JPH0218392B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) Regarding grain-oriented silicon steel sheets with low iron loss and their manufacturing methods, the technical content described in this specification is to reduce the tensile strength formed over the coating on the surface of the silicon steel sheet, especially the forsterite coating. It is related to improving core loss by imparting non-uniformity to the applied insulating coating film and defining regions where different tensions act on the surface. Grain-oriented silicon steel sheets are mainly used as iron cores for transformers and other electrical equipment, and are required to have excellent magnetization characteristics, especially low iron loss (represented by W17/50). For this purpose, firstly, it is necessary to align the <001> grain direction of the secondary recrystallized grains in the steel sheet to a high degree in the rolling direction, and secondly, it is necessary to align the <001> grain direction of the secondary recrystallized grains in the steel sheet with a high degree of alignment, and secondly, it is necessary to prevent impurities present in the final product steel. It is necessary to reduce precipitates as much as possible. Grain-oriented silicon steel sheets manufactured with this consideration have been improved over the years through many improvement efforts, and recently, the thickness of the grain-oriented silicon steel sheets has increased to 0.30.
mm product with a W17/50 value of 1.05W/Kg and low core loss. However, after the energy crisis a few years ago,
The trend for electrical equipment with lower power loss has become stronger, and grain-oriented silicon steel sheets with even lower core loss have been required as core materials for these devices. (Prior art) By the way, methods to reduce the iron loss of grain-oriented silicon steel sheets include increasing the Si content, reducing the thickness of the product sheet, making secondary recrystallized grains finer, and reducing the impurity content. Metallurgical methods are generally known, such as aligning secondary recrystallized grains with (110) [001] orientation to a higher degree, but these methods have reached their limits with current production methods. It has reached
Further improvement is extremely difficult, and even if some improvement is recognized, the effectiveness of iron loss improvement is small compared to the efforts made. Apart from these methods, as disclosed in Japanese Patent Publication No. 54-23647, a method has been proposed in which secondary recrystallization grains are made finer by forming a secondary recrystallization inhibiting region on the surface of the steel sheet. has been done. However, this method cannot be said to be practical because control of the secondary recrystallized grain size is not stable. In addition, Japanese Patent Publication No. 58-5968 discloses that micro-strain is introduced into the surface layer of the steel plate after secondary recrystallization using ballpoint pen-shaped balls, thereby making the width of the magnetic domain finer and reducing iron loss. The technology is also
Publication No. 57-2252 discloses that the width of the magnetic domain is refined by irradiating the surface of the final product sheet with a laser beam at intervals of several mm almost perpendicular to the rolling direction to introduce high dislocation density regions in the surface layer of the steel sheet. Techniques have been proposed to reduce iron loss. Further, JP-A-57-188810 proposes a similar technique of introducing micro-strain into the surface layer of a steel sheet by electrical discharge machining, thereby refining the magnetic domain width and reducing iron loss. (Problems to be Solved by the Invention) These three methods all introduce minute plastic strain into the surface layer of the steel sheet after secondary recrystallization to refine the magnetic domain width and reduce iron loss. Although it is uniformly practical and has an excellent iron loss reduction effect, heat treatment such as strain relief annealing after punching, shearing, and winding of steel plates, and baking treatment of coatings This has the disadvantage that the effect of introducing plastic strain is diminished. Note that if a minute plastic strain is introduced after the coating treatment, the insulating coating must be reapplied to maintain insulation, as disclosed in Japanese Patent Application Laid-open No. 57-192223, and the strain This results in a significant increase in the number of processes, including the application process and re-coating process, resulting in an increase in costs. This invention has a magnetic domain width refining means that is different from the above-mentioned prior art, and has no characteristic deterioration even after strain relief annealing at high temperature.
The object of the present invention is to provide a grain-oriented silicon steel sheet that can ensure the effectiveness of magnetic domain width refinement in a product. (Means for Solving the Problems) This invention is directed to a tensile strength coating formed on a normal forsterite coating constituting the surface coating of a grain-oriented silicon steel sheet for the purpose of improving magnetic properties and surface properties. This work is based on the new finding that the magnetic domain width refinement of the steel sheet is facilitated by forming regions with different tension-applying effects in the applying-type coating. First, I will explain how the solution was discovered. In the manufacturing process of grain-oriented silicon steel sheets, the steel sheets that have been cold-rolled to the final thickness are usually subjected to decarburization annealing to remove harmful carbon. Through such annealing, the steel sheet becomes a primary recrystallized texture containing an inhibitor consisting of a finely dispersed second phase, but at the same time, the surface layer of the steel sheet has fine SiO ₂ particles dispersed within the base steel. It has a subscale structure. After applying an annealing separator containing MgO as a main component to the surface of this decarburized/primary recrystallized plate, it is subjected to secondary recrystallization annealing, followed by high-temperature purification annealing at around 1200°C. As a result of this secondary recrystallization annealing, the crystal grains of the steel sheet become coarse grains with (110) [001] orientation. Furthermore, some of the inhibitors such as S, Se, and N that were present inside the steel sheet due to high-temperature purification annealing are removed from the steel sheet base metal. Furthermore, in this purification annealing, SiO ₂ in the subscale of the steel sheet surface layer and MgO in the annealing separator applied to the surface react as shown in the following formula, 2MgO + SiO ₂ → Mg ₂ SiO ₄ and , a film made of polycrystalline forsterite (Mg ₂ SiO ₄ ) is formed.
At this time, excess MgO acts as an unreacted substance to prevent fusion between the steel plates. After high-temperature purification annealing, the steel sheet is processed to remove unreacted annealing separator and to remove the top coat of insulation coating and coil set. At this time, as the insulating coating, a tension-applying coating is often applied for the purpose of improving magnetostrictive properties and iron loss. When this tension-applying coating is formed on the surface of a steel sheet, it exhibits a coefficient of thermal expansion smaller than that of silicon steel, and therefore can apply tension to the steel sheet. In other words, when the material that forms on the surface of the steel sheet in a stress-free state during high-temperature baking is cooled to room temperature, the amount of shrinkage differs between the steel sheet base and the coating film, depending on the difference in their thermal expansion coefficients. As a result, an elastic tension force acts on the surface of the steel plate, while an elastic compression force acts on the coating film. Therefore, performing the baking treatment at a high temperature is more advantageous in terms of tension imparting effect. The width of the magnetic domain of the steel sheet is subdivided to some extent by this tension-applying insulating coating film, but as a result of various studies, the inventors have found that the tension-applying insulating coating film is able to locally apply tension to the base steel. They found that by defining regions that do not substantially contribute to the addition of magnetic particles, the width of the magnetic domains of the steel sheet is further subdivided, and the iron loss of the steel sheet is further improved. This invention is derived from the above knowledge. That is, in this invention, a hot-rolled sheet obtained by hot rolling a silicon-containing steel slab is subjected to cold rolling once or twice with intermediate annealing to achieve the final thickness, and then decarburized and A grain-oriented silicon steel sheet is produced by a series of steps of first recrystallization annealing, then applying an annealing separator containing MgO as a main component to the surface of the steel sheet, final annealing, and then applying a top insulating coating. In the manufacturing method, when applying a tension-applying insulation coating film as a top insulation coating on the surface of a grain-oriented silicon steel sheet with a forsterite coating that has undergone final finish annealing, prior to applying the coating treatment liquid, By forming a continuous or discontinuous linear insulating film that is liquid repellent to the coating treatment liquid and is non-tension-applying type, and then applying and baking the coating treatment liquid, a tension-applying type insulation coating is formed. It consists of forming linear heterogeneous regions in the insulating coating that do not contribute to imparting tension to the base steel.
This is a method for manufacturing grain-oriented silicon steel sheets with low iron loss that does not cause deterioration of properties due to strain relief annealing. This invention will be specifically explained below. In the steel sheet of this invention, we investigated the influence of the shape and orientation of the heterogeneous regions formed in the tension-applying coating on the subdivision of the magnetic domain, and found that the shape was as shown in Figure 1A. It has been found that continuous or discontinuous linear shapes are particularly effective in reducing iron loss. However, in discontinuous linear regions, the effect decreased when the distance between points was 0.5 mm or more.
In this respect, even if a portion of the line was gradually removed as in the case of a broken line, the effect of reducing iron loss was almost the same as in the case of a linear line. In addition, regarding the direction of the heterogeneous region in the insulating coating film, as shown in Figure 1B and Figure 2,
An angle of 60 to 90 degrees with respect to the direction of rolling was particularly effective. Furthermore, particularly excellent effects were obtained when the width of the continuous or discontinuous linear region was in the range of 0.015 to 1.5 mm, as shown in FIG. It is effective to repeatedly form the heterogeneous regions in a direction transverse to the rolling direction in order to reduce the core loss of the entire steel plate. For example, the spacing between the regions as shown in Fig. It is desirable to set it in the range of 0.5 mm to 15 mm as is clear from the experimental results. Further, the effect is almost the same whether such regions are formed on both sides of the steel plate or only on one side. Furthermore, in this invention, linear does not mean only straight lines in the strict sense, but also includes curves with small curvature, wavy lines, and the like. Next, we investigated the effect of the thermal expansion coefficient of the non-tensioned insulating coating that constitutes the linear heterogeneous region on the iron loss reduction effect, and found that the It has been found that a range of 8 to 20×10 ⁻⁶ 1/° C. is suitable for the coefficient of thermal expansion. Inorganic heat-resistant adhesives containing borosiloxane resins, titanium compounds, alumina compounds, and cobalt compounds as main raw materials are advantageously suitable as agents for forming such non-tension-applying insulating films with liquid repellency. do. On the other hand, it is desirable that the thermal expansion coefficient of the tension-applied insulating coating film is 6×10 ^-6 1/°C or less, and the treatment liquid for this purpose includes at least one of magnesium phosphate and aluminum phosphate, and a colloidal A coating liquid containing silica and at least one of chromic anhydride and chromate as a main component is suitable. Further, the thickness of the insulating coating film is desirably about 0.5 to 10 g/m ² per side in consideration of magnetic properties, insulation, space factor, rust resistance, etc. Incidentally, FIGS. 6A and 6B show examples of suitable division formation of linear heterogeneous regions. As shown in FIG. 2B, it does not matter at all that the thickness of the non-tension-applied insulation coating forming the linear heterogeneous region is different from that of the tension-applied insulation coating. Next, a method for manufacturing a grain-oriented silicon steel sheet according to the present invention will be explained. The material of this invention is produced by a known steel-making method, such as a converter electric furnace, and then into a slab (steel billet) by an ingot-blowing method or a continuous casting method.
After that, a hot rolled coil obtained by hot rolling is used. This hot rolled sheet needs to have a composition containing approximately 2.0 to 4.0% Si. This is because if Si is less than 2.0%, the iron loss will deteriorate significantly, and if it exceeds 4.0%, cold workability will deteriorate. As for the other components, any material components of grain-oriented silicon steel sheets can be used. Next, cold rolling is performed to achieve the final target thickness, but cold rolling is performed once or twice with intermediate annealing.
This is done by cold rolling twice. At this time, if necessary, uniform annealing of the hot rolled sheet or warm rolling instead of cold rolling may be performed. The cold-rolled sheet having the final thickness is subjected to primary recrystallization annealing in an oxidizing atmosphere that allows decarburization or a weakly oxidizing atmosphere that allows subscale formation. Next, after applying an annealing separator mainly composed of MgO to the surface of the steel sheet, secondary recrystallization annealing, high-temperature purification annealing, and final finishing annealing are performed to form a forsterite coating. Thereafter, a tension-applying insulating coating film is applied to the surface of the grain-oriented silicon steel sheet having the uniform forsterite coating obtained in this way. Therefore, it is important to form a continuous or discontinuous linear insulating coating that is liquid repellent to the coating treatment liquid and does not substantially contribute to imparting tension to the base steel. It is. Next, on the surface of the steel plate on which such a non-tensioned insulation coating has been formed in a continuous or discontinuous line, a tensioned insulation coating treatment liquid is applied and then baked to form a tensioned insulation coating. . In this way, a tension-applying insulating coating film is formed in which heterogeneous regions that do not substantially contribute to imparting tension to the base iron are formed in continuous or discontinuous lines. (Function) The reason why the iron loss characteristics are improved by this method is considered to be as follows. In other words, by providing a linear heterogeneous region in the tension-applying insulating coating film, a region of different tension is created on the surface of the steel sheet, but this different tension introduces elastic strain to the surface of the steel sheet, and as a result, the magnetic domains are effectively subdivided. This is because it will be made into Unlike the conventional method in which plastic strain areas and high dislocation density areas such as laser irradiation marks are present in the surface layer of the steel plate, there are no artificial plastic strain areas, so it is usually heated to around 800℃ for 1 minute. It has the notable advantage that there is no deterioration in iron loss even after strain relief annealing is performed over several hours. In the former case, the plastic strain in the surface layer of the steel base disappears at high temperatures, leading to deterioration of iron loss, which is the biggest drawback. Indicates iron loss. (Example) Example 1 Polysiloxane resin ( Polysiloxane resin 100: silylon resin 50: kaolinite 10) was repeatedly applied in a continuous straight line perpendicular to the rolling direction with a width of 0.3 mm and an interval of 5 mm, and then dried at 300°C. Next, add 40g of magnesium phosphate to 100ml of water.
Colloidal silica and silica microparticles (50-1000 Å) containing 3 g of chromic anhydride, 15 g of SiO ₂ min 0.8
A tension-applying insulating coating liquid (coefficient of thermal expansion after film formation: 4 × 10 ^-6 1/°C) containing g
It was applied uniformly to the surface of a steel plate and baked at 800℃. The product board thus obtained was further heated to 800℃, 3
Table 1 shows the results of investigating the iron loss characteristics after time stress relief annealing. For comparison, Table 1 shows the case where a uniform insulating coating was formed on the entire surface of the steel plate (Comparative Example A),
In addition, a laser beam is directed onto the surface of the steel plate in a row of dots at 0.4 mm intervals in a direction perpendicular to the rolling direction.
The investigation results obtained when irradiation was performed under the condition that the distance between rows was 4 mm (Comparative Example B) are also shown.

[Table] As is clear from the table, the iron loss characteristics of the product sheets obtained according to the present invention were significantly improved, and this effect did not deteriorate even after strain relief annealing. On the other hand, Comparative Example A, in which an insulating coating was simply applied to the entire surface of the steel sheet, did not achieve a sufficiently satisfactory iron loss reduction effect, and Comparative Example B, in which laser light was used, did not achieve a satisfactory iron loss reduction effect with laser light irradiation. Although a good iron loss value was obtained, the iron loss characteristics significantly deteriorated after strain relief annealing. Example 2 The same porosiloxane resin as in Example 1 was applied to the surface of a finish-annealed grain-oriented silicon steel plate (thickness: 0.30 mm) containing 3.3 wt% Si and having a uniform forsterite coating on the surface. Repeated application and heating at 200℃
dried with. Then, in the same manner as in Example 1, a tension-applying insulating coating film was formed. Table 2 shows the results of examining the iron loss characteristics of the thus obtained product sheets before and after the insulation coating treatment and after strain relief annealing at 800° C. for 5 hours in N ₂ . For comparison, Table 2 shows the case where a uniform insulating coating film is formed on the entire surface of the steel plate (Comparative Example C),
In addition, a laser beam is directed in a row of dots at 0.4 mm intervals on the surface of the steel plate in a direction perpendicular to the rolling direction.
The investigation results obtained when irradiation was performed under the condition that the distance between rows was 4 mm (Comparative Example D) are also shown.

[Table] As is clear from the table, the iron loss characteristics of the product sheets obtained according to the present invention were significantly improved, and this effect did not deteriorate even after strain relief annealing. On the other hand, Comparative Example C, in which an insulating coating was simply applied to the entire surface of the steel sheet, did not achieve a sufficiently satisfactory iron loss reduction effect, and Comparative Example D, in which laser light was used, did not achieve a satisfactory iron loss reduction effect with laser light irradiation. Although a good iron loss value was obtained, the iron loss characteristics significantly deteriorated after strain relief annealing. (Effects of the Invention) Thus, according to the present invention, it is possible to obtain a grain-oriented silicon steel sheet with low iron loss that does not cause deterioration of properties even when subjected to strain relief annealing.

[Brief explanation of drawings]

Figure 1 A, B, and C are diagrams showing the measurement procedure for the shape, inclination to the rolling direction, and spacing of the heterogeneous regions formed in the insulating coating, respectively. Figure 2 shows the linear heterogeneity regions and the rolling direction. Figure 3 is a graph showing the relationship between the width of the linear heterogeneous region and the iron loss value, and Figure 4 is a graph showing the relationship between the width of the linear heterogeneous region and the iron loss characteristic. Figure 5 is a graph showing the relationship between spacing and iron loss value.
Figure 6 A and B, which are graphs showing the influence of the thermal expansion coefficient of the different regions in the tension-applied insulating coating film on the iron loss characteristics, both show the case where the tension-applying insulating coating film exerts different tension on the steel sheet. FIG. 3 is a diagram illustrating an example of effective heterogeneous region division formation.

Claims (1)

[Scope of Claims] 1. A hot-rolled plate obtained by hot rolling a silicon-containing steel slab is subjected to cold rolling once or twice with intermediate annealing to obtain the final thickness, and then de-rolled. Directed silicon consists of a series of steps: charcoal/primary recrystallization annealing, then applying an annealing separator mainly composed of MgO to the surface of the steel sheet, final annealing, and then applying a top insulating coating. In the method for producing a steel sheet, when a tension-applying insulation coating film is applied as a top insulation coating on the surface of a grain-oriented silicon steel sheet with a forsterite film that has undergone final finish annealing, prior to applying the coating treatment liquid. Then, by forming a continuous or discontinuous line-shaped insulating film that is liquid repellent to the coating solution and does not apply tension, the coating solution is applied and baked to create tension. A method for manufacturing a grain-oriented silicon steel sheet with low core loss, which does not cause deterioration in properties due to strain relief annealing, characterized by forming linear heterogeneous regions that do not contribute to imparting tension to the base steel in an imparted insulating coating film.