Process for manufacturing double oriented electrical steel sheet having high magnetic flux density

The present invention provides a process for manufacturing a double oriented electrical steel sheet having a high flux density by suppressing the growth of the secondary recrystallization of {110} <uvw> oriented grains from the surface of the steel sheet in the hot-rolling stage or cold-rolling stage, which process comprises subjecting a hot rolled sheet comprised of 0.8-6.7% by weight of Si, 0.008-0.048% by weight of acid soluble Al, 0.010% by weight or less of N, and the balance being Fe and unavoidable impurities to a cold-rolling at a reduction rate of 40-80%, and then subjecting the resulting sheet to another cold-rolling in the direction vertical to the above cold-rolled direction at the reduction rate of 30-70% in the final thickness, followed by the steps of annealing for the primary recrystallization, applying an annealing separator, and applying finishing annealing for the secondary recrystallization and purification of steel, wherein the rolling in the finishing hot-rolling stage is carried out at the accumulated reduction rate of 20% or more under the condition that the friction coefficient between the rolls and the steel sheet is not more than 0.25; and wherein the accumulated reduction rate in the last three passes in the hot-rolling is not more than 80%; and further, wherein material of more than 1/10 of the total thickness is removed from both surfaces of the hot-rolled sheet; or wherein the cold-rolling is carried out using a work roll having a diameter of not less than 150 mm.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to a process for manufacturing a double oriented 
electrical steel sheet including recrystallized grains whose easy axis 
&lt;001&gt; of magnetization is oriented both in the longitudinal orientation 
and in the direction vertical thereto, together with the rolled surfaces 
exhibiting {100} planes (those crystallographic orientations can be 
represented as {100} &lt;001&gt; in the Miller indices). 
(2) Description of the Related Art 
Since the double oriented electrical steel sheet has excellent magnetic 
properties in two different directions, because of its easy axis (&lt;001&gt; 
axis) in the rolled direction and in the direction vertical thereto, it 
can be more advantageously used for a magnetic core material of a specific 
apparatus, e.g., a large-scale rotating machine, where the magnetic flux 
flows in two different directions in comparison with a grain oriented 
electrical steel sheet which exhibits excellent magnetic properties in 
only one rolled direction. Non-oriented magnetic steel sheet, whose easy 
axis is not densely accumulated, are generally used for a small stationary 
machine or installation. The use of double oriented electrical steel 
sheet, however makes it possible to miniaturize the machine with an 
increased efficienty. 
The double oriented electrical steel sheet, which has excellent magnetic 
properties as described above, has long been expected to be put into mass 
production, but the general use of such a type of sheet as an industrial 
product is still limited at present. 
The following two methods in the prior art have been proposed for 
manufacturing a double oriented electrical steel sheet: 
A method wherein an initial steel sheet is annealed at a high temperature 
in an atmosphere containing a polar gas, e.g., hydrogen sulfide, to 
secondarily recrystallize out {100} &lt;001&gt; oriented grains with the aid of 
surface energy, as described in Japanese Examined Patent Publication 
No.37-7110. This method is inadequate for mass production, however, 
because it requires a very accurate control of the surface energy of the 
sheet. 
An other method wherein a steel sheet is cold-rolled in one direction and 
then cold-rolled in a direction vertical thereto, i.e., a cross cold r 
olling method", as described in Japanese Examined Patent Publication No. 
35-2657. The magnetic flux density (B.sub.8) of the products obtained by 
this method is not more than 1.85 Tesla, and accordingly, a significant 
improvement of the magnetic properties can not be obtained in spite of the 
complicated manufacturing process, which in turn requires an increased 
cost. The double oriented electrical steel sheet obtained by this method 
is not preferable to the conventional grain oriented electrical steel 
sheet. 
The magnetic flux density (B.sub.8) of the grain oriented electrical steel 
sheet has steadily improved, since the techniques disclosed in Japanese 
Examined Patent Publication No.40-15644 and Japanese Examined Patent 
Publication No. 51-13469 were disclosed. At present, the magnetic flux 
density (B.sub.8) of the commercially available products is as high as 
1.92 T. 
An improved method has been proposed to enhance the magnetic properties in 
a double oriented electrical steel sheet, as disclosed in Japanese 
Examined Patent Publication No. 35-17208 and Japanese Examined Patent 
Publication No. 38-8213. Nevertheless, the magnetic flux density of the 
resulting products has not been made higher than that of the grain 
oriented electrical sheet. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a process for stably 
manufacturing a double oriented electrical steel sheet having a high 
magnetic flux density. 
Specifically, the object of this invention is to suppress the growth of 
{110} &lt;uvw&gt; oriented grains which are initiated from the surface of the 
steel sheet due to the secondary recrystallization, since these grains 
deteriorate the magnetic properties of the double oriented electrical 
steel sheet. 
According to the present invention, the concrete means of suppression are 
as follows: 
The present invention is intended to provide a process for manufacturing a 
double oriented electrical steel sheet having a high flux density by 
suppressing the growth of the secondary recrystallization of {110} &lt;uvw&gt; 
oriented grains from the surface of the steel sheet in the hot-rolling 
stage or cold-rolling stage, which process is characterized by a process 
which comprises subjecting a hot-rolled sheet comprised of 0.8-6.7% by 
weight of Si, 0.008-0.048% by weight of acid soluble Al, 0.010% or less by 
weight of N, and the balance being Fe and unavoidable impurities to a 
cold-rolling at a reduction rate of 40-80%, and then subjecting the 
resulting sheet to another cold-rolling in the direction vertical to the 
above cold-rolled direction at the reduction rate of 30-70% in the final 
thickness, followed by annealing for the primary recrystallization, 
applying an annealing separator, and applying finishing annealing for the 
secondary recrystallization and steel purification, wherein the rolling in 
the finishing hot-rolling stage is carried at the accumulated reduction 
rate of 20% or more under the condition that the friction coefficient 
between the rolls and the steel sheet is not more than 0.25; wherein the 
accumulated reduction rate in the last three passes in the hot-rolling is 
not more than 80%; wherein more than 1/10 of the total thickness of the 
material is removed from both surfaces of the hot-rolled sheet; or wherein 
the cold-rolling is carried out using a work roll having a diameter of not 
less than 150 mm.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The inventors studied products of double oriented . electrical steel sheet 
manufactured by the cross cold-rolling method, and found the following. 
The crystalline orientation optimal for a double oriented electrical steel 
sheet is of {100} &lt;001&gt;. In crystalline grains after the secondary 
recrystallization, however, {110} &lt;uvw&gt; oriented grains exist together 
with the above-mentioned grains of {100} &lt;001&gt;, and the former lowers the 
magnetic density. Accordingly, {110} &lt;uvw&gt; oriented grains after the 
secondary recrystallization must be suppressed to obtain a high magnetic 
flux density. 
After a further study in detail of the orientation of these grains, it was 
found that the sheet created by the primary recrystallization prior to the 
secondary recrystallization exhibited a different texture in the varied 
thickness of the sheet, i.e., {110} &lt;uvw&gt; oriented grains start to grow 
from the surface layer, whereas {100} &lt;001&gt; oriented grains grow from the 
central layer. 
This has been confirmed by the following experiments: A hot-rolled 1.8 mm 
thickness sheet comprised of 0.055% of C, 3.3% of Si, 0.028% of acid 
soluble Al, 0.007% of N, and the balance being Fe and unavoidable 
impurities was annealed at 1125.degree. C. for 2 minutes, and then 
cold-rolled at a reduction rate of 55% in the same direction as in the 
hot-rolled direction, and further, cold cross-rolled at a reduction rate 
of 55% in the direction vertical to the above rolled direction to form a 
sheet having a final thickness of 0.35 mm. The sheet thus cold rolled was 
annealed for the primary recrystallization at 810.degree. C. for 210 
seconds in a wet hydrogen atmosphere; this heat treatment also served for 
a decarburization of the sheet. An examination of the texture in the sheet 
thus recrystallized showed that the main orientations of the grains were 
{110} &lt;001&gt; and {111} &lt;uvw&gt; in the vicinity of the surface shown in FIG. 
1(a), whereas they were was {211} &lt;124&gt; and {211} &lt;231&gt; at the central 
portions, as shown in FIG. 1(b). This implies that the crystalline 
orientation of major grains varies from sheet depth to sheet depth. It 
should be noted that the recrystalline orientation of grains in the 
secondary recrystallization is strongly influenced by the texture in the 
primary recrystallization as reported, for instance, by K. T. Aust, J. W. 
Rutter in Trans. Met. Soc. AIME, 215 (1959), pp. 119-127., and by Ushigami 
et al. in Abstract of 96th Symposium of Metallurgy Society of Japan, pp. 
375. The dependence of the texture on the depth of the sheet treated by 
the primary recrystallization was further studied, and as shown in FIG. 2, 
it is found that the dependence is largely influenced by the inclination 
of the texture versus the depth of the hot-rolled sheet. To determine 
this, test pieces were selectively prepared by cutting same from the 
hot-rolled sheet at the surface and central portions, respectively. These 
pieces were primarily recrystallized under the same conditions of the 
primary recrystallization as mentioned above, and then annealed in the 
finishing stage after an annealing separator containing MgO as a main 
component was applied. 
FIG. 3 shows the orientation distribution of the secondary recrystallized 
grains of the respective test pieces thus prepared. From FIG. 3, it can be 
seen that grains having {110} &lt;uvw&gt; orientations grow from the surface of 
the hot-rolled sheet, whereas grains having {100} &lt;001&gt; orientations grow 
from the central area. 
Therefore, it is considered that {110} &lt;uvw&gt; oriented grains resulting in a 
decreased magnetic flux density may be successfully suppressed by reducing 
the {110} texture in the hot-rolled sheet during the course of the primary 
recrystallization. 
On the basis of the above finding, a further study was made of the 
conditions of hot- and cold-rolling in detail, and the following means for 
suppressing such an undesirable texture determined: 
(1) By setting the friction coefficient between a steel sheet and 
hot-rolling rolls in an amount of less than 0.25, {110} &lt;uvw&gt; oriented 
grains grown from the surface areas are suppressed in the secondary 
recrystallization due to the change of the texture in the hot-rolled 
sheet, thereby ensuring the stable manufacture of a double oriented 
electrical steel sheet having a high magnetic flux density. 
The experimental results obtained are now described. A slab containing the 
same components as mentioned above was hot-rolled with a varied friction 
coefficient, and then annealed at 1050.degree. C. for 2 minutes. 
Thereafter, the sheet thus rolled was cold-rolled at a reduction rate of 
50% in the same direction as the hot-rolled direction, and further cold 
cross-rolled at a reduction rate of 50% in the direction vertical to the 
above-mentioned direction. Moreover, the sheet was annealed for both the 
primary recrystallization and decarburization at 800.degree. C. for 90 
seconds in a wet hydrogen atmosphere, and further annealed for finishing 
after applying an annealing separator. 
FIG. 4 shows the relationship between the friction coefficient employed and 
the magnetic flux density (B.sub.8) of the product obtained at an 
accumulated reduction rate of 50% in the finishing rolling process of the 
hot rolling. It can be seen from FIG. 4 that a product having a high 
magnetic flux density of more than 1.90 Tesla can be obtained when the 
friction coefficient is less than 0.25. 
An examination of the texture of the hot-rolled sheet obtained with a 
friction coefficient of less than 0.25 reveals that the grains having 
{110} surfaces are markedly eliminated. The results suggest that secondary 
recrystallization of {110} &lt;uvw&gt; oriented grains grown from the surface 
areas is suppressed. 
Taking into account these results, the effect of the accumulated reduction 
rate in the hot-rolling was further studied under the fixed condition for 
a friction coefficient of 0.22 in the finishing rolling process. As shown 
in FIG. 5, products having a high magnetic flux density of more than 1.90 
Tesla can successfully obtained when the accumulated reduction rate is not 
less than 20% is employed. 
Since the difference in the texture obtained with varied friction 
coefficients is concealed due to the recrystallization, etc., in the 
initial stage of the hot-rolling, the coefficient may be adjusted at the 
final stage, i.e., the finishing rolling stage at which difference in the 
texture is clarified. 
(2) By setting an accumulated reduction rate of less than 80% in the final 
three passes of the hot-rolling process, and setting a temperature of 
950.degree. C. or more for finishing hot-rolling, the growth of {110} 
&lt;uvw&gt; oriented grains from the surface is suppressed due to change of 
texture in the hot-rolled sheet, thereby ensuring the stable manufacture 
of a double oriented electrical steel sheet having a high magnetic flux 
density. 
The experimental results obtained will be described. A 40 mm-thick slab 
having the same components as described previously was hot-rolled into a 
2.0 mm thickness sheet, using six passes with a varied pass schedule. The 
temperature in the final hot-rolling was 900.degree.-950.degree. C. The 
sheet was then annealed for 2 minutes at 1050.degree. C. Subsequently, the 
sheet was cold-rolled at a reduction rate of 50% in the same direction as 
the hot-rolled direction, and further cold cross-rolled at a reduction 
rate of 50% in the direction vertical to the above rolled direction. 
Furthermore, the sheet was annealed for the primary recrystallization and 
the decarbonization at 800.degree. C. for 90 seconds in a wet hydrogen 
atmosphere. Finally, the sheet was annealed for finishing after applying 
an annealing separator. 
FIG. 6 shows the relationship between the accumulated reduction rate in the 
final three passes of the hot-rolling and the magnetic property (B.sub.8 
value) of the product obtained. From this diagram, it can be seen that a 
product having a high magnetic flux density of more than 1.90 Tesla at an 
accumulated reduction rate of less than 80% was obtained. 
On the basis of the experimental results, the effect of the final 
temperature in the stage of hot-rolling on the magnetic property was 
studied at an accumulated reduction rate of 80% in the final three passes 
with varied delay time, and as a result, it was found that the magnetic 
flux density was further increased when the temperature of the final 
hot-rolling was not less than 950.degree. C. 
An examination of the texture in the hot-rolled sheet reveals that a 
hot-rolled sheet having a high magnetic flux density always contained less 
{110} oriented grains in the vicinity of the surface layer. In accordance 
with the present invention, therefore, it can be concluded that {110} 
texture formed was reduced due to the recrystallization, in which case the 
crystal rotation due to the shear deformation at the surface is 
suppressed, when the accumulated reduction rate at the final three passes 
was kept at less than 80%, and/or the temperature of the final hot-rolling 
was kept at more than 950.degree. C. 
(3) By removing the surface layers at both sides of a hot-rolled sheet by a 
depth of 1/10-1/3 total thickness, {110} texture formed at the surface 
layers of a hot-rolled sheet was reduced to suppress {110} &lt;uvw&gt; oriented 
grains grown from the both surfaces in the secondary recrystallization, 
thereby ensuring the stable manufacture of a double oriented electrical 
steel sheet having a high magnetic flux density. 
The experimental results obtained will be described. A slab containing the 
same components as described above was hot-rolled into a 1.8 mm thickness 
hot-rolled sheet under the same conditions. The surface layers of the 1.8 
mm thick hot rolled sheet were removed by a grinder. 
In FIG. 7, the relationship between the amount of material removed from 
both surfaces of the hot-rolled sheet and the magnetic flux density 
(B.sub.8) value of the product is given. It can be seen from the results 
that a double oriented electrical steel sheet having a high magnetic flux 
density can successfully be obtained, when material of more than 1/10, 
preferably 1/5, of the total thickness is removed from both surfaces. When 
the material is removed from the both surfaces to a thickness of 
approximately 1/3 the total thickness, the magnetic property is saturated. 
(4) By using work rolls having a diameter of more than a specific value for 
cold-rolling, the state of the metal flow at the surfaces of a hot-rolled 
sheet can be varied to suppress the growth of {110} &lt;uvw&gt; grains from the 
surface in the secondary recrystallization, thereby ensuring the stable 
manufacture of a double oriented electrical steel sheet having a high 
magnetic flux density. 
The experimental results obtained will be described. A slab containing the 
same components as described previously was hot-rolled and cold 
cross-rolled under the same conditions as described above to obtain a 
cold-rolled sheet having a final thickness of 0.35 mm. Five different work 
rolls having a diameter of 60 mm, 100 mm, 150 mm, 270 mm, or 490 mm were 
used in the cold-rolling. The sheets thus cold-rolled were annealed for 
210 seconds in a wet hydrogen for both decarburization and primary 
recrystallization. Thereafter, the sheets were finally annealed after 
applying an annealing separator containing MgO as a main ingredient. 
FIG. 8 shows the relationship between the diameter of work roll used and 
the magnetic flux density (B.sub.8) of a product. It can been seen from 
FIG. 8 that a product having a high magnetic flux density value of more 
than 1.90 Tesla, when the diameter of the work rolls in the cold-rolling 
was more than 150 mm. This effect becomes saturated at a diameter of more 
than 270 mm. 
FIG. 9 shows the distribution of crystal grain orientations of the products 
in the secondary recrystallization where the work roll diameter in the 
cold-rolling is 60 mm (a) or 490 mm (b). From both pole figures, it can be 
seen that the growth of {110} &lt;uvw&gt; oriented grains can be successfully 
suppressed by an increased diameter of the work rolls. The reasons for 
this are probably as follows: 
The work roll diameter in the cold-rolling exerts a significant influence 
on the metal flow in the thickness direction, and the rotation of crystals 
in the vicinity of the surface promotes an increased growth of {110} &lt;uvw&gt; 
oriented grains in the recrystallization as the diameter of the work rolls 
becomes larger. 
Other limited conditions or elements will be described. 
A molten sheet used in the present invention may be prepared in any manner, 
such as in a revolving furnace or electric furnace, and must contain the 
following components in the following contents: 
A high content of Si improves iron loss properties, but decreases the 
magnetic flux density inevitably. Watt loss is minimum at an Si content of 
approximately 6.5%, while no improvement can be obtained with the further 
increase of the content. The upper limit of Si content should, therefore, 
be specified to be 6.7%. An increased content of Si makes the product 
brittle, and cold cracks appear at an Si content of more than 4.5%, but 
worm-rolling can be principally applied to solve this problem. On the 
other hand, a lower content of Si provides an increased transformation of 
.alpha. into .gamma., thereby deteriorating the crystal orientation. The 
lower limit of the Si content should be determined at 0.8%, which has no 
substantial influence. 
Acid soluble Al forms a nitride such as AlN, (Al,Si)N, which acts as an 
inhibitor. The Al content is restricted to be 0.008-0.048%, preferably 
0.018-0.036%, where the magnetic flux density of the product increases. 
If the content of N exceeds 0.010%, gaps called blisters appear, and thus 
the upper limit is defined as 0.010%. For the lower limit, the content of 
N can be adjusted via nitriding in intermediate process steps, and thus it 
need not be specified. 
Furthermore, inhibitor constitution elements such as Mn, S, Se, B, Bl, Nb, 
Sn, Ti, and Cr may be added. 
The molten steel comprised of the above-mentioned components can be used in 
the present invention as a hot-rolled sheet in the usual manner or to 
produce a thin cast strip in a continuous casting manner. The hot-rolled 
sheet or cast strip is cold-rolled directly or after a short time 
annealing. 
This annealing is usually carried out at 750.degree.-1200.degree. C. for 30 
seconds to 30 minutes, and effectively enhances the magnetic flux density 
of products. Therefore, this annealing should be adopted in accordance 
with the desired level of the magnetic flux density. 
The successive reduction rates in the cold-rolling can be selected in the 
same manner as disclosed in Japanese Examined Patent Publication No. 
35-2675 or Japanese Examined Patent Publication No. 38-8213. 
The material after being cold-rolled is annealed for the primary 
recrystallization at a temperature of 750.degree.-1000.degree. C. for a 
short time of 30 seconds to 10 minutes. Usually, this annealing serves for 
decarburization of the steel under a controlled dew point in the 
atmosphere. 
Thereafter, the sheet is applied with an annealing separator containing MgO 
as a main component and for annealing finishing. This finishing annealing 
effects the secondary recrystallization and purification. 
In particular, it is desirable to carry out the secondary recrystallization 
and the purification separately under specific conditions. In this case, 
the sheet is controlled to be secondarily recrystallized at a temperature 
of 950.degree.-1100.degree. C., and then heated to a temperature of more 
than 1100.degree. C. for purification. 
Example 
(1) A slab containing 0.05% by weight of C, 3.2% by weight of Si, 0.1% by 
weight of Mn, 0.03% by weight of acid soluble Al, 0.008% by weight of N 
was heated to 1150.degree. C., and reduced into a 25 mm thickness by 
coarse rolling, and subsequently, was rolled for finishing into a 1.8 mm 
thick sheet. A lubricant was applied at the time of the finishing rolling, 
to reduce friction coefficient. Thereafter, the sheet was annealed at 
1100.degree. C. for 2 minutes, was cold-rolled at a reduction rate of 55% 
in the same direction as the hot-rolled direction, and then cold 
cross-rolled in the direction vertical to the above-mentioned cold-rolled 
direction at a reduction rate of 50%. After the annealing for the primary 
crystallization, which also served for the decarburization, was carried 
out at 800.degree. C. for 210 seconds in a wet hydrogen atmosphere, an 
annealing separator was applied, and then annealed for finishing. The 
finishing annealing was carried out by heating to 1200 .degree. C. at a 
heating rate of 15.degree. C./hr in an atmosphere of 50% N.sub.2 +50% 
H.sub.2, and then annealed with the atmosphere being changed to 100% 
H.sub.2. The properties of the resulting products are as follows. 
TABLE 1 
______________________________________ 
Friction Magnetic Flux Density (B.sub.8 : Tesla) 
Coefficient Direction 
Lubricating 
at hot- Hot-rolled vertical 
Properties 
rolling Direction thereto 
______________________________________ 
No 0.30 1.84 1.79 
Yes 0.15 1.92 1.91 
______________________________________ 
(2) A slab having a 26 mm thickness and containing 0.05% by weight of C, 
3.2% by weight of Si, 0.1% by weight of Mn, 0.03% by weight of acid 
soluble Al, and 0.08% by weight of N was heated to 1150.degree. C., and 
then hot-rolled into a thickness on the following order: 
(1) 26.fwdarw.20.fwdarw.18.fwdarw.15.fwdarw.8.fwdarw.4.fwdarw.2 (mm) or 
(2) 26.fwdarw.15.fwdarw.7.fwdarw.3.5.fwdarw.3.fwdarw.2.5.fwdarw.2 (mm) 
to prepare a hot-rolled sheet having a 2.0 mm thickness. After the 
completion of hot-rolling, the sheet was air-cooled for 1 second, cooled 
to 550.degree. C. in water, maintained at this temperature for 1 hour, and 
then cooled by the furnace. The hot-rolled sheet was annealed at 1120 
C.degree. for 2 minutes, cold-rolled in the hot-rolled direction at a 
reduction rate of 50%, and then cold cross-rolled in the direction 
vertical to the above-mentioned cold-rolled direction at a reduction rate 
of 50%. An annealing for the primary crystal, which also served as 
decarburization, was carried out at 800.degree. C. for 210 minutes, an 
annealing separating agent was applied, and then a finishing annealing for 
the purpose of the secondary recrystallization and purification was 
carried out. The magnetic properties of the resulting products are shown 
in Table 2. 
TABLE 2 
______________________________________ 
Accumulated Magnetic Flux Density 
reduction (B.sub.8 : Tesla) 
Hot- rate in Hot- Direction 
Rolling the last 3 rolled vatical 
Conditions 
passes (%) Direction thereto Remarks 
______________________________________ 
(1) 87 1.83 1.75 Comp. Ex. 
(2) 73 1.91 1.90 Ex. 
______________________________________ 
(3) The same slab as in Example 2 was hot-rolled at the initial hot rolling 
temperature of (1) 1100.degree. C., (2) 1000.degree. C., or (3) 
900.degree. C. via the following six passes, i.e., 
26.fwdarw.15.fwdarw.6.fwdarw.3.2.fwdarw.2.8.fwdarw.2.4.fwdarw.2 (mm) to 
prepare a sheet having a 2 mm thickness. The sheet was then annealed for 
finishing under the same conditions as in Example 2. The magnetic 
properties of the resulting products are shown in Table 3. 
TABLE 3 
______________________________________ 
Hot- Hot- Magnetic Flux Density (B.sub.8 : Tesla) 
rolling rolling Direction 
Initiation 
complete Hot-rolled vertical 
Temp. (.degree.C.) 
Temp. (.degree.C.) 
Direction thereto 
______________________________________ 
1100 1000 1.92 1.92 
1000 910 1.91 1.90 
900 830 1.90 1.90 
______________________________________ 
(4) Two samples, i.e. a hot rolled steel sheets containing 0.048% by weight 
of C, 3.40% by weight of Si, 0.14% by weight of Mn, 0.023% by weight of 
acid soluble Al, and the balance being Fe and unavoidable impurities 
having a 1.8 mm thickness in which both surfaces had been ground down to 
1/4 of the total thickness, by a grinder (sample A), and the hot-rolled 
sheet, which had not been ground (sample B), were prepared. The cold 
cross-rolling was applied to these samples by cold-rolling in the same 
direction as the hot- rolled direction at a reduction rate of 55% and then 
cold-rolled in the direction vertical to the former cold rolled direction 
at a reduction rate of 55%. These cold rolled sheets were subjected to 
annealing for the primary crystallization, which also served for 
decarburization, at 810.degree. C. for 120 minutes. Subsequently, MgO was 
applied to the sheets as an annealing separator, the sheets were heated to 
1025.degree. C. at a heating rate of 15.degree. C./hr, and then were 
maintained at 1025.degree. C. for 20 hours to complete the secondary 
recrystallization. Thereafter, the purification and annealing were carried 
out at 1200.degree. C. for 20 hours in 100% H.sub.2 atmosphere. The 
magnetic properties of these products are as shown in Table 4. 
TABLE 4 
______________________________________ 
Magnetic Flux Density (B.sub.8 : Telsla) 
Grinding Direction 
Sample hot-rolled Hot-rolled vertical 
No. Sheet Direction thereto 
______________________________________ 
(A) Yes 1.88 1.87 
(B) No 1.84 1.85 
______________________________________ 
(5) Two samples, i.e. the hot rolled steel sheets as in Example 4 in which 
both surfaces had been ground down to 1/4 of the total thickness, by a 
grinder (sample A), and the hot-rolled sheet, which had not been ground 
(sample B), were prepared. These samples were annealed at 1070.degree. C. 
for 2 minutes, followed by the same treatments in the same stages as in 
Example 4. 
The magnetic properties of these products are as shown in Table 5. 
TABLE 5 
______________________________________ 
Magnetic Flux Density (B.sub.8 : Tesla) 
Grinding Direction 
Sample hot-rolled Hot-rolled Vertical 
No. sheet Direction thereto 
______________________________________ 
(A) Yes 1.95 1.93 
(B) No 1.92 1.92 
______________________________________ 
(6) A molten steel comprising 0.04% by weight of C, 3.0% by weight of Si, 
0.1% by weight of Mn, 0.025% by weight of acid soluble Al, and the balance 
being Fe and unavoidable impurities was coagulated by suddenly cooling to 
prepare a thin cast strip having a 1.0 mm thickness. The cast strip was 
annealed at 1050.degree. C. for 2 minutes, then cold rolled at a reduction 
rate of 50%, and cold cross rolled in the direction vertical to the 
cold-rolled direction at a reduce rate of 50%. The diameters of the work 
rolls in this cold-rolling were 50 mm and 270 mm, respectively. These cold 
rolled sheets were subjected to the annealing for the primary 
crystallization at 800.degree. C. for 90 second in a wet hydrogen 
atmosphere to also serve as decarburization. Thereafter, an annealing 
separator was applied to the sheets, and then a finishing annealing was 
carried out. In the finishing annealing, the sheets were heated up to 
1030.degree. C. at a heating rate of 30.degree. C./hr, maintained at 
1030.degree. C. for 20 hours to complete the secondary crystallization, 
and then maintained at 1200.degree. C. for 20 hours to be purified. The 
magnetic properties of these products are as shown in Table 6. 
TABLE 6 
______________________________________ 
Work roll Magnetic Flux Density (B.sub.8 : Tesla) 
Diameter in Direction 
Cold-Rolling 
Hot-rolled vertical 
(mm) Direction thereto Remarks 
______________________________________ 
50 1.83 1.74 Comp. Ex. 
270 1.93 1.94 Ex. 
______________________________________ 
(7) A hot rolled sheet having a 1.6 mm thickness, comprised of 0.05% by 
weight of C, 3.3% by weight of Si, 0.15% by weight of Mn, 0.027% by weight 
of acid soluble Al, and the balance being Fe and unavoidable impurities 
was annealed at 1120.degree. C. for 2 minutes. Subsequently, the sheet was 
cold-rolled in the rolled direction mentioned above at a reduction rate of 
50%, and then cold cross-rolled in the direction vertical to the 
cold-rolled direction at a reduction rate of 50%. Thereafter, the sheet 
was annealed at 800.degree. for 210 seconds in a wet hydrogen atmosphere, 
which also served for decarburization, an annealing separator was applied 
thereto, and then a finishing annealing was carried out. The schedule of 
cold rolling was changed by using work roll for the cold-rolling having a 
deameter of 50 mm or 270 mm. The magnetic properties of these products are 
as shown in Table 7. From the results, it can be understood that the use 
of the working rolls having a larger diameter in at least one of two cold 
rolling steps is most effective. 
TABLE 7 
______________________________________ 
Work roll 
Work roll Magnetic Flux Density 
Diameter 
Diameter (B.sub.8 : Tesla) 
in 1st Cold- 
in 2nd Cold- Direction 
Rolling Rolling Hot-rolled 
vertical 
(mm) (mm) Direction thereto Remark 
______________________________________ 
50 50 1.85 1.79 Comp. Ex. 
50 270 1.90 1.91 Ex. 
270 50 1.92 1.90 Ex. 
270 270 1.92 1.91 Ex. 
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