JPH0218391B2 - - 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 orientation of the secondary recrystallized grains in the steel sheet to a high degree in the rolling direction, and secondly, it is necessary to ensure that the impurities present in the final product steel are It is necessary to reduce precipitates as much as possible. Grain-oriented silicon steel sheets manufactured with such consideration have been improved over the years through many improvement efforts to date, and recently the sheet thickness has improved.
A 0.30mm product with a W17/50 value of 1.05W/Kg and low iron loss has been obtained. However, after the energy crisis a few years ago,
The trend for electrical equipment with lower power loss has become stronger, and raw steel sheets with even lower iron loss have been required as core materials for these devices. (Prior Art) By the way, methods for lowering the iron loss of grain-oriented silicon steel sheets include increasing the Si content, reducing the thickness of the product sheet, and making the secondary recrystallized grains thinner. Mainly metallurgical methods are generally known, such as reducing impurity content and aligning secondary recrystallized grains with (110)[001] orientation to a higher degree, but these methods are difficult to achieve in current production. We have reached the limit of our means,
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 made finer by irradiating the surface of the final product sheet with a laser beam at intervals of several mm approximately perpendicular to the rolling direction to introduce high dislocation density regions into 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 by forming regions with different tension imparting effects in the applied coating film, the refinement of the magnetic domain width of the steel sheet is facilitated. First, I will explain the method of solving the problem. 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 grain size 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 inside the base steel. This results in a dispersed 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. Through this secondary recrystallization annealing, the crystal grains of the steel sheet become coarse grains with a (110) [001] orientation. Also, by high-temperature purification annealing, some of the inhibitors present inside the steel sheet, such as S, Se, and N, are removed to the outside of the steel sheet base steel. Furthermore, in this purification annealing, the MgO in the annealing separator applied to the surface of SiO ₂ in the subscale of the steel plate surface layer reacts with the MgO in the annealing separator as shown in the following formula: 2MgO + SiO ₂ →Mg ₂ SiO ₄ on the steel plate surface. A film made of polycrystalline forsterite (Mg ₂ SiO ₄ ) is formed.
At this time, excess MgO serves as an unreacted substance and serves 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-applied insulating coating film, but as a result of various studies, the inventors found that by dividing and forming defective regions in the tension-applying insulating coating film, , Furthermore, the width of the magnetic domain of the steel plate is subdivided,
They discovered that the iron loss of steel sheets could be further improved. This invention is derived from the above knowledge. That is, the present invention provides a grain-oriented silicon steel sheet with a forsterite coating and a tension-applying insulating coating, in which no plastic strain region is observed in the surface layer of the steel, the insulating coating being continuous or discontinuous. The present invention is a low core loss grain-oriented silicon steel sheet characterized by having a shape defect region and whose properties do not deteriorate due to strain relief annealing. In addition, this invention provides a hot-rolled plate obtained by hot-rolling a silicon-containing steel slab, which is cold-rolled once or twice with intermediate annealing to obtain the final plate thickness.
After decarburization and primary recrystallization annealing, the surface of the steel plate is
In a method for manufacturing grain-oriented silicon steel sheets, which consists of a series of steps of applying an annealing separator mainly composed of MgO, final annealing, and then applying a top insulating coating, the forsterite coating after final annealing is applied. When applying a tension-applying insulating coating film as a top insulating coating to the surface of a grain-oriented silicon steel sheet, prior to applying the coating treatment liquid, a coating solution that is liquid repellent to the coating treatment liquid is applied. In addition, an organic film that disappears by burning or volatilization in the subsequent baking process is formed in a continuous or discontinuous line, and then the coating treatment solution is applied and baked to form a tension-applied insulating coating film. This is a method for manufacturing a grain-oriented silicon steel sheet with low iron loss, which does not deteriorate in properties due to strain relief annealing, and is characterized by forming linear defect areas. In this invention, the material steel sheets are limited to those in which no plastic strain region is observed because, as mentioned above, the method of subdividing magnetic domains by introducing plastic strain leads to significant deterioration of properties due to strain relief annealing. It is. This invention will be specifically explained below. In the steel sheet of this invention, we investigated the influence of the shape and orientation of defective regions formed in the tension-applied insulating coating on the subdivision of magnetic domains, and found that the shape was as shown in Figure 1A. It was recognized 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. Regarding the direction of the different tension region of 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, as for the width of the continuous or discontinuous linear region, as shown in FIG. 3, particularly excellent effects were obtained when the width was in the range of 0.015 to 0.8 mm. It should be noted that forming different tension regions repeatedly in a direction transverse to the rolling direction is effective in reducing the iron loss of the entire steel plate. As is clear from the experimental results, a range of 0.5 mm to 15 mm is desirable. 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. FIG. 5 shows an example of effective linear defect region formation when the tension-applying insulating coating film applies different tension to the steel plate. 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 manufactured by a known steel manufacturing method such as a converter or an electric furnace, and then made into a slab (steel billet) by an ingot-blowing method or a continuous casting method. A hot-rolled coil obtained by 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 containing MgO as a main component 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. , an organic film (hereinafter simply referred to as an evanescent film) that is liquid repellent to the coating treatment solution and disappears by burning or volatilizing in the subsequent baking process is formed in a continuous or discontinuous line. That is essential. Examples of the liquid-repellent, fugitive coating forming agent include resins such as alkyd, acrylic acid, epoxy, phenol, melanin and silicone, paints containing these, and oil-based magic ink. Next, a tension-imparting insulating coating treatment liquid is applied to the surface of the steel plate to which such a fugitive film has been attached, and the tension-imparting insulating coating film is formed by baking. High-temperature heating of 600 to 1000°C is required, and thus a tensile insulating coating with defect areas is obtained. In other words, by performing baking treatment at such a high temperature, the fugitive coating that has been formed in advance evaporates or volatilizes and disappears, so that the coating film after baking treatment has linear defect areas. will be formed. Since this linear defect region is only a very narrow region as described above, there is almost no deterioration in the insulation between the layers, and there is no problem in practice. The thickness of the insulating coating film is preferably about 0.5 g/m ² to 10 g/m ² (per side) in consideration of rust resistance and space factor. Furthermore, in the steel sheet of the present invention, the shape-changing portion is limited to the coating film portion, so the amount of change is small, and therefore the space factor is hardly reduced. The tension-applying insulating coating preferably has a coefficient of thermal expansion of about 6 x 0 ^-6 /°C or less, and the coating liquid contains at least one of magnesium phosphate and aluminum phosphate, and colloidal silica. Also suitable is a treatment liquid containing at least one of chromic anhydride and chromate as a main component. (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 defective region in the tension-applying coating, 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 to be done. 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 biggest drawback is that the plastic strain in the surface layer of the steel base disappears at high temperatures, which leads to deterioration of iron loss, but in the case of this invention, the results are good regardless of the presence or absence of strain relief annealing. Indicates iron loss. (Example) Example 1 A fugitive film-forming agent was applied to the surface of a finish-annealed grain-oriented silicon steel sheet (thickness: 0.23 mm) containing 3.3% Si and having a uniform forsterite film on the surface. The varnish was repeatedly printed in a continuous straight line with a width of 0.2 mm and an interval of 5 mm in a direction perpendicular to the rolling direction, and then dried at 300°C. Next, add 40g of magnesium phosphate to 100ml of water.
Tension-applied insulating coating liquid containing 3 g of chromic anhydride and 0.8 g of colloidal silica particles (50 to 1000 Å) containing 15 g of _SiO2 (coefficient of thermal expansion after film formation: 4 x 10 ^-6 1/℃) was applied uniformly onto the surface of the steel plate and baked at 800℃. As a result of this baking process, the varnish disappeared and a linear defect area was formed in the insulating coating. 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, an investigation was conducted when the surface of such a steel plate was irradiated with laser light in a row of dots at 0.4 mm intervals, facing the rolling direction and the angular direction, with the interval between rows being 4 mm (Comparative Example B). The results 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 Varnish was applied perpendicularly to the rolling direction on the surface of a finish-annealed grain-oriented silicon steel plate (thickness: 0.30 mm) containing 3.3% Si and having a uniform forsterite coating on the surface. It was repeatedly printed in a continuous straight line with a width of 0.1 mm and an interval of 3 mm, and dried at 150°C. Then, the same coating treatment solution as in Example 1 was applied.
After applying it evenly to the steel plate surface and drying it at 400℃,
Baked at 800℃. As a result of this baking process, the varnish was burned away, so that no tension-applying coating film was formed in the varnished area, and linear defect areas were 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 shape, inclination to the rolling direction, and interval measurement procedures of the defect area formed in the insulating coating, respectively. Figure 2 shows the linear defect area and the rolling A graph showing the influence of the angle with the direction on iron loss characteristics. Figure 3 is a graph showing the relationship between the width of the linear defect area and the iron loss value. Figure 4 is a graph showing the relationship between the width of the linear defect area and the iron loss value. FIG. 5 is a graph showing the relationship between the interval and iron loss value, and is a diagram showing an example of effective defect region formation when the tension-applying insulating coating film exerts a different tension on the steel plate.

Claims (1)

[Scope of Claims] 1. A grain-oriented silicon steel sheet with a forsterite coating and a tension-applying insulating coating film, in which no plastic strain region is observed in the surface layer of the base metal, the tension-applying insulating coating film comprising: A low iron loss grain-oriented silicon steel sheet characterized by having continuous or discontinuous linear defect areas, and whose properties do not deteriorate due to strain relief annealing. 2. The continuous or discontinuous linear defect area of the tension-applying insulating coating forms an angle of 60° to 90° with respect to the rolling direction of the steel plate, and the width of the linear defect area is 0.015 to 0.8 mm. and the interval between each linear region is
The low iron loss grain-oriented silicon steel sheet according to claim 1, which has a thickness of 0.5 to 15 mm. 3 A hot-rolled sheet obtained by hot rolling a silicon-containing steel slab is cold-rolled once or twice with intermediate annealing to achieve the final thickness, and then decarburized and primary recrystallized. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps of annealing, then applying an annealing separator containing MgO as a main component to the surface of the steel sheet, performing final annealing, and then applying a top insulating coating, When applying a tension-applying insulating coating as a top insulating coating to the surface of a grain-oriented silicon steel sheet with a forsterite coating that has undergone final finish annealing, the coating treatment solution is applied prior to application of the coating treatment solution. By forming a continuous or discontinuous linear organic film that has liquid repellency against the surface of the product and disappears by burning or volatilizing in the subsequent baking process, then applying the coating treatment liquid and then baking, A method for producing a grain-oriented silicon steel sheet with low core loss, which does not cause deterioration in properties due to strain relief annealing, the method comprising forming linear defect areas in a tension-applied insulating coating film.