Directional electromagnetic 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

[Technical Field]

[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. [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, known as the Goss orientation, is formed during the purification annealing. <001> It is formed through a phenomenon called secondary recrystallization, which causes preferential giant growth of grains in the orientation.

[0003] A common technique for forming this alloy 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 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, technologies have been developed that use physical methods to introduce non-uniformity into the surface of a steel sheet, thereby refining the width of magnetic domains and reducing iron loss, i.e., magnetic domain refining technologies. For example, Patent Document 4 proposes a technology in which a final product sheet is irradiated with a laser to introduce high dislocation density regions into the surface layer of the steel sheet, thereby narrowing the magnetic domain width and thereby reducing iron loss in the steel sheet. Furthermore, Patent Document 5 proposes a technology in which magnetic domain width is controlled by irradiation with an electron beam. While aligning the orientation after secondary recrystallization to a high degree in the Goss orientation and reducing impurities reduces hysteresis loss, applying magnetic domain refinement technology primarily reduces eddy current loss. [Prior art documents] [Patent documents]

[0008] [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 Summary of the Invention [Problem to be solved by the invention]

[0009] As mentioned above, grain-oriented electrical steel sheets are primarily used as transformer cores. Generally, there is a discrepancy between the iron loss value of a transformer core and the iron loss value of the grain-oriented electrical steel sheet that is used as the material, with the transformer core having a higher iron loss. The ratio of these two iron losses is called the building factor. In other words, even if the material has good iron loss, if the building factor is high, the iron loss of the transformer core will be large, resulting in the problem of not being able to demonstrate sufficient performance. 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.

[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. [Means for solving the problem]

[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. They 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 ​​written before and after "to" as the lower and upper limits, respectively. <Experiment 1> To primarily vary the La content in the base steel sheet, steel slabs 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, were produced by continuous casting. The steel slabs were 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 humid atmosphere with a dew point of 50°C. An MgO-based annealing separator was then applied to both surfaces of the resulting decarburized annealed sheet, which was then subjected to purification annealing at 1200°C for 10 hours to form a forsterite-based undercoat. The heating rate up to 1200°C was 20°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. Furthermore, an H2 atmosphere was used during holding, and an Ar atmosphere was used during cooling. A coating liquid was then applied to the resulting steel sheet to form an insulating coating 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 according to the method described in JIS C2550-1. Furthermore, in order to measure the amount of La 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 in accordance with the method described in Tanabe Isao, Mizumaki Katsumi, Masuyama Yoshio, and Takase Shozo: Castings, Vol. 32, No. 8, p. 580 (hereinafter referred to as the reference). The C amount 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 amounts 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 / 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 measurement results thus obtained, the building factor F17 of the model transformer and 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 amount of La (unit: mass%) in the base steel sheet was investigated, and the results are shown in FIG.

[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 can be 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 / 50 When R17 and R18 are divided into Group A, where R18 / R17 is 1.50 or less, and Group B, where R17 is R18 (unitless), we found that a general trend can be seen in the building factor F17. Figure 2 shows the results of collating the data from Figure 1 with respect to R18 / R17. In Figure 2, each circle represents a building factor F17, with larger circle (bubble) diameters indicating larger building factors. The results shown in Figure 2 show that there is a relationship of R18 / R17≦1.50, i.e., the steel belongs to Group A, and the La content in the base steel sheet is in the range of 0.0001 to 0.0200%, and a favorable building factor of 1.25 or less is exhibited. In FIG. 2, whether each bubble belongs to group A or B can be determined by the region in which the center of the circle of each bubble exists.

[0017] <Experiment 2> A steel slab containing, by mass%, 0.0010% La, 0.037% C, 3.0% Si, 0.18% Mn, 0.009% Al, 0.0036% N, 0.007% Se, 0.062% Sn, and 0.0080% Co, with the remainder consisting of Fe and unavoidable impurities, was produced by continuous casting. The 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. The 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. Furthermore, an annealing separator containing TiO2 mixed in various amounts in the range of 0 to 15 parts by mass relative to MgO was applied to the surface of the resulting decarburized annealed sheet, followed by purification annealing at 1220°C for 5 hours to form a forsterite coating. 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 an H2 atmosphere was used from above 1100°C to 1200°C. In this way, by changing the H2 / N2 mixture ratio in the atmosphere during the heating process, the Ti content in the resulting grain-oriented electrical steel sheet as a whole, and particularly in the base-coated steel sheet, was controlled. The atmosphere was H2 during holding and Ar during cooling. A coating liquid was then applied to the resulting steel sheet to form an insulating coating 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 The hysteresis losses (when excited to 1.7 T and 1.8 T, respectively) were measured according to the method described in JIS C2550-1.

[0019] The Ti content of the grain-oriented electrical steel sheets having the forsterite-based base coating and insulating coating was measured by the method specified in JIS G1223. Furthermore, to measure the La content in 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 coating and insulating coating, and the La content was measured according to the method described in the reference document. As a result, the La content was 0.0010%, which was the same as the content in the steel slab. The C amount 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 amounts 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 obtained, as in Experiment 1. 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 subjects were divided into Group A, where the ratio R18 of R17 was 1.50 or less, and Group B, where the ratio R18 was 1.50 or less. As in Experiment 1, a three-phase, three-legged model transformer was fabricated with an external dimension of 500mm square and a plate width of 100mm for each leg and yoke. The iron loss W 17 / 50 The building factor F17 (unitless) was calculated from the values. The relationship between the Ti content (unit: mass%) in grain-oriented electrical steel sheets with the base coating and insulating coating still attached 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 discovered that when the Ti content in grain-oriented electrical steel sheets with the base coating and insulating coating still attached is 0.0050% or more and 0.1500% or less, the steel belongs to Group A, and the building factor is low and favorable.

[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 a grain-oriented electrical steel sheet in which a forsterite-based primer coating and an insulating coating are formed in that order on the surface of the base steel sheet is not clear. However, the inventors believe as follows. Specifically, transformers are manufactured by shearing grain-oriented electrical steel sheets and assembling the sheared steel sheets. Strain introduced during this shearing process can cause problems, such as increased iron loss. However, adding a certain amount of La to the base steel sheet is thought to have the effect of reducing this strain. La forms carbides and nitrides in the steel sheet, mitigating 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. Since La carbides and nitrides can also act as inhibitors, excessive addition of La has a negative effect on secondary recrystallization behavior. Taking this into consideration, the La content in the base steel sheet is set to 0.0001% or more and 0.0200% or less.

[0022] However, in both experiments 1 and 2, there were two instances where the building factor was poor even when La was added. The first point is the iron loss W when excited at 1.7T. 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 This is the case when the ratio R18 of R17 and R18 does not satisfy the relationship R18 / R17≦1.50. Hysteresis loss has a high correlation with the magnetic flux density B8 at a magnetic field strength of 800 A / m, and it is thought that there will be no significant fluctuations in hysteresis loss at the same B8. Therefore, when 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, which is thought to increase eddy current loss, which is highly frequency-dependent. In this way, it is thought that a high eddy current loss ratio will increase the building factor.

[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 sheet. In this case, the eddy current loss ratio decreases, which is the opposite of the 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 and configuration of the present invention are as follows. [1] A grain-oriented electrical steel sheet having, in order on the surface of 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 remainder being Fe and unavoidable impurities, a base coating containing forsterite as a main component and an insulating coating, The amount of Ti in the grain-oriented electrical steel sheet is 0.0050 to 0.1500 mass%, Iron loss W when excited at 1.7T 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 Grain-oriented electrical steel sheet that satisfies the following formula (1) when R18 is used. R18 / R17≦1.50 (1)

[0025] [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.

[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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

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

[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] [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 composition of the base steel sheet will be described. Note that "%" and "ppm" in the composition of the element represent "% by mass" and "ppm by mass" unless otherwise specified. C: 0.0050% or less If the C content exceeds 0.0050%, iron loss increases due to magnetic aging, so 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 to 8.0% Silicon is an element necessary for increasing the resistivity of steel and improving iron loss, but if it is less than 1.5%, this effect 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 to 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 the Si content is 2.50 to 4.50%.

[0033] 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 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%. The La content of 0.0001% or more exceeds the content of unavoidable impurities that may be mixed into a normal base steel sheet.

[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 for the purpose of further improving the magnetic properties. Ga: 0.0001 to 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 grain-oriented electrical steel sheet as a finished product. 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 characteristics, the better the transformer characteristics, such as the building factor. Furthermore, Ga acts as an inhibitor during secondary recrystallization, suppressing the normal grain growth of grains that deviate from the Goss orientation. However, Ga is not completely removed during purification and remains finely dispersed in the steel. This finely dispersed Ga serves as the origin of rotational magnetic flux without impairing iron loss, 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 is preferably 0.0050% or less, more preferably 0.0040% or less, and even more preferably 0.0030% or less. The Ga content is more preferably in the range of 0.0005 to 0.0040%, and even more preferably 0.0010 to 0.0030%.

[0037] Similarly, in order to further improve the magnetic properties, one or more of Sn: 0.500% or less, Cr: 0.500% or less, Cu: 0.50% or less, Ni: 0.50% or less, Bi: 0.500% or less, P: 0.500% or less, Sb: 0.500% or less, Mo: 0.500% or less, B: 25.0 ppm or less, Nb: 0.020% or less, V: 0.020% or less, As: 0.0200% or less, Zn: 0.020% or less, Pb: 0.0100% or less, W: 0.0500% or less, Co: 0.050% or less, and Ge: 0.0050% or less can be added to the base steel sheet in combination. That is, each of the optional elements described above can be added within the range of the upper limit described above in order to further improve the magnetic properties. If the amount of each optional element added exceeds the upper limit described above, the growth of secondary recrystallized grains may be inhibited, and the magnetic properties may be deteriorated.

[0038] The lower limit of the above-mentioned selectively added elements does not need to be particularly limited, but is preferably within the following range. 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 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 a forsterite base coating and an insulating coating are not formed. 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 can be removed from the grain-oriented electrical steel sheet, and then the content of each element can be checked, as shown in Experiment 1, for example.

[0041] [Composition of grain-oriented electrical steel sheet and base coating] In the present invention, the Ti content in a grain-oriented electrical steel sheet having a base coating and an insulating coating mainly composed of forsterite 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 the 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. Typically, it refers to 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 (grain-oriented electrical steel sheet) having a base coating and an insulating coating 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 sheets] 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), R18 / R17≦1.50. 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. The value of R18 / R17 is not particularly limited, and can be controlled, for example, by changing the conditions of each manufacturing process to change the magnetic flux density B8.

[0046] [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 above-mentioned predetermined composition by a conventional ingot-making method or continuous casting method. Alternatively, thin cast pieces with a thickness of 100 mm or less may be manufactured from the molten steel by a direct casting method. The molten steel may be manufactured by a blast furnace method or an electric furnace method. Since it is difficult to add the above-mentioned optional elements during the process, it is desirable to add them at 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 necessary. 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 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.

[0050] 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.

[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 introducing a 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 0.1500%, 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 requirement for Ti may be met by other methods, such as adding Ti as a 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] Thereafter, flattening annealing is performed to correct the shape, which is effective for reducing iron loss. Furthermore, when grain-oriented electrical steel sheets are used in a stack, it is effective to apply an insulating coating to the steel sheet surface (more specifically, the surface of the base coating) before or after planarization annealing to improve 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, an inorganic coating is used as the insulating coating. 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 method using a binder, a physical vapor deposition method, and a chemical vapor deposition method. Using such a method of forming a coating by vapor-depositing an inorganic substance onto the steel sheet surface is desirable because it provides excellent coating adhesion and tends to enhance the iron loss reduction effect. When using the method of applying a coating treatment liquid, the coating can be applied before planarization annealing and then baked by performing planarization annealing. The composition of the coating treatment liquid is not particularly limited, but a treatment liquid containing phosphate and silica can be used, for example. [Example]

[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%, with the balance consisting 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%, with the balance consisting 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, with soaking at 1200°C for 40 minutes. They were then hot-rolled to a thickness of 2.2 mm. The hot-rolled sheet was then annealed at 1000°C for 60 seconds in a N2 atmosphere. The resulting hot-rolled and annealed sheet was then cold-rolled to a thickness of 0.23 mm. The cold-rolled sheet was then subjected to primary recrystallization annealing, which also served as decarburization annealing, at 850°C for 90 seconds in a humid atmosphere of 60% H2-40% N2 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 (primarily recrystallized sheet) after decarburization annealing. The annealing separator was prepared by adding 5 parts by mass of perhydrated TiO powder, which had been prepared by adding TiO powder to hot water at 50°C and stirring for 24 hours. The specimens were then held at 1100°C for 25 hours, followed by purification annealing at 1200°C for 10 hours. During this temperature rise process, the atmosphere was N2 from room temperature to 700°C, atmospheres with various N2 and H2 mixture ratios were used from above 700°C to 1100°C, and H2 from the start of holding above 1100°C to the end of holding at 1200°C. Furthermore, an Ar atmosphere was used during cooling.

[0057] The Ti content of the thus obtained sample, 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 iron loss W of the grain-oriented electrical steel sheet thus obtained, in which the base coating and the insulating coating were formed in that order on the surface of the base steel sheet, was measured. 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 of R18 to 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 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. As is clear from the table, good iron loss characteristics (building factor) are obtained under conditions within the range of the present invention.

[0061] [Table 1] [Example]

[0062] 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.

[0063] The surfaces (both sides) of the obtained decarburized annealed sheet were then coated with an annealing separator mainly composed of MgO (MgO: 88%). For the annealing separator, TiO powder was added to hot water at 50°C, stirred for 24 hours, and then filtered to obtain perhydrated TiO. Five parts by mass of per 1000 parts by mass of the powdered MgO was added. Further purification annealing was performed by holding the specimen at 1200°C for 10 hours to form a base coating primarily composed of forsterite. During this process, 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.

[0064] [Table 2] TIFF0007806973000003.tif154170

[0065] The Ti content of the thus obtained sample, 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 iron loss W of the grain-oriented electrical steel sheet thus obtained, in which the base coating and the insulating coating were formed in that order on the surface of the base steel sheet, was measured. 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 Wh17 R17, which is the ratio of the iron loss W 18 / 50 and hysteresis loss Wh 18 The ratio of R18 to R18 was calculated. 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 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 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 film. 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 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 3. As is clear from the table, good core loss characteristics are obtained under conditions within the range of the present invention.

[0069] [Table 3] TIFF0007806973000005.tif153170

Claims

1. A grain-oriented electrical steel sheet having, in order on a surface of 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%, La: 0.0010 to 0.0200%, and Ti: 0.0035% or less, with the balance being Fe and unavoidable impurities, the Ti content in the grain-oriented electrical steel sheet is 0.0050 to 0.1500 mass%, Iron loss W when excited at 1.7T 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 used, a grain-oriented electrical steel sheet that satisfies the following formula (1): R18 / R17≦1.50...(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, wherein the base steel sheet further contains Ga: 0.0001 to 0.0050 mass%.

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

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

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