Note: Descriptions are shown in the official language in which they were submitted.
ExpressMail #B97619309
1 ~n744~
PATENT
Attorney's Docket No. RL-1356
~IETHOD OF PRODUCING GRAIN-ORIENTED
SILICON STEEL WITH SMALL sORoN ADDITIONS
BACKGROUND OF THE INVENTION
This invention relates to a method of produclng con-
ventional grain-oriented silicon steel with improved magnetic
properties. More particularly, this invention relates to a
method of improving cube-on-edge grain-oriented silicon steel
processing by providing small but sufficient amounts of boron
in the cold-rolled strip so as to improve magnetic permeability
and core loss values.
In the manufacture of grain-oriented silicon steel,
it is known that the Goss secondary recrystallization texture,
[110] [001], in accordance with Miller's Indices, results in
improved magnetic properties, particularly permeability and
core loss over nonoriented steels. The Goss texture refers
to the body-centered cubic lattice comprising the grain or crystal
being oriented in the cube-on-edge position. The texture or
grain orientation o~ this type has a cube edge parallel to the
rolling direction in the plane of rolling, with the (110) plane
being in the sheet plane. As is well known, steels having this
orientation are characterized by a relatively high permeability
in the rolling direction and a relatively low permeability in
a direction at right angles thereto.
In the manufacture of grain-oriented silicon steel,
typical steps include providing a melt on the order of 2-4.5~
silicon, casting the melt, such as by ingot or continuous casting
processes, hot rolling the steel, cold rolling the steel to
final gauge with an intermediate annealing when two or more
cold-rolling stages are used, decarburizing the steel, applying
a refractory oxide base coating, such as magnesium o~ide coating,
to the steel, and final texture annealing the steel at elevated
~k
~ 30744~
temperatures in order to produce the desired secondary recrystal-
lization and purification treatment to remove impurities, such
as nitrogen and sulfur. The development of the cube-on-edge
orientations is dependent upon the mechanism of secondary recrystal-
5 lization wherein during recrystallization, secondary cube-on-edge
oriented grains are preferentially grown at the expense of primary
grains having a different and undesirable orientation.
Grain-oriented silicon steel is conventionally used
in electrical applications, such as power transformers, distribution
transformers, generators, and the like. The silicon content
o~ the steel and electrical applications permit cyclic variation
of the applied magnetic field with limited energy loss, which
is termed core loss. It is desirable, therefore, in steel of
this type, to reduce core loss. It is known that the core loss
lS is made up of two main components, that due to the hysteresis
effect, and that due to eddy currents. The magnitude of the
eddy currents is also limited by the resistance of the path
through which they flow. The resistance of the core material
is determined by the resistivity of the material and its thickness
or cross-sectional area. Consequently, it is desirable as shown
by a trend in the industry that magnetic materials having a
high resistivity be produced in thin sheets in order that eddy
current losses be kept to a minimum.
Numerous attempts have been made for improving the
quality of cube-on-edge grain-oriented electromagnetic silicon
steels by the addition of boron to the steel melt. For example,
U.S. Patent 3,873,381, issued May 25, 1975, uses boron and nitrogen
additions to control grain growth during the primary grain-growth
stage in addition to the presence of manganese and sulfur.
The reference discloses the need for large amounts of boron
on the order of 20 to 120 parts per million (ppm), nitrogen
on the order of 3 to 100 ppm in the steel melt. The resulting
cold-rolled strip is then subject to special processing including
a wet decarburizing atmosphere.
1 307444
Other attempts to improve magnetic properties include
the addition to the silicon-iron melt of a smaller amount of
boron to the melt such that the hot-rolled band contains a small
but critical amount of boron in critical proportions to the
nitrogen content of the metal while controlling the manganese
and sulfur to achieve high permeability silicon steels. u.s.
Patent 3,905,842 r issued September 16, 1975, discloses adding
a source of boron to the melt and therefter processing the melt
to provide a cold-rolled sheet containing 5 to 45 ppm boron
and from 15 to 95 ppm nitrogen and the proportions of nitrogen
and boron being in the ratio of 2 to 4 parts of nitrogen to
one part of boron. Sulfur may range from 0.007 to 0.06% and
manganese from 0.002 to 0.1~, by weight. The steel of the reference
includes at least 0.007~ sulfur in solute form during final
texture annealing. A similar steel is disclosed in U.S. Patent
3,905,843, issued September 16, 1975, wherein the ratio of nitrogen
to boron ranges from 1 to 15 and the ratio of manganese to sulfur
is maintained to less than 2.1. The cold-rolling schedules
for the processes of both of these references includes an intermediate
annealing step between the cold-rolling stages and a final heavy
cold reduction on the order of greater than 70%, or 80~ or more,
to final gauge.
Other attempts have been made to simplify the silicon-
iron sheet production process by eliminating one processing
step, such as by changing a two-stage cold-rolling operation
to a direct cold-rolling process. U.S. Patent 3,957,546, issued
May 18, 1976, discloses that when the manganese-to-sulfur ratio
is less than 1.8, the ho~-rolled band can be cold rolled directly
to final thickness without intermediate anneals. An improvement
on the direct cold-rolling process is disclosed in U.S. Patent
4,078,952, issued March 14, 1978. That reference disclosed
preparing a band from a melt having 6 to 18 ppm boron and producing
a hot-rolled band having a manganese-t-o-sulfur ratio of at least
1 307444
1.83 for the purpose of providing uniformity between the poor
end and the good end of coils.
Although it is known from the above-cited patents
that the quality of electromagnetic silicon steel can be improved
by adding controlled amounts of boron to the melt to produce
so~called high permeability steels having permeabilities of
at least 1870 (G/Oe) at 10 oersteds and core loss of no more
than 0.700 watts per pound (WPP) at 17 kilogauss, as with most
all processes, they are in need of improvement. u.s. Patent
4,000,015, issued December 2~, 1976, discloses a method of con-
trolling the dew point of the hydrogen-bearing atmosphere used
to decarburize boron-bearing grain-oriented silicon steels having
a cube-on-edge orientation. To such steels, it has also been
disclosed in U.S. Patent 4,054,470, issued October 18, 1977,
that copper may be present in the steel melt for the purpose
of inhibiting primary grain growth. U.S. Patent 4,338,144,
issued July 6, 1982, discloses modifying the boron-bearing com-
position to have less than 20 ppm solutè nitrogen and a
manganese-to-sulfur ratio of at least 2.1 and thereafter heating
the sheet in a nitrogen-bearing hydrogen atmosphere to a temperature
sufficient to effect secondary recrystallization. It is also
known that large boron levels in silicon steel tend to promote
brittleness and reduce the capability of welding the steel.
Welding can be an important operation within the process to
facilitate processing, increase yield and cut costs of manufacturing
production. Although it is preferable to weld hot-rolled band
prior to further processing, welding can occur at other stages
of production. For example, U.S. Patent 4,244,757, issued
January 13, 1981, discloses a method of controlling nitrogen
30 and phosphorus, as both of those elements were found to adversely
affect the weldability of the steelO
It is also known that grain-oriented silicon steels
containing relatively large amounts of boron result in an increase
1 307444
in the secondary grain size. Typical high permeabillty silicon
steels have grain sizes greater than 10 mm. The eddy current
portion of the core loss is directly related to the size of
the secondary grains. The larger the grain size, the larger
the core loss. Attempts hav~ been made, such as in U.S. Patent
4,548,655, issued October 22, 1985, to reduce watt loss by achieving
fine secondary grain size in boron-bearing silicon steels during
final texture annealing. Another manner of reducing core loss
values is by reducing the sheet thickness. U.S. Patent 4,608,100,
issued August 26, 1986, discloses a method of producing thin
gauge oriented silicon steel.
Generally, all of the development work related to
the boron-bearing steels in the above-cited patents was done
on cube-on-edge grain-oriented silicon steels having a final
gauge of about 10 mils or greater. Such steels rely on the
high boron content for the primary grain growth inhibition for
providing high permeability silicon steels. Such silicon steels
also generally undergo cold reduction operations to final gauge
wherein a final heavy cold reduction on the order of greater
than 80% is made in order to facilitate the grain orientation.
What is needed is a method for producing conventional
grain-oriented silicon steel which takes advantage of the benefits
of boron additions without the disadvantages thereof. It is
desirable that a method be developed for reducing the final
25 gauge of the boron-containing steels to less than nominally
10 mils while maintaining the secondary grain size on the order
of conventional grain-oriented silicon steels which do not contain
boron. Furthermore, it is desirable to improve the weldability
of the steel produced thereby over high permeability steels,
such as in U.S. Patent 3,905,842, cited above. The improved
process should result in s~licon-iron sheet of nominally 10
mils or less characterized by magnetic permeability of at least
1850 (G/Oe) at 10 oersteds and improved core loss values over
that of conventional grain-oriented silicon steels.
1 307444
SUMMARY OF TME INVENTION
_
In accordance with the present invention, a method
is provided for producing cube-on-edge grain-oriented silicon
steel having improved core loss and magnetic permeability values
g wherein the method includes making a silicon ste~l melt composition
of about 2 to 4.5% silicon and controlling the manganese and
sulfur levels and thereafter producing 3 to 10 ppm boron in
a final gauge steel strip prior to final texture annealing.
The method includes casting the melt to form a casting thereof,
hot rolling the casting to a hot~roll band having a manganese-to-
sulfur ratio of greater than 2.5 and cold working the hot-roll
band in two stages. The hot-roll band is cold worked to an
intermediate gauge strip of about 0.018 to 0.026 inch by a re-
duction of at least 60%, annealing and thereafter cold working
to a final gauge of less than 10 mils by a final cold reduction
of about 65% to 75%. The cold-worked final gauge strip is annealed
to effect decarburization, a refractory oxide coating is applied,
and the final gauge strip having a 3 to 10 ppm boron therein
is final texture annealed to develop a permeability of 1850
or more at 10 oersteds with secondary grain sizes of less than
10 millimeters, preferably, with grain sizes comparable to con-
ventional grain-oriented silicon steels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Broadly, the method of the present invention is directed
to producing conventional grain-oriented silicon steel having
a cube-on-ed~e orientation having a modified steel chemistry
and modified processing steps.
The manganese, sulfur and/or selenium are necessary
as they form the primary grain growth inhibitors which are essential
for controlling the steel's orientation and its properties which
are dependent thereon. More specifically, the manganese combines
with sulfur and/or selenium to form manganese sulfide and/or
manganese selenide, as well as other compounds. Together, these
1 307444
compounds inhibit normal grain growth during the final texture
anneal, while at the same time aiding in the development of
secondary recrystal~ized grains having the desired cuhe-on-edge
orientation.
It is necessary to the present invention that the
ratio of manganese-to-sulfur and/or selenium be at least 2.5
or greater. For that reason, the manganese is kept relatively
high within the broad range and sulfur and/or selenium is kept
at a relatively low level. As a result of keeping such manganese,
sulfur, and selenium levels so as to provide the ratio of at
least 2.5 or greater, there are differences in the MnS and/or
MnSe solubilities which result in differences in the MnS and/or
MnSe precipitation behavior for conventional grain-oriented
silicon steel compositions than those of the high permeability
compositions set forth in the above-cited patent references.
The solubility products also relate to the stability of the
inclusions on heating during final texture annealing; the higher
the solubility product, the more stable the inclusions of MnS
and/or MnSe.
The manganese content of the steel may range up to
0.10% by weight and preferably from a minumum of at least 0.04%.
Manganese .is necessary to the inhibition system of the steel.
More preferably, manganese ranges from 0.068 to 0.085%.
The primary grain growth inhibition system also requires
the presence of sulfur and/or selenium. Up to 0.035% of material
selected from the group consisting of sulfur and selenium is
present~ preferably with a minimum of at least 0.016%. More
preferably, a low and narrow range of 0.024 to 0.028% is present.
Copper may also be present in the steel up to 0.4
and preferably 0.1 to 0.4%. When copper is present it will
combine with manganese and/or sulfur and/or selenium to form
various copper compounds, including manganese copper sulfide
and/or manganese copper selenide. Together with MnS and/or
1 307444
MnSe inclusions, these compounds inhibit normal grain growth
during final texture annealing. As an added advantage, copper
may also be beneficial during processing, as well as for increasing
the steel's resistivity.
The steel melt of the present invention includes up
to .01% nitrogen, preferably .0005~ to .008%, and more preferably
.003 to .0065% nitrogen; up to .08~ carbon, preferably .028
to .04~ carbon; and no more than .008% aluminum; the balance
iron and other incidental impurities and residuals.
The boron content of the steel is essential to the
steel in accordance with the present claimed invention. Unlike
the prior art processes using relatively large amounts of boron
to combine with other elements to act as a primary grain growth
inhibitor and to effect secondary recrystallization, the present
claimed invention uses manganese to improve magnetic properties
of a steel wherein the manganese, sulfur, selenide, and related
compounds are the primary grain growth inhibition system with
solute boron perhaps providing further inhibition effect, either
directly as a solute in the grain boundaries, or by controlling
the activity of other elements, perhaps such as nitrogen and
solute sulfur.
It is known that residual amounts of boron on the
order of up to about 3 ppm may be present in the silicon steel
melt. The source of the boron may be from the refractory materials
used in the metallurgical vessels, any residual amounts of metal
left in the vessels, as well as minor impurities resulting from
the sources of the iron and steel used to provide the steel
melt. In accordance with the invention; however, the cold-rolled
strip must be produced having a boron content of 3 to 10 ppm.
This may be achieved by adding boron to the silicon steel melt
or, alternatively, the boron may be added at some later stage
of the processing. The combination of adding boron to the melt
and to the annealing separator coating may be used.
1 307444
The critical aspect in accordance with the invention
is that the final gauge strip prior to final texture annealing
have a boron content of 3 to 10 ppm, and more preferably a boron
content of 3 to 7 ppm. If the boron exceeds 10 ppm, then the
advantages of the present claimed invention are negated by the
tendency to increase the secondary grain sizes which may result
from the boron having more effect in the primary grain growth
inhibition system. There will also be a tendency to increase
the brittleness and the weldability problems with such higher
boron contents. If boron is present of less than 3 ppm, such
as in residual levels, it will have little effect to improve
the magnetic properties of a conventional grain-oriented steel
using a manganese-sulfide and/or selenide inhibition system.
If boron is added to the melt, then a sufficient amount of boron
should be added in order to produce the desired boron in the
final gauge steel strip prior to final texture annealing. Boron
should be added to the ladle at appropriate stages in order
to minimize any boron loss as a result of refining the steel
melt or in any high temperature soaking prior to processing
into a hot-roll band. As a practical matter, with proper processing,
no significant loss of boron from the metal occurs through hot
and cold rolling and heating stages prior to the final texture
annealing. Care must be taken, however, to assure that such
small amounts of boron, 3 to 10 ppm, as well as a desired
manganese-to-sulfur and/or selenium ratio of at least 2.5, is
present in the hot-rolled band strip and more preferably in
the cold-rolled final gauge strip prior to final texture annealing.
Specific processing up to the steps of cold reduction
of the steel and including steps through hot rolled band may
be conventional and are not critical to the present invention
although it is desirable to minimize any loss of boron if it
is added during the melting stage. The steel of the present
invention may be processed in a conventional manner by cast-ng,
1 307~4
which may be continuous casting or ingot casting, and hot rolling
to form hot rolled band. Conventionally, the hot rolled band
may have a gauge ranging from 0.06 to 0.10 inch (1.52 to 2.54
mm). Typically, the hot rolled band has a gauge of about 0.08
inch (2.03 mm). It is important that the hot rolled band contain
the desired manganese-to-sulfur ratio and the required boron
content. After annealing the hot rolled band, the process includes
an initial cold working of the hot rolled band to an intermediate
gauge by a reduction of at least 60% and preferably 60 to 70~.
The intermediate gauge steel is then subject to an intermediate
anneal which is followed by a second cold working, having a
final reduction of less than 75% and preferably less than 70%,
more preferably 65 to 70% from intermediate gauge to final gauge
of nominally 10 mils or less. The hot-roll band is first cold
lS worked to a desired intermediate gauge of about 0.018 to 0.026
inch (0.46 to 0.66 mm) and preferably from 0.020 to 0.026 inch
(0.51 to 0.66 mm). The precise intermediate gauge will depend
somewhat on the desired final gauge. A thicker intermediate
gauge may be used for the thicker final gauge.
Thereafter, the intermediate gauge steel is subjected
to an intermediate anneal before further cold reduction. The
purpose of such anneal is to effect a fine grain primary recrystal-
lized structure~ The annealing step may be batch or continuous
and generally ranges from temperatures of 1700 to 1800F (926
to 982C) in a protective, nonoxidizing atmosphere, such as
nitrogen or hydrogen or mixtures thereof.
After the intermediate annealing, the intermediate
gauge is subjected to further cold working and it is important
that the final reduction from intermediate to final gauge be
about 65% or more and less than 75%, and more preferably less
than 70~. Such processing is unique to boron-containing silicon
steels for the prior art making of high permeability silicon
steels requires a single cold reduction or a final heavy cold
reduction in multiple cold reduction processes.
1 307444
The final gauge material is less than 10 mils, may
be as low as 4 mils, and typically may be on the order of a
nominal 7 or 9 mils (0.17~ to 0.229 mm). The material at final
gauge is then decarburized, provided with a refractory oxide
base coating, such as magnesium oxide, and final texture annealed,
such as in a hydrogen atmosphere, to produce the desired secondary
recrystallization and purification treatment to remove impurities,
such as nitrogen and sulfur.
In order to better understand the present invention,
the following examples are illustrative of several aspects of
the invention.
Example I
Mill Heat 189002 was prepared having the following
melt composition, by weight percent:
C Mn S Cu Si N B Fe
.030 .069 .025 .15 3.25 .0057 7 ppm Bal.
The composition was similar to conventional cube-on-edge grain-oriented
silicon steel using a sulfide/selenide inhibition system except
sufficient boron was added to the melt to achieve 7 ppm boron
content. The steel was then conventionally processed through
the hot rolled band to a gauge of 0.080 inch (2.03 mm) in the
mill. Representative samples of hot rolled band were then processed
in the laboratory by cold reduction to a final gauge of nominally
7 mils through the step of final texture annealing. ~he experiment
included variations in intermediate gauge of 0.026 inch, 0.023
inch, 0.020 inch, and 0.01~ inch. The analysis of the available
data indicated that the intermediate gauge range of 0.023 to
0.020 inch was optimum for the 7-mil finish gauge for that Heat.
The anneal of the intermediate cold-rolled gauge and the decarburizing
anneal of the cold-rolled final gauge were done in a conventional
manner. The annealing separator coating applied to the decarburized
strip was a conventional MgO coating containing 5.2~ MgSO4.
The strip was then final texture annealed in a hydrogen atmosphere
1 307444
to develop the cube-on-edge orientation. Epsteins samples were
prepared and the magnetic properties were measured in a conventional
manner including core loss in watts per pound at 60 ~ertz at
15 and 17 KG, and permeability (G/Oe) at 10 oersteds.
TABLE I
Lab Processing from Mill ~ot-Rolled sand
Heat 189002
Inter.
Coil/ Gauge Core Loss tWPP)
Location (Inch)_5KG @17KG ~@lOH
5/HT .023 .444 .635 1887
5/BT .023 .445 .636 1891
5/~T .020 .442 .636 1888
5/BT .020 .426 .613 1891
HT means hot top
BT means butt top
The data in Table I lllustrate that all samples exhibited
good magnetlc permeability and core loss when compared to typical
conventional grain-oriented silicon steels without the modified
chemistry. Typical conventional grain-oriented steel core loss
values during that production period were .426 WPP at 15 KG
and .665 WPP at 17 KG and permeability was 1837 at 10 oersteds.
The cold-rolled strip prior to final texture annealing contained
7 ppm boron and a manganese-to-sulfur ratio of 2.8. The final
texture annealed strip exhibited grain size on the order of
8 mm which is larger than typical 5 mm grain size of conventional
grain-oriented silicon steel but substantially smaller than
tyical high permeability silicon steel grain sizes of 10 mm
and larger. The data of Table I clearly shows that additions
of small amounts of boron to the steel to provide a small but
critical amount of boron in the strip prior to final texture
annealing results in higher permeabilities.
Example II
The samples of Example I were tested for their response
to scribing techniques. Each sample was coated with a stress
coating (disclosed in U.S. Patent 4,032,366) and then mechanically
12
1 3~744~
scribed using a tool steel stylus to mark substantially parallel
lines, about 5 mm apart, and substantially transverse to the
rolling direc~ion. All of the ~pstein samples showed improvement
in core loss values upon scribing as shown in Table II, while
maintaining good high permeability values.
TAB~E II
Heat 189002
Inter.
Coil/ GaugeCore Loss (WPP
Location (inch) @ 15 KG @ 17 KG ~ @ 10H
5/HT .023 .346 .500 1870
5/BT .023 .347 .504 1872
5/HT .020 .340 .495 1869
5/BT .020 .381 .491 1875
Example III
A total of six mill heats were made having the following
ladle composition wlth the balance being iron:
Heat No. Tvpe C Mn S Cu Si N B
1 Exper. .030 .072 .026 .27 3.28 .0050 .0006
2 Exper. .031 .071 .026 .25 3.28 .0054 .0006
3 Exper. .031 .076 .026 .25 3.24 .0056 .0007
4 Exper. .029 .079 .026 .21 3.26 .0047 .0006
Control .031 .071 .025 .26 3.22 .0060 .0002
6 Control .030 .078 .026 .23 3.23 .0043 .0002
An addition of 5 ppm boron was made to the ladle for each of
the experimental heats. Each of the above heats was cast into
numerous ingots and hot rolled in accordance~with Example I.
All of the Control Heats and some of the Experimental Heats
were cold rolled in accordance with Example I to an intermediate
gauge of 0.020 inch. Some of the experimental coils were cold
rolled to an intermediate gauge of 0.022 inch. All of the coils
were then conventionally annealed and final cold rolled to nominally
7 mils, subjected to a decarburizing anneal and coated with
a conventional MgO coating and final texture annealed. The
results are shown in the following Table III.
1 3n7444
TABLE III
Inter. Grain
Gauge Core LosS (WPP) _ Size
Heat No. (inch) @ 15 KG @ 17 KG ~ @ 10~ (mm)
1-4 Exper. .020 .426 .663 1850 7-8
1-4 Exper. .022 .418 .643 1853 6-7
5,6 Control .020 .42~ .666 1834 ~-5
Example IV
Twelve mill heats were melted having a modified con-
ventional grain-oriented chemistry to include boron additions
and modified processing to produce 9-mil or 7-mil material.
S The ladle melt chemistry was as follows:
TABLE IV
Heat No. C Mn S Cu Si N B
1 .031.075 .026 .21 3.27.0042 .0006
2 .030.078 .027 .23 3.25.0033 .0005
3 .030.079 .026 .25 3.19.0040 .0005
4 .028.080 .027 .20 3.23.0040 .0004
.030.073 .026 .21 3.24.0031 .0006
6 .030.072 .026 .25 3.23.0046 .0005
7 .030.072 .026 .25 3.23.00~2 .0005
8 .032.073 .027 .22 3.29.0044 .0006
9 .030.077 .025 .22 3.25.0038 .0004
.032.073 .029 .24 3.23.0043 .0005
11 .030.076 .026 .23 3.25.0044 .0003
12 .030.071 .025 .24 3.24.0043 .0004
The melt chemistries of each of the heats were melted having
incidental impurity levels at most containing 0.1~ Cr, 0.13~
Ni, and 0.015% P and the balance iron. An addition of 3 ppm
boron was made to the ladle for each of the heats. Each of
the heats was cast into ingot and hot rolled as in Example I.
Each of the coils from the heats was cold rolled in two stages
with an intermediate anneal. Four of the heats, 1 through 4,
were cold rolled to nominally 7 mils from an intermediate gauge
1 3074~
of 0.022 lnch so that the cold work from intermediate gauge
to final gauge was on the order of 68% reduction. Eight of
the heats, 5 through 12, were cold rolled to nominally 9~mil
final gauge from an intermediate gauge of 0.026 inch having
a final reduction of about 67%. Each of the coils were conventionally
decarburize annealed, coated with an MgO coating and final texture
annealed. Nu~erous Epstein samples were taken and the average
of the good~end and poor-end magnetic properties of each coil
strip are set forth in the following Table v.
TABLE V
Avg. G.E. and P.E.
No. of NominalNumber Core Loss (WPP) Avg.
Heats Gauqeof Samples @15KG @17KG
4 7 mils16 .391 .599 1854
8 9 mils30 .417 .619 1859
When compared to typical average values for 7-mil
conventional grain-oriented material of .408 WPP at 15 KG and
.638 WPP at 17 KG and a permeability of 1837 at 10 oersteds,
the present claimed invention provides better magnetic properties.
When compared to typical average values for 9-mil ~aterial at
.424 WPP at 15 KG and .634 WPP at 17 KG and a permability of
1850 at 10 oersteds, the present claimed invention provides
better properties. The typical grain size of the grain-oriented
silicon steel processed in accordance with the present invention
was about 4 to 5 mm. The boron content in the cold-rolled strip
analyzed prior to final texture annealing was about 5 ppm.
The manganese-to-sulfur ratio in the strip was about 3.
~ s was an objective of the present lnvention, conventional
grain-oriented silicon steel using the sulfide primary grain
growth inhibition system has been modified through composition
and processing to provide improved magnetic properties. The
addition of boron has not substantially enlarged the grain size
which would adversely affect the core loss values; however,
it has resulted in comparable or better core loss and permeability
1 3074~
values. The method of the present invention uses the benefits
of boron additions without the disadvantages of brittleness
problems that are normally associated with boron-containing
grain-oriented silicon steels. The process is also useful in
thinner gauges of nominally less than 10 mils, on the order
of 7 mils, and maybe as low as as 4 mils. An advantage of the
steel is that it responds well to scribing techniques, unlike
conventional grain-oriented silicon steels.
