Grain-oriented electrical steel sheet

Abstract

The present invention provides a grain-oriented electrical steel sheet having magnetic characteristics with which it is possible to sufficiently suppress the building factor. This grain-oriented electrical steel sheet sequentially has an underlayer film and an insulating film on the surface of a base steel sheet that contains at least 0.0001-0.0200% of La, wherein the amount of Ti in the steel sheet is set to 0.0050-0.1500%, and the ratio R17 of Wh17 to W17 / 50 and the ratio R18 of Wh18 to W18 / 50 satisfy R18 / R17 ≤ 1.50.

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 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 during primary recrystallization, thereby enabling 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, it does not require high-temperature slab heating, which is essential in methods that use inhibitors, and has 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, 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 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 be large, resulting in the problem of not being able to perform to its full potential. In the carbon-neutral era, what needs to be reduced is the iron loss of the final product, the transformer; no matter how low the material's iron loss, a high building factor makes no sense. The building factor is affected not only by the transformer design but also by the material's properties, so properties that reduce the building factor as well as the material's iron loss are desirable.

[0010] That is, an object of the present invention is to provide a grain-oriented electrical steel sheet having magnetic properties that can sufficiently suppress the building factor.

[0011] As a result of extensive research, the present inventors have focused on the La content in a base steel sheet and the Ti content in the entire grain-oriented electrical steel sheet after the base coating and insulating coating, which are primarily composed of forsterite, have been formed on the base steel sheet, and have found that by controlling the La 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.

[0012] 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 La content in the base steel sheet, a steel slab containing, by mass%, La: 0-0.0210%, C: 0.050-0.081%, Si: 3.1-3.3%, 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: 0.008-0.009%, and Co: 0.0030-0.0040%, 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 at 1200°C for 10 hours to form a base coat 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 Atmospheres with various mixture ratios of H ２ The atmosphere was also H ２ The steel sheet was heated in a nitrogen atmosphere, and cooled in an Ar atmosphere. The coating liquid was then applied to the steel sheet, and an insulating coating was formed on the undercoat.

[0013] The grain-oriented electrical steel sheets thus obtained, in which a forsterite-based undercoat (forsterite coating) and an insulating coating were formed in this order on the surface of the base steel sheet, were used as samples. 17 / 50 and W 18 / 50 (iron loss when excited to 1.7T and 1.8T at 50Hz) and hysteresis loss Wh 17 and Wh 18 The hysteresis losses (when excited to 1.7 T and 1.8 T, respectively) were measured using the method described in JIS C2550-1. To measure the La 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 undercoat and insulating coating, and then the sample was subjected to measurement using the method described in Isao Tanabe, Katsumi Mizumaki, Yoshio Masuyama, and Shozo Takase, Castings, Vol. 32, No. 8, p. 580 (hereinafter referred to as the reference). The C content in the base steel sheet of the obtained grain-oriented electrical steel sheet was 0.0050% or less, and the Si, Mn, Sb, and Co contents were all the same as those in the steel slab.

[0014] Next, a three-phase, three-legged model transformer was fabricated from the obtained sample, simulating a transformer, with an external dimension of 500mm square and a plate width of 100mm for each leg and yoke. 17 / 50The model transformer had 50 laminated samples, with two laminated layers alternately stacked. From the measurement results thus obtained, the building factor F17 of the model transformer and the model transformer iron loss WT 17 / 50 The iron loss W of the sample 17 / 50 The value divided by (WT 17 / 50 / W 17 / 50 The relationship between F17 and the amount of La (unit: mass%) in the base steel sheet was investigated, and the results are shown in Figure 1.

[0015] These results did not reveal a clear correlation between the building factor F17 and the amount of La. 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.

[0016] 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 Hysteresis loss Wh 17 Ratio of Wh 17 / W 17 / 50 When R17 (unitless) is used and the excitation is 1.8T, the iron loss W 18 / 50 Hysteresis loss Wh 18 Ratio of Wh 18 / W 18 / 50When R17 and R18 are divided into Group A, where the relationship R18 / R17 ≦1.50, and Group B, where the relationship R18 / R17 ≦1.50, we found that a general trend in the building factor F17 can be observed. Figure 2 shows the results of organizing the data in Figure 1 in terms of R18 / R17. In Figure 2, each circle represents a building factor F17, and the larger the circle (bubble) diameter, the larger the building factor. From the results shown in Figure 2, we found that a good building factor of 1.25 or less is observed when the relationship R18 / R17 ≦1.50 exists, i.e., the bubble belongs to Group A, and the La content in the base steel sheet is in the range of 0.0001 to 0.0200%. In Figure 2, whether each bubble belongs to Group A or Group B can be determined by the region in which the circle center of the bubble is located.

[0017] <Experiment 2> A steel slab containing, by mass%, La: 0.0010%, C: 0.037%, Si: 3.0%, Mn: 0.18%, Al: 0.009%, N: 0.0036%, Se: 0.007%, Sn: 0.062%, and Co: 0.0080%, with the balance being 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 hot-rolling to obtain a hot-rolled sheet having a thickness of 2.2 mm. 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 then 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 forsterite film. The temperature was raised to 1220°C at a rate of 15°C / h, and during the temperature rise process, N was added from room temperature to 700°C. ２ Atmosphere: N from 700℃ to 1100℃ ２ and H ２The atmosphere was changed in various mixing ratios, and H ２ In this way, the H ２ and N ２ By changing the mixing ratio of H, the Ti content in the grain-oriented electrical steel sheet obtained later, and in particular the Ti content in the steel sheet with the undercoat, was controlled. ２ The steel sheet was heated in a nitrogen atmosphere, and cooled in an Ar atmosphere. The coating liquid was then applied to the steel sheet, and an insulating coating was formed on the undercoat.

[0018] The grain-oriented electrical steel sheets thus obtained, in which the forsterite film and the insulating film were formed in this order on the surface of the base steel sheet, were used as samples. 17 / 50 and W 18 / 50 (iron loss when excited to 1.7T and 1.8T at 50Hz) and hysteresis loss Wh 17 and Wh 18 (hysteresis loss when excited to 1.7 T and 1.8 T, respectively) was measured according to the method described in JIS C2550-1.

[0019] The Ti content of the grain-oriented electrical steel sheet with a forsterite-based base coating and an insulating coating was measured using the method described in JIS G1223. Furthermore, to measure the La 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 insulating coating, and the La content was measured according to the method described in the above-mentioned reference. The La content was found to be 0.0010%, which was the same as the content in the steel slab. The C content in the base steel sheet of the obtained grain-oriented electrical steel sheet was 0.0050% or less, and the Si, Mn, Sn, and Co contents were all the same as those in the steel slab.

[0020] From the obtained magnetic properties, the iron loss W when excited at 1.7 T was 17 / 50 Hysteresis loss Wh 17 The ratio R17 and the iron loss W when excited at 1.8T 18 / 50 Hysteresis loss Wh 18The results were divided into two groups: Group A, where the ratio R18 of R17 to R18 is 1.50, and Group B, where the ratio is 1.50. As in Experiment 1, a three-phase, three-legged model transformer was fabricated with an outer shape of 500mm square and a plate width of 100mm for each leg and yoke. The iron loss Wt 17 / 50 The building factor F17 (unitless) was calculated from the value. The relationship between the Ti content (unit: mass%) in grain-oriented electrical steel sheets still having the base coating and insulating coating and the building factor F17 was summarized for samples belonging to Group A and Group B, and the results are shown in Figure 3. In Figure 3, Group A is indicated by black squares, and Group B is indicated by black circles. From the results shown in Figure 3, it was found that grain-oriented electrical steel sheets still having the base coating and insulating coating with a Ti content of 0.0050% or more and 0.1500% or less belong to Group A, and have a low, favorable building factor.

[0021] As described above, the mechanism by which the building factor of a model transformer is improved by controlling the La content in the base steel sheet and the Ti content in the grain-oriented electrical steel sheet, which is composed of a forsterite-based base coating and an insulating coating formed on the surface of the base steel sheet in that order, is unclear. However, the inventors believe as follows: Transformers are manufactured by shearing grain-oriented electrical steel sheets and assembling the sheared steel sheets. Strain introduced during shearing can cause an increase in iron loss. Adding a certain amount of La to the base steel sheet is thought to reduce this strain. La 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 La carbides and nitrides can also function as inhibitors, excessive addition of La can adversely affect secondary recrystallization behavior. Taking this into consideration, the amount of La added to the base steel sheet is set to 0.0001% or more and 0.0200% or less.

[0022] However, in Experiments 1 and 2, there were two cases where the building factor was not good even when La was added. The first was the iron loss W when excited at 1.7 T. 17 / 50 Hysteresis loss Wh 17 The ratio R17 and the iron loss W when excited at 1.8T 18 / 50 Hysteresis loss Wh 18 The ratio R18 of R17 and R18 does not satisfy the relationship R18 / R17≦1.50. Hysteresis loss is the loss of the magnetic flux density B at a magnetic field strength of 800 A / m. ８ It has a high correlation with the same B ８ If this is the case, it is thought that there will be no significant fluctuations in hysteresis loss. Therefore, if R18 / R17 exceeds 1.50, it is thought that eddy current loss is 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. In this way, it is thought that when the eddy current loss ratio increases, the building factor will increase.

[0023] The second issue concerns cases where the Ti content of the base coating and the insulating coated steel sheet (grain-oriented electrical steel sheet) is less than 0.0050% or more than 0.1500%. It is believed that the presence of a certain amount of Ti in the forsterite coating improves the coating properties. For example, if the presence of Ti increases the coating tension of the base coating, the magnetic domains in the base steel sheet may become finer, potentially reducing the 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 case with a high R18 / R17 ratio mentioned above, and therefore the building factor is thought to decrease. 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 base coating. This is thought to result in an increase in the building factor.

[0024] 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 having a base steel sheet having a chemical composition containing, by mass%, C: 0.0050% or less, Si: 1.5 to 8.0%, Mn: 0.02 to 1.00%, and La: 0.0001 to 0.0200%, with the balance being Fe and unavoidable impurities, and having an undercoat film and an insulating film mainly composed of forsterite on the surface of the base steel sheet, in that order, wherein the amount of Ti in the grain-oriented electrical steel sheet is 0.0050 to 0.1500 mass%, and wherein the iron loss W when excited at 1.7 T is 17 / 50 Hysteresis loss Wh 17 Ratio of Wh 17 / W 17 / 50 When R17 is used and the coil is excited at 1.8T, the iron loss W 18 / 50 Hysteresis loss Wh 18 Ratio of Wh 18 / W 18 / 50 When R18 is R18, the grain-oriented electrical steel sheet satisfies the following formula (1): R18 / R17≦1.50 (1)

[0025] [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.

[0026] [3] The grain-oriented electrical steel sheet according to the above [1] or [2], wherein the base steel sheet further contains Ga: 0.0001 to 0.0050 mass%.

[0027] [4] The grain-oriented electrical steel sheet according to any one of [1] to [3] above, wherein the base steel sheet further contains one or more elements selected from Sn: 0.500% by mass or less, Cr: 0.500% by mass or less, Cu: 0.50% by mass or less, Ni: 0.50% by mass or less, Bi: 0.500% by mass or less, P: 0.500% by mass or less, Sb: 0.500% by mass or less, Mo: 0.500% by mass or less, B: 25.0 ppm by mass or less, Nb: 0.020% by mass or less, V: 0.020% by mass or less, As: 0.0200% by mass or less, Zn: 0.020% by mass or less, Pb: 0.0100% by mass or less, W: 0.0500% by mass or less, Co: 0.050% by mass or less, and Ge: 0.0050% by mass or less.

[0028] According to the present invention, by controlling the La content in the base steel sheet and the Ti content in a grain-oriented electrical steel sheet having a base coating and an insulating coating in that order on the surface of the base steel sheet within a predetermined range and satisfying a predetermined loss relationship, it is possible to provide a grain-oriented electrical steel sheet that can reduce the building factor.

[0029] 1 is a graph showing the relationship between the La content in a base steel sheet and the building factor; 2 is a graph showing the influence of the La content in a base steel sheet and the R18 / R17 value on the building factor; and 3 is a graph showing the relationship between the Ti content in a grain-oriented electrical steel sheet and the building factor.

[0030] (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 La, a base coating composed mainly of forsterite formed on one or both surfaces of the base steel sheet, and an insulating coating formed on the base coating. 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.

[0031] [Composition of the Base Steel Sheet] Next, the reasons for limiting the constituent elements of the present invention will be described. First, the amount of each element in the composition of the base steel sheet will be described. Note that "%" and "ppm" in the composition of the steel sheet refer to "mass %" and "mass ppm" unless otherwise specified. C: 0.0050% or less Since C content in excess of 0.0050% increases iron loss due to magnetic aging, it is limited to 0.0050% or less. Preferably, the C content is 0.0030% or less. On the other hand, if the C content is less than 0.0010%, the magnetic flux density may decrease. Therefore, the preferable lower limit of the C content is 0.0010%.

[0032] Si: 1.5-8.0% Si is an element necessary for increasing the resistivity of steel and improving iron loss, but if it is less than 1.5%, it is ineffective. On the other hand, if the Si content exceeds 8.0%, the workability of the steel deteriorates and rolling becomes difficult. Therefore, the Si content is limited to 1.5-8.0%. The Si content is preferably 1.50% or more, more preferably 2.50% or more, and preferably 8.00% or less, and more preferably 4.50% or less. The preferred range of Si content is 2.50-4.50%.

[0033] Mn: 0.02 to 1.00% Mn is an element necessary for improving hot workability, but if it is less than 0.02%, this effect is lost. On the other hand, if the Mn content exceeds 1.00%, the magnetic flux density of the finished grain-oriented electrical steel sheet decreases. Therefore, the Mn content is set to 0.02 to 1.00%. The Mn content is preferably 0.04% or more and preferably 0.20% or less. The Mn content range is preferably 0.04 to 0.20%.

[0034] La: 0.0001 to 0.0200% For the reasons mentioned above, it is essential that La be contained in the range of 0.0001 to 0.0200%. The La content is preferably 0.0005% or more, preferably 0.0150% or less, and more preferably 0.0100% or less. The La content range is preferably 0.0001 to 0.0150%, and even more preferably 0.0005 to 0.0100%. A La content of 0.0001% or more exceeds the content of unavoidable impurities that may be mixed into ordinary base steel sheets.

[0035] The base steel sheet of the grain-oriented electrical steel sheet of the present invention has a composition containing 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.

[0036] Ga can be suitably added to the base steel sheet to further improve magnetic properties. Ga: 0.0001-0.0050% Ga is an element that contributes to reducing the building factor. The mechanism by which Ga in the base steel sheet improves the building factor of a model transformer is unclear, but the inventors believe it is due to the influence of Ga precipitates remaining in the finished grain-oriented electrical steel sheet. Specifically, because the yoke and legs of a transformer have a fixed width, the magnetic path varies in length between the inside and outside, similar to an athletics track. Therefore, during excitation, the magnetic flux tends to be biased toward the inside, where the magnetic path is shorter. Even when the entire steel sheet is excited to 1.7 T, the magnetic flux density on the inside of the steel sheet exceeds that. Therefore, it is presumed that the more advantageous the high magnetic field properties, the better the transformer characteristics, such as the building factor. Ga also acts as an inhibitor during secondary recrystallization, suppressing the normal grain growth of grains that are misoriented from the Goss orientation. However, Ga is not completely removed during purification and remains finely dispersed in the steel. This finely dispersed Ga acts as the origin of the rotating magnetic flux without impairing iron loss, which is presumably why the building factor is improved. The Ga content is preferably 0.0001% or more, more preferably 0.0005% or more, even more preferably 0.0010% or more, and preferably 0.0050% or less, more preferably 0.0040% or less, and even more preferably 0.0030% or less. The Ga content range is more preferably 0.0005 to 0.0040%, and even more preferably 0.0010 to 0.0030%.

[0037] Similarly, to further improve the magnetic properties, the base steel sheet may contain one or more of the following elements: 0.500% or less Sn, 0.500% or less Cr, 0.500% or less Cu, 0.50% or less Ni, 0.500% or less Bi, 0.500% or less P, 0.500% or less Sb, 0.500% or less Mo, 25.0 ppm or less B, 0.020% or less Nb, 0.020% or less V, 0.0200% or less As, 0.020% or less Zn, 0.0100% or less Pb, 0.0500% or less W, 0.0500% or less Co, and 0.0050% or less Ge. In other words, each of the above-mentioned optional elements may be added within the above-mentioned upper limit range in order to further improve the magnetic properties. If the amount of each optional element added exceeds the upper limit, the development of secondary recrystallized grains is inhibited, which may result in deterioration of magnetic properties.

[0038] The lower limits of the above-mentioned selectively added elements do not need to be particularly limited, but are preferably within the following ranges: Sn: 0.005% or more, Cr: 0.005% or more, Cu: 0.01% or more, Ni: 0.01% or more, Bi: 0.005% or more, P: 0.005% or more, Sb: 0.005% or more, Mo: 0.005% or more, B: 0.1 ppm or more, Nb: 0.001% or more, V: 0.001% or more, As: 0.0010% or more, Zn: 0.001% or more, Pb: 0.0001% or more, W: 0.0010% or more, Co: 0.002% or more, and Ge: 0.0001% or more.

[0039] 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.

[0040] The above-mentioned composition is the composition of a base steel sheet on which a forsterite base coating and an insulating coating are not formed on the surface. When checking the composition of a grain-oriented electrical steel sheet in which a forsterite coating and an insulating coating are formed on the surface of the base steel sheet, the forsterite coating and the insulating coating may be removed from the grain-oriented electrical steel sheet, and then the content of each element may be checked, as shown in Experiment 1, for example.

[0041] [Composition of Grain-Oriented Electrical Steel Sheet and Undercoat] In the present invention, the Ti content in the grain-oriented electrical steel sheet having a forsterite-based undercoat and insulating coating is further limited to 0.0050 to 0.1500%. The Ti content in the grain-oriented electrical steel sheet is preferably 0.0060% or more and preferably 0.0150% or less. The Ti content range in the grain-oriented electrical steel sheet is preferably 0.0060 to 0.0150%. This is because, as mentioned above, the presence of a certain amount of Ti in the forsterite coating is thought to improve coating properties and reduce eddy current loss, but if the content is less than 0.0050%, this effect is limited.

[0042] The Ti content in grain-oriented electrical steel sheet refers to the ratio (mass %) of the total amount of Ti present in the base steel sheet, base coating, and insulating coating to the total mass (solids content) of the base steel sheet, base coating, and insulating coating. It is usually the ratio (mass %) of the total amount of Ti present in the base steel sheet and base coating to the total mass (solids content). The Ti content in grain-oriented electrical steel sheet can be measured according to JIS G1223, regardless of whether the base coating and insulating coating are 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 0.0150% or less, and more preferably 0.0120% or less.

[0044] Here, when limiting the Ti content in a steel sheet having a base coating and an insulating coating (grain-oriented electrical steel sheet) to 0.0050 to 0.1500%, 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 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 Hysteresis loss Wh 17 The ratio R17 (=Wh 17 / W 17 / 50 ) and iron loss W when excited at 1.8T 18 / 50 Hysteresis loss Wh 18 The ratio R18 (=Wh 18 / W 18 / 50 ) must satisfy the relationship of formula (1) expressed as R18 / R17≦1.50. 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. The value of R18 / R17 is not particularly limited, and can be changed, for example, 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

[0046] [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.

[0047] The slab can be heated and hot-rolled in the usual way. Alternatively, the slab can be cast and hot-rolled immediately without heating. When heating, for component systems with a low inhibitor content, high-temperature heating to dissolve the inhibitor is not required, 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 can be according to the usual methods. In this way, a hot-rolled sheet can be obtained.

[0048] Next, the obtained hot-rolled sheet can be subjected to hot-rolled sheet annealing as needed. The hot-rolled sheet annealing temperature is preferably 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, and preferably 1150°C or lower, and more preferably 1100°C or lower. The hot-rolled sheet 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.

[0049] The hot-rolled sheet after hot rolling or the hot-rolled and annealed sheet after hot-rolled sheet annealing can be cold-rolled to the final thickness by one cold rolling or two or more cold rollings with intermediate annealing in between. The annealing temperature for the intermediate annealing is preferably 900°C or higher, preferably 1200°C or lower, and more preferably in the range of 900 to 1200°C. If the intermediate annealing temperature is lower than 900°C, the recrystallized grains after the intermediate annealing tend to become finer. Furthermore, the number of Goss nuclei in the primary recrystallized structure may decrease, potentially resulting in a deterioration in the magnetic properties of the grain-oriented electrical steel sheet product. On the other hand, if the intermediate annealing temperature exceeds 1200°C, the grains may become too coarse, as with hot-rolled sheet annealing, making it difficult to obtain a uniformly sized primary recrystallized structure. In this way, a cold-rolled sheet can be obtained.

[0050] 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.

[0051] 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 purification annealing to purify the components. This allows the secondary recrystallization structure to develop and a forsterite coating to form on the surface of the steel sheet. In this way, a base-coated steel sheet can be obtained, in which a base coating is formed on the surface of the base steel sheet. Here, "mainly composed of MgO" means that the annealing separator contains 75 mass % or more of MgO in terms of solid content.

[0052] 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 0.1500%, TiO2 and TiN are preferred as Ti compounds, with TiO2 being more preferred. Furthermore, the content of this compound in the annealing separator is preferably 2 parts by mass or more and 15 parts by mass or less relative to MgO. However, other methods may be used to achieve the above Ti requirement. Examples of other methods include adding Ti as a raw material component and changing the purification annealing conditions.

[0053] Next, 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 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.

[0054] Subsequent flattening annealing to correct the shape is effective for reducing iron loss. Furthermore, when grain-oriented electrical steel sheets are used in a stacked configuration, applying an insulating coating to the steel sheet surface (more specifically, the surface of the base coating) before or after flattening annealing is effective for improving iron loss. This insulating coating is preferably a coating that can apply tension to the grain-oriented electrical steel sheet to reduce iron loss. The material of the insulating coating is not particularly limited, and it can be a coating made of any insulating material. Generally, inorganic coatings are used as insulating coatings. The method for forming the insulating coating is not particularly limited, but examples include a method of applying a coating treatment liquid, a tension coating application method using a binder, a physical vapor deposition method, and a chemical vapor deposition method. Forming a coating by vapor-depositing an inorganic substance onto the surface of the steel sheet is desirable because it provides excellent coating adhesion and is likely to enhance the iron loss reduction effect. When using a method of applying a coating treatment liquid, the coating can be applied before flattening annealing and then baked by performing flattening annealing. The composition of the coating treatment liquid is not particularly limited, but for example, a treatment liquid containing phosphate and silica can be used.

[0055] Steel slab A contains C: 0.070%, Si: 3.5%, Mn: 0.07%, Al: 0.0085%, N: 0.0050%, La: 0.0080%, Mo: 0.026%, Ti: 0.0022%, and the balance is composed of Fe and unavoidable impurities. Steel slab B contains C: 0.072%, Si: 3.51%, Mn: 0.07%, Al: 0.0080%, N: 0.0047%, La: 0.0100%, Mo: 0.025%, Ti: 0.0020%, and the balance is composed of Fe and unavoidable impurities. Steel slab C, consisting of 3.49% i, 0.07% Mn, 0.0090% Al, 0.0051% N, 0.0250% La, 0.025% Mo, and 0.0017% Ti, with the balance being Fe and unavoidable impurities, and steel slab D, consisting of 0.070% C, 3.48% Si, 0.07% Mn, 0.0087% Al, 0.0049% N, 0.0170% La, 0.025% Mo, and 0.0020% Ti, with the balance being Fe and unavoidable impurities, were each produced by continuous casting. Steel slabs A, B, C, and D were subjected to slab heating by soaking at 1200°C for 40 minutes. They were then hot-rolled to a thickness of 2.2 mm. 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.

[0056] 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. ２ The powder was placed in hot water at 50°C and stirred for 24 hours. The recovered perhydrated TiO ２ Five parts by mass of MgO powder was added to the sample. After that, the sample 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 ２The atmosphere was changed in various mixture ratios, and H ２ Furthermore, the atmosphere was Ar during cooling.

[0057] The Ti content of the thus obtained samples, i.e., the base steel sheet on the surface of which a primer coating mainly composed of forsterite was formed, was measured according to the method specified in JIS G1223. The results are also shown in Table 1. 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 sheet.

[0058] An insulating coating containing magnesium phosphate and silica as its main components was applied to the base coating of the steel sheet. The thus obtained sample, i.e., a grain-oriented electrical steel sheet having a base coating and an insulating coating formed in that order on the surface of the base steel sheet, was subjected to iron loss measurement. 17 / 50 and W 18 / 50 (iron loss when excited to 1.7T and 1.8T at 50Hz) and hysteresis loss Wh 17 and Wh 18 (Hysteresis loss when excited to 1.7T and 1.8T, 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 18 / 50 and hysteresis loss Wh 18 The ratio R18 was calculated. The results are shown in Table 1.

[0059] Furthermore, to measure the Ti content of the base steel sheet, a portion of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite film and insulating film, and then subjected to measurement in accordance with the method specified in JIS G1223. The measurement results are also shown in Table 1. The C content of the base steel sheet was measured according to the method specified in JIS G1211-3:2018 and is also shown in Table 1. The Si content, Mn content, and La content of the base steel sheet were also measured according to the methods specified in JIS G1212:1997, JIS G1213:2001, and the above-mentioned references, and it was confirmed that they were the same as the contents in each steel slab.

[0060] Next, a three-phase, three-legged model transformer was fabricated from the sample with the insulating coating, with an external dimension of 500mm square and a plate width of 100mm for each leg and yoke. 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 also shown in Table 1. As is clear from the table, good iron loss characteristics (building factor) are obtained under conditions within the range of the present invention.

[0061]

[0062] 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 25% H atmosphere. ２ -75%N ２ The intermediate cold-rolled sheet was then cold-rolled to a thickness of 0.23 mm. This cold-rolled sheet was then subjected to a 40% H atmosphere at 825°C for 150 seconds. ２ -60%N ２ The steel sheets were then subjected to decarburization annealing in a humid atmosphere with a dew point of 45°C.

[0063] Then, an annealing separator mainly composed of MgO (88% MgO) 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. ２Five parts by mass of MgO powder was added. Further, purification annealing was performed by holding at 1200°C for 10 hours to form a base coating mainly composed of forsterite. At this time, the rate of temperature increase up to 1200°C was 15°C / h. Furthermore, during the temperature increase 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.

[0064]

[0065] The Ti content of the thus obtained samples, i.e., the base steel sheet on the surface of which a primer coating mainly composed of forsterite was formed, was measured according to the method specified in JIS G1223. The results are shown in Table 3. 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 sheet.

[0066] An insulating coating containing magnesium phosphate and silica as its main components was applied to the base coating of the steel sheet. The thus obtained sample, i.e., a grain-oriented electrical steel sheet having a base coating and an insulating coating formed in that order on the surface of the base steel sheet, was subjected to iron loss measurement. 17 / 50 and W 18 / 50 (iron loss when excited to 1.7T and 1.8T at 50Hz) and hysteresis loss Wh 17 and Wh 18 (Hysteresis loss when excited to 1.7T and 1.8T, 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 18 / 50 and hysteresis loss Wh 18 The results are shown in Table 3.

[0067] Furthermore, to measure the Ti content of the base steel sheet, a portion of the obtained sample was immersed in a 10% hydrochloric acid solution at 80°C for 180 seconds to remove the forsterite coating and insulating coating, and the sample was subjected to measurement in accordance with the method specified in JIS G1223. The measurement results are also shown in Table 3. The C content of the base steel sheet was measured using the same method as in Example 1 and is also shown in Table 3. Note that the Ti content in the base steel sheet does not change due to the formation of the insulating coating. The amounts of other elements in the base steel sheet were also measured using the same method as in Example 1 and ICP atomic emission spectroscopy, and it was confirmed that the amounts of Si, Mn, La, Ga, and other elements in the base steel sheet were the same as those in each steel slab.

[0068] Next, a three-phase, three-legged model transformer was fabricated from the sample with the insulating coating, with an external dimension of 500mm square and a plate width of 100mm for each leg and yoke. 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 also shown in Table 3. As is clear from the table, good iron loss characteristics are obtained under conditions within the range of the present invention.

[0069]

Claims

1. A grain-oriented electrical steel sheet having, on the surface of a base steel sheet with a component composition containing, by mass%, C: 0.0050% or less, Si: 1.5 to 8.0%, Mn: 0.02 to 1.00% and La: 0.0001 to 0.0200%, the balance being Fe and unavoidable impurities, a base coating mainly composed of forsterite and an insulating coating in this order, wherein the Ti content in the grain-oriented electrical steel sheet is 0.0050 to 0.1500% by mass, and the hysteresis loss Wh 17 / 50 with respect to the iron loss W 17 is defined as Wh 17 / W 17 / 50 and is designated as R17, and the ratio Wh 18 / 50 of the hysteresis loss Wh 18 with respect to the iron loss W 18 when excited at 1.8 T is defined as Wh 18 / 50 / W and is designated as R18, and the grain-oriented electrical steel sheet satisfies the following formula (1): R18 / R17 ≤ 1.50... (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, wherein the base steel sheet further contains Ga: 0.0001 to 0.0050% by mass.

4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the base steel sheet further contains one or more selected from the group consisting of Sn: 0.500% by mass or less, Cr: 0.500% by mass or less, Cu: 0.50% by mass or less, Ni: 0.50% by mass or less, Bi: 0.500% by mass or less, P: 0.500% by mass or less, Sb: 0.500% by mass or less, Mo: 0.500% by mass or less, B: 25.0 mass ppm or less, Nb: 0.020% by mass or less, V: 0.020% by mass or less, As: 0.0200% by mass or less, Zn: 0.020% by mass or less, Pb: 0.0100% by mass or less, W: 0.0500% by mass or less, Co: 0.050% by mass or less, and Ge: 0.0050% by mass or less.

Images