered another important factor in the preferred growth of Goss grains.
R~sum~--Une 6tude exp6rimentale du r61e des joints CSL dans le processus de croissance des grains dans du Fe 3%Si nous a apport6 des informations importantes 5. propos du dgveloppement 5. des temp6ratures tout ',i la lois plus basses et plus dlevdes que la temp6rature de recristallation secondaire. Nous avons analys6 la texture de ces specimens et nous avons calcul6 la fr6quencie des joints CSL ~, partir de tousles grains. En plus, nous avons calcul6 la fr6quence des joints CSL par rapport aux grains { 100} <001 >, pour les sp6cimens 6tudi6s. On a pu pr6dire quels joints CSL affectent la croissance des grains de Goss pendant le recristallation secondaire et comparant la distribution des joints CSL obtenus pour les grains de Goss et la distribution des joints CSL de tousles grains.
Nos analyses indiquent que les grains de Goss ayant une plus grande quantit6 de joints •5 CSL avant la recristallisation secondaire, ont moins de ces joints pendant la croissances des grains. L'analyse d'autres types de grains montre que le d6veloppement des textures { 100} <001 ) darts l'acier au silicium n'est pas influenc6 par le nombre total de joints CSL mais plut6t par la fr~quence specifique des joints CSL comme les joints 25 CSL. Pour les sp6cimens 6tudi6s, les grains de Goss, par leur taille, ont un avantage par rapport aux autres grains, ce qui peut 6tre consid6r6 comme un autre facteur important de croissance pr&6rentielle des grains de Goss.
1. I N T R O D U C T I O N
F e - 3 % S i with a sharp {100} <001) texture has been widely used to build high power t ransformers . This texture, also called the Goss texture [1], is developed dur ing secondary recrys- tallization. In this process, a few grains having {100} <001) or ienta t ion grow very large at the expense of the su r rounding grains. In order for secondary recrystall ization to occur, the growth of o ther pr imary grains must be restrained. For this purpose a variety of precipitates such as manganese sulphide and a luminium nitr ide have been used [2~4]. Recent studies indicate tha t the character of grain boundar ies influences the Goss texture deve lopment dur ing the initial stage of secondary recrystall ization and the coincidence site lattice (CSL) bound- aries play a special role [5 7]. These CSL boundar ies , especially low-Y boundaries , have low energy: therefore, they are less
often occupied by precipitates and are mobile while other gen- eral boundar ies are inhibited, Unt i l now it has not been clearly unders tood what role the CSL boundar ies play and why Goss grains grow while other grains do not dur ing the initial stage of secondary recrystallization.
This paper reports new experimental data , which provide addi t ional a rguments in discussing the role of CSL boundaries . The experiments were carried out on decarburized silicon steel specimens tha t were annealed at tempera tures bo th below and above the tempera ture of secondary recrystallization, An etch- pit method [8] was used to identify the or ien ta t ion of each grain and the grain misor ienta t ion of each grain boundary . The frequency of CSL boundar ies f rom all grains and the frequency of CSL boundar ies between {100} <001) grains and neigh- bour ing grains were obtained. This data was used to analyze the effect of CSL boundar ies on Goss texture development.
257
258 K. T. LEE and J. A, SZPUNAR : THE ROLE OF SPECIAL GRAIN BOUNDARIES DURING THE GRAIN GROWTH IN Fe-3%Si
Table 1. Chemical composition of the grain oriented silicon steel
Conventional grain oriented silicon steel, for which MnS precipitates are the principle grain boundary inhibitor, was used for this study. The chemical composit ion of this steel is listed in Table 1. Two stages of cold rolling were used, with an inter- mediate anneal between them, to reduce the sheet thickness. Decarburization annealing was carried out in a wet hydrogen (H2) atmosphere to reduce the carbon content. The decar- burized steel sheet was cut into 15 × 25 mm samples, which were then annealed at temperatures just below and above the temperature at which secondary recrystallization starts in the helium atmosphere. The annealing and quenching were done in a high-temperature stage attached to a Rigaku x-ray diffract- ometer system and controlled by a Rigaku temperature con- troller (PTC-10C). The temperature was first increased at 30°C/rain up to 660°C, and then at 2°C/min to the final tem- perature (Fig. 1). The orientation distribution function (ODF) of both the decarburized and annealed specimens was measured using a Siemens texture measuring system consisting of a con- trolled horizontal diffractometer with a Huber Eulerian cradle.
A layer that was about 22-23/am thick (about 1/5 of the half- thickness of the steel sheet) was removed from the surface by mechanical polishing. According to lnokuti [9] and Abbur- uzzese [10], secondary recrystallization starts in this area, and thus it is the most interesting area throughout the entire cross- section of specimen. Etch-pits were produced both for the decar- burized and annealed specimens using the following procedure. First, specimens were immersed in a 5% H F + 9 5 % H202 solu- tion for 20 s for surface conditioning. They were then immersed in a 15% H F + 8 5 % H202 solution for 1 2 s. Etch-pits were made during the second step, and their size and number were very sensitive to the immersion time and temperature. After the second immersion, specimens were kept in a 1% H F + 4 %
I 0 0 0 [ 860 ~..~e~ ~ °
00o p "k =~.600 I- / x_ ~
I / .~ ~_ ~.~ ',, ',:, 4 0 0 l 1=~ ~ ~,X
0 ~ f ~ t
0 50 100 150 t ( r a i n )
Fig. 1. Annealing procedure for the specimens.
200
H2O 2 + 20% H3PO 4+ 75% H20 (distilled water) solution for 10 s. After this stage, the shape of the etch-pits became clearer and grain boundaries were revealed. Depending on the etching condition, a third step of etching was used to colour the surface of each grain with a different tone of brown as a function of their orientation.
Photographs of the grain and etch pits were taken with a camera connected to an optical microscope. Each photograph contains about 20 25 grains. The etch-pit figures and grain boundaries on the photographs were digitized using an image analyzer, and the digitized data was then analyzed by computer. Through computer analysis, the orientation of each grain was obtained. From this, the frequency of CSL boundaries was also obtained. The coincidence boundaries were identified using Brandon's criterion [11].
3. R E S U L T S AND D I S C U S S I O N
The results of the texture measurements for the specimens annealed at various annealing temperatures are shown in Fig. 2. The O D F obtained from the decarburized specimen shows typical primary recrystallization texture components, consisting of a relatively strong gamma fibre (~ = 55.4 °, 42 = 45 °, 0 < 4, < 90") and a weak alpha fibre (41 = 0 , 42 = 45", 0 < • < 90"). Apart from these components, other recrys- tallization components spread along the eta fibre (4~ = 0°, 42 = 0% 0= < • < 90 °) was observed. The strong {100} (112) component of the gamma fibre is shown in the 4~ = 90" section of the ODF. There was no significant change in the Goss com- ponent in the specimen annealed to 860°C as compared to that in the decarburized specimen, except that the gamma fibre became weaker. In the specimen annealed to 900°C the gamma fibre decreased and the { 100} (001) texture component (Goss component) increased. In the specimen annealed to 910°C the primary recrystallization texture along the gamma fibre was still observed, although a significant increase of the Goss texture was observed [Fig. 2 (d)]. It was assumed that secondary recrys- tallization started at a temperature between 9 0 0 C and 910'C. Microscopic analysis on the grain size distribution was carried out for the annealed specimens. In the specimen annealed to 9 1 0 C large Goss grains, with a diameter of more than several hundred micrometers, were observed.
To evaluate the size and orientation of each grain the etch- pit method was used. Figure 3 shows sample results from the computer analysis of the grain orientation. Assuming there are three grains having etch-pits, the Miller indices {hkl} and Euler angles cp~, ~, ~02 are calculated using the digitized data charac- terizing etch-pits and grain boundaries. As the number of etch-
K, T. LEE and J. A. SZPUNAR: THE ROLE OF SPECIAL GRAIN BOUNDARIES D U R I N G THE GRAIN G R O W T H IN Fe-3%Si 259
(a) I, bi
\ \ N \
Coatou~: 1.0, 3.0, 4.0, 5.0
l, ki2
p~ (b)
Contours: 1.0, 3.0, 4.0
Pt~
(c)
7
% %
o % 326 .. 0
o
(d)
.o
• o
%
~0
C o n l , o u l ~ :
C,,. / v
0 % k3
o
J v t . / v
5.0, 10.0, 20.0, 30.0
Fig. 2. Orientation distribution function (ODF) obtained from (a) the decarburized specimen, (b) the specimen annealed at 860 C, (c) the specimen annealed at 900 C, (d) the specimen annealed at 910:C.
260 K. T. LEE and J. A. SZPUNAR : THE ROLE OF SPECIAL GRAIN BOUNDARIES DURING THE GRAIN GROWTH IN Fe 3%Si
Fig. 3. Sample results on grain orientation from the etch-pit method.
pits in a grain increases, the determination of the grain orien- tation becomes more accurate. The orientation and grain sizes of about 600 grains were obtained for each specimen.
Figure 4 shows the mean diameter of grains for the major texture components. The names of the specimens according to their annealing temperatures are shown on the x-axis: "DC'" represents the decarburized specimen. In the specimen amlealed to 91OC, large Goss grains were observed that were several hundred micrometers in diameter. Because of their huge size compared to the other matrix grains, any Goss grains greater than 50 #m in diameter were excluded from the grain size distribution analysis and analysis of the volume fraction chan- ges. For this reason the real mean grain diameter of the ~1001 <001> grains is marked with a dashed line. Except for some Goss grains, other grains were smaller than 50/xm. As shown
24
ZZ
._. 20
.~ i8! lea 16
14
12
Fig. 4. Grain
o - - All g r a i n s e ~111~<112> n - - ~1111<110> ~--~iooI<ooI> / - 7 x-- ~1001<011> /
I I I " I)C 860 900 910
T (°C)
size changes of matrix grains and components.
major texture
in Fig. 4, the {110} (001) grains and {100} <011> grains were slightly larger than other grains after the decarburization annealing, and they did not grow until the temperature reached 860C. At this temperature, the {100} <001> and {111} <110> grains began to grow. Other grains also grew at a temperature between 860"C and 9 0 0 C , especially the Goss grains. It seems that the Goss grains had a size advantage over other grains for secondary recrystallization. After the secondary recrys- tallization started at a temperature between 900 'C and 910"C, the Goss grains grew abruptly, while other grains, especially ~ 100} <011) grains, shrank. One exception was the growth of ~1001 <001 ) grains ; however, these grains seem to be too small to compete with the large Goss grains.
Figure 5 shows the volume fraction changes of the major texture components. The Goss grains were a minor texture component in the decarburized specimen, and their amount
Fig. 5. Volume fraction of major texture components.
K. T. LEE and J. A. SZPUNAR: THE ROLE OF SPECIAL GRA1N BOUNDARIES DUR1NG THE GRAIN GROWTH IN Fe 3%Si 261
became even smaller as the annealing temperature increased to 860'JC. However, the volume fraction of Goss grains started to increase above this temperature due to the increase in their size. The real volume fraction of Goss grains after secondary recrystallization is shown with a dashed line. The volume tYac- tion of other grains is in fact much less than that shown in this figure, because Goss grains larger than 50/~m were not counted in the specimen annealed at 910 C. The ~jl00 ~, {001) grains behaved similarly to the Goss grains before secondary recrys- tallization. Their volume decreased during the annealing up to 860C and increased as annealing temperature increased to 900C. This corresponds to the ODF changes presented in Fig. 2. The volume fraction of {1001 (001) grains decreased abruptly after secondary recrystallization started, even though some of them survived and their diameter increased (Fig. 4). As the annealing temperature increased to 860 C, the volume fraction of [111} {110) grains increased, while the volume fractions of other texture components decreased. This fraction along with the {111} {112), ~tl00} {001) and '~100} {011} fractions decreased after secondary recrystallization started.
One of the advantages of the method used in this work is that the coincidence orientation relationship can be obtained directly from the specimens by identifying the orientation of each grain. For each specimen, the orientation of about 600 grains was analyzed and the frequency of CSL boundaries up to 1233 was obtained. To understand the development of [110} {001) texture in grain oriented silicon steel, it is important to investigate the CSL relationship with respect to {1101 (001) grains. Thus, the frequency of CSL boundaries between Goss grains and neighbouring grains was also calculated for each specimen. In the specimen annealed at 910C, the {110} (001) grains with a diameter smaller than 50 tim and those with a diameter larger than 50 ,urn were analyzed separately for the calculation of the frequency of CSL boundaries.
Figure 6 shows the distribution of CSL boundaries up to 5233 in the decarburized and annealed specimens. In the decar- burized specimen, Goss grains had higher frequency of 125, 223, 5227 and 5229 CSL boundaries than the general matrix grains. On the other hand, Goss grains did not have any of 123,537 and 129 CSL boundaries. As the annealing temperature reached 860°C, the Goss grains had higher amounts of 535, 5323, 1227 and 5229 CSL boundaries, but no other CSL boundaries. At 900°C, the frequency of 125, 1213, 5225 and Z29 CSL boundaries calculated from all grains increased and the frequency of 523 boundaries decreased. The Goss grains had a high amount of 525 and 5229 CSL boundaries. However, the frequency of 525 CSL boundaries decreased compared to the previous stage. The large Goss grains in the specimen annealed at 910 C are suspected to be nuclei for secondary grains, and may grow bigger using the size advantage. By comparing the distribution of CSL boundaries of large Goss grains to that of CSL bound- aries of small Goss grains that did not grow after secondary recrystallization started, it is clear which CSL boundaries affect the Goss grain growth during secondary recrystallization. A dot hatched area in Fig. 6(d) shows the frequency of CSL boundaries between large Goss grains and neighbouring grains. After secondary recrystallization, large Goss grains did not have as many 125 CSL boundaries as did the small Goss grains. It is known that the low-E CSL boundaries have relatively higher mobility than other boundaries. It seems that Goss
grains having higher amounts of Z5 CSL boundaries before secondary recrystallization grew faster than other grains as the temperature increased. As a result, the frequency of 525 CSL boundaries with respect to large Goss grains decreased. The consumption of Z5 CSE boundaries during annealing from 860 C to 900' C may contribute to the preference of growth of Goss grains. The growth of other grains during annealing from 860 C to 900C is also explained by consumption of I23 CSL boundaries. The Goss grains that did not have enough 525 CSL boundaries for grain growth before secondary recrystallization, and so remained the same size, began to have a high amount of 5"5 as the temperature increased to 910°C. Harase [12] pointed out that the mechanism of the {110} {001) secondary recrys- tallization texture evolution in the silicon steel with single-stage cold rolling is due to 529 CSL boundaries, and that the {616} (372) secondary recrystallization evolves if the 125 value is high. However, Goss grains did not have 29 CSL boundaries until secondary recrystallization started in the specimen used for this work. The result obtained in this work does not correspond with Harase's result, possibly due to the difference of specimen processing. Also, MnS and AIN precipitates were used as grain boundary inhibitors for Harase's specimens, while only MnS precipitates were used as a grain boundary inhibitor for the specimens used in this work. Because of stronger grain bound- ary inhibition, the secondary recrystallization occurred at a higher temperature, around 1070"C, in his material. It is also noticeable that the frequency of 229 CSL boundaries is high for the large Goss grains, just after the start of secondary recrystallization. It seems that Goss grains keep the 5229 coinci- dence relationship with neighbouring grains, while the 525 CSL boundaries move faster than other boundaries during the initial stage of secondary recrystallization. In the specimen annealed at 910 C, Goss grains having 529 CSL boundaries were observed.
The frequency changes of some CSL boundaries through the annealing process are shown in Fig. 7. As shown in Fig. 7(a), two types of CSL boundary were observed. The frequency of Y~3. Y~7, E9 and 5319 CSL boundaries decreased just before secondary recrystallization started; however, their frequency increased after secondary recrystallization started. Other types of CSL boundary, such as 535, 5213, El7, 2;25 and 5229 bound- aries, were active before secondary recrystallization started and were consumed abruptly afterwards. The frequency changes of certain CSL boundaries with respect to Goss grains is shown in Fig. 7(b), For the specimen annealed at 910~C, the frequency change of CSL boundaries with respect to large Goss grains is marked by a dashed line. Goss grains did not have 5"3 and 127 CSL boundaries throughout the annealing process. It is clear that the large Goss grains have fewer 525 boundaries and more 539 and E29 boundaries than the small Goss grains. The large Goss grains did not have 1213 boundaries.
Figure 8 shows the change of the total amount of CSL bound- aries up to 1233. In the decarburized specimen 19% of grain boundaries were CSL boundaries. In the specimen annealed at 860:C the frequency of CSL boundaries decreased to 18 %, and increased to 24% as annealing temperature reached 900:C. It seems that CSL boundaries become more active before the start secondary recrystallization. When secondary recrystallization started the frequency of CSL boundaries decreased abruptly, owing to the growth of a strong {ll0} {001) texture. Fortes and Ralph [7] reported that boundaries with a high density of
262 K.T. LEE and J. A. SZPUNAR : THE ROLE OF SPECIAL GRAIN BOUNDARIES DURING THE GRAIN GROWTH IN Fe 3%Si
(a)
ii l,kddL 3 5 7 9 I t 13 15 17 19 21 23 25 27 29 31 33
X value
ft.
1 4 - (b)
1 2 - -
1 0 - -
8 - -
6 -
4 1 i111 i , , ] l ] ,, o • •
3 7 9 I I 13 15 17 19 21 23 25 27 29 31 33
E value
Frequency of CSL boundaries from all grains. (C) 14
7 " ~ Frequency of CSL boundaries from Goss and neighbouring grains.
12
Frequency of CSL boundaries from large Goss and neighbouring grains.
I0 10
~" 61 ~r 6
4i 4'
o = _ - I~ _ i t . l f l 3 5 7 9 I1 13 15 17 19 21 23 25 27 29 31 33 0
E value Fig. 6. Distribution of CSL boundaries in (a) the decarburized specimen, (b) the specimen annealed at
860 C, (c) the specimen annealed at 900 C, (d) the specimen annealed at 910 C.
coincidence sites are less often occupied by impurities. In silicon steel, MnS precipitates are less segregated at CSL boundaries: therefore, CSL boundaries can move while other general bound- aries are inhibited. However, in this work Goss grains have lower amounts of CSL boundaries than general grains before the start of secondary recrystaltization. It seems that the [1101 (001) texture development in silicon steel is not influenced by the total number of CSL boundaries, but more likely by some specific CSL relationship such as the E5 boundary. After sec-
ondary recrystallization started, large Goss grains had slightly higher amounts of CSL boundaries (27%) than small Goss grains (23%), while the Goss grains before secondary recrys- tallization have about 22% CSL boundaries.
4. C O N C L U S I O N S
The changes in the distribution of CSL boundaries up to E33 for all matrix grains and from the Goss and neighbouring
K. T. LEE and J. A. SZPUNAR: THE ROLE OF SPECIAL GRAIN BOUNDARIES DURING THE GRAIN GROWTH IN Fe 3%Si 263
6 (a)
• Sigma 3 + Sigma 7 , , ~ x Sigma5 O Sigma 13 / ~
5 * Sigma 9 o Sigma 19 /
2~
!
D e 860 900 910 T (°C)
14 (b)
12 /~
13(2 860 900 910 T (°C)
Fig. 7. Frequency changes of some CSL boundaries through the anneal- ing process. (a) Frequency changes of CSL boundaries from general grains. (b) Frequency changes of CSL boundaries with respect to Goss
grains.
3o ! [ • Frequency of CSL boundaries from all grains_ l I
| + Frequency of CSL boundaries from Goss t "" "] 25 1 and neighbouring g r a i ~
.-, 2 0 ~ ~ ~ " ~ ' ' ~
grains, were analyzed to study the role of CSL boundaries in the development of { 1101 (001 ~ texture in grain oriented silicon steel.
The results obtained support the conclusions that the Goss texture development in Fe-3%Si is associated with Z5 CSL boundaries. The consumption of these boundaries during annealing from 860 C to 900 C may contribute to the p r e f erential growth of Goss grains. The Goss grains also have a size advantage over other grains during the secondary grain growth. The grain growth of other grains during the annealing process
IO
5 L
DC I I
860 900 910 T (°C)
Fig. 8. The change of total amount of CSL boundaries up to Z33.
in the temperature range 860-900 C is related to the decrease of frequency of E3 CSL boundaries. In the initial stage of secondary recrystallization, Goss grains having more Z5 CSL boundaries grew faster than other grains, due to high mobility of E5 boundaries. As a result, the frequency of Z5 CSL bound- aries with respect to large Goss grains decreased.
The Goss grains have fewer CSL boundaries than general grains before the start of secondary recrystallization. It seems that the development of {110} (001) texture in silicon steel is not influenced by the total amount of CSL boundaries but by the amount of some specific CSL boundaries such as the Z5 boundaries.
R E F E R E N C E S
1. N. P, Goss, Trans. Am. Soc. Metals23, 511 (1935). 2. J, E. May and D. Turnbull, Trans, Am. Inst. Min. Eng. 212, 769
(1958). 3. F. Assmus, K. Detert and G. Ibe, Z. Metallkd. 48, 344 (1957). 4. S. Taguchi, A. Sakakura, S. Matsumoto, K. Takasima and K.
Kuroki, J. Magn. Mater. 2, 121 (1976). 5. K. T. Aust, in Proceedings of the International Symposium on Tex-
tures in Research and Practice, p. 160. Springer, Berlin 1968. 6. S. Ranganathan, Acta Crystallogr. 21, 197 (1966). 7. M. A. Fortes and B. Ralph, Aeta Metall. 15, 707 (1967). 8. K. T. Lee, G. deWit, A. Morawiec and J. A. Szpunar, J. Mater.
Sci. 30, 1327 (1995). 9. Y. lnokuti. C. Maeda and Y. lto, Trans. ISIJ27~ 139 (1987).
10. G. Abbruzzese and R. R. Bitti, J. Magn. Mater. 41, 11 (1984). I 1. D. G. Brandon, Acta Metall. 14, 1479 (1966). 12. J. Harase, R. Shimizu, Y. Yoshitomi, Y. Ushigami and N. Taka-
hashi, in Proc. Materials I4~,ek '92, Chicago, Illinois, 1992.
