Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates to an improvement in the ~ ~.
manufacture of grain-oriented silicon steel.
United States Patent Nos. 3,873,381, 3,905,842,
3,905,843 and 3,957,546 describe processing for producing boron-
inhibited grain oriented electromagnetic silic~n steel. Described
therein are processes for producing steel of high magnetic
quality from boron-bearing silicon steel melts. Through this
invention, I now provide a process which improves upon those of
f the cited patents~ Speaking broadly, I provide a process which
improves llpon those of said patents by incorporating controlled
amounts of both boron and SiO2 in the base coating, which is
applied prior to the final texture anneal.
- It is accordingly an object of the present invention
to provide an improvement in the manufacture of grain-oriented
:. silicon steels.
. In accordance with the present invention a melt of
silicon steel containing from 0.02 to 0.06~ carbon, from 0.0006 :.
to 0.0080~ boron, up to 0.0100% nitrogen, no more than 0.008%
: aluminum and from 2.5 to 4.0% silicon is subjected to the con-
.~ 20 ventional steps of casting, hot rolling, one or more cold
;` rollings, an intermediate normalize when two or more cold
rollings are employed, decarburizing, application of a refractory
oxide coating and final texture annealing; and to the improvement
comprising the steps o~ coating the surface of the steel with a
refractory oxide coating consisting essentially of:
~a) 100 parts, by weight, of at least one substance from
the group consisting o~ oxides, hydroxides, carbonates
; . and boron compounds of magnesium, calcium~ aluminum and
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:~ . titanium;
. 30 (b) up to 100 parts, by weight, of at least one other
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1 substance from the group consisting of boron and
compounds thereof, said coating containing at least
0.1%, by weight of boron;
(c) from 0.5 to A0 parts, by weiyht, of SiO2;
~d) up to 20 parts, by weight, of inhibiting substances or
compounds thereof; and
(e) up to 10 parts, by weight, of fluxing agents;
and final texture annealing said steel with said coating thereon.
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For purposes of definition, "one part" equals the total weight
lO of (a~ hereinabove, divided by 100. -~
Specific processing as to the convention steps, is not
critical and can be in accordance with that specified in any
- number of publications including United States Patent No.
2,867,557 and the other patents cited hereinabove. Moreover,
the term casting is intended to include continuous casting
processes. A hot rolled band heat treatment is also includable
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within the scope of the present invention. It is howeyer,
preferred to cold roll the steel to a thickness no greater than
0.020 inch, without an intermediate anneal between cold rolling
passes; from a hot rolled band having a thickness of from about
0.050 to about 0.120 inch. Melts consisting essen~ially of, by
weight, 0.02 to 0.06% carbon, 0.015 to 0.15% ~anganese, 0 01 to
! 0-05% of material from the group consisting o sul~ur and
~elenium, 0.0006 to 0.0080~ boron, up ~o 0.0100% nitrogen, ~.5
to 4.0% silicon, up to 1.0% copper, no more than 0.008% aluminum,
balance iron, have proven to be particularly adaptable to ~he
subject invention. Boron levels are usually in excess of 0.0008%.
Steel produced in accordance with the present invention has a
permeability of at least 1870 tG/Oe) at 10 oersteds. Preferably,
' 30 the steel has a permeability of at least 1900 (G/Oe) at 10 ~;
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1 oersteds and a core loss o~ no more than 0.700 watts per pound
at 17 kilogauss. ~ ~ ;
The specific mode of applying the coating of the subject
invention is not critical thereto. It is just as much within the
scope of the subject invention to mix the coating with water and
apply it as a slurry, as it is to apply it electrolytically. Like-
wise, the constituents which make up the coating can be applied
together or as individual layers. It is, however, preferred to ;~
have at laast 0.2%, by weight, of boron and/or at least 3 parts,
by weight, of SiO2, in the coating. Boron levels usually do not
exceed 15%. They are generally, however, below 5%. Silica levels
' are generally not in excess of 20 parts by weight. The additional
inhibiting substances includable with the coating are usually
~ from the group consisting of sulfur, sulfur compounds, nitrogen
Z~ compounds, selenium and selenium compounds. Typical sources of
Z~ boron are boric acid, fused boric acid (B203), ammonium penta-
' ~ -borate and sodium borate. Typical fluxing agents include lithium
Zl oxide, sodium oxide and other oxides known to those skilled in
the art. Those skllled in the art are, of course, aware o
various ways of adding silica. Colloidal silica is, however,
preferred.
Also includable as part of the subject invention is the
steel in its primary recrystallized state with the coating of the
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! subject invention adhered thereto. The primary recrystalliæed
steel has a thickness no greater than 0.020 inch and is, in
accordance with the present invention, suitable for processing
into grain oriented silicon steel having a permeability of at
least 1870 ~G/Oe) at 10 oersteds. Primary recrystallization takes
Z~ place during the final normalize.
'~ ~ 30 The following examples are illustrative of several
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Example _I
Samples from ~hree heats (Healts A, B and C) of silicon
steel were cast and processed into silicon steel having a cube-
on-edge orientation. The chemistry of the heats appears
hereinbelow in Table I.
TABLE I
Com osition (wt. %)
P
Heat C Mn S B N Si Cu Al Fe
A0.031 0.0320.020 0.0011 0.0047 3.15 0.32 0.004 Bal.
lO B0.032 0.036 0.020 0.0013 0.0043 3.15 0.35 0.004 Bal.
C0.030 0.0350.020 0.0013 0.0046 3.15 0.34 0.004 Bal.
Processing for the samples involved soaking at an
elevated temperature for several hours, hot rolling to a nominal
gage o~ 0.080 inch, hot roll band normalizing at a temperature o
approximately 1740F, cold rolling to final gage, decarburizing,
coating as described hereinbelow in Table II, and final ~exture
annealing at a maximum temperature of 2150F in hydrogen. As
for Table II, and in particular the sample identification, the
letter referes to the heat and the number -to the sample from that
20 heat. For example, Al refers to Heat A, Sample 1.
TABI,E II
MgO H3BO3
Sample ~Parts, by wt.) (Parts, by wt.)
A~, Bl Cl ~ 100 o
A2 B2 C2 L00 2.3 (o.496 B)
A3 B3 C3 100 4.6 (0.8% B)
The samples were tested Eor permeabllity and core loss.
The results of the tests appear hereinbelow in Table III.
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1 TABLE III
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Permeability Core Loss
( P at 17 KB)
Al 1882 0.736
A 1892 0.725
A32 1921 0.668
Bl 1903 0.708
B2 1902 0.708
B3 1927 0.677
Cl 1558 1.27
C2 1891 0.697
C3 1908 0.677
The benefit of boron in the coating is clearly evident
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from Table III. Improvement in both permeability and core loss
can be attributed thereto. Moreover, Samples A3, B3 and C3,
with more than 0.5% boron in the coating, each attained a
permeability in excess of 1900 (G/Oe) at 10 oersteds and a core
loss below 0.700 watts per pound at 17 kilogauss.
Example II
- Additional groups of samples ~Group 4 through 8) were
processed as were Group 1 through 3 samples, with the exception
of the coating. The coatings applied to the Group 4 through 8
samples appear hereinbelow in Table IV, along with that applied
to the Group 2 and 3 samples.
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TABLE IV
I MgO H3BO3 SiO2
; Sample (Parts, by wt.) (Parts, by wt .L (Parts, by wt.)
A2 B2 C2 100 2.3 ~0.4~ B) 0
A4 B4 C4 100 2.3 1.8
A5 B5 C5 100 2.3 3.6
A3 B3 C3 100 4.6 (0.8% B) 0
~6 B6 C6 100 4.6 1.8
A7 B7 C7 100 4.6 3.6
A8 B8 C8 100 4.6 7.3
The samples were tested for permeability and core loss.
The results of the tests appear hereinbelow in Table V.
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1 TABLE V
Permeability Core Loss
Sample (at 10 O ) (WPP at 17 KB)
e
A~ 1892 0.725 .
A4 1899 Q.705
A5 1901 0.702
B2 1902 0.708
: B4 1909 0.706
B5 1923 0.690
C2 1891 0.697
C41889929 0 708
A3 1921 0.668
A6 1933 0.654
A7 1929 0.645
A8 1925 0.654
B3 1927 0.677
B6 1936 0.651
B7 1934 0.655
B8 1928 0.653
C3 1908 0.677
C 191~ 0.660
6 1901 0.649
C781908 0.655
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From Table V, a further improvement in magne',:ic properties i9
attributable to the additlon of SiO~ to the base coating~ SiOz increases
permeabilities and decreases core losses. Moreover, as notable from
Table VI, hereinbelow SiO2 improves the insulating characteristic of the
subject base coating, Table VI lists the Franklin values at 900 psi for the
C2, C4 and Cs and C3, C6, C7 and C8 samples; and as known to those skilled
in the art, a perfect insulator has a Fr~klin value of 0~ whereas a perfect
conductor has a Franklin value of 1 ampere.
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:; . TABLE VI
. Franklin Value
- Sample .(at 900 psi)
C2 . 0,97
C4 0,96
, . C~ 0, 90
1 5 . , (::3 ~ 93
~i C6 0,95
C7 0, 90
C8 0,88
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Note how the Franklin values decrease with increasing SiO2
addition~. Most favorable results were obtained when the coating contained
mor e than 3, O parts SiC)~,
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~j It will be apparent to tho9e 9killed in tha art that the novel
principles of the invention disclosed hereis~ in connection wîth specific
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examples thereof will suggest variou9 other modification9 and applications of
the same, It is accordingly desired th~t in construing the breadth of the
~j appended claims they shall not be limited to the specific examples of the
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invention described herein,
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