Method of refining magnetic domains of electrical steels using phosphorus

A method is provided for refining the magnetic domain wall spacing of grain-oriented silicon steel having a forsterite base coating thereon by removing portions of the base coating to expose a pattern of the underlying silicon steel, providing the exposed silicon steel with an environment selected from the group of phosphorus and phosphorus-bearing compounds, and then annealing the exposed steel, which is free of thermal and plastic stresses, in the phosphorus environment in a reducing atmosphere to produce in the steel a line of permanent bodies containing a phosphorus-bearing compound to effect heat resistant domain refinement and reduced core loss. A semi-finished sheet product of final texture annealed grain-oriented silicon steel is also provided.

BACKGROUND OF THE INVENTION 
This invention relates to a method of improving core loss by refining the 
magnetic domain wall spacing. More particularly, the invention relates to 
a method of processing final texture annealed grain-oriented silicon steel 
having a forsterite base coating thereon to effect heat resistant domain 
refinement using the intrusion of phosphorus. 
Grain-oriented silicon steel is conventionally used in electrical 
applications, such as power transformers, distribution transformers, 
generators, and the like. The steel's ability to permit cyclic reversals 
of the applied magnetic field with only limited energy loss is a most 
important property. Reductions of this loss, which is termed "core loss", 
is desirable. 
In the manufacture of grain-oriented silicon steel, it is known that the 
Goss secondary recrystallization texture, (110)[001] in terms of Miller's 
indices, results in improved magnetic properties, particularly 
permeability and core loss over nonoriented silicon steels. The Goss 
texture refers to the body-centered cubic lattice comprising the grain or 
crystal being oriented in the cube-on-edge position. The texture or grain 
orientation of this type has a cube edge parallel to the rolling direction 
and in the plane of rolling, with the (110) plane being in the sheet 
plane. As is well known, steels having this orientation are characterized 
by a relatively high permeability in the rolling direction and a 
relatively low permeability in a direction at right angles thereto. 
In the manufacture of grain-oriented silicon steel, typical steps include 
providing a melt having on the order of 2-4.5% silicon, casting the melt, 
hot rolling, cold rolling the steel to final gauge typically or 7 or 9 
mils, and up to 14 mils with an intermediate annealing when two or more 
cold rollings are used, decarburizing the steel, applying a refractory 
oxide base coating, such as a magnesium oxide coating, to the steel, and 
final texture annealing the steel at elevated temperature in order to 
produce the desired secondary recrystallization and purification treatment 
to remove impurities such as nitrogen and sulfur. The development of the 
cube-on-edge orientation is dependent upon the mechanism of secondary 
recrystallization wherein during recrystallization, secondary cube-on-edge 
oriented grains are preferentially grown at the expense of primary grains 
having a different and undesirable orientation. 
As used herein, "sheet" and "strip" are used interchangeably and mean the 
same unless otherwise specified. 
It is also known that through the efforts of many prior art workers, 
cube-on-edge grain-oriented silicon steels generally fall into two basic 
categories: first, regular or conventional grain-oriented silicon steel, 
and second, high permeability grain-oriented silicon steel. Regular 
grain-oriented silicon steel is generally characterized by permeabilities 
of less than 1850 at 10 Oersteds with a core loss of greater than 0.400 
watts per pound (WPP) at 1.5 Tesla at 60 Hertz for nominally 9-mil 
material. High permeability grain-oriented silicon steels are 
characterized by higher permeabilities which may be the result of 
compositional changes alone or together with process changes. For example, 
high permeability silicon steels may contain nitrides, sulfides, and/or 
borides which contribute to the precipitates and inclusions of the 
inhibition system which contribute to the properties of the final steel 
product. Furthermore, such high permeability silicon steels generally 
undergo cold reduction operations to final gauge wherein a final heavy 
cold reduction on the order of greater than 80% is made in order to 
facilitate the grain orientation. While such higher permeability materials 
are desirable, such materials tend to produce larger magnetic domains than 
conventional materials. Generally, larger domains are deleterious to core 
loss. 
It is known that one of the ways that domain size and thereby core loss 
values of electrical steels may be reduced is if the steel is subjected to 
any of various practices designed to induce localized strains in the 
surface of the steel. Such practices may be generally referred to as 
.cent.domain refining by scribing" and are performed after the final high 
temperature annealing operation. If the steel is scribed after the final 
texture annealing, then there is induced a localized stress state in the 
texture-annealed sheet so that the domain wall spacing is reduced. These 
disturbances typically are relatively narrow, straight lines, or scribes 
generally spaced at regular intervals. The scribe lines are substantially 
transverse to the rolling direction and typically are applied to only one 
side of the steel. 
In fabricating these electrical steel into transformers, the steel 
inevitably suffers some deterioration in core loss quality due to cutting, 
bending, and construction of cores during fabrication, all of which impart 
undesirable stresses in the material. During fabrication incident to the 
production of stacked core transformers and, more particularly, in the 
power transformers of the United States, the deterioration in core loss 
quality due to fabrication is not so severe that a stress relief anneal 
(SRA) is essential to restore usable properties. For such end uses, there 
is a need for a flat, domain-refined silicon steel which will not be 
subjected to stress relief annealing. In other words, the scribed steel 
used for this purpose does not have to possess domain refinement which is 
heat resistant. 
However, during the fabrication incident to the production of most 
distribution transformers in the United States, the steel strip is cut and 
subjected to various bending and shaping operations which produce much 
more worked stresses in the steel than in the case of power transformers. 
In such instances, it is necessary and conventional for manufacturers to 
stress relief anneal (SRA) the product to relieve such stresses. During 
stress relief annealing, it has been found that the beneficial effect on 
core loss resulting from some scribing techniques, such as mechanical and 
thermal scribing, are lost. For such end uses, it is required and desired 
that the product exhibit heat resistant domain refinement (HRDR) in order 
to retain the improvements in core loss values resulting from scribing. 
It has been suggested in prior patent art that contaminants or intruders 
may be effective for refining the magnetic domain wall spacing of 
grain-oriented silicon steel. Takashina et al, U.S. Pat. No. 
3,990,923--dated Nov. 9, 1976, discloses that chemical treatment may be 
used on primary recrystallized silicon steel to control or inhibit the 
growth of secondary recrystallization grains. British patent application 
No. 2,167,324A discloses a method of subdividing magnetic domains of 
grain-oriented silicon steels to survive an SRA. The method includes 
imparting a strain to the sheet, forming an intruder on the grain-oriented 
sheet, the intruder being of a different component or structure than the 
electrical sheet and doing so either prior to or after straining and 
thereafter annealing such as in a hydrogen reducing atmosphere to result 
in imparting the intruders into the steel body. Numerous metals and 
nonmetals are identified as suitable intruder materials. 
Japanese Patent Document 61-133321A discloses removing surface coatings 
from final texture annealed magnetic steel sheet, forming permeable 
material coating on the sheet and heat treating to form material having 
components or structure different than those of the steel matrix at 
intervals which provide heat resistant domain refinement. 
Japanese Patent Document 61-139-679A discloses a process of coating final 
texture annealed oriented magnetic steel sheet in the form of linear or 
spot shapes, at intervals with at least one compound selected from the 
group of phosphoric acid, phosphates, boric acid, borates, sulfates, 
nitrates, and silicates, and thereafter baking at 300.degree.-1200.degree. 
C., and forming a penetrated body different from that of the steel to 
refine the magnetic domains. 
Japanese Patent Document 61-284529A discloses a method of removing the 
surface coatings from final texture annealed magnetic steel sheets at 
intervals, coating one or more of zinc, zinc alloys, and zincated alloy at 
specific coating weights, coating with one or more of metals having a 
lower vapor pressure than zinc, forming impregnated bodies different from 
the steel in composition or in structure at intervals by heat treatment or 
insulating film coating treatment to refine the magnetic domains. 
Japanese Patent Document 62-51202 discloses a process for improving the 
core loss of silicon steel by removing the forsterite film formed after 
final finish annealing, and adhering different metal, such as copper, 
nickel, antimony by heating. 
A copending application, Ser. No. 205,711, filed June 10, 1988, by the 
Assignee of this invention discloses a method for refining the magnetic 
domain wall spacing of grain-oriented silicon steels having an insulation 
base coating thereon by the use of metallic contaminants. In another 
copending application, Ser. No. 206,051, filed June 10, 1988, by the 
Assignee of this invention, there is disclosed another method for refining 
the domain wall spacing by applying a barrier coating to the forsterite 
prior to applying a metallic contaminant to a pattern of exposed steel 
being free of thermal and plastic stresses. 
What is needed is a method for providing heat resistant domain refinement 
which is compatible with conventional processing of regular and high 
permeability grain-oriented silicon steels and which is not dependent on a 
particular technology, such as laser, electrical discharge, or electron 
beam technology, for removing the base coating in desired patterns on the 
steel. The method should use the insulative coating, i.e., the forsterite 
base coating, on grain-oriented silicon steel sheet to facilitate domain 
refining. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a method of refining the magnetic 
domain wall spacing of grain-oriented silicon steel having an insulation 
coating is provided. The method comprises removing portions of the 
insulation coating to provide a limited exposure of the underling silicon 
steel in a pattern of lines, providing the silicon steel with an 
environment selected from the group of phosphorus and phosphorus-bearing 
compounds to the exposed steel which is free of thermal and plastic 
stresses and is not dependent on such stresses for effective domain 
refinement. Thereafter, annealing the exposed steel having the phosphorus 
environment in a reducing atmosphere at time and temperature to produces 
line of permanent bodies containing a phosphorus-bearing compound in the 
exposed steel area to effect heat resistant domain refinement and reduced 
core loss.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Broadly, in accordance with the present invention, a method is provided for 
improving the magnetic properties of regular and high permeability 
grain-oriented silicon steels having relatively large grain size and 
correspondingly relatively large magnetic domain wall spacing. Preferably, 
the method is useful for treating such steels to effect a refinement of 
the magnetic domain wall spacing for improving core loss values of the 
steel strip such that they are heat resistant. The width of the scribed or 
treated lines and the spacing of the treated regions or lines being 
substantially transverse to the rolling direction of the silicon strip may 
be conventional. What is not conventional, however, is the method of the 
present invention for effecting such magnetic domain wall spacing by the 
controlled contamination, in surface bands or stripes, using phosphorus 
and phosphorus compounds such that the steel so treated has improved 
magnetic properties of core loss resulting from the produced heat 
resistant domain refinement. 
Although the present invention described in detail herein has utility with 
electrical steel generally, and particularly 2.0-4.5% silicon electrical 
steels, such steels may be of the conventional grain-oriented or high 
permeability grain-oriented type. Such steels having relatively high 
permeability such as greater than 1850 at10 Oersteds usually have 
correspondingly relatively large grain size and would respond well to 
various types of domain refining techniques. As used herein, the steel 
melt initially contained the nominal composition of: 
______________________________________ 
C N Mn S Si Cu B Fe 
______________________________________ 
.030 Less .038 .017 3.15 .30 10 ppm 
Bal. 
than 
50 ppm 
______________________________________ 
The steel is a high permeability grain-oriented silicon steel. Unless 
otherwise noted herein, all composition ranges are in weight percent. 
The method starting material for the chemical striping process of the 
present invention includes final texture annealed grain-oriented silicon 
steel sheet having an insulation coating thereon. Such an insulative 
coating can be the conventional base coating, also called forsterite or 
mill glass, typically found on such silicon steels. Preferably, the 
as-scrubbed final texture annealed grain-oriented silicon steels may be 
used. 
The method includes removing portions of the base coating to expose a line 
pattern of the underlying silicon steel so as to expose that steel. In 
accordance with the present invention, it is important that portions of 
the coating be removed to expose a pattern of the underlying silicon 
steel. How the coating is removed is not critical to the present invention 
except that the underlying steel need not be subjected to any mechanical, 
thermal, or other stresses and strains as a result of the coating removal 
operation. In other words, the exposed steel must be free of any thermal 
and plastic stresses prior to any subsequent steps of applying the 
metallic contaminant. An advantage of the present invention is that any of 
various techniques may be used to remove the selected portions of the base 
coating. For example, conventional mechanical scribing or laser means may 
be used to develop a controlled pattern of markings on the strip surface. 
The line or stripe pattern selected for the removed base coating may be 
conventional patterns used in prior art scribing techniques. Preferably, 
the pattern may comprise removing the coating in lines substantially 
transverse to the rolling direction of the steel having a line width and 
spacing as may be conventional. Other patterns may also be useful, 
depending on whether the grain-oriented silicon steel is of the 
cube-on-edge, cube-on-face, or other orientation. As used herein, the 
pattern of exposed bare metal lines is referred to as "metal stripes." 
The method also provides the silicon steel with an environment selected 
from the group of phosphorus and phosphorus-bearing compounds from which 
the controlled contamination of phosphorus into the steel surface can 
occur. By phosphorus or phosphorus-bearing compounds, it is meant that the 
environment contains sufficient phosphorus in order to react with the 
steel and to attack and diffuse into the exposed silicon steel in the 
pattern defined by the removal of portions of the base coating. Typical 
phosphorus-bearing coating compounds are shown in Table I, the composition 
mixtures based on 1 liter of water. Although it is preferred to provide 
phosphorus-bearing compounds in the form of coatings, other sources of 
phosphors may be equally suitable, such as pure phosphorus in powder or 
solid form. The amount of concentration of phosphorus present does not 
appear to be critical because even minute amounts seem to preferentially 
attack the limited or constricted exposure of silicon-iron steel. 
TABLE I 
______________________________________ 
Designation 
Composition Concentration 
______________________________________ 
SC Phosphoric Acid (85%) 
202 gm/l 
Magnesium Oxide 22 gm/l 
Nalcoag (1050) 318 ml/l 
Chromic Trioxide 46 gm/l 
Water Balance 
Cured: 1000.degree. F. - 1 min. (air) 
PS Phosphoric Acid (85%) 
120 gm/l 
Magnesium Oxide 18 gm/l 
Kasil #1 22 gm/l 
Ammonium Hydroxide (58%) 
21 ml/l 
Chromic Trioxide .34 gm/l 
Dupanol (2%) 1.0 ml/l 
Water Balance 
Cured: 800.degree. F. - 1 min. (air) 
P Phosphoric Acid 118 gm/l 
Magnesium Oxide 18 gm/l 
Ammonium Hydroxide (58%) 
20 ml/l 
Chromic Trioxide .34 gm/l 
Dupanol (2%) 1.0 ml/l 
Water Balance 
Cured: 800.degree. F. - 1 min. (air) 
______________________________________ 
When applied to the silicon steel surface, the phosphorus-source layer may 
be applied by any conventional means such as dip or roller coating and 
subsequently air cured. The coating may be applied in thicknesses ranging 
from about 0.03 to 0.15 mils (0.75 to 2.25 microns) and may be applied at 
such thickness to either one or both sides of the steel strip. When 
applied directly to the steel strip either on or in the vicinity of the 
exposed metal stripes, and subsequently heated in a reducing atmosphere, 
the phosphorus will migrate along the silicon steel surface to the areas 
of exposed iron where it reacts to form wedge-shaped iron phosphide bodies 
or particles rooted in the steel. The phosphorus and phosphorus-bearing 
compounds in the environment may also be vapor deposited into the silicon 
steel exposed areas by techniques, such as described below. If the 
phosphorus and phosphorus-bearing compounds are provided as a coating to 
the silicon steel on the surface wherein the base coating has or will be 
removed to expose the underlying silicon steel metal stripes, then the 
coating may be applied either before or after metal striping. If the 
phosphorus is to be provided through vapor deposition, then the metal 
striping must be done prior to providing the phosphorus in vapor form. 
The method includes annealing the exposed steel having the phosphorus 
environment in a reducing atmosphere at time and temperature to produce a 
line of permanent wedge-shaped bodies or particles. The reducing 
atmosphere may include hydrogen and hydrogen mixtures such as 
nitrogen-hydrogen mixtures. Hydrogen is a known reducing atmosphere for 
phosphorus-containing compounds. 
In order to better understand the present invention, the following examples 
are presented. For each example, the steel was produced by casting, hot 
rolling, normalizing, cold rolling to final gauge with an intermediate 
annealing when two or more cold rolling stages were used, decarburizing, 
coating with MgO and final texture annealing to achieve the desired 
secondary recrystallization of cube-on-edge orientation. After 
decarburizing the steel, a refractory oxide base coating containing 
primarily magnesium oxide was applied before final texture annealing at 
elevated temperature, such annealing causing a reaction at the steel 
surface to create a forsterite base coating. Although the steel melts 
initially contained the nominal compositions recited above, after final 
texture annealing, the C, N, and S were reduced to trace levels of less 
than about 0.001% by weight. 
Example I 
To illustrate the several aspects of the domain refining process of the 
present invention, silicon steel having the composition described above 
was processed as described above to a final gauge of about 9 mils. The 
samples were magnetically tested as received and used as control samples. 
One surface of the steel was coated with the "P" coating identified in 
Table I and then mechanically scratched to remove portions of the base 
coating to expose the underlying silicon steel as metal stripes. The 
removed base coating was in generally parallel lines extending 
substantially transverse to the rolling direction of the steel about 5 mm 
apart and with each line typically about 100 microns wide. All of the 
samples were then annealed at 1650.degree. F. (899.degree. C.) in a 
reducing atmosphere of either hydrogen or a mixture of 90/10 
nitrogen/hydrogen as indicated. All of the strips (base coated, then 
coated with the "P" coating) were 30 cm long.times.3 cm wide so to be able 
to form Epstein test packs. The magnetic properties of core loss at 60 
Hertz (Hz) at 1.5 and 1.7 Tesla, permeability at 10 Oersteds (H) were 
determined in a conventional manner for Epstein packs after final texture 
annealing (original tests) and after domain refined in accordance with the 
present invention. Percentages in parentheses indicate change compared to 
original properties. 
TABLE II 
______________________________________ 
Magnetic Properties 
Core Loss 
Pack Permeability 
@1.5T @1.7T 
No. Sample Condition 
@10H (wpp) (wpp) 
______________________________________ 
Hydrogen Reaction - Anneal 
B6 As P Coated 1947 .460 .621 
Striped, + 5 hr. anneal 
1952 .428 .574 
at 1650.degree. F. (-7) (-8) 
As above + further 
1953 .429 .579 
5 hr. anneal at 1650.degree. F. 
(-7) (-7) 
90/10 Nitrogen/Hydrogen Reaction - Anneal 
B8 As P Coated 1943 .436 .595 
Striped + 5 hr. anneal 
1946 .425 .581 
at 1650.degree. F. (-3) (-2) 
As above + further 
1947 .400 .540 
5 hr. anneal at 1650.degree. F. 
(-8) (-9) 
______________________________________ 
Under the experimental conditions described above, Table II shows the 
effects of the domain refinement on the magnetic properties of the 
grain-oriented silicon steel samples. The magnetic properties were 
determined after 5 hours at 1650.degree. F. and again after an additional 
5 hours at that temperature. The data show that a 7 to 8% improvement in 
core loss at 1.5 and 1.7 Tesla were obtained with the improvements 
occurring at shorter annealing cycles for the material annealed in 100% 
hydrogen. 
Examination under the Scanning Electron Microscope (SEM) revealed massive 
phosphorus attack in the pattern marks on the surface of the exposed 
silicon steel. The attack was most intense in the periphery of the scribe 
line resulting from the surface migration of the phosphorus and is 
visualized as starting at the small ridges of metal often found to have 
been forced upwards at edges of scribe marks when mechanical scribing 
occurs. FIG. 1 illustrates a photomicrograph at 800X in cross section 
through the groove in the base coating and shows the attack along the 
edges of the groove. More particularly, the iron phosphide growth as the 
"wedge-like" body is typical resulting from the phosphorus attack in 
accordance with the method of the present invention. Such a wedge-like 
body buries itself into the matrix of the silicon steel substrate. FIG. 2 
is a photomicrograph of 800X in cross section showing another typical 
growth of the phosphide but this time completely filling the groove or 
channel marked through the base coating. 
In addition to the iron phosphide in the vicinity of the patterned grooves 
in the base coating, a random dispersion of relatively small phosphide 
nodules were also sometimes found on the surface of the silicon steel. SEM 
photographs of such nodules also shows the wedge-like appearance which 
could adversely affect the magnetic domain structure of the silicon steel. 
Such random dispersion of the nodules probably results from pores, cracks, 
or other defects in the forsterite base coating. To further assess such 
random dispersion of the phosphides, similar tests were performed on final 
texture annealed silicon steels having the forsterite or base coatings 
removed. Following the "P" coating and anneal at 1650.degree. F. in 
hydrogen, the iron phosphides were found to have formed uniformly as a 
thin film covering the whole sample. No wedge-like particles were embedded 
in the steel matrix. It would appear that a constricted or limited access 
to the underlying steel matrix as provided by metal striping is necessary 
and important for the wedge shaped particles to be formed. 
Example II 
By way of further examples, additional tests were performed to demonstrate 
a lower diffusion annealing temperature. All of the samples were obtained 
from various heats of nominally 9-mil gauge material and were prepared in 
a manner similar to that in Example I but annealed under the experimental 
conditions described in Table III. The magnetic properties were measured 
both as single strip and as an Epstein pack containing eight strips. 
Percentages in parentheses indicate change compared to initial properties. 
TABLE III 
__________________________________________________________________________ 
P-Coated and 
Annealed 71/2 Hrs. @ 
Second Anneal 71/2 Hrs. 
Initial As-Scrubbed Properties 
Metal Striped 
1525.degree. F. in Hydrogen 
@ 1525.degree. F. in 
Hydrogen 
Sample Core Loss 
Perme- 
Core Loss Core Loss Core Loss 
No. Permeability 
@1.5T 
@1.7T 
ability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
VDTS @10H (wpp) 
(wpp) 
@10H 
(wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
__________________________________________________________________________ 
49 1903 .523 
.738 
1898 
.367 
.508 
1893 .404 
.567 
1871 .385 
.560 
50 1881 .543 
.783 
1873 
.373 
.528 
1866 .532 
.768 
1855 .376 
.554 
51 1928 .596 
.780 
1921 
.356 
.485 
1909 .431 
.593 
1887 .368 
.507 
52 1892 .471 
.704 
1885 
.406 
.576 
1881 .463 
.670 
1857 .376 
.542 
53 1926 .463 
.644 
1923 
.365 
.508 
1911 .407 
.558 
1889 .384 
.531 
54 1887 .538 
.770 
1883 
.395 
.571 
1876 .538 
.762 
1859 .402 
.593 
55 1909 .475 
.653 
1890 
.400 
.563 
1894 .434 
.593 
1877 .407 
.559 
56 1932 .435 
.592 
1918 
.353 
.477 
1915 .394 
.529 
1895 .379 
.514 
Average 
1909 .505 
.711 
1900 
.364 
.527 
1893 .450 
.630 
1874 .385 
.545 
Single Strip (-28) 
(-26) (-11) 
(-11) (-24) 
(-23) 
Epstein 
1916 .446 
.623 
1902 
.385 
.532 
1903 .401 
.545 
1887 .372 
.512 
Pack Test (-14) 
(-15) (-10) 
(-13) (-17) 
(-18) 
on above 
8 strips 
__________________________________________________________________________ 
Under the experimental conditions described, good results were obtained 
when compared to the initial as-scrubbed condition having the forsterite 
coating thereon and as compared to the properties resulting in the removal 
of the base coating and the inherent improvement resulting from the 
unintentional marking of the steel resulting from the mechanical removal 
process. The data show that even after 15 hours at the lower temperature 
of 1525.degree., the permanent body containing a phosphorus-bearing 
compound effected heat resistant domain refinement and reduced core loss. 
The core loss improvements range from 17 to 18% for the Epstein packs and 
about 23 to 24% for the Epstein single strip properties. 
FIG. 3 is a photomicrograph in cross section at 3000X showing the 
wedge-like shape of the permanent body, i.e., the iron phosphide particle, 
found as a randomly dispersed nodule on the surface of the steel. 
Example III 
By way of further examples, additional tests were performed to demonstrate 
the phosphorizing effect through a vapor phase. Each sample was prepared 
in a manner similar to that in Example I except that the as-scrubbed 
silicon steels having the forsterite coating thereon were subjected to 
mechanical scratching for removing portions of the base coating without 
applying a coating containing phosphorus or phosphorus-bearing compounds. 
Dummy samples of 11-mil electrical silicon steel were coated with the "P" 
coating of Table I and were to be used as the phosphorus source. The 
samples and the dummy donor sample strips were stacked alternately with a 
layer of alumina powder interposed to prevent direct contact between the 
test samples and the dummy samples. The whole pack of 17 strips was then 
heated in hydrogen at 1650.degree. F. for 5 hours. Magnetic properties 
were obtained in a conventional manner on two sets of eight Epstein strips 
tested both as single strips and as Epstein packs. 
The data of Tables IV and V clearly demonstrate that the phosphorus 
contamination or striping by vapor deposition or vapor transfer can be an 
effective heat resistant domain refinement. The level of core loss 
achieved as a result of the method of the present invention is an 
improvement even over conventional mechanical scribing which does not, in 
fact, survive subsequent heat treatment or annealing. An examination under 
SEM identified several characteristic differences between the samples 
treated in accordance with the vapor transfer and those resulting from the 
surface migration of phosphorus. In the Examples I and II, the phosphorus 
attack primarily occurred at the peripheral of the grooves in the base 
coating whereas for the vapor transfer of Example III, the phosphorus 
attack was substantially in the center of the groove through the base 
coating. As a result, the groove became filled and if allowed to continue 
would become overflowing and protrude upwardly from the top surface of the 
steel sheet. 
FIG. 4 is a photomicrograph at 300X showing as a typical example the 
phosphide particles in the groove in the base coating after vapor 
deposition in accordance with the method of the present invention as 
described in Example III. FIG. 5 is a photomicrograph in cross section 
through the groove in the base coating containing the phosphides resulting 
from the vapor transfer of Example III at 800X. In contrast to the 
Examples I and II, there were virtually no random phosphide modules on the 
surface of the silicon steel resulting from the vapor deposition method. 
TABLE IV 
__________________________________________________________________________ 
Properties After Vapor 
Deposition Treatment 
Initial As-Scrubbed Properties 
Metal Striped Properties 
(5 hr/1650.degree. F. Hydrogen) 
Core Loss Core Loss Core Loss 
Sample 
Permeability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
No. @10H (wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
__________________________________________________________________________ 
PS-1 1947 .379 
.499 
1942 .340 
.460 
1948 .328 
.449 
(-10) (-13) 
PS-2 1927 .370 
.513 
1919 .374 
.520 
1919 .381 
.536 
(+1) (+3) 
PS-3 1958 .443 
.590 
1949 .347 
.463 
1959 .405 
.517 
(-22) (-9) 
PS-4 1917 .419 
.583 
1900 .391 
.544 
1918 .376 
.521 
(-7) (-10) 
PS-5 1964 .401 
.556 
1950 .347 
.471 
1957 .347 
.475 
(-13) (-13) 
PS-6 1954 .369 
.487 
1945 .333 
.459 
1950 .345 
.471 
(-10) (-7) 
PS-7 1948 .427 
.573 
1936 .342 
.470 
1949 .400 
.527 
(-20) (-6) 
PS-8 1943 .452 
.615 
1935 .360 
.492 
1948 .421 
.569 
(-20) (-7) 
Ave. 1945 .408 
.552 
1935 .354 
.485 
1944 .375 
.508 
S.S. (-13) 
(-12) (-8) 
(-8) 
Props. 
Epstein 
1945 .416 
.559 1953 .375 
.493 
Pack Test (-10) 
(-12) 
on above 
8 strips 
__________________________________________________________________________ 
TABLE V 
__________________________________________________________________________ 
Properties After Vapor 
Deposition Treatment 
Initial As-Scrubbed Properties 
Metal Striped Properties 
(5 hr/1650.degree. F. Hydrogen) 
Sample Core Loss Core Loss Core Loss 
No. Permeability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
Permeability 
@1.5T 
@1.7T 
VDTS @10H (wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
@10H (wpp) 
(wpp) 
__________________________________________________________________________ 
11 1920 .438 
.601 
1918 .387 
.539 
1904 .409 
.576 
(-12) 
(-10) (-7) 
(-4) 
12 1923 .399 
.554 
1916 .403 
.551 
1906 .377 
.532 
(+1) 
(-1) (-6) 
(-4) 
13 1885 .503 
.704 
1877 .437 
.628 
1876 .409 
.587 
(-13) 
(-11) (-19) 
(-17) 
14 1866 .470 
.656 
1855 .445 
.623 
1853 .442 
.630 
(-5) 
(-5) (-6) 
(-4) 
15 1868 .459 
.659 
1859 .416 
.612 
1860 .420 
.612 
(-9) 
(-7) (-8) 
(-7) 
16 1924 .435 
.612 
1912 .377 
.529 
1908 .363 
.514 
(-13) 
(-14) (-17) 
(-16) 
17 1937 .420 
.596 
1930 .359 
.492 
1918 .356 
.485 
(-15) 
(-17) (-15) 
(-19) 
18 1911 .361 
.519 
1902 .361 
.526 
1895 .343 
.486 
(0) (+1) (-5) 
(-6) 
Ave. S.S. 
1904 .436 
.613 
1896 .398 
.563 
1890 .390 
.553 
Props. (-9) 
(-8) (.11) 
(-10) 
Epstein 
1913 .425 
.557 
1905 .390 
.548 
1901 .376 
.528 
Pack Test (-8) 
(-2) (-12) 
(-5) 
on above 
8 strips 
__________________________________________________________________________ 
In the phosphorus attack resulting from the vapor state, any pores, cracks 
or defects in the surface of the forsterite coating afforded no 
significant degree of access for the phosphorus to the iron and thus 
eliminated the random dispersion of iron phosphide nodules, whereas for 
the surface migration type, the pores, cracks or defects in the forsterite 
base coating provided paths to the underlying silicon steel when the 
phosphides were generated on the surface. 
Example IV 
By way of further examples, additional tests were performed to demonstrate 
that prior to annealing the exposed steel to reduce the phosphorus 
environment, the exposed steel does not have to be subject to plastic 
deformation or thermal stresses in order to result in the improved core 
loss values. Each sample of steel having composition described above was 
prepared in a manner similar to that in Example I to provide a 9-mil gauge 
material but treated under the experimental conditions described in Table 
VI. Instead of using mechanical means to remove portions of the base 
coating and form the grooved patterns, either laser or electron beam 
techniques were used. To assure that any effects resulting from the laser 
and electron beam and providing thermal stresses to the steel which could 
affect magnetic properties, an intermediate anneal at 1500.degree. F. 
(816.degree. C.) in nitrogen was performed. All of the magnetic properties 
are single strip Epstein results. 
TABLE VI 
__________________________________________________________________________ 
Phosphorus-striped 
Initial Properties 
S.R.A. at 1500.degree. F./Nitrogen 
4 hrs. @ 1650.degree. F. 
Perme- 
Core Loss Core Loss Perme- 
Core Loss 
Sample ability 
@1.3T 
@1.5T 
@1.7T 
Permeability 
@1.3T 
@1.5T 
@1.7T 
ability 
@1.3T 
@1.5T 
@1.7T 
No. .mu.10H 
(wpp) 
(wpp) 
(wpp) 
.mu.10H 
(wpp) 
(wpp) 
(wpp) 
.mu.10H 
(wpp) 
(wpp) 
(wpp) 
__________________________________________________________________________ 
LASER 
LP-15-7 1909 
N.D. 
.402 
.563 
1909 .293 
.401 
.568 
1900 
.278 
.375 .528 
-- (0) (+1%) (-7%) 
(-7%) 
ELECTRON BEAM 
H-16 1919 
N.D. 
.388 
.531 
1919 .271 
.380 
.526 
1898 
.260 
.350 .489 
-- (-2%) 
(-1%) -- (-10%) 
(-8%) 
__________________________________________________________________________ 
The data of Table VI clearly demonstrate an important feature of the 
present invention. The magnetic property benefit through chemical striping 
in accordance with the present invention is in no way dependent on prior 
magnetic benefits attained through any technique used for removing the 
base coating, i.e., either through mechanical, plastic, or thermal 
stresses. As a result, the advantage of the present invention is that any 
convenient method of exposing the bare metal stripes can be used. Any 
effect on magnetic properties as a result of the metal striping step is 
both incidental and temporary with respect to the subsequent heat 
treatment in which the chemical striping by the phosphorus intrusion can 
affect properties. Although there is no intent to be bound by theory, it 
appears that when phosphorus is used as the main contaminant, there 
results a massive attack resulting from the formation and crowding of 
wedge-shaped particles into the matrix of the underlying steel body. 
As was an object of the present invention, a method has been developed for 
effecting domain refinement of electrical steels which is heat resistant. 
Furthermore, the method has more universal application in that numerous 
conventional or convenient techniques may be used for removing the 
naturally-occurring forsterite base coating on the final texture annealed 
silicon steel. 
Although a preferred and alternative embodiments have been described, it 
would be apparent to one skilled in the art that changes can be made 
therein without departing from the scope of the invention.