Grain-oriented electrical steel sheet

Abstract

Provided is a grain-oriented electrical steel sheet capable of sufficiently suppressing building factor when used as an iron core material for a transformer. A grain-oriented electrical steel sheet according to the present invention includes a base material steel sheet containing at least 0.0010-0.0500% of W, and a foundation coating. In the grain-oriented electrical steel sheet, the Ti content in the steel sheet overall is 0.0050-0.0200%, and R19 / R17≤1.30 is satisfied between the ratio R17 of W17 / 50 and Wh17 and the ratio R19 of W19 / 50 and Wh19.

Description

grain-oriented electrical steel sheet

[0001] The present invention relates to a grain-oriented electrical steel sheet, and more particularly 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 crystal grains in the orientation.

[0003] Regarding this formation method, a commonly used technique involves using 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 and other publications disclose a technique for developing Goss-oriented grains through secondary recrystallization in materials that do 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. Therefore, this method has significant advantages in terms of cost and maintenance, such as eliminating the need for high-temperature slab heating, which is essential in methods that use inhibitors.

[0006] Grain-oriented electrical steel sheets are primarily used as transformer cores, and are required to have excellent magnetization properties, especially 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 to reduce impurities in the finished sheet.

[0007] Furthermore, a technology has been developed that uses physical methods to introduce nonuniformity into the surface of a 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 a steel sheet by irradiating the final product sheet with a laser to introduce high dislocation density regions into 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. Highly aligning the orientation after secondary recrystallization to the Goss orientation and reducing impurities as described above reduces hysteresis loss. In contrast, applying magnetic domain refinement technology primarily reduces eddy current loss.

[0008] 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

[0009] 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.

[0010] In the carbon-neutral era, what needs to be reduced is the iron loss of the final product, the transformer, and no matter how low the iron loss of a material is, it is meaningless if the building factor is high. Since the building factor is affected not only by the design of the transformer but also by the properties of the material, properties that lower the building factor as well as the iron loss of the material are desired.

[0011] Therefore, an 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 a transformer.

[0012] As a result of extensive research, the present inventors have focused on the W 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 grain-oriented electrical steel sheet as a whole after the base coating has been formed, and have found that by controlling the W 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.

[0013] 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 W content in the base steel plate, a steel slab containing, by mass%, C: 0.050-0.081%, Si: 3.15-3.31%, Mn: 0.07-0.10%, Al: 0.020-0.025%, N: 0.0069-0.0085%, S: 0.0011-0.0031%, Sb: 0.025-0.036%, Ti: 0.0080-0.0090%, Co: 0.0030-0.0040%, and W: 0-0.0600%, with the balance being Fe and unavoidable impurities, 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. Thereafter, this hot-rolled sheet was subjected to 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 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. An annealing separator mainly composed of MgO was then applied to the surfaces (both sides) of the obtained decarburized annealed sheet, and purification annealing was carried out by holding the sheet at 1200°C for 10 hours, forming a base film mainly composed of forsterite. At this time, the rate of temperature rise up to 1200°C was 20°C / h. Furthermore, during the temperature rise 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.

[0014] 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 using the method described in JIS C2550-1. To measure the W content in 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 film, and the sample was then subjected to measurement using the method described in JIS G1220. The amounts of Si, Mn, Al, N, S, Sb, Ti, and Co in the base steel sheet of the obtained grain-oriented electrical steel sheet were all the same as those in the steel slab.

[0015] 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 / 50The 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 relationship between this F17 and the amount of W (unit: mass%) in the base steel sheet was then investigated. The results are shown in Figure 1.

[0016] These results did not reveal a clear correlation between the building factor F17 and the amount of W. However, Figure 1 indicates that the building factor F17 can be divided into two groups: good values ​​of 1.25 or less and high values ​​of 1.30 or more.

[0017] 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 / 50When R17 and R19 are defined as R19 (unitless), we found that when the R17 and R19 are divided into Group A, where the relationship between R19 / R17 and R19 is 1.30, and Group B, where the R19 / R17 and R19 are 1.30 or less, a general trend in the building factor F17 can be observed. Figure 2 shows the results of redrawing the data in Figure 1 to show the relationship between the W content in the base steel sheet and the R19 / R17 value (i.e., Group A and Group B), as well as the relationship with the building factor. In Figure 2, each circle represents the building factor F17, with the larger the diameter of the circle, the larger the building factor. From the results shown in Figure 2, we found that when the relationship between R19 / R17 and R19 is 1.30, i.e., the steel sheet belongs to Group A, and the W content in the base steel sheet is in the range of 0.0010 to 0.0500 mass%, a good building factor of 1.25 or less is observed. In Figure 2, whether each circle belongs to Group A or Group B can be determined by the region in which the center of the circle is located.

[0018] <Experiment 2> A steel slab containing, by mass%, 0.037% C, 3.05% Si, 0.18% Mn, 0.009% Al, 0.0036% N, 0.007% Se, 0.062% Sn, 0.0080% Co, and 0.0200% W, 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 having 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. ２Atmosphere: N from 700℃ to 1100℃ ２ and H ２ The atmosphere was mixed with various ratios of H and H. ２ In addition, the N atmosphere in the temperature range from over 700°C to 1100°C ２ and H ２ By changing the mixing ratio of the Ti content in the steel sheet with the base coating, that is, the Ti content in the entire grain-oriented electrical steel sheet consisting of the base steel sheet and the base coating, was controlled. ２ The atmosphere was Ar during cooling.

[0019] 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 Wh 17 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.

[0020] The Ti content of the grain-oriented electrical steel sheet having a base coating mainly composed of forsterite was measured using the method described in JIS G1223. Furthermore, to measure the W content in 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 sample was subjected to the measurement method described in JIS G1220. The W content was found to be 0.0200 mass%, which was the same as that of the steel slab. The amounts of Si, Mn, Al, N, Se, Sn, and Co in the base steel sheet of the obtained grain-oriented electrical steel sheet were all the same as those in the steel slab.

[0021] 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 19The samples were divided into Group A, where the ratio R19 of R17 to R17 satisfies the relationship R19 / R17≦1.30, 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 mainly composed of forsterite was formed on the surface of the base steel sheet are shown in Figure 3.

[0022] The results shown in Figure 3 indicate that grain-oriented electrical steel sheets with a Ti content of 0.0050% by mass or more and 0.0200% by mass or less tend to belong to Group A. Furthermore, as in Experiment 1, a three-phase, three-legged model transformer was fabricated with an external dimension of 500 mm square and a plate width of 100 mm for each leg and yoke. The iron loss Wt 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.

[0023] The results shown in Figure 4 show that the building factor is high when the Ti content in the grain-oriented electrical steel sheet is less than 0.0050% by mass and more than 0.0200% by mass. In other words, it was found that the building factor is low and favorable when the Ti content in the grain-oriented electrical steel sheet, in which a base coating mainly composed of forsterite is formed on the surface of the base steel sheet, is 0.0050 to 0.0200% by mass.

[0024] As described above, the mechanism by which the building factor of a model transformer is improved by controlling the W 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 speculate as follows: Transformers are manufactured by shearing and assembling grain-oriented electrical steel sheets. Strain introduced during shearing increases iron loss. However, it is speculated that adding a certain amount of W to the base steel sheet reduces this strain. Specifically, W forms carbides and nitrides in the steel sheet, alleviating stress concentration. This reduces the shear strain experienced by the steel sheet during transformer fabrication, preventing an increase in iron loss and enabling the building factor to remain low. However, because W carbides and nitrides can also act as inhibitors, adding excessive W can adversely affect secondary recrystallization behavior. Taking this into consideration, the amount of W added to the base steel sheet is set to a range of 0.0010 mass% to 0.0500 mass%. In Experiments 1 and 2, there were two cases where the building factor was poor even when W was added.

[0025] The first point is the iron loss W when excited at 1.7T. 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 ratio R19 of R17 to R19 does not satisfy the relationship R19 / R17≦1.30. Hysteresis loss is the loss due to the magnetic flux density B ８ It has a high correlation with the same B ８ If R19 / R17 is greater than 1.30, it is thought that there will be no significant fluctuations in hysteresis loss. Therefore, if R19 / R17 exceeds 1.30, it is thought that eddy current loss is extremely large. In transformers, even when excited with a sine wave, high-frequency components are superimposed and the waveform is distorted, so it is thought that eddy current loss, which is highly frequency-dependent, will increase. Therefore, it is thought that a high eddy current loss ratio will increase the building factor.

[0026] The second issue concerns the Ti content of steel sheets with a basecoat (grain-oriented electrical steel sheets) less than 0.0050% by mass or more than 0.0200% by mass. It is speculated that the presence of a certain amount of Ti in a forsterite coating improves the coating properties. For example, if the presence of Ti improves the coating tension of the basecoat, the magnetic domains in the base steel sheet may become finer, potentially reducing eddy current loss in transformers using grain-oriented electrical steel sheets. In this case, the eddy current loss ratio decreases, which is the opposite of the high R17 and R19 values ​​mentioned above, and therefore the building factor is likely to be reduced. However, if the Ti content is too high, a large amount of substances with compositions different from forsterite, such as Ti nitrides and / or Ti oxides, may be formed, potentially reducing the coating tension of the forsterite basecoat. This is likely to result in an increase in the building factor.

[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 0.0010 to 0.0500 mass% W, 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 0.0200 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 / 50 When R19 is R19, the grain-oriented electrical steel sheet satisfies the following formula (1): R19 / R17≦1.30 (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, in mass% or mass ppm, Sn: 0.005 to 0.500%, Cr: 0.005 to 0.500%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, Bi: 0.005 to 0.500%, P: 0.005 to 0.500%, Sb: 0.005 to 0.500%, Mo: 0.005 to 0.500%, B: 0.1 to 25.0 ppm, Nb: 0.001 to The grain-oriented electrical steel sheet according to any one of the above [1] to [3], containing one or more elements selected from the group consisting of 0.020%, Ga: 0.0001 to 0.0050%, V: 0.001 to 0.020%, As: 0.0010 to 0.0200%, Zn: 0.001 to 0.020%, Pb: 0.0001 to 0.0100%, Co: 0.002 to 0.050%, and Ge: 0.0001 to 0.0050%.

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

[0032] 1 is a graph showing the relationship between the W content in a base steel sheet and the building factor. 2 is a graph showing the relationship between the W content in a base steel sheet and the R19 / R17 value, and the relationship between the W content in a base steel sheet and the R19 / R17 value, and the relationship between the W content in a base steel sheet and the building factor. 3 is a graph showing the Ti content in grain-oriented electrical steel sheets in Group A having the relationship R19 / R17≦1.30 and Group B. 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 W, 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] The reasons for limiting the constituent elements of the present invention are described below. First, the amount of each element in the composition is described. Note that "%" and "ppm" in the composition indicate "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 content is less than 1.50%, it is ineffective. 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%, it is ineffective. 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] W: 0.0010 to 0.0500% For the reasons mentioned above, it is essential that the W content be in the range of 0.0010 to 0.0500% in the base steel sheet. The W content is preferably 0.0050% or more, and more preferably 0.0080% or more. On the other hand, the W content is preferably 0.0150% or less. A W content of 0.0010% 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 contains at least the basic components described above, with the balance being Fe and unavoidable impurities. In addition to the basic components, the base steel sheet may contain the optional elements described below as needed.

[0038] 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: 0.1-25.0ppm, Nb: 0.001-0. One or more of the following elements may be added: 0.020%, Ga: 0.0001-0.0050%, V: 0.001-0.020%, As: 0.0010-0.0200%, Zn: 0.001-0.020%, Pb: 0.0001-0.0100%, Co: 0.002-0.050%, 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.

[0039] The mechanism by which the building factor of a model transformer improves when Ga is further added in the range of 0.0001 to 0.0050% is unclear, but the inventors believe it is due to the influence of Ga precipitates remaining in the finished grain-oriented electrical steel sheet. Because the yoke and legs of a transformer have a certain 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.

[0040] During secondary recrystallization, Ga acts as an inhibitor, suppressing 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 finely dispersed Ga serves as the origin of rotational magnetic flux without impairing iron loss, presumably improving the building factor. The Ga content is more preferably 0.0005% or more, and even more preferably 0.0010% or more. Furthermore, the Ga content is more preferably 0.0040% or less, and even more preferably 0.0030% or less.

[0041] Ti: 0.0030% or less The amount of Ti in the base steel sheet is preferably 0.0030% or less, more preferably 0.0015% 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.

[0042] 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.

[0043] [Composition of Grain-Oriented Electrical Steel Sheet and Undercoating] In the present invention, the Ti content in a grain-oriented electrical steel sheet having a forsterite-based undercoating formed on its surface is limited to 0.0050 to 0.0200% for the reasons described above. The Ti content in the grain-oriented electrical steel sheet is preferably 0.0060% or more. The Ti content in the grain-oriented electrical steel sheet is preferably 0.0100% or less. The reason why the lower limit of the Ti content in a grain-oriented electrical steel sheet having a undercoating is 0.0050% is that, as described above, the presence of a certain amount of Ti in the forsterite coating is thought to improve the coating properties and reduce eddy current loss, but if the amount is less than 0.0050%, this effect is limited.

[0044] 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.

[0045] 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 0.0150% or less.

[0046] Here, when limiting the Ti content in a steel sheet (grain-oriented electrical steel sheet) having a base coating to 0.0050 to 0.0200%, as described above, the Ti content in the base steel sheet is preferably 0.0030% or less.

[0047] [Magnetic Properties of Grain-Oriented Electrical Steel Sheet] Furthermore, in the present invention, as described above, the parameters calculated from the hysteresis loss and iron loss of the grain-oriented electrical steel sheet as the product steel sheet must satisfy a predetermined range. That is, the iron loss W when excited at 1.7 T 17 / 50 and hysteresis loss Wh 17 The ratio R17 (=Wh 17 / W 17 / 50 ) and iron loss W when excited at 1.9T19 / 50 and hysteresis loss Wh 19 Ratio R19 (=Wh 19 / W 19 / 50 ) must satisfy the relationship of formula (1) expressed as R19 / R17≦1.30. If the grain-oriented electrical steel sheet does not satisfy the above formula (1), it will not be able to exhibit a low building factor. These values ​​can be measured using the method described in JIS C2550-1. In addition, in order to match the hysteresis loss with the iron loss at 50 Hz, it can be calculated by multiplying the energy loss of the iron core in one turn of the hysteresis loop by 50, which is the excitation frequency. In addition, the value of R19 / R17 is not particularly limited, and for example, it can be calculated by changing the conditions of each process in the manufacturing process to change the magnetic flux density B ８ It can be controlled by changing

[0048] [Method for manufacturing grain-oriented electrical steel sheet] Next, an example of a manufacturing method by which the grain-oriented electrical steel sheet of the present invention can be obtained 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 having 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 the molten steel stage.

[0049] The slab can be heated and hot-rolled in a conventional manner. Alternatively, the slab may be cast and hot-rolled immediately without heating. When heating, a component system with a low inhibitor content does not require high-temperature heating to dissolve the inhibitor, so a low temperature of 1300°C or less is effective for reducing costs. The heating temperature of the slab is preferably 1250°C or less. Hot-rolling conditions may be in accordance with conventional methods. In this way, a hot-rolled sheet can be obtained.

[0050] The resulting hot-rolled sheet can then be annealed as needed. The annealing temperature is preferably about 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, and preferably 1150°C or lower, and more preferably 1100°C or lower. The annealing temperature range is preferably 1000°C or higher and 1100°C or lower. In this manner, a hot-rolled annealed sheet can be obtained.

[0051] The hot-rolled sheet after hot rolling or the hot-rolled and annealed sheet after hot-rolled sheet annealing can be cold-rolled to a 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.

[0052] 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.

[0053] Next, 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 purification annealing to purify the components. This allows the secondary recrystallization structure to develop in the steel and forsterite coating to form on the surface of the steel sheet. Thus, according to the present invention, a grain-oriented electrical steel sheet having a base coating mainly composed of forsterite formed on the surface of the base steel sheet can be suitably obtained. Note that "mainly composed of MgO" means that the annealing separator contains 75 mass% or more of MgO in terms of solid content.

[0054] 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 0.0200%, 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 also be used to achieve the above Ti requirement. Examples of other methods include adding Ti as a raw material component and changing the purification annealing conditions.

[0055] Furthermore, 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 desirable to raise the temperature to 1100°C or higher. The longer the holding time, the greater the degree of purification, but 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.

[0056] 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 surface of the steel sheet (more specifically, the surface of the base coating) having the base coating before or after flattening annealing in order to improve iron loss. This insulating coating is preferably a coating 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 application 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.

[0057] Steel slab A contains C: 0.070%, Si: 3.55%, Mn: 0.07%, Al: 0.0080%, N: 0.0050%, W: 0.0120%, Mo: 0.026%, Ti: 0.0150%, with the balance being Fe and unavoidable impurities; Steel slab B contains C: 0.072%, Si: 3.51%, Mn: 0.07%, Al: 0.0080%, N: 0.0047%, W: 0.0210%, Mo: 0.025%, Ti: 0.0023%, with the balance being Fe and unavoidable impurities; Steel slabs C and D, consisting of 0.072% C, 3.49% Si, 0.07% Mn, 0.0090% Al, 0.0051% N, 0.0005% W, 0.025% Mo, and 0.0180% Ti, with the balance being Fe and unavoidable impurities, were produced by continuous casting. Steel slabs A, B, C, and D were subjected to slab heating, where they were soaked at 1200°C for 40 minutes. They were then hot-rolled to a thickness of 2.2 mm. Then, the hot-rolled sheet was heated at 1000°C for 60 seconds with N ２ The hot-rolled sheet was then annealed in a 0.23 mm thick atmosphere at 850°C for 90 seconds. 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.

[0058] 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, it was held at 1100°C for 25 hours, and then purified by annealing at 1200°C for 10 hours. During this temperature rise process, 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.

[0059] 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.

[0060] 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 R17, which is the ratio of the iron loss W 19 / 50 and hysteresis loss Wh 19 The ratio R19 was calculated. The results are shown in Table 1.

[0061] Furthermore, to measure the W and Ti contents of the base steel plate, 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 measurements according to the methods specified in JIS G1220 and JIS G1223. The measurement results are also shown in Table 1. The Si and Mn contents of the base steel plate were also measured according to the methods specified in JIS G1212:1997 and JIS G1213:2001, respectively, and it was confirmed that they were the same as the contents in each steel slab.

[0062] 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 ) were calculated as shown in Table 1.

[0063]

[0064] 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.

[0065] 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 hot-rolled sheet having a thickness of 2.4 mm. The hot-rolled sheet was then subjected to a N treatment at 1100°C for 20 seconds. ２ The hot-rolled sheet was then annealed in a 1.5 mm thick intermediate cold-rolled sheet by cold rolling. ２ -75%N ２The 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 40% H atmosphere at 825°C for 150 seconds. ２ -60%N ２ The steel sheets were subjected to decarburization annealing in a humid atmosphere with a dew point of 45°C.

[0066] Thereafter, an annealing separator mainly composed of MgO (MgO: 88%) was applied to the surfaces (both sides) of the obtained decarburized annealed sheet. 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 Five parts by mass of MgO powder was added. Furthermore, purification annealing was performed by holding at 1200°C for 10 hours to form a base coating mainly composed of forsterite. The heating rate up to 1200°C was 15°C / h. Furthermore, during the heating 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.

[0067] The Ti content of the thus obtained samples, i.e., grain-oriented electrical steel sheets having a base coating primarily composed of forsterite formed on the surface thereof, was measured according to the method specified in JIS G1223. The measurement results are also shown in Table 2. Note that in this example, the Ti content does not change due to the formation of an insulating coating in a subsequent process. Therefore, the measurement results are shown in the table as the Ti content of the grain-oriented electrical steel sheets.

[0068]

[0069] Furthermore, an insulating coating containing magnesium phosphate and silica as its main components was applied onto the base coating of the steel sheet. The iron loss W of the grain-oriented electrical steel sheet thus obtained, i.e., the base coating and the insulating coating formed in this order on the surface of the base steel sheet, was measured. 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 R17, which is the ratio of iron loss W 19 / 50 and hysteresis loss Wh 19 The ratio of R19 to R19 was calculated. The results are shown in Table 2.

[0070] Furthermore, to measure various elements 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 film and insulating film, and measurements were performed using the same method as in Example 1. When no method specified in JIS was available, the sample was subjected to ICP emission spectroscopy. The amounts of Si, Mn, W, Ga, and other elements in the base steel sheet were confirmed to be the same as those contained in each steel slab. The measurement results are also shown in Table 2.

[0071] 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 2.

[0072] As is clear from Table 2, it can be seen that 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 0.0010 to 0.0500% by mass of W, with the balance being Fe and unavoidable impurities, and a base coating mainly composed of forsterite formed on the surface of the base steel sheet, the grain-oriented electrical steel sheet having a Ti content of 0.0050 to 0.0200% by mass in the grain-oriented electrical steel sheet, and the iron loss W 17 / 50 and the hysteresis loss Wh 17 and the ratio of Wh 17 / W 17 / 50 is defined as R17, and the iron loss W 19 / 50 and the hysteresis loss Wh 19 and the ratio of Wh 19 / W 19 / 50 is defined as R19, the grain-oriented electrical steel sheet satisfying the following formula (1). R19 / R17 ≦ 1.30... (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, comprising an insulating film on the surface of the base film.

4. The base steel sheet further contains, in mass% or mass ppm, one or more selected from 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, Nb: 0.001 - 0.020%, Ga: 0.0001 - 0.0050%, V: 0.001 - 0.020%, As: 0.0010 - 0.0200%, Zn: 0.001 - 0.020%, Pb: 0.0001 - 0.0100%, Co: 0.002 - 0.050% and Ge: 0.0001 - 0.0050%. The grain-oriented electrical steel sheet according to any one of claims 1 to 3.

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