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Coincidence grain boundary and role of primary recrystallized grain growth on secondary recrystallization texture evolution in Fe3%Si alloy
Acta metall, mater. Vol. 42, No. 8, pp. 2593-2602, 1994
Pergamon
0956-7151(94)E0073-P
Copyright© 1994ElsevierScienceLtd Printed in Great Britain. All fights reserved 0956-7151/94$7.00+ 0.00
COINCIDENCE GRAIN BOUNDARY A N D ROLE OF PRIMARY RECRYSTALLIZED GRAIN GROWTH ON SECONDARY RECRYSTALLIZATION TEXTURE EVOLUTION IN Fe-3 % Si ALLOY Y. Y O S H I T O M I 1, Y. USHIGAMI z, J. HARASE 2, T. NAKAYAMA2, H. MASUI 2 and N. TAKAHASHI3 SYawata R&D Laboratory, Nippon Steel Corporation, Kitakyushu, 2Electromagnetic Materials Laboratory, Steel Research Laboratories, Nippon Steel Corporation, Futtsu, Chiba and 3Technical Development Bureau, Nippon Steel Corporation, Kitakyushu, Japan (Received 8 April 1993; in revised form 11 January 1994)
Al~traet--Secondary recrystallization behavior in the presence of AIN in Fe-3%Si alloy was investigated with special reference to the influence of primary recrystallized grain growth on secondary recrystallization texture. The more dominant grain growth was marked by the evolution of {110}(001> secondary recrystallized grains in the higher temperature range. In the case of smaller primary reerystailized grains, the {110}(227> secondary recrystallized grains were mainly evolved on annealing at the lower temperature range. The frequency of ~9 coincidence boundaries in relation to the {110}(001> texture component was higher than that of I:5 coincidence boundaries in relation to {110}(227) component. The mechanism of these evolutions of secondary recrystallization texture can be explained by the assumption that the ~5 coincidence boundaries are more mobile than the ~9 coincidence boundaries in the lower temperature range. The primary recrystallized grain growth is considered to have a role in determining what should be the secondary recrystallization temperature.
1. INTRODUCTION Grain oriented silicon steel is characterized by the presence of a sharp {110}(001) texture, i.e. Goss texture, which is produced by secondary recrystallization [1]. It has been pointed out that, in an Fe-3%Si alloy in which there were precipitates, evolution of Goss texture is associated with the special grain boundary migration characteristics of Y9 type coincidence boundaries [2, 3]. It has been also reported that primary recrystallized grain growth during secondary recrystallization annealing has an influence on secondary recrystallization behavior [4]. In order to further clarify the role of primary recrystallized grain growth on secondary recrystallization behavior, the present authors have investigated the relationship between the primary recrystallized grain growth and the secondary recrystallization texture. In this study, both the primary recrystallized grain growth during primary recrystallization annealing and that during secondary recrystallization annealing were investigated for finding out the general relationship between the primary recrystallized grain growth and the secondary recrystallization texture. The alloy selected to study was Fe-3%Si alloy in which AIN precipi-
tates were present in the microstructure as a grain growth inhibitor. The alloy was processed using a one stage cold rolling method [5]. 2. SHG METHOD [3] During grain growth, a growing grain will eventually come in contact with matrix grains not initially into direct contact with it. Therefore, it is necessary to know the orientation relationships between a growing grain and the matrix grains. In this connection, a method termed SH (Simulation by Hypothetical nucleus) has been developed [2]. The term nucleus refers to a growing grain. However, the SH method is time consuming as the orientations of several hundreds of grains have had to be measured by Electron Channeling Patterns (ECP) in the SEM. The SHG method (SH method in Generalized form) has thus been developed which uses the three-dimensional orientation distribution of grains as obtained by applying the vector method [6] to pole figures measured by X-ray diffraction. In the vector method, grain orientation is represented by three parameters co, ~b and ~. The unit triangle Tz, in which plane normals are to be presented, is divided into 36
2593
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
2594
"Boxes" of equal angular areas defined by to, ~ and numbered 1-36 with a representative orientation (HKL) assigned to each "Box" (Fig. 1). For example, (HKL) for Box No. 1, Box No. 29 and Box No. 36 are (001), (011) and (111), respectively. Rotations, (, about each orientation are divided into 72 intervals at steps of 5°. As another unit triangle T2 of mirror symmetry with TI is required to represent the entire orientation space, any orientation can be classified by one of 5184 orientations {2(unit triangle) x 36(Box) x 72(()} in the Vector method. Parameters co, ~ and ( used in the Vector Method and Euler angle ~bl, ~b2and • used in th harmonic method by Bunge [7] are in the following relationship sin ~b2= sin ~
(1)
sin ~l = sin ~, cos ( + cos ~, sin (
(2)
cos • = cos ~/(cos 2 @ + tan 2 to)l/2
(3)
sin ~ = sin ~2
(4)
tan to = - cos ~b2 tan •
(5)
or
sin ~ = cos q~] cos ~b2+ sin q~l cos • cos ~2 + sin ~1 sin2
~ cos ~2/(1 + cos 4).
(6)
Due to the symmetrical nature of the existing texture, 1296 orientations {35(Box) x 36(~)} can be used in the SHG method to represent orientations space. Mutual coincidence orientations from YA to Z33c with respect to each of the 1296 orientation are then calculated. In the calculation of coincidence orientation, Brandon's criterion [8] is used. The intensity of any coincidence orientation, Y4, for a nucleus orientation N is expressed as lcZi. The intensity of the nucleus orientation N is expressed as (if1) 45 °
3 9 . 8
°
a4.4~
~ /'l.--~
~ ,
23,4° ~
17"70 ~
:,
,,
~=
I (001)
6.9 °
12.0 °
17.2 °
22.4 °
27.7 °
333 °
=
~.9 °
I(o:1) 39.0 °
45°(011)
to------->
Fig. I. Definitionof box used in the vector method. Stereographic triangleT~ is divided into 36 parts of cqui-sphcdcal areas (boxes) by o) and ~#. A representative (IIKL) is assigned to each box.
IN. The probability of selective growth of a nucleus grain can be considered to be associated with the number of nucleus grains in the matrix and the number of grains that could come into coincidence with it. This is based on the assumption that coincidence boundaries (except Z 1 and Z3) are more mobile than random boundaries in the presence of solutes [9] or precipitates [10]. 3. EXPERIMENTAL
3.1. Experimental conditions 3.1.1. Case of primary recrystallized grain growth during secondary recrystallization annealing (Specimen A). The starting material was Fe-3%Si hot-rolled sheet, Specimen A, with the following chemical compositions; C: 0.07, Si: 3.2, AI: 0.028, N: 0.0079mass %. Primary recrystallized sheets for Specimen A were prepared as follows. Hot-rolled sheets 2.3ram thick were annealed at I I00°C for 120 s, followed by cold rolling to 0.285 mm thickness. Primary recrystallization annealing was carried out at 830°C for 150s in a 25% N2-H 2 gas mixture of dew point 68°C. Then, the primary recrystallized specimens were heated up to II00°C at a heating rate of 15°C/h in (a) 90%N1-H 2 or (b) 100%H 2 gasses. The specimens were extracted during this heating stage, and were quenched. The annealing condition (a) was chosen to inhibit the primary recrystallized grain growth more effectively before the onset of secondary recrystallization, because of the effect of nitriding from the annealing atmosphere. On the other hand, the annealing condition (b) was chosen to produce decreasing amount of inhibitors so that the primary recrystallized grain growth before the onset of secondary recrystallization would be easier.
3.1.2. Case of primary recrystallized grain growth during primary recrystallization annealing (Specimen B). The starting material was Fc-3%Si hot-rolled sheet, Specimen B, with the following chemical compositions; C: 0.05, Si: 3.3, AI: 0.026, N: 0.0074mass%. Primary recrystallized sheets for Specimen B were prepared as follows. Hot-rolled sheets 2.3mm thick were annealed at ll00°C for 120 s, cold rolled to 0.285 mm thickness followed by primary recrystallization annealing at (1) 750°C, (2) 770°C, (3) 810°C, (4) 830°C, (5) 850°C, for 150s, in a 25%N2-H2 gas mixture of dew point 60°C In order to inhibit the primary recrystallized grain growth effectively before the onset of secondary recrystallization, a nitriding with NH3 gas was used for the primary recrystallized specimens under the conditions, temperature 750°C, time 30 s, gas mixture 25%N2-H2, dew point <0°C. The amount of N after this nitriding was about 0.023 mass%. Then, the specimens were heated to 1150°C at a heating rate of 15°C/h in 25%N2-H2 gas mixture. The specimens were extracted during this heating stage and quenched.
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
3.2. Investigations Microstructure and macrostructure changes during secondary recrystallization annealing were investigated by eye and using optical microscopy. The grain size of the primary recrystallized specimens was measured using Phase Contrast image analysis [11]. Here, large grains which penetrated through the whole thickness of the specimen were judged as secondary recrystallized grains. Precipitate changes during secondary recrystallization annealing were investigated using chemical analysis of N and A1N. For the investigation of the primary texture, 70/~m thick specimens were extracted from the surface layer, from a depth of 1/5th the thickness and from the central section of the primary recrystallized sheet. The complete {100} pole figures were determined by X-ray measurement and three-dimensional texture analyses were carried out by the vector method [6]. Orientations of the secondary recrystallized grains were investigated by back-reflection Laue diffraction method. The orientation relationships between secondary recrystallized grains and matrix primary recrystallized grains were investigated using the SHG method [3]. 4. RESULTS
4.1. Case of primary recrystallized gra& growth during secondary recrystallization annealing (Specimen A) 4. I. 1. Secondary recrystallization behavior and N, AIN changes during secondary recrystallization annealing. The average grain diameter of the primary recrystallized specimen after primary recrystallization annealing was 8.4pm and that of a specimen extracted at 925°C, just before the onset of secondary recrystallization during the heating stage of secondary recrystallization annealing, was 9.1/tm in the case of treatment (a) and 10.0 #m in the case of treatment (b). In the case of treatment (b), the growth of the primary recrystallized grains was more striking, especially, in the surface region of the specimen, during the secondary recrystallization annealing, compared with the case (a). Figure 2 shows the secondary recrystallization behavior. In the case of treatment (a), thd secondary recrystallization temperature at 50% secondary recrystallized was lower than that for treatment (b) by 40°C. This suggests that the secondary recrystallization temperature is lower the smaller the primary recrystallized matrix grains, and this is because e r a bigger driving force for grain growth. The number of secondary recrystallized grains obtained in treatment (a) was about twice as many as in (b). In the case of treatment (a), with increasing temperature in the range 800-925°C during the heating stage of secondary recrystallization annealing, the amounts of N and N as AIN increased to 0.017 and 0.014mass% by 925°C, respectively. Then, in both cases, with increasing
2595
temperature in above 925°C, the amounts of N and N as AIN decreased by 0.02 to 0.03mass% by 1100°C.
4.1.2. Texture of primary recrystallized grains and orientation of secondary recrystallized grains. Figure 3 shows three-dimensional textures calculated from the complete {100} pole figures of the surface layer of primary recrystallized Specimens A, extracted at 925°C, just before the onset of secondary recrystallization. In Fig. 3, the orientation is specified by its (, ~o, ¢ value. Along the top of the figure are the respective axes for the appropriate co, ~b values, and next to each is box number as given in Fig. 1. The main texture components in any case were {111}<112>, {411}<148> and {100}<025>. Figure 4 shows the final orientations of secondary recrystaliized grains of Specimen A. In the case of treatment (a), {110}<227> secondary recrystallized grains were mainly evolved. In the case of treatment (b), {110}<001> secondary recrystallized grains were evolved. 4.2. Case of primary recrystallized grain growth during primary recrystallization annealing (Specimen
B) 4.2.1. Secondary recrystallization behavior and N change during secondary recrystallization annealing. The average diameters of primary recrystallized grains in Specimen B before secondary Number of secondary
recrystallized grains~m-z)
5.8
1.0
2.8
?--
/ /
Anneal ing atmosphere
/ /
90~N2-H2
"~ ¢D 0.8
/ / / /
100~/6Hz
0.6 b
/ 0.4 .
II I I I
o.2
I ,t
0
I
_
I 1o I
I
]
j
950 1000 Temperature, T/~3 Fig. 2. Secondary recrystallization in the heating stage of secondary recystallization annealing (Specimen A).
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
2596
recrystallization annealing were 13.7, 17.0, 23.0, 26.9 and 29.1/~m in the cases of annealing at (1) 750°C, (2) 770°C, (3) 810°C, (4) 830°C and (5) 850°C, respectively. The higher the primary recrystallization annealing temperature, the larger the average grain diameter of primary recrystallized specimen. In all cases, the primary recrystallized grain growth was less than 0.4#m in diameter in the heating stage of secondary recrystallization annealing before the onset of secondary recrystallization. Figure 5 shows the secondary recrystallization behavior of specimen B. The higher the primary recrystallization annealing
A
~80o8-~~,~ ' = '= ~ '= '~ ~ '~ '~ '~ '~ '-. '± -~ ~ ~ ~ ~ ~ ~ ~ 150° I20
60°
0
1 2 3 ,~
5
,~
5
~
oO 15o 30° ~ O)( ~-= 45 °)
o
~ (o)----45°)*--
(.o ( ~ = 0°)~---
temperature, the higher the secondary recrystallization temperature. On annealing at the lowest temperature, 750°C, the number of secondary recrystallized grains obtained was 3-6 times as grains obtained on annealing at 770 and 810°C. In all cases, with increasing temperature in the range above 950°C, during the heating stage of secondary recrystallization annealing, the amount of N decreased to about 0.016 mass% by 1150°C.
4.2.2. Texture of primary recrystallized grains and orientation of secondary recrystallized grains. Figure 6 shows three-dimensional textures calculated from the complete {100} pole figures of the surface layer of primary recrystallized Specimen B before the secondary recrystallization annealing. In Fig. 6, the orientation is presented in the same mode as Fig. 3. The main texture components in all cases were {111}(112), {411}(148) and {100}(025). Figure 7 shows the orientations of secondary recrystallized grains in Specimen B. With increasing temperature of the primary recrystallization annealing, the number of secondary recrystallized grains with the orientation deviation from {110}(001> decreased, mainly high decrease in the {110}(227) population. In the case of (3), the highest temperature condition of primary recrystallization annealing to achieve perfect secondary recrystallization, the sharpest {110}(001) secondary recrystallized grains were evolved. 5. DISCUSSION
6
0
~.
4 6°
3
~
o ~1
2
1
* 15" 30° 45° 80" 15" ~ o ) ( a p = 45 ° ) ~p((o =45°)*--
C
~t~eec~,
O
,~,
~ ~(o(¢=
45 °)
~ ,
, , ~
m ( if-= 0°)~-~,~,.~,~..~ ~
o ¢(co=4C).-
co(¢=0°) *-
3. Three dimensional orientation distributions of the primary recrystallized specimens. (A) After primary reerystallization annealing. (B, C) Taken at 925°C in the heating stage of secondary recrystallization annealing. (B) Annealed in 90%N2-H2; (C) Annealed in 100%H 2 (Specimen A). Fig.
It has been shown that the texture evolved by grain growth in the presence of precipitates is associated with the intensity of the inhibitors and the intensity of grains with coincidence orientation relationships (ICE/) [12]. When both the inhibitor intensity and IcZi value are higher than critical values, the orientation N which has greater intensity than a critical value and has the highest IcEi value (except E1 and E3 type coincidence orientations) among these nucleus orientations in the matrix, becomes the major orientation after grain growth. The secondary recrystaUization by this mechanism is referred to as the "Ic mechanism". When either the inhibitor intensity or IcZi value is smaller than their critical values, the orientation (N) having the highest PeN Ei value in the matrix becomes the major orientation after grain growth. The secondary recrystallization by this mechanism is referred to as the "PEN mechanism". For the same PcNEi (=ICE/ x/N) value, the weaker the inhibitor level, the more dominant IN, and conversely stronger the inhibitor level, the more dominant IcEi. The inhibitor effect on PcNE1 value increases with increase in the inhibitor intensity. For example, the mechanism of the (110)[001] secondary recrystallization [5] or (100) [001 ] secondary recrystallization [ 13] developed by Taguchi et al. is the Ic mechanism and that of the (110)[001] secondary recrystallization [14] developed by Goss is the Pcr~ mechanism. Based on this back-
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
90~/~N2_H2
A n n e a l ing
atmosphere
2597
1 0 0 ~ H2
KD
RD
.
-.t
D
L
Fig. 4. {100} pole figures of secondary recrystallized grains in the specimen taken at 1050°Cin the heating stage of secondary recrystallization annealing (Specimen A). ground, the influence of the primary recrystallized grain growth on the secondary recrystallization is discussed. The mechanism of the secondary recrystallization in the present experiment is considered to be the "lc mechanism" as specimens were processed Number of s e c o n d a r y r eerys tal I ized grains(cm -z) 0.27 08 2 *.!5 tim
1.0
•~
08
~
0.6
D
Temperature L3 of primary recrys tal I izat ion ann eal ing
0 e~ m
o
0.4
¢
~5(
.--- 770
~810
? 0.2
!I
J w
950
/~830
/ ~/ 1000
i /l 1050
1100
/I ?{/s5o 1150
Temperature ,T/~C Fig. 5. Secondary recrystallization in the heating stage of secondary recrystallization annealing (Specimen B). AM
42/8--D
basically the same condition as the so called single stage cold rolling method [5]. Figure 8 shows the number density of secondary recrystallized grains and the distribution of I c Z9 and IcZ5 as determined by the SHG method for the surface layer and the central layer of Specimen A extracted at 925°C, just before the onset of secondary recystallization. In Fig. 8, the orientation near {110}<001 > is expressed with the notation of vector method. The position of {ll0}<001> orientation is shown by the symbol " m " . In Fig. 8, the orientation is presented in the same mode as Fig. 3. Here, through investigating the distribution of I c Z i (i = l ~ 33c) in relation to a nucleus orientation, it was found that of all the I c value calculated, the orientation which can grow into the secondary recrystallized grain has the highest Ic value, except IcZ1 and ICE3, in lcZ9 or IcZS. Therefore, in Fig. 8, lcZ9 and IcE5 are shown for discussion. The threedimensional textures of the surface layer of primary recrystallized Specimens A was shown in Fig. 3. In the orientation region near {110}<001 > shown in Fig. 8, in both cases, the relative intensity of primary recrystallization texture was locally highest in the {110}(227> texture component in the surface layer and the central layer. It can be seen from Fig. 8 that the only {110}<001> secondary recrystallized grains with the highest frequency of IcE9 are evolved in the case of (b) secondary recrystallization annealing in 100%H~ and that the {110}<227>, more accurately {661}<216>, secondary recrystallized grains with the highest frequency of IcE5 rather than IcE9 are mainly evolved in the case of (a) secondary recrystallization annealing in 90%N2-H 2. In the case of treatment (a), the secondary recrystallization temperature is lower than that for treatment (b). The {110}<001> secondary recrystallized grains are evolved in both the low temperature range and the
2598
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
O
0°
15"
~
30*
45 °
~co(qt= 45°)
~ o
o
~ 0)(~=
o
N °
~
15 °
?
~(a) =45°)*-
o
45 ° )
o
~(0)
30 °
15°
w ( T t = 0 ° ) , --
,o
:4SO)~ --
o O) ( ~ =
0*)~--
t
O0 °
15 °
30 °
45 °
80*
15 °
i*
80 °
15 °
~ co(¢,= 45°) ,k(co=45°). w (q,= o*)~Fig. 6. Three dimensional orientation distributions of the primary recrystallized specimens. Temperature of the primary reerystallization annealing: (A) 750°C; (B) 810°C; (C) 850°C (Specimen B). A
B
RD
TD
high one. On the other hand, the {110}(227) secondary recrystallized grains are evolved only in the low temperature range. Figure 9 shows the number density of secondary recrystallized grains and the distribution of Ic Z9 and IcZ5 in the surface layer of Specimen B before the secondary recrystallization annealing, using the same notation as in Fig. 8. Because of the same reason mentioned for Fig. 8, IcZ9 and IcZ5 are selected for discussion. The three-dimensional textures of the surface layer of primary recrystallized Specimens B was shown in Fig. 6. In the orientation region near { 110} (001) shown in Fig. 9, in all cases, the relative intensity of primary recrystallization texture was locally highest in the {110}(227) texture component in the surface layer and the central layer. As shown in Fig. 9, the {110}(001) secondary recrystallized grains with the highest frequency of Ic Z9 are evolved in the case of (3) primary recrystallization annealing at 810°C and the {110}(227), more accurately {661}(216), secondary recrystallized grains with the highest frequency of IcY5 are mainly evolved in the case of (1) primary recrystallization annealing at 750°C. In the case of (2) primary recrystallization annealing at 770°C, the analysis result on the relationship between IcZ9 or Ic~5 and the secondary recrystallization texture can be described as a cross between the analysis results in the eases of treatments (1) and (3), as shown in Fig. 10. As shown in Fig. 5, the higher the primary recrystallization annealing temperature, the higher the secondary recrystallization temperature. Therefore, it can be seen from Fig. 5 and Fig. 9 that the {110}(001) secondary recrystallized grains are evolved in both the low temperature range and the high one and that the {110}(227) secondary recrystallized grains are evolved only in the low temperature range. In the ease of Specimen A of the treatment (a) and the case of Specimen B of the condition (1), the evolution of { 110}(227) secondary recrystallized grains can be associated with the special grain boundary migration characteristics of Y.5 type coincidence boundaries. The secondary recrystallization temperature in these two cases is commonly lower than fin other cases of the same specimen, C
RD
TD
KD
TD
Fig. 7. {100) pole figures of secondary recrystallized grains in the specimen taken at 1150°C in the heating stage of secondary recrystallization annealing. Temperature of the primary recrystaUization annealing: (A) 750°C, (B) 770°C, (C) 810°C (Specimen B).
2599
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si Annealing atmosphere
90% N2-
H~
100%
H2
e0
•~
'
i,
T ~ 150"I
o
~i..~ :~ :g ~"
15°'I 1'5.
0.,5.
1
~0-
15.
'
'~ '.
'~- '
'
'
'~ 'G
?
~ L,5o. [,,.,1
'~ '~ '~- '~ '~o '~o '~o '~o '~o
0"45"
15" 0"45" 30" ~(e.,=45" )~(a(~=O" )~'--
30"
)"-'- ( a ( ~ = 0
.
)'-
,~ ,~ ,~ ,~ ,~ ,~ ,~ ,.-~ ,~ '-4
~
~0.
L,5o15" ~(~=45"
~,
0.45.
~'(~=45"i),---~(~'=0" )'-
~(~=45" ) . - ~ ( ~ ' = 0 " ) ~
~
,50,
~
0
0
0
0
0"45"
I
,
,
(,o"
30"
q"(e~=45" )'-- w ( ~ =
,
, 0
Z,50-
' 15"
,~ , ,
0
15"
0" )*-"
F(m=45"
0
,
0"45"
30"
)'-- ~ ( t./f= 0" ) ~
Fig. 8. Relation between distributions lcX5 and IcY9 values of the primary recrystallized specimen taken at 925°C and secondary recrystallization texture in the specimen taken at 1050°C in the heating stage of secondary recrystallization annealing (Specimen A). Specimen A of the treatment (b) and Specimen B of the condition (3), in which the evolution of {110}<001> secondary recrystallized grains is associTemperature (°C) of primary recrystallization annealing 180
ated with the special grain boundary migration characteristics of Y9 type coincidence boundaries [2, 3]. In this study, the frequency of Y9 coincidence
750
770
15" o "45" 30" ~ ( ~ = 4 5 " ) ~ ~ ( F = O" ) ~
~'(m:45" ) ~ m ( ~ = 0" ) ~
810
"I
~,so°F 15"
0 "45"
30"
"I
0 "45"
30"
15"
0 "45"
30"
18°" I
180 o
15"
~(~=45")~(~f=0") ~
2~s0[
'.. { i
"20-
,, "20 ] ]'-
IcY5
,
15" 0 "45" 30" ~ ( e = 4 5 " ) ~ a , ( F = 0" ) ~
L~o.I
L ~so.I
-.,:.!~,1~,o..,0 i I
15"
,
0 "45"
T
30"
~'(~=45" ) ~ a , ( ~ = 0" ) ~
~'(~, =45" ) ~ (a(~= O" ) ~
Fig. 9. Relation between distributions lcY5 and leT-9 values of the primary recrystallized specimen and secondary recrystallization texture in the specimen taken at 1150'C in the heating stage of secondary reerystailization annealing (Specimen B).
2600
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si ~9 p..
./
/\.
\.
Critical value for secondary recrysta] 1izag ion
High t~perature M~s ~ M~s [ Primary I recrystall ized I~" I grain size \ [I I.~rge
*---~ ~age of the sec(xdary reerystall ization 2 [L
Small
.J
texture to be obtained
/\ Low temperature ] Mz9 < M z s
/ {110}<001~>
/
\
\
{110 }<~227~
Orientation of the hypothetical nucleus Fig. 10. A schematic diagram of the relation between the primary recrystallized grain growth and the formation of secondary recrystallization texture in Fe-3%Si alloy. IcZi: the frequency of Ei coincidence oriented grains in relation to a hypothetical nucleus; M~: the pseudo-mobility of Y~icoincidence boundary; ~t: the average pseudo-mobility of the boundary.
boundaries in relation to the {110}(001) texture component is higher than the frequency of Z5 coincidence boundaries in relation to the {110}(227) texture component• The mechanism of these evolutions of secondary recrystallization texture can be explained by the temperature dependence of specific grain boundary migration characteristics in the presence of inhibitor• Namely, the Z5 coincidence boundaries can be considered to be more mobile than the Z9 coincidence boundaries in the lower temperature range because Y.5 coincidence boundaries have better mutual lattice adjustment, causing lower frequency of grain boundary segregation, between two grains attached than Y,9 coincidence boundaries. On the other hand, in the case of Specimen A of the treatment (b) and the case of the Specimen B of the condition (3), the mobility difference and the frequency difference of grain boundary segregation between Y.9 coincidence boundaries and Y.5 coincidence boundaries are considered to be smaller during secondary recrystallization because the secondary recrystallization temperature is higher. Accordingly, in these cases, the evolution of secondary recrystallized grains can be associated with the frequency of coincidence boundaries• Therefore, the {110}(001) primary recrystallized grains with higher frequency of
Z9 coincidence oriented grains compared with the frequency of Y.5 coincidence oriented grains in relation to the {110}(227) texture component grow into secondary grains in these cases. In the case of specimen similar to Specimen A, even when increasing inhibitor intensity in the temperature range higher than 950°C, the only {110}(001 ) secondary recrystallized grains were evolved [15]. This experimental result can be also explained by the fact that the secondary recrystallized grains were evolved in the high temperature range. In the case of Specimen A of the treatment (a), the number of secondary recrystallized grains obtained were about twice as many as that for the treatment (b), as shown in Fig. 2. This result can be explained by the fact that the {110}(227) primary recrystallization texture component with the highest frequency of IcY~5 in the case of treatment (a) was more than the {110}(001) primary recrystallization texture component with the highest frequency of IcE9 in the case of treatment (b). In the case of Specimen B of the condition (1), the number of secondary recrystallized grains obtained were about three times as many as grains obtained in the case of condition (3), as shown in Fig. 5. This result can be also explained by the fact that the {110}(227) primary recrystallization texture
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si component with the highest frequency of ICY,5 in the case of condition (1) was more than the { 110} (001) primary recrystallization texture component with the highest frequency of Ic Y,9 in the case of condition (3). A schematic diagram explaining the relation between the grain growth of the primary recrystallized grains and the formation of the secondary recrystallized texture is shown in Fig. 10, based on the findings in the present study. The frequency of E9 coincidence boundaries in relation to the { 110}(001 ) texture component is higher than the frequency of E5 coincidence boundaries in relation to {110}(227) texture. F o r explaining the formation mechanism on the secondary recrystallization texture in the present study, it can be necessary to assume the temperature dependence of specific grain boundary migration characteristics of Z5 and Y9 coincidence boundaries in the presence of inhibitor. Namely, the evolution of secondary recrystallized grains can be associated with I c E i x (Mzi/A-I) value, where Mz~: the pseudo-mobility of Ei coincidence boundary, At': the average pseudo-mobility of the boundary. In this case, pseudo-mobility means the factor concerning mobility and grain boundary segregation and this factor is considered to be larger than those of other grain boundaries when the grain boundary is more mobile compared with others. Figure 10 shows that there is a critical value of l c E i x (Mzi/ffl) in relation to a hypothetical nucleus in the matrix for a hypothetical nucleus orientation to go grow into the secondary orientation. The primary recrystallized grains with higher value than a critical value of I c ~ i x ( M ~ / M ) for a hypothetical nucleus orientation is considered to grow into the secondary recrystallized grains. The E5 coincidence boundaries are considered to be more mobile than the ~z9 coincidence boundaries in the lower temperature range, where Mz9 < Mzs. On the other hand, the mobility difference and the frequency difference of grain boundary segregation between E9 and E5 coincidence boundaries are considered to be smaller in the higher temperature range, where M ~ 9 - M ~ 5 . Accordingly, the {110}(227) primary recrystallized grains with the higher value than a critical one of IcEi × ( M ~ / M ) in the lower temperature range are considered to grow into secondary grains in that temperature range. On the other hand, the { 110}(001 ) primary recrystallized grains with the higher value than critical one of Ic~,i x (M~i/A'[) in both the high temperature range and the low one are considered to grow into secondary recystallized grains in both temperature ranges. The primary recrystallized grain growth is considered to have a role of determining what should be the secondary recrystallization temperature which influences specific grain boundary migration characteristics. In addition to the most dominant factor, I c Z i x ( M ~ / M ) , the larger primary recrystallized grains with the same I c E i x (M~i/hTI) value are considered to be easier to grow into secondary recrystallized grains.
2601
6. CONCLUSIONS 1, Secondary recrystallization behavior in the presence of A1N in Fe--3%Si alloy, processed by a one stage cold rolling method, was investigated with special reference to the influence of primary recrystallized grain growth on secondary recrystallization texture. The more dominant grain growth was marked by the evolution of the { 110 }( 001 ) secondary recrystallized grains in the higher temperature range. On the other hand, in the case of smaller primary recrystallized grains, the {110}(227) secondary recrystallized grains were mainly evolved on annealing at the lower temperature range. The evolution of the { 110}(001) secondary recrystallized grains is considered to be due to the highest frequency of Z9 coincidence boundaries and the evolution of the {110}(227) secondary recrystallized grains is considered to be due to the highest frequency of E5 coincidence boundaries. The frequency of E9 coincidence boundaries in relation to the {110}(001) texture component was higher than the frequency of E5 coincidence boundaries in relation to { 110}(227) component. 2. The mechanism of these evolutions of secondary recrystallization texture can be explained by the assumption that the E5 coincidence boundaries are considered to be more mobile than the E9 coincidence boundaries in the lower temperature range. The primary recrystallized grain growth is considered to have a role of determining what should be the secondary recrystallization temperature.
Acknowledgements--The authors wish to thank Dr S.
Nagashima, former Professor of Yokohama National University, for his valuable suggestion for the use of the Vector Method. In the present investigation, the authors used a computer program of the Vector Method. This program was introduced to Japan by Dr S. Nagashima through the courtesy of Professors Ruer and Baro at the ICOTOM 6 in Japan. The authors wish to thank Professors Ruer and Baro for the permission to use this program. The authors wish to thank Dr R. Shimizu for his valuable suggestion for the use of the SHG method.
REFERENCES
1. J. E. May and D. Turnbull, Trans. metall. Soc. A.LM.E. 212, 769 (1958). 2. J. Harase, R. Shimuzu, K. Kuroki, T. Nakayama, T. Wada and T. Watanabe, Proe. 4th Japan Inst. Metals Syrup. on Grain Boundary Structure and Related Phenomena, Trans. Japan Inst. Metals, Suppl. Vol. 27,
p. 563 (1986). 3. R. Shimizu, J. Harase and D. J. Dingley, Acta metall. mater. 38, 973 (1990). 4. J. Harase, R. Shimizu, K. Takashima and T. Watanabe, Trans. Iron Steel Inst. Japan 27, 965 (1987). 5. S. Taguchi, A. Sakakura and H. Takashima, U.S. Patent 3287183 (1966). 6. D. Ruer and R. Baro, J. appl. Crystallogr. 10, 458 (1977). 7. H. J. Bunge, Z. Metallk. 51, 535 (1960). 8. D. G. Brandon, Acta metall. 14, 1479 (1966).
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YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
9. K. T. Aust and J. W. Rutter, Trans. metall. Soc. A.I.M.E. 215, 119 (1959). 10. J. Harase, R. Shimizu and T. Watanabe, Proc. 7th Riso Int. Symp. on Metall. Maters. Sci., p. 343 (1986). 11. Y. Yoshitomi, Y. Matuo and N. Takahashi, Mater. Forum 14, 308 (1990).
12. J. Harase and R. Simizu, Acta metall, mater. 38, 1395 (1990). 13. S. Taguchi, A. Sakakura, H. Takechi and H. Takashima, U.S. Patent 313614 (1964). 14. N. P. Goss, Trans. Am. Soc. Metals 23, 511 (1935). 15. Y. Yoshitomi, K. lwayama, T. Nagashima, J. Harase and N. Takahashi, Acta metall, mater. 41, 1577 (1993).
Pergamon
0956-7151(94)E0073-P
Copyright© 1994ElsevierScienceLtd Printed in Great Britain. All fights reserved 0956-7151/94$7.00+ 0.00
COINCIDENCE GRAIN BOUNDARY A N D ROLE OF PRIMARY RECRYSTALLIZED GRAIN GROWTH ON SECONDARY RECRYSTALLIZATION TEXTURE EVOLUTION IN Fe-3 % Si ALLOY Y. Y O S H I T O M I 1, Y. USHIGAMI z, J. HARASE 2, T. NAKAYAMA2, H. MASUI 2 and N. TAKAHASHI3 SYawata R&D Laboratory, Nippon Steel Corporation, Kitakyushu, 2Electromagnetic Materials Laboratory, Steel Research Laboratories, Nippon Steel Corporation, Futtsu, Chiba and 3Technical Development Bureau, Nippon Steel Corporation, Kitakyushu, Japan (Received 8 April 1993; in revised form 11 January 1994)
Al~traet--Secondary recrystallization behavior in the presence of AIN in Fe-3%Si alloy was investigated with special reference to the influence of primary recrystallized grain growth on secondary recrystallization texture. The more dominant grain growth was marked by the evolution of {110}(001> secondary recrystallized grains in the higher temperature range. In the case of smaller primary reerystailized grains, the {110}(227> secondary recrystallized grains were mainly evolved on annealing at the lower temperature range. The frequency of ~9 coincidence boundaries in relation to the {110}(001> texture component was higher than that of I:5 coincidence boundaries in relation to {110}(227) component. The mechanism of these evolutions of secondary recrystallization texture can be explained by the assumption that the ~5 coincidence boundaries are more mobile than the ~9 coincidence boundaries in the lower temperature range. The primary recrystallized grain growth is considered to have a role in determining what should be the secondary recrystallization temperature.
1. INTRODUCTION Grain oriented silicon steel is characterized by the presence of a sharp {110}(001) texture, i.e. Goss texture, which is produced by secondary recrystallization [1]. It has been pointed out that, in an Fe-3%Si alloy in which there were precipitates, evolution of Goss texture is associated with the special grain boundary migration characteristics of Y9 type coincidence boundaries [2, 3]. It has been also reported that primary recrystallized grain growth during secondary recrystallization annealing has an influence on secondary recrystallization behavior [4]. In order to further clarify the role of primary recrystallized grain growth on secondary recrystallization behavior, the present authors have investigated the relationship between the primary recrystallized grain growth and the secondary recrystallization texture. In this study, both the primary recrystallized grain growth during primary recrystallization annealing and that during secondary recrystallization annealing were investigated for finding out the general relationship between the primary recrystallized grain growth and the secondary recrystallization texture. The alloy selected to study was Fe-3%Si alloy in which AIN precipi-
tates were present in the microstructure as a grain growth inhibitor. The alloy was processed using a one stage cold rolling method [5]. 2. SHG METHOD [3] During grain growth, a growing grain will eventually come in contact with matrix grains not initially into direct contact with it. Therefore, it is necessary to know the orientation relationships between a growing grain and the matrix grains. In this connection, a method termed SH (Simulation by Hypothetical nucleus) has been developed [2]. The term nucleus refers to a growing grain. However, the SH method is time consuming as the orientations of several hundreds of grains have had to be measured by Electron Channeling Patterns (ECP) in the SEM. The SHG method (SH method in Generalized form) has thus been developed which uses the three-dimensional orientation distribution of grains as obtained by applying the vector method [6] to pole figures measured by X-ray diffraction. In the vector method, grain orientation is represented by three parameters co, ~b and ~. The unit triangle Tz, in which plane normals are to be presented, is divided into 36
2593
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
2594
"Boxes" of equal angular areas defined by to, ~ and numbered 1-36 with a representative orientation (HKL) assigned to each "Box" (Fig. 1). For example, (HKL) for Box No. 1, Box No. 29 and Box No. 36 are (001), (011) and (111), respectively. Rotations, (, about each orientation are divided into 72 intervals at steps of 5°. As another unit triangle T2 of mirror symmetry with TI is required to represent the entire orientation space, any orientation can be classified by one of 5184 orientations {2(unit triangle) x 36(Box) x 72(()} in the Vector method. Parameters co, ~ and ( used in the Vector Method and Euler angle ~bl, ~b2and • used in th harmonic method by Bunge [7] are in the following relationship sin ~b2= sin ~
(1)
sin ~l = sin ~, cos ( + cos ~, sin (
(2)
cos • = cos ~/(cos 2 @ + tan 2 to)l/2
(3)
sin ~ = sin ~2
(4)
tan to = - cos ~b2 tan •
(5)
or
sin ~ = cos q~] cos ~b2+ sin q~l cos • cos ~2 + sin ~1 sin2
~ cos ~2/(1 + cos 4).
(6)
Due to the symmetrical nature of the existing texture, 1296 orientations {35(Box) x 36(~)} can be used in the SHG method to represent orientations space. Mutual coincidence orientations from YA to Z33c with respect to each of the 1296 orientation are then calculated. In the calculation of coincidence orientation, Brandon's criterion [8] is used. The intensity of any coincidence orientation, Y4, for a nucleus orientation N is expressed as lcZi. The intensity of the nucleus orientation N is expressed as (if1) 45 °
3 9 . 8
°
a4.4~
~ /'l.--~
~ ,
23,4° ~
17"70 ~
:,
,,
~=
I (001)
6.9 °
12.0 °
17.2 °
22.4 °
27.7 °
333 °
=
~.9 °
I(o:1) 39.0 °
45°(011)
to------->
Fig. I. Definitionof box used in the vector method. Stereographic triangleT~ is divided into 36 parts of cqui-sphcdcal areas (boxes) by o) and ~#. A representative (IIKL) is assigned to each box.
IN. The probability of selective growth of a nucleus grain can be considered to be associated with the number of nucleus grains in the matrix and the number of grains that could come into coincidence with it. This is based on the assumption that coincidence boundaries (except Z 1 and Z3) are more mobile than random boundaries in the presence of solutes [9] or precipitates [10]. 3. EXPERIMENTAL
3.1. Experimental conditions 3.1.1. Case of primary recrystallized grain growth during secondary recrystallization annealing (Specimen A). The starting material was Fe-3%Si hot-rolled sheet, Specimen A, with the following chemical compositions; C: 0.07, Si: 3.2, AI: 0.028, N: 0.0079mass %. Primary recrystallized sheets for Specimen A were prepared as follows. Hot-rolled sheets 2.3ram thick were annealed at I I00°C for 120 s, followed by cold rolling to 0.285 mm thickness. Primary recrystallization annealing was carried out at 830°C for 150s in a 25% N2-H 2 gas mixture of dew point 68°C. Then, the primary recrystallized specimens were heated up to II00°C at a heating rate of 15°C/h in (a) 90%N1-H 2 or (b) 100%H 2 gasses. The specimens were extracted during this heating stage, and were quenched. The annealing condition (a) was chosen to inhibit the primary recrystallized grain growth more effectively before the onset of secondary recrystallization, because of the effect of nitriding from the annealing atmosphere. On the other hand, the annealing condition (b) was chosen to produce decreasing amount of inhibitors so that the primary recrystallized grain growth before the onset of secondary recrystallization would be easier.
3.1.2. Case of primary recrystallized grain growth during primary recrystallization annealing (Specimen B). The starting material was Fc-3%Si hot-rolled sheet, Specimen B, with the following chemical compositions; C: 0.05, Si: 3.3, AI: 0.026, N: 0.0074mass%. Primary recrystallized sheets for Specimen B were prepared as follows. Hot-rolled sheets 2.3mm thick were annealed at ll00°C for 120 s, cold rolled to 0.285 mm thickness followed by primary recrystallization annealing at (1) 750°C, (2) 770°C, (3) 810°C, (4) 830°C, (5) 850°C, for 150s, in a 25%N2-H2 gas mixture of dew point 60°C In order to inhibit the primary recrystallized grain growth effectively before the onset of secondary recrystallization, a nitriding with NH3 gas was used for the primary recrystallized specimens under the conditions, temperature 750°C, time 30 s, gas mixture 25%N2-H2, dew point <0°C. The amount of N after this nitriding was about 0.023 mass%. Then, the specimens were heated to 1150°C at a heating rate of 15°C/h in 25%N2-H2 gas mixture. The specimens were extracted during this heating stage and quenched.
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
3.2. Investigations Microstructure and macrostructure changes during secondary recrystallization annealing were investigated by eye and using optical microscopy. The grain size of the primary recrystallized specimens was measured using Phase Contrast image analysis [11]. Here, large grains which penetrated through the whole thickness of the specimen were judged as secondary recrystallized grains. Precipitate changes during secondary recrystallization annealing were investigated using chemical analysis of N and A1N. For the investigation of the primary texture, 70/~m thick specimens were extracted from the surface layer, from a depth of 1/5th the thickness and from the central section of the primary recrystallized sheet. The complete {100} pole figures were determined by X-ray measurement and three-dimensional texture analyses were carried out by the vector method [6]. Orientations of the secondary recrystallized grains were investigated by back-reflection Laue diffraction method. The orientation relationships between secondary recrystallized grains and matrix primary recrystallized grains were investigated using the SHG method [3]. 4. RESULTS
4.1. Case of primary recrystallized gra& growth during secondary recrystallization annealing (Specimen A) 4. I. 1. Secondary recrystallization behavior and N, AIN changes during secondary recrystallization annealing. The average grain diameter of the primary recrystallized specimen after primary recrystallization annealing was 8.4pm and that of a specimen extracted at 925°C, just before the onset of secondary recrystallization during the heating stage of secondary recrystallization annealing, was 9.1/tm in the case of treatment (a) and 10.0 #m in the case of treatment (b). In the case of treatment (b), the growth of the primary recrystallized grains was more striking, especially, in the surface region of the specimen, during the secondary recrystallization annealing, compared with the case (a). Figure 2 shows the secondary recrystallization behavior. In the case of treatment (a), thd secondary recrystallization temperature at 50% secondary recrystallized was lower than that for treatment (b) by 40°C. This suggests that the secondary recrystallization temperature is lower the smaller the primary recrystallized matrix grains, and this is because e r a bigger driving force for grain growth. The number of secondary recrystallized grains obtained in treatment (a) was about twice as many as in (b). In the case of treatment (a), with increasing temperature in the range 800-925°C during the heating stage of secondary recrystallization annealing, the amounts of N and N as AIN increased to 0.017 and 0.014mass% by 925°C, respectively. Then, in both cases, with increasing
2595
temperature in above 925°C, the amounts of N and N as AIN decreased by 0.02 to 0.03mass% by 1100°C.
4.1.2. Texture of primary recrystallized grains and orientation of secondary recrystallized grains. Figure 3 shows three-dimensional textures calculated from the complete {100} pole figures of the surface layer of primary recrystallized Specimens A, extracted at 925°C, just before the onset of secondary recrystallization. In Fig. 3, the orientation is specified by its (, ~o, ¢ value. Along the top of the figure are the respective axes for the appropriate co, ~b values, and next to each is box number as given in Fig. 1. The main texture components in any case were {111}<112>, {411}<148> and {100}<025>. Figure 4 shows the final orientations of secondary recrystaliized grains of Specimen A. In the case of treatment (a), {110}<227> secondary recrystallized grains were mainly evolved. In the case of treatment (b), {110}<001> secondary recrystallized grains were evolved. 4.2. Case of primary recrystallized grain growth during primary recrystallization annealing (Specimen
B) 4.2.1. Secondary recrystallization behavior and N change during secondary recrystallization annealing. The average diameters of primary recrystallized grains in Specimen B before secondary Number of secondary
recrystallized grains~m-z)
5.8
1.0
2.8
?--
/ /
Anneal ing atmosphere
/ /
90~N2-H2
"~ ¢D 0.8
/ / / /
100~/6Hz
0.6 b
/ 0.4 .
II I I I
o.2
I ,t
0
I
_
I 1o I
I
]
j
950 1000 Temperature, T/~3 Fig. 2. Secondary recrystallization in the heating stage of secondary recystallization annealing (Specimen A).
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
2596
recrystallization annealing were 13.7, 17.0, 23.0, 26.9 and 29.1/~m in the cases of annealing at (1) 750°C, (2) 770°C, (3) 810°C, (4) 830°C and (5) 850°C, respectively. The higher the primary recrystallization annealing temperature, the larger the average grain diameter of primary recrystallized specimen. In all cases, the primary recrystallized grain growth was less than 0.4#m in diameter in the heating stage of secondary recrystallization annealing before the onset of secondary recrystallization. Figure 5 shows the secondary recrystallization behavior of specimen B. The higher the primary recrystallization annealing
A
~80o8-~~,~ ' = '= ~ '= '~ ~ '~ '~ '~ '~ '-. '± -~ ~ ~ ~ ~ ~ ~ ~ 150° I20
60°
0
1 2 3 ,~
5
,~
5
~
oO 15o 30° ~ O)( ~-= 45 °)
o
~ (o)----45°)*--
(.o ( ~ = 0°)~---
temperature, the higher the secondary recrystallization temperature. On annealing at the lowest temperature, 750°C, the number of secondary recrystallized grains obtained was 3-6 times as grains obtained on annealing at 770 and 810°C. In all cases, with increasing temperature in the range above 950°C, during the heating stage of secondary recrystallization annealing, the amount of N decreased to about 0.016 mass% by 1150°C.
4.2.2. Texture of primary recrystallized grains and orientation of secondary recrystallized grains. Figure 6 shows three-dimensional textures calculated from the complete {100} pole figures of the surface layer of primary recrystallized Specimen B before the secondary recrystallization annealing. In Fig. 6, the orientation is presented in the same mode as Fig. 3. The main texture components in all cases were {111}(112), {411}(148) and {100}(025). Figure 7 shows the orientations of secondary recrystallized grains in Specimen B. With increasing temperature of the primary recrystallization annealing, the number of secondary recrystallized grains with the orientation deviation from {110}(001> decreased, mainly high decrease in the {110}(227) population. In the case of (3), the highest temperature condition of primary recrystallization annealing to achieve perfect secondary recrystallization, the sharpest {110}(001) secondary recrystallized grains were evolved. 5. DISCUSSION
6
0
~.
4 6°
3
~
o ~1
2
1
* 15" 30° 45° 80" 15" ~ o ) ( a p = 45 ° ) ~p((o =45°)*--
C
~t~eec~,
O
,~,
~ ~(o(¢=
45 °)
~ ,
, , ~
m ( if-= 0°)~-~,~,.~,~..~ ~
o ¢(co=4C).-
co(¢=0°) *-
3. Three dimensional orientation distributions of the primary recrystallized specimens. (A) After primary reerystallization annealing. (B, C) Taken at 925°C in the heating stage of secondary recrystallization annealing. (B) Annealed in 90%N2-H2; (C) Annealed in 100%H 2 (Specimen A). Fig.
It has been shown that the texture evolved by grain growth in the presence of precipitates is associated with the intensity of the inhibitors and the intensity of grains with coincidence orientation relationships (ICE/) [12]. When both the inhibitor intensity and IcZi value are higher than critical values, the orientation N which has greater intensity than a critical value and has the highest IcEi value (except E1 and E3 type coincidence orientations) among these nucleus orientations in the matrix, becomes the major orientation after grain growth. The secondary recrystaUization by this mechanism is referred to as the "Ic mechanism". When either the inhibitor intensity or IcZi value is smaller than their critical values, the orientation (N) having the highest PeN Ei value in the matrix becomes the major orientation after grain growth. The secondary recrystallization by this mechanism is referred to as the "PEN mechanism". For the same PcNEi (=ICE/ x/N) value, the weaker the inhibitor level, the more dominant IN, and conversely stronger the inhibitor level, the more dominant IcEi. The inhibitor effect on PcNE1 value increases with increase in the inhibitor intensity. For example, the mechanism of the (110)[001] secondary recrystallization [5] or (100) [001 ] secondary recrystallization [ 13] developed by Taguchi et al. is the Ic mechanism and that of the (110)[001] secondary recrystallization [14] developed by Goss is the Pcr~ mechanism. Based on this back-
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
90~/~N2_H2
A n n e a l ing
atmosphere
2597
1 0 0 ~ H2
KD
RD
.
-.t
D
L
Fig. 4. {100} pole figures of secondary recrystallized grains in the specimen taken at 1050°Cin the heating stage of secondary recrystallization annealing (Specimen A). ground, the influence of the primary recrystallized grain growth on the secondary recrystallization is discussed. The mechanism of the secondary recrystallization in the present experiment is considered to be the "lc mechanism" as specimens were processed Number of s e c o n d a r y r eerys tal I ized grains(cm -z) 0.27 08 2 *.!5 tim
1.0
•~
08
~
0.6
D
Temperature L3 of primary recrys tal I izat ion ann eal ing
0 e~ m
o
0.4
¢
~5(
.--- 770
~810
? 0.2
!I
J w
950
/~830
/ ~/ 1000
i /l 1050
1100
/I ?{/s5o 1150
Temperature ,T/~C Fig. 5. Secondary recrystallization in the heating stage of secondary recrystallization annealing (Specimen B). AM
42/8--D
basically the same condition as the so called single stage cold rolling method [5]. Figure 8 shows the number density of secondary recrystallized grains and the distribution of I c Z9 and IcZ5 as determined by the SHG method for the surface layer and the central layer of Specimen A extracted at 925°C, just before the onset of secondary recystallization. In Fig. 8, the orientation near {110}<001 > is expressed with the notation of vector method. The position of {ll0}<001> orientation is shown by the symbol " m " . In Fig. 8, the orientation is presented in the same mode as Fig. 3. Here, through investigating the distribution of I c Z i (i = l ~ 33c) in relation to a nucleus orientation, it was found that of all the I c value calculated, the orientation which can grow into the secondary recrystallized grain has the highest Ic value, except IcZ1 and ICE3, in lcZ9 or IcZS. Therefore, in Fig. 8, lcZ9 and IcE5 are shown for discussion. The threedimensional textures of the surface layer of primary recrystallized Specimens A was shown in Fig. 3. In the orientation region near {110}<001 > shown in Fig. 8, in both cases, the relative intensity of primary recrystallization texture was locally highest in the {110}(227> texture component in the surface layer and the central layer. It can be seen from Fig. 8 that the only {110}<001> secondary recrystallized grains with the highest frequency of IcE9 are evolved in the case of (b) secondary recrystallization annealing in 100%H~ and that the {110}<227>, more accurately {661}<216>, secondary recrystallized grains with the highest frequency of IcE5 rather than IcE9 are mainly evolved in the case of (a) secondary recrystallization annealing in 90%N2-H 2. In the case of treatment (a), the secondary recrystallization temperature is lower than that for treatment (b). The {110}<001> secondary recrystallized grains are evolved in both the low temperature range and the
2598
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
O
0°
15"
~
30*
45 °
~co(qt= 45°)
~ o
o
~ 0)(~=
o
N °
~
15 °
?
~(a) =45°)*-
o
45 ° )
o
~(0)
30 °
15°
w ( T t = 0 ° ) , --
,o
:4SO)~ --
o O) ( ~ =
0*)~--
t
O0 °
15 °
30 °
45 °
80*
15 °
i*
80 °
15 °
~ co(¢,= 45°) ,k(co=45°). w (q,= o*)~Fig. 6. Three dimensional orientation distributions of the primary recrystallized specimens. Temperature of the primary reerystallization annealing: (A) 750°C; (B) 810°C; (C) 850°C (Specimen B). A
B
RD
TD
high one. On the other hand, the {110}(227) secondary recrystallized grains are evolved only in the low temperature range. Figure 9 shows the number density of secondary recrystallized grains and the distribution of Ic Z9 and IcZ5 in the surface layer of Specimen B before the secondary recrystallization annealing, using the same notation as in Fig. 8. Because of the same reason mentioned for Fig. 8, IcZ9 and IcZ5 are selected for discussion. The three-dimensional textures of the surface layer of primary recrystallized Specimens B was shown in Fig. 6. In the orientation region near { 110} (001) shown in Fig. 9, in all cases, the relative intensity of primary recrystallization texture was locally highest in the {110}(227) texture component in the surface layer and the central layer. As shown in Fig. 9, the {110}(001) secondary recrystallized grains with the highest frequency of Ic Z9 are evolved in the case of (3) primary recrystallization annealing at 810°C and the {110}(227), more accurately {661}(216), secondary recrystallized grains with the highest frequency of IcY5 are mainly evolved in the case of (1) primary recrystallization annealing at 750°C. In the case of (2) primary recrystallization annealing at 770°C, the analysis result on the relationship between IcZ9 or Ic~5 and the secondary recrystallization texture can be described as a cross between the analysis results in the eases of treatments (1) and (3), as shown in Fig. 10. As shown in Fig. 5, the higher the primary recrystallization annealing temperature, the higher the secondary recrystallization temperature. Therefore, it can be seen from Fig. 5 and Fig. 9 that the {110}(001) secondary recrystallized grains are evolved in both the low temperature range and the high one and that the {110}(227) secondary recrystallized grains are evolved only in the low temperature range. In the ease of Specimen A of the treatment (a) and the case of Specimen B of the condition (1), the evolution of { 110}(227) secondary recrystallized grains can be associated with the special grain boundary migration characteristics of Y.5 type coincidence boundaries. The secondary recrystallization temperature in these two cases is commonly lower than fin other cases of the same specimen, C
RD
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Fig. 7. {100) pole figures of secondary recrystallized grains in the specimen taken at 1150°C in the heating stage of secondary recrystallization annealing. Temperature of the primary recrystaUization annealing: (A) 750°C, (B) 770°C, (C) 810°C (Specimen B).
2599
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si Annealing atmosphere
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Fig. 8. Relation between distributions lcX5 and IcY9 values of the primary recrystallized specimen taken at 925°C and secondary recrystallization texture in the specimen taken at 1050°C in the heating stage of secondary recrystallization annealing (Specimen A). Specimen A of the treatment (b) and Specimen B of the condition (3), in which the evolution of {110}<001> secondary recrystallized grains is associTemperature (°C) of primary recrystallization annealing 180
ated with the special grain boundary migration characteristics of Y9 type coincidence boundaries [2, 3]. In this study, the frequency of Y9 coincidence
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2600
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si ~9 p..
./
/\.
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Orientation of the hypothetical nucleus Fig. 10. A schematic diagram of the relation between the primary recrystallized grain growth and the formation of secondary recrystallization texture in Fe-3%Si alloy. IcZi: the frequency of Ei coincidence oriented grains in relation to a hypothetical nucleus; M~: the pseudo-mobility of Y~icoincidence boundary; ~t: the average pseudo-mobility of the boundary.
boundaries in relation to the {110}(001) texture component is higher than the frequency of Z5 coincidence boundaries in relation to the {110}(227) texture component• The mechanism of these evolutions of secondary recrystallization texture can be explained by the temperature dependence of specific grain boundary migration characteristics in the presence of inhibitor• Namely, the Z5 coincidence boundaries can be considered to be more mobile than the Z9 coincidence boundaries in the lower temperature range because Y.5 coincidence boundaries have better mutual lattice adjustment, causing lower frequency of grain boundary segregation, between two grains attached than Y,9 coincidence boundaries. On the other hand, in the case of Specimen A of the treatment (b) and the case of the Specimen B of the condition (3), the mobility difference and the frequency difference of grain boundary segregation between Y.9 coincidence boundaries and Y.5 coincidence boundaries are considered to be smaller during secondary recrystallization because the secondary recrystallization temperature is higher. Accordingly, in these cases, the evolution of secondary recrystallized grains can be associated with the frequency of coincidence boundaries• Therefore, the {110}(001) primary recrystallized grains with higher frequency of
Z9 coincidence oriented grains compared with the frequency of Y.5 coincidence oriented grains in relation to the {110}(227) texture component grow into secondary grains in these cases. In the case of specimen similar to Specimen A, even when increasing inhibitor intensity in the temperature range higher than 950°C, the only {110}(001 ) secondary recrystallized grains were evolved [15]. This experimental result can be also explained by the fact that the secondary recrystallized grains were evolved in the high temperature range. In the case of Specimen A of the treatment (a), the number of secondary recrystallized grains obtained were about twice as many as that for the treatment (b), as shown in Fig. 2. This result can be explained by the fact that the {110}(227) primary recrystallization texture component with the highest frequency of IcY~5 in the case of treatment (a) was more than the {110}(001) primary recrystallization texture component with the highest frequency of IcE9 in the case of treatment (b). In the case of Specimen B of the condition (1), the number of secondary recrystallized grains obtained were about three times as many as grains obtained in the case of condition (3), as shown in Fig. 5. This result can be also explained by the fact that the {110}(227) primary recrystallization texture
YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si component with the highest frequency of ICY,5 in the case of condition (1) was more than the { 110} (001) primary recrystallization texture component with the highest frequency of Ic Y,9 in the case of condition (3). A schematic diagram explaining the relation between the grain growth of the primary recrystallized grains and the formation of the secondary recrystallized texture is shown in Fig. 10, based on the findings in the present study. The frequency of E9 coincidence boundaries in relation to the { 110}(001 ) texture component is higher than the frequency of E5 coincidence boundaries in relation to {110}(227) texture. F o r explaining the formation mechanism on the secondary recrystallization texture in the present study, it can be necessary to assume the temperature dependence of specific grain boundary migration characteristics of Z5 and Y9 coincidence boundaries in the presence of inhibitor. Namely, the evolution of secondary recrystallized grains can be associated with I c E i x (Mzi/A-I) value, where Mz~: the pseudo-mobility of Ei coincidence boundary, At': the average pseudo-mobility of the boundary. In this case, pseudo-mobility means the factor concerning mobility and grain boundary segregation and this factor is considered to be larger than those of other grain boundaries when the grain boundary is more mobile compared with others. Figure 10 shows that there is a critical value of l c E i x (Mzi/ffl) in relation to a hypothetical nucleus in the matrix for a hypothetical nucleus orientation to go grow into the secondary orientation. The primary recrystallized grains with higher value than a critical value of I c ~ i x ( M ~ / M ) for a hypothetical nucleus orientation is considered to grow into the secondary recrystallized grains. The E5 coincidence boundaries are considered to be more mobile than the ~z9 coincidence boundaries in the lower temperature range, where Mz9 < Mzs. On the other hand, the mobility difference and the frequency difference of grain boundary segregation between E9 and E5 coincidence boundaries are considered to be smaller in the higher temperature range, where M ~ 9 - M ~ 5 . Accordingly, the {110}(227) primary recrystallized grains with the higher value than a critical one of IcEi × ( M ~ / M ) in the lower temperature range are considered to grow into secondary grains in that temperature range. On the other hand, the { 110}(001 ) primary recrystallized grains with the higher value than critical one of Ic~,i x (M~i/A'[) in both the high temperature range and the low one are considered to grow into secondary recystallized grains in both temperature ranges. The primary recrystallized grain growth is considered to have a role of determining what should be the secondary recrystallization temperature which influences specific grain boundary migration characteristics. In addition to the most dominant factor, I c Z i x ( M ~ / M ) , the larger primary recrystallized grains with the same I c E i x (M~i/hTI) value are considered to be easier to grow into secondary recrystallized grains.
2601
6. CONCLUSIONS 1, Secondary recrystallization behavior in the presence of A1N in Fe--3%Si alloy, processed by a one stage cold rolling method, was investigated with special reference to the influence of primary recrystallized grain growth on secondary recrystallization texture. The more dominant grain growth was marked by the evolution of the { 110 }( 001 ) secondary recrystallized grains in the higher temperature range. On the other hand, in the case of smaller primary recrystallized grains, the {110}(227) secondary recrystallized grains were mainly evolved on annealing at the lower temperature range. The evolution of the { 110}(001) secondary recrystallized grains is considered to be due to the highest frequency of Z9 coincidence boundaries and the evolution of the {110}(227) secondary recrystallized grains is considered to be due to the highest frequency of E5 coincidence boundaries. The frequency of E9 coincidence boundaries in relation to the {110}(001) texture component was higher than the frequency of E5 coincidence boundaries in relation to { 110}(227) component. 2. The mechanism of these evolutions of secondary recrystallization texture can be explained by the assumption that the E5 coincidence boundaries are considered to be more mobile than the E9 coincidence boundaries in the lower temperature range. The primary recrystallized grain growth is considered to have a role of determining what should be the secondary recrystallization temperature.
Acknowledgements--The authors wish to thank Dr S.
Nagashima, former Professor of Yokohama National University, for his valuable suggestion for the use of the Vector Method. In the present investigation, the authors used a computer program of the Vector Method. This program was introduced to Japan by Dr S. Nagashima through the courtesy of Professors Ruer and Baro at the ICOTOM 6 in Japan. The authors wish to thank Professors Ruer and Baro for the permission to use this program. The authors wish to thank Dr R. Shimizu for his valuable suggestion for the use of the SHG method.
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YOSHITOMI et al.: TEXTURE EVOLUTION IN Fe-3%Si
9. K. T. Aust and J. W. Rutter, Trans. metall. Soc. A.I.M.E. 215, 119 (1959). 10. J. Harase, R. Shimizu and T. Watanabe, Proc. 7th Riso Int. Symp. on Metall. Maters. Sci., p. 343 (1986). 11. Y. Yoshitomi, Y. Matuo and N. Takahashi, Mater. Forum 14, 308 (1990).
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