JPS60131976A - Manufacture of grain-oriented silicon steel sheet having superior iron loss characteristic - Google Patents

Abstract

PURPOSE:To obtain a grain-oriented silicon steel sheet having improved iron loss characteristics by working a silicon steel sheet after finish annealing to provide mirror finished surfaces, heat-treating it to form SiO2 layers on the surfaces, and coating the layers with tension applying insulating films. CONSTITUTION:A silicon steel slab is hot-rolled, cold-rolled, process-annealed, and cold-rolled. The cold-rolled steel sheet is subjected to decarburization, primary recrystallization annealing and final finish annealing, and it is worked to provide mirror finished surfaces. The steel sheet is heat-treated in a low oxidizing atmosphere to form SiO2 layers on the surfaces to 0.05-0.5mum thickness per one side. At the same time, flattening annealing is carried out. The layers are then coated with tension applying insulating films each consisting of silica, magnesium phosphate and chromic anhydride. By this method a grain-oriented silicon steel sheet having superior iron loss characteristics is obtd. without deteriorating the adhesive strength of the films.

Description

[Detailed Description of the Invention] Technical Field The technical content described in this specification regarding a method for manufacturing a unidirectional silicon steel sheet with excellent iron loss characteristics is a method for manufacturing a unidirectional silicon steel sheet with excellent iron loss characteristics. , is related to further improving iron loss characteristics.

Technical Background The basic properties required of unidirectional silicon steel sheets, which are mainly used as transformer core materials, are a constant magnetizing force, I;
) has a high magnetic flux density (represented by the B10 value), and when a constant magnetic flux density is applied, its iron loss is low (represented by the 17/B. value). Forsterei) is used on the surface of grain-oriented silicon steel sheet.
(Mg25104) A two-layer insulating film consisting of a purchased film and a coating film mainly composed of phosphate is formed, and when laminated to create an iron core, it maintains the insulation between the steel plates and This prevents deterioration of loss characteristics. Recently, demand for high magnetic flux density unidirectional silicon steel sheets has been increasing, and iron loss has been reduced by applying tension to the steel sheets using a false dry film and a silica-phosphate coating film. It has been found that it is possible to do so, and from this fact, it is considered that good formation of an insulating film is essential in order to improve the magnetism of the material. In addition, due to the current energy situation, materials with extremely low iron loss are being sought.

As one of the methods for improving iron loss characteristics,
4499 and Japanese Patent Publication No. 56-4150, the surface of the material after finish annealing is polished extremely flat by chemical polishing or electrolytic polishing. There is a way to be smart,
This method has made it possible to obtain lower iron loss than ever before.

However, stacking the above-mentioned smoothed materials without any insulation treatment causes electrical conduction between the steel plates, making it impossible to utilize the excellent iron loss characteristics of the materials in actual equipment. Therefore, it is necessary to form an insulating layer even on materials whose surfaces have been smoothed (hereinafter referred to as mirror-finished materials), and such treatment includes a tension-applied insulating coating mainly composed of silica-phosphate. Possible methods include coating and baking. However, when coating such mirror-finished materials with a tension-applied insulating film, baking at a temperature of 700°C or higher, where the tension is fully exerted, the resulting coating film is not only non-uniform, but also peels off. Therefore, satisfactory insulation between the steel plates could not be expected. Therefore, it is desired to develop a method for forming a good coating film on mirror-finished materials at a temperature that can apply sufficient tension, but to date, such a method has not yet been found. Not yet.

Purpose of the Invention The present invention advantageously satisfies the above-mentioned requirements by making it possible to perform an insulating coating treatment on mirror-finished materials at a temperature at which sufficient tension is exerted without impairing coating adhesion. In addition to further improving the magnetic properties of the material,
It is also possible to obtain good electrical insulation between steel plates.
The purpose of this paper is to propose a method for manufacturing unidirectional silicon steel sheets.

Prior art and its problems Normally, unidirectional silicon steel sheets contain S, Se, At and N.
A hot-rolled sheet containing an inhibitor-forming component such as Mg0 It is manufactured by applying an annealing separator mainly composed of and then box annealing at a high temperature. In this box annealing, Sin generated during decarburization annealing, MgO as an oxide layer and an annealing separator
reacts with forsterite (Kg, 5i04
) is formed. As mentioned above, this forsterite coating is useful for improving magnetism and for insulating between steel plates. However, in such steel sheets, the interface between the base iron and the 7-orsterite coating is not smooth, which impedes magnetic domain movement during magnetization and causes magnetic deterioration. As mentioned above, iron loss can be improved by making the surface extremely smooth after removal. By the way, with materials that have such extremely low iron loss characteristics, when laminated and assembled into an iron core, Maintaining the insulation properties of steel is an extremely important issue, and since conventionally a low iron loss value has been obtained due to the smooth surface condition, it is necessary to form an insulating film without damaging the surface condition. In order to maintain such smoothness, various measures as described below have been taken.

For example, Japanese Patent Publication No. 52-24499 discloses a method in which the surface is protected by plating immediately after mirror polishing, and then coated. however,
This method has the disadvantage that, after assembly into an actual iron core, during strain relief annealing for the purpose of removing processing strain, the plated metal diffuses into the steel, causing magnetic deterioration. Further, Japanese Patent Publication No. 56-4150 discloses a method of coating a mirror-finished material with a ceramic thin film. Vacuum deposition, chemical vapor deposition, sputtering, etc. have been proposed as methods for forming ceramic coatings, but these methods require continuous processing of the copper strip in vacuum or under reduced pressure, making them extremely expensive and controlled. However, it requires difficult equipment, it takes an extremely long time to coat the coating with a thickness of 0.5 to 5 μm, and it is difficult to maintain the untreated portion of the coating in a mirror-like state for a long time. For some reason, it was almost impossible to put it into practical use.

Background of the Elucidation of the Solution The inventors investigated a method that could easily form a tension-applied insulating coating on a mirror-finished material without incurring any process burden, and that could also improve magnetic properties. As a treatment solution for obtaining such a coating, there may be used a colloidal silica-aluminum phosphate-chromic acid anhydride system disclosed in Japanese Patent Publication No. 58-28375, or Japanese Patent Publication [+'
d Colloidal silica-aluminum phosphate-magnesium phosphate system disclosed in Japanese Patent Publication No. 56-84638, and colloidal silica-magnesium phosphate-magnesium anhydride system disclosed in Japanese Patent Publication No. 56-52117. Compositions such as can be used.

In all conventional methods, maintaining the surface condition of the mirror-finished material was considered to be an important factor in preventing iron loss deterioration. For example, even if some iron loss deterioration occurs in the pretreatment, the deterioration can be recovered by adding tension through the coating.As a result of various experiments, we found that the insulating coating treatment If a thin oxide film is first formed on the surface of the mirror-treated steel sheet in a weakly oxidizing atmosphere, then the tension-applied insulating coating will be baked at a temperature of 100°C or more during the baking process. I learned that it is possible.

Tension is applied to the steel plate due to the difference in the coefficient of thermal expansion between the coating film and the steel plate, so if the humidity is low, sufficient tension will not be applied for seizure. In this regard, the fact that baking can increase the temperature means that the added tension to the steel plate can be increased, that is, the effect of improving iron loss is increased. It is derived from

In other words, in this invention, a hot-rolled sheet obtained by hot rolling a silicon-containing steel slab is subjected to necessary heat treatment and then cold-rolled once or twice with intermediate annealing in between to form a final sheet. In a method for manufacturing a unidirectional silicon steel sheet, which comprises a series of steps of thickening, decarburization, primary recrystallization annealing, finish annealing, and then further flattening annealing, the steel plate after finish annealing is After processing the surface into a mirror-like state, heat treatment is performed in a weakly oxidizing atmosphere to form a SiO oxide layer with a film thickness of 0.05 to 0.5 μm per side on the steel sheet surface, and then a tension-applied type This is a method of manufacturing a unidirectional silicon steel sheet with excellent iron loss characteristics, which comprises coating the steel sheet with an insulating coating film.

In this invention, the oxidized layer of Sin, which is formed on the surface of the steel sheet prior to the insulating coating treatment, is
, because the grains have a dispersed structure,
io, when a layer is formed, the surface condition deteriorates, and the iron loss characteristics also deteriorate slightly accordingly. However, by adding tension through the subsequent coating process, the iron loss characteristics are greatly improved to more than compensate for the deterioration, and as a result, good iron loss characteristics are finally obtained, and the film adhesion is also greatly improved. .

In this way, the present invention differs from the conventional techniques mentioned above in that even if temporary deterioration of iron loss occurs during the manufacturing process, it is possible to obtain iron loss characteristics that are even better than those in a mirror-finished state through subsequent processing. The technology is completely different from the conventional one in that it does not require the continuation of a mirror-like state. The reason why is limited to the above range will be explained.

As for the thickness of the Sin layer, the thicker the layer, the better the coating's seizure properties, but conversely the magnetic deterioration is significant.1 On the other hand, if it is too thin, the coating's seizure properties are insufficient and sufficient tension cannot be applied to the steel plate. It disappears.

Figure 1 shows the results when a silica-magnesium phosphate-chromium anhydride insulating coating is baked on the mirror-finished material after forming a Si0□ oxide layer in various oxidizing atmospheres, which also serves as planarization annealing. , the relationship between the thickness of the Si0□ oxide layer and iron loss, as well as the results of investigating the adhesion of the coating film, are summarized together with conventional examples. If the coating peels off even on a part of the steel plate surface, it will not serve any purpose as insulation and will not be usable, and uneven stress will be applied to the steel plate, causing iron loss to deteriorate compared to a stress-free state. is remarkable.

As can be seen from Fig. 1, the oxide layer thickness is 0.05 to 0.
Tension is substantially applied to the steel plate within the range of 5 μm. Therefore, the oxide layer thickness was limited to a range of 0.05 to 0.5 μm.

Any known method such as chemical polishing or electrolytic polishing may be used to mirror the surface of the steel plate, and any known tension-applied insulating coating treatment may be used, such as one mainly composed of silica and phosphate. Any of these can be used.

Furthermore, the formation of the SiOs oxide layer according to the present invention does not necessarily require a special process, and is usually performed by continuous flattening over several minutes at a temperature range of 750 to 850°C, which is usually done to straighten coil curls. During chemical annealing, Si
-02 formation layer can also be formed simultaneously.

Next, embodiments of this invention will be described.

Example 1 00.048%, 5i8-25%, Mn0.070%,
seo. A steel slab containing 018% SbO and 025% SbO was hot rolled and cold rolled twice with intermediate annealing interposed therebetween to obtain a cold rolled plate having a thickness of 9.3 mm. Next, after decarburization annealing which also served as primary recrystallization annealing, MgO was applied, and final finish annealing was performed. After final annealing, the forsterite coating was removed by pickling, and then a mirror polishing treatment was performed by immersing it in a solution of HF, H, and Og for 80 seconds.

Immediately thereafter, flattening annealing is performed to obtain a thickness of 5 mm as shown in Table 1.
A 102 oxide layer was formed. A silica-magnesium phosphate-chromic anhydride tension-adding type insulation coating was baked on this steel plate at 750°C.

For comparison, a similar experiment was also conducted without mirror polishing or coating.

Table 1 also shows the results of investigating the magnetic properties and film adhesion of each product obtained.

With materials that do not form a 510g layer, the coating has extremely poor seizure resistance and poor magnetic properties, but when the method of this invention is followed, a good coating film is formed and the magnetic properties are also significantly improved. There is.

Effects of the Invention Thus, according to the present invention, a tension-applied coating film can be effectively formed on the surface of a steel sheet after mirror polishing treatment without impairing the adhesion of the film, and therefore the iron loss characteristics can be improved. Improvements can also be realized, which is advantageous.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the thickness of the S10□ oxide layer and iron loss together with the adhesion of the coating film.

Claims (1)

[Scope of Claims] 1 A hot-rolled plate obtained by hot rolling a silicon-containing steel slab is subjected to necessary heat treatment and then cold-rolled once or twice with intermediate annealing in between to form the final product. After making the plate thick, decarburization 1
In a method for manufacturing a unidirectional silicon steel sheet, which comprises a series of steps of performing finish annealing with subsequent recrystallization annealing, and then further flattening annealing, the surface of the steel sheet after the above finish annealing is processed into a mirror-like state, and then A 5in2 oxide layer with a film thickness of 0.05 to 0.5 μm per side is formed on the surface of the steel plate by heat treatment in a weakly oxidizing atmosphere, and then a tension-applied insulating coating film is formed. A method for manufacturing a unidirectional silicon steel sheet with excellent iron loss characteristics.