Note: Descriptions are shown in the official language in which they were submitted.
ELECTRICAL STEEL PROCESSING WITHOUT
A POST COLD-ROLLING INTERMEDIATE ANNEAL
[0001]
BACKGROUND
[0002] This invention relates generally to the field of semi-processed
electrical
steel sheet manufacturing, and more particularly embodiments of the invention
relate to
achieving electrical steel sheet products with the desired final magnetic
properties after
they have been annealed at the customer. Semi-processed electrical steel
sheets are
different from fully processed electrical steel sheets in that the semi-
processed electrical
steel sheets manufactured at a steel facility require an additional customer
annealing step
performed by the customer before the material can be used. Fully processed
electrical
steel sheets, on the other hand, do not require an additional customer
annealing step, and
thus, can be used by the customer without further annealing.
BRIEF SUMMARY
[0003] The present invention relates to manufacturing semi-processed
electrical
steel sheets, formed by systems using methods of manufacturing without the
need for
annealing after final cold rolling by the electrical steel sheet manufacturer,
and before the
customer annealing step. The customer annealing step described herein may also
be
referred to a -final anneal."
[0004] In various applications, such as electrical motors, lighting ballasts,
electrical generators, etc., it may be desirable to use electrical steel
products that have
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high saturation, high permeability, and low core loss properties. Moreover,
for electrical
motors that operate at high frequencies, such as for electrical motors in cars
or aircraft,
the electrical steel sheets often have thickness less than 0.015 inches (e.g.,
between 0.011
to 0.013 inches, 0.007 to 0.010 inches, or the like). For electrical steels,
there comes a
point in production that improving one or more of the high saturation, high
permeability,
and low core loss properties becomes a detriment to one or more of these
properties, or
other properties.
[0005] The saturation of the electrical steel is an indication of the highest
induction that the steel can achieve. The permeability of the electrical steel
is the
measure of the ability of the steel to support the formation of a magnetic
field within
itself and is expressed as the ratio of the magnetic flux to the field of
strength. Electrical
steel with high permeability allows for an increased induction for a given
magnetic field,
and thus, with respect to motor applications, reduces the need for copper
windings,
which results in lower copper costs. The core loss is the energy wasted in the
electrical
steel. Low core loss in electrical steels results in a higher efficiency in
the end products,
such as motors, generators, ballasts, and the like. Therefore, it may be
desirable in many
products to use electrical steels with a high ability to support a magnetic
field and a high
efficiency (e.g., high permeability and low core loss) if it is not
detrimental to the cost of
manufacturing or other desirable steel properties.
[0006] Electrical steel is processed with specific compositions, using
specific
systems, and using specific methods in order to achieve electrical steels with
the desired
saturation, permeability, and core loss, as well as other properties.
Improving one
property may come at the detriment of another. For example, when increasing
the
permeability a higher core loss may result (and vice versa). Consequently,
electrical
steels are processed with specific compositions using specific methods in
order to
optimize the desired magnetic properties.
[0007] Electrical steel sheets are typically produced by melting scrap steel
or iron
in an electric furnace (e.g. through compact strip production (CSP) when steel
is fed
directly into the tunnel furnace, or through another process in which the
steel is cast and
reheated at a later point in time), or processing molten steel from iron ore
in a blast
furnace, described as integrated production. In the integrated process molten
steel is
produced in a blast furnace, and in the CSP process the molten steel is
produced using an
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electric furnace (e.g., electric arc furnace, or other like furnace). A
decarburizer (e.g.,
vacuum degasser, argon decarburizer, etc.) is used to create a vacuum, or
change the
pressure, in order to utilize oxygen to remove the carbon from the molten
metal.
Thereafter, the molten steel that is at least substantially free of oxygen is
sent to a ladle
metallurgy facility to add the alloying materials to the steel in order to
create the desired
steel composition. The steel is then poured into ladles and cast into slabs.
The steel
slabs are hot rolled (e.g., in one or more stages), annealed, cold rolled
(e.g., in one or
more stages), and intermediately annealed. Thereafter, the steel sheets are
sent to the
customer for stamping, and customer annealing in the case of semi-processed
steels.
These steps occur under various conditions to produce electrical steel sheets
with the
desired magnetic properties and physical properties (e.g., thickness, surface
finish, etc.).
Other steps may also be performed in order to achieve the desired magnetic
properties.
[0008] During the hot rolling step (or between multiple hot rolling steps the
electrical steel sheet may be maintained at a temperature above the
recrystallization
temperature, which is a temperature at which deformed grains are replaced by a
new set
of undeformed grains. Recrystallization is usually accompanied by a reduction
in the
strength and hardness of a material and a simultaneous increase in the
ductility. The hot
rolling process reduces the thickness of the steel sheet and controls the
grain structure of
the electrical steel. After the hot rolling stage(s) the steel is potentially
pickled in a bath
(e.g., sulfuric, nitric, hydrochloric, other acids, or combinations of these,
etc.) in order to
remove scale on the surface of the steel from oxidization. Thereafter, the
electrical steel
sheet is annealed to change the magnetic properties of the steel. During
annealing the
steel is heated, and thereafter cooled, to coarsen the structure of the steel,
and improve
cold working properties. The electrical steel sheet is then cold rolled after
annealing,
which comprises rolling the electrical steel sheet below the recrystallization
temperature.
Cold rolling may begin at room temperatures; however, the temperature of the
steel sheet
may be elevated at the beginning of the cold rolling process, or otherwise
rise during
cold rolling due to the cold rolling process itself. The cold rolling process
increases the
strength of the steel, improves the surface finish, and rolls the steel sheet
to the desired
thickness.
[0009] Electrical steel sheets undergoing traditional processing are annealed
directly after the cold rolling process in order to recrystallize the steel
and achieve the
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desired permeability and core loss for the electrical steel in the finished
product. The
annealing process, both before and after cold rolling, can be done via a
continuous
annealing process or a batch annealing process. In continuous annealing the
sheets of
steel are passed through a heating furnace and thereafter cooled in a
continuous sheet. In
batch annealing the steel sheets are coiled into rolls and are heated and
cooled in batches
of coiled rolls.
[0010] Temper rolling, in the case of semi-processed steels, may be performed
after annealing in order to improve the surface finish of the electrical steel
sheet, enhance
the stamping characteristics, and provide improved magnetic properties after
the
customer has stamped (e.g., punched, or the like) the electrical steel sheet
and performed
a final customer annealing step (e.g., heating the stamped part).
[0011] After temper rolling, in the case of semi-processed steels produced
using
batch annealing, or after continuous annealing of the semi-processed steels,
the electrical
steel sheet is sent to the customer for further processing. The customer
typically stamps
the electrical steel sheet into the required shapes, and thereafter, further
anneals the
stamped shapes in a customer annealing process. The customer anneal is
performed by
heating the stamped shapes to a specific temperature and letting them cool in
order to
maximize the magnetic properties of the stamped electrical steel part. The
annealing
process after stamping is performed by the customer because after stamping the
stamped
shapes have cold-worked edges and the customer annealing process removes the
cold-
worked edges, relieves any stress caused by stamping, and maximizes the final
magnetic
properties of the stamped part. Therefore, in traditional semi-processed
electrical steel
manufacturing there are three annealing steps, a pre-anneal before cold
rolling, a post
cold rolling intermediate anneal, and a final anneal at the customer. In still
other
embodiments of the invention annealing steps may also occur between the
individual
stages of multiple hot rolling or cold rolling passes.
[0012] The present invention provides methods and systems that can be used to
produce electrical steels with compositions that provide the same, similar,
and/or better
magnetic properties (e.g., saturation, permeability, and core loss) than
steels that are
produced using traditional electrical steel processing that utilizes an
intermediate
annealing step after the final cold rolling pass and before additional steel
processing, or
customer stamping and annealing.
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[0013] In the present invention, as is the case with traditional electrical
steel
processing, scrap steel and/or iron is melted into molten steel or molten
steel is produced
from iron ore; the molten steel is sent for decarburization and for alloy
additions; the
steel is poured into ladles and cast into slabs (or continuously cast in some
embodiments
described later); and the slabs are hot rolled, pickled, annealed (e.g., batch
annealed or
continuously annealed), and cold rolled into sheets. However, unlike
traditional
electrical steel processing, in the present invention, the intermediate
annealing step (e.g.,
the batch annealing step, or alternatively, the continuous annealing step)
after cold
rolling is not performed. Instead, in the present invention, after cold
rolling a tension
leveling step may be performed or a coating may be applied to the semi-
processed
electrical steel sheet before it is sent to the customer. At the customer
locations, as is the
case with the traditional method for manufacturing semi-processed electrical
steels, the
customers stamp the electrical steel sheets into the desired shapes, and
thereafter,
perform a customer annealing step to remove distortions created by the
stamping and to
maximize the magnetic properties of the electrical steel.
[0014] One embodiment of the invention comprises a method of manufacturing
an electrical steel. The method comprises hot rolling steel into a steel sheet
in one or
more hot rolling passes to a post hot rolling thickness of less than 0.1
inches; annealing
the steel sheet in a first anneal after hot rolling; cold rolling the steel
sheet in one or more
first cold rolling passes after the first anneal to a post first cold rolling
thickness less than
0.05 inches; annealing the steel sheet in a second anneal after the one or
more first cold
rolling passes; cold rolling the steel sheet in one or more final cold rolling
passes after
the second annealing process to a thickness of less than 0.015 inches; and
whereby final
magnetic properties are achieved in the steel sheet after the steel sheet is
stamped and
final annealed without an intermediate annealing process after the one or more
final cold
rolling passes, and before the stamping and the final annealing.
[0015] In further accord with an embodiment of the invention, the method
comprises manufacturing electrical steel with a composition of silicon (Si) in
a range of
0.15-3.5% weight; manganese (Mn) in a range of 0.005-1% weight; aluminum (Al)
less
than or equal to 1% weight; carbon (C) less than or equal to 0.04% weight;
antimony
(Sb) or tin (Sn) less than or equal to 0.1% weight; and wherein the remainder
comprises
unavoidable impurities and iron.
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[0016] In another embodiment of the invention, the method comprises
manufacturing electrical steel with a composition of silicon (Si) is in the
range of 2.8-
3.5% weight; manganese (Mn) in a range of 0.2-0.4% weight; and aluminum (Al)
in a
range of 0.5-0.75% weight.
[0017] In still another embodiment of the invention, the method further
comprises sending the steel sheet to a customer for the stamping and the final
annealing
after the stamping.
[0018] In yet another embodiment of the method, the first anneal comprises a
batch anneal above 1600 degrees F, and the second anneal comprises a batch
anneal
above 1500 degrees F.
[0019] In further accord with an embodiment of the method, the final thickness
of the steel sheet is 0.011 to 0.013 and the final magnetic properties
comprise a
permeability of greater than 7500 G/Oe and a core loss of less than 16.0 w/kg
when
tested at 1.0T at 400Hz.
[0020] In another embodiment of the method, the final thickness of the steel
sheet is 0.007 to 0.010 and the final magnetic properties comprise a
permeability greater
than 8500 G/Oe and a core loss less than 13.0 w/kg when tested at 1.0T at
400Hz.
[0021] Another embodiment of the invention comprises a method of
manufacturing an electrical steel. The method comprises procuring a thin strip
cast steel,
wherein the thickness of the thin strip cast steel is less than or equal to
0.05 inches;
annealing the thin strip cast steel; cold rolling the steel sheet in one or
more cold rolling
passes after annealing to a thickness of less than 0.015 inches; and whereby
final
magnetic properties are achieved in the steel sheet after the steel sheet is
stamped and
final annealed without an intermediate annealing process after the one or more
cold
rolling passes, and before the stamping and the final annealing.
[0022] In further accord with an embodiment of the invention, the method
comprises manufacturing electrical steel with a composition comprising silicon
(Si) in a
range of 0.15-3.5% weight; manganese (Mn) in a range of 0.005-1% weight;
aluminum
(Al) less than or equal to 1% weight; carbon (C) less than or equal to 0.04%
weight;
antimony (Sb) or tin (Sn) less than or equal to 0.1% weight; and wherein the
remainder
comprises unavoidable impurities and iron.
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100231 In another embodiment of the invention, the method comprises
manufacturing electrical steel with a composition comprising silicon (Si) is
in the range
of 2.8-3.5% weight; manganese (Mn) in a range of 0.2-0.4% weight; and aluminum
(Al)
in a range of 0.5-0.75% weight.
[0024] In still another embodiment, the method further comprises sending the
steel sheet to a customer for the stamping and the final annealing after the
stamping.
[0025] In yet another embodiment of the method, the annealing comprises a
batch anneal above 1500 degrees F.
[0026] In further accord with an embodiment of the method, the thickness of
the
steel sheet is 0.011 to 0.013 and the final magnetic properties comprise a
permeability of
greater than 7500 G/Oe and a core loss of less than 16.0 w/kg when tested at
1.0T at
400Hz.
[0027] In another embodiment of the method, the thickness of the steel sheet
is
0.007 to 0.010 and the final magnetic properties comprise a permeability
greater than
8500 G/Oe and a core loss less than 13.0 w/kg when tested at 1.0T @ 400 Hz.
[0028] Another embodiment of the invention is an electrical steel, comprising
silicon (Si) in a range of 0.15-3.5% weight and the remainder comprises
unavoidable
impurities and iron. The electrical steel is produced by hot rolling steel in
one or more
hot rolling passes into a steel sheet to a post hot rolling thickness of less
than 0.1 inches;
annealing the steel sheet in a first anneal after hot rolling; cold rolling
the steel sheet in
one or more first cold rolling passes after the first anneal to a thickness
less than 0.05
inches; annealing the steel sheet in a second anneal after the one or more
first cold rolling
passes; cold rolling the steel sheet in one or more final cold rolling passes
after the
second annealing process to a thickness of less than 0.015 inches; and whereby
final
magnetic properties are achieved in the steel sheet after the steel sheet is
stamped and
final annealed without an intermediate annealing process after the one or more
final cold
rolling passes, and before the stamping and the final annealing.
[0029] In further accord with an embodiment of the invention, the electrical
steel
further comprises manganese (Mn) in a range of 0.005-1% weight; aluminum (Al)
less
than or equal to 1% weight; carbon (C) less than or equal to 0.04% weight; and
antimony
(Sb) or tin (Sn) less than or equal to 0.1% weight.
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[0030] In another embodiment of the invention, the electrical steel comprises
silicon (Si) is in the range of 2.8-3.5% weight; manganese (Mn) in a range of
0.2-0.4%
weight; and aluminum (Al) in a range of 0.5-0.75% weight.
[0031] In still another embodiment of the invention, the electrical steel is
further
produced by sending the steel sheet to a customer for the stamping and the
final
annealing after the stamping.
[0032] In yet another embodiment of the invention, the first anneal comprises
a
batch anneal above 1600 degrees F, and the second anneal comprises a batch
anneal
above 1500 degrees F.
[0033] In further accord with an embodiment of the invention, the final
thickness
of the steel sheet is 0.011 to 0.013 and the final magnetic properties
comprise a
permeability of greater than 7500 G/Oe and a core loss of less than 16.0 w/kg
when
tested at 400Hz at 1.0T.
[0034] In another embodiment of the invention, the final thickness of the
steel
sheet is 0.007 to 0.010 and the final magnetic properties comprise a
permeability greater
than 8500 G/Oe and a core loss less than 13.0 w/kg.
[0035] Another embodiment of the invention is an electrical steel comprising
silicon (Si) in a range of 0.15-3.5% weight and the remainder of the
composition of the
electrical steel comprises unavoidable impurities and iron. The electrical
steel is
produced by procuring a thin strip cast steel, wherein the thickness of the
thin strip cast
steel is less than or equal to 0.05 inches; annealing the thin strip cast
steel; cold rolling
the thin strip cast steel in one or more cold rolling passes after the
annealing into a steel
sheet with a thickness less than 0.015 inches; and whereby final magnetic
properties are
achieved in the steel sheet after the steel sheet is stamped and final
annealed without an
intermediate annealing process after the one or more cold rolling passes, and
before the
stamping and the final annealing.
[0036] In further accord with an embodiment of the invention, the electrical
steel
further comprises manganese (Mn) in a range of 0.005-1% weight; aluminum (Al)
less
than or equal to 1% weight; carbon (C) less than or equal to 0.04% weight; and
antimony
(Sb) or tin (Sn) less than or equal to 0.1% weight.
[0037] In another embodiment of the invention, the composition of the
electrical
steel comprises silicon (Si) is in the range of 2.8-3.5% weight; manganese
(Mn) in a
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range of 0.2-0.4% weight; and aluminum (Al) in a range of 0.5-0.75% weight.
[0038] In still another embodiment of the invention, wherein the electrical
steel is
further produced by sending the steel sheet to a customer for the stamping and
the final
annealing after the stamping.
[0039] In yet another embodiment of the invention, annealing the thin strip
cast
steel comprises a batch anneal above 1500 degrees F.
[0040] In further accord with an embodiment of the invention, the final
thickness
of the steel sheet is 0.011 to 0.013 and the final magnetic properties
comprise a
permeability of greater than 7500 G/Oe and a core loss of less than 16.0 w/kg
when
tested at 1.0T at 400Hz.
[0041] In another embodiment of the invention, the final thickness of the
steel
sheet is 0.007 to 0.010 and the final magnetic properties comprise a
permeability greater
than 8500 G/Oe and a core loss less than 13.0 w/kg when tested at 1.0T at
400Hz.
[0042] To the accomplishment of the foregoing and the related ends, the one or
more embodiments comprise the features hereinafter fully described and
particularly
pointed out in the claims. The following description and the annexed drawings
set forth
certain illustrative features of the one or more embodiments. These features
are
indicative, however, of but a few of the various ways in which the principles
of various
embodiments may be employed, and this description is intended to include all
such
embodiments and their equivalents.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0043] Having thus described embodiments of the invention in general terms,
reference will now be made to the accompanying drawings, wherein:
[0044] Figure 1A provides a process flow for producing electrical steel, in
accordance with one embodiment of the invention;
[0045] Figure 1B provides a process flow for producing electrical steel, in
accordance with one embodiment of the invention;
[0046] Figure 2 provides an electrical steel processing system environment in
accordance with one embodiment of the invention;
[0047] Figure 3 provides a process flow for producing electrical steels with
lower
thicknesses using multiple cold rolling steps with intermediate annealing and
without
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annealing after the final cold rolling step; and
[0048] Figure 4 provides a process flow for producing electrical steels with
lower
thicknesses using thin strip cast steel.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0049] Embodiments of the present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which some, but
not all,
embodiments of the invention are shown. Indeed, the invention may be embodied
in
many different forms and should not be construed as limited to the embodiments
set
forth herein; rather, these embodiments are provided so that this disclosure
will satisfy
applicable legal requirements. Like numbers refer to like elements throughout.
Furthermore, the ranges discussed herein are inclusive ranges.
[0050] Figures IA and 1B illustrate flow charts for electrical steel
production
processes 1, 2 for manufacturing electrical steels with desirable magnetic
properties (e.g.,
high saturation, high permeability, and low core loss) without the need for an
annealing
step (e.g., continuous annealing or batch annealing) directly after cold
rolling (e.g., the
final cold rolling pass). Figure IA illustrates an electrical steel production
process 1 for
manufacturing electrical steel with a tension leveling and/or coating after
cold rolling,
while Figure 1B illustrates an electrical steel production process 2 for
manufacturing
electrical steel with a surface rouging or temper rolling, and tension
leveling after cold
rolling. Figure 2 illustrates an electrical steel processing system
environment 200 used
in manufacturing the electrical steels in accordance with the process
described in Figures
IA and 1B.
[0051] As illustrated by block 10 in Figures 1A and 1B, scrap steel or iron
may
be melted into molten steel in an electric arc furnace 202, as illustrated in
Figure 2. In
other embodiments of the invention other types of furnaces may also be used to
produce
molten steel from scrap steel. In other embodiments of the invention, molten
steel may
alternatively be produced from iron ore. As illustrated by block 20 in Figures
1 A and
1B, the molten steel may be decarburized by removing all, or substantially
all, of the
oxygen from the molten steel, and thereafter, alloys may be added to produce
the desired
composition of the electrical steel. The decarburized process step may be
performed in a
CA 02897668 2015-07-16
vacuum degasser, argon decarburizer, or other like system, while the alloying
additions
may be made in a ladle metallurgy facility, or other like system. Embodiments
of the
compositions of various electrical steels will be described in detail below.
[0052] As illustrated in block 30 of Figures IA and 1B, the molten steel is
transferred to a ladle 204 as illustrated in Figure 2. Thereafter, as
illustrated by block 40
in Figures IA and 1B the ladle 204 supplies a tundish 206 with the molten
steel and the
steel is cast 208 into slabs, as illustrated in Figure 2. After being cast,
the slabs may be
sent through a tunnel furnace 209 to maintain the desired temperature of the
slab, as
illustrated by block 45 in Figures lA and 1B, as well as in Figure 2. Upon
exiting the
tunnel furnace 209 the slabs may be sent directly to the rolling mill for hot
rolling. In
other embodiments of the invention the steel may be cast 208 into slabs,
allowed to cool,
and thereafter, at a later time, sent to a re-heater at the rolling mill
before being hot
rolled. In still other embodiments of the invention the steel may be
continuously cast
into a thin steel sheet and thereafter sent for further processing, as
discussed later with
respect to Figure 4.
[0053] As illustrated by block 50 in Figures lA and 1B, the cast slabs are hot
rolled into sheets in one or more hot rolling passes through one or more sets
of hot rollers
210. As illustrated by block 55, after hot rolling, the formed sheet may be
pickled in
order to remove scale (e.g., iron oxide) from the steel sheet. Thereafter, as
illustrated by
block 60 of Figures IA and 1B the pickled sheet is coiled and sent for batch
annealing
212 with one or more other coiled sheets as illustrated in Figure 2.
Alternatively, in
some embodiments the sheets may be continuously annealed if the manufacturing
facility
has a continuous annealing line. As illustrated by block 70 in Figures IA and
1B, after
batch annealing 212 (or continuous annealing in alternative processes) the
coiled rolls are
uncoiled and cold rolled into thinner sheets in one or more cold rolling
passes through
one or more sets of cold rolls 214, as illustrated in Figure 2.
[0054] After cold rolling, unlike traditional electrical steel processing, the
cold
rolled electrical steel sheets arc not processed using further annealing. The
cold rolling
process may produce sheets that have wavy edges or buckling throughout the
sheet, such
that a customer may not be able to use the sheets for end products. In
traditional
electrical steel processing, annealing the sheets after cold rolling removes
the wavy
edges and/or buckling from the sheet. However, in the present invention, since
there is
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no annealing step directly after cold rolling (e.g., the final cold rolling
pass) the sheet
may need to undergo a tension leveling step as illustrated by block 80 in
Figure 1A.
During tension leveling penetrating rollers 216, as illustrated in Figure 2,
transform the
sheet having wavy edges and/or buckling back into a flat sheet (e.g., no wavy
edges or
buckling), which may be needed in order to allow a customer to properly feed
the sheet
through a press for the stamping process. During tension leveling the sheet is
bent over
and under (or vice versa) the penetrating rollers 216, as illustrated in
Figure 2. The
penetrating rolls 216 deform and apply tension to the sheet in order to
stretch the sheet to
remove the wavy edges and/or buckling.
[0055] As illustrated by block 90 in Figure 1A, after tension leveling a
coating
may be added to the electrical steel sheet. The coating may be added by
running the
sheet through a bath or rolling a coating onto the sheet when passing the
sheet through a
set of coating rolls 218, as illustrated in Figure 2. The coating (or a rough
surface as
described below) may be applied to the sheet because when the customer
performs an
annealing step after the sheet has been stamped, the stamped shapes may stick
together
such that they may not be separated if the sheet does not have a coating (or a
rough
surface). Different types of coatings (or rough surfaces) may be applied to
the electrical
steel sheets depending on the needs of the customer.
[0056] In some embodiments of the invention, instead of applying a coating,
the
electrical steel sheets are produced with a rough surface, as illustrated in
Figure 1B. In
some embodiments of the invention, the rough surface may be applied during the
cold
rolling process using high roughness rolls, as illustrated by block 75 in
Figure 18. In
other embodiments of the invention, instead of applying a rough surface to the
electrical
steel sheet during cold rolling, the electrical steel sheet may be passed
through a temper
rolling process (off-line or continuously) after cold rolling and before
tension leveling, in
order to achieve the desired rough surface, as also illustrated by block 75 in
Figure 1B.
In most applications an electrical steel sheet would not be manufactured
having both a
rough surface and a coating, however, there may be applications where this
would be
desirable.
[0057] Block 100 in Figures IA and 1B illustrates that after the coating is
applied
to the electrical steel sheet, the sheet is coiled and sent to the customer
222, as illustrated
in Figure 2. As illustrated by block 110, the customer stamps the electrical
steel sheet
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into the desired shapes (e.g., the shapes necessary for use in motor cores,
ballast lighting,
electrical generators, or the like). Thereafter, the customer may perform a
final customer
annealing step as illustrated by block 120 in Figures IA and 1B, as is
customary in
processing semi-processed electrical steels. During the customer annealing
step the
stamped shapes are heated in a heating furnace 224 to remove stresses and to
maximize
the final magnetic properties, as illustrated in Figure 2.
[0058] The desired properties (e.g., saturation, permeability, and core loss)
produced during the manufacturing process of the electrical steel are
dependent, at least
in part, on the grain size of the electrical steel, composition, and
processing conditions.
The grain sizes, compositions, and process conditions of the electrical steels
produced
using the process of the present invention, for achieving the desired magnetic
properties,
are described below in more detail in contrast to the traditional processes
used for
creating electrical steels and the associated magnetic properties obtained
from the
traditional processing methods. When discussing the properties of the
electrical steels
herein, the properties are all measured after the final customer annealing
step.
[0059] In electrical steels processed using traditional manufacturing (e.g.,
with an
annealing step after cold rolling and before the customer annealing step), the
electrical
steel sheets typically have a grain size in the range of 70 to 150 microns. In
the present
invention the grain size of electrical steels produced without performing the
intermediate
annealing step after cold rolling are in the range of 20 to 70 microns, and
preferably
around 40 microns. The smaller grain size in the present invention helps to
create high
permeability in the electrical steel because it is easier to magnetize smaller
domain
structures. Magnetic domain structures are regions within the grains that have
the same
magnetic orientation. The boundary (e.g., walls) of the domains move when an
applied
magnetic field changes size or direction. The smaller the grain size the
smaller the
domain structure, and thus, the easier it is to support the magnetic field.
Therefore, the
permeability of the magnetic structure is increased.
[0060] Alternatively, the smaller grain size may have a negative effect on the
core loss, that is, the smaller the grain size the greater the hysteresis
portion of core loss
realized in the electrical steel. At the lower levels of grain size, such as
around 20
microns, the increased core loss may not be ideal for some electrical steels
depending on
the products in which they are used. Therefore, reducing the grain size in the
new
13
CA 02897668 2015-07-16
process to 20 to 70 microns from the 70-150 microns seen in traditional
processing, may
greatly improve permeability with only a minor increase in core loss. The
optimal grain
size for electrical steel sheets in some products, such as motors, may be
around 40 (e.g.,
30 to 50) microns in order to achieve the desired permeability and core
losses.
[0061] The grain texture may also play a role in improving the permeability
and
reducing the core loss. The grain texture is described as the orientation of
the grains.
Developing non-oriented electrical steels with improved grain texture (e.g.,
more
oriented grains in various directions) may increase the permeability and/or
reduce the
core loss.
[0062] The grain size, and thus, the magnetic properties of the electrical
steels
can be controlled, in part, by the composition of the electrical steels. The
compositions
of the electrical steels used in the present invention may have the ranges
disclosed in
Table 1. The ranges disclosed in Table 1 illustrate examples of the percent
weight of
Silicon, Aluminum, Manganese, Carbon, and/or Antimony that provide the desired
electrical steel sheets with high permeability and low core loss using the
process of the
present invention that excludes the intermediate annealing step after cold
rolling and
before the customer annealing step. In other embodiments of the invention
smaller
ranges of these elements may be more acceptable in producing the desired high
permeability and low core loss. Furthermore, in some embodiments of the
invention Tin
(Sn) may replace Antimony (Sb) or be used in combination with Antimony, to
achieve
the desired magnetic properties. The composition of Sn may be less than or
equal to
0.1% weight. In other embodiments of the invention various combinations of the
elements in Table 1, as well as other elements (e.g., Sn, etc.), may be used
to produce
electrical steels with the desired magnetic properties without the need for
the
intermediate annealing step directly after cold rolling and before customer
annealing.
For example, in some embodiments only the silicon, aluminum, and manganese
alloys
are controlled and/or added to the molten steel. In still other embodiments of
the
invention only the silicon is controlled and/or added, and thus, the other
elements are not
controlled and/or added outside of any unavoidable impurities. In the
embodiments
presented herein the compositions may have one or more other elements that are
present
as unavoidable impurities with the remainder of the compositions comprising
iron. In
still other embodiments of the invention the composition of electrical steels
may include
14
CA 02897668 2015-07-16
ranges between, overlapping, or outside of two or more specific recitations of
element
percentages described herein (e.g., 0.15%, 0.4%, 0.6%, 1.05%, 1.35%, 2.2%,
2.24%,
2.6%, 3.0%, 3.5%, or the like of Si).
Table 1 ¨ Range of Elements for Desired Electrical Steel Permeability and Core
Loss Properties
Element Composition (by weight percent)
Silicon (Si) 0.15-3.5%
Aluminum (Al) <= 1% (or 0.15-1%)
Manganese (Mn) 0.005-1%
Carbon (C) <=0.04% (or <=0.02%)
Antimony (Sb) <=0.1%
[0063] The amount of silicon used in the electrical steel controls many
aspects of
the magnetic properties of the electrical steel. Silicon may be added to
electrical steels to
raise the resistivity of the material and concurrently reduce the eddy current
loss
component of the core loss. Alternatively, the lower the silicon level the
higher the
permeability and the higher the saturation. Thus, there is also a benefit to
reducing the
silicon in order to increase the permeability and allow the electrical steel
to more easily
support a magnetic field (e.g., at high magnitude inductions). Furthermore,
the purer the
electrical steel the higher the saturation level, and thus, the more magnetic
induction can
occur.
[0064] In the present invention the removal of the annealing step after cold
rolling results in a minor degradation in core loss (e.g., core loss increases
a small
amount), but the permeability is much higher than electrical steels processed
using
traditional methods (e.g., as tested above 1.3 Tesla, 1.4 Tesla, 1.5 Tesla, or
more than 1.5
Tesla, or outside of these Tesla ranges for example at 1.0 Tesla for thinner
steels used in
high frequency applications). The small degradation in core loss can be
recovered by
increasing the level of silicon, such that the final product produced using
the process in
the present invention can have the same or better core loss and much better
permeability
than electrical steels produced using the traditional processes that
incorporate an
intermediate annealing step after cold rolling and before stamping and
annealing at the
customer.
[0065] The processing conditions may also have an impact on the magnetic
properties of the electrical steel. The ranges of conditions for processing
the electrical
steel in the present invention may vary based on the composition of the steels
and/or
CA 02897668 2015-07-16
magnetic properties desired. Examples of the ranges of processing temperatures
are
provided in Table 2A.
Table 2A ¨ Conditions for Producing the Electrical Steels with the Desired
Permeability and Core
Loss
Process Step Temperature Range
Tunnel Furnace Exit Temperature 1800 to 2300 Degrees F
Hot Rolling Finish Temperature 1450 to 1800 Degrees F
Coiling Temperature 900 to1500 Degrees F
Batch Anneal Soak Temp (in lieu of Continuous 1000 to 1900 Degrees F (or
2100 Deg F)
Anneal)
Continuous Anneal Temp (in lieu of Batch Anneal) 1400 to 2000 Degrees F (or
2100 Deg F)
Cold Rolling Temperature Ambient, or greater (May need > 100 F for
Si >
2.0%)
Customer Anneal 1400 to 1675 F, or greater, for 45 min. to
1 hour
[0066] Table 2B illustrates temperature ranges, which are narrower than the
ranges described in Table 2A, in accordance with other embodiments of the
processing
conditions for manufacturing the electrical steels with the magnetic
properties described
herein. In still other embodiments of the invention the ranges of conditions
for
processing the electrical steels in the present invention may be a combination
of the
ranges described in Tables 2A and 2B, within the ranges described in Tables 2A
and 2B,
overlapping the ranges described in Tables 2A and 2B, or outside of the ranges
described
in Tables 2A and 2B.
Table 2B ¨ Conditions for Producing the Electrical Steels with the Desired
Permeability and Core
Loss
Process Step Temperature Range
Tunnel Furnace Exit Temperature 1800 to 2150 Degrees F
Hot Rolling Finish Temperature 1500 to 1700 Degrees F
Coiling Temperature 950 to 1450 Degrees F
Batch Anneal Soak Temp (in lieu of Continuous 1000 to 1550 Degrees F (or to
1900 Deg F)
Anneal)
Continuous Anneal Temp (in lieu of Batch Anneal) 1550 to 1900 Degrees F
Cold Rolling Temperature Ambient, or greater (May need > 100 F for
Si >
2.0%)
Customer Anneal 1450 to 1550 F, or greater, for 45 min. to
1 hour
16
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[0067] For the higher levels of silicon content (e.g., greater than or equal
to
2.2%, 2.6%, and/or 3.0%) the pre-annealing step between hot rolling and cold
rolling
may have to occur at the higher end of the listed temperature ranges. For
example, the
annealing temperature may be required to be at or above 1450, 1500, 1550,
1600, 1650,
1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, or 2100 degrees F. The
annealing
temperature range may be within, overlapping, or outside of any of these
annealing
temperatures. These temperatures for annealing may be needed to achieve the
desired
grain sizes in the steel. These annealing temperatures may also be used at the
lower
silicon levels if needed.
[0068] The core loss is also a function of the thickness of the electrical
steel
sheet. After hot rolling, the electrical steel sheet may have a thickness
between 0.060" to
0.120." After cold rolling, the electrical steel sheet may have a thickness
between 0.005"
to 0.035." The thinner the final thickness of the steel sheet the lower the
core loss and
the better the efficiency of the electrical steel (e.g., with other parameters
being equal).
In other embodiments of the invention, the thickness of the electrical steel
sheet after hot
rolling and cold rolling may be within, overlap, or be outside of these
ranges.
[0069] The following examples illustrate the improved magnetic properties that
may be achieved using the present invention. As a first example, electrical
steel of the
composition illustrated in Table 3 was processed using the traditional process
versus the
process of the present invention according to the processing temperatures
illustrated in
Table 4 (e.g., there may be other process steps in addition to the steps
illustrated in Table
4, for example in the traditional process a tempering rolling step may occur
after batch
annealing). The resulting electrical properties of the electrical steels are
contrasted in
Table 5. As disclosed in Table 3, the electrical steels tested in this example
had a silicon
composition of 1.35% weight.
Table 3 ¨ Composition of Electrical Steel Tested ¨ 1.35% Si Sample
Element
Composition (by weight percent)_
Silicon 1.35%
Aluminum 0.33%
Manganese 0.65%
Carbon 0.005%
Antimony 0.065%
17
CA 02897668 2015-07-16
Table 4 ¨ Conditions for Producing The Electrical Steel ¨ 1.35% Si Sample
Process Step Temperature Product
Thickness
Tunnel Furnace Exit 2000 Degrees F 2.0"
Temperature
Hot Rolling Finish 1550 Degrees F 0.080"
Temperature
Coiling Temperature 1000 Degrees F 0.080"
Batch Anneal Soak 1530 Degrees F 0.080"
Temperature
Cold Rolling Temperature Ambient 0.0197"
Batch Anneal Soak 1240 Degrees F 0.0197"
Temperature (For Traditional
Process ONLY)
Customer Anneal 1450 Degrees F for one hour at 55 Degrees F 0.0197"
Dewpoint
Table 5 ¨ Electrical Steel Properties ¨ 1.35% Si Sample
Properties New Process Traditional Process
(1 Sample in 4 areas) (10 Samples in
various areas)
Core Loss 1.99-2.05W/lb 1.81-1.93 W/lb
Permeability 3180-3429 Gauss/Oersted 1716-1944
Gauss/Oersted
[0070] Table 5 provides the ranges of core loss and permeability for
electrical
steels produced using the process of the present invention versus electrical
steels
produced using the traditional process that utilizes an annealing step after
cold rolling
and before customer annealing. All of the electrical steels tested in Table 5
had the same
compositions, as illustrated in Table 3, were produced using the conditions
illustrated in
Table 4 (e.g., new process or traditional process), and were tested at the
universal
standard of 1.5 Tesla cu 60 Hz. Table 5 illustrates that the core loss using
the new
process only slightly increased to 1.99-2.05 W/lb from 1.81-1.93 W/lb using
the
traditional process, while the permeability using the new process greatly
increased to a
range of 3180-3429 G/Oe from 1716-1944 G/Oe using the traditional process. As
illustrated by Table 5, the electrical steels produced using the new process
have magnetic
properties with a slightly increased core loss and much better permeability
than the
electrical steels produced using the traditional processing methods.
[0071] By increasing the silicon level in the composition and using the new
processing method of the present invention, electrical steels may be produced
that have
the same or lower core loss and higher permeability while removing the need
for an
intermediate annealing step directly after cold rolling, as explained in
further detail
18
CA 02897668 2015-07-16
below with respect to Tables 6, 7, and 8.
[0072] As a second example, Table 8 provides the ranges of core loss and
permeability for electrical steels produced using the process of the present
invention
versus electrical steels produced using the traditional process that utilizes
an intermediate
annealing step after cold rolling. The electrical steels tested had the same
compositions,
as illustrated in Table 6, were produced using the conditions illustrated in
Table 7 (with
the exception of the customer annealing temperature), and were tested at the
universal
standard of 1.5 Tesla @ 60 Hz. Table 8 illustrates that the core loss using
the new
process only slightly increased to 1.58-1.63 W/lb from 1.50-1.54 W/lb using
the
traditional process, while the permeability using the new process greatly
increased to a
range of 2379-2655 G/Oe from 1259-1318 Ga/Oe using the traditional process. As
illustrated by Table 8, the electrical steels produced using the new process
have magnetic
properties with a slightly increased core loss and much better permeability
than the
electrical steels produced using the traditional processing methods as
explained below.
Table 6 ¨ Composition of Electrical Steel Tested ¨ 2.24% Si Sample
Element Composition (by weight percent)
Silicon 2.24%
Aluminum 0.41%
Manganese 0.35%
Carbon 0.005%
Antimony 0.066%
Table 7 ¨ Conditions for Producing The Electrical Steel ¨ 2.24% Si Sample
Process Step Temperature Product Thickness
Tunnel Furnace Exit 2000 Degrees F 2.0"
Temperature
Hot Rolling Finish 1550 Degrees F 0.080"
Temperature
Coiling Temperature 1000 Degrees F 0.080"
Batch Anneal Soak 1530 Degrees F 0.080"
Temperature
Cold Rolling Temperature Ambient New process = 0.0193 -
0.0197"
Traditional Process 0.0187"
Batch Anneal Soak 1240 Degrees F New process = 0.0193 -
Temperature (For Traditional 0.0197"
Process ONLY) Traditional
Process 0.0187"
Customer Anneal 1550 Degrees F for the new
process New process = 0.0193 -
(1450 Degrees for the traditional 0.0197"
process) for one hour at 55 Degrees F Traditional Process z 0.0187"
Dcwpoint
19
CA 02897668 2015-07-16
Table 8 ¨ Electrical Steel Properties
Properties New Process Traditional Process
(1 Sample at head and tail) (1 Sample at head and tail)
Core Loss 1.58-1.63W/lb 1.50-1.54W/lb
Permeability 2379-2655 Gauss/Oersted 1259-1318 Gauss/Oersted
[0073] As disclosed in Table 6, the electrical steel produced had a silicon
composition of 2.24% weight, which was an increase of 0.89% weight over the
composition tested in Table 3. Furthermore, the composition of Aluminum in the
steel
increased from 0.33% weight to 0.41% weight, the composition of Manganese
decreased
from 0.65% weight to 0.35% weight, while the composition of Carbon and
Antimony did
not change or had only minor differences between the steel tested in Table 3
and the steel
tested in Table 6.
[0074] Table 7 illustrates the process conditions for producing the electrical
steel
with the 2.24% Silicon weight composition. As illustrated in Table 7, the
process
conditions are the same as previously described with respect to Table 4 except
for the
increase in the customer annealing temperature from 1450 degrees F using the
traditional
process to 1550 degrees F for the new process without the intermediate
annealing step
after cold rolling. As explained in further detail later, the increase in the
customer
annealing temperature may also play a role in improving the magnetic
properties of the
electrical steel (e.g., reducing the core loss and/or improving the
permeability). There is
also a minor difference in the samples tested for the 2.24% Silicon steel
using the new
process and the sample tested for the 2.24% Silicon steel using the
traditional process, in
that the steel tested in the new process is slightly thicker than the steel
tested using the
traditional process. The small differences in thickness may have a small
effect on the
magnetic properties of the electrical steel. However, small changes in
thicknesses may
also occur over the span of a steel sheet itself, and thus, may only
negligibly affect the
magnetic properties of the steel. In addition, small differences in core loss,
permeability,
or other magnetic or material properties may be a function of the hot rolling
parameters.
For example, the head of the coil and the tail of the coil may experience
different hot
rolling parameters (e.g., small differences in temperature, pressure, or the
like). For
example, as illustrated in Table 8 the thickness differences between the head
and tail or
differences in the hot rolling parameters may affect the core loss and
permeability, such
that core loss and permeability at the head may be 1.58 w/lb and 2379, while
the core
CA 02897668 2015-07-16
loss and permeability at the tail may be 1.63 w/lb and 2655.
[0075] As was the case with the first example, illustrated in Tables 3-5, in
the
second example, as illustrated in Tables 6-8, the electrical steels produced
using the new
process have magnetic properties with a slightly increased core loss and much
better
permeability than the electrical steels produced using the traditional
processing methods.
[0076] As described throughout the specification, in order to improve the
magnetic properties of the steel over the traditional processing methods,
steel may be
produced using the new process without an intermediate step of annealing after
cold
rolling and before the optional steps of tension leveling and coating or
temper rolling, as
well as before the customer annealing step.
[0077] As illustrated by the examples set forth herein, by removing the
intermediate annealing step after cold rolling (e.g., a final cold rolling
pass) and
increasing the amount of silicon in the steel, the present invention has
improved upon the
magnetic properties found in the electrical steels processed in the
traditional way using
an intermediate annealing step after cold rolling and before the customer
annealing step.
This point is illustrated in a comparison of Table 5 and Table 8, which
illustrates that by
using the new processing method and increasing the Silicon composition from
1.35%
weight to 2.24% weight, improved magnetic properties can be achieved that
result in
both improved core loss (illustrated as a reduction in core loss from the
range of 1.81-
1.93W/lb to the range of 1.58-1.63W/lb) and improved permeability (illustrated
as an
increase in permeability from the range of 1716-1944 Gauss/Oersted to the
range of
2379-2655 Gauss/Oersted).
[0078] Table 9 further illustrates the changes in core loss and permeability
as the
Silicon content of a steel increases and as the customer annealing temperature
increases.
As explained herein, core loss generally improves (illustrated as a decrease
in core loss)
as Silicon content increases, except when reaching the higher end the in the
Silicon range
(0.15-3.5%). As illustrated in Table 9, when the Silicon content reaches
levels of
approximately 2.6% to 3.5% the core loss may generally degrade (illustrated as
an
increase in core loss). The effects of the degraded core loss at the elevated
Silicon levels
may be mitigated or reversed by increasing the customer annealing temperature.
As
illustrated in Table 9, as the customer annealing temperature is raised from
1450 degrees
F to 1550 degrees F (or higher) the core loss improves (illustrated as a
decrease in core
21
CA 02897668 2015-07-16
loss) across the ranges of Silicon from 2.2%-3.0%, such that the core loss
only has slight
variations with the changing Silicon levels at the higher annealing
temperatures.
Furthermore, core loss may be improved across the entire range of Silicon
content when
the customer annealing temperature increases, however, this benefit may be
more
noticeable as the level of Silicon increases. In some embodiments of the
invention the
annealing temperature may be increased up to 1600 degrees F or 1700 degrees F,
or
more as described throughout this specification, in order to improve the core
loss
(illustrated as a decrease in value of the core loss). The carbon content of
the steels may
also play a role in the magnetic properties. The 2.6% and 3.0% Silicon steels
illustrated
in Table 9 had slightly higher carbon levels than the 2.2% Silicon steel, and
as such the
core loss measurements were relatively the same or slightly increased over the
2.2%
Silicon steel core loss. If the carbon content in the 2.6% and the 3.0%
Silicon steels
were the same as the 2.2% Silicon steel the core loss in the 2.6% Silicon
steel may have
been reduced when compared to the 2.2% Silicon steel, and the core loss in the
3.0%
Silicon steel may have been reduced when compared to the 2.2% Silicon steel
and the
2.6% Silicon steel.
Table 9 ¨ Si Content vs. Properties vs. Intermediate Batch Annealing
Temperatures For 0.0198"
Thickness
1450 F Customer Annealing 1550 F Customer Annealing
Si Content Core Loss Permeability Core Loss Permeability
2.2% 1.79 Wilk) 2436 G/Oe 1.61-1.67 W/lb 2328-2645 G/Oe
2.6% 1.69-1.71 W/lb 2215-2308 G/Oe 1.62-1.63 W/lb
2175-2191 G/Oe
3.0% 1.71-1.81 W/lb 1665-1733 G/Oe 1.64-1.70 W/lb
1592-1745 G/Oe
[0079] The improvement to the core loss by increasing the customer annealing
temperature is also present at various sheet thicknesses. Table 10 illustrates
the changes
in magnetic properties of a 2.2% Silicon steel having a thickness of 0.0147"
between
customer annealing processes taking place at 1470 degrees F and at 1550
degrees F. As
illustrated in Table 10, as the customer annealing temperature increases the
core loss
decreases. Moreover, additional improvements in core loss or permeability may
be
realized by further increasing the customer annealing temperature to greater
than 1600,
1650, 1700, 1750, or the like degrees F, or more as described throughout this
22
CA 02897668 2015-07-16
specification. Furthermore, this improvement may occur at other levels of
Silicon
content (e.g., Silicon from 0.15 to 3.5%). Moreover, a comparison of the 2.2%
Silicon
electrical steel of Table 9 and the 2.2% Silicon electrical steel of Table 10
illustrates that
as the thickness of the electrical steel sheet is reduced the core loss is
improved (e.g., it
decreases), with a small degradation in the permeability (e.g., it decreases).
Table 10 ¨ Properties vs. Customer Annealing Temperatures For Approximately
0.0147"
Thickness
1470 F Customer Annealing 1550 F Customer Annealing
Si Content Core Loss Permeability Core Loss Permeability
2.2% 1.525 W/lb 2149 G/Oe 1.380-1.396 W/lb 2312-2343 G/Oe
[0080] In still other embodiments of the invention improvements in core loss
and
permeability may be achieved as the Silicon content of a steel increases by
increasing the
annealing temperature between hot-rolling and cold-rolling. As explained
herein, core
loss generally improves (illustrated as decrease in core loss) as Silicon
content increases,
except potentially when reaching the higher end of the Silicon range (0.15-
3.5%), for
example, with a Silicon content of approximately 2.6% to 3.5%, the core loss
may
generally degrade (illustrated as an increase in core loss). The effects of
the degraded
core loss at the elevated Silicon levels may be mitigated or reversed by
increasing the
temperature of the annealing process between the hot-rolling and cold-rolling
steps. For
example, increasing the annealing temperature to greater than 1600, 1650,
1700, 1750
degrees F, or more, as described throughout this specification, improves the
core loss. In
some embodiments, batch annealing at our around 1700 degrees F may be the most
cost
effective for a batch annealing process. As temperatures for the batch
annealing process
increase over 1700, 1750, 1800, or the like, the furnaces in which the batch
annealing
occurs may require more expensive materials in order to protect the furnace
from the
high temperatures. As such, the most cost effective temperature for batch
annealing that
produces the desired results herein may be 1600, 1650, 1700, 1725, 1750, 1775,
or 1800
degrees F, or any temperature or range of temperatures that fall within or
overlap these
temperature values.
[0081] By controlling the processing times, processing temperatures, and steel
compositions within the new process, electrical steels with the desired
magnetic
23
CA 02897668 2015-07-16
properties required by the customers are developed without the need for an
intermediate
annealing step after cold rolling and before the customer stamping and
customer
annealing process. Moreover, these improvements may also be achieved using a
batch
annealing process instead of a continuous annealing line, which would require
a large
capital investment (e.g., 150 million US dollars or more). Batch annealing
furnaces are
much less expensive than installing a continuous annealing line. In some
embodiments
of the invention it is also noted that adding a coating, as described herein,
may further
improve the permeability of the electrical steel.
[0082] Another difference between electrical steels produced using traditional
processing methods and electrical steels produced without an intermediate
annealing step
directly after cold rolling is that in the present invention the electrical
steels are harder.
For example, in the present invention the Rb hardness, which is a standardize
hardness
measurement, of the electrical steel may generally be in the range of 90 to
100 (or in
some embodiments outside of this range), or more specifically in the high
90's.
Alternatively, the hardness of the electrical steels manufactured using the
traditional
method may be 50 to 80 Rb.
[0083] Based on a number of factors, including but not limited to the silicon
content of the steel, the thickness of the steel sheet, the annealing
temperatures, and the
process of performing an annealing step between hot rolling and before cold
rolling and
forgoing an annealing step after the last cold rolling pass before the sheet
is sent to the
customer for further processing, the core losses and permeability may fall
within a
number of different ranges. In some embodiments of the invention the core loss
may be
below 3.5, 3.25, 3, 2.75, 2.50, 2.25, 2, 1.75, 1.5, 1.25, or 1 W/lb, may be
within,
overlapping, or outside of any ranges between these core loss values or other
core loss
values not specifically recited. In addition to these core loss values, the
permeability
may be greater than 1000, 1100, 1200, 1250, 1300, 1350, 1400, 1450, 1500,
1550, 1600,
1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250,
2300,
2350, 2400, 2450, 2500, 2550, 2600, 2650, 2700, 2750, 2800, 2850, 2900, 2950,
3000,
3050, 3100, 3150, 3200, 3250, 3300, 3350, 3400, 3450, or 3500 G/Oe, may be
within,
overlapping, or outside of any ranges between these permeability values or
other
permeability values not specifically recited.
24
CA 02897668 2015-07-16
[0084] As illustrated by some of the testing results, a silicon content of up
to
3.5% (or in other embodiments up to 3.0%) may result in permeability values
that may
exceed 1400, 1450, 1500, 1550, or 1600 G/Oe, or any other type of permeability
values
illustrated herein (e.g., when tested at 1.5T and 60Hz). At these levels of
silicon (e.g.,
3.5%, 3%, or the like) the core loss may be less than 2, 1.75, 1.50, 1.25, 1
W/lb or other
like core loss values. In other embodiments of the invention, the permeability
values and
the core less values may be within, outside of, or overlap these values or
other values
discussed herein. Generally, as the silicon level drops the core loss and the
permeability
will both increase (e.g., the core loss is degraded and the permeability
improves). This
statement is applicable when all other factors remain unchanged because other
factors
such as the thickness of the steel sheets and the temperatures of the
annealing steps may
impact the core loss and permeability values. At the lower levels of silicon,
for example
0.6%, the core loss may be less than 4.5, 4.0, 3.5, 3.0, 2.6, 2.5 WIlb, and
the permeability
may be greater than 2000, 2050, 2100, 2150, and 2200 G/Oe (or greater than
other levels
discussed herein) (e.g., when tested at 1.5T and 60Hz). In other embodiments
of the
invention the core loss and permeability values may fall within, be located
outside of, or
overlap any of these values.
[0085] Table 11 below illustrates additional testing that has occurred for
various
types of steel with various types of silicon formed from the processes of the
present
invention discussed herein. As illustrated in Table 11, the concepts that were
previously
discussed herein are further supported by the additional testing of steel
sheets processed
without a post cold-rolled anneal after the last cold-rolling step and before
the steel is
shipped to a customer for stamping and final annealing. For the 2.2% silicon
content
steel, Table 11 illustrates generally that as the customer annealing
temperature is
increased the core loss value decreases (e.g., is improved). Moreover, with
respect to
steel with the 2.6% silicon, Table 11 illustrates generally that as the
customer annealing
temperature is increased the core loss value decreases (e.g., is improved).
Finally, with
respect to the 3% silicon content steel, Table 11 also illustrates generally
that as the
customer annealing temperature is increased the core loss value decreases
(e.g., is
improved). Table 11 further indicates that as the customer annealing
temperature
changes the permeability fluctuates. The changes in permeability may be based
not only
on the changes in Silicon content, but also on the thickness, location on the
steel sheet at
CA 02897668 2015-07-16
which the permeability is tested, composition of the steel (e.g., carbon
content, or other
element), and/or other factors.
Table 11 ¨ Si Content vs. Thickness vs. Customer Annealing Temperature vs.
Magnetic Properties
Si Content Thickness Customer Core Loss Permeability
Annealing
Temperature
2.2% 0.0198" 1450 Deg F 1.787 W/lb 2436 G/Oe
2.2% 0.0184" 1550 Deg F 1.67 Will) 2449 G/Oe
2.2% 0.0197" 1550 Deg F 1.617 W/lb 2328 G/Oe
2.2% 0.0197" 1550 Deg F 1.667 W/lb 2645 G/Oe
2.2% 0.01975" 1550 Deg F 1.72 W/lb 2232 G/Oe
2.6% 0.0196" 1450 Deg F 1.694 W/lb 2308 G/Oe
2.6% 0.0205" 1450 Deg F 1.617 W/lb 2175 G/Oe
2.6% 0.0199" 1550 Deg F 1.628 W/lb 2191 G/Oe
2.6% 0.0206" 1550 Deg F 1.617 W/lb 2175 G/Oe
3% 0.0206" 1450 Deg F 1.711 W/lb 1665 G/Oe
3% 0.0206" 1450 Deg F 1.805 W/lb 1733 G/Oe
3% 0.0206" 1550 Deg F 1.642 W/lb 1592 G/Oe
3% 0.0206" 1550 Deg F 1.696 W/lb 1745 G/Oe
[0086] In other embodiments of the invention additional process steps may be
added, or processing steps may be changed, in order to achieve the desired
magnetic
properties (e.g., core loss, permeability, or the like) of a steel sheet
manufactured by
performing an annealing step between hot rolling and cold-rolling without an
annealing
step after a final cold-rolling pass and before customer stamping and
annealing. As
described above, one embodiment of the present invention may comprise hot
rolling,
pickling, annealing (e.g., batch annealing or continuous annealing), cold
rolling, and
tension leveling and coating, or surface roughing or temper rolling and
tension leveling.
As such, there is no annealing step after the last cold rolling step and
before the tension
leveling and coating, or roughing or temper rolling and tension leveling, as
well as
before shipment to the customer for stamping and final annealing. In alternate
embodiments of the invention described above, the cold rolling process may
occur in
multiple steps of two or more cold rolling passes through one or more cold
rolling
stands, which may further include annealing steps between the two or more cold
rolling
26
CA 02897668 2015-07-16
passes. Regardless of the number of cold rolling passes and annealing steps
between the
cold rolling passes, in the present invention there is no intermediate
annealing step after
the final cold rolling pass and before the tension leveling and coating, or
roughing or
temper rolling and tension leveling, as well as before the customer stamping
and
annealing.
[0087] As discussed above, the thicknesses of the steel sheets after cold
rolling
are described herein as ranging between 0.005" to 0.035." At the lower end of
the range
of the thickness of the steel sheets, such as from approximately 0.005 inches
to 0.01,
0.0125, 0.015, 0.018, 0.02 inches (or other ranges that fall within, outside
of, or overlap
these ranges), multiple cold rolling passes may be needed with one or more
annealing
steps between the multiple cold rolling passes in order to achieve the desired
mechanical
properties at the lower end of the thickness ranges for the steel sheets. In
other
embodiments, multiple cold rolling steps may also be used up to thicknesses of
0.025",
0.031", and/or 0.035." In addition
to the multiple cold rolling steps, in some
embodiments the amount of silicon in the composition of the steel may also
play a role in
the thickness of the steel sheets, or otherwise determine how many cold
rolling steps are
needed. For example, depending on the equipment used during the rolling
processes, the
higher silicon content the harder it may be to achieve the thinner steel
sheets. In just one
example, when using steel with a silicon content that is approximately 3%
(e.g., greater
than 2.9 percent) it may be difficult to roll the steel strips to lower than
0.014, 0.013,
0.012, 0.011, or the like inches with one cold-rolling pass. As such, in some
embodiments multiple cold-rolling steps may be needed to achieve the recited
thickness
ranges. In other embodiments, regardless of the number of cold rolling steps,
thicknesses lower than the recited values, or other like values not
specifically listed, may
not be reached at all.
[0088] Table 12 illustrates a comparison of steels that are on the lower end
of the
thickness range and have the same compositions (e.g., 2.2% silicon), but are
processed
using different types of routings. The first routing process in Table 12
includes a batch
anneal before cold rolling and a batch anneal at 1450 Deg F after the final
cold rolling
step (e.g., single cold rolling step) before shipping to the customer for
stamping and final
annealing (e.g., defined as a motor lam semi-processed steel). The second
routing
process in Table 12 includes a batch anneal before cold rolling and a batch
anneal at
27
CA 02897668 2015-07-16
1550 Deg F after cold rolling step (e.g., single cold rolling step) before
shipping to the
customer for stamping and final annealing (e.g., also defined as a motor lam
semi-
processed steel). The final routing process illustrated in Table 12 does not
include an
annealing step after cold rolling and before customer stamping and customer
final
annealing (e.g., the new process of the present invention). As illustrated in
Table 12 the
steel of the present invention (e.g., the third routing) has approximately the
same core
loss (1.595 vs. 1.59 W/lb) as the steel produced from the traditional process
that is
customer annealed at 1550 Deg F, and has a better permeability (2240 vs. 1904
G/Oe).
The present invention also has slightly worse core loss (1.595 vs. 1.265 W/lb)
than steel
produced from the traditional process that is customer annealed at 1450 Deg F,
and a
much better permeability (2240 vs. 1179 G/Oe). As such, in order to improve
the core
loss with only slightly losing some permeability, the silicon content of the
steel in the
present invention is increased. The increase in the silicon content allows the
steel to
achieve the same or better magnetic properties of the semi-processed motor lam
steel
without the annealing step after the last cold-rolling process.
Table 12 ¨ Routing Process vs. Thickness vs. Customer Annealing Temperature
vs. Magnetic
Properties
Si Routing Process Thickness Customer Core
Perm.
Content Anneal Loss
Temp
2.2% 1) Hot Rolling, Batch Annealing, Cold 0.0137" 1450 Deg F
1.26 1179
Rolling, Batch Annealing, Temper Rolling, 5 G/Oe
Customer Stamping and Annealing With
2.2% 2) Hot Rolling, Batch Annealing, Cold 0.0137" 1550 Deg F
1.59 1904
Rolling, Batch Annealing, Customer W/lb G/Oe
Stamping and Annealing
2.2% 3) Present Invention: Hot Rolling, Batch 0.0139" 1550 Deg F
1.59 2240
Annealing, Cold Rolling, Customer 5 G/Oe
Stamping and Annealing W/lb
[0089] As previously discussed, it may be difficult to achieve the thicknesses
illustrated in Table 12 for the higher levels of silicon (e.g., greater than
2.6%, such as
3%, or the like). In some embodiments of the present invention, as illustrated
in Figure
3, the steelmaking process may include the same steps as illustrated in
Figures I A and
1B with an additional cold rolling step and/or an additional annealing step
between the
cold rolling steps. As such, after melting, alloying, transferring to a ladle,
casting into
slabs, and heating the slabs or direct hot-rolling from casting (as
illustrated in blocks 10-
28
CA 02897668 2015-07-16
45), the slabs are hot rolled for one or more passes into sheets as
illustrated by block 50
of Figure 3. As illustrated by block 55, the hot-rolled sheets are pickled. An
annealing
step (e.g., batch annealing or continuous annealing) follows the hot rolling
step and the
pickling step, as illustrated by block 60. This annealing step, as previously
discussed,
may occur at a temperature within a range of 1000 to 1900 or 2100 Degrees F,
or fall
within, be outside of, or overlap these ranges. After annealing, the sheet is
passed
through a first cold rolling step (e.g., in one or more passes) as illustrated
by block 71, in
order to reduce the thickness of the sheet to a range of less than
approximately 0.100,"
0.090," 0.080" to 0.060", 0.050", 0.040" or 0.020" (or other ranges that fall
within, are
outside of, or overlap these ranges). As illustrated by block 72, an annealing
step (e.g.,
batch annealing or continuous annealing) after the first cold-rolling pass may
be
performed in order to recover the ductility of the sheet, to reduce the
dislocation density
of the sheet for reducing residual stresses in the sheet, and to help achieve
the desired
electrical steel properties. The annealing step after the first cold rolling
step may be
performed at a temperature of 1000 to 1900 or 2100 Deg F, or fall within, be
outside of,
or overlap these ranges (as described throughout). After the intermediate
annealing step
after the first cold-rolling step, a subsequent (e.g., final, last, or the
like) cold rolling step
(e.g., in one or more passes) is performed to further reduce the thickness of
the sheet to
the desired thickness range of 0.005" to 0.018" or 0.02" (or other ranges that
fall within,
outside of, or overlap these ranges such as up to 0.025", 0.031", or 0.035"),
as illustrated
in block 73 of Figure 3. In other embodiments of the invention there may be
additional
cold rolling passes (e.g., second, third, fourth, fifth, or more), each with
intermediate
annealing steps, before the final cold rolling step. However, in some
embodiments there
may only be two cold rolling steps (e.g., each with one or more passes) with a
single
annealing step between the two cold rolling steps. After the final (e.g.,
last) cold rolling
step, further annealing of the steel sheet is not performed before the
optional steps of
roughing or temper rolling, tension leveling, and/or coating, as illustrated
by blocks 75,
80, 90 of Figure 3. Moreover, there is no annealing step after cold rolling
and before the
sheet is shipped to the customer for stamping and customer annealing, as
illustrated by
blocks 100, 110, and 120. As such, while there are one or more intermediate
annealing
steps between the multiple cold rolling passes there is no annealing step
after the final
cold rolling pass and before the semi-processed steel is sent to the customer
for stamping
29
CA 02897668 2015-07-16
and final annealing. Table 13 illustrates one embodiment of the process of the
present
invention using two cold rolling steps.
Table 13 ¨ Conditions for Producing the Electrical Steels with the Desired
Permeability and Core
Loss
Process Step Temperature Range
Tunnel Furnace Exit Temperature 1800 to 2300 Degrees F (or 1800 to 2150
Deg. F)
Hot Rolling Finish Temperature 1450 to 1800 Degrees F (or 1500 to 1700
Deg. F)
Coiling Temperature 900 to1500 Degrees F (or 950 to 1450 Deg.
F)
Batch Anneal Soak Temp (in lieu of Continuous 1000 to 1900 Degrees F (or
2100 Deg F), or
Ann 1000 to 1550 Deg. F (or 1900 Deg F), or
1450
eal)
Deg. F to 2100 Deg F.
Continuous Anneal Temp (in lieu of Batch Anneal) 1400 to 2000 Degrees F (or
2100 Deg F), or
1550 to 1900 Deg. F (or 2100 Deg F)
First Cold Rolling Temperature Ambient, or greater (May need > 100 F for
Si >
2.0%)
Batch Anneal Soak Temp (in lieu of Continuous 1000 to 1900 Degrees F (or
2100 Deg F), or
Anneal) 1000 to 1550 Deg. F (or 1900 Deg F), or
1450
Deg. F to 2100 Deg F.
Continuous Anneal Temp (in lieu of Batch Anneal) 1400 to 2000 Degrees F (or
2100 Deg F), or
1550 to 1900 Deg. F (or 2100 Deg F)
Second Cold Rolling Temperature Ambient, or greater (May need > 100 F for
Si >
2.0%)
Customer Anneal 1400 to 1800 F (or 1400 to 1675 F), or
greater,
for 45 min. to 1 hour (or outside of this duration)
[0090] The multiple cold rolling steps with an intermediate annealing step
between the cold rolling steps allows for the desired magnetic properties for
the thinner
ranges of steel sheets (e.g., 0.005" to 0.018", 0.02" or the like), and
particularly with
respect to steel sheets with silicon levels greater than 2.6%, 2.7%, 2.8%,
2.9%, 3.0%, or
the like. In one example, using a silicon steel of 3% and including an
annealing step
after hot rolling and before a first cold rolling step (e.g., one or more
first cold rolling
passes), an intermediate annealing step after the first cold rolling step, a
final (e.g.,
second) cold rolling step (e.g., one or second cold rolling passes) and no
additional
intermediate annealing steps until stamping and customer annealing, a steel
sheet with a
thickness of approximately 0.015" may be achieved (see Table 14). Other
thicknesses
described herein may also be achieved, as described in other examples
presented below.
The magnetic properties achieved using this particular type of routing,
silicon content
(e.g., silicon content above 2.8%, such as 3% or other like silicon content
described
herein), and steel sheet thickness of less than 0.018", may include a core
loss range of
0.80 w/lb to 1.6 w/lb (or to 1.8 w/lb) and a permeability range of 800 G/Oe to
2000 G/Oe
CA 02897668 2015-07-16
(or to 2500 G/Oe) (e.g., measured at 1.5 Tesla), or core loss or permeability
ranges that
fall within, overlap, or fall outside of these stated ranges. Table 14
illustrates that using
the higher silicon levels, thinner steel thicknesses (e.g., multiple cold
rolling steps or the
thin cast strip steel described below), and higher customer annealing
temperatures, the
present invention can achieve similar core losses and better permeability than
the steels
with the same, similar, or lower silicon content that were produced using an
annealing
step after cold rolling (see Table 12 routings 1 and 2).
Table 14 ¨ Si Content vs. Thickness vs. Customer Annealing Temperature vs.
Magnetic Properties
Si Content Thickness Customer Core Loss Permeability
Annealing
Temperature
3% 0.0178" 1600 Deg F 1.48 W/lb 2022 G/Oe
3% 0.0152" 1600 Deg F 1.4 W/Ib 1849 G/Oe
3% 0.0152 1700 Deg F 1.38 Wilb 1611 G/Oe
[0091] In another embodiment of the invention, instead of, or in addition to,
utilizing multiple cold rolling steps to produce steels at the lower end of
the range of the
thickness of the steel sheets (e.g., from approximately 0.005" to 0.015",
0.018", 0.02",
0.031", 0.035", or the like), the present invention may begin by utilizing
thinner steel
sheets at the beginning of the process. For example as described above, the
thicknesses
of the steel sheets after hot rolling are typically 0.060" to 0.120," which
are produced
from steel slabs that typically have thicknesses that range between 1.5" to 3"
(or slabs
that fall within, overlap, or are outside of this range). In some embodiments
of the
invention, instead of using steel slabs and hot rolling the steel slabs in one
or more hot
rolling passes to the desired thicknesses, continuously cast thin steel strips
(e.g., thin strip
cast steel) may be utilized in order to begin the process of the present
invention with a
thinner steel sheet.
[0092] In one embodiment of the invention, as illustrated in Figure 4, the
process
may begin with manufacturing or purchasing (e.g., from another manufacturer)
thin strip
cast steel, as illustrated by block 12. Thin strip cast steel may be
manufactured by a
process that includes melting scrap steel in an EAF and tapping the EAF so
that the
molten metal flows into a ladle. Ladle treatments may be performed, such as
applying
components for alloying the steel to the desired composition, achieving the
desired
31
CA 02897668 2015-07-16
temperature for the molten metal, or the like. The ladle is positioned over a
tundish and
the molten metal is transferred to the tundish. The tundish is drained into a
water cooled
mold that is used to solidify the molten metal. In the mold a thin shell of
metal is
solidified near the walls of the mold while steel in the middle of the mold
remains
molten. As the metal exits the mold the metal has a hard shell with a molten
interior, at
this point the metal is called a strand. The strand is then passed through
multiple pairs of
water-cooled rollers, which support and cool the strand as the molten metal
within the
interior of the strand solidifies. The strand may also pass through a cooling
chamber that
sprays cooling liquid, such as water, on the strand to help further solidify
the core of the
strand. The strand may pass through various rolling operations to straighten,
smooth,
reduce the thickness, or the like of the strand and form a coil. In some
embodiments of
the invention the thin strip cast steel produced by the continuous casting
process may
have a thickness less than or equal to 0.035", 0.065", 0.1 or other thickness
described
herein. In one embodiment of the invention, the thickness of the thin strip
cast steel may
have a thickness that is less than or equal to 0.04" 0.05", 0.06", 0.07",
0.08", 0.09",
0.10", 0.11", 0.12", 0.15, or 0.2". In other embodiments of the invention the
ranges of
the thicknesses of the thin strip cast steel may be within, overlap, or fall
outside of these
values.
[0093] The present invention may include utilizing the continuous casting
process to produce, or otherwise purchase, steel coils with a thickness less
than 0.15",
0.125", 0.1", 0.8", 0.065", or 0.04" (or other like thickness whether or not
specifically
discussed herein). In the present invention, the process may utilize the thin
strip cast
steel in order to avoid the need for hot rolling a slab and performing
multiple cold rolling
steps to manufacture steel sheets with the desired thicknesses. In some
embodiments of
the invention since the thickness of the continuously cast steel sheet is less
than 0.1",
0.065", or 0.04" (or other like thickness discussed herein) the steel sheet is
thin enough
to roll into a thickness between 0.005" to 0.015", 0.018", 0.02", 0.031",
0.035", or the
like, in a single cold rolling pass. Therefore, in some embodiments of the
present
invention the process for manufacturing steel sheets with the desired magnetic
properties
would include procuring (e.g., manufacturing or obtaining) a continuously cast
steel
sheet with a thickness equal to or less than 0.1" (or other thickness
described herein), as
illustrated by block 12 of Figure 4. As illustrated by block 55, the thin
strip cast steel
32
CA 02897668 2015-07-16
sheet may be optionally pickled. An
annealing step (e.g., batch annealing or
continuously annealing) is performed on the cast steel sheet, as illustrated
by block 60 of
Figure 4. For example, in one embodiment of the invention the annealing step
is a high
temperature annealing step, such as annealing at a temperature of 1550 degrees
F (or
within a range of 1000 to 2100 degrees F). In one embodiment of the invention,
after
annealing only a single cold rolling step (e.g., with one or more cold rolling
passes) is
needed to produce the steel of the desired thickness between 0.005" to 0.015",
0.018",
0.020", 0.031", 0.035", or the like, as illustrated by block 70. In other
embodiments of
the invention, as previously discussed two or more cold rolling steps (e.g.,
each with one
or more cold rolling passes) may be utilized with or without intra-annealing
steps
between the multiple cold rolling steps and/or passes. However, regardless of
the
number of cold rolling steps or passes there is no annealing step after the
last cold rolling
step and before the optional tension leveling and coating, or optional
roughing or temper
rolling and tension leveling, as illustrated by blocks 75, 80, 90 of Figure 4.
Moreover,
there is no annealing step after cold rolling and before stamping and
annealing at the
customer, as illustrated by blocks, 100, 110, and 120 of Figure 4.
[0094] The use of a thin strip cast steel product with a reduced thickness in
the
present invention allows for the desired magnetic properties for the thinner
ranges of
steel sheets (e.g., 0.005" to 0.010", 0.015", 0.018", 0.02", 0.031", or the
like). The
magnetic properties achieved using this particular type of routing may include
a core loss
range of 0.80 w/lb to 1.25 w/lb (or to 1.6 w/lb, 1.8 w/lb, or more) and a
permeability
range of 800 G/Oe to 1500 G/Oe (or to 2500 G/Oe) (e.g., measured at 1.5
Tesla), or core
loss or permeability ranges that fall within, overlap, or fall outside of
these stated ranges,
as discussed throughout this specification.
[0095] In one example embodiment of the invention two rolled samples of the
electrical steel discussed herein were produced for high frequency
applications, in which
steel was produced having a composition of 2.90% wt Si; 0.62% wt Al; and 0.28%
Mn.
In some embodiments, in order to achieve the desired properties at the thinner
steel
thicknesses the composition of particular elements previously described herein
are
controlled to tighter ranges, as illustrated in Table 15.
33
CA 02897668 2015-07-16
Table 15 ¨ Range of Elements for Desired Electrical Steel Permeability and
Core Loss Properties at
Thicknesses less than 0.015 inches
Element Composition (by weight Specific Composition of Samples
(by
percent) weight percent)
Silicon (Si) 2.8-3.5% 2.9%
Aluminum (Al) 0.5-0.75% 0.62%
Manganese (Mn) 0.2-0.4% 0.28%
[0096] The steel in the example embodiment was produced by hot rolling a 2-
inch slab down to a steel sheet with a thickness of 0.073 inches in multiple
hot rolling
passes (e.g., in 6 hot-rolling passes). Thereafter, the steel sheet with the
0.073 inch
thickness after hot rolling was pickled to remove scale from the steel sheet
surface. After
pickling, the steel sheet was coiled and batch annealed at a temperature of
1700 degrees
F. After batch annealing the steel sheet was cold rolled to a post first cold
rolled
thickness of 0.036 inches in one or more cold rolling steps (e.g., one cold
rolling pass).
Thereafter, the steel sheet with a 0.036 inch post first cold roll thickness
was batch
annealed again at a temperature of 1550 degrees F.
[0097] The steel sheet was then split into two separate steel rolls, one of
which
was cold rolled to a post second (or final) cold rolled thickness of 0.0118
inches in one
or more cold rolling passes (e.g., 6 passes), while the other roll was rolled
to a post
second (or final) cold rolled thickness of 0.008 inches in one or more cold
rolling passes
(e.g., greater than 6 cold rolling passes). At these thicknesses, the steel
sheets may need
a very smooth surface to achieve the desired electrical and mechanical
properties in the
final applications (e.g., after customer stamping and final customer
annealing), as such,
the steels may be produced with a surface roughness that is less than 15, 14,
13, 12, 11,
10, 9, 8, 7, 6, or 5 microns, or the like. The samples produced herein had an
average
surface roughness of 6 microns. The steel coils were tension leveled after the
second (or
final) cold rolling step in order to flatten the edges of the steel sheets. In
some
embodiment, it is at this point that the steel coils may be coated, however,
the examples
produced herein were not coated. At this point in the process the steel coils
would be
sent to the customer without an annealing step after the second (or final)
cold rolling
step, for the customer stamping step and customer final annealing step after
stamping in
order to create the desired products. To simulate this process samples were
taken from
the steel coils and annealed. With respect to the steel samples having a
thickness of
0.0118 inches the samples were annealed at 1550 degrees F at 55 F dewpoint in
a
34
CA 02897668 2015-07-16
Hydrogen/Nitrogen (HNx) atmosphere. The steel samples having a thickness of
0.008
inches were annealed at 1600 degrees F at 55 dewpoint in the H-Nx atmosphere.
The
samples were then tested over various frequencies as illustrated below in
Table 16. We
note that the samples discussed in Tables 16-18 are illustrated as having a
core loss
measured using the units of w/kg instead of the w/lbs previously discussed
herein. The
unit changes is used in order to compare the samples made in the present
invention with
products that are on the market that utilize the traditional process that
includes an
annealing step after final cold rolling (e.g., using a continuous annealing
line) and before
the products are shipped to the customer for stamping and final customer
annealing.
However, we again, further note that the core loss and permeability values
discussed
herein, are the values that would be achieved after the final customer
annealing.
Table 16: Core Loss and Pernleabilitli of 0 01 18 and 0.006 Steel Sheet
Thicknesses Measured at the Head ( HI and Tail (T) of the Coll
Location HT H T H T H T H T H
Thick- Units 50 50 60 60 200 200 400 400 000
000 600 600 1000 1 000
ness H7 H7 117 H7 Hz H7 H7 a Hz 0 Hz a H7
H7 ,a H7 a H7 a HZ a
3 at 3 0 a IOT 10 T 101 a 1 0 T 1.0
T 0 T 0 T
1.5T .51 1.5 T 1ST LOT 10T LOT
011C wkg 2.31 231 2.87 186 5.78 164 :5 32 28 73
275 44 44 42.75 65 04 1,433
G,Oe 1610 1744 1003 1745 9861 7986 8137 6347 6712 5301 5676 4620 4063
w kg 2.51 31)6 5.5 12 30 12.01 45 45
44.26
Oe 1576 1510 0644 9054 9674 6919 7181
850 Tesia 1.60 69
[0098] The samples described with respect to Table 16 were compared against
similar products on the market that were made utilizing an annealing step
after the final
cold rolling process and utilizing a continuous annealing process instead of
batch
annealing. Table 17 illustrates the comparisons of products on the market that
utilize
annealing after final cold rolling before stamping and customer annealing at
various test
points and the samples of the present invention for steels of approximately
0.0118
inches. Table 18 illustrates the comparisons of products on the market that
utilize
annealing after final cold rolling before stamping and customer annealing at
various test
points and the samples of the present invention for steels of approximately
0.008 inches.
CA 02897668 2015-07-16
'
Table 17: Comparison of 0.0118 inch Steels of the Present Invention with
Products on the Market that
Utilize Annealing after the Final Cold Rolling Step
Comparison Test Products With 0.0118 Thickness Present
Invention
Product Annealing after Products of the Improvement
Final Cold Rolling , present invention
1(0.0118 inch 1.0 T w/kg @ 16.0 15.35 Improvement
thickness) 400Hz
B50 Perm 1.62 1.69 Improvement
2 (0.0118 inch 1.0 T w/kg Cc6, 14.5 15.35
thickness) 400Hz
B50 Perm 1.66 1.69 Improvement
3 (0.0118 inch 1.0 T w/kg g 15.0 15.35
thickness) 400Hz
B50 Perm 1.60 1.69 Improvement
4(0.0118 inch 1.0 T w/kg @ 15.0 15.35
thickness) 400Hz
(0.0118 inch 1.0 T w/kg @ 15.0 15.35
thickness) 400Hz
B50 Perm 1.60 1.69 Improvement
6(0.0118 inch 1.0 T w/kg @ 16.0 15.35 Improvement
thickness) 400Hz
B50 Perm 1.64 1.69 Improvement
Table 18: Comparison of 0.008 inch Steels of the Present Invention with
Products on the Market that
Utilize Annealing after the Final Cold Rolling Step
Comparison Test Products With 0.008 Thickness Present
Invention
Product Annealing after Products of the Improvement
Final Cold Rolling present invention
1(0.007 inch 0.9 T w/kg @ 13.2 10.2 Improvement
thickness) 400Hz
1.01 Perm 5982 9814 Improvement
2(0.010 inch 1.0 11 w/kg g 12.8 12.5 Improvement
thickness) 400Hz
B50 Perm 1.63 1.69 Improvement
3(0.008 inch 1.0 T w/kg @ 11.9 12.5
thickness) 400Hz
B50 Perm 1.64 1.69 Improvement
4(0.008 inch 1.0 T w/kg @ 12.7 12.5 Improvement
thickness) 400Hz
B50 Perm 1.67 1.69 Improvement
5 (0.008 inch 1.0 T w/kg Eaj 12.2 12.5
thickness) 4001z
1.0 T Perm 8035 9814 Improvement
6 (0.008 inch 1.0 T w/kg g 12.9 12.5 ' Improvement
thickness) 400Hz
1.0 T Perm 7955 9814 Improvement
1
36
CA 02897668 2015-07-16
[0099] Based on a number of factors, including but not limited to the silicon
content of the steel, the thickness of the steel sheet, the annealing
temperatures, and the
process of performing an annealing step between hot rolling and before cold
rolling and
forgoing an annealing step after the last cold rolling pass before the sheet
is sent to the
customer for further processing, the core losses and permeability may fall
within a
number of different ranges for steels of the present invention which have
thicknesses that
are less than 0.02, 0.018, 0.015, 0.012, 0.01, 0.008, or the like. In some
embodiments of
the invention the core loss measured at 1.0T at 400Hz may be below 20.0, 19.0,
18.0,
17.0, 16.0, 15.5, 15.0, 14.5, 14.0, 13.5, 13.0, 12.5, 12.0, 11.5, 11.0, 10.5,
10.0, or the like
w/kg, may be within, overlapping, or outside of any ranges between these core
loss
values or other core loss values not specifically recited. In addition to
these core loss
values, the permeability measured at 1.0T at 400Hz may be greater than 4000,
4500,
5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, or 9500 G/Oe, may be
within,
overlapping, or outside of any ranges between these permeability values or
other
permeability values not specifically recited. In addition to the permeability
measured at
1.0T at 400Hz, the B50 Penn measurement may be greater than 1.55, 1.56, 1.57,
1.58,
1.59, 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.66, 1.67, 1.68, 1.69, 1.70, 1.71,
1.72, 1.73, L74,
1.75, or the like Tesla, may be within, overlapping, or outside of any ranges
between
these B50 measurement values or other values not specifically recited.
[00100] Another
feature of the electrical steel of the present invention is
that in addition to the improved core loss and permeability properties, the
electrical steel
has improved mechanical properties. Table 19 below illustrates the improved
mechanical properties both before and after customer annealing of the steel of
the present
invention (e.g., steel manufactured from a process that includes an annealing
step
between hot rolling and cold rolling, and after customer stamping, but not
between the
last cold rolling step and the customer annealing step). As illustrated in
Table 19, before
the customer annealing step the yield strength and the ultimate tensile
strength of the
electrical steels made from the new process of the present invention are
almost twice as
high as the electrical steels made from the traditional process. Moreover,
after the
customer annealing step the mechanical properties of the electrical steels
made from the
new process are similar to, or are an improvement over, the mechanical
properties of the
electrical steels made from the traditional process.
37
CA 02897668 2015-07-16
[00101] Table 19 also illustrates that the hardness of the electrical
steels
made from the new process are higher than the electrical steels made from the
traditional
process both before and after customer annealing. In addition, Table 19
illustrates the
elongation percent (El%) value for the steels, which is a measurement of the
ductility of
the steel. In some embodiments of the invention, lower El percentages may be
desired
because it may be easier to stamp parts from steels with lower El percentages.
Table 19- Mechanical Properties of Electrical Steels of the New Process vs.
Traditional Process
Routing Steel Product Before Customer Anneal After
Customer Anneal
Type (Si wt%) _____________________________________________________
YS UTS El Hardness YS UTS El Hardness
(ksi) (ksi) (%) (Rb) (ksi) (ksi) (%) (Rb)
Traditional Si 0.25 'Yo 56.6 62.3 20.8 68 16.9 43.4
32.7 58
Traditional Si 0.4% 56.9 66.9 33.3 70 21.0 45.9 33.3
46
Traditional Si 1.05 A 61.0 72.3 15.1 73 29.1 51.9
30.8 69
New Si 1.05 % 129.4 130.1 1.1 98 35.6 58.6 24.2
71
Traditional Si 1.35 % 66.1 75.5 13.5 70 33.5 53.6 26.6
64
Traditional Si 2.2 % 72.9 87.4 14.4 80 47.3 58.1 16.2
68
New Si 2.2% 138.1 141.7 1.1 , 99 46.1 64.3 17.8
75
[00102] Table 19 illustrates a single test result for particular types
of steel.
It should be understood that the mechanical properties achieved in the present
invention
may fall within various ranges. For example, the Silicon 1.05 wt% steel may
have the
following property ranges before customer annealing: YS - 100 to 160ksi; UTS -
100 to
160ksi; El of 0.5 to 2; and Hardness of 90 to 110; and after customer
annealing: YS - 25
to 45ksi; UTS - 40 to 80ksi; El of 15 to 35; and Hardness of 60 to 80. In
another
example, the Silicon 2.2 wt% steel may have the following property ranges
before
customer annealing: YS - 110 to 170ksi; UTS - 110 to 170ksi; El of 0.5 to 2;
and
Hardness of 90 to 110; and after customer annealing: YS - 35 to 55ksi; UTS -
45 to
85ksi; El of 10 to 25; and Hardness of 65 to 85. In other embodiments of the
invention
the ranges may fall within, overlap, or fall outside of these stated ranges.
[00103] For steels with higher silicon levels (e.g., above 2.2% Si)
the
mechanical properties of steels manufactured using the new process may also be
improved over the mechanical properties of steels manufactured using the
traditional
process. For example, for steels with silicon contents of 2.6%, 3.0%, or more,
the
hardness of the steels may be greater than 80, 85, 90, 95, or 100 Rb.
Moreover, the
mechanical properties of YS, UTS, and El may be greater than the values (or
ranges)
38
CA 02897668 2015-07-16
described with respect to Table 19.
[00104] The
electrical steels of the present invention described herein may
be utilized for various electric motor applications. For example, the
electrical steels from
the present invention may be utilized for applications in which higher
strength electrical
steels are needed, applications in which higher frequencies are required, or
the like.
[00105] In some
applications electric motors have a stationary stator that
has windings or permanent magnets that surround a core comprising layers of
electrical
steel sheets. The rotor is located within the stator and has conductors that
carry currents
that interact with the magnetic field of the stator for driving a shaft
attached to the rotor.
In other applications electric motors may have rotors that are coupled to the
permanent
magnets instead of the stator, while the stator includes the conductors. The
electrical
steels of the present invention can be used in both applications, but in one
embodiment
of the invention the electrical steels may be particularly useful in electric
motors in
which the rotor has the permanent magnets and the stator has the conductors.
In this
embodiment, electrical steels made from the traditional process described
herein (e.g.,
having an annealing step after cold rolling and before customer stamping and
annealing)
may be used to create the stator portion of the electrical steel, but not the
rotor portion.
For example, when permanent magnets are used on the rotor itself, the rotor is
not
magnetized because the magnets create the magnetic field. As such, in
these
applications the polarity of the stator is changed to rotate the rotor within
the stator. In
order to improve the efficiency of the motor for rotating at higher levels of
rotations per
minute (RPM) and higher levels of torque, the rotor strength has to be
improved. As
such, high strength steel can be used for the rotor to result in higher levels
of RPM and
torque for the electric motor. When customers use electrical steels made from
the
traditional process described herein, the electrical steel sheets are
annealing after cold
rolling, then the electrical steel is shipped to the customer for stamping and
customer
annealing to achieve the desired magnetic properties. The stator and rotor
parts are
stamped out of the electrical steel sheets in a single stamping process.
However, the
rotor parts made from the electrical steels produced from the traditional
process do not
have the required strength to meet the desired motor applications which
require higher
levels of RPMs and torque. As such, the rotor parts cannot be used and are
scraped or
used for other applications. Instead, the rotor parts are made from steel
products that
39
CA 02897668 2015-07-16
have higher strengths and the permanent magnets are coupled to the rotors made
from
the higher strength material. Alternatively, the stamped stator parts are
customer
annealed to achieve the desired magnetic properties. This situation creates
waste within
the manufacturing process and increases the costs of the electric motors
(e.g., additional
stamping process costs, additional high strength steel material costs, and the
like).
[00106] Alternatively, the electrical steels of the present invention
(e.g.,
which do not include an annealing step after cold rolling and before customer
stamping
and customer annealing) have a higher strength before stamping and customer
annealing
(see Table 19). As such, the electrical steels of the present invention may be
stamped by
the customer to create the rotor and stator parts. The stator parts may then
be annealed
by the customer to achieve the desired magnetic properties, while the rotor
parts stamped
from the same electrical steel sheet may be utilized without the customer
annealing step
or annealed at a lower customer annealing temperature to preserve the higher
strength of
the steel (see Table 19). By annealing at lower customer annealing
temperatures the
rotor parts may retain some of the mechanical properties (e.g., better than
the stator)
while the core loss and permeability would still be improved (e.g., not as
good as the
stator), but the costs could be reduced due to increased productivity and the
lower
annealing temperature (e.g., don't have to anneal as long and can save
electricity that is
usually required to reach higher temperature annealing). The present invention
allows
the customer to stamp the stator and rotor parts from the same sheet of metal
without
having to replace the stamped rotor parts with parts stamped from higher
strength steels.
In the traditional process by annealing the electrical steel sheet after the
final cold rolling
step and before shipping to the customer for stamping and final annealing the
desired
magnetic properties may be achieved, but the strength of the electrical steel
sheet is
sacrificed.
[00107] Another application of the electrical steels of the present
invention
may include applications (e.g., motors, or the like) that require higher
operating
frequencies. For example, some electric motors may only require frequencies of
around
60 Hz (e.g., the alternating current switches from + to - at a rate of 60
times per second),
or other like frequencies. However, other electric motors, such as electric
motors used in
cars may be required to operate at approximately 400 Hz, 500Hz, 600Hz, 700Hz,
800Hz,
900Hz, 1000Hz, or higher (or any ranges that fall within, overlap, or are
outside of these
CA 02897668 2015-07-16
ranges). For example, in some applications steels with silicon values greater
than 2.2
wt% and with thicknesses less than or equal to 0.02 inches (or less than or
equal to
0.014") may be particularly useful in motor applications with high
frequencies. In order
to achieve the desired properties at these higher frequency levels the size of
the grains in
the electrical steel sheets are kept to smaller grain sizes. When a cycle
occurs within the
electrical steel, the domains of the grain flip back and forth between two
different
orientations. As such, the domains of the grains are aligned in a first
direction and are
flipped into a second direction and back to the first direction for each
cycle. The larger
the grain size the larger the domain of the grain, which requires more energy
to reach the
higher frequencies because of the larger area that has to be covered in a
shorter amount
of time. At lower frequencies, larger grain sizes arc not an issue because the
amount of
energy needed to flip the domain is not restrictive. However, at higher
frequencies (e.g.,
400 Hertz or more as described above) it is harder to flip the domain fast
enough to reach
frequencies of 400 Hz or higher, and as such, it takes more energy to flip the
domain
when the size of the grains are larger. The additional energy required to
achieve the
higher frequency levels increases the heat loss and reduces the efficiency of
the electric
motor. As such, smaller grain sizes are more efficient at higher frequencies.
The process
of the present invention can produce electrical steels with smaller grain
sizes than the
grain sizes of the electrical steels produced by the traditional process (as
described
above). In addition to the smaller gain sizes, the present invention still
achieves the
same, similar, or improved magnetic properties (e.g., core loss, permeability,
or the like)
and mechanical properties as can be achieved using the traditional process (as
described
above).
[0100] It should be understood that when discussing the magnetic
properties of
the electrical steel, the magnetic properties of the electrical steel are
based on the
composition of the electrical steel, the processing of the semi-processed
electrical steel
sheet, and the customer stamping and final customer anneal occurring at the
customer.
The final magnetic properties of the steel are provided after processing at
the customer,
and may or may not be dependent on the shape of the stamped part made from the
electrical sheet steel sent to the customer.
[0101] Moreover, it should be understood that the lower limit of any of
the
components discussed herein may be 0.0005, 0.001, 0.005, 0.01, or the like.
41
CA 02897668 2015-07-16
[0102] While certain exemplary embodiments have been described herein, and
shown in the accompanying drawings, it is to be understood that such
embodiments are
merely illustrative of and not restrictive on the broad invention, and that
this invention
not be limited to the specific constructions and arrangements shown and
described, since
various other changes, combinations, omissions, modifications and
substitutions, in
addition to those set forth in the above paragraphs, are possible. Those
skilled in the art
will appreciate that various adaptations and modifications of the just
described
embodiments can be configured without departing from the scope and spirit of
the
invention. Therefore, it is to be understood that, within the scope of the
appended
claims, the invention may be practiced other than as specifically described
herein.
42
