Method for making non-oriented magnetic steel sheet

This invention is directed to a method of producing a non-oriented magnetic steel sheet involving a series of processes including performing hot rolling process on a steel slab containing no more than about 0.01 wt % C, no more than about 4.0 wt % Si, no more than about 1.5 wt % Mn, no more than about 1.5 wt % Al, no more than about 0.2 wt % P, and no more than about 0.01 wt % S, performing thereto at least one cold rolling process including an optional intermediate annealing process, and then performing a finishing annealing process. The hot rolling process further includes a step which reduces thermal irregularity formed during slab heating; this step involves maintaining a sheet bar, obtained by rough-rolling of the steel slab, at a temperature ranging from about 850.degree. to 150.degree. C. The hot rolling process also includes a step which promotes the growth of fine precipitated particles by applying strain to the sheet bar. Magnetic steel sheet thusly obtained possess uniform magnetic properties and thickness in the coil.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for making a non-oriented 
magnetic steel sheet having uniform magnetic characteristics and sheet 
shape in the coil product. 
2. Description of the Related Art 
Non-oriented magnetic steel sheets have been used in motors, 
dynamo-electric generators, and cores of transformers. Low core loss and 
high magnetic flux density are important magnetic properties required of 
non-oriented magnetic steel sheets, as these properties enhance the energy 
characteristics of the above-described devices. 
A demand for less irregularity in motor characteristics has coincided with 
the recent development of motors which are highly controllable through 
integrated circuits. Thus, non-oriented magnetic steel sheets which 
possess uniform magnetic characteristics and sheet shape, especially sheet 
thickness in the coil product of a non-oriented magnetic steel sheet, are 
in great demand as motor core materials. 
As a prior art method of producing uniform sheet thickness in the coil 
product, Japanese Patent Publication No. 57-60408 discloses a method which 
involves maintaining the finishing temperature of the hot rolling process 
within the .alpha.-phase temperature range. Furthermore, Japanese Patent 
Laid-Open No. 5-140649 discloses a steel containing extremely low 
quantities of N and S as a method of producing uniform sheet thickness in 
the coil product. However, these prior art techniques cannot produce the 
uniformity presently demanded, thus there remains a great need for marked 
improvement. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a method of producing a 
non-oriented magnetic steel sheet having uniform magnetic properties and 
uniform thickness in the coil product. 
This invention is directed to a method for producing a non-oriented 
magnetic steel sheet which includes hot rolling a steel slab containing no 
more than about 0.01 wt % C, no more than about 4.0 wt % Si, no more than 
about 1.5 wt % Mn, no more than about 1.5 wt % Al, no more than about 0.2 
wt % P, and no more than about 0.01 wt % S, performing at least one 
cold-rolling process including an optional intermediate annealing process, 
and then performing a finishing annealing process. The hot-rolling process 
includes a step which reduces thermal irregularity formed during slab 
heating. The step involves forming a sheet bar by rough-rolling the steel 
slab, and thereafter holding the sheet bar at a temperature ranging from 
about 850 to 1,150.degree. C. The hot-rolling process also includes a step 
which promotes the growth of fine precipitated particles by applying 
strain to the sheet bar. 
This invention is further directed to a method for producing a non-oriented 
magnetic steel sheet which includes hot rolling a steel slab containing no 
more than about 0.01 wt % C, no more than about 4.0 wt % Si, no more than 
about 1.5 wt % Mn, no more than about 1.5 wt % Al, no more than about 0.2 
wt % P, and no more than about 0.01 wt % S, performing at least one 
cold-rolling process including an optional intermediate annealing process, 
and then performing the finishing annealing process. The hot-rolling 
process further includes the steps of: coiling a sheet bar, obtained by 
rough-rolling the steel slab, into a coil having an inside diameter of at 
least about 100 mm and an outside diameter of no more than about 3,600 mm 
at a temperature ranging from about 850.degree. to 1,150.degree. C.; 
uncoiling the coil; and performing a finishing hot rolling. 
According to the invention, the coiling of the sheet bar is preferably 
performed at a temperature T (.degree. C.) satisfying the following 
equation (1): 
##EQU1## 
Furthermore, a light rolling step involving about a 3 to 15% rolling 
reduction is preferably performed after the finishing annealing process in 
order to improve the magnetic properties.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The results of the experiments which led to the discovery of the present 
invention will be explained in detail below. 
Two steel slabs obtained by a continuous casting process and containing 
0.003 wt % C, 0.4 wt % Si, 0.2 wt % Mn, 0.25 wt % Al, 0.05 wt % P, 0.005 
wt % S, and the balance substantially Fe were heated to 1,150.degree. C. 
and roughly rolled so as to form sheet bars 30 mm thick. One of the sheet 
bars was immediately processed into a hot-rolled sheet by a finishing hot 
rolling. Another sheet bar was wound at 970.degree. C. into a coil having 
an inside diameter of 500 mm and an outside diameter of 1,400 mm, unwound 
and finish hot-rolled to form another hot-rolled sheet. The final 
temperature during the finish hot rolling of each sample was 840.degree. 
C. Each hot-rolled sheet was cold-rolled to a thickness of 0.5 mm, and 
continuously annealed at 770.degree. C. for 30 seconds, then the thickness 
and magnetic properties in the longitudinal direction of each coil were 
measured. 
The evaluations of the magnetic properties and coil thickness were carried 
out at 30 m intervals on each coil product length, and the final results 
were determined by arithmetic average (X) and standard deviation .sigma. 
as defined by the following equations (2) and (3): 
##EQU2## 
where X.sub.i represents a core loss W.sub.15/50 measurement or a 
thickness measurement, and n represents the number points on the coil from 
which the measurements were taken (n=133 in the experiments). 
In FIG. 1, blackened circles represent the results obtained from the 
conventionally-produced coil, i.e., the coil produced without winding 
(coiling) the sheet bar. FIG. 1 reveals that the core loss of the 
conventionally-produced coil significantly fluctuates at different 
positions on the coil. It was discovered that the positions on the coil 
which exhibited poor core loss corresponded to the positions between skids 
which were heated to a high temperature during the slab heating (a skid is 
a member supporting the slab in the slab heating furnace, and is usually 
cooled by water). 
Because non-homogeneous precipitated particles which worsen core loss 
values (i.e. increase core loss) are readily formed at higher slab heating 
temperatures, more non-homogeneous precipitated particles will be produced 
between skids (i.e., high temperature slab sections) during slab heating 
than at skid contact sections (i.e., low temperature slab sections) during 
the slab heating. Therefore, core loss values between skids are worse 
(higher) than core loss values at each skid contact section. 
The empty circles in FIG. 1 represent the results obtained from the coil 
produced with sheet bar coiling. FIG. 1 shows that there is less core loss 
fluctuation in the coil produced with sheet bar coiling as compared with 
the coil produced conventionally, i.e., without sheet bar coiling. 
The results of the magnetic property and thickness evaluations are shown in 
Table 1. The process of winding the sheet bar after rough-rolling 
minimized standard deviations of the magnetic properties and thickness. 
Further, excellent average magnetic properties were achieved as compared 
with the conventional process in which the sheet bar was rolled 
immediately after the rough-rolling. 
The thickness fluctuations in the coil produced by the conventional process 
(without sheet bar coiling) is due to the variable resistance to 
deformation across the hot-rolled sheet during finishing rolling. This 
variable resistance results from the temperature difference during slab 
heating between the skid section and the intermediate section between 
skids. 
TABLE 1 
______________________________________ 
Magnetic Core Loss Sheet Number of 
Induction W.sub.15/50 
Thickness Measuring 
B.sub.50 (T) (W/kg) (mm) Points 
(X) .sigma. 
(X) .sigma. 
(X) .sigma. 
n 
______________________________________ 
Without 1.751 0.004 5.706 
0.122 
0.50 0.003 
133 
Sheet Bar 
Coiling 
With Sheet 
1.762 0.001 5.315 
0.031 
0.50 0.001 
133 
Bar Coiling 
______________________________________ 
FIG. 1 and Table 1 clearly demonstrate that magnetic properties are 
improved and that both magnetic properties and thickness become uniform in 
a coil by winding the sheet bar after rough-rolling. 
Possible mechanisms behind these improvements are as follows: 
(1) temperature fluctuation within the sheet bar during slab heating can be 
reduced by winding the sheet bar; and/or 
(2) strain caused by sheet bar coiling can promote the growth of fine 
precipitated particles. 
Thus, the present invention is not limited to the winding or coiling of the 
sheet bar, but encompasses a hot-rolling process which reduces the 
temperature fluctuation in a sheet bar formed during a steel slab 
rough-rolling process by maintaining the sheet bar at a temperature 
ranging from about 850.degree. to 1,150.degree. C., and which promotes the 
growth of fine precipitated particles in the sheet bar by applying strain 
to the sheet bar. As an example of means other than sheet bar coiling 
through which the invention may be accomplished, a method which places a 
sheet bar in a heat maintaining furnace after applying about 0.5 to 5% 
strain by rolling can be used. However, this method requires a long 
furnace which can receive the sheet bar without coiling. 
We conducted several investigations regarding the shape of the sheet bar. 
FIG. 2 shows the effects of the inside and outside diameter of the coil on 
magnetic properties. 
An outside diameter over about 3,600 mm causes an increased core loss 
average and a greater core loss standard deviation within a coil. Please 
refer to FIG. 2A and 2B, respectively. 
A larger outside diameter promotes non-uniform temperature and results in 
less strain being incorporated into the sheet bar during winding, thus 
precipitated particle growth may be hindered. Therefore, the outside 
diameter of the coil should not be over about 3,600 mm in order to promote 
uniform temperature and increase the strain from winding. On the other 
hand, an inside diameter of less than about 100 mm causes some surface 
defects in the form of cracks on the sheet bar. Consequently, the inside 
diameter of the coil should be about 100 mm or more. 
The results of our investigation into the effects of steel composition and 
sheet bar coiling temperature on the magnetic properties will be detailed 
below. 
Three steels, A, B and C, having the compositions shown in Table 2 were 
melted in a converter and vacuum degassing device, and slabs were prepared 
by a continuous casting process. The slabs were again heated, then 
rough-rolled to form sheet bars 40 mm thick. After coiling the sheet bars 
at various temperatures, a finishing hot rolling was performed on each 
sample. 
For the comparison, some sheet bars were hot-rolled without sheet bar 
coiling. The thickness of the each hot-rolled sheet after the finishing 
hot rolling was 2.0 mm. Then, the hot-rolled sheet was annealed at 
900.degree. C. for 1 minute, cold-rolled to be 0.5 mm thick. Thereafter, 
continuous finishing annealing was performed at 800.degree. C. for 30 
seconds, and an insulating coating treatment was performed to form the 
sheet product. The magnetic properties of test pieces cut from the plate 
product were evaluated through an Epstein test. 
TABLE 2 
______________________________________ 
Composition (wt %) Sheet Bar Coiling 
Steel 
C Si Mn P Al Temperature (.degree.C.) 
______________________________________ 
A 0.003 0.5 0.25 0.08 0.25 908 
950 
985 
1020 
1050 
Without coiling 
B 0.003 0.25 0.25 0.08 0.5 910 
985 
1040 
1050 
1080 
Without coiling 
C 0.003 0.4 0.45 0.08 0.25 900 
920 
980 
1000 
1080 
Without coiling 
______________________________________ 
The results are plotted in FIGS. 3A and 3B. FIG. 3A illustrates the 
correlation between .alpha.-phase stabilizing coefficient G (calculated 
from the sheet bar coiling temperature, see below) and average coil core 
loss, while FIG. 3B shows the correlation between the .alpha.-phase 
stabilizing coefficient G and the core loss standard deviation of a coil. 
The .alpha.-phase stabilizing coefficient G represents an index reflecting 
the stability of .alpha.-phase at a measured temperature. At a given 
temperature T (.degree. C.), G is expressed through the following equation 
(1): 
##EQU3## 
As shown FIG. 4 (discussed in detail below), G correlates well with 
.alpha.-phase fraction. Specifically, the .alpha.-phase fraction increases 
as G increases beyond 0, reflecting the stabilization of the 
.alpha.-phase. 
On the other hand, FIG. 3 shows the significant improvement in the average 
core loss, W.sub.15/50, and the core loss standard deviation g on a coil 
after sheet bar coiling at a temperature satisfying G&gt;0 in equation (1). 
The reason for these improvements can be explained as follows. 
Fine precipitated particles which are formed during rough-rolling and 
improve core loss values can grow by means of the sheet bar coiling. With 
sheet bar coiling, the diffusion rate of the .alpha.-phase is about 10 
times faster than that of the .gamma.-phase, and the diffusion is a 
rate-determining stage in the growth of the fine precipitated particles. 
Thus, higher a .alpha.-phase fraction in a sheet bar coil promotes fine 
precipitated particle growth, increases the improvement of in core loss 
values, and reduces the standard deviation among core loss values within a 
coil. 
Accordingly, by controlling steel composition and coiling temperature so as 
to satisfy G&gt;0, a non-oriented magnetic steel having uniform core loss 
throughout the coil can be produced. 
The steel composition of the invention and a process illustrating the 
invention will now be explained in detail. 
C content should be not more than about 0.01 wt %. When the C content 
exceeds about 0.01 wt %, magnetic properties deteriorate due to C 
precipitation. The lower C content limit should be about 0.0001 wt % in 
view of economic feasibility. 
Si content should be not more than about 4.0 wt %. Although Si is a useful 
component for increasing specific resistance and decreasing core loss, an 
Si content over about 4.0 wt % causes poor formability during cold 
rolling. The lower limit is preferably set to about 0.05 wt % to ensure 
satisfactory specific resistance. 
Mn content should be not more than about 1.5 wt %. Although Mn is a useful 
component for increasing specific resistance and decreasing core loss, 
costs become prohibitively high when Mn content exceeds about 1.5 wt %. On 
the other hand, Mn can fix S as MnS, S being otherwise harmful to magnetic 
properties. Therefore, the lower limit of Mn is preferably set to about 
0.1 wt % to ensure satisfactory magnetic properties. 
Al content should be not more than about 1.5 wt %. Although Al is a useful 
component for increasing specific resistance and decreasing core loss, an 
Al content over about 1.5 wt % causes poor formability during cold 
rolling. 
P content should be not more than about 0.2 wt %. Although P can be added 
to improve blanking ability, a P content over about 0.2 wt % causes poor 
formability during cold rolling. The lower P content limit should be about 
0.0001 wt % in view of economic feasibility. 
S content should be not more than about 0.01 wt %. Because S forms MnS 
finely precipitated particles which hinder transfer of the magnetic domain 
walls and the growth of fine precipitated particles from the application 
of strain to the sheet bar, S content should be as small as possible. 
Any known additives, such as Sb, Sn, Bi, Ge, B, Ca, and rare earth metals, 
can be added to the steel to improve magnetic properties. The content of 
each additive is suitably not more than about 0.2 wt % in view of economic 
feasibility. 
A sheet bar is formed from a slab having the above composition by directly 
rough-rolling the slab or after re-heating the slab. The sheet bar is 
wound into a coil having an inside diameter not less than about 100 mm and 
outside diameter not more than about 3,600 mm. The winding is conducted 
within a temperature range of about 850.degree. to 1,150.degree. C. 
When the sheet bar temperature exceeds about 1,150.degree. C., fine 
precipitated particle content increases during finishing hot rolling such 
that decreased uniformity in core loss within a coil and between coils 
results. On the other hand, a sheet bar coiling temperature less than 
about 850.degree. C. is not effective due to prolonged time required to 
cancel non-homogeneous precipitated particles and textures. 
A coiled sheet bar having an inside diameter of less than about 100 mm 
tends to form cracks or defects on the surface due to the larger 
curvature. A coiled sheet bar having an outside diameter of over about 
3,600 mm exhibits poor temperature uniformity and experiences less strain 
during the coiling process, thereby inhibiting uniformity in magnetic 
properties and thickness. 
By coiling the sheet bar under the above conditions, uniform core loss and 
thickness can be attained in a coiled, non-oriented magnetic steel sheet. 
In addition, by controlling the sheet bar coiling temperature so that the 
.alpha.-phase stability index G satisfies G&gt;0, the average core loss as 
well as core loss uniformity will further improve. Thus, the sheet bar is 
preferably wound at a temperature satisfying G&gt;0. 
The sheet bar coiling temperature represents the sheet bar average 
temperature during coiling, and remains substantially unchanged during 
coiling and uncoiling in general. However, when the average sheet bar 
temperature decreases during an extended coiling time, at least one 
average temperature during coiling or uncoiling should satisfy G&gt;0. 
The coiled sheet bar is then unwound and hot-rolled for finishing to make 
hot-rolled sheet. Any self-annealing or hot-rolled sheet annealing may be 
incorporated as the need arises. The hot-rolled sheet annealing may be 
accomplished by either batch annealing (box annealing) or continuous 
annealing. 
Thereafter, a sheet having a predetermined thickness, for example 0.5 mm, 
is obtained by one or more cold rolling steps, and may include optional 
intermediate annealing steps. Subsequently, finishing annealing is 
performed to form the final product. 
Any insulating coating process may be performed after the finishing 
annealing. A continuous annealing may be preferably used for the finishing 
annealing in view of productivity and economics. 
Furthermore, a light-rolling process involving a rolling reduction of about 
3 to 15% may be performed after the finishing annealing or the insulating 
coating process. A rolling reduction of less than about 3% or over about 
15% diminishes the light-rolling effect of improving core loss values 
through the growth of coarse grains during the straightening annealing 
treatment. 
The invention will now be described through illustrative examples. The 
examples are not intended to limit the scope of the appended claims. 
EXAMPLE 1 
After adjusting the steel composition in a converter and vacuum degassing 
device, slabs were prepared by continuous casting. When the slab 
temperature fell to 300.degree. C., the slabs were reheated in a reheating 
furnace. Then, sheet bars 30 mm thick were obtained by rough-rolling the 
reheated slabs. After coiling the sheet bars, hot-rolled sheets were 
prepared from the sheet bar coil by finishing hot rolling. Some of the 
hot-rolled sheets were annealed. The hot-rolled sheets were then 
cold-rolled to a thickness of 0.5 mm, and continuous annealing was 
performed at 850.degree. C. for 30 seconds. The magnetic properties in the 
longitudinal direction and thickness of the coil products were measured. 
The length of the coil product was 4,000 m, and a measurement of the 
magnetic properties was carried out every 30 m on the coils. 
Table 3 shows the results of the magnetic property evaluations and 
thickness measurements, in addition to slab composition and the conditions 
under which hot rolling and sheet bar coiling were conducted. 
TABLE 3 
__________________________________________________________________________ 
Sheet bar coiling temperature 
Coiling condition 
Slab heating Inside 
Outside 
Sample 
Composition (%) temperature 
Temperature 
diameter 
diameter 
.alpha.-phase 
stability index 
No. C Si Mn P S Al (.degree.C.) 
(.degree.C.) 
(mm) (mm) G 
__________________________________________________________________________ 
1 0.0026 
0.12 
0.2 0.05 
0.0031 
0.25 
1150 950 200 1500 2.01 
2 1150 920 500 3500 7.36 
3 1150 950 1500 3800 2.01 
4 1150 950 90 800 2.01 
5 1250 1000 500 1500 -4.76 
6 1150 820 500 1500 32.84 
7 1150 -- -- -- -- 
8 0.003 
0.5 0.5 0.05 
0.002 
0.6 1100 860 2000 3400 29.84 
9 1100 950 150 2000 10.69 
10 1100 -- -- -- -- 
11 1150 1060 800 2000 -0.97 
12 1100 950 90 800 10.69 
13 0.003 
2.5 0.5 0.01 
0.002 
0.3 1100 950 500 1500 25.86 
14 1250 1100 500 1500 12.73 
15 1100 -- -- -- -- 
16 1100 1000 2700 3800 19.09 
17 1250 1180 500 1500 13.53 
__________________________________________________________________________ 
Note: 
For Nos. 8 to 12, self annealing was performed on hotrolled sheets at 
850.degree. C. for 30 minutes, and for Nos. 13 to 17, continuous annealin 
was performed on hotrolled sheets at 950.degree. C. for 90 seconds. 
Underlining indicates values out of the claimed range or properties 
inferior to Examples of the Invention. 
No sheet bar coiling was conducted for Nos. 7, 10 and 15. 
Magnetic induction B.sub.50 
Iron loss W.sub.15/50 
Sheet Thickness 
Standard Standard Standard 
Sample 
Average 
Deviation 
Average 
Deviation 
Average 
Deviation 
Surface 
No. (X) (T) 
.sigma. (T) 
(X) (w/kg) 
.sigma. (w/kg) 
(X) (mm) 
.sigma. (mm) 
defects 
Remarks 
__________________________________________________________________________ 
1 1.772 0.001 5.65 0.03 0.50 0.001 nil Example of Invention 
2 1.770 0.001 5.50 0.02 0.50 0.001 nil Example of Invention 
3 1.755 0.004 6.21 0.19 0.50 0.003 nil Comparative Ex. 
4 1.771 0.001 5.60 0.03 0.50 0.001 present 
Comparative Ex. 
5 1.765 0.002 5.85 0.05 0.50 0.001 nil Example of Invention 
6 1.745 0.005 6.20 0.15 0.50 0.004 nil Comparative Ex. 
7 1.755 0.004 6.40 0.18 0.50 0.003 nil Comparative Ex. 
8 1.765 0.001 4.05 0.02 0.50 0.001 nil Example of Invention 
9 1.765 0.001 4.20 0.02 0.50 0.001 nil Example of Invention 
10 1.750 0.004 4.89 0.15 0.50 0.003 nil Comparative Ex. 
11 1.760 0.002 4.35 0.04 0.50 0.001 nil Example of Invention 
12 1.762 0.001 4.20 0.02 0.50 0.001 present 
Comparative Ex. 
13 1.688 0.001 2.81 0.02 0.50 0.001 nil Example of Invention 
14 1.689 0.001 2.85 0.02 0.50 0.001 nil Example of Invention 
15 1.655 0.004 3.35 0.08 0.50 0.004 nil Comparative Ex. 
16 1.670 0.003 3.22 0.09 0.50 0.003 nil Comparative Ex. 
17 1.655 0.004 3.26 0.08 0.50 0.002 nil Comparative 
__________________________________________________________________________ 
Ex. 
Note: 
For Nos. 8 to 12, self annealing was performed on hotrolled sheets at 
850.degree. C. for 30 minutes, and for Nos. 13 to 17, continuous annealin 
was performed on hotrolled sheets at 950.degree. C. for 90 seconds. 
Underlining indicates values out of the claimed range or properties 
inferior to the Examples of the Invention. 
No sheet bar coiling was conducted for Nos. 7, 10 and 15. 
Table 3 reveals that examples where sheet bar coiling was performed after 
rough-rolling have superior (smaller) standard deviations of the magnetic 
properties and thickness, and superior (larger) average magnetic property 
values compared to those comparative examples conventionally produced in 
that finishing hot rolling was carried out immediately after 
rough-rolling. Among the Examples of the Invention, sample Nos. 1, 2, 8, 
9, 13 and 14 satisfying G&gt;0 exhibit excellent properties. Nos. 3 and 16, 
having a coiled sheet bar outside diameter over about 3,600 mm, failed to 
produce adequate sheet bar coiling effects. Nos. 4 and 12, having coiled 
sheet bar inside diameters under about 100 mm, formed many surface defects 
on the produced sheet. Furthermore, in No. 6, where the sheet bar coiling 
temperature was less than about 850.degree. C., large deviations in the 
magnetic properties remained. Similarly, in No. 17, treated at a sheet bar 
coiling temperature over about 1,150.degree. C., the averages and 
deviations of the magnetic properties are inferior to No. 13, which had a 
sheet bar coiling temperature less than about 1,150.degree. C. 
EXAMPLE 2 
After adjusting the steel composition in a converter and vacuum degassing 
device, slabs were prepared by continuous casting. When the slab 
temperature fell to 850.degree. C., the slabs were reheated in a reheating 
furnace. Then, sheet bars 30 mm thick were obtained by rough-rolling the 
reheated slabs. After coiling the sheet bars, hot-rolled sheets were 
prepared from the sheet bar coil by finishing hot rolling. Some of the 
hot-rolled sheets were annealed. The hot-rolled sheets were then 
cold-rolled, and continuous annealing was performed at 770.degree. C. for 
30 seconds, and thereafter a 5% light rolling was performed to obtain 
products 0.5 mm thick. Magnetic properties in the longitudinal direction 
and thickness of the coil products were measured. 
Table 4 shows the results of the magnetic property evaluations and 
thickness measurements, in addition to slab compositions and the 
conditions under which hot rolling and sheet bar coiling were conducted. 
TABLE 4 
__________________________________________________________________________ 
Sheet bar coiling condition 
Coiling condition 
Slab heating Inside 
Outside 
Sample 
Composition (%) temperature 
Temperature 
diameter 
diameter 
.alpha.-phase 
stability index 
No. C Si Mn P S Al (.degree.C.) 
(.degree.C.) 
(mm) (mm) G 
__________________________________________________________________________ 
18 0.0026 
0.12 
0.2 0.05 
0.003 
0.25 
1150 950 200 1500 2.01 
19 1150 920 500 3500 7.36 
20 1150 950 1500 3800 2.01 
21 1150 950 90 800 2.01 
22 1250 1000 500 1500 -4.76 
23 1150 820 500 1500 32.84 
24 1150 -- -- -- -- 
25 0.003 
0.5 0.5 0.05 
0.002 
0.6 1100 860 2000 3400 29.84 
26 1100 950 150 2000 10.68 
27 1100 -- -- -- -- 
28 1100 1060 800 2000 -0.97 
29 1100 950 90 800 10.69 
30 0.003 
2.5 0.5 0.01 
0.002 
0.3 1100 950 500 1500 25.86 
31 1250 1100 500 1500 12.73 
32 1100 -- -- -- -- 
33 1100 1000 2700 3800 19.09 
34 1250 1180 500 1500 13.53 
__________________________________________________________________________ 
Note: 
For Nos. 25 to 29, self annealing was performed on hotrolled sheets at 
850.degree. C. for one hour, and for Nos. 30 to 34, continuous annealing 
was performed on hotrolled sheets at 950.degree. C. for 90 seconds. 
Magnetic property measurements were carried out after straightening 
annealing at 850.degree. C. for 2 hours. 
Underlining indicates values out of the claimed range or properties 
inferior to the Examples of the Invention. 
No sheet bar coiling was conducted for Nos. 24, 27 and 32. 
Magnetic Induction B.sub.50 
Iron loss W.sub.15/50 
Sheet Thickness 
Skin pass Standard Standard Standard 
Serial 
Rolling 
Average 
Deviation 
Average 
Deviation 
Average 
Deviation 
Surface 
No. reduction 
(X) (T) 
.sigma. (T) 
(X) (w/kg) 
.sigma. (w/kg) 
(X) (mm) 
.sigma. (mm) 
defects 
Remarks 
__________________________________________________________________________ 
18 8 1.770 0.001 4.56 0.03 0.50 0.001 nil Example of the 
Invention 
19 5 1.765 0.001 4.55 0.02 0.50 0.001 nil Example of the 
Invention 
20 8 1.745 0.003 5.30 0.15 0.50 0.003 nil Comparative Ex. 
21 10 1.768 0.001 4.50 0.03 0.50 0.001 present 
Comparative Ex. 
22 8 1.760 0.002 4.75 0.04 0.50 0.001 nil Example of the 
Invention 
23 7 1.735 0.005 5.30 0.15 0.50 0.004 nil Comparative Ex. 
24 5 1.740 0.005 5.21 0.18 0.50 0.004 nil Comparative Ex. 
25 8 1.760 0.001 3.05 0.02 0.50 0.001 nil Example of the 
Invention 
26 2 1.762 0.001 3.77 0.02 0.50 0.001 nil Example of the 
Invention 
27 10 1.740 0.004 4.85 0.13 0.50 0.003 nil Comparative Ex. 
28 10 1.755 0.002 3.21 0.04 0.50 0.001 nil Example of the 
Invention 
29 10 1.762 0.001 3.08 0.02 0.50 0.001 present 
Comparative Ex. 
30 8 1.768 0.001 2.65 0.02 0.50 0.001 nil Example of the 
Invention 
31 18 1.640 0.001 3.05 0.02 0.50 0.001 nil Example of the 
Invention 
32 12 1.640 0.004 3.25 0.09 0.50 0.004 nil Comparative Ex. 
33 8 1.648 0.003 3.05 0.08 0.50 0.003 nil Comparative Ex. 
34 8 1.645 0.004 3.12 0.08 0.50 0.002 nil Comparative 
__________________________________________________________________________ 
Ex. 
Note: 
For Nos. 25 to 29, self annealing was performed on hotrolled sheets at 
850.degree. C. for one hour, and for Nos. 30 to 34, continuous annealing 
was performed on hotrolled sheets at 950.degree. C. for 90 seconds. 
Magnetic property measurements were carried out after straightening 
annealing at 850.degree. C. for 2 hours. 
Underlining represents the conditions out of the claimed range or 
properties inferior to the Examples of the Invention. 
No sheet bar coiling was conducted for Nos. 24, 27 and 32. 
Table 4 reveals that examples where sheet bar coiling was performed after 
rough-rolling have superior (smaller) standard deviations of the magnetic 
properties and thickness, and superior (larger) average magnetic property 
values compared to those comparative examples conventionally produced in 
that hot rolling finishing was carried out immediately after 
rough-rolling. Among the Examples of the Inventions, sample Nos. 18, 19, 
25 and 30 satisfying G&gt;0 exhibited excellent properties. Nos. 20 and 33, 
having a coiled sheet bar outside diameter over about 3,600 mm, failed to 
produce adequate sheet bar effects. Nos. 21 and 29, having coiled sheet 
bar diameters under about 100 mm, formed many surface defects on the 
produced sheet. Furthermore, in No. 23, where the sheet bar coiling 
temperature was less than about 850.degree. C., large deviations in the 
magnetic properties remained. Similarly, in No. 34, treated at a sheet bar 
coiling temperature over about 1,150.degree. C., the averages and 
deviations of the magnetic properties are inferior to No. 30, which had a 
sheet bar coiling temperature less than about 1,150.degree. C. 
Although this invention has been described in connection with specific 
forms thereof, it will be appreciated that a wide variety of equivalents 
may be substituted for the specific elements described herein without 
departing from the spirit and scope of this invention defined in the 
appended claims.