JPS5942750B2 - Method for producing electrically insulating glass film on silicon steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of cube-on-edge silicon steel strip or sheet material with very high magnetic permeability (greater than 1850 at 796 A/m), and more particularly to the production of cube-on-edge silicon steel strip or sheet materials with very high magnetic permeability (greater than 1850 at 796 A/m) The present invention relates to a method of providing a strip or sheet material having an electrically pure glass membrane.

The method of the present invention includes adjusting the amount of boron in the magnesia annealing separator composition relative to the particle size distribution, citric acid activity (described below), and surface area of the magnesia, thereby creating a cube-on-edge composition. Improved core loss properties and improved glass film formation are obtained in the manufacture of silicon steel strip and sheet materials having a structure, while at the same time retaining very high magnetic permeability. The manufacture of silicon steel strip or sheet material with very high magnetic permeability is described in US Pat. Nos. 3,873,381 and 3,855,019.
It is disclosed in the specification of No.

No. 3,873,381 adds critical amounts of boron and nitrogen to the silicon steel melt, along with conventional manganese and sulfur (or selenium) additions to obtain very high magnetic permeability. No. 385
No. 5019 discloses the addition of copper to silicon steel melts in which aluminum nitride is likewise present as a primary grain growth inhibitor in order to obtain improved permeability values. Matsumoto et al., U.S. Pat. No. 3,676,227, 1972.・7.11 issue (transferred to Nippon Steel Corporation) contains less than 4% silicon and 0.010 to 0.0
A process for making a cube-on-edge silicon steel containing 65% acid-soluble aluminum, having very high magnetic permeability and "low core loss" is disclosed, which involves cold rolling and removing an annealed separator composition. The method includes coating the surface of a carbonized silicon steel material, drying the separator composition, and subjecting the material to a final anneal in hydrogen or nitrogen for at least 5 hours at a temperature of about 1000°C.

The annealing separator may be magnesium oxide, calcium oxide, aluminum oxide, titanium dioxide, or mixtures thereof, with a weight of 0.01 to 1.0% based on the amount of annealing separator. Contains boron or boron compounds. U.S. Pat. No. 3,700,506 discloses the addition of boron compounds to magnetic mallet compositions which also contain titanium, manganese and sulfur for use on silicon steel containing aluminum nitride.

The addition of boron compounds to magnesium oxide annealing separator compositions is also described in British Patent No. 13985.
No. 04; U.S. Patent Nos. 3,583,887 and 3,841,925, assigned to Molton Norpitch Products, Inc.; U.S. Patent No. 3,697,322, assigned to Talc Corporation;
No. 3785879, No. 3932202, No. 3941
No. 621 and No. 3,945,862; and U.S. Pat.
No. 10050.

Many of the above patents are based on the addition of boron compounds to 796A/
The present invention relates to the formation of electrically insulating glass films and the improvement of blanklin resistivity in silicon steel materials having magnetic permeability of less than 1850 m.

Such materials usually do not contain significant amounts of acid-soluble aluminum and are therefore not relevant to similar techniques required for very high magnetic permeability (ie greater than 1850 at 796 A/m) materials for reasons discussed below. The physical properties of the glass film and the final silicon steel in the manufacture of a material in which Japanese magnesia containing approximately 0.08% boron based on the weight of the magnesia is arranged in a very high permeability cube-on-edge material. It has been found that glass-coated silicon steels can be produced that are superior both in terms of the magnetic properties of the material.

However, it was found that it was not possible to reproduce these results with other sources of magnesia doped with the same amount of boron and to obtain consistently high magnetic permeability, low iron loss, and good glass film properties. Studies have shown that variations in magnesia's sodium, calcium and chloride content have little effect. On the other hand, it was observed that variations in citric acid activity and surface area had a significant effect. Despite this knowledge that hydration rate and surface area influence the performance of magnesia, specifying a specific citric acid activity and surface area range still does not work uniformly, especially for different market sources of magnesia. It was observed that reproducible results could not be obtained.

It has been observed that even with different patches of magnesia from the same commercial source, certain or other difficulties arise despite the values of citric acid activity and surface area that should be optimal according to the prior art. Considering the above background, market source magnesia has approximately 0.
It is clear that attempts to improve the magnetic properties of highly permeable silicon steels by adding 0.8% boron have been at best only occasionally successful, and performance has been unpredictable.

The main object of the present invention is to provide a method for solving the above-mentioned problems in the production of silicon steels with very high magnetic permeability according to any of the above-mentioned US patents. Simply put,
The boron added to the magnesia coating is volatile at the final high annealing temperature (at or near 1200°C), with some of the boron diffusing into the interior through the surface of the silicon steel material and the rest being an ineffective annealing temperature. Anonymous atmosphere - known to escape inside.

It has now been found that the amount of boron volatilized into the annealing atmosphere is a direct function of the bulk density or packing factor of the dry magnesia coating. (It will be appreciated that the coating may be applied as an aqueous slurry by any conventional method such as dipping, spraying, conditioning rolls, etc. and then dried at relatively low temperatures.) Bulk density or packing factor is also directly dependent on the particle size distribution and degree of hydration of the magnesia. Although the citric acid activity of magnesia can be controlled, at least within wide limits, when produced industrially in large quantities, the particle size distribution depends on the particular manufacturing process and cannot be easily changed by the industrial producer.

From this, the novel concept of the present invention is to compensate for different particle size distributions by adjusting the boron loading in relation to particle size distribution, surface area and citric acid activity. I=*pu:
Adjusted inversely to the I-[meg factor. Due to the thinness of the dried coating and the relatively rough surface of the silicon steel material, the bulk density of the dried coating cannot be measured with currently available equipment or techniques.

The addition of boron is therefore tailored to the three parameters that most directly affect bulk density: particle size distribution, surface area, and degree of hydration as determined by citric acid activity. It has been found that good adhesion of dry magnesia coatings on silicon steel surfaces usually results in coatings with high bulk densities and therefore requires the addition of relatively small amounts of boron.

It has further been recognized that the stiffness or tension in the winding of the coil during the final high temperature anneal can affect the amount of boric acid required.

Loose overlap or entrainment allows more boron to escape into the annealing atmosphere. It will be seen that the formation of magnesium hydroxide in conjunction with hydration reduces the density and changes the morphology of the original Mgnesia particles.

Water of hydration is not removed by the relatively low heat used in drying the coating. However, this water is removed by heating to a higher sludge, such as occurs in a high-mix final annealing, thus increasing the porosity of the magnesia coating. This is why the degree of hydration directly affects bulk density. Regarding the influence of particle size distribution on packing or bulk density, see Introduction to Ceramics (NtrOduct) by David Kinzieri.
iOntOCeramics)], J. WileyaS
Ons, Ine. (1960), Figures 3 and 2 may be referred to.

It is shown therein that a composition containing approximately 70% coarse material provides a minimum porosity. According to the invention, after a final high-temperature annealing in a reducing atmosphere, the
A method is provided for improving the core loss properties of cube-on-edge disposed silicon steel strip and sheet materials having a magnetic permeability greater than 50, the method comprising adding a boron compound to an aqueous magnesia slurry, and adding a boron compound to an aqueous magnesia slurry. applying it to the surface of the material and drying the coating so applied before final annealing, the boron compound being between 0.07 and 0.30% based on the weight of the magnesia.
is added to give an umbrella boron content inversely proportional to the bulk density of the dry coating within a range of A certain amount of boron diffuses into the interior through the magnesia coating.

Referring to the accompanying drawings, FIG. 1 is a graph showing the particle size distribution of magnesia from the first source of the prior art, FIG. 2 is a graph showing the particle size distribution of magnesia from the second source, and FIG. 3 is a graph showing the particle size distribution of magnesia from the third source. 2 is a graph showing the particle size distribution of magnesia.

The preferred method of the present invention for producing silicon steel strip and sheet materials having a magnetic permeability greater than 1850 at 796 A/m after final high temperature annealing includes 2-4% silicon, 0.01-0.15% manganese. , 0.002~
0.005% carbon, 0.01-0.03% sulfur, 0
．． Cold rolled decarburized silicon steel strip containing up to 0.010% boron, 0.005-0.010% nitrogen, 0.010-0.065% acid-soluble aluminum, and the balance iron and incidental impurities. and preparing a sheet material, magnesium oxide, at least one boron compound,
and by applying an aqueous slurry containing up to 20% titanium dioxide by weight of magnesium oxide to the surface of the material and heating it to a temperature sufficient to cause the water to evaporate and leave a dry coating on the surface. Dry the coated slurry and dry the coated material in a non-oxidizing atmosphere for approximately 1 hour.
annealing at a temperature of 095 to 1260°C to form an insulating film and developing a cube-on-edge structure by secondary recrystallization, in which the boron compound in slurry 1 is The particle size distribution, surface area and citric acid activity of the magnesium oxide are adjusted to provide a total boron content of 0.07-0.30% by weight based on the weight of the magnesium oxide.

The method of the present invention forms a thin continuous glass film that improves core loss characteristics while preserving the very high magnetic permeability of the material. It will be appreciated that a thin continuous glass film is advantageous in promoting improved magnetic properties, good space factor, good magnetostriction and good adhesion.

Furthermore, when applying a second coating such as that disclosed in Evans U.S. Pat. Must be thin and continuous. The thickness of a dried Negnesia coating cannot be accurately measured for reasons similar to those discussed above with respect to measuring the bulk density of the coating. Therefore, the coverage of the dried coating is used for control purposes and the dry coating forming a continuous thin glass film with the advantageous properties mentioned above is applied to magnesia with a citric acid activity greater than 50 seconds. .3~1
5.65f! /Tll dry coverage. Cold rolled decarburized silicon steel strip and sheet stock may be produced by conventional methods in which a suitable melt is cast as an ingot or continuously cast in slab form.

If cast into ingots, the steel is conventionally bloomed into slabs and the slabs are hot rolled to medium thickness at a vorticity of about 1260 DEG to 1400 DEG C. and annealed after hot rolling.
The hot mill scale is then removed and the material is cold rolled in one or more stages to final gauge and then decarburized in a hydrogen atmosphere. If the steel is continuously cast into a slab shape with a columnar grain structure, Littmann's U.S. Pat.
Preferably, the method disclosed in No. 64406 is followed.

In this method, a continuously cast slab having a thickness of about 10-30 CWL is heated to a temperature of 750-1250°C, initially before reheating the slab to a temperature of 1260-1400°C for conventional hot rolling. Hot rolling with a thickness reduction of 5-50%. Hot rolling, annealing, cold rolling and decarburization are then carried out as described above. The cold-rolled and decarburized material is then coated with an aqueous magnesia slurry by dipping, spraying, or conditioning rolls and dried by heating to a depth of approximately 200 to 300°C to a depth of 6.3 to 15.69/m. The coated strip or sheet material is then subjected to a final high temperature annealing, which may be a box annealing or an open coil annealing. A convenient aqueous slurry concentration is When using conditioning rolls, 0.096 to 0.1929 magnesia per ml of water and up to 20%, preferably about 5%, titanium dioxide, based on the weight of magnesia, may be added to the slurry. Known methods. A final high temperature annealing in which a cube-on-edge structure is produced by secondary recrystallization in a reducing atmosphere is
It is carried out at 1260°C.

It will be appreciated that the magnesia reacts with the silicon in the steel during this annealing to form a glass film. The heating section of the final annealing is preferably carried out in a nitrogen-hydrogen atmosphere to optimize the formation of nitrides used as grain growth inhibitors. The final part of the annealing involves soaking and cooling and is preferably carried out in hydrogen as refining of steel is known to aid secondary recrystallization. It was found that the type of boron compound and the time of addition are not particularly important.

Thus, boric acid, calcium borate or other commonly available boron compounds may be used. These compounds may be added to the magnesia before or during treatment, or after forming an aqueous slurry. Also, a boron F5 compound can be applied to the strip surface before the magnesia slurry is applied to the strip surface. Therefore, the term "adding a boron compound to an aqueous magnesia slurry" used in this specification is used broadly to cover the addition or coating of a boron compound at any stage before coating the slurry on the surface of a silicon steel material. Referring to FIG. 1, the particle size distribution of magnesia from a first source is illustrated.

It will be noticed that two peaks or peaks occur where the particles are about 10% between 5 and 10 microns and about 22% between 0.8 and 2 microns. Does magnesia from this source typically weigh? The particle size distribution of the type illustrated in FIG. 1 is similar to the two-component system shown in FIGS. 3 and 2 of the above-mentioned "Introduction to Ceramics".

The magnesia of FIG. 1 therefore produces a relatively dense dry coating. From this source magnesia with a citric acid activity greater than 50 seconds can be obtained. Nominal 0.0
It was found that an addition of 8% boron gave excellent results. FIG. 2 shows the particle size distribution of magnesia from a second source, with some spread in particle size between larger and smaller particles.

However, there is a large amount below 1 micron. A typical particle size distribution for this source is as follows: magnesia of the type shown in FIG. 2 produces a less dense dry coating than the magnesia of FIG.

Therefore, when the particle size distribution is 75-90% below 1 micron, approximately 0.0
．． 10-0.15% boron is required for magnesia of the type in Figure 2 with citric acid activity greater than 50 seconds. Magnesia from this source has a citric acid activity of about 55 to 120.
Even if it's a second, it's fine (G). FIG. 3 shows the particle size distribution of magnesia from the third source.

It will be noticed that there is very little spread into larger and smaller particle sizes and a large amount within the 2-5 micron size range. A typical particle size distribution of magnesia from this source is as follows: The bulk density of the dry coating of magnesia shown in FIG. 3 was observed to be relatively low, less than that of both FIGS. 1 and 2.

Therefore, the boron content of about 0.15-0.20% is greater than 50 seconds to compensate for the boron loss into the annealing atmosphere when the particle size distribution is 80-90% in 2-5 microns. It was found that citric acid is necessary along with citric acid activity. Magnesia from this source has a citric acid activity of about 60~
It may be 200 seconds. Although less critical than citric acid activity and particle size distribution, magnesia surface area is still important in controlling magnesia activity or hydration rate.

Very fine materials have a large surface area and hydrate very quickly;
As mentioned above, it tends to have an undesirable effect on the bulk density of the dried coating. Materials that are too coarse in grain size and have very little surface area tend to settle out of the aqueous slurry and do not readily proceed to react with the silica to form a thin continuous glass film during the final high temperature anneal.
It has been found that a surface area of about 10-20w1/9 gives excellent results in combination with the other parameters of the invention. The silicon steel compositions described above are commonly used and have been found to be optimal for obtaining optimum magnetic properties.

The presence of manganese sulfide and aluminum nitride within the indicated ranges is necessary for preferential grain growth during the final high temperature anneal, which may have a total duration of about 8 to 30 hours. Although not required, J.M. Jack
Boron may be added to the silicon steel melt along with a significant amount of nitrogen according to the teachings of U.S. Pat. These additions of boron and nitrogen to the steel melt are to control grain growth during the primary grain growth stage of the final anneal. Also, U.S. Patent No. 3700
No. 506 discloses adding a boron compound to a magnetic separator composition, which composition also contains aluminum nitride as a primary grain growth inhibitor during final annealing in silicon steel. Contains titanium, manganese, and sulfur or selenium to suppress the growth of secondary crystal grains.

The presence of aluminum in silicon steel results in the formation of small amounts of aluminum oxide on the surface of silicon steel, which makes it more difficult to form a thin, coherent, continuous glass film.

However, the addition of about 5-20% titanium dioxide minimizes this difficulty. A series of tests were conducted, all of which were cold-rolled and decarburized silicon steel strip stock, with approximately 2 to 4
% silicon, about 0.01-0.15% manganese, about 0
．． 0.002-0.005% carbon, approximately 0.01-0.03
? of sulfur, about 0.005-0.010% nitrogen, about 0.00% nitrogen.
0.010-0.065% acid soluble aluminum, approx.
It has a composition of up to 0.01.0% boron and the balance iron and associated impurities.

Magnesia from the first source (Figure 1) was used as a standard of comparison for all tests.

This is because it has been successfully used for several years with a nominal boron content of about 0.08% (total). Trial 1 trial data are shown in the table.

Table 1 contains the origin indication, citric acid activity, surface area, coverage (dry coating) and boron content of the various samples. It will be understood that the source designation refers to the source shown in Figures 1-3 for the particle size distribution. Table H summarizes the magnetic properties of the coated and annealed coils of the samples in Table 1.

All values shown in the table represent the average of front and rear specimens of coils modified to a thickness of 11.6 mils. All magnesia coating slurries contained 5% titanium dioxide, based on the weight of magnesia, and slurry concentrations ranged from 0.085 to 0.1219 parts magnesia per part water. Citric acid activity is a measure of the rate of hydration of magnesium oxide and is determined by measuring the time required for a required weight of magnesia to provide hydroxyl ions that neutralize a required weight of citric acid.

The test is identical to the test shown in US Pat. No. 3,841,925. Namely: 100 ml of 0.400N aqueous citric acid containing 2 ml of 1.1% phenolpthalene indicator is brought to 30° C. in an 8 oz jar.

The bottle is equipped with a screw cap and a magnetic stirring bar. 2.2.
Pour 009 magnesia into the bottle and start the stopwatch at the same time.

3. Cap the jar immediately after adding the magnesia sample.

At 5 seconds, shake the bottle and contents vigorously.

Shaking ends at 10 seconds. 4. Place the sample on the magnetic stirrer at 10 seconds.

For mechanical stirring, the inner diameter of the bottle is 6c! At the time of RL, a vortex with a depth of about 2 cIn must be generated at the center of the width. 5. Stop the stopwatch when the suspension turns light pink and record the time.

This time in seconds is the citric acid activity. It is clear that lower values represent relatively active magnesia, ie, rapidly hydrating magnesia.

Although the rate of hydration is more important than the degree of terminal hydration, a fast rate also usually indicates a high degree of hydration at equilibrium. Sample B from Source 2 showed no problems with the coating.

The slurry wetted the strip and produced a smooth, even coating on both sides. Hydration of the magnesia in the aqueous slurry did not occur quickly and the adhesion of the dried coating was good. The magnetic properties were comparable to its control sample A from source 1, thus indicating that a boron content of 0.12% was close to optimum for sample B. Sample D from source 3 also contained 0.12% boron and likewise did not cause coating problems. Although the slurry wetted both surfaces well and produced an excellent dry coating, the adhesion of the dried coating was fair rather than good. After final annealing, the glass film had a smooth, continuous appearance and a light gray color. However, the iron loss of sample D does not exhibit the value of its control sample C from Source 1, and the difference of 0.047 Watts/K9 appears to be significant. The magnetic permeability was also somewhat lower than Control Sample C. Therefore, the optimal boron content for sample D is 0.12? is clearly larger than that of boron. Samples F and C from source 2 are 7.6 and 20.8 respectively! ! 0.07 coated with two different coating amounts of /m'? It was the same magnesia containing boron. These indicate that coverage is a variable that can influence the final magnetic properties. The low coverage of Sample F resulted in a thin, discontinuous glass film containing only a few small sulfide particles. The thicker glass film of Sample G contained many large sulfide particles, and the silica particles on the inner surface were large and relatively few in number. However, both samples F and G did not exhibit the values of their control sample E (from Source 1) in core loss values or magnetic permeability. This is 0
．． It was shown that the boron level of 0.7% was not sufficient. Laboratory evaluation of some magnesia from a second source with the particle size distribution of Figure 2 showed variations in magnetic properties (at some citric acid activity values) as a function of boron content. These values are summarized in a table. 1st
Magnesia from the first source (Sample H, Source 1) was used as a control for Samples J and K, and another batch of magnesia from the first source (Sample L) was used as a control for Samples M-R. The data in the table (average corrected to 11.6 mil gauge) indicate that the 0.08% boron content in sample J (second source) exhibited the magnetic properties of control sample H, but the 0.13% boron content in sample K It shows that substantially better magnetic properties were obtained at boron levels.

Samples M and P showed that the boron level of 0.077% was not sufficient to exhibit the magnetic properties of the control (sample L), and that the boron level of 0.077% was
．． It shows that a boron level of 1-0.12% is required. However, samples N and O (C.A.A. 80 seconds) and sample Q
and R (C.A.A. 36 seconds) shows that the higher the citric acid activity, the less boron is required to exhibit the magnetic properties of the control. Furthermore, in the case of samples N and O.
Better core loss was obtained at a boron level of 0.1% than at 12%. This shows that for a given citric acid activity and particle size distribution, this is the optimum range and that boron content less or more than the optimum has a negative effect on the magnetic properties. Therefore, a boron range of 0.10-0.30% is considered to be critical, and this further adds to the secondary source magnesia with a citric acid activity of 72 seconds, each based on the weight of the magnesia. .03%, 0.08%, 0
．． This is demonstrated by laboratory evaluations performed with boron additions in amounts of 15%, 0.20%, 0.25% and 0.30%.

The optimal boron range for the above sample is 0.08-020%
It is clear that it was.

In addition to magnetic properties, a number of other factors are important in forming electrically insulating glass films.

These include the viscosity of the magnesia slurry, the wettability of the material surface with the aqueous slurry, the adhesion of the dry coating, and the thickness, smoothness, and physical appearance of the glass film. The viscosity is usually 0.096 to 0.192 magnesia per η of water.
There is no problem with the slurry concentration of g as long as the hydration rate is not high.

Under these conditions the degree of heat gradually increases during the running process as the magnesia gradually hydrates to a greater degree.
This results in excessive ignition loss of the dried coating and undesirably thick glass films. This can be avoided in the practice of the invention by ensuring a citric acid activity greater than 50 seconds, which will significantly reduce the hydration rate. It becomes more difficult to obtain a smooth, uniform, dry magnesia coating when the viscosity increases. Streaks in the coating may occur due to viscosity. The adhesion of the dried coating is clearly a function of porosity, which is also influenced by particle size distribution and citric acid activity. It has been found that if these parameters are controlled according to the invention, the adhesion of the dried coating is satisfactory in all cases. The thickness of the glass film and the reason for controlling it were previously shown.

The control of particle size distribution and citric acid activity according to the present invention will be sufficiently repeatable to produce the desired thin, continuous glass films. Similarly, smoothness of the glass-metal interface is achieved directly or indirectly by controlling these parameters. Regarding the physical appearance of the film, discoloration usually occurs as a result of iron oxide formation. Excess water present in the coating during the final annealing usually results in a porous glass film that does not protect the steel or prevent the formation of iron oxides.
This is also controlled in the practice of this invention by providing citric acid activity greater than 50 seconds and minimizing hydration. In general, typically for magnesias having a particle size distribution as illustrated in FIG. A 15% boron addition gives excellent results.

For magnesias with a particle size distribution as typically illustrated in Figure 3 and a citric acid activity of greater than 50 seconds up to about 200 seconds, the
．． Boron additions of 15-0.20% give excellent results. In a general embodiment, the invention provides 1850
Provided is a method for making silicon steel strip or sheet material having greater magnetic permeability, the method comprising cold rolling containing about 2-4% silicon and about 0.01-0.065% acid-soluble aluminum. , prepare decarburized silicon steel strip and sheet materials, and coat the surface of the materials with magnesium oxide,
At least one boron compound and 20% by weight? The applied slurry is dried to form a dry coating, and the coated material is subjected to a final high temperature annealing to form a glass film. The total boron content is based on the weight of the magnesium oxide depending on the particle size distribution of the magnesium oxide and the citric acid activity. It is adjusted within approximately 0.07-0.3% by weight, thereby improving the core loss properties and at the same time obtaining a very high magnetic permeability in the material.

Preferably the final high temperature annealing is about 1095-1260
C. for up to about 30 hours in a reducing atmosphere.

Preferred silicon steel compositions, in their cold rolled, decarburized state, contain substantially from about 2 to 4% silicon by weight, about 0.01% by weight.
~0.15% manganese, approximately 0.002-0.005%
of carbon, about 0.01-0.03% sulfur, about 0.005
Consisting of ~0,010% nitrogen, approximately 0.010-0,065% acid soluble aluminum and the balance iron and incidental impurities. The embodiments of the present invention are as follows. 1. Claims 1 or 2, wherein the slurry is coated at a rate giving a dry coverage of 6.3 to 15.659/M°, and the citric acid activity of the magnesium oxide is greater than 50 seconds. Method described.

2. The citric acid activity of the magnesium oxide is greater than 50 seconds and up to 120 seconds, and the particle size distribution is 1, 4-,
, 81 c: Claim 1 in which boron is added in an amount of 0.10 to 0.15% based on the weight of magnesium oxide.
or the method described in paragraph 2.

3. When the citric acid activity of the magnesium oxide is greater than 50 seconds and up to 200 seconds, and its particle size distribution is, the boron content is 0.15% based on the weight of the magnesium oxide.
Claim 1 or 2 added by ~0.25%
The method described in section.

4. Claim 1 or 2, wherein the slurry contains 5 to 20% titanium dioxide based on the weight of magnesia.
The method described in section.

[Brief explanation of the drawing]

Figure 1. , 2 and 3 are graphs showing typical particle size distribution examples of magnesia from the first, second and third sources, respectively.

Claims (1)

[Claims] 1. 796A after the final high temperature annealing in a reducing atmosphere
In order to improve the core loss properties of cube gun edge oriented silicon steel strip and sheet materials having magnetic permeabilities greater than 1850 at /m, boron compounds are added to an aqueous magnesia slurry and the slurry is applied to the surface of the material. applying and drying the applied coating before said final annealing, wherein said boron compound is 0.07 to 0.30 based on the weight of magnesia.
% to give a total boron content inversely proportional to the bulk density of the dry coating, so that the final annealing is independent of the amount of boron that volatilizes from the coating into the annealing atmosphere. A method for improving iron loss characteristics, characterized in that a certain amount of boron between the holes diffuses into the interior through the magnesia coating. 2. The slurry contains up to 20% by weight of titanium dioxide based on the weight of magnesium oxide, and the neuron compound is adjusted by any two of particle size distribution, citric acid activity, and surface area. The manufacturing method according to claim 1. 3. The silicon steel strip material contains substantially 2-4% silicon, 0.01-0.15% manganese, 0.002-4% silicon, 0.01-0.15% manganese,
0.005% carbon, 0.01-0.03% sulfur, 0
．． 005-0.010% nitrogen, 0.10-0.065
% acid soluble aluminum and the balance iron and incidental impurities. 4 The citric acid activity is greater than 50 seconds and up to 120 seconds, and the particle size distribution of magnesium oxide is less than 1 micron.
3. A method according to claim 1 or 2, wherein boron is added in an amount of 0.01 to 0.15% based on the weight of the magnesium oxide when the amount is 5 to 90%. 5 The citric acid activity is greater than 50 seconds and up to 200 seconds, and the particle size distribution of magnesium oxide is 2 to 5 microns.
3. A method according to claim 1 or claim 2, wherein boron is added in an amount of 0.15 to 0.20%, based on the weight of the magnesium oxide, when it is 0 to 90%. 6 The surface area of the magnesium is 10 to 20 m^2/g
The method according to claim 1.