KR820000675B1 - Boron -containing electrical steel having a calcium borate coating and magnesia over coating and process therefor - Google Patents

Abstract

Grain-oriented B-containing Si steel sheets with improved magnetic properties are produced by electrodeposition of Ca(BO2)2 onto fine-grained primary recrystd. Si steel using an aq. electrolyte at >=65≰C and pH 7 contg. Ca(AcO)2 boric acid, and solid Ca(BO2)2 followed by electrodeposition of Mg(OH)2 using an aq. electrolyte contg. MgO-buffered Mg(AcO)2 and heating the duplex-coated sheet to develop secondary recrystn. texture in the Si steel.

Description

Coating method of silicon iron plate

1 is a perspective view of a silicon iron plate coated by the method of the first embodiment of the present invention.

2 is a perspective view of a silicon iron plate coated by the method of the second embodiment of the present invention.

3 is a perspective view of a silicon iron plate coated by the method of the third embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for electric steel, and more particularly, to a coating method for electrically welding a film having electrical insulation to a boron-containing silicon iron plate.

Grenoble can effectively promote secondary recrystallization reactions during annealing to form the final tissue by containing boron in the siliceous iron in small amounts and in proportional amounts relative to nitrogen (as described in US Pat. No. 3,905,842). Following the discovery, Mochion can promote secondary recrystallization by adding very small amounts of boron to the coating of these boron-containing steels and still improve the magnetic properties of the final product (see US Patent 677,147). Found). Mozion also found that secondary recrystallization reactions can occur even when boron is not contained by incorporating boron into the coating, and when boron is not contained in the metal itself, it is final to include boron in the insulating coating. It was found that it did not affect the occurrence or promotion of secondary recrystallization reactions early in the annealing.

Until now, brushing boron compound solution suitable for the refractory oxide film which is magnesium hydroxide [M (OH) ₂ ] always according to the method of Macquard-U.S. Patent No. 3,054,732 in carrying out the teaching of Mochion. Or boron has been incorporated into the refractory oxide film through spraying or dipping operations.

According to the present invention to be described later, it was found that it is possible to deposit an electrically insulating film containing boron on the boron-containing electric steel.

This welding according to the invention provides a number of important advantages. One of the advantages is that the final product is very different from the products obtained by the soaking, spraying and brushing processes, but has substantially the same properties as the surface of the film produced by the Macquard method. In particular, the coated article of the present invention is characterized in that such an electrical steel does not tend to peel off or split when the sheet or strip is processed into a sheet or coil form and is stacked in a continuous layer and moved in sliding contact with each other. The manufacturing process required for commercial use of the material can be performed.

Another advantage of the present invention is that according to the present invention, the amount of boron contained in the insulating film can be better controlled and the boron can be uniformly annealed throughout the film.

Another advantage of the present invention is to limit the boron content of the film to a somewhat lower rate to prevent premature departure of boron from the silicon iron plate during the final annealing process and to eliminate the adverse effects caused by excessive boron in the final product. It can be done. Another advantage of the present invention is that by providing a sulfur getter on the insulating film itself, it is possible to further increase the magnetism of the final plate.

According to the first embodiment of the present invention, it is possible to electrolytically co-weld boron and magnesium oxide under certain specific conditions. This simultaneous deposition of Mg (OH) ₂ and boron-containing compounds similar to well-mixed mixtures or solid solutions allows for more uniform distribution of boron in the coating than conventional soaking, brushing and spraying methods. In addition, the amount of boron contained in Mg (OH) ₂ can be more precisely controlled in that the boron content of the electrolyte solution used in the present method can be easily adjusted.

According to the first embodiment of the present invention, a solution of magnesium metaborate and magnesium acetate containing magnesia dispersed in the second solid phase can be electrolyzed to provide a uniformly distributed coating on the silicon iron of the negative electrode in the required amount. Is based on This co-welding method is also based on the fact that a satisfactory film is provided only when the temperature of the electrolyte is maintained above about 65 ° C. during the co-welding period. In addition, it was found that a new electrolyte solution as described above can be prepared by adding an appropriate amount of boron in the form of boronic acid to a magnesium acetate solution containing a second solid magnesia. In addition, bromine or other suitable sources of boron (such as boron-containing magnesia or magnesium metaborate of solid solution) in the electrolyte may be used to maintain the magnesium metaborate content of the electrolyte in the required amount so as to deposit a coating containing boron in the required amount. It was found that the continuous process can be achieved by adding the same) continuously or discontinuously.

Further, according to the second embodiment of the present invention, while providing the advantages of the first embodiment, it is possible to prevent premature departure of boron from the silicon iron plate during the final annealing and to exclude the adverse effects caused by excessive inclusion in the final product. It is possible to achieve the purpose of limiting the boron content of the film to a rather low rate. In particular, in this regard, it has been found that it is possible to provide boron in the form of a relatively thin first layer or a first film, which is necessary to adhere to a metal substrate during final annealing and prevent the boron from detaching too easily. Also, by providing a rather thick second coating containing little or no boron, it can be seen that the boron of the first coating can be held close enough to the metal surface to sufficiently form the secondary recrystallized structure required for the silicon iron sheet. Found. As a result, the demand for boron concentration and the demand for boron content of the coating are met.

Although the total thickness of the double or combined coating of the present invention is not critically important for obtaining new results, the first coating containing boron is thick enough to provide the required amount of boron required for boron release prevention purposes. I found it important to do. As a result, the thinner the first film is, the better, and the thickness should be about 0.07 mil or less because boron has very limited fluidity under relatively low temperature at the time of final annealing.

Besides, it is also possible to provide the second film by using a method other than the electrolytic method, but it is not suitable for the actual manufacturing process because of the problems in the subsequent processing steps as described above. It was also found that Mg (OH) ₂ is selected for this purpose, but other refractory oxides as described in Macquard's U.S. Patent No. 3,054,732 can also be used.

In addition, according to the third embodiment of the present invention, in addition to the above-described embodiments are provided with advantages, the final plate by providing the first film of the second embodiment as calcium metaborate to act as an inductor in the silicon iron substrate It has been found that an advantage is provided to increase the magnetism of the person. In particular, at least 65 ℃ preferably solid calcium at a temperature of about 95 ℃ at a temperature of metaborate Ca (BO ₂₎ using a homogeneous solution in which calcium acetate and boric acid buffer with ₂ calcium metaborate by Ca (BO _{2) 2} It was found that the coating can be electrolytically coated.

As in the case of the embodiments described above, the calcium metaborate Ca (BO ₂₎ The first film of the _second are the final annealing gives to effectively prevent the boron departure from a silicon steel plate during, and the Ca (BO _{2) 2} By providing a second film of Mg (OH) ₂ , it is possible to keep the boron close to the plate at the beginning of final annealing even if the second film itself contains little or no boron. Thus, the boron necessary for the secondary recrystallization of silicon during tissue formation annealing will not be thick enough to provide the required insulation, or contain boron that will adversely affect the magnetism of the final silicon plate product. Will be retained in the metal without.

In addition, it was found that the first film according to the third embodiment of the present invention effectively works to getter phosphorus in the silicon iron substrate, thereby increasing the magnetic properties of the final plate.

In addition, in the case of the third embodiment of the present invention, it was found that satisfactory coating can be coated only when the electrolyte is maintained at a temperature of 65 ° C. or higher, and preferably at a temperature of about 90 to 95 ° C. during the welding process.

According to one feature of the first embodiment of the present invention, there is provided a silicon iron plate material, which is boron-containing electrical steel, and the silicon iron plate material is immersed in an aqueous solution of magnesium methborate and magnesium acetate having a pH of 8.0 to 9.0 with a cathode, followed by Electrolytic coating containing boron on the sheet by electrolysis while maintaining it at a temperature of about 65 ° C., and finally heat-treating the coated sheet to form a (110) [001] secondary recrystallized structure on the silicon iron sheet. A method is provided.

In addition, according to another feature of the first embodiment of the present invention, there is provided a primary recrystallized product coated with magnesia by the above method. In addition, as another feature in the first embodiment of the present invention, a new electrolyte solution containing magnesium solid borate containing a secondary solid magnesia and having a pH of 8.0 to 9.0 and magnesium acetate is used in the method. will be.

In addition, according to one feature of the second embodiment of the present invention, by providing a silicon iron plate of the boron-containing electrical steel, the silicon iron plate of the pH 8.0 to 9.0 buffered with solid MgO as an anode in an aqueous solution of magnesium methaborate and magnesium acetate After immersion, the aqueous solution was electrolyzed while maintaining at a temperature of at least 65 ° C. to coat the plate with a relatively thin, boron-containing electrical insulating film, and the coated plate was essentially composed of magnesium acetate and buffered with MgO. After immersing with a cathode in an electrolytic solution, the magnesium acetate solution was electrolyzed to coat a thicker boron-containing Mg (OH) ₂ film, and then the double-coated window was finally heat-treated to a (110) [001] secondary film. A method is provided that includes processes for forming a recrystallized structure.

In addition, according to another feature of the second embodiment of the present invention, a double-coated with a first boron-containing film having a thickness of 0.02 to 0.07 mils and a second film having a thickness of about 0.10 to 0.18 mils and generally containing no boron Primary recrystallization products are provided.

Finally, according to one feature of the third embodiment of the present invention, there is provided a silicon iron plate material, a boron-containing electrical steel, the silicon acetate and boronic acid buffered with Ca (BO ₂ ) ₂ pH less than 7.0 After immersing in an aqueous solution of the cathode with a cathode, the aqueous solution was electrolytically maintained at a temperature of at least 65 ° C. to coat a relatively thin electrically insulating Ca (BO ₂ ) ₂ film on the plate, and the coated plate was composed of magnesium acetate and was solid The negative electrode was immersed in an aqueous solution buffered with MgO, followed by electrolysis of the aqueous solution to electro-weld a thicker Mg (OH) ₂ film on the coated plate, and the double coated plate was finally heat treated to a silicon iron plate (110). [001] A method is provided that includes processes for forming a secondary recrystallized structure.

According to still another feature of the third embodiment of the present invention, a primary recrystallized silicon iron plate product which is double coated by the welding process of the above method and contains boron is provided.

Hereinafter, with reference to the accompanying drawings will be described in more detail the present invention.

As shown in FIG. 1, the first embodiment of the present invention uses a boron-containing electrical steel substrate to uniformly coat a film of a suitable refractory material having electrical insulating properties on its substrate and having a substantially uniform distribution of magnesium metaborate. It is achieved by coating in thickness.

As an initial step of the process of the present invention, a molten silicon melt is prepared, cast and hot rolled to a medium thickness to form a substrate metal plate. In the infusion process, the melt has a ratio of 2.2 to 4.5 percent of silicon and manganese to sulfur of less than 2.3. And a predetermined amount of manganese and sulfur, about 3 to 50 ppm of boron, and about 15 to 95 ppm of nitrogen, the ratio of nitrogen to boron being in the range of 1 to 15 parts of nitrogen per boron, It is an incidental impurity of iron and a small amount of carbon, aluminum, copper and oxygen. After the annealing process, the hot band is cold rolled to a final thickness without undergoing an intermediate annealing process or undergoing an intermediate annealing process, followed by decarburization.

The fine recrystallized silicon iron sheet material thus provided is processed to provide the boron-containing coating of the present invention which enables the annealing process to form the final structure. In this process, the above-described findings of the applicant and the method of the present invention for electrolytically co-welding Mg (OH) ₂ and the boron compound source become important. A negative electrode was connected to a circuit as described in U.S. Patent No. 3,054,732 referring to the plate material and immersed in the electrolyte solution of the present invention as described above, so that a uniform thickness (suitably about 0.05 to 0.4 mil, Preferably about 0.2 mil) of Mg (OH) ₂ .XMg (BO ₂ ) ₂ .YH ₂ O film (X is 1 or less and Y is 0 to 15) is coated.

The electrolyte solution used in the present method is preferably prepared by adding boronic acid to a water-soluble magnesium acetate containing magnesia on a secondary dispersed solid. This magnesium acedate solution suitably has a concentration of 0.05 to 1.0 mol, preferably 0.2 mol. In addition, the electrolyte is set to 8.0 to 9.0 in consideration of the fact that the pH contains an excessive amount of magnesia. The amount of boronic acid added is set to be preferably 10 to 70 ppm in the case of silicon iron substrates as described in pending US informative application of US Pat. No. 677,146. At the beginning of the electrolytic co-welding process, the electrolyte is maintained at a temperature of at least about 65 ° C., preferably at a temperature of about 90-95 ° C. and maintained at that temperature for the duration of the co-welding.

As a final process of the first embodiment of the present invention, as the temperature rises to about 50 ° C./1000° C. per hour, the recrystallization reaction is completed and, if desired, up to 1175 ° C. to completely remove residual carbon, sulfur, and nitrogen. The heating process may be performed.

The following describes, by way of example, the method of the first embodiment of the present invention that yields new results as described above. However, the present invention is not limited only to these examples.

[Example 1]

By the method as described in US Pat. No. 3,905,843, an 11 mil silicon iron strip having the following composition was prepared.

The melt having this composition is prepared through a series of hot rolling processes into a plate of medium thickness (about 100 mils), followed by pickling and annealing of the sheet, followed by cold rolling to a thickness of 60 mils, followed by reheating, and then final After cold rolling to thickness, the cold worked plate was decarburized at 800 ° C. for 8 minutes in a hydrogen atmosphere (at room temperature dew point).

The Epsteinstrip formed by cutting the plate was immersed in an electrolyte prepared by adding boronic acid to a slurry of distilled water, magnesium acetate and magnesia. The amount of boronic acid added to the slurry is such that, in the case of silicon steel strips, boron can be contained in the film having a mass density of about 0.0275 ounces per square foot of steel surface as much as 50 ppm. The amount is converted to 0.0070 mol / liter in terms of the concentration in the electrolyte, which can be expressed as 0.4317 liter ^-1 H ₃ BO ₃ as calculated as follows.

M: required mass density of electrolytically coated coating, oz.ft ^-2 (steel)

b: Boron content of the film in the river

G: strip thickness, wheat

If,

, Then

Becomes

Assuming the composition of the film is M _gQ B ₂ O _{3 + Q} ,

C _{B + 2} = boronic acid concentration in electrolyte, mol / liter

C ^o _{Mg + 2} = concentration of magnesium acetate per magnesium in electrolyte, mol / liter

If,

Becomes

0.2 mils of boron-containing Mg (OH) ₂ on the entire surface of the strip by connecting the strip to the electrical circuit as a cathode, applying a voltage of 8 volts through the terminals at a current density of 90 amperes per square foot for 40 seconds of electrolysis. The film was coated.

The strip was removed from the electrolyte and observed to show that a representative Mg (OH) ₂ coating formed according to the method described in Macquard's US Patent No. 3,054,732 was coated, and the coating had a uniform thickness (about 0.2 mil). It was smooth and hard. As a result of the test, the film contained boron which was generally uniformly distributed in an amount very close to 50 ppm as the behavior of Mg (BO ₂ ) ₂ · 1 ₂ H ₂ O in the case of silicon iron substrate. The Franklin insulation values for these samples were made uniform at about 0.2 ampere by annealing at a temperature of about 1175 ° C. for 8 hours in a hydrogen atmosphere.

[Example 2]

In another similar test for the first embodiment of the present invention, the boronic acid concentration of the coating solution or slurry is somewhat higher and the mass density of the electrolytically coated film is only 0.004 oz.fE ² (steel). An 11 mil Epstein strip similar to that of Example 1 was coated by the same method as one. To the slurry was added 0.0604 mol / liter or 3.7337 g / liter of H ₃ BO ₃ calculated as described above. The coated strips were thus not measured for Plancklin insulation and the coating had only a thickness of about 0.03 mils and the weld duration was adequately limited so that the required results under other conditions as described above could be obtained approximately the same. It had the same characteristics as described in Example 1 above.

As shown in FIG. 2, the second embodiment of the present invention is a fairly thin material made of a suitable refractory material that prepares a boron-containing electrical steel substrate, has electrical insulation properties on its substrate, and has a substantially uniform distribution of magnesium metaborate. It is achieved by coating one coat and by coating a generally thick coat of fire resistant material suitable for the coated electrical steel sheet.

As an initial step of the method, a substrate metal plate is provided by preparing and casting a silicon iron melt followed by hot rolling to an intermediate thickness. During the injection process, the melt contains 2.2 to 4.5 percent silicon, manganese and sulfur in an amount determined to have a manganese sulfur ratio of less than 2.3, about 3 to 50 ppm of boron, and the ratio of nitrogen to boron is nitrogen per 1 part of boron. It contains about 15 to 95 ppm of nitrogen, which is set to be in the range of 1 to 15 parts, and the remainder is iron and minor amounts of incidental impurities such as carbon, aluminum, copper, and oxygen. After the annealing process, the hot band is cold rolled to final thickness without intermediate annealing or without intermediate annealing and then decarburized.

The resultant fine grained primary recrystallized silicon iron sheet material is processed to provide the boron-containing first and second coatings of the present invention that enable annealing process to form the final structure. The treatment process at this time includes an electrolytic welding process of the Mg (OH) ₂ and boron compound source as described through the first embodiment of the present invention.

The plate is connected to the circuit as described in US Pat. No. 3,054,732 with a negative electrode and immersed in the electrolyte as described above, so that a uniform thickness (suitably about 0.05 to 0.4 mil, preferably about 0.2 mil) of Mg (OH) ₂ .XMg (BO ₂ ) ₂ .YH ₂ O film (X is 1 or less and Y is 0 to 15).

The electrolyte solution used in the present method is preferably prepared by adding boronic acid to a water-soluble magnesium acetate containing magnesia in a secondary dispersion solid phase. This magnesium acetate solution suitably has a concentration of 0.05 to 1.0 mol, preferably 0.2 mol. In addition, the pH of the electrolyte is set to 8.0 to 9.0 in consideration of the fact that an excessive amount of magnesia is contained. The amount of boronic acid added is set to be preferably 10 to 70 ppm in the case of the silicon iron substrate as described in pending US Pat. No. 677,146. At the beginning of the electrolytic co-welding process, the electrolyte is maintained at a temperature of at least about 65 ° C., preferably at a temperature of about 90 to 95 ° C. and maintained at that temperature for the duration of the co-deposition.

As a next step to the second embodiment of the present invention, Mg (OH) ₂ is electrolytically deposited on the boron-containing first film by greeting the current through the terminals by dipping the coated sheet with a cathode in an aqueous magnesium acetate solution buffered with solid MgO. Let's go.

This process is suitably performed as described in US Pat. No. 3,054,732 so that the thickness of the double coating is in the range as described above. In addition, in practicing the second embodiment of the present invention, the second film is boron to limit the content of boron to the first film, thereby preventing boron deviating and not causing the boron to be present in an excessive amount, particularly in the second film. Contains little or no If the boron is excessively far away from the surface of the sheet, such boron will have significant fluidity under the temperature conditions present at the end of the annealing process of growing the final tissue.

As a final process of the second embodiment of the present invention, the double-coated plates are heated in hydrogen or in a mixture of nitrogen and hydrogen to achieve secondary grain growth that begins to occur at about 950 ° C. As the temperature rises to about 1000 ° C. at about 50 ° C. per hour, the recrystallization process is complete, and if desired, heating up to 1175 ° C. may be performed to completely remove residual carbon, sulfur and nitrogen.

In the following, the method of the second embodiment of the present invention for achieving a new result as described above will be described by way of example. However, the present invention is not limited only to these examples.

Example 3

By the method as described in US Pat. No. 3,905,843, an 11 mil silicon iron strip having the following composition was prepared.

The melt having this composition is prepared into a sheet of medium thickness (about 100 mils) through a series of hot rolling processes, followed by pickling and annealing of the sheet, followed by cold rolling to a thickness of 60 mils, followed by reheating, and then final After cold rolling to thickness, the cold worked plate was decarbonized at 800 ° C. for 8 minutes in a hydrogen atmosphere (at room temperature dew point).

The plates were cut to form an Epstein strip to prepare seven packs for use in a conventional final magnetic test. Strips constituting one of these leaf plates were immersed in a magnesium acetate electrolyte as described in US Pat. No. 3,054,732, and the strips were connected to the electrical circuit with a cathode, covering about 83.00 milligrams, or square, of coating mass on each strip. By applying a voltage of 8 volts at a current density of 90 amps per square foot through the terminals, at 0.0285 ounces per foot, i.e., until the average film thickness over the entire surface of the strip is about 0.22 mils, Mg (OH ) ₂ was coated. The Franklin insulation values of the other six leaf plates prepared as described below, as well as the Franklin insulation values of these strips, were made uniform at about 0.2 ampere by annealing for 8 hours at a temperature of about 1175 ° C. in a minor atmosphere.

The strips of the other six leaf plates are each provided with _two coatings, except that the first coating is an Mg (OH) ₂ coating and the second coating is an Mg (OH) ₂ coating similar to the coating of the first leaf as described above. It was electrocoated in a similar manner.

The electrolyte solution used for the deposition of the first film was prepared by adding boronic acid to a slurry of distilled water, magnesium acetate and magnesia. The amount of boronic acid added to the slurry was 0.4317 mol / liter as calculated through the first example.

In order to determine the effect of thickness on the magnetic properties in the final electrical steel product, the strips of six double-coated Epstein leaf plates, as shown in Table 1, were kept constant, respectively, of the strips of the seven leaf plates. The thicknesses of the first film and the second film were changed. In addition, of the "film mass" described in Table 1, the upper one represents the mass of the first Mg (OH) ₂ coating and the lower one represents the mass (ie, the relative thickness) of the second coating.

TABLE 1

The ratio of MgO to B ₂ O ₃ ranged from 2.5 to .0 for the first coat of the strips of leaf 2, 3, 4 and only 1.5 to 2.0 for the corresponding boron saline coating of leaf 5, 6, 7.

Example 4

In another test of the method of the second embodiment of the present invention, 10 mils of Epsteinstrip, similar to the Epsteinstrip of Example 3, were coated with the results as described in Tables 2 and 3 through the process as described above.

TABLE 2

TABLE 3

Example 5

All 31 samples selected from different steel heat / coil combinations were treated by the method of the present invention (1.5 MgO.B ₂ O ₃ first coating) and the method of Example 3 described in Mochion US Patent 677,147. Otherwise, the method of the second embodiment of the present invention was tested again in a manner similar to that described in Examples 3 and 4. The samples had a changeable magnetism, but the average result is as follows.

The weight or thickness of the coating can be expressed in terms of density in units of ounces per square inch of the steel strip surface, such that the density of 0.0275 oz / ft ² is equal to the weight of 77 mg per Ibstein strip. In addition, the weight of 77 mg / Epstein strip is made to match the film thickness of 0.05 mils.

In the third embodiment of the present invention as shown in FIG. 3, a boron-containing electrical steel substrate is prepared, and a relatively thin Ca (BO ₂ ) ₂ coating is generally uniformly coated on the sheet, and then the sheet is coated on the coated sheet. This is achieved by coating a Mg (OH) ₂ film which is somewhat thicker than the film.

As an initial step of the method, a molten silicon melt is prepared, cast and hot rolled to an intermediate thickness to provide a substrate metal plate. In the infusion process, the melt contains 2.2 to 4.5 percent silicon, manganese and sulfur in an amount determined to be less than 2.3 in manganese sulfur, about 3 to 50 ppm of boron, and the ratio of nitrogen to boron is nitrogen per boron. It contains about 15 to 95 ppm of nitrogen, which is set in the range of 1 to 15 parts, and the remainder is iron and a small amount of incidental impurities such as carbon, aluminum, copper, and oxygen. After the annealing process, the hot band is cold rolled to final thickness without intermediate annealing or without intermediate annealing and then decarburized.

The resultant fine grain secondary recrystallized silicon iron sheet material is processed to provide the boron-containing film of the present invention which enables the annealing process to form the final structure. The treatment process at this time includes the steps of electrolytically welding the first film of Ca (BO ₂ ) ₂ and then electrolytically welding the second film of Mg (OH) _{2 which} is somewhat thicker thereafter. Will be used.

The plate is connected to a circuit as described in U.S. Patent No. 3,054,732 with a negative electrode and immersed in an aqueous solution of calcium acetate and botonic acid buffered with solid Ca (BO ₂ ) ₂ , thereby providing a substantially uniform thickness on the entire plate surface in contact with the electrolyte solution. The Ca (BO ₂ ) ₂ film of is coated. Mg (OH) ₂ coating is Ca (BO ₂₎ is welded around the pirate to about 0.10 to 0.40 mils thickness to the _second film, the Ca (BO _{2) 2} film was Mg (OH) thinner than the _second film of about 0.02 to 0.07 mill It is electrolytically welded.

As a final step of the method of the third embodiment of the present invention, the double coated plate is heated in an atmosphere of hydrogen or a mixture of hydrogen and nitrogen to achieve secondary grain growth starting to occur at about 950 ° C. As the temperature is raised to 1000 ° C. by about 50 ° C. per hour, the recrystallization process is completed and, if desired, a heating step up to 1175 ° C. may be performed to completely remove residual carbon, sulfur and nitrogen.

The following describes, by way of example, the method of the third embodiment of the present invention which yields new results as described above. However, the present invention is not limited only to these examples.

Example 6

By the method as described in US Pat. No. 3,905,843, an 11 mil silicon iron strip having the following composition was prepared.

The melt having this composition is prepared through a series of hot rolling processes into a plate of medium thickness (about 100 mils), followed by pickling and annealing of the sheet, followed by cold rolling to a thickness of 60 mils, followed by reheating, and then final After cold rolling to thickness, the cold worked plate was decarburized at 800 ° C. for 8 minutes in a hydrogen atmosphere (at room temperature dew point).

The Epstein strips formed by cutting the plates to provide nine Epstein leaf plates were immersed in the prepared electrolyte solution by adding bronic acid and Ca (BO ₂ ) ₂ to 10% aqueous calcium acetate solution. Sufficient amount of boronic acid was added to the aqueous solution to raise the pH of the aqueous solution to about 7.0.

Subsequently, the strips were connected to an electrical circuit to serve as a cathode, and a voltage of 8 volts was applied through the terminals at a current density of 90 amperes per square foot, with varying application times. ₂ ) ₂ films were coated. After removing the strips from the first coated electrolyte solution, again immersed in the manganese acetate electrolyte solution as described in US Pat. No. 3,054,732 to connect the strips to the electrical circuit negatively, and then applying a voltage of 8 volts through the terminals, The Mg (OH) ₂ film having a film mass as described in Table 4 was coated on the strip.

By annealing the double coated strip for about 8 hours in a hydrogen atmosphere at a temperature of 1175 ° C., the strip became magnetic as described in Table 4.

TABLE 4

By comparing the data in Tables 1 and 2 with each other, the results obtained through the method of the third embodiment of the present invention are generally covered with Mg (OH) ₂ -Mg (BO ₂ ) ₂ double coat. It turns out that it is the same as the obtained result.

Example 7

Twenty-five Epstein leaf plates taken from different steel heat / coil combinations were treated as described in Example 6 to obtain a first Ca having a density (ie, thickness) obtained by the method of Example 3 of Mochion Patent Application No. 677,147. The method of the third embodiment of the present invention was again tested in a similar manner except that the (BO ₂ ) ₂ film and the thicker 2Mg (OH) ₂ 1 film were coated. As a result, each strip had a film density of 0.025 to 0.030 ounces per square foot, with the first Ca (BO ₂ ) ₂ coating accounting for about 15% thereof. In addition, as a final annealing process, the double coated plate is heated in a hydrogen atmosphere to form secondary grain formation that begins to occur at about 950 ° C, and recrystallizes as the temperature rises by about 50 ° C per hour to about 50 ° C. The reaction process is completed and the heating process up to 1175 ° C is performed as described in Example 6. Table 5 compares the magnetism of the final strip with the magnetism of the strip treated according to Example 3 of the Mochion patent application.

TABLE 5

The weight or thickness of the coating can be expressed in terms of density in ounces per square foot of the steel strip surface, such that the density of 0.0275 oz / ft ² is equal to the weight of 77 milligrams per Ibstein strip. The weight of 77 milligrams per Epstein strip is equal to the film thickness of 0.05 mils.

Claims (1)

In the method of coating a silicon iron sheet having a grain direction, 2.2 to 4.5 percent silicon, manganese and sulfur in an amount determined to have a ratio of manganese sulfur to less than 2.3, about 3 to 50 ppm of boron, and nitrogen to the boron A fine-grained primary recrystallized silicon iron plate containing about 15 to 95 ppm of nitrogen was set such that the ratio was in the range of 1 to 15 parts of nitrogen per boron, and the silicon iron plate was an aqueous solution of magnesium acetate and magnesium metaborate containing magnesia. After immersing the cathode in a cathode, the aqueous solution was electrolytically maintained at a temperature of at least about 65 ° C. to cover the Mg (OH) ₂ film containing boron and electrically insulated, and the coated plate was finally heat treated to silicon A method for coating a silicon iron plate, comprising the steps of forming a (110) [001] secondary recrystallized structure on the iron plate.

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