JPH028028B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field Regarding grain-oriented silicon steel sheets with low core loss and their manufacturing methods, the technical content described in this specification is particularly focused on imparting non-uniformity to the coating on the surface of the steel sheet to define areas where different tensions act on the surface. This is related to improving iron loss. BACKGROUND TECHNOLOGY 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). . To achieve this, 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 highly align the <001> grain orientation of the secondary recrystallized grains in the steel sheet, 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 under these considerations have been improved over the years through many improvement efforts, and have recently reached a thickness of 0.30 mm.
A low iron loss product with a W17/50 value of 1.05W/Kg has been obtained. However, after the energy crisis a few years ago,
There is a growing trend for electrical equipment with lower power loss, and unidirectional silicon steel sheets with even lower core loss are now required as core materials for these devices. Technical technology and its problems 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 plate, making the secondary recrystallized grains finer, and reducing the impurity content. Mainly metallurgical methods are generally known, such as aligning the secondary recrystallized grains in the (110) [001] orientation to a higher degree, but these methods are based on current production methods. has already reached its limit, and it is extremely difficult to improve it any further, and even if some improvement is recognized, the effective effect of improving iron loss 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. These three methods are
Both methods aim to reduce iron loss by refining the magnetic domain width by introducing minute plastic strain into the surface layer of the steel sheet after secondary recrystallization, and are both practical and uniform in reducing iron loss. Although the effect is excellent, it has the disadvantage that the effect of introducing plastic strain is diminished by heat treatment such as strain relief annealing after punching, shearing, and winding of the steel plate, and baking treatment of the coating. In addition, if a minute plastic strain is introduced after the coating process, the insulating coating must be reapplied to maintain insulation, resulting in a significant increase in the number of processes including the strain imparting process and reapplying process.
This results in increased costs. Purpose of the Invention The present invention has a magnetic domain width refining means that is different in concept from the above-mentioned prior art, so that even after strain relief annealing at high temperature, the characteristics do not deteriorate.
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. Origin of the Invention The present invention provides that the existence of regions of different thicknesses, that is, regions of different thickness in the forsterite coating constituting the surface coating of a grain-oriented silicon steel sheet, extremely advantageously contributes to the refinement of the magnetic domain width of the product; This is based on the new finding that if a tension-applying insulating coating is applied in the presence of such a region of different thickness, the combined action of both will further enhance the desired effect. History of elucidation of the solution 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. This decarburized and primary recrystallized plate is coated with an annealing separator mainly composed of MgO on its surface, then subjected to secondary recrystallization annealing, followed by high-temperature purification annealing at around 1200°C. Due to this secondary recrystallization annealing, the crystal grains of the steel sheet are coarse grains with (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, during this purification annealing, the SiO ₂ in the subscale of the surface layer of the steel sheet and the MgO applied to the surface during the annealing process react as shown in the following equation, 2MgO + SiO ₂ → Mg ₂ SiO ₄ , forming a phosphorus on the surface of the steel sheet. A film made of polycrystalline tellite (MgO 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 any unreacted annealing separator and, if necessary, to remove the top coat of insulation coating and coil set. By the way, the inventors re-investigated the role of the forsterite coating and found that this coating applies tension to the steel sheet and subdivides the magnetic domains, similar to a tension-applied coating.Moreover, the effect of subdivision of the magnetic domain width of the steel sheet is significant. It was found that there were slight differences depending on the location. Therefore, as a result of a thorough study of the tendency of the magnetic domain width of steel sheets to become finer, it was discovered that the effect of magnetic domain fineness is significant in areas where the thickness of the forsterite coating changes. Structure of the Invention The present invention is derived from the above knowledge. In other words, the present invention provides a grain-oriented silicon steel sheet in which no plastic strain region is observed in the surface layer of the base metal, and which has a forsterite coating on the entire surface, wherein the forsterite coating has a continuous or discontinuous linear uneven thickness. A tension-applying insulating coating film having a thermal expansion coefficient of 9.8×10 ^-6 1/°C or less is provided on the coating, and the properties do not deteriorate even when subjected to strain relief annealing. It is a grain-oriented silicon steel plate with low iron loss. In this invention, the material steel sheets are limited to those in which no plastic strain region is observed because, as will be described later, the method of subdividing magnetic domains by introducing plastic strain causes significant deterioration of properties due to strain relief annealing. be. This invention will be specifically explained below. Now, the inventors locally changed the thickness of the forsterite coating in the laboratory, conducted various studies on the effects of the area, shape, thickness difference, orientation, etc. on the subdivision of magnetic domains, and calculated the iron loss. We investigated the relationship between In this experiment, the thickness could be locally reduced by chemically dissolving forsterite using an HF solution, and the thickness could be increased by adding forsterite using electrostatic coating. I went. As a result, it was found that a continuous or discontinuous linear uneven shape as shown in FIG. 1A is particularly effective in reducing iron loss as the shape of the different thickness region of forsterite. However, in discontinuous linear uneven areas, the distance between points is
The effect decreased when the distance was 0.5 mm or more. If part of the line is missing little by little like this dot-dashed line,
The iron loss reduction effect was almost the same as in the linear case. Next, regarding the direction of the linear uneven thickness regions of the forsterite coating, it is particularly effective to set the direction at an angle of 60 to 90 degrees with respect to the rolling direction, as shown in Figure 1B and Figure 2. . Furthermore, regarding the thickness difference in the forsterite different thickness region, almost the same results were obtained whether the forsterite was made thicker or thinner, as shown in Figure 3, and in either case, the thickness difference was 0.3μ.
It was found that it is effective if it is more than m. Next, regarding the width of the continuous or discontinuous linear uneven area,
As shown in Figure 4, 0.05~2.0mm, especially 0.8~1.5
Excellent effects were obtained in the mm range. Note that the linear uneven thickness region of the forsterite coating is
Repeatedly forming in a direction transverse to the rolling direction
It is effective to reduce the iron loss of the entire steel plate, and it is desirable that the interval between the regions shown in FIG. 1C be in the range of 1 mm to 30 mm as shown in FIG. 5, for example. Furthermore, the effect of forming linear regions of different thickness in the forsterite coating is almost the same whether it is formed on both sides of the steel plate or only on one side. Next, after the coating was formed, a steel plate with a forsterite coating having such a linear region of different thickness was coated with a 5x
When we measured the iron loss after coating and baking a coating liquid with a thermal expansion coefficient of 10 ^-6 1/°C to form a tension-applying insulating coating film, we found that it was simply a false film, as shown in Figure 6. A significant iron loss improvement effect was observed compared to the case where linear regions of different thickness were formed in the telite coating. It was also found that the effect of tension coating was greater than that in the case where linear regions of different thickness were not formed. Accordingly, we tested various coatings with different coefficients of thermal expansion on a grain-oriented silicon steel sheet with a forsterite coating that has linear regions of different thickness, and found that the coefficient of thermal expansion was 9.8×
It was found that a satisfactory iron loss reduction effect can be obtained if the temperature is below 10 ^-6 1/℃. Here, as a method for forming linear regions of different thickness in the forsterite coating, we use the same primary recrystallized steel sheet as the starting material and control the thickness of the coating by utilizing the forsterite coating formation reaction during high-temperature purification annealing. For example, by creating an unapplied area of the annealing separator on the surface of the steel sheet after decarburization annealing, or applying the annealing separator to the steel sheet surface prior to applying the separator.
A method for attaching reaction inhibitors with SiO ₂ , water-repellent substances for annealing separator slurry, and oxidizing agents for Si in steel in continuous or discontinuous lines, for uniform forsterite coating after high-temperature purification annealing. A method of reducing the thickness of the forsterite coating by dissolving it in continuous or discontinuous lines through chemical dissolution treatment. A disc-shaped rotating grindstone is lightly contacted with the uniform forsterite coating after high-temperature purification annealing. A method of reducing the coating thickness by removing the forsterite coating in a continuous or discontinuous line. A tension-applied coating is applied on the uniform forsterite coating after high-temperature purification annealing, and then a pulsed coating is applied on top of the uniform forsterite coating after high-temperature purification annealing. A method of reducing the thickness of the forsterite film by irradiating the coating film and the forsterite film with a high-power laser beam to volatilize the coating film and the forsterite film in a continuous or discontinuous line, and a method of reducing the thickness of the forsterite film after high-temperature purification annealing. The thickness of the forsterite coating is reduced by applying a tension coating on the coating, applying light pressure with a fine-tipped iron needle, and removing part of the coating and forsterite coating in continuous or discontinuous lines. I tried this method. In addition, regarding , after this,
The same tension-applied coating was applied. As a result, ~W17/50 for both
An extremely low core loss of 0.96 to 0.99 W/Kg was obtained. However, after strain relief annealing at 800℃ for 1 hour, low iron loss of 0.96 to 0.99W/Kg was obtained for , , and , but significantly lower core loss of 1.04W/Kg was obtained for , , and . The iron loss deteriorated. As a result of investigating the cause of this, it was found that among the samples before strain relief annealing, a plastic strain region was formed in the surface layer of the steel base directly under the forsterite thickness reduction area, and this plastic strain was caused by strain relief annealing. It was discovered that it had been released and disappeared. Therefore, in order to prevent the characteristics from deteriorating due to strain relief annealing, it is important to prevent the introduction of a plastic strain region in the surface layer of the steel plate base. Regarding the steel plate after strain relief annealing, the annealing restores the coating removal area to a uniform surface by causing the surrounding coating to flow into the coating removal area, which is preferable from the standpoint of insulation and rust resistance. I found out. When we investigated the annealing temperature required to repair such coatings, we found that
A temperature range of 600-900°C was found to be suitable. Next, a more effective range of the different thickness region in the forsterite coating according to the present invention will be described. The shape of the different thickness region is particularly effective if it is a continuous linear unevenness, but it can also be replaced by a non-continuous shape, that is, a row of dots. However, in the case of such discontinuous linear unevenness, the effect becomes small if the distance between the points is 0.5 mm or more. Also, the width of such a linear uneven thickness region is 0.05
A range between 2.0 mm and 2.0 mm is particularly advantageous in terms of effectiveness. Next, regarding the orientation of the linear uneven regions, it is particularly preferable that the angle range is from 60 to 90 degrees with respect to the rolling direction. There is no effect when the direction is parallel to the rolling direction, and the maximum effect is obtained when the direction is perpendicular to the rolling direction. This angle with respect to the steel plate rolling direction is particularly important.
The reason why the iron loss reduction effect weakens when the width of the different thickness region is too wide or when it is an isolated point is thought to be because its directionality becomes unclear. These continuous or discontinuous linear uneven areas are
It is preferable that the regions are repeatedly present, including those having different shapes, widths, and angles with respect to the rolling direction, and a range of 1.0 to 30 mm is particularly effective for the interval between regions at this time. Note that in this invention, linear does not mean only a straight line in the strict sense, but also includes curves with small curvature, wavy lines, and the like. Further, whether the regions of different thicknesses of the forsterite coating are present on both sides of the steel plate or only on one side, the effect is almost the same. A 9.8
Grain-oriented silicon steel sheets according to the invention can be produced by applying a tensioned insulating coating having a coefficient of thermal expansion of less than 10 ^-6 1/°C. Another method is to apply 9.8×
10 ^-6 After coating with a tension-applied coating film exhibiting a coefficient of thermal expansion of 1/℃ or less, topcoating is applied in continuous or discontinuous lines without imparting plastic strain to the surface layer of the steel plate. There is a method in which a linear thinning region is formed in the forsterite coating by removing the forsterite coating and a part of the forsterite coating, and then annealing is performed in a temperature range of 600 to 900°C to lead to repair of the coating defect. . As for the type of coating, since surface tension is imparted by the difference in coefficient of thermal expansion between the steel sheet and the coating film, there must be a certain degree of difference in the coefficient value.
It has been confirmed that if the material has a thermal expansion coefficient of 10 ^-6 1/℃ or less, a satisfactory low core loss value can be obtained due to the synergistic effect of the different thickness effect of the forsterite coating and the coating surface tension imparting effect. It is being The thickness of the coating 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 formation change part is limited to the coating part, so
The amount of change is small and therefore hardly reduces the space factor. The reason why the iron loss characteristics are improved by forming linear regions of different thickness in the forsterite coating according to the present invention is considered to be as follows. In other words, by providing linear regions of different thickness in the coating, different tension regions are 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. It is. 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. Examples Example 1 A silicon steel material containing 3.2% Si is made into a cold-rolled steel plate with a thickness of 0.30 mm according to a conventional method, and then decarburized and
After primary recrystallization annealing, the steel plate is divided into two parts, one of which is coated with an annealing separator mainly composed of MgO, and final finish annealing consisting of secondary recrystallization annealing and purification annealing at 1200°C for 5 hours is performed. provided. Another method is to apply an annealing dividing agent and Al ₂ O ₃ powder, which is a reaction inhibitor with SiO ₂ in the steel plate subscale, to the surface of the steel plate at an adhesion amount of 0.5 g/m ² and an angle of 90° with respect to the rolling direction. Width: 2mm and repeat interval 4mm in rolling direction
After that, an annealing separator was applied thereon and final annealing was performed. As a result, in the former case, a uniform gray film was formed, but in the latter case, a forsterite film with a thickness of 0.8 μm was formed in the area where the Al ₂ O ₃ powder was applied. The iron loss values of these semi-finished products were as follows. Those with a uniform coating W17/50 = 1.06W/Kg Those with a reduced thickness area W17/50 = 1.02W/Kg Next, on such a steel plate as shown in Table 1 ~
A top insulating film was formed by applying and baking the coating liquid. Table 2 shows the iron loss values of the obtained products. Regarding comparative examples,
The iron loss value was also investigated when a high-power laser beam was irradiated in a row of dots at 0.4 mm intervals in a direction perpendicular to the rolling direction, with the row spacing being 7 mm. When a cross section of the laser irradiated area was etched and observed under an optical microscope, it was confirmed that plastic strain had been introduced into the surface layer of the steel base. Next, the iron loss value after strain relief annealing at 800° C. for 2 hours was also investigated, and the obtained results are also listed in Table 2.

【table】

【table】

[Table] From Table 2, the thermal expansion coefficient of the forsterite coating with different thickness regions is 9.8×10 ^-6 1/℃
It can be seen that a significant improvement in iron loss is achieved due to the presence of the smaller coating film. Moreover, this effect did not change at all even after strain relief annealing. On the other hand, in those using pulsed laser light, the magnetic properties deteriorate as the plastic strain introduced into the steel sheet during strain relief annealing is released. Example 2 A grain-oriented silicon steel plate with a thickness of 0.28 mm containing 2.8% Si and having a uniform forsterite coating on the surface exhibiting an iron loss value of 1.08 W/Kg at W17/50 was , B and C pieces, the A piece was coated with the coating shown in Table 1, and the B and C pieces were coated with the coatings shown in Table 1, and baked to produce a grain-oriented silicon steel plate with an overcoating film. Of these, regarding C, the coating film and part of the forsterite film were removed by applying light pressure with a fine-tipped iron needle and drawing the line, so as not to damage the steel plate base surface. , forming a thinned region of linear forsterite coating with a width of 0.5 mm and making an angle of 90° with the rolling direction. Note that the interval of this region in the rolling direction is 3
mm. Pieces A, B, and C were then annealed at 700°C for 1 minute, but the defects in the coating film on the surface of C had been repaired. The obtained iron loss values for each product are A W17/50 = 1.08W/Kg (comparative example), B W17/50 = 1.06W/Kg (comparative example), C W17/50 = 1.01W/Kg (implemented example). Example), it was. Furthermore, when these steel plates were further subjected to strain relief annealing at 800°C for 5 hours, the iron loss values were investigated: A W17/50 = 1.08 W/Kg (comparative example), B W17/50 = 1.06 W/Kg (Comparative example), C W17/50=1.00W/Kg (Example), were obtained. Example 3 A silicon steel material containing 3.3% Si was made into a cold-rolled plate with a thickness of 0.23 mm according to a conventional method, and then subjected to decarburization and primary recrystallization annealing, and then the steel plate was It is divided into two parts, and one part is coated with an annealing separation agent mainly composed of MgO, and then subjected to secondary recrystallization annealing and 1200°C.
A final finishing annealing was performed consisting of a purification annealing at ℃ for 5 hours. Another method is that when applying an annealing separator, ZnO powder, which acts as an oxidizing agent for Si in the steel, is applied to the surface of the steel sheet at a coating amount of 0.8 g/m ² and at an angle of 90° with the rolling direction. , the adhesion width: 1 mm, and the repetition interval in the rolling direction: 6 mm. After that, the annealing separator was uniformly applied, and then final annealing was performed under the same conditions. As a result, a uniform gray film was formed on the former, but a 0.5 μm thick forsterite film was formed on the region where the ZnO powder was attached on the latter. Next, the tension coating liquid shown in Table 1 was applied to the surface of the steel plate and baked to obtain a product. The iron loss values of each product version thus obtained were as follows. Uniform coating W _17/50 = 0.94W/Kg (Comparative example) Excessive thickness area W _17/50 = 0.84W/Kg (Example) Furthermore, for some of the comparative examples, a high power laser beam of 0.5 In rows of dots at intervals of mm, in the direction perpendicular to the rolling direction, spacing between rows: 8
When irradiated with 2 mm, the iron loss value was reduced to W _17/50 = 0.85 W/Kg. When the cross section of the laser irradiated area was etched and observed under an optical microscope, it was confirmed that plastic strain had been introduced into the surface layer of the steel base. Thereafter, when these samples were subjected to strain relief annealing at 800°C for 3 hours, the iron loss values were investigated, and the following values were obtained. W _17/50 Comparative example 0.94W/Kg Comparative example (laser irradiation) 0.96W/Kg Example 0.84W/Kg Effects of the invention Thus, according to this invention, even when strain relief annealing is performed, the characteristics deteriorate. This is advantageous because it is possible to obtain grain-oriented silicon steel with excellent core loss characteristics.

[Brief explanation of drawings]

Figures 1A, 2B and 2C are diagrams showing the shape, inclination with respect to the rolling direction, and interval measurement procedures of the different thickness regions of the forsterite film, respectively. Figure 3 is a graph showing the influence of the angle that the thick region makes with the rolling direction on iron loss characteristics. Figure 5 is a graph showing the relationship between the width of the thick region and the iron loss value. Figure 6 is a graph showing the relationship between the interval between the different thickness regions and the iron loss value. 3 is a graph comparing and showing the relationship between the width of a region called a forsterite coating and the iron loss value in cases where the forsterite coating is formed and cases where the forsterite coating is not formed.

Claims (1)

[Scope of Claims] 1. A grain-oriented silicon steel sheet in which no plastic strain region is observed in the surface layer of the base metal and having a forsterite coating on the entire surface, wherein the forsterite coating has a continuous or discontinuous linear shape. The characteristics are improved by strain relief annealing, which is characterized by having a tension-applying insulating coating film having different thickness regions and having a thermal expansion coefficient of 9.8×10 ^-6 1/°C or less on the film. Grain-oriented silicon steel plate with low iron loss that does not deteriorate. 2. The grain-oriented silicon steel sheet according to claim 1, wherein the continuous or discontinuous linear different thickness regions form an angle of 60 to 90 degrees with respect to the rolling direction of the steel sheet. 3. The grain-oriented silicon steel sheet according to claim 1 or 2, wherein the thickness difference in the linear different thickness region of the forsterite coating is 0.3 μm or more. 4 A hot-rolled plate 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 the manufacturing method of grain-oriented silicon steel sheet, which consists of a series of steps of annealing, then applying an annealing separator mainly composed of MgO to the surface of the steel sheet, and then performing final annealing and top coating treatment. Alternatively, a tension-applying insulating coating liquid having a coefficient of thermal expansion of 9.8×10 ^-6 1/°C or less is applied after film formation on a forsterite film in which discontinuous linear regions of different thickness are formed, and then
A method for producing a grain-oriented silicon steel sheet with low iron loss whose properties do not deteriorate through strain relief annealing, which is characterized by baking in a temperature range of 600 to 900°C. 5 A hot-rolled plate obtained by hot rolling a silicon-containing steel slab is cold-rolled once or twice with intermediate annealing to obtain the final plate thickness, and then decarburized and primary recrystallized. In a method for manufacturing grain-oriented silicon steel sheets, 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, and then performing final annealing and top coating treatment, a top coating treatment liquid is used. After forming a tension-imparting top coating film having a coefficient of thermal expansion of 9.8×10 ^-6 1/°C or less on the forsterite film using a tension-imparting insulating coating liquid as By removing part of the top coating film and the forsterite coating in a continuous or discontinuous line without imparting plastic strain to the inside of the iron, a linear region of different thickness is formed in the forsterite coating, and then A method for producing a grain-oriented silicon steel sheet with low core loss and whose properties do not deteriorate due to strain relief annealing, the method comprising annealing in a temperature range of 600 to 900°C that leads to repair of the top coating film.