JPS5846547B2 - Method for forming insulation coating on grain-oriented silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an insulating film on a grain-oriented silicon steel plate,
In particular, the present invention relates to a method for forming an insulating coating on a grain-oriented silicon steel sheet made of MgO-8iO2 and having excellent adhesion, uniformity, and smoothness.

When a grain-oriented silicon steel plate is used as a laminated or wound core of a transformer, its surface is coated with an electrically insulating film so that insulation between layers is maintained.

In addition to electrical insulation, this coating meets many requirements such as adhesion to the substrate, uniformity, heat resistance, smoothness, and space factor.
Good characteristics are required.

Normally, unidirectional silicon steel sheets are produced by hot rolling a silicon steel material containing 4.0% or less of Si, and performing one or two cold rolling processes with intermediate annealing to obtain a cold rolled sheet with the final thickness. Next, primary recrystallization annealing is performed which also serves as decarburization, and further (i'to)
It is manufactured through a series of processes including high-temperature finish annealing to develop secondary and recrystallized grains with (ooi) orientation and to remove harmful impurities in the steel.

As a method for simultaneously forming the MgO5i02-based insulating film in this series of steps, the above-mentioned recrystallization annealing is performed using H,
By continuously performing the process for several minutes at a temperature of 700 to 900°C in an atmosphere containing 20 and H2, the silicon in the steel is oxidized at the same time as decarburization, and an oxide film containing silica (Sin9) is formed on the surface. , a substance mainly containing magnesia (MgO) is applied as an annealing separator, wound into a coil, and subjected to high-temperature finishing annealing at 1100 to 1300°C, thereby causing the SiO2 and MgO to react, and forming mainly forsterite (2Mgo- A method of forming a glass-like insulating film (hereinafter referred to as a glass film) made of 8iO2) is known.

In this method, the first important factor that determines the quality of the glass coating is the composition and amount of the oxide film formed during the continuous annealing that also serves as decarburization (hereinafter referred to as decarburization annealing).

The composition of the oxide film is silica (5102) and fayalite (F12SiO4).

Each phase of iron oxide (FeO-Fe304) is involved in this,
The ratio is influenced by the annealing atmosphere, temperature, and time, but it is dominated by the oxidizing nature of the atmosphere;
) increases.

According to the experience of the present inventors, when annealing is performed in the FeO generation region, the resulting glass coating has some point-like defects in some parts, resulting in poor electrical insulation, and the overall surface is severely uneven. It was found that this method tends to cause problems such as poor space factor, and is extremely disadvantageous in obtaining a uniform and smooth glass coating.

In other words, the main components of the oxide film are silica and fayalite, and the total amount (evaluated by the amount of oxygen in the film) must be controlled within a certain range to ensure a good glass film. This is a necessary condition for obtaining it.

However, when the oxidizing property of the decarburization annealing atmosphere (determined by the ratio of H2O partial pressure to H2 partial pressure) is reduced to a region where FeO is not produced, the rate of oxide film formation decreases due to the low diffusion rate of Si in the steel. The amount of oxygen decreases significantly, making it impossible to obtain the required amount of oxygen.

As a result, the glass coating becomes thin and weak, resulting in a decrease in adhesion.

Extending the decarburization annealing time as a countermeasure to this problem immediately leads to a decrease in productivity, which is extremely disadvantageous from an industrial perspective.

On the other hand, in the annealing separator applied after decarburization annealing, 8
Many ideas have been proposed to supplement the SiO2 component that contributes to the formation of the glass film by adding 102 or silicate compounds, but even in this case, if the oxygen basis weight during decarburization annealing is small, the uniformity of the glass film will be reduced. However, if the oxygen basis weight is large, it may be effective in improving uniformity, but the surface layer becomes thicker than necessary and a decrease in space factor is avoided. do not have.

As described above, according to the conventional technology, it is difficult to fully satisfy the favorable glass coating formation conditions with industrial equipment.
As a compromise between the two, decarburization annealing conditions near the boundary between FeO generation and suppression are often adopted, and as a result, the formation of a glass coating and its quality have become quite unstable.

An object of the present invention is to provide a method for forming an insulating film on a grain-oriented silicon steel sheet, which eliminates and improves the drawbacks of the insulation film on a grain-oriented silicon steel sheet according to the prior art. Essentially S on the surface of rolled silicon steel strip
Silicon compounds containing i, O, H or essentially Si
After immediately adhering one type of silicon compound containing 0.0 to 0.5 to 70 Si per inch on one side of the steel plate, decarburization annealing was performed, then an annealing separator was applied, and high-temperature finishing annealing was performed. By applying this, the above objective can be achieved.

Next, the present invention will be explained in detail.

The inventors have determined that, without resulting in the production of excess FeO,
In order to form a necessary and sufficient amount of oxide film, we have extensively researched not only the atmosphere and temperature of decarburization annealing, but also the surface condition before annealing. By adhering FeO, the formation of FeO is suppressed, and even in the decarburization annealing atmosphere in the region where FeO is not formed, the formation rate of oxides in the form of silica and heptayarite can be significantly increased, and thereby, The present invention was completed based on the discovery that a smooth glass coating that is uniform and has good adhesion can be stably obtained.

In the present invention, the Si compound used is essentially Si
,0. Consisting of H or Si, O, i.e. 8102
・It is a compound expressed in the form of XH2O, and includes orthosilicic acid (H4S t 04 ), metasilicic acid (H2SiO3),
These include water-soluble ultrafine particles of SiO2 such as colloidal silica, 5i02 which is electrodeposited when a steel plate is electrolytically treated in an aqueous alkali silicate solution, or a compound in which H2O is bonded to this.

Next, the present invention will be explained using experimental data.

Figure 1 shows three cold-rolled silicon steel sheets whose surfaces have been thoroughly cleaned.
% Si adhesion when electrolytically treated in a sodium orthosilicate aqueous solution, the amount of oxide film formed after decarburizing annealing the steel sheet (oxygen basis weight), the amount of decarburization (substrate carbon), and the surface iron oxide ( The graph shows the relationship between the degree of FeO) formation and the appearance of the glass coating after coating with MgO and high-temperature finish annealing.

When a steel plate is electrolytically treated in an aqueous solution containing sodium silicate, it is generally recognized that up to several tens of square meters/m' of SiO2 or a compound in which H2O is bonded to SiO2 is electrodeposited on the surface of the steel plate, depending on the electrical quantity conditions. As described in the specific implementation method, this electrolytic treatment can be employed as one of the means of the present invention for depositing a certain amount of Si compound on the surface of a silicon steel sheet after cold rolling.

In determining the Si adhesion amount, a fluorescent X-ray analyzer was used, and it was converted into the basis weight from a calibration curve prepared in a rough manner.

In this case, the background is the state of the surface of the silicon steel sheet after cold rolling and degreasing without any Si adhesion treatment, and is taken as zero.

The degree of FeO biodegradation was judged from the shape of the external absorption spectrum and the degree of blackening of the appearance.

It can be seen that the effect of suppressing FeO generation due to the adhesion of the Si compound is already seen when the amount of Si per In on one side of the steel plate is 0.2 m9, and increases continuously as the amount of the adhesion of the Si compound increases.

FIG. 2 shows a surface reflection infrared absorption spectrum measured after decarburizing and annealing a cold-rolled silicon steel sheet with a Si adhesion amount of O and 3 .mu./d.

A broad absorption between 700 and 400 CrIl-1 indicates the presence of FeO, and a relatively sharp absorption near 1 000 CrIl-1 or 600 cfIL-1 indicates the presence of fayalite, but it may be due to the attachment of Si compounds. While the formation of fayalite is promoted by Fe
It is clear that the production of O is suppressed.

On the other hand, according to FIG. 1, the amount of oxide film formed after decarburization annealing (oxygen basis weight) increases continuously with the amount of Si adhesion in the following ranges, with the amount of Si adhesion being approximately 6/cm.

An important feature newly discovered by the present inventors is that this increase in the amount of oxygen per unit area is much larger than the amount of oxygen coordinated to the attached Si compound. It has been found that the effect is not only obtained by using a Si compound to compensate for the lack of material before decarburization annealing.

If the Si compound exceeds 7 .mu./7ri" in terms of Si, decarburization of the base silicon steel sheet is inhibited, and the amount of oxide film formed also decreases rapidly.

This is thought to be due to the formation of a dense and highly protective film on the surface.

In the case of grain-oriented silicon steel, poor decarburization has a fatal negative effect on magnetic properties, and in the present invention,
This is the reason why the upper limit of the amount of Si compound deposited is set at 7 .mu./d.

The effect of producing a good glass coating is when the Si adhesion amount is 0.2.
Although hail occurs from 0.57n9/m2, it is not very noticeable if it is less than 0.57n9/m2.

In the present invention, the lower limit is 0.51nI? This is the reason why it is set to /rrl.

The effect of suppressing FeO production and increasing the amount of oxide film formed due to the adhesion of Si compounds can be utilized to obtain an oxide film with desired components and oxygen content, and can also be used to adjust the various conditions of decarburization annealing. It also helps to expand the selection range.

This is because normally, a strongly oxidizing atmosphere where the formation of FeO is unavoidable or a weakly oxidizing atmosphere where the oxidation rate is low can be applied to a silicon steel sheet to which a Si compound is attached.

This means that in the long continuous annealing furnace used for actual production,
It is also advantageous in that extremely difficult control of maintaining the atmosphere throughout the furnace at a constant composition is not necessarily required.

According to the present invention, a silicon steel plate can be used as a starting material by hot rolling a conventional silicon steel containing 2 to 4% Si, followed by appropriate annealing and cold rolling to obtain a final thickness. .

That is, materials whose composition range is within the range of conventional grain-oriented silicon steel materials, for example, materials containing elements such as Se, S, Sb, A1 as primary grain growth inhibitors, and final cold rolled materials. The starting material of the present invention is a material that has been subjected to various treatments such as hot rolling, intermediate annealing, and cold rolling that are applied to conventional grain-oriented silicon steel materials until the final thickness is achieved by Can be used.

According to the present invention, two methods can be used to adhere a Si compound onto a steel plate, which can be roughly divided into a coating method and an electrolytic treatment method.

If a coating method is chosen, the surface must be thoroughly degreased in advance to ensure good wettability so that the coating solution does not repel.

As a coating agent, colloidal silica having a particle size of 10 to 20 μm, or silicic acid (S r 02.XH20), which has low solubility in water, can be used.

The specific means for coating, the components of the coating liquid, the concentration, etc. may be any, as long as they satisfy the coating amount according to the present invention.

For example, it is preferable to use a coating roll with grooves cut at intervals of about 0.5 to 2.0 mm, since the coating amount can be controlled arbitrarily by selecting the coating liquid concentration and roll reduction blade.

Next, a method using electrolytic treatment will be described.

After the final cold rolling of grain-oriented silicon steel sheets, rolling oil and iron powder adhering to the surface, as well as scale particles formed in various processes prior to the final cold rolling, are removed to obtain a clean surface. Cleaning is performed for this purpose.

Cleaning methods include immersion degreasing, spray degreasing,
In addition to brushing degreasing, there is so-called electrolytic degreasing, which involves electrolysis using a steel plate as an electrode in an alkaline degreasing bath.

In this electrolytic degreasing, an aqueous solution containing one or more of caustic soda, soda carbonate, sodium phosphate, sodium silicate, etc. is usually used as a degreasing bath. Then, silicic acid, silicate, or a compound containing iron hydroxide and silicic acid is electrodeposited on the surface of the steel sheet.

This phenomenon is particularly noticeable at the cathode.

It is the gist of the present invention to electrolytically degrease the grain-oriented silicon steel sheet after final cold rolling in a degreasing bath containing silicate, or to attach an electrode for electrolysis at the end of normal immersion degreasing at the same time as degreasing.
This is extremely advantageous because it allows the attachment of i-compounds.

Another advantage is that the amount of Si compound deposited can be arbitrarily selected by controlling the amount of electricity.

The silicates used in this electrolytic bath are sodium silicates, that is, sodium orthosilicate (Na 4 S t 04 ), sodium metasilicate (
Suitable are Na2 S 103 ) or so-called water glass, which is a liquid mixture of various sodium silicates.

It is also possible to use potassium or lithium silicates.

In either case, the molar ratio of metal ions to Si does not matter.

The composition of the electrolytic bath includes the above-mentioned silicic acid compound, and other components such as NaOH, Na2 co3 °Na
4 P 207 , Na 3 PO 4 , etc., and their concentration does not matter, but if the concentration of silicate is 0.5
At about 5%, it is possible to achieve the desired purpose in both degreasing and Si adhesion.

There is no need to limit the electrolysis method or conditions, such as the current application method, electrode shape or temperature, current density, or electrolysis time.
All you have to do is choose the conditions under which the desired amount of

The steps of continuous decarburization annealing, application of an annealing separator, and high-temperature finish annealing that follow after depositing the Si compound can be carried out according to methods known today in the production of grain-oriented silicon steel sheets.

In other words, as already detailed, decarburization annealing is performed using N2-N
Continuous annealing is performed in an atmosphere containing 2O to form an oxide film containing silica and fayalite as main components, and the temperature is suitably 750 to 850°C.

The treatment time and atmosphere composition can be arbitrarily selected from the above-mentioned viewpoints within a range that allows appropriate decarburization and oxide film formation.

Usually, N260 to 70φ and dew point of 50 to 70°C are appropriate.

As an annealing separator, the uniformity and adhesion of the film are improved not only when magnesia is used alone, but also when one or more of titanium oxide, manganese oxide, or other additives are added.

Furthermore, for final annealing, 11
Box annealing at 00 to 1300°C may be performed.

The present invention will be explained below by comparing examples with comparative examples.

Example 1 3.3% Si cold rolled to a thickness of 0.3 yytm
A silicon steel plate containing S as an inhibitor was heated at 80°C with sodium orthosilicate as the main ingredient and a nonionic activator added.
After degreasing by immersion using an alkaline degreaser, sufficient water washing and drying were performed.

This steel plate was coated with saturated silicic acid (SiO2/XN2) at 80°C.
0) An aqueous solution was applied using a grooved ringer roll and dried.

The amount of Si deposited on the surface was approximately 0.8 .mu./m'.

Subsequently, the dew point is 60°C, which is the FeO generation region. N240φ,
820°C in an atmosphere consisting of residual N2.

Decarburization annealing was performed for 2.5 minutes.

The oxygen basis weight of the oxide film after decarburization annealing was 1697 m''.

Next, an aqueous suspension of MgO powder was applied as an annealing separator and dried by heating.

The coating amount of MgO was approximately 6 g/m on one side after drying.

After winding it into a coil, it was heated at 12000C, 1 in a N2 stream.
Finish annealing was performed for 5 hours, and after cooling, unreacted separating agent was removed, and the appearance uniformity of the formed glass coating was semi-determined.

Furthermore, a treatment solution containing magnesium phosphate as the main ingredient and colloidal silica and chromic anhydride was applied.
After forming a coating film by baking at °C for 60 seconds, the flexural releasability, space factor, and interlayer resistance were measured.

These results are shown in the table along with the results of other examples.

Example 2 A silicon steel plate for high magnetic flux density containing 2.9% Si and Se and Sb as inhibitors was cold rolled at 80°C.
Electrolytic treatment was carried out for degreasing in a 3% sodium orthosilicate bath.

The electrolysis conditions were an alternating polarity system and a charge density of 10 C/di.

Thereafter, it was thoroughly washed with water and dried, and the amount of Si deposited on the surface was examined and was found to be approximately 2/.1.

Subsequently, the dew point was 60°C. H248φ, remaining at 820°C in an atmosphere consisting of N2.

Decarburization annealing was performed for 3 minutes.

The oxygen basis weight of the oxide film was 1.69/rn''.

After this, MgO added with 1φ T i 02 was applied to one side for 6
．． Coat 5 g/711, wind up into a coil and roll 85
0'C, retention for 30 hours secondary recrystallization and 1200
'C, finish annealing including high temperature holding for 15 hours was performed.

Thereafter, it was treated under the same conditions as in Example 1.

Example 3 The same silicon steel plate as in Example 2 was immersed and degreased in the same manner as in Example 1, thoroughly washed with water, and then dried.
A 3φ colloidal silica aqueous solution was applied and dried.

The amount of Si deposited at this time was approximately 5 .mu./d.

Subsequently, the dew point was 61°C and the temperature was 252%. Decarburization annealing was performed at 820° C. for 3 minutes in an atmosphere consisting of residual N2.

The oxygen density of the oxide film was 1.89/m''.

Thereafter, it was treated under the same conditions as in Example 2.

Reference Example The same silicon steel plate as in Example 2 was electrolytically treated in the same sodium orthosilicate bath as in Example 2, also for degreasing.

The electrolysis conditions are alternating polarity, and the electricity density is 45C/dr.
It was rl.

After thorough washing and drying, the amount of Si deposited on the surface was approximately 9.
yn9/m”.

Subsequently, decarburization annealing was performed at 820°C for 3 minutes in an atmosphere with a dew point of 600C2H250 and the remainder being N2.

The oxygen basis weight of the oxide film was 0.8 g/m''.

Thereafter, it was treated under the same conditions as in Example 2.

Comparative Example 1 The same silicon steel plate as in Example 1 was cold-rolled, then immersed and degreased in the same manner as in Example 1, thoroughly washed with water, and dried, and then heated to a dew point of 60°C and H247 without any Si adhesion treatment.
Decarburization annealing was carried out at 820° C. for 5.3 minutes in an atmosphere consisting of % and N2.

The oxygen basis weight of the oxide film was L3 fl/m.

Thereafter, it was treated under the same conditions as in Example 1.

Comparative Example 2 The same silicon steel plate as in Example 2 was immersed and degreased by the same method as in Example 1, washed with water and dried, and then FeO was produced without any Si adhesion treatment. Dew point: 60°C, H2: 40%
Decarburization annealing was carried out at 820° C. for 4.5 minutes in an atmosphere consisting of the remaining N2, and the following treatment was carried out under the same conditions as in Example 2.

Note that the oxygen basis weight of the oxide film was 1.6 g/lri'.

According to the table summarizing these results, a comparison between Example 1 and Comparative Example 2 shows that even if the method of the present invention is decarburized annealed in an atmosphere in the FeO generation region, less FeO is generated and a uniform glass is produced. Forming a coating, and from Examples 1 to 3,
It can be seen that all of the methods of the present invention can ensure the required amount of oxygen basis weight in a short time decarburization annealing and form a uniform glass coating.

Furthermore, it can be seen that the releasability, space factor, and interlayer resistance of this glass coating are also sufficiently excellent.

Note that the reference example is a case in which more Si is deposited than according to the present invention, and it shows that oxide film formation is suppressed and normal glass film formation is also inhibited.

From the above results, it can be concluded that the method of the present invention is effective in expanding the selection range of decarburization annealing atmospheres, increasing the productivity of decarburization annealing, and forming a glass coating with uniform and good properties. is obvious.

[Brief explanation of drawings]

Figure 1 shows the amount of Si deposited on the surface before decarburization annealing, the oxygen basis weight of the oxide film after decarburization annealing, and the C content of the base steel, according to the present invention.
A diagram showing the relationship between iron oxide on the surface and the appearance of the glass coating after final annealing. Figure 2 shows the reflection infrared absorption spectrum of the oxide film surface after decarburization annealing, and shows the presence or absence of Si adhesion on the surface before decarburization annealing. FIG.

Claims (1)

[Claims] 1 A silicon steel strip cold-rolled to a desired final thickness is subjected to decarburization annealing to decarburize it and at the same time oxidize the Si in the steel to form 5i0
After forming an oxide film containing 2 on the surface, a material mainly composed of MgO is applied as an annealing separation agent, and the material is further wound into a coil and subjected to high-temperature finish annealing to form SiO2-Mj.
In the method for forming an insulating coating on a grain-oriented silicon steel sheet in which an iO-based coating is formed, the surface of the silicon steel strip before decarburization annealing is essentially Si, 0. After depositing a silicon compound containing H or a silicon compound containing essentially Si, 0 at a weight of Si of 0.5 to 7.0 cm per li on one side of the steel plate,
A method for forming an insulating film on a grain-oriented silicon steel sheet, which comprises performing decarburization annealing, then applying an annealing separator, and further performing high-temperature finish smelting.