JPS6110963B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a grain-oriented silicon steel sheet having an insulating coating in which a crystalline phase is precipitated in a vitreous material (hereinafter simply referred to as a crystallized glass insulating coating). In particular, the present invention relates to a grain-oriented silicon steel sheet having a crystallized glass insulating coating that improves iron loss and magnetostriction characteristics and has good heat resistance. Grain-oriented silicon steel sheets are manufactured commercially by appropriately rolling and heat treating silicon steel ingots or slabs containing at most 4% by weight, but usually about 3% by weight, of Si, such that the axis of easy magnetization aligned in the direction
It has a (110) [001] crystal structure as expressed by cube-on-edge or Miller index. Grain-oriented silicon steel sheets are mostly laminated and assembled and used as power transformers. In recent years, with the concentration of population in urban areas and the increase in demand for electricity, large-capacity transformers are being installed in densely populated areas.
Noise generated from transformers has become a pollution problem. The main cause of transformer noise is the magnetostriction of the grain-oriented silicon steel plate used as the iron core. This is a phenomenon in which the steel plate stretches and vibrates when it is magnetized with alternating current.The cause of this is that the magnetization process of the steel plate includes 90° domain wall movement and rotational magnetization, and compressive stress in the rolling direction is applied to the steel plate. When added, magnetostriction increases significantly. When assembling a transformer by laminating grain-oriented silicon steel plates, compressive stress is inevitably added, increasing magnetostriction and causing an increase in transformer noise. Therefore, if tensile stress is applied to the steel plate in advance through an insulating coating on the surface, the compressive stress that inevitably occurs when assembling the transformer can be canceled out, and an increase in magnetostriction can be prevented. It is known that the tensile stress imparted by the surface insulation coating is effective not only in improving the magnetostrictive compressive stress characteristics of grain-oriented silicon steel sheets, but also in improving core loss. This effect is particularly great in the case of recent high magnetic flux density grain-oriented silicon steel sheets with well-aligned orientation. The surface coating of grain-oriented silicon steel sheets usually consists of a crystalline forsterite coating formed during high-temperature finish annealing and a phosphate-based coating applied thereon. Of these, the top coat is what applies tensile stress to the steel plate, and this can be formed by coating and baking a suspension of glass frit, or by coating and baking a liquid containing phosphate and colloidal silica. It is broadly divided into two methods. For example, Tokko Sho 31-8242, Tokko Sho No.
The method disclosed in Japanese Patent Application Laid-Open No. 46-18603 belongs to, for example, the method disclosed in Japanese Patent Application Publication No. 48-39338 or Japanese Patent Application Publication No. 50-79442. Of these methods, the coating formed by the method using glass frit (hereinafter simply referred to as vitreous coating) is superior to the coating formed by the method using phosphate and colloidal silica (hereinafter simply referred to as vitreous coating). (hereinafter simply referred to as a phosphate-based coating), it applies a greater tensile stress to the steel sheet. Furthermore, even if a glassy coating and a phosphate coating have the same coefficient of thermal expansion, the tensile stress imparted to the steel sheet is greater in the former. Although the details of this reason are not clear,
Since the glassy coating is melt-formed on the steel plate, it is denser than the phosphate coating, and forms a coating that reacts well with the forsterite coating formed during final annealing, giving tensile stress to the steel plate. It is presumed that this is because a glassy coating is more suitable for the purpose. In this way, the vitreous coating is very good as a top coating for adding tensile stress to grain-oriented silicon steel sheets, but since glass softens at high temperatures, grain-oriented silicon steel sheets with vitreous coatings are laminated and heated at temperatures of around 800°C. When stress relief annealing is performed at high temperature, adjacent coatings fuse together, causing deterioration of interlayer resistance and magnetic properties.In the case of wrap-core type wound iron cores, the coating may be removed if forcibly peeled off for assembly. It has drawbacks in terms of heat resistance and fusion resistance, as it peels off and makes assembly impossible. Particularly when assembling wound iron core type transformers, the heat resistance of the coating is important, and for this reason, although glass coatings are excellent as coatings for applying tensile stress, they are less suitable for industrial use than phosphate coatings. It was difficult to put it into practical use. An object of the present invention is to provide a grain-oriented silicon steel sheet having an insulating coating that eliminates and improves the shortcoming of the glassy coating, such as low heat resistance, and improves magnetostrictive properties by increasing tensile stress. It is something to do. That is, the present invention provides a grain-oriented silicon steel sheet having a low thermal expansion insulating coating, the insulating coating comprising:
A crystalline phase with a melting point of 900°C or higher is precipitated in a range of 5 to 70% by weight in a glassy film formed by melting a glass frit with a low coefficient of thermal expansion of 8.5×10 ^-6 /°C or less. This is a grain-oriented silicon steel sheet that has a crystallized glass-like insulating coating that has excellent heat resistance and magnetostrictive properties. Next, the present invention will be explained in detail. The present inventors have developed a phenomenon called crystallization of glass as a measure to improve the heat resistance, which is a drawback of the glassy coating mentioned above, and to increase the tensile stress applied to the steel sheet more than the conventional glassy coating, thereby improving the magnetostrictive properties. Using this, we conceived of a crystallized glass film in which a crystalline phase with a high melting point and low thermal expansion is precipitated in the glass film.
Various studies were conducted. As a result, we coated and baked glass frit onto a silicon steel plate to form a glassy coating, and at the same time, precipitated 5 to 70% by weight of a crystalline phase with a melting point of 900°C or higher into the glassy coating, thereby improving heat resistance. It has been newly discovered that the magnetostrictive properties can be improved by increasing the tensile stress applied to the steel sheet by reducing the thermal expansion of the coating as it crystallizes. Glass crystallization is a technology that has been attracting attention in the ceramic industry in recent years, and it has led to the achievement of higher strength and improved thermal shock resistance of glass materials, and is expected to be put to practical use in various materials as glass ceramics. It became. For example, it is well known that by appropriately selecting a glass component system and crystallizing it, the coefficient of thermal expansion can be significantly lowered. This is due to the low thermal expansion of the material. The present invention aims to improve the characteristics of the top insulating coating of grain-oriented silicon steel sheets by utilizing the technique of glass crystallization. Japanese Patent Publication No. 18603 (1973) is known as a method for forming a glassy coating as a top coat on grain-oriented silicon steel sheets, and the method described therein is 8.5×10 ^-6 /℃.
The following low thermal expansion glass frit is coated and baked to form a top glass film, and the silicon steel plate with the glass film is heated to fuse the glass film between the layers to manufacture the transformer. The structure is fundamentally different from that of the present invention, which improves fusion resistance by precipitating a crystalline phase in a glassy coating. In addition, one possible method to improve the heat resistance of the glassy coating is to add high-melting-point oxide powder to the glass frit, but this method does not improve the heat resistance sufficiently, and on the contrary, the adhesion of the coating deteriorates. deteriorates and is not desirable. In the present invention, a glass frit that crystallizes a crystalline phase is used as described above, but this glass frit does not need to be limited to a specific component system.
It is sufficient as long as it crystallizes ~70% of the crystal phase, and examples of suitable component systems include, for example, Li ₂ O—A ₂ O ₃ —
ZnO―SiO ₂ system, Li ₂ O―A ₂ O ₃ -PbO―GiO ₂ system,
SiO ₂ ―B ₂ O ₃ ―ZnO system can be used, and when glass frit with these components is coated and baked on a silicon steel plate, Li ₂ O・A is formed in the glassy coating.
₂ O ₃・2SiO ₂ (β-eucryptite), 2ZnO・
Crystals of SiO ₂ (willemite) or 5ZnO.2B ₂ O ₃ precipitate. The most preferred embodiment of the present invention is SiO ₂ --B ₂ O ₃ --
When using ZnO-based glass frit, SiO ₂ 3
~25% by weight, 20~45% by weight _{of B2O3} , and 100 parts of the basic composition consisting of the balance ZnO and _Li2O , _Na2O , as necessary.
_K2O , MgO, CaO, SrO, BaO, _{A2O3 ,
P2O5} , _{TiO2 , Cr2O3} , _{Fe2O3 , CoO} , NiO, _ZnO2
Any one or two or more types transported from 15
A glass frit consisting of less than It precipitates 5 to 70% by weight of the crystalline phase having the above properties, and can form a crystallized glass-like insulating film that has excellent magnetostrictive properties, improves iron loss, and has excellent heat resistance and adhesion. In the present invention, the reason why the coefficient of thermal expansion of the glass frit is limited to 8.5×10 ^-6 /℃ or less is that when the coefficient of thermal expansion is larger than 8.5×10 ^-6 /℃, the tensile stress that the glassy coating gives to the steel sheet is small, and the magnetostrictive Since there is no effect of improving the properties, the coefficient of thermal expansion of the glass frit used must be limited to 8.5×10 ^-6 /°C or less. The reason why the melting point of the crystalline phase to be precipitated in the glass coating is limited to 900°C or higher is that the strain relief annealing temperature of grain-oriented silicon steel sheets is usually around 800°C,
A crystalline phase with a melting point lower than 900°C has no effect on improving heat resistance, and it is necessary to precipitate a crystalline phase with a melting point of 900°C or higher. In the present invention, in order to improve the heat resistance of the glassy coating, 5 to 70% by weight of a crystalline phase having a melting point of 900°C or higher is precipitated in the glassy coating. The relationship between the heat resistance and the heat resistance of the crystallized glass film was investigated using the following method. The glass frit of the present invention was applied to a grain-oriented silicon steel sheet having a forsterite coating to form a coating with a thickness of 2 microns, and the baking heat treatment time was varied to produce a crystallized glass-ceramic coating with various degrees of crystallinity. After the specimens were obtained, they were sheared into 10 specimens of 50 x 50 mm, stacked as a set of 10 specimens, and annealed at a temperature of 820° C. under a compressive load of 2 kg/cm ² . After annealing, the 10 test pieces are united by the fusion of the film between the layers, but the strength of this fusion can be determined by dropping a weight from above and applying an impact to the 10 test pieces. This can be determined based on the state of separation and the presence or absence of film peeling between the layers of the test piece separated by impact. The shock is applied by dropping a 1 kg weight from a height of 5 cm to 50 cm at 5 cm intervals. The heat resistance of the coating can be strictly evaluated by this method of examining the strength of fusion of the interlayer coating after compressive load annealing. Figure 1 shows Li ₂ O 7% by weight, A ₂ O ₃ 8% by weight,
Glass frits having a composition of 5% by weight of ZnO and 50% by weight of SiO ₂ were coated on a steel plate to obtain a film with a thickness of 2 microns, and baked at 900°C for 30 seconds to 40 minutes. FIG. 2 is a diagram showing the relationship between heat resistance and crystallinity of a glass-ceraminous film having a crystallinity of . The ○ mark in the same figure is 10.
Those marked with ● completely separate into 10 sheets, but the coating peels off due to fusion, △ indicates those that partially separate, ▲ indicates that they partially separate, but the coating peels off due to fusion. Those with a mark, and those marked with an x, are those that are not separated at all. Figure 2 shows SiO ₂ 10% by weight,
A glass frit having a composition of 28% by weight of B ₂ O ₃ and 62% by weight of ZnO was coated on a steel plate to a film thickness of 2 microns as in the case of Fig. 1, and heated at 850°C.
FIG. 2 is a diagram showing an investigation of crystallized glass films having various degrees of crystallinity obtained by varying the baking time from 30 seconds to 30 minutes. In the case of Fig. 1, the precipitated crystal seeds are as follows:
2ZnO, SiO ₂ (willemite), Li ₂ O・A ₂ O ₃・
In the case of 2SiO ₂ (β-eucryptite), in the case of Figure 2, 2ZnO·SiO ₂ and 5ZnO·2B ₂ O ₃ were mainly precipitated, and ZnO·B ₂ O ₃ was also precipitated. The degree of crystallinity increased as the heat treatment time increased. Note that the various marks in the figure represent the same things as in Figure 1. As is clear from Figs. 1 and 2, the heat resistance of a crystallized glass coating depends more on the proportion of the crystalline phase precipitated in the glass coating than on the type of precipitated crystal phase or the form of crystal precipitation. It was found through the research of the present invention that it strongly depends on the degree of crystallinity. If the crystallinity is less than 5% by weight, it is necessary to use a 1 kg weight at 30 cm to separate 10 veneer specimens.
It is necessary to drop it from a higher height, and,
In this case, the strength of the fusion between the layers was greater than the strength of the adhesion between the films themselves, and as a result, after the impact test, the film inevitably peeled off due to fusion, resulting in a serious defect. . Therefore, in order to improve the heat resistance of the crystallized glass coating, it is necessary to precipitate 5% by weight or more of the crystalline phase. In the present invention, 5 to 70% by weight of crystalline phase is precipitated in order to improve the heat resistance of the glassy coating, but the lower limit of this crystallinity range was determined by the above-mentioned fusion strength test after compressive load annealing. The upper limit value is
It can be determined by measuring the surface roughness of the crystallized glass film. FIG. 3 is a diagram showing the relationship between surface roughness and crystallinity of a crystalline glass coating prepared by the same method as in FIG. 2. As is clear from Figure 3, the center line average roughness (Ra: 0.8mm cut off) is 70
The degree of crystallinity must be limited to 70% by weight or less because it increases rapidly after reaching % by weight and deteriorates the space factor. In the present invention, as described above, a crystallized glass coating with excellent heat resistance is formed, and the tensile stress applied to the steel sheet is increased by using crystallization more than that of conventional glass coatings, thereby improving magnetostrictive properties. However, this increase in tensile stress is due to the lower thermal expansion of the glassy coating as it crystallizes. FIG. 4 shows changes in thermal expansion characteristics that occur with crystallization of SiO ₂ --B ₂ O ₃ --ZnO glass.
SiO ₂ 13% by weight, B ₂ O ₃ 26% by weight, ZnO 59% by weight,
Glass with a composition of ₂ % TiO 2 by weight is molded into a rod shape,
Thermal expansion characteristics and crystallinity were measured for rod-shaped samples that were heat-treated for crystallization at 800°C and 850°C for 1 hour. The figure shows the crystallinity of each sample and the average coefficient of thermal expansion between 100 and 400°C determined from the thermal expansion curve. It can be seen that the coefficient of thermal expansion decreases significantly with crystallization. As can be seen from Figure 4, in the case of a rod-shaped sample, it softens at around 700°C due to the glass that remains even after crystallization, but in the case of the crystallized glass film of the present invention, even if it softens, it has a high melting point crystalline phase. exists on the surface, it exhibits excellent heat resistance during strain relief annealing at approximately 800°C. SiO ₂ ―B ₂ O ₃ ―
In addition to ZnO-based glasses, examples of glasses that can be made to have low thermal expansion through crystallization include glasses having components No. 1 to 5 shown in Table 1 below.

【table】

[Table] Precipitated crystal phase Li ₂ O・A ₂ O ₃・2SiO ₂ (β
- Eucryptite) is well known as a crystalline phase with low thermal expansion, and if it has good adhesion,
It is considered that the lower the coefficient of thermal expansion of the coating, the greater the tensile stress applied to the steel plate. In the case of the crystallized glass film of the present invention, since it crystallizes after being melted and coated on a steel plate, there is no deterioration in adhesion due to crystallization, and the coefficient of thermal expansion of the steel plate (13×10 ⁶ /℃)
Since it is significantly smaller than that of phosphate coatings, it is possible to apply a larger tensile stress to the steel sheet than not only phosphate coatings but also conventional glass coatings, and the effect of improving magnetostrictive properties brought about by this is significant. As described above, crystals with improved heat resistance and magnetostrictive properties are obtained by precipitating 5 to 70% by weight of a crystalline phase having a melting point of 900°C or higher in a glassy coating having a thermal expansion coefficient of 8.5×10 ^-6 or lower. A vitrified insulating film can be formed. The glass frit forming the top coat for imparting tensile stress to the grain-oriented silicon steel plate is required to have a small coefficient of thermal expansion and a low glass softening temperature. Baking the top coat of grain-oriented silicon steel plate
Usually, this is carried out at the same time as flattening annealing to remove curls in the steel sheet after final annealing. This heat treatment is 800
It only takes about 1 to 3 minutes at a temperature of ~900°C. Therefore, glass frit is used to form a smooth and dense glassy coating on steel sheets.
It is necessary to achieve a viscous state (10 ³ to 10 ⁴ poise) that allows melting and coating by heat treatment at 800 to 900°C for about 1 to 3 minutes. Improves heat resistance by crystallizing the glassy coating,
Furthermore, the glass frit used for the purpose of the present invention, which is to improve the magnetostrictive properties by increasing the tensile stress applied to the steel sheet, must not only have a small coefficient of thermal expansion and a low softening temperature, but also be easily crystallized. As long as the glass component system satisfies the following, the glass frit need not be limited to a specific component system. Suitable component systems include, for example, those mainly composed of SiO ₂ as shown in Table 1 above.
Li ₂ O―A ₂ O ₃ ―PbO―SiO ₂ system and Li ₂ O―A ₂ O ₃
-ZnO-SiO ₂ system, or SiO ₂ -B ₂ O ₃ -ZnO system, which is mainly composed of B ₂ O ₃ -ZnO system. Glasses with a composition mainly composed of SiO ₂ are generally difficult to crystallize, so it is advantageous to add crystal nucleation components such as TiO ₂ and Cr ₂ O ₃ as necessary to promote crystallization. be. In this way, the glass frit to be applied does not need to be limited to a specific composition system, but the heat resistance, magnetostriction properties, moisture absorption resistance, interlayer insulation resistance, and adhesion required for the top-coating insulation coating of grain-oriented silicon steel sheets are important. As a result of various studies on the composition system of glass frit that satisfies a wide range of film characteristics such as space factor, SiO ₂ ―B ₂ O ₃ ―
They discovered that a crystallized glass coating with the best coating properties can be obtained when ZnO-based glass frit is used. Figure 5 shows the vitrification range of the SiO ₂ --B ₂ O ₃ --ZnO system. The shaded area in the figure shows the glass batch prepared by weighing and adjusting each component of SiO ₂ , B ₂ O ₃ , and ZnO to obtain 100 g of glass, melted at 1100 to 1200°C, and then rapidly cooled in water to devitrify. (crystallization) without
This is an area that can be obtained as 100% glass. Therefore, the basic composition of the glass frit suitable for the present invention is 3 to 25% by weight of SiO ₂ , 20 to 45% by weight of B ₂ O ₃ , and the balance
This is a composition range consisting of ZnO. The reason why this range is preferable is that if SiO ₂ is less than 3% by weight, the resulting film will not have sufficient moisture absorption resistance, and if it exceeds 25% by weight, it will deviate from the vitrification range shown in Figure 5. , B ₂ O ₃ falls outside the vitrification range shown in FIG. 5 when it is less than 20% by weight, and when it is more than 45% by weight, the moisture absorption resistance of the film becomes poor. Therefore,
The basic composition of glass frit is SiO ₂ 3-25% by weight,
Advantageously, the composition ranges from 20 to 45% by weight of B ₂ O ₃ and the balance ZnO. The top insulating coating for grain-oriented silicon steel sheets must satisfy many coating properties as described above.
In the case of SiO ₂ --B ₂ O ₃ --ZnO-based crystallized glass coatings, the coating properties are greatly influenced by the crystallization behavior of the glass frit, and among these, the crystallization rate is an issue. The crystallization rate depends on the composition of the glass frit and the heat treatment temperature and time for baking.
Depending on the composition of the glass frit and the baking conditions, the crystallization rate may be too high and more than 70% by weight may crystallize, resulting in an uneven coating with a poor space factor, or conversely, crystallization In some cases, the rate of crystallization was so slow that less than 5% by weight crystallized, resulting in a coating with poor heat resistance. Moreover, since the baking of the coating usually also serves as flattening annealing, the baking conditions are subject to restrictions. In such cases, in order to obtain good film properties, SiO ₂ -
B ₂ O ₃ - Li ₂ O, Na ₂ O, K ₂ O, MgO,
CaO, SrO, BaO, A ₂ O ₃ , P ₂ O ₅ , TiO ₂ ,
One or more components selected from Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, and ZrO ₂ can be added. In the present invention, these crystallization rate adjusting components are contained in an amount of 15 parts or less per 100 parts of the basic composition of SiO ₂ , B ₂ O ₃ , and ZnO. The coefficient of thermal expansion of the glass becomes large, which is disadvantageous for the purpose of applying tensile stress to the steel plate, so it should be 15 parts or less. In the present invention, SiO ₂ -B ₂ O ₃ -ZnO glass frit is applied and baked on a silicon steel plate at the same time.
5-70% by weight of crystalline phase with a melting point of 900℃ or higher
It is precipitated to form a glass-ceramic coating with improved heat resistance and magnetostriction properties. Melting point of precipitated crystal species
The reason for limiting the temperature to 900°C or higher is that the strain relief annealing temperature for grain-oriented silicon steel sheets is usually around 800°C;
A crystalline phase with a melting point lower than that cannot improve heat resistance, so it is necessary to limit the temperature to 900°C or higher.
In the case of the SiO ₂ -B ₂ O ₃ -ZnO-based crystallized glassy coating of the present invention, the precipitated crystal species are 2ZnO, SiO ₂ (willemite), 5ZnO・B ₂ O ₃ , ZnO・B ₂ O ₃ , Their melting points are 1512℃, 1045℃, and 980℃, respectively, which are much higher than the stress relief annealing temperature. This is the reason why the crystallized glass film of the present invention has good heat resistance. The reason for limiting the ratio of the precipitated crystal phase, that is, the degree of crystallinity, to 5 to 70% by weight is the second reason.
As shown in Figure and Figure 3, if it is less than 5% by weight, the heat resistance will not be improved, and if it is more than 70% by weight, the coating surface will not be smooth, the surface roughness will increase, and the space factor will decrease. let Therefore, the proportion of the crystalline phase in the crystallized glass film must be limited to 5 to 70% by weight. In the present invention, SiO ₂ -B ₂ O ₃ -ZnO-based glass frit is coated on a silicon steel plate and baked at a temperature of 750 to 950°C for 30 seconds to 20 minutes to form a glassy coating, and at the same time, A crystalline phase is precipitated. The reason for setting the baking temperature to 750 to 950℃ is 750
Although a glassy film is formed at temperatures lower than 950°C, the crystalline phase required to improve heat resistance does not precipitate in the glassy film, and baking at temperatures higher than 950°C is simply uneconomical. or cause deterioration of magnetic properties. Therefore, the baking temperature is 750-950
It needs to be at ℃. The reason for setting the baking time to 30 seconds to 20 minutes is that if the baking time is shorter than 30 seconds, the crystal phase required to improve heat resistance cannot be precipitated, and if it is longer than 20 minutes, productivity will decrease. .
Therefore, the baking time needs to be 30 seconds to 20 minutes. Glass frit crystallizes after being fused and coated on a steel plate during the baking process, and the rate of crystallization is influenced by three factors: the composition of the glass frit, baking temperature, and baking time. In order to obtain a crystallized glass coating with good properties, it is necessary to set an appropriate baking temperature and baking time in accordance with the glass frit composition. SiO ₂ -B ₂ O ₃
- In the case of ZnO-based glass frits, the SiO ₂ content has a large effect on the crystallization rate, and the lower the SiO ₂ content, the faster the crystallization progresses on the steel plate. Therefore, when glass frit with a low SiO ₂ content is baked, the baking temperature is set low, and conversely, when glass frit with a high SiO ₂ content is baked, the baking temperature is set high. Table 2 shows specific examples of the glass frit composition and baking conditions along with the characteristics of the crystallized glass coating obtained.

[Table] Glass frit having the composition shown in Table 2 was applied to a 0.30 mm thick grain-oriented silicon steel plate having a forsterite film to form a 2 micron thick film, and baked as shown in the table. The characteristics of crystallized glass coatings obtained by heat treatment under these conditions were investigated. The higher the baking temperature and the longer the baking time, the greater the degree of crystallinity of the glass-ceramic coating, and the heat resistance improves, but the space factor slightly decreases. The baking temperature and baking time are determined by comprehensively weighing the crystallization characteristics of the glass frit and the characteristics of the resulting coating. Experiments No. 11 and 13 in Table 2 are
When a glass frit consisting only of the SiO ₂ -B ₂ O ₃ -ZnO system is processed under the baking conditions shown in the table,
This is an example in which a film with poor space factor and heat resistance was obtained, and by adding a crystallization rate adjusting component to this, Experiment No.
As shown in 12 and 14, the film properties can be improved. Figure 6 shows SiO ₂ 10% by weight, B ₂ O ₃ 30% by weight,
A glass frit prepared by adding 6 parts of A ₂ O ₃ to a total of 100 parts by weight of 60 ZnO was coated on a silicon steel plate having a forsterite coating to a film thickness of 2 microns, and heated at 850°C for 1 hour. This figure shows a scanning micrograph of the surface of a crystallized glass film obtained by baking in a nitrogen atmosphere. 2-3 on the coating surface
It can be seen that fine crystals on the order of microns are uniformly precipitated. Figures 7 and 8 show a 30 x 280 mm Epstein specimen prepared by shearing a 0.35 mm thick coil from adjacent positions after final annealing and subjecting it to strain relief annealing. Showa 50-79442
This figure shows the magnetostrictive compressive stress characteristics of a grain-oriented silicon steel sheet on which a crystallized glass film and a phosphate film with a film thickness of 2 microns were formed by coating and baking the coating treatment solution disclosed in the above issue. . Glass frit composition: 13 parts by weight of SiO ₂
2 parts by weight of TiO was added to 31 parts by weight of B ₂ O ₃ , 56 parts by weight of ZnO, a total of 100 parts by weight, and the phosphate coating treatment liquid was a colloid containing 20% by weight of SiO ₂ . Add 35% by weight monomagnesium phosphate solution to 100m of aqueous silica dispersion.
50m and 3g of chromic anhydride. Apply it to the Epstein test piece mentioned above,
The magnetostrictive compressive stress characteristics are shown for those baked at 800°C for 1 minute in a nitrogen atmosphere and those subjected to strain relief annealing at 800°C for 3 hours in a nitrogen atmosphere. As is clear from FIGS. 7 and 8, the crystallized glass coating of the present invention exhibits far less increase in magnetostriction due to compressive stress than conventional phosphate coatings intended for adding tensile stress. This shows that strong tensile stress is applied to the steel plate. Next, a method for measuring the proportion of the crystalline phase in the crystallized glass film of the present invention, that is, the degree of crystallinity, will be described. Crystallization of thin glass on a steel plate takes a shorter heat treatment time than crystallization of bulk glass, so in order to make measurements that are more in line with actual conditions, the degree of crystallinity in the case of the present invention is measured using a stainless steel plate. After coating and heat-treating under the same baking conditions as those used for coating grain-oriented silicon steel sheets, the peeled powder obtained by peeling it was tested. Since crystallization generally occurs when two or more types of crystal phases precipitate simultaneously, it is difficult to determine the degree of crystallinity from the height of the crystalline diffraction peak in the powder X-ray diffraction pattern. The glass powder X-ray diffraction pattern gives a broad diffraction pattern due to amorphous scattering without any diffraction peaks characteristic of amorphous materials. The intensity of this amorphous scattering decreases continuously as the glass crystallizes. The degree of crystallinity in the present invention refers to a specific 2θ without a crystalline diffraction peak.
It was calculated from the degree of decrease in the amorphous scattering intensity at each position using the following formula. α=(Ig-Ix)×100/(Ig-Ic) Here, α is the degree of crystallinity (wt%), and Ig, Ix,
Ic denotes the amorphous scattering intensity of completely uncrystallized glass, sample and completely crystallized glass, respectively. The glass frit used in the present invention can be manufactured by the same method as the glass frit for the enamel industry. That is, various raw materials weighed so as to obtain glass of a predetermined composition are sufficiently pulverized and mixed, reacted and melted at high temperature, and then the molten fluid is poured into water at room temperature from high temperature and quenched to form a crushed glass material. There are several methods to obtain glass flakes, including passing them between water-cooled metal rolls.
Glass frit is prepared by pulverizing them using a ball mill or the like. In the process of manufacturing glass frit, components not described in the present invention may be unavoidably mixed, but these components can be tolerated in small amounts within a range that does not affect the coefficient of thermal expansion or crystallization characteristics of glass frit. can. The particle size of the glass frit is preferably as fine as possible in order to obtain a smooth and dense coating with a thickness of about 2 microns. The coating on the steel plate can be carried out continuously by the usual coating method in which the steel plate is immersed in glass frit obtained by dispersing glass frit in water and then squeezed with a rubber roll. The coating amount is preferably such that the thickness of the coating after baking is 1 to 3 microns. The baking atmosphere is preferably a neutral or reducing atmosphere to avoid oxidation of the steel plate itself. The top coat of grain-oriented silicon steel sheet is usually applied and baked on the surface of the forsterite coating formed during final annealing, but the crystallized vitrified coating of the present invention can be applied onto the silicon steel sheet having the forsterite coating. It can also be formed on a silicon steel sheet with a metallic luster and without a forsterite film, which is produced by using alumina or the like instead of magnesia as an annealing separator. A stress applying coating is formed. The present invention will be described below with reference to Examples and Comparative Examples. Example After final annealing of a grain-oriented silicon steel plate with a thickness of 0.30 mm, a 30 x 280 mm Epstein test piece was sheared and collected from a position adjacent to the coil from which the unreacted separator of magnesia on the surface had been removed, and strain relief annealing was performed. A material for coating was prepared. These samples include the three types of glass frits of the present invention shown in Table 3, the two types of glass frits described in Japanese Patent Publication No. 18603/1983 as comparative examples, and a glass frit having a typical pin glass composition as a glass mainly composed of _SiO2 . Glass frit was applied using a grooved rubber roll and heat treated in a nitrogen atmosphere under the baking conditions shown in Table 3 to obtain a silicon steel plate having a coating with a thickness of 2 microns. Table 3 shows the properties of these coated silicon steel sheets and coating materials having only the forsterite coating. It can be seen that the crystallized glass-ceramic coatings of the present invention in Examples 1 to 3 have superior heat resistance and magnetostrictive properties compared to the conventional glass-ceramic coatings shown in the comparative examples.

【table】

【table】

[Table] Coating materials were prepared in the same manner as in Examples 1 to 3. Six types of SiO ₂ -B ₂ O ₃ -ZnO glass frits shown in Table 4 were coated and heat treated under the baking conditions shown in the table to obtain a silicon steel plate with a coating of 2 microns thick. Ta. Table 4 shows the properties of these silicon steel sheets. The SiO ₂ -B ₂ O ₃ -ZnO glass frits of the present invention shown in Examples 4 to 7 had improved iron loss and magnetostrictive properties by baking at 800 to 850°C for a short time of 1 to 2 minutes. A crystallized glass-like coating having a good space factor and adhesion was formed, and it did not adhere at all during strain relief annealing, and even after strain relief annealing, it had a smooth and beautiful appearance.

【table】

【table】 [Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the relationship between the degree of crystallinity of the vitrified coating of the present invention and the heat resistance of the coating, and Figure 3 is a diagram showing the relationship between the degree of crystallinity and the heat resistance of the vitrified coating of the present invention. Figure 4 is a diagram showing the change in thermal expansion characteristics due to crystallization of the crystallized glass of the present invention, and Figure 5 is a diagram showing the relationship between SiO ₂ -B ₂ O ₃ -ZnO system. Figure 6 is a scanning electron micrograph of the surface of the crystallized vitrified coating of the present invention, and Figure 7 is the magnetostriction compression of the grain-oriented silicon steel sheet having the crystallized vitrified coating of the present invention. Diagram showing stress characteristics. FIG. 8 is a diagram showing magnetostrictive compressive stress characteristics of a grain-oriented silicon steel sheet having a phosphate coating disclosed in JP-A-50-79442.

Claims (1)

[Claims] 1. A grain-oriented silicon steel sheet having an insulating coating with low thermal expansion, the insulating coating having a vitreous coating formed by melt-forming glass frit having a low coefficient of thermal expansion of 8.5×10 ^-6 /°C or less. melting point
A grain-oriented silicon steel sheet having an insulating coating with a crystalline phase precipitated in a vitreous material, which has excellent heat resistance and magnetostriction properties, and has an insulating coating in which a crystalline phase of 900°C or higher is precipitated in a range of 5 to 70% by weight.