Grain-oriented electromagnetic steel sheet

Abstract

Provided is a grain-oriented electromagnetic steel sheet that can sufficiently suppress the building factor when used as an iron core material for a transformer. This grain-oriented electromagnetic steel sheet includes: a parent material steel sheet that contains at least Ga (0.0001%–0.0050%); and an undercoating film. The Ti content of the grain-oriented electromagnetic steel sheet is 0.0050%–0.0210%. The ratio R17 of W17 / 50 and Wh17 and the ratio R19 of W19 / 50 and Wh19 satisfies R17≤R19≤0.70.

Description

grain-oriented electrical steel sheet

[0001] The present invention relates to a grain-oriented electrical steel sheet suitable for use as an iron core material for transformers.

[0002] Grain-oriented electrical steel is a soft magnetic material used as the iron core material of a transformer. <001> This texture is formed by the crystallographic structure in which the orientation is highly aligned in the rolling direction of the steel sheet. During the manufacturing process of grain-oriented electrical steel sheet, the {110} orientation, known as the Goss orientation, is formed during the purification annealing. <001> It is formed through a phenomenon called secondary recrystallization, which causes preferential giant growth of grains in the orientation.

[0003] A common technique for this formation method is to use a precipitate called an inhibitor to induce secondary recrystallization of grains having the Goss orientation during purification annealing. For example, the method using AlN described in Patent Document 1 and the method using MnS and MnSe described in Patent Document 2 have been put into industrial use.

[0004] The use of these inhibitors is a useful method for stably developing secondary recrystallized grains, but in order to finely disperse the inhibitors in the steel, it is necessary to heat the slab at high temperatures of 1300°C or higher and first dissolve the inhibitor components.

[0005] On the other hand, Patent Document 3, for example, discloses a technique for developing Goss-oriented grains by secondary recrystallization in a material that does not contain inhibitor components. This technique minimizes impurities such as inhibitor components, thereby revealing the grain boundary misorientation angle dependence of the grain boundary energy of the grain boundaries during primary recrystallization and allowing secondary recrystallization of Goss-oriented grains without the use of inhibitors. This effect is called the texture inhibition effect. This method does not require fine dispersion of inhibitors in the steel, and therefore does not require high-temperature slab heating, which is essential when using inhibitors. As such, this method offers significant advantages in terms of both cost and maintenance.

[0006] Grain-oriented electrical steel sheets are primarily used as transformer cores, and are required to have excellent magnetization properties, particularly low iron loss. To achieve this, it is important to highly align the secondary recrystallized grains in the steel sheet with the Goss orientation and reduce impurities in the finished sheet. Furthermore, technologies have been developed that physically introduce nonuniformity into the surface of the steel sheet, thereby refining the width of magnetic domains and reducing iron loss, i.e., magnetic domain refinement technology. For example, Patent Document 4 proposes a technology that reduces iron loss in steel sheets by irradiating the final product sheet with a laser to introduce high dislocation density regions in the surface layer of the steel sheet and narrowing the magnetic domain width. Patent Document 5 also proposes a technology that controls magnetic domain width by irradiating with an electron beam. Note that aligning the orientation after secondary recrystallization with the Goss orientation and reducing impurities as described above reduces hysteresis loss. In contrast, applying magnetic domain refinement technology primarily reduces eddy current loss.

[0007] Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 Japanese Patent Publication No. 2000-129356 Japanese Patent Publication No. 57-2252 Japanese Patent Publication No. 6-72266 Japanese Patent Publication No. 2008-196016

[0008] As mentioned above, grain-oriented electrical steel sheets are primarily used as transformer cores. Generally, there is a discrepancy between the iron loss value of a transformer core and the iron loss value of the grain-oriented electrical steel sheet that is used as the material, with the transformer core having a higher iron loss. The ratio of these two iron losses is called the building factor. In other words, even if the material has good iron loss, if the building factor is high, the iron loss of the transformer core will be large, resulting in the problem of not being able to demonstrate sufficient performance.

[0009] In the carbon-neutral era, what needs to be reduced is the iron loss of the final product, the transformer. However low the iron loss of a material, it is meaningless if the building factor is high. Since the building factor is affected not only by the transformer design but also by the characteristics of the material, properties that reduce the building factor as well as the iron loss of the material are desired. Therefore, the object of the present invention is to provide a grain-oriented electrical steel sheet that can sufficiently suppress the building factor when used as an iron core material for transformers.

[0010] As a result of extensive research, the present inventors have focused on the Ga content in a base steel sheet when forming a base coating containing forsterite as a main component on the base steel sheet, and the Ti content in the entire grain-oriented electrical steel sheet after the base coating has been formed, and have found that by controlling the Ga and Ti contents in particular within a predetermined range and satisfying the predetermined formula (1), a grain-oriented electrical steel sheet that can exhibit a low building factor can be obtained.

[0011] The experiments that led to the success of the present invention are described below. In this specification, any numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. <Experiment 1> In order to mainly vary the Ga content in the base steel sheet, a steel slab containing, by mass%, C: 0.0500-0.0810%, Si: 3.15-3.31%, Mn: 0.07-0.10%, Al: 0.0200-0.0250%, N: 0.0069-0.0085%, S: 0.0011-0.0031%, Sb: 0.025-0.036%, Ti: 0.0080-0.0090%, and Ga: 0.0000-0.0058% was produced by continuous casting. This steel slab was subjected to slab heating by soaking at 1400°C for 20 minutes, and then hot-rolled to a hot-rolled sheet having a thickness of 2.4 mm. ２ The hot-rolled sheet was then annealed in a 25% H atmosphere. The annealed hot-rolled sheet was then cold-rolled to a thickness of 1.5 mm. ２ -75%N ２ The intermediate cold-rolled sheet after annealing was then cold-rolled to a thickness of 0.23 mm. This cold-rolled sheet was then subjected to a 50% H atmosphere at 850°C for 150 seconds. ２ -50%N ２The decarburization annealing was carried out in a humid atmosphere with a dew point of 50°C. Furthermore, an annealing separator mainly composed of MgO was applied to the surfaces (both sides) of the obtained decarburized annealed sheet, and purification annealing was carried out by holding at 1200°C for 10 hours, forming a base coat mainly composed of forsterite. At this time, the heating rate up to 1200°C was 20°C / h. Furthermore, during the heating process, N ２ Atmosphere: N from 700℃ to 1100℃ ２ and H ２ The atmosphere was mixed with various ratios of H and H. ２ The atmosphere was also H ２ The atmosphere was Ar during cooling.

[0012] The grain-oriented electrical steel sheets thus obtained, in which a base film (forsterite film) mainly composed of forsterite was formed on the surface of the base steel sheet, were used as samples. 17 / 50 and W 19 / 50 (iron loss when excited to 1.7T and 1.9T at 50Hz) and hysteresis loss Wh 17 and Wh 19 The hysteresis losses (when excited to 1.7 T and 1.9 T, respectively) were measured by the method described in JIS C2550-1. In addition, to measure the Ga content of the base steel sheet, a part of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite film, and the sample was subjected to measurement by the method described in JIS K0133, General Rules for High Frequency Plasma Mass Spectrometry.

[0013] Next, a three-phase, three-legged model transformer was fabricated from the obtained sample, with an external shape of 500 mm square and a plate width of 100 mm for each leg and yoke. The iron loss W 17 / 50 The model transformer had 50 laminated samples, with two laminated layers alternately stacked. From the results obtained, the building factor F17 of the model transformer and the iron loss WT of the model transformer were calculated. 17 / 50 The iron loss W of the sample 17 / 50 The value divided by (WT17 / 50 / W 17 / 50 The relationship between this F17 and the Ga content (unit: mass%) in the base steel sheet was investigated. The results are shown in Figure 1.

[0014] These results did not reveal a clear correlation between the building factor F17 and the amount of Ga. However, Figure 1 indicates that the building factor F17 is divided into two groups: good values ​​of 1.25 or less and high values ​​of 1.30 or more.

[0015] Therefore, we investigated whether this difference in the building factor F17 could be explained by the relationship between the iron loss and hysteresis loss of the sample. As a result, the iron loss W 17 / 50 and hysteresis loss Wh 17 Ratio to Wh 17 / W 17 / 50 When R17 (unitless) is used and the excitation is 1.9T, the iron loss W 19 / 50 and hysteresis loss Wh 19 Ratio to Wh 19 / W 19 / 50 When R17 and R19 are defined as R19 (unitless), it was found that when R17 and R19 are divided into Group A, where R17≦R19≦0.70, and Group B, where R17≦R19≦0.70, a general trend in the building factor F17 can be seen. Figure 2 shows the results of redrawing Figure 1 by dividing it into Group A and Group B. In Figure 2, Group A is indicated by white circles, and Group B is indicated by black triangles. The results shown in Figure 2 show that a good building factor is exhibited when the relationship R17≦R19≦0.70 exists, i.e., when the steel sheet belongs to Group A and the Ga content in the base steel sheet is in the range of 0.0001 to 0.0050 mass%.

[0016] <Experiment 2> A steel slab containing, by mass%, 0.0370% C, 3.05% Si, 0.18% Mn, 0.0090% Al, 0.0036% N, 0.0070% Se, 0.062% Sn, and 0.0030% Ga, with the remainder consisting of Fe and unavoidable impurities, was produced by continuous casting. This steel slab was subjected to slab heating by soaking at 1300°C for 30 minutes, and then hot-rolled to a hot-rolled sheet with a thickness of 2.2 mm. Thereafter, this hot-rolled sheet was subjected to a soaking at 1100°C for 30 seconds, followed by a soaking at 1100°C for 30 seconds. ２ The hot-rolled sheet was then annealed in a 40% H atmosphere. The annealed hot-rolled sheet was then cold-rolled to a thickness of 0.23 mm. ２ -60%N ２ The decarburization annealing was performed in a humid atmosphere with a dew point of 40°C. ２ The annealing separator was mixed with various amounts of MgO in the range of 0 to 15 parts by mass, and then purified by annealing at 1220°C for 5 hours to form a base film mainly composed of forsterite. ２ Atmosphere: N from 700℃ to 1100℃ ２ and H ２ The atmosphere was mixed with various ratios of H and H. ２ The atmosphere was also H ２ The atmosphere was Ar during cooling. ２ and H ２ By changing the mixing ratio of the above, the amount of Ti in the steel sheet with the base coating still on, that is, the entire grain-oriented electrical steel sheet made up of the base steel sheet and the base coating, was controlled.

[0017] The grain-oriented electrical steel sheets thus obtained, in which a forsterite film was formed on the surface of the base steel sheet, were used as samples. 17 / 50 and W 19 / 50 (iron loss when excited to 1.7T and 1.9T at 50Hz) and hysteresis loss Wh17 and Wh 19 (hysteresis loss when excited to 1.7 T and 1.9 T, respectively) was measured according to the method described in JIS C2550-1.

[0018] The Ti content of the grain-oriented electrical steel sheet having a base coating mainly composed of forsterite was measured by the method described in JIS G 1223. Furthermore, to measure the Ga content of the base steel sheet, a portion of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite coating, and the resultant was subjected to measurement in the same manner as in Experiment 1. As a result, the Ga content was 0.0030 mass%, which was the same as the content in the steel slab.

[0019] From the obtained magnetic properties, the iron loss W when excited at 1.7 T was 17 / 50 and hysteresis loss Wh 17 The ratio R17 and the iron loss W when excited at 1.9T 19 / 50 and hysteresis loss Wh 19 The samples were divided into Group A, where the ratio R19 of R to R satisfies the relationship R17≦R19≦0.70, and Group B, where the rest of the samples are grouped together. The results of comparing the samples belonging to Groups A and B with the Ti content (unit: mass%) in the grain-oriented electrical steel sheet in which a base coating containing forsterite as the main component was formed on the surface of the base steel sheet are shown in Figure 3.

[0020] The results shown in Figure 3 show that grain-oriented electrical steel sheets with a Ti content of 0.0050% by mass or more and 0.0210% by mass or less tend to belong to Group A. The reason why Ti content within this range belongs to Group A is thought to be because it suppresses nitriding of the steel sheet during purification annealing, reducing hysteresis loss. Cases that do not belong to Group A are when the Ti content is too high or too low. When the Ti content is too high, it is thought that domain wall pinning increases hysteresis loss. Furthermore, when the Ti content is too low, it is thought that nitrides are formed in the steel sheet during purification annealing, increasing hysteresis loss.

[0021] Furthermore, as in Experiment 1, a three-phase three-leg model transformer was fabricated with an external dimension of 500 mm square and a plate width of 100 mm for each leg and each yoke. The iron loss W 17 / 50 Building Factor F17 (WT 17 / 50 / W 17 / 50 The relationship between the calculated building factor and the Ti content in the grain-oriented electrical steel sheet is shown in Figure 4.

[0022] The results shown in Figure 4 indicate that the building factor is high when the Ti content in the grain-oriented electrical steel sheet is less than 0.0050 mass% and more than 0.0210 mass%. In other words, we found that the building factor is low and favorable when the Ti content is 0.0050 to 0.0210 mass% in grain-oriented electrical steel sheets in which a forsterite-based base coating is formed on the surface of the base steel sheet. Although this is speculation, it is believed that the presence of a certain amount of Ti in the forsterite coating improves the coating properties. For example, if the presence of Ti improves the coating tension of the base coating, magnetostrictive vibration can be suppressed, thereby suppressing the magnetostrictive vibration increased by the addition of Ga. This suppresses the fluttering of the steel sheet caused by magnetostriction and smooths the transfer of magnetic flux at the joint in the transformer, thereby reducing the building factor.

[0023] As described above, the mechanism by which the building factor of a model transformer is improved by controlling the Ga content of the base steel sheet and the Ti content of the grain-oriented electrical steel sheet on the surface of which a forsterite-based undercoat is formed is unclear. However, the inventors believe the following: Because the yoke and legs of a transformer have a fixed width, the magnetic path varies in length between the inside and outside, similar to an athletics track. Therefore, during excitation, the magnetic flux tends to be biased toward the inside, where the magnetic path is shorter. Even when the entire steel sheet is excited to 1.7 T, the magnetic flux density on the inside exceeds that. Therefore, it is presumed that the more advantageous the high magnetic field characteristics, the better the transformer characteristics, such as the building factor.

[0024] During secondary recrystallization, Ga acts as an inhibitor that suppresses the normal grain growth of grains that deviate from the Goss orientation. However, Ga is not completely removed during purification and remains finely dispersed in the steel. This appropriate amount of finely dispersed Ga serves as the origin of rotational magnetic flux without impairing iron loss, which is thought to improve the building factor.

[0025] On the other hand, the building factor deteriorated when too much Ga was added. Excessive Ga addition increases magnetostriction, so it is thought that the effect of magnetostriction was greater than the improvement in coating properties that Ti has. As a result, when assembled into a transformer, the steel sheet fluttered due to magnetostriction, preventing smooth magnetic flux transfer, which is thought to have increased the building factor.

[0026] Incidentally, Patent Document 6 discloses a manufacturing technique for grain-oriented electrical steel sheets containing Ga. However, this document refers to a manufacturing method that allows the electrical steel sheets to exhibit high magnetic flux density throughout their entire length. Therefore, this technique is completely different from the present invention, which reduces the building factor by also using a technique for adding Ti to grain-oriented electrical steel sheets having a forsterite coating.

[0027] The present invention is based on the above findings. That is, the gist of the present invention is as follows: [1] A grain-oriented electrical steel sheet comprising a base steel sheet having a chemical composition containing 1.50 to 8.00 mass% Si, 0.02 to 1.00 mass% Mn, and 0.0001 to 0.0050 mass% Ga, with the balance being Fe and unavoidable impurities, and an undercoat film containing forsterite as a main component formed on the surface of the base steel sheet, wherein the amount of Ti in the grain-oriented electrical steel sheet is 0.0050 to 0.0210 mass%, and the iron loss W when excited at 1.7 T is 17 / 50 and hysteresis loss Wh 17 Ratio to Wh 17 / W 17 / 50 When R17 is used and the coil is excited at 1.9T, the iron loss W 19 / 50 and hysteresis loss Wh 19 Ratio to Wh 19 / W 19 / 50When R19 is taken as R17, the grain-oriented electrical steel sheet satisfies the following formula (1): R17≦R19≦0.70 (1)

[0028] [2] The grain-oriented electrical steel sheet according to the above [1], wherein the Ti content of the base steel sheet is 0.0030 mass% or less.

[0029] [3] The grain-oriented electrical steel sheet according to the above [1] or [2], which comprises an insulating coating on the surface of the base coating.

[0030] [4] The base steel sheet further contains Sn: 0.005 to 0.500 mass%, Cr: 0.005 to 0.500 mass%, Cu: 0.01 to 0.50 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.500 mass%, P: 0.005 to 0.500 mass%, Sb: 0.005 to 0.500 mass%, Mo: 0.005 to 0.500 mass%, B: 0.1 to 25.0 mass ppm, Nb: 0.001 to 0.020 mass ppm % by mass, V: 0.001 to 0.020% by mass, As: 0.0010 to 0.0200% by mass, Zn: 0.001 to 0.020% by mass, Pb: 0.0001 to 0.0100% by mass, Co: 0.002 to 0.050% by mass, W: 0.0010 to 0.0100% by mass, and Ge: 0.0001 to 0.0050% by mass.

[0031] According to the present invention, by appropriately controlling the amount of Ga in the base steel sheet and the amount of Ti in the grain-oriented electrical steel sheet having a base coating on the surface of the base steel sheet and satisfying a predetermined loss relationship, it is possible to obtain a grain-oriented electrical steel sheet that can reduce the building factor.

[0032] 1 is a graph showing the relationship between the Ga content in a base steel sheet and the building factor; 2 is a graph showing the relationship between the Ga content in a base steel sheet and Group A and Group B, and the relationship with their building factors; 3 is a graph showing the Ti content in grain-oriented electrical steel sheets in Group A and Group B; and 4 is a graph showing the relationship between the Ti content in grain-oriented electrical steel sheets and the building factor.

[0033] <Grain-oriented electrical steel sheet> The grain-oriented electrical steel sheet of the present invention comprises a base steel sheet containing predetermined amounts of predetermined elements including Ga, and a base coating composed primarily of forsterite formed on one or both surfaces of the base steel sheet. The grain-oriented electrical steel sheet of the present invention also contains a predetermined amount of Ti overall. Furthermore, the grain-oriented electrical steel sheet of the present invention satisfies the predetermined formula (1) regarding loss. Because the grain-oriented electrical steel sheet of the present invention has these characteristics, it can exhibit a good building factor when used as an iron core material for a transformer. The grain-oriented electrical steel sheet of the present invention can be obtained, for example, according to the manufacturing method described below.

[0034] [Composition of the Base Steel Sheet] Next, the reasons for limiting the constituent elements of the present invention will be described. First, the amount of each element in the composition will be explained. Note that, hereinafter, the "%" and "ppm" designations for the composition refer to "mass %" and "mass ppm" unless otherwise specified. Si: 1.50 to 8.00% Si is an element necessary for increasing the resistivity of steel and improving iron loss, but if the Si content is less than 1.50%, this effect is lost. On the other hand, if the Si content exceeds 8.00%, the workability of the steel deteriorates and rolling becomes difficult. Therefore, the Si content in the base steel sheet is limited to the range of 1.50 to 8.00%. Preferably, the Si content is 2.50% or more. On the other hand, preferably, the Si content is 4.50% or less.

[0035] Mn: 0.02 to 1.00% Mn is an element necessary for improving hot workability, but if it is less than 0.02%, this effect is lost. On the other hand, if the Mn content exceeds 1.00%, the magnetic flux density of the grain-oriented electrical steel sheet product decreases. Therefore, the Mn content in the base steel sheet is set to the range of 0.02 to 1.00%. Preferably, the Mn content is 0.04% or more. On the other hand, preferably, the Mn content is 0.20% or less.

[0036] Ga: 0.0001 to 0.0050% For the reasons mentioned above, it is essential that the Ga content be in the range of 0.0001 to 0.0050% in the base steel sheet. The Ga content is preferably 0.0005% or more, and more preferably 0.0010% or more. On the other hand, the Ga content is preferably 0.0040% or less, and more preferably 0.0030% or less. A Ga content of 0.0001% or more exceeds the content of unavoidable impurities that may be mixed into ordinary base steel sheets.

[0037] The composition of the base steel sheet of the grain-oriented electrical steel sheet of the present invention includes at least the basic components described above, with the remainder being Fe and unavoidable impurities. In addition to the basic components, the base steel sheet may contain the following optional elements as needed: Sn: 0.005-0.500%, Cr: 0.005-0.500%, Cu: 0.01-0.50%, Ni: 0.01-0.50%, Bi: 0.005-0.500%, P: 0.005-0.500%, Sb: 0.005-0.500%, Mo: 0.005-0.500%, B: 0.1-25.0 ppm, One or more elements selected from the group consisting of Nb: 0.001-0.020%, V: 0.001-0.020%, As: 0.0010-0.0200%, Zn: 0.001-0.020%, Pb: 0.0001-0.0100%, W: 0.0010-0.0100%, and Ge: 0.0001-0.0050%. These optional elements can be added to further improve the magnetic properties of grain-oriented electrical steel sheets. If the amount of each element added is less than the minimum amount, the magnetic properties will not be improved. Furthermore, if the amount of each element added exceeds the maximum amount, the development of secondary recrystallized grains will be suppressed, resulting in a deterioration of the magnetic properties.

[0038] Co: 0.002-0.050% In addition to the elements listed above, or in addition to the elements listed above, the building factor of the model transformer is further improved by adding 0.002-0.050% Co to the base steel sheet. Therefore, adding Co within this range is preferable. While the mechanism by which the building factor is improved is unclear, it is believed that dissolving Co in iron increases the saturation magnetic flux density of the iron, improving its high-field characteristics. Therefore, it is believed that the building factor of the model transformer can be further improved. The Co content in the base steel sheet is preferably 0.002% or more, more preferably 0.006% or more, and even more preferably 0.008% or more. The Co content in the base steel sheet is preferably 0.050% or less, more preferably 0.020% or less, and even more preferably 0.015% or less. The Co content is preferably 0.006-0.020%, and more preferably 0.008-0.015%.

[0039] Ti: 0.0030% or less The amount of Ti in the base steel sheet is preferably 0.0030% or less, more preferably 0.0010% or less, and may be 0% (none). This is because if the amount of Ti in the base steel sheet exceeds 0.0030%, Ti precipitates are likely to form in the steel, which may significantly deteriorate the iron loss.

[0040] The above-mentioned composition is that of a base steel sheet on which no forsterite base coating is formed on the surface. When checking the composition of a grain-oriented electrical steel sheet in which a forsterite coating is formed on the surface of the base steel sheet, the forsterite coating may be removed from the grain-oriented electrical steel sheet, and then the content of each element may be checked, as shown in Experiment 1, for example.

[0041] [Composition of Grain-Oriented Electrical Steel Sheet and Undercoat] The Ti content in grain-orientated electrical steel sheets having a forsterite-based undercoat formed on the surface is limited to 0.0050-0.0210% for the reasons mentioned above. The Ti content in grain-orientated electrical steel sheets is preferably 0.0060% or more. The lower limit of the Ti content in grain-orientated electrical steel sheets with undercoats is 0.0050% because, as mentioned above, the presence of a certain amount of Ti in the forsterite coating is thought to improve coating properties, reduce magnetostriction, and improve eddy current loss. However, these effects are limited at less than 0.0050%. Furthermore, the Ti content in grain-orientated electrical steel sheets is 0.0210% or less, preferably 0.0150% or less. Excessive Ti content is undesirable because it increases costs. Furthermore, too much Ti penetrates into the base steel sheet through the annealing separator used to form the forsterite coating.

[0042] The Ti content in grain-oriented electrical steel sheet is the ratio (mass %) of the total amount of Ti present in the base steel sheet and the base coating to the total mass (solid content equivalent) of the base steel sheet and the base coating. The Ti content in grain-oriented electrical steel sheet can be measured in accordance with JIS G1223, regardless of whether the base coating is formed on only one side or both sides of the base steel sheet.

[0043] From the above viewpoints, the Ti content in the forsterite coating is preferably 0.0020% or more, more preferably 0.0050% or more, and even more preferably 0.0060% or more. The Ti content in the forsterite coating is preferably 0.0210% or less, and more preferably 0.0150% or less.

[0044] Here, when limiting the Ti content in a steel sheet (grain-oriented electrical steel sheet) having a base coating to 0.0050 to 0.0210%, as described above, the Ti content in the base steel sheet is preferably 0.0030% or less.

[0045] [Magnetic Properties of Grain-Oriented Electrical Steel Sheets] For the reasons mentioned above, grain-oriented electrical steel sheets as product steel sheets must satisfy the parameters calculated from the hysteresis loss and iron loss within a predetermined range.17 / 50 and hysteresis loss Wh 17 The ratio R17 (=Wh 17 / W 17 / 50 ) and iron loss W when excited at 1.9T 19 / 50 and hysteresis loss Wh 19 Ratio R19 (=Wh 19 / W 19 / 50 ) must satisfy the relationship of formula (1), where R17≦R19≦0.70. If grain-oriented electrical steel sheet does not satisfy formula (1), it will not be able to achieve a low building factor. These values ​​can be measured using the method described in JIS C2550-1. In addition, to match the hysteresis loss with the iron loss at 50 Hz, the value can be calculated by multiplying the energy loss of the iron core for one revolution of the hysteresis loop by 50, which is the excitation frequency.

[0046] [Other Properties of Grain-Oriented Electrical Steel Sheets] Grain-orientated electrical steel sheets preferably have an insulating coating on the surface of the base coating. This insulating coating is preferably a coating that can impart tension to the grain-orientated electrical steel sheet. In particular, when grain-orientated electrical steel sheets are stacked to form a transformer core, iron loss can be further improved by imparting additional tension to the steel sheets. The insulating coating can be formed well, for example, according to the manufacturing method described below.

[0047] [Method for manufacturing grain-oriented electrical steel sheet] Next, an example of a manufacturing method for obtaining the grain-oriented electrical steel sheet of the present invention will be described. A typical method for manufacturing electrical steel sheet can be used as the manufacturing method. For example, slabs may be manufactured from molten steel adjusted to the above-mentioned predetermined composition by a conventional ingot-making method or continuous casting method. Alternatively, thin cast pieces with a thickness of 100 mm or less may be manufactured from the molten steel by a direct casting method. The molten steel may be manufactured by a blast furnace method or an electric furnace method. Since it is difficult to add the above-mentioned optional elements during the process, it is desirable to add them at this molten steel stage.

[0048] The slab can be heated and hot-rolled by a conventional method. Alternatively, the slab may be hot-rolled immediately after casting without heating. When such heating is performed, for component systems with a low inhibitor content, high-temperature heating to dissolve the inhibitor is not required, and therefore, it is effective to perform the heating at a low temperature of 1300°C or less in order to reduce costs. The heating temperature of the slab is preferably 1250°C or less. The hot-rolling conditions may be the same as those of conventional methods. In this way, a hot-rolled sheet can be obtained.

[0049] The resulting hot-rolled sheet can then be annealed as needed. The annealing temperature is preferably in the range of approximately 950 to 1150°C. If the annealing temperature is less than 950°C, unrecrystallized portions are likely to remain in the steel. On the other hand, if the annealing temperature exceeds 1150°C, the grain size in the steel after annealing may become too coarse, which may result in an inappropriate primary recrystallization texture. The annealing temperature is preferably 950°C or higher, more preferably 1000°C or higher. The annealing temperature is preferably 1150°C or lower, more preferably 1100°C or lower. In this manner, a hot-rolled annealed sheet can be obtained.

[0050] The hot-rolled sheet after hot rolling or the hot-rolled and annealed sheet after hot-rolled sheet annealing can be cold-rolled to the final thickness by one cold rolling or two or more cold rollings with intermediate annealing in between. The annealing temperature for the intermediate annealing is preferably 900°C or higher, preferably 1200°C or lower, and more preferably in the range of 900 to 1200°C. If the intermediate annealing temperature is lower than 900°C, the recrystallized grains after the intermediate annealing tend to become finer. Furthermore, the number of Goss nuclei in the primary recrystallized structure may decrease, potentially resulting in a deterioration in the magnetic properties of the grain-oriented electrical steel sheet product. On the other hand, if the intermediate annealing temperature exceeds 1200°C, the grains may become too coarse, as with hot-rolled sheet annealing, making it difficult to obtain a uniformly sized primary recrystallized structure. In this way, a cold-rolled sheet can be obtained.

[0051] The cold-rolled sheet having the final thickness can then be subjected to primary recrystallization annealing, which also serves as decarburization annealing. When decarburization annealing is involved, the annealing temperature in this primary recrystallization annealing is preferably 800°C or higher, preferably 900°C or lower, and more preferably in the range of 800 to 900°C, from the viewpoint of rapidly progressing the decarburization reaction. Furthermore, the atmosphere during the primary recrystallization annealing, which also serves as decarburization annealing, is preferably a humid atmosphere. In this way, a primary recrystallized sheet (decarburization annealed sheet) can be obtained.

[0052] Subsequently, an annealing separator mainly composed of MgO can be applied to one or both surfaces of the primary recrystallized sheet, followed by secondary recrystallization annealing. The secondary recrystallization annealing may also serve as a purification annealing to purify the components. This allows the secondary recrystallization structure to develop in the steel and also allows a forsterite coating to form on the surface of the steel sheet. In this way, a grain-oriented electrical steel sheet can be obtained in which a base coating is formed on the surface of the base steel sheet. Here, "mainly composed of MgO" means that the annealing separator contains 75 mass % or more of MgO in terms of solid content.

[0053] Here, by adding a Ti compound to the annealing separator and by adding N during purification annealing (when heating and holding), ２ By introducing this atmosphere, Ti can be effectively present in the forsterite coating. From the viewpoint of incorporating Ti into the base coating and effectively controlling the Ti content in the grain-oriented electrical steel sheet to 0.0050 to 0.0210 mass%, TiO2 and TiN are preferred as Ti compounds, with TiO2 being more preferred. Furthermore, the content of this compound in the annealing separator is preferably 2 parts by mass or more and 15 parts by mass or less relative to MgO. However, other methods may be used to achieve the Ti requirements for grain-oriented electrical steel sheets. As another method, for example, when Ti in excess of 30 ppm is added to a slab, the Ti can be concentrated on the surface by annealing in a nitrogen atmosphere during the annealing process before finish annealing, and the Ti concentration in the steel sheet can be controlled by descaling.

[0054] Secondary recrystallization annealing is preferably performed at 800°C or higher to induce secondary recrystallization in the Goss orientation. From the perspective of purification, it is also desirable to raise the temperature to 1100°C or higher. The longer the holding time, the greater the degree of purification, but if it is too long, shape deterioration due to high-temperature creep may occur. Therefore, the holding time for purification annealing is preferably 3 hours or more, and 15 hours or less. After secondary recrystallization annealing, it is preferable to perform water washing, brushing, or pickling to remove any adhering annealing separator.

[0055] Subsequent flattening annealing to correct the shape is effective in reducing iron loss. When grain-oriented electrical steel sheets are used in a stacked configuration, it is effective to apply an insulating coating to the steel sheet surface (more specifically, the surface of the base coating) before or after flattening annealing in order to improve iron loss. This insulating coating is preferably one that can impart tension to the grain-oriented electrical steel sheet in order to reduce iron loss. It is desirable to employ a method of forming a coating by depositing an inorganic substance on the surface of the steel sheet using a binder-mediated tension coating method, physical vapor deposition, or chemical vapor deposition, as this method provides excellent coating adhesion and is likely to enhance the iron loss reduction effect.

[0056] Steel slab A contains C: 0.0700%, Si: 3.55%, Mn: 0.07%, Al: 0.0080%, N: 0.0050%, Ga: 0.0040%, Mo: 0.026%, Ti: 0.0250%, and the balance is Fe and unavoidable impurities. Steel slab B, which contained 0.025%, 0.0025% Ti, and the balance being Fe and unavoidable impurities, and steel slab C, which contained 0.0720%, 3.49%, 0.07%, 0.0090%, 0.0051%, 0.00001%, 0.025%, 0.0240% Ti, and the balance being Fe and unavoidable impurities, were each produced by continuous casting. Steel slabs A, B, and C were subjected to slab heating by soaking at 1200°C for 40 minutes. They were then hot-rolled to a thickness of 2.2 mm. The hot-rolled sheets were then subjected to a slab heating at 1000°C for 60 seconds, followed by a N ２The hot-rolled sheet was then annealed in a 0.23 mm thick atmosphere. The resulting hot-rolled and annealed sheet was then cold-rolled to a thickness of 0.23 mm. The cold-rolled sheet was then further annealed at 850°C for 90 seconds in a 60% H atmosphere. ２ -40%N ２ The steel sheets were subjected to primary recrystallization annealing, which also served as decarburization annealing, in a humid atmosphere with a dew point of 60°C.

[0057] Next, an annealing separator mainly composed of MgO (97% MgO) was applied to both surfaces of the base steel sheet (primary recrystallized sheet) after decarburization annealing. After that, the sheet was held at 1100°C for 25 hours, and then purified by annealing at 1200°C for 10 hours. During the temperature rise process of this heat treatment, N ２ Atmosphere: N from 700℃ to 1100℃ ２ and H ２ The atmosphere was changed in various mixture ratios, and H ２ Furthermore, the atmosphere was Ar during cooling.

[0058] The thus obtained base steel sheet with the base coating formed on its surface was used as a sample. The Ti content of the sample, i.e., the grain-oriented electrical steel sheet with the forsterite-based base coating still attached, was measured according to the method specified in JIS G1223. The results are also shown in Table 1.

[0059] An insulating coating containing magnesium phosphate and silica as its main components was applied to the undercoat of the grain-oriented electrical steel sheet. 17 / 50 and W 19 / 50 (iron loss when excited to 1.7T and 1.9T at 50Hz) and hysteresis loss Wh 17 and Wh 19 (Hysteresis loss when excited to 1.7T and 1.9T, respectively) was measured according to the method specified in JIS C2550-1. 17 / 50 and hysteresis loss Wh 17 Ratio to Wh 17 / W 17 / 50 R17 and iron loss W 19 / 50 and hysteresis loss Wh 19 Ratio to Wh 19 / W 19 / 50 The results are shown in Table 1.

[0060] Furthermore, to measure the Ga and Ti contents of the base steel sheets, a portion of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite film, and the sample was subjected to measurement according to the methods specified in JIS K0133 and JIS G1223. The measurement results for Ti are also shown in Table 1. The Si, Mn, and Ga contents in the base steel sheets were the same as those in each steel slab.

[0061] Next, a three-phase, three-legged model transformer was fabricated from the sample with the insulating coating, with an external shape of 500mm square and a plate width of 100mm for each leg and yoke. The iron loss W 17 / 50 The model transformer had 50 laminated samples, with two laminated layers alternately stacked. From the results obtained, the building factor F17 of the model transformer and the iron loss WT of the model transformer were calculated. 17 / 50 The iron loss W of the sample 17 / 50 The value divided by (WT 17 / 50 / W 17 / 50 The results are shown in Table 1.

[0062]

[0063] As is clear from Table 1, it can be seen that good iron loss characteristics (building factor) are obtained under conditions within the range of the present invention.

[0064] Steel slabs containing the elements shown in Table 2, with the balance being Fe and unavoidable impurities, were produced by continuous casting. Each steel slab was subjected to slab heating by soaking at 1410°C for 20 minutes, and then hot-rolled to a thickness of 2.4 mm. The hot-rolled sheet was then heated at 1100°C for 20 seconds, and N ２ The hot-rolled sheet was then annealed in a 25% H atmosphere. The annealed hot-rolled sheet was then cold-rolled to a thickness of 1.5 mm. ２ -75%N ２The intermediate cold-rolled sheet was then cold-rolled to a thickness of 0.23 mm. This cold-rolled sheet was then subjected to a 40% H atmosphere at 825°C for 150 seconds. ２ -60%N ２ The decarburization annealing was carried out in a humid atmosphere with a dew point of 45°C. An annealing separator mainly composed of MgO (88% MgO) was applied to the surfaces (both sides) of the obtained decarburized annealed sheet. The annealing separator contained TiO ２ The powder was added to hot water at 50°C and stirred for 24 hours, and then the perhydrated TiO was filtered off. ２ was added in an amount of 5 parts by mass relative to the powdered MgO.

[0065] Furthermore, purification annealing was performed by holding at 1200°C for 10 hours to form a base film mainly composed of forsterite. At that time, the temperature rise rate up to 1200°C was 15°C / h. Furthermore, during the temperature rise process, N ２ Atmosphere: N from 700℃ to 1100℃ ２ and H ２ Atmospheres with various mixture ratios of H ２ The atmosphere was also H ２ The atmosphere was Ar during cooling.

[0066] Furthermore, an insulating coating composed mainly of magnesium phosphate and silica was applied. Note that in Tables 2, 3, and 4, only sample No. 25 was not coated with an insulating coating. Furthermore, the numbers in Tables 3 and 4 indicate that the steel slabs of the same number in Table 2 were used. Thus, for example, steel plate No. 4 in Table 3 uses steel slab No. 4 in Table 2, and steel plate No. 31 in Table 4 uses steel slab No. 31 in Table 2.

[0067]

[0068] The grain-oriented electrical steel sheets thus obtained, in which a base coating mainly composed of forsterite was formed on the surface of the base steel sheet, were used as samples. 17 / 50 and W 19 / 50(iron loss when excited to 1.7T and 1.9T at 50Hz) and hysteresis loss Wh 17 and Wh 19 (Hysteresis loss when excited to 1.7T and 1.9T, respectively) was measured according to the method specified in JIS C2550-1. 17 / 50 and hysteresis loss Wh 17 Ratio of Wh 17 / W 17 / 50 R17 and iron loss W 19 / 50 and hysteresis loss Wh 19 Ratio of Wh 19 / W 19 / 50 The results are shown in Tables 3 and 4.

[0069] Furthermore, the Ti content of the thus obtained samples, i.e., grain-oriented electrical steel sheets still bearing the forsterite-based undercoat on the surface of the base steel sheet, was measured according to the method specified in JIS G1223. The measurement results are shown in Tables 3 and 4. Furthermore, to measure the composition of the base steel sheet, a portion of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite coating, and the sample was subjected to measurement according to the same method as in Example 1. The measurement results are shown in Tables 3 and 4. The amounts of Si, Mn, Ga, Co, and other elements in the base steel sheet were equivalent to those in each steel slab.

[0070] Next, a three-phase, three-legged model transformer was fabricated from the sample with the insulating coating, with an external shape of 500mm square and a plate width of 100mm for each leg and yoke. The iron loss W 17 / 50 The model transformer had 50 laminated samples, with two laminated layers alternately stacked. From the results obtained, the building factor F17 of the model transformer and the iron loss WT of the model transformer were calculated. 17 / 50 The iron loss W of the sample 17 / 50 The value divided by (WT 17 / 50 / W 17 / 50 The results are shown in Tables 3 and 4.

[0071]

[0072]

[0073] As is clear from Tables 3 and 4, good iron loss characteristics (building factor) are obtained under conditions within the range of the present invention.

Claims

1. A base steel sheet having a component composition containing 1.50 to 8.00% by mass of Si, 0.02 to 1.00% by mass of Mn, and 0.0001 to 0.0050% by mass of Ga, with the balance being Fe and inevitable impurities, and a base coating mainly composed of forsterite formed on the surface of the base steel sheet, wherein the Ti content in the grain-oriented electrical steel sheet is 0.0050 to 0.0210% by mass, and the iron loss W 17 / 50 and the hysteresis loss Wh 17 ratio Wh 17 / W 17 / 50 is defined as R17, and the iron loss W 19 / 50 and the hysteresis loss Wh 19 ratio Wh 19 / W 19 / 50 is defined as R19, and the grain-oriented electrical steel sheet satisfies the following formula (1): R17 ≤ R19 ≤ 0.70... (1) 2. The grain-oriented electrical steel sheet according to claim 1, wherein the Ti content of the base steel sheet is 0.0030% by mass or less.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, further comprising an insulating film on the surface of the underlying film.

4. The base steel sheet further contains one or more selected from Sn: 0.005 to 0.500% by mass, Cr: 0.005 to 0.500% by mass, Cu: 0.01 to 0.50% by mass, Ni: 0.01 to 0.50% by mass, Bi: 0.005 to 0.500% by mass, P: 0.005 to 0.500% by mass, Sb: 0.005 to 0.500% by mass, Mo: 0.005 to 0.500% by mass, B: 0.1 to 25.0 mass ppm, Nb: 0.001 to 0.020% by mass, V: 0.001 to 0.020% by mass, As: 0.0010 to 0.0200% by mass, Zn: 0.001 to 0.020% by mass, Pb: 0.0001 to 0.0100% by mass, Co: 0.002 to 0.050% by mass, W: 0.0010 to 0.0100% by mass, and Ge: 0.0001 to 0.0050% by mass. The grain-oriented electrical steel sheet according to any one of claims 1 to 3.

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