Directional 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

[Technical Field]

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

[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, which is called 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 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, 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 to 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 refining 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 it with an electron beam. Furthermore, hysteresis loss is reduced by aligning the orientation after secondary recrystallization to a high degree in the Goss orientation and by reducing impurities, while eddy current loss is primarily reduced by applying magnetic domain refinement technology. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 40-15644 [Patent Document 2] Special Publication No. 51-13469 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-129356 [Patent Document 4] Special Publication No. 57-2252 [Patent Document 5] Special Publication No. 6-72266 [Patent Document 6] Japanese Patent Application Laid-Open No. 2008-196016 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, grain-oriented electrical steel sheets are mainly used as iron cores in transformers. 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 iron loss of the transformer core being greater. The ratio of these 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 increase, 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, 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. 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. [Means for solving the problem]

[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. They 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 ​​written before and after "to" as the lower and upper limits, respectively. <Experiment 1> To primarily vary the Ga content in the base steel sheet, a steel slab containing, by mass%, 0.0500-0.0810% C, 3.15-3.31% Si, 0.07-0.10% Mn, 0.0200-0.0250% Al, 0.0069-0.0085% N, 0.0011-0.0031% S, 0.025-0.036% Sb, 0.0080-0.0090% Ti, and 0.0000-0.0058% Ga was used, with the remainder consisting of Fe and unavoidable impurities. This steel slab was subjected to slab heating by soaking at 1400°C for 20 minutes, and then hot-rolled to a thickness of 2.4 mm. The hot-rolled sheet was then annealed at 1000°C for 30 seconds in an N2 atmosphere. The annealed hot-rolled sheet was then cold-rolled to a 1.5 mm thick intermediate cold-rolled sheet, which was then further annealed at 1000°C for 100 seconds in a 25% H2-75% N2 atmosphere. The annealed intermediate cold-rolled sheet was then cold-rolled to a 0.23 mm thick cold-rolled sheet. This cold-rolled sheet was then decarburized at 850°C for 150 seconds in a 50% H2-50% N2 atmosphere with a dew point of 50°C. The decarburized annealed sheet was then coated on both surfaces with an annealing separator primarily composed of MgO and subjected to purification annealing at 1200°C for 10 hours, forming a forsterite-based undercoat. The heating rate to 1200°C was 20°C / h. Furthermore, during the temperature rise process, an N2 atmosphere was used from room temperature to 700°C, an atmosphere with various N2 and H2 mixture ratios was used from over 700°C to 1100°C, and an H2 atmosphere was used from over 1100°C to 1200°C. In addition, an H2 atmosphere was used during holding, and an Ar atmosphere was used during cooling.

[0012] The grain-oriented electrical steel sheets thus obtained, in which a forsterite-based undercoat (forsterite coating) 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 19The hysteresis losses (when excited to 1.7 T and 1.9 T, respectively) were measured according to 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 aqueous solution at 80°C for 180 seconds to remove the forsterite coating, and the sample was subjected to measurement using 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, simulating a transformer with an external dimension of 500 mm square and a plate width of 100 mm for each leg and each yoke. Then, the iron loss W 17 / 50 The iron loss of the transformer was measured when it was excited up to 1.7 T at 50 Hz. The model transformer had 50 laminated samples, with two laminates stacked alternately. From the obtained results, the building factor F17 of the model transformer is calculated as the iron loss WT 17 / 50 The iron loss W of the sample 17 / 50 Divided by (WT 17 / 50 / W 17 / 50 The relationship between F17 and the Ga content (unit: mass%) in the base steel sheet was then 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 expressed as R19 (unitless), we found that when the building factor F17 is divided into group A where R17≦R19≦0.70 and group B where R17≦R19≦0.70, a general trend can be seen in the building factor F17. Figure 2 shows the results of redrawing Figure 1, 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 there is a relationship of R17≦R19≦0.70, that is, it belongs to Group A, and a good building factor is exhibited when 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 and used. This steel slab was subjected to slab heating by soaking at 1300°C for 30 minutes, and then hot-rolled to a 2.2 mm thick hot-rolled sheet. This hot-rolled sheet was then annealed at 1100°C for 30 seconds in a N atmosphere. The annealed hot-rolled sheet was then cold-rolled to a 0.23 mm thick cold-rolled sheet. This cold-rolled sheet was subjected to decarburization annealing at 840°C for 120 seconds in a 40% H2-60% N2 humid atmosphere with a dew point of 40°C. The surface of the resulting decarburized annealed sheet was then coated with an annealing separator containing TiO2 in a range of 0 to 15 parts by mass relative to MgO, followed by purification annealing at 1220°C for 5 hours to form a forsterite-based undercoat. The heating rate up to 1220°C was 15°C / h. During the heating process, the N2 atmosphere was used from room temperature to 700°C, and various N2 / H2 mixture ratio atmospheres were used from above 700°C to 1100°C, and the H2 atmosphere was used from above 1100°C to 1200°C. The H2 atmosphere was used during the holding period, and the Ar atmosphere was used during cooling. By changing the mixture ratio of N2 and H2 in the atmosphere in the temperature range from above 700°C to 1100°C, the Ti content in the steel sheet with the base coating still on, i.e., the entire grain-oriented electrical steel sheet composed 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 Wh 17 and Wh 19 The hysteresis losses (when excited to 1.7 T and 1.9 T, respectively) were measured according to the method described in JIS C2550-1.

[0018] The Ti content of the grain-oriented electrical steel sheets having an undercoating mainly composed of forsterite was measured by the method described in JIS G1223. Furthermore, 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 in the same manner as in Experiment 1. As a result, the Ga content was 0.0030 mass%, which was the same content as in the steel slab.

[0019] From the obtained magnetic properties, the iron loss W when excited at 1.7 T was obtained, as in Experiment 1. 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. Figure 3 shows the results of comparing the samples in Groups A and B with the Ti content (unit: mass%) in grain-oriented electrical steel sheets in which a forsterite-based undercoating film is formed on the surface of the base steel sheet.

[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 a 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 hysteresis loss increases due to domain wall pinning. 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 amount of Ti 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 thought 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 a grain-oriented electrical steel sheet on the surface of which a base coating mainly composed of forsterite is formed is not clear, but the inventors believe as follows. Because the yoke and legs of a transformer have a fixed width, the magnetic path varies in distance between the inside and outside, like an athletics track. For this reason, when excited, the magnetic flux tends to be biased toward the inside where the magnetic path is shorter. Even when the entire steel plate is excited to 1.7 T, the magnetic flux density on the inside exceeds that. Therefore, it is estimated 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 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 and configuration of the present invention are 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 undercoating formed on the surface of the base steel sheet and containing forsterite as a main component, 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 / 50 Grain-oriented electrical steel sheet that satisfies the following formula (1) when R19 is used. R17≦R19≦0.70 (1)

[0028] [2] The grain-oriented electrical steel sheet according to [1] above, 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 [1] or [2] above, further comprising 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, and Nb: 0.001 to 0.020 mass ppm. 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 V: ​​0.001 to 0.020 mass%, As: 0.0010 to 0.0200 mass%, Zn: 0.001 to 0.020 mass%, Pb: 0.0001 to 0.0100 mass%, Co: 0.002 to 0.050 mass%, W: 0.0010 to 0.0100 mass%, and Ge: 0.0001 to 0.0050 mass%. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a graph showing the relationship between the Ga content in a base steel sheet and the building factor. [Figure 2] 1 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. [Figure 3] 1 is a graph showing the Ti content in grain-oriented electrical steel sheets in Group A and Group B. [Figure 4] 1 is a graph showing the relationship between the Ti content in grain-oriented electrical steel sheets and the building factor. DETAILED DESCRIPTION OF THE INVENTION

[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) relating to 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] [Component composition of base steel plate] Next, the reasons for limiting the constituent elements of the present invention will be described. First, the amount of each element in the component composition will be explained. Note that hereinafter, "%" and "ppm" indications regarding the component composition refer to "% by mass" and "ppm by mass" unless otherwise specified. Si: 1.50 to 8.00% Silicon is an element necessary for increasing the resistivity of steel and improving iron loss, but if the 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 the Mn content 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 as a finished sheet decreases. Therefore, the Mn content in the base steel sheet is set to the range of 0.02 to 1.00%. The Mn content is preferably 0.04% or more. On the other hand, the Mn content is preferably 0.20% or less.

[0036] Ga: 0.0001 to 0.0050% For the reasons mentioned above, it is essential that the Ga content in the base steel sheet be in the range of 0.0001 to 0.0050%. 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 a normal base steel sheet.

[0037] The composition of the base steel sheet of the grain-oriented electrical steel sheet of the present invention contains at least the above-mentioned basic components, with the remainder being Fe and unavoidable impurities. In addition to the above 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:0.1~25.0ppm, One or more elements selected from 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% 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 lower limit, the magnetic properties will not be improved. If the amount of each element added exceeds the upper limit, the development of secondary recrystallized grains will be inhibited, resulting in a deterioration of the magnetic properties.

[0038] Co: 0.002 to 0.050% In addition to the above-mentioned elements that can be optionally contained, or in addition to the above-mentioned elements that can be optionally contained, if the Co content of the base steel sheet is in the range of 0.002 to 0.050%, the building factor of the model transformer will be further improved. Therefore, it is preferable to further add Co in this range. Although the mechanism by which the building factor is improved in this way is not clear, when Co is dissolved in iron, it is expected that the saturation magnetic flux density of iron will increase, thereby improving high magnetic field characteristics. Therefore, it is presumed that the building factor of the model transformer can be further improved. The Co content of the base steel sheet is preferably 0.002% or more, more preferably 0.006% or more, and even more preferably 0.008% or more. Furthermore, the Co content of 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 to 0.020%, and more preferably 0.008 to 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 contained), 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 above-mentioned composition of a grain-oriented electrical steel sheet in which a forsterite coating is formed on the surface of the base steel sheet, for example, as shown in Experiment 1, the forsterite coating can be removed from the grain-oriented electrical steel sheet and the content of each element can be checked.

[0041] [Composition of grain-oriented electrical steel sheet and base coating] The Ti content in grain-oriented electrical steel sheets having a forsterite-based undercoating formed on the surface thereof is limited to 0.0050 to 0.0210% for the reasons mentioned above. The Ti content in grain-oriented electrical steel sheets is preferably 0.0060% or more. The reason why the lower limit of the Ti content in grain-oriented electrical steel sheets having a undercoating is 0.0050% is that, as mentioned above, the presence of a certain amount of Ti in the forsterite coating is thought to improve the coating properties, reduce magnetostriction, and improve eddy current loss, but if the content is less than 0.0050%, these effects are insufficient. The Ti content in grain-oriented electrical steel sheets is 0.0210% or less, and preferably 0.0150% or less. Excessive Ti content is undesirable because it increases costs. Also, too much Ti penetrates into the base steel sheet from the annealing separator used to form the forsterite film.

[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) with 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, the parameters calculated from the hysteresis loss and iron loss of grain-oriented electrical steel sheets used as product steel sheets must satisfy a specified range. That is, the iron loss W when excited at 1.7T is 17 / 50 and hysteresis loss Wh 17 Ratio to R17 (=Wh 17 / W 17 / 50 ) and iron loss W when excited at 1.9T 19 / 50 and hysteresis loss Wh 19 Ratio to R19 (=Wh 19 / W 19 / 50 ) must satisfy the relationship of formula (1), where R17≦R19≦0.70. If grain-oriented electrical steel sheets do not satisfy the above formula (1), they will not be able to achieve a low building factor. These values ​​can be measured using the method described in JIS C2550-1. Note that, in order to match the hysteresis loss with the iron loss at 50 Hz, the hysteresis loss can be calculated by multiplying the energy loss in 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] Furthermore, grain-oriented 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-oriented electrical steel sheet. In particular, when grain-oriented electrical steel sheets are stacked to form a transformer core, iron loss can be further improved by imparting additional tension to the steel sheet. The insulating coating can be formed satisfactorily, for example, according to the manufacturing method described below.

[0047] [Method of manufacturing grain-oriented electrical steel sheets] 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 sheets can be used as the manufacturing method. For example, slabs may be manufactured from molten steel adjusted to the predetermined chemical composition described above by a conventional ingot casting 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 aforementioned optional elements during the process, it is desirable to add them at this stage of molten steel production.

[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] Next, the obtained hot-rolled sheet can be subjected to hot-rolled sheet annealing as necessary. The hot-rolled sheet annealing temperature is preferably in the range of about 950 to 1150°C. If the hot-rolled sheet annealing temperature is less than 950°C, unrecrystallized portions are likely to remain in the steel. On the other hand, if the hot-rolled sheet 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 hot-rolled sheet annealing temperature is preferably 950°C or higher, more preferably 1000°C or higher. Furthermore, the hot-rolled sheet annealing temperature is preferably 1150°C or lower, more preferably 1100°C or lower. In this way, 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 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 crystal grains may become too coarse, as in the case of 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 reached 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 having a base coating formed on the surface of the base steel sheet can be obtained. 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 introducing an N2 atmosphere during purification annealing (heating and holding), 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 the compound in the annealing separator is preferably 2 parts by mass or more and 15 parts by mass or less relative to MgO. However, the above Ti requirement for grain-oriented electrical steel sheets may be met by other methods, such as, for example, when more than 30 ppm of Ti is added to the slab, the Ti can be concentrated on the surface by annealing in a nitrogen atmosphere in an annealing step before the final 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 stack, applying an insulating coating to the steel sheet surface (more specifically, the surface of the base coating) before or after flattening annealing is effective in improving iron loss. A coating that can impart tension to the grain-oriented electrical steel sheet is desirable as this insulating coating. It is desirable to employ a method of forming a coating by depositing an inorganic substance onto the steel sheet surface 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. [Example]

[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 remainder is Fe and unavoidable impurities. Steel slab B, which contained 0.025% Mn, 0.0025% Ti, and the balance Fe and unavoidable impurities, and steel slab C, which contained 0.0720% C, 3.49% Si, 0.07% Mn, 0.0090% Al, 0.0051% N, 0.00001% Ga, 0.025% Mo, 0.0240% Ti, and the balance 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 2.2 mm thick hot-rolled sheet. The hot-rolled sheet was then hot-rolled and annealed at 1000°C for 60 seconds in a N2 atmosphere. The resulting hot-rolled and annealed sheet was then cold-rolled to a 0.23 mm thick cold-rolled sheet. Furthermore, the cold-rolled sheet was subjected to primary recrystallization annealing, which also served as decarburization annealing, in a humid atmosphere of 60% H2-40% N2 with a dew point of 60°C at 850°C for 90 seconds.

[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, followed by purification annealing at 1200°C for 10 hours. During the temperature rise process of this heat treatment, an N2 atmosphere was used from room temperature to 700°C, an atmosphere with various N2 and H2 mixture ratios was used from above 700°C to 1100°C, and an H2 atmosphere was used from the start of holding above 1100°C to the end of holding at 1200°C. Furthermore, an Ar atmosphere was used 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 still bearing the forsterite-based base coating, 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 then 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 / 50The iron loss of the transformer was measured when it was excited up to 1.7 T at 50 Hz. The model transformer had 50 laminated samples, with two laminates stacked alternately. From the obtained results, the building factor F17 of the model transformer is calculated as the iron loss WT 17 / 50 The iron loss W of the sample 17 / 50 Divided by (WT 17 / 50 / W 17 / 50 The results are shown in Table 1.

[0062] [Table 1]

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

[0064] Steel slabs containing the elements listed in Table 2, with the remainder consisting of 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 2.4 mm thick hot-rolled sheet. This hot-rolled sheet was then annealed at 1100°C for 20 seconds in an N2 atmosphere. The annealed hot-rolled sheet was then cold-rolled to a 1.5 mm thick intermediate cold-rolled sheet, which was then subjected to intermediate annealing at 900°C for 100 seconds in a 25% H2-75% N2 atmosphere. The annealed intermediate cold-rolled sheet was then cold-rolled to a 0.23 mm thick cold-rolled sheet. This cold-rolled sheet was then decarburized at 825°C for 150 seconds in a humid atmosphere of 40% H2-60% N2 with a dew point of 45°C. Furthermore, an annealing separator mainly composed of MgO (MgO: 88%) was applied to the surfaces (both sides) of the obtained decarburized annealed sheet. To prepare the annealing separator, TiO powder was added to hot water at 50°C, stirred for 24 hours, and then filtered to obtain perhydrated TiO powder. Five parts by mass of perhydrated TiO powder was added to the annealing separator.

[0065] Further purification annealing was performed by holding at 1200°C for 10 hours to form a base coating primarily composed of forsterite. The heating rate up to 1200°C was 15°C / h. Furthermore, during the heating process, an N2 atmosphere was used from room temperature to 700°C, an atmosphere with various N2 and H2 mixture ratios was used from above 700°C to 1100°C, and an H2 atmosphere was used from above 1100°C to 1200°C. The H2 atmosphere was used during holding, and an Ar atmosphere was used 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. Therefore, 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] [Table 2] TIFF0007800777000003.tif168170

[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 R19 was calculated. 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 having the forsterite-based undercoating on the surface of the base steel sheet, was measured according to the method specified in JIS G 1223. The measurement results are shown in Tables 3 and 4. Furthermore, in order to measure the composition of the base steel sheet, a part of the obtained sample was immersed in a 10% hydrochloric acid aqueous solution at 80°C for 180 seconds to remove the forsterite coating, and the sample was subjected to measurement in the same manner 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 plate were the same as 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 iron loss of the transformer was measured when it was excited up to 1.7 T at 50 Hz. The model transformer had 50 laminated samples, with two laminates stacked alternately. From the obtained results, the building factor F17 of the model transformer is calculated as the iron loss WT 17 / 50 The iron loss W of the sample 17 / 50 Divided by (WT 17 / 50 / W 17 / 50 ) was calculated. The results are shown in Tables 3 and 4.

[0071] [Table 3]

[0072] [Table 4]

[0073] As is clear from Tables 3 and 4, 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 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, 0.0001 to 0.0050 mass% Ga, and 0.0032 mass% or less Ti, with the balance being Fe and unavoidable impurities; and a base coating containing forsterite as a main component, formed on the surface of the base steel sheet, The amount of Ti in the grain-oriented electrical steel sheet is 0.0050 to 0.0210 mass%, Iron loss W when excited at 1.7T 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 Grain-oriented electrical steel sheet that satisfies the following formula (1), where R19 is the R17≦R19≦0.70 (1)

2. The grain-oriented electrical steel sheet according to claim 1, wherein the base steel sheet has a Ti content of 0.0030 mass% or less.

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

4. The base steel plate 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 3. The grain-oriented electrical steel sheet according to claim 1, further comprising one or more elements selected from the group consisting of 0.001 to 0.020 mass% V, 0.0010 to 0.0200 mass% As, 0.001 to 0.020 mass% Zn, 0.0001 to 0.0100 mass% Pb, 0.002 to 0.050 mass% Co, 0.0010 to 0.0100 mass% W, and 0.0001 to 0.0050 mass% Ge.

5. The base steel plate 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 0.0 4. The grain-oriented electrical steel sheet according to claim 3, comprising one or more elements selected from the group consisting of 0.20% by mass of As, 0.001 to 0.020% by mass of V, 0.001 to 0.020% by mass of As, 0.0010 to 0.0200% by mass of Zn, 0.001 to 0.020% by mass of Pb, 0.0001 to 0.0100% by mass of Co, 0.002 to 0.050% by mass of W, and 0.0001 to 0.0050% by mass of Ge.

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