Grain-oriented electromagnetic steel sheet and method for manufacturing same

Abstract

Provided is a grain-oriented electromagnetic steel sheet having stably exceptional magnetic properties over the entire length of a coil in production of a grain-oriented electromagnetic steel sheet using an inhibitor-less method. This grain-oriented electromagnetic steel sheet has a component composition comprising, in mass%, 2.0-4.5% of Si, 0.01-0.5% of Mn, less than 50 ppm of each of Se, Te and O, less than 30 ppm of S, at least 2 ppm and less than 30 ppm of acid-soluble Al, and at least 5 ppm to less than 80 ppm of Ga, the balance being iron and unavoidable impurities, wherein B8 in a rolling direction is 1.900 T or greater, and the hysteresis loss Whys at B = 1.7 T satisfies relationship (1).　Relationship 1: Whys ≤ −2.5 × B8 + 5.15

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a grain-oriented electrical steel sheet with high manufacturing stability and a manufacturing method thereof.

[0002] For grain-oriented electrical steel sheets, a common technique is to use precipitates called inhibitors to induce secondary recrystallization of grains having the Goss orientation during final annealing. For example, Patent Document 1 discloses a method using AlN, and Patent Document 2 discloses a method using MnS and MnSe, both of which have been put into industrial use. Furthermore, Patent Document 3 discloses a method using Pb, Sb, Nb, and Te, and Patent Document 4 discloses a method using Zr, Ti, B, Nb, Ta, V, Cr, and Mo, in order to enhance the function of these inhibitors.

[0003] As methods for manufacturing grain-oriented electrical steel sheets at lower costs are being developed, studies have been conducted on techniques for inducing secondary recrystallization without adding inhibitor components to steel slabs. For example, Patent Document 5 proposes the development of a technique (inhibitor-less method) that can induce secondary recrystallization without adding inhibitor components. The inhibitor-less method is a technique that uses highly purified steel and induces secondary recrystallization by texture (control of texture).

[0004] When grain-oriented electrical steel sheets are manufactured using an inhibitor-less process that does not substantially contain strong inhibitors, if trace amounts of impurity elements are unevenly precipitated in the steel, the structure becomes non-uniform and a stable secondary recrystallization structure cannot be obtained, resulting in problems such as fluctuations in the properties of the coil of the final grain-oriented electrical steel sheet.

[0005] To address this problem, Patent Document 6 proposes a technique for obtaining stable magnetic properties by reducing oxides containing Ca and / or Mg with diameters of 1 to 3 μm. Patent Document 7 also proposes a technique for obtaining stable magnetic properties over the entire length of the coil by appropriately controlling the form of trace amounts of Ti.

[0006] Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 Japanese Patent Publication No. 38-8214 Japanese Patent Publication No. 52-24116 Japanese Patent Application Laid-Open No. 2000-129356 Japanese Patent Application Laid-Open No. 2006-152387 International Publication No. 2021 / 045212

[0007] In the inhibitor-less process, secondary recrystallization is induced by controlling the texture, so the uniformity of the texture during secondary recrystallization annealing is extremely important. In particular, the precipitation of trace elements can often be a major problem depending on their state.

[0008] For example, an appropriate amount of Al is added as a deoxidizer to reduce oxygen in steel during steelmaking, or to mitigate the effects of the annealing atmosphere during secondary recrystallization annealing. However, Al is known to be a raw material for AlN, which inhibits grain growth. Since N is also sufficiently reduced, the amount of precipitation is extremely small, and it is thought to be difficult to fully function as a so-called inhibitor during secondary recrystallization annealing. On the other hand, N may affect grain growth during primary recrystallization annealing, which is performed at a relatively low temperature for a short time. Because the amounts of these elements added are also extremely small, they are likely to precipitate non-uniformly, which is expected to contribute to the destabilization of magnetic properties in coils.

[0009] The present invention advantageously solves the above problems, and aims to provide a grain-oriented electrical steel sheet that has stable and excellent magnetic properties over the entire coil length when produced using an inhibitor-less process.

[0010] In order to solve the above problem, the inventors evaluated the characteristics of materials that had large fluctuations in magnetic properties within coils, which actually occur with a certain frequency. As a result, it became clear that one of the causes of fluctuations in magnetic properties within coils was that the Al contained in the steel precipitated unevenly in the steel, promoting a non-uniform structure and destabilizing the behavior of secondary recrystallization.

[0011] Therefore, the inventors conducted extensive research into a method for preventing uneven precipitation of Al when added in extremely small amounts. MnS is one example of a precipitate that is actively used in grain-oriented electrical steel sheets. It has been found that adding Se, an element of the same group as S in the periodic table, results in good magnetic properties. This utilizes the fact that MnS and MnSe are precipitates that can have the same morphology (crystal structure), and that each element affects the other's precipitation.

[0012] Based on the above findings, the inventors thought that it might be possible to control the precipitation of trace amounts of Al by adding Al and Ga, an element of the same group as Al. Since both AlN and GaN have two types of crystal structures, the wurtzite structure and the zinc blende structure, and can take on a state such as AlGaN, the relationship between AlN and GaN can be seen as being very similar to the relationship between MnS and MnSe.

[0013] Therefore, the inventors decided to investigate controlling the Ga content depending on the Al content. Since Al is used as a deoxidizer during steelmaking, there exists acid-soluble Al and insoluble Al in the form of oxide. Here, the inventors investigated acid-soluble Al, which is thought to function as a precipitate. As a result, they found that mixing Ga at an atomic weight ratio of 3% to 100% of the Al content tends to reduce the variation in magnetic properties within the coil.

[0014] Although it is unclear whether the above results are due to the assumed mechanism, it is thought that when one of the elements, such as MnS or MnSe, acts as a nucleus for the other, the precipitates are more uniformly distributed within the coil. Furthermore, by maintaining a composite precipitate state after precipitation, Ostwald ripening is suppressed, and localization due to coarsening of the precipitates is improved.

[0015] In this way, the inventors discovered that by adding an appropriate amount of Ga according to the amount of Al added to the steel sheet, it is possible to suppress uneven precipitation of Al and obtain a grain-oriented electrical steel sheet with stable and excellent magnetic properties throughout the entire length of the coil, and thus completed the present invention.

[0016] That is, the gist of the present invention is as follows: [1] A grain-oriented electrical steel sheet having a chemical composition containing, in mass%, Si: 2.0% to 4.5%, Mn: 0.01% to 0.5%, and, in ppm by mass, Se, Te, and O each less than 50 ppm, S less than 30 ppm, acid-soluble Al 2 ppm to less than 30 ppm, Ga 5 ppm to less than 80 ppm, and the balance being iron and unavoidable impurities, ８ is 1.900T or more, and the hysteresis loss W at B = 1.7T ｈｙｓ Grain-oriented electrical steel sheet that satisfies the following formula (1). ｈｙｓ ≦-2.5×B ８ +5.15 ​​(1)

[0017] [2] The grain-oriented electrical steel sheet according to [1], wherein the chemical composition further contains, in mass%, one or more elements selected from Ni: 1.50% or less, Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less, P: 0.50% or less, Cr: 1.50% or less, Mo: 0.50% or less, B: 0.0050% or less, Nb: 0.0100% or less, Co: 0.0100% or less, Ti: 0.0050% or less, Zn: 0.050% or less, Bi: 0.0200% or less, W: 0.0030% or less, Pb: 0.0010% or less, Ge: 0.0010% or less, As: 0.0010% or less, and Ag: 0.0010% or less.

[0018] [3] A method for producing the grain-oriented electrical steel sheet according to the above [1] or [2], wherein, in mass%, C: 0.08% or less, Si: 2.0% to 4.5%, Mn: 0.01% to 0.5%, and in ppm by mass, Se, Te, and O: less than 50 ppm each, acid-soluble Al: 20 ppm to less than 100 ppm, S: less than 50 ppm, N: 80 ppm or less, and Ga: the concentration of acid-soluble Al satisfies the following formula (2), i.e., 0.030×Al×2.58≦Ga≦1.000×Al×2.58 (2). In a method for producing a grain-oriented electrical steel sheet, a steel slab is cast from molten steel having a composition satisfying the formula (I) above, with the remainder being Fe and unavoidable impurities, and the resulting slab is hot-rolled to form a hot-rolled sheet, which is then annealed and rolled to form a cold-rolled sheet of a final thickness, which is then subjected to primary recrystallization annealing, further subjected to secondary recrystallization annealing, and then an insulating coating is formed, ２ atmosphere, Ar atmosphere, or N ２ and Ar, and the temperature range of 800°C to 900°C was maintained for 35 hours or more. ２ % or more of ammonium nitrate, and then soaking the steel sheet at a maximum temperature exceeding 1150°C for 3 hours or more in an atmosphere containing 5 volume % or more of ammonium nitrate, and then cooling the steel sheet for 10 hours or more in a temperature range of 1100°C or less and 900°C or more.

[0019] [4] The method for producing a grain-oriented electrical steel sheet according to [3], wherein the chemical composition further contains, in mass%, one or more elements selected from Ni: 1.50% or less, Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less, P: 0.50% or less, Cr: 1.50% or less, Mo: 0.50% or less, B: 0.0050% or less, Nb: 0.0100% or less, Co: 0.0100% or less, Ti: 0.0050% or less, Zn: 0.050% or less, Bi: 0.0200% or less, W: 0.0030% or less, Pb: 0.0010% or less, Ge: 0.0010% or less, As: 0.0010% or less, and Ag: 0.0010% or less.

[0020] According to the present invention, in the production of grain-oriented electrical steel sheets using an inhibitorless process, it is possible to provide grain-oriented electrical steel sheets that have stable and excellent magnetic properties throughout the entire length of the coil.

[0021] The atomic ratio of Ga to Al and B ８ 10 is a graph showing the relationship between the average value of

[0022] Hereinafter, examples of embodiments of the present invention will be specifically described. Note that the following description is merely illustrative of embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0023] In the present invention, a steel slab for grain-oriented electrical steel sheet (hereinafter, sometimes simply referred to as a steel slab) obtained by casting molten steel having the following chemical composition is used as a starting material. In the following description of the chemical composition, "%" represents "mass %" and "ppm" represents "mass ppm" unless otherwise specified.

[0024] C: 0.08% or less C suppresses grain coarsening during hot rolling and improves the structure before cold rolling. It also improves the texture after primary recrystallization during cold rolling by interacting with dislocations. However, if C remains in the final product sheet, it can cause magnetic aging and lead to magnetic deterioration. If the C content exceeds 0.08%, the load in the decarburization process becomes too high and cannot be sufficiently reduced. Therefore, the C content is limited to 0.08% or less. Furthermore, to obtain the above-mentioned structure improvement effect, the C content is preferably 0.01% or more.

[0025] Si: 2.0% or more and 4.5% or less Si is a useful element that increases the electrical resistance of steel and improves iron loss. If the Si content is less than 2.0%, a sufficient iron loss reduction effect cannot be expected. On the other hand, if the Si content exceeds 4.5%, cold rolling becomes significantly difficult. Therefore, the Si content is limited to the range of 2.0% or more and 4.5% or less.

[0026] Mn: 0.01% or more and 0.5% or less Mn is a useful element for improving hot workability. If the Mn content exceeds 0.5%, the primary recrystallization texture deteriorates, making it difficult to obtain secondary recrystallized grains highly concentrated in the Goss orientation. Therefore, the Mn content is limited to a range of 0.5% or less. Furthermore, in order to improve hot workability, the Mn content must be 0.01% or more. The Mn content is preferably 0.02% or more and 0.3% or less.

[0027] Se, Te, and O: Less than 50 ppm each. Excessive Se and Te form selenides and tellurides, making secondary recrystallization difficult. This is because coarsened precipitates caused by slab heating cause the primary recrystallization structure to become non-uniform. Therefore, to prevent them from acting as inhibitors, the Se and Te contents are each limited to less than 50 ppm. The Se and Te contents are preferably 30 ppm or less. On the other hand, O forms oxides and remains as inclusions in the final product, degrading magnetic properties. Therefore, the O content must be limited to less than 50 ppm. The Se, Te, and O contents may be 0%.

[0028] Acid-soluble Al: 20 ppm or more but less than 100 ppm, S: less than 50 ppm, N: 80 ppm or less. When the inhibitor-less process is applied, these precipitate-forming elements are not necessarily required when only secondary recrystallization is considered. However, Al is effective as a deoxidizer in the smelting process to reduce inclusions that cause problems. In addition, by including an appropriate amount of Al, dense Al particles are formed on the surface during secondary recrystallization annealing. ２ O ３This can form a film, reducing the effects of nitriding and other nitriding from the atmosphere. Therefore, the content of acid-soluble Al is preferably in the range of 20 ppm or more and less than 100 ppm. Furthermore, if the S content and N content are 50 ppm or more and more than 80 ppm, respectively, the precipitates formed during slab heating will coarsen, similar to Se and Te, and deteriorate the primary recrystallized structure. Therefore, the S content and N content are limited to less than 50 ppm and less than 80 ppm, respectively. While it is preferable to set the S content and N content to 0%, these elements are difficult to completely remove. In fact, setting the S content to less than 10 ppm and the N content to less than 20 ppm leads to a significant increase in manufacturing costs. Therefore, the S content and N content are preferably set to 10 ppm or more and 20 ppm or more, respectively. This reduces the burden on manufacturing grain-oriented electrical steel sheets using the inhibitor-less method, which aims to produce high-quality grain-oriented electrical steel sheets at low cost.

[0029] Ga: 0.030 × Al × 2.58 ≦ Ga ≦ 1.000 × Al × 2.58 relative to the concentration of acid-soluble Al. In the present invention, the addition of Ga in accordance with the amount of acid-soluble Al added is essential. Ga has a high boiling point but a low melting point, making it difficult to add as metallic Ga. At the laboratory level, various Ga concentrations can be achieved by adding metallic Ga. However, in conventional refining processes, when adding Al, it is preferable to add Ga using techniques such as using Al containing Ga or scrap containing a certain amount of Ga. However, currently, there are technical challenges in adding high concentrations of Ga. Using an electric furnace process using low-temperature scrap or an iron source as a raw material is relatively easy to use compared to the general blast furnace-converter process.

[0030] The amount of Ga added is determined based on the amount of acid-soluble Al added. The magnetic property stabilization effect was observed when the Ga content was 3.0% or more, in atomic number terms, relative to the amount of acid-soluble Al added. Because the atomic weight difference between Al and Ga is approximately 2.58 times, the target mass percentage is multiplied by this. While the mechanism behind the optimum Ga content range is unclear, a relationship with the amount of Al added has been confirmed, suggesting that complex precipitation with Al is likely the cause. It is believed that the effect is insufficient at less than 3.0% relative to the Al content. On the other hand, although the effect saturates at the upper limit, increasing the amount does not necessarily result in deterioration. However, given that Ga is more expensive as a raw material than Al, there is no reason to actively add it within a range where the effect is small. Furthermore, embrittlement behavior is also observed. Therefore, the Ga content, in atomic number terms, is preferably 100.0% or less, more preferably 50.0% or less, and even more preferably 30.0% or less, relative to the amount of Al added.

[0031] The essential components and inhibitory components have been described above, but in the present invention, one or more of the elements described below may also be appropriately contained.

[0032] Ni: 1.50% or less Ni improves the magnetic properties by increasing the uniformity of the hot-rolled sheet structure. When the Ni content is 0.005% or more, the effect of adding Ni is manifested. On the other hand, when the Ni content exceeds 1.50%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, it is preferable that the Ni content be within the above range.

[0033] Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less Sn, Sb, and Cu are elements that are sometimes considered auxiliary inhibitors through grain boundary segregation, and may be useful in inhibitor-less processes that do not actively utilize inhibitors due to precipitates. The effects of adding Sn, Sb, and Cu are manifested by setting the contents of Sn, Sb, and Cu to 0.01% or more, 0.005% or more, and 0.01% or more, respectively. On the other hand, exceeding the upper limit increases the possibility of secondary recrystallization defects. Therefore, it is preferable that the contents of Sn, Sb, and Cu be within the above ranges.

[0034] P: 0.50% or less, Cr: 1.50% or less P and Cr have the effect of improving the reaction during the formation of the forsterite film. The effects of adding these elements are manifested when the P content and Cr content are 0.0050% or more and 0.01% or more, respectively. On the other hand, if the P content and Cr content exceed 0.50% and 1.50%, respectively, the formation of the forsterite film is excessively promoted, resulting in problems such as peeling of the film. Therefore, it is preferable to set the P content and Cr content within the above ranges.

[0035] Mo: 0.50% or less, B: 0.0050% or less, Nb: 0.0100% or less Mo, B, and Nb all contribute to suppressing grain growth and have the effects of improving texture and stabilizing secondary recrystallization. Therefore, the effects of adding Mo, B, and Nb are manifested by setting the Mo content, B content, and Nb content to 0.01% or more, 0.0001% or more, and 0.0005% or more, respectively. On the other hand, if Mo, B, and Nb are added in excess, they precipitate and function as strong inhibitors. Therefore, in the inhibitorless process, it is preferable to set the Mo content, B content, and Nb content to the above-mentioned upper limits or less.

[0036] Co: 0.0100% or less Ti: 0.0050% or less Zn: 0.050% or less Bi: 0.0200% or less W: 0.0030% or less Pb, Ge, As, Ag: 0.0010% or less each Since it is difficult to control grain size by precipitates in the inhibitorless process, by using elements that segregate at grain boundaries, it is possible to control grain growth to some extent and improve magnetic properties. In addition, elements with significantly different atomic structures also have the effect of suppressing grain boundary migration. Examples of elements that have the function of suppressing grain growth and grain boundary migration include Co, Ti, Zn, Bi, W, Pb, Ge, As, and Ag. The effects of adding these elements are manifested when Co is 0.0005% or more, Ti is 0.0010% or more, Zn is 0.0001% or more, Bi is 0.0005% or more, W is 0.0001% or more, and Pb, Ge, As, and Ag are each 0.0001% or more. Therefore, they can be contained within the above-mentioned ranges. These elements can be used alone or in combination, and they can mainly improve magnetic flux density.

[0037] The balance is preferably iron and impurities other than those mentioned above, particularly unavoidable impurities.

[0038] A steel slab adjusted to the above-mentioned range of chemical composition is cast. Since Ga-added steel may be slightly embrittled in hot conditions, when casting a slab with a thickness exceeding the usual 200 mm, it is preferable to use a casting machine with minimal excessive bending back. Furthermore, if the bending of the casting machine is so great that breakout occurs, a medium-thickness slab with a thickness of 30 mm to 180 mm may be used.

[0039] The cast steel slab is subjected to hot rolling to produce a hot-rolled sheet, either without reheating or after reheating. When the steel slab is reheated, the reheating temperature is preferably about 1100° C. or higher and 1300° C. or lower. Slab heating above 1300° C. is meaningless in the present invention, in which the steel slab contains almost no inhibitors, and is unnecessary because it increases costs.

[0040] When a steel slab is subjected to rough rolling directly after casting, the rough rolling is preferably started when the slab surface temperature is in the range of 900°C to 1150°C. If the surface layer of the steel slab is not cooled sufficiently, breakout may occur, in which unsolidified molten steel in the center of the steel slab breaks through the solidified surface layer and flows out. However, with the inhibitor-free component system used in the present invention, there is little concern about the precipitation of inhibitor components due to low temperatures. Therefore, it is possible to cool the steel slab to 1200°C or less while suppressing the precipitation of inhibitor components in the steel slab, allowing for more stable production of grain-oriented electrical steel sheets.

[0041] The hot-rolled sheet is then annealed as necessary, and then cold-rolled once or twice or more times with intermediate annealing therebetween to obtain a cold-rolled sheet. This cold-rolling may be performed at room temperature, or may be warm-rolled by raising the steel sheet temperature to a temperature higher than room temperature, for example, about 250°C.

[0042] Subsequently, the cold-rolled sheet is subjected to primary recrystallization annealing. The purpose of this primary recrystallization annealing is to subject the cold-rolled sheet having a rolled texture to primary recrystallization and adjust the primary recrystallized grain size to an optimal size for secondary recrystallization. Another purpose is to decarburize the carbon contained in the steel by using a wet hydrogen-nitrogen atmosphere or a wet hydrogen-argon atmosphere as the annealing atmosphere, and simultaneously form an oxide film on the surface. For this purpose, the annealing temperature (holding temperature) of the primary recrystallization annealing is preferably a temperature of about 800°C or higher and lower than 950°C. In addition, to further improve the texture, it is effective to increase the heating rate during the heating process of the primary recrystallization annealing. Specifically, it is preferable to set the heating rate in the temperature range from 500°C to 700°C to 80°C / s or higher. This can improve the texture.

[0043] After the primary recrystallization annealing, an annealing separator is applied to the surface of the steel sheet. To form a forsterite film on the surface of the steel sheet after secondary recrystallization annealing, for example, magnesia (MgO) can be used as the main component of the annealing separator. In this case, adding an appropriate amount of Ti oxide, Sr compound, etc. to the separator can further advantageously form a forsterite film.

[0044] Following the application of the annealing separator, secondary recrystallization annealing (finish annealing) is carried out to perform secondary recrystallization and form a forsterite film. ２ Does not contain (mix) N ２ atmosphere, Ar atmosphere, or N ２ In a mixed atmosphere of Ar and H, the temperature range of 800°C to 900°C is maintained for 35 hours or more. ２ It is preferable to soak the material at a maximum temperature exceeding 1150°C for 3 hours or more in an atmosphere containing 5% by volume or more of methylcellulose, and then to keep the material in a temperature range of 1100°C or lower and 900°C or higher for 10 hours or more during the cooling process.

[0045] By carrying out secondary recrystallization annealing as described above, Al in the steel is in a state of complex precipitation with Ga, which makes it more difficult to remove from the steel than usual, and if it remains in excess, it will cause deterioration of hysteresis loss in the finished sheet. When MgO is used as an annealing separator, oxidation of the steel sheet progresses during annealing, but at this time, Al in the steel is converted into Al in the surface layer. ２ O ３ In order to obtain this effect of removing Al properly, N ２ , Ar, or N ２ It is necessary to set the residence time in the temperature range of 800° C. to 900° C. in a mixed atmosphere of Ar and SiO 2 for 35 hours or more.

[0046] Also, H ２ When high-temperature annealing is performed in an atmosphere containing H, a forsterite film is formed on the surface of the steel sheet, and impurity components including Ga are removed even if the interface between the steel sheet and the forsterite film serves as a precipitation site. ２It is necessary to soak the steel sheet at a maximum temperature exceeding 1150°C for 3 hours or longer in an atmosphere containing 5% by volume or more of ammonium nitrate. By carrying out this heat pattern, grain growth of the crystal grains during secondary recrystallization progresses, and the average crystal grain size in the rolling direction becomes 15 mm or more and the average crystal grain size in the direction perpendicular to the rolling direction becomes 10 mm or more.

[0047] Furthermore, with regard to Al and Ga, which could not be completely removed by high-temperature soaking treatment, their influence on hysteresis loss can be reduced by actively precipitating them coarsely during the cooling process. In particular, the residence time in the temperature range of 1100°C to 900°C during the cooling process is important, and by ensuring a residence time in this temperature range of 10 hours or more, improvement in hysteresis loss can be expected. In systems containing both Al and Ga as slab components, there have been many cases where hysteresis loss, but not total iron loss, deteriorated relative to the obtained magnetic flux density. However, by utilizing the above heat pattern, it has become possible to maintain hysteresis loss W at B = 1.7 T while containing Ga. ｈｙｓ But, W ｈｙｓ ≦-2.5×B ８ According to the present invention, grain-oriented electrical steel sheets have little variation in magnetic properties within the coil, and therefore, in consideration of economy, it is preferable to perform finish annealing on coils having a mass of 5 tons or more, more preferably 10 tons or more.

[0048] After the above-mentioned finish annealing, an insulating coating can be further applied to the surface of the steel sheet and baked. The type of such insulating coating is not particularly limited, and any conventionally known insulating coating is suitable. For example, a method in which a coating liquid containing phosphate, chromate, and colloidal silica, as described in JP-A-50-79442 and JP-A-48-39338, is applied to the steel sheet and baked at about 800°C, is suitable.

[0049] The obtained final product contains, by mass %, Si: 2.0% or more and 4.5% or less, Mn: 0.01% or more and 0.5% or less, as a result of purification during finish annealing, and the steel sheet substrate from which the insulating coating and undercoating have been removed contains Se, Te, and O each at less than 50 ppm, S at less than 30 ppm, acid-soluble Al at 2 ppm or more and less than 30 ppm, Ga at 5 ppm or more and less than 80 ppm, with the balance being iron and unavoidable impurities, and has a composition in which B in the rolling direction is ８ is 1.900T or more and B = 1.7T, the hysteresis loss W ｈｙｓ But, W ｈｙｓ ≦-2.5×B ８ The grain-oriented electrical steel sheet satisfies +5.15. Note that C and N are unavoidable impurities that do not need to remain in the finished sheet, and the lower the amount, the better. From the viewpoint of preventing magnetic aging, C is preferably contained in the steel sheet substrate at 50 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less. N is also preferably contained in the steel sheet substrate at 50 ppm or less, more preferably 30 ppm or less, and even more preferably 20 ppm or less.

[0050] Furthermore, when one or more elements selected from Ni, Sn, Sb, Cu, P, Cr, Mo, B, Nb, Co, Ti, Zn, Bi, W, Pb, Ge, As, and Ag are contained in the above-mentioned amounts, Ni: 1.50% or less, Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less, P: 0.50% or less, Cr: 1.50% or less, Mo: 0.50% or less, B: 0.0050% or less, Nb: 0. and further containing one or more selected from the group consisting of 0.0100% or less, Co: 0.0100% or less, Ti: 0.0050% or less, Zn: 0.050% or less, Bi: 0.0200% or less, W: 0.0030% or less, Pb: 0.0010% or less, Ge: 0.0010% or less, As: 0.0010% or less, and Ag: 0.0010% or less, with the balance being iron and unavoidable impurities, and ８ is 1.900T or more and B = 1.7T, the hysteresis loss W ｈｙｓ But, W ｈｙｓ ≦-2.5×B ８ It is a directional electrical steel sheet that satisfies +5.15.

[0051] The evaluation of the variation in the magnetic properties of the coil was carried out by taking Epstein test pieces from the center of the coil width every 500 m, with the point where 100 m of the end of the coil in the longitudinal direction was cut off as the origin, and measuring the magnetic flux density (B ８ ) and measure the B obtained at each point of the coil. ８ The standard deviation was used as the amount of variation.

[0052] Furthermore, with regard to other added elements, depending on the finish annealing conditions, the content of these elements in the steel may decrease as a result of being incorporated into the forsterite coating or being released into the gas phase, and therefore the content of these elements will be lower than the concentration when contained in the slab.

[0053] Example 1 When steel having the following chemical compositions was produced, metallic Ga was added in a laboratory to produce vacuum steel ingots having various Ga contents as shown in Table 1. Each steel ingot was then heated to 1200°C and hot-rolled to a thickness of 2 mm. Subsequently, 50 hot-rolled sheets, each 100 mm wide and 300 mm long, were used as test materials and subjected to hot-rolled sheet annealing at 1000°C for 50 seconds. These were then cold-rolled to a final thickness of 0.27 mm and subjected to annealing for decarburization and primary recrystallization. Subsequently, an annealing separator containing MgO as a main component was applied to the surface of the steel sheet, and annealing including a secondary recrystallization process and a purification process was performed. ２ The mixture was heated at 850°C for 40 hours in a H ２ :N ２ After soaking at 1200°C for 5 hours in a gas mixture atmosphere with a carbon dioxide ratio of 25:75, the cooling rate in the temperature range from 1100°C to 900°C was 10°C / h, resulting in a residence time of 20 hours. An insulating coating consisting of 60% colloidal silica and aluminum phosphate was applied to the surface of the resulting steel sheet and baked at 800°C. The C and N contents of the finished sheet were 30 ppm or less at all levels.

[0054] Epstein test pieces were cut out from the test materials obtained from the 50 hot-rolled sheets, and the magnetic flux density (B ８ ) and hysteresis loss at a magnetic flux density of 1.7 T (W ｈｙｓ ) was measured. ８ The standard deviation of the 50 measurement points was evaluated as the amount of variation. The results are shown in Table 1. After the magnetic measurements, the coating was removed from the test pieces by pickling, and then the steel composition was analyzed. As is clear from the results, when Ga was added in an atomic ratio of 3.0% or more to Al (hereinafter also referred to as "Al:Ga atomic ratio"), B ８ It can be seen that the amount of variation decreases. Note that, for the test pieces with an Al:Ga atomic ratio of 48.4%, one out of 50 test pieces was broken during the manufacturing process, making it impossible to evaluate the product characteristics. Also, for the test pieces with an Al:Ga atomic ratio of 96.9%, two out of 50 test pieces were broken during the manufacturing process, making it impossible to evaluate the product characteristics. Furthermore, for the test pieces with an Al:Ga atomic ratio of 116.3%, five test pieces were similarly broken during the manufacturing process, making it impossible to evaluate the final magnetic properties.

[0055]

[0056] (Example 2) The components were C: 0.055%, Si: 3.2%, Mn: 0.07%, Cr: 0.01%, P: 0.03%, S: 15 ppm, N: 35 ppm, and acid-soluble Al of 20 ppm or more but less than 100 ppm. Scrap containing a trace amount of Ga was used as a raw material and melted in an electric furnace to obtain a cast slab having the composition shown in Table 2. The resulting cast slab was then heated, and hot rolling was initiated when the slab surface temperature reached 1120°C to obtain a hot-rolled sheet with a thickness of 2 mm. Subsequently, the resulting hot-rolled sheet (hot-rolled coil) was subjected to hot-rolled sheet annealing at 1050°C for 30 seconds. Thereafter, the resulting sheet was cold-rolled to a final thickness of 0.23 mm and subjected to annealing for decarburization and primary recrystallization. Thereafter, an annealing separator containing MgO as the main component was applied, and the steel sheet was wound into a coil with a total weight of 8 tons, followed by annealing including a secondary recrystallization process and a purification process. In the secondary recrystallization annealing, a single soaking treatment was performed at 850°C during the temperature rise process. The soaking treatment at the maximum annealing temperature and the cooling conditions were controlled to be the conditions shown in Table 2. An insulating coating consisting of 60% colloidal silica and aluminum phosphate was applied to the surface of the obtained steel sheet, and the steel sheet was baked at 830°C. In order to measure the variation in magnetic properties of the coil, Epstein test pieces were taken from the center of the width of the coil every 500m, with the point where 100m of the end in the longitudinal direction of the coil was cut off as the origin, and the magnetic flux density (B ８ ) and hysteresis loss at a magnetic flux density of 1.7 T (W ｈｙｓ ) was measured. Also, the B ８ The standard deviation of the magnetic field was evaluated as the amount of variation. The results are shown in Table 2. After the magnetic field measurements, the coating was removed from the test pieces by pickling, and then the steel components were analyzed. As shown in Table 2, it was confirmed that the steel sheets of the invention examples had good magnetic properties. The C and N contents of the finished sheets were 30 ppm or less at all levels.

[0057]

[0058] Example 3 A steel slab was produced having the composition shown in Table 3 as the main components, in addition to 0.06% C, 3.35% Si, and 0.03% Mn. The Al content was adjusted using an alloy containing a trace amount of Ga. The resulting steel slab was then heated at 1250°C and hot-rolled under typical conditions to produce a hot-rolled sheet (hot-rolled coil) with a thickness of 2.5 mm. The resulting hot-rolled coil was then annealed at 900°C, cold-rolled to 1.3 mm, and then subjected to intermediate annealing. The intermediate annealing was performed at 1050°C, and the annealed coil was cold-rolled to a final thickness of 0.23 mm and subjected to annealing for decarburization and primary recrystallization. An annealing separator primarily composed of MgO was then applied to the surface of the steel sheet, followed by final annealing, which included a secondary recrystallization process and a purification process. The final annealing was performed in an Ar atmosphere at 850°C for 40 hours. ２ :N ２ The coil was soaked at 1200°C for 10 hours in a mixed gas atmosphere with a carbon dioxide ratio of 25:75, and the cooling rate in the temperature range from 1100°C to 900°C was 10°C / h, resulting in a residence time in the temperature range of 20 hours. The obtained coil was coated with a coating solution containing phosphate-chromate-colloidal silica in a weight ratio of 3:1:2, and then subjected to planarization annealing at 850°C for 30 seconds.

[0059] In order to measure the variation in the magnetic properties of the coil, test pieces were taken from the center of the coil width every 500 m, with the point where 100 m of the end of the coil in the longitudinal direction was cut off as the origin, so that the total weight was 500 g or more. The magnetic flux density (B ８ ) and hysteresis loss at a magnetic flux density of 1.7 T (W ｈｙｓ ) was measured. Also, the B ８ The standard deviation of the magnetic field was evaluated as the amount of variation. The results are shown in Table 3. After the magnetic field measurements, the coating was removed from the test specimens by pickling, and the steel composition was also analyzed. As shown in Table 3, it was confirmed that even better properties could be obtained by adding various additive elements. The C and N contents of the finished steel sheets were 30 ppm or less at all levels.

[0060]

[0061] According to the present invention, in the production of grain-oriented electrical steel sheets using an inhibitorless process, it is possible to provide grain-oriented electrical steel sheets that have stable and excellent magnetic properties throughout the entire length of the coil.

Claims

1. A grain-oriented electrical steel sheet having a composition containing, by mass%, Si: 2.0% to 4.5%, Mn: 0.01% to 0.5%, and, by mass ppm, Se, Te, and O each less than 50 ppm, S less than 30 ppm, acid-soluble Al 2 ppm to less than 30 ppm, Ga 5 ppm to less than 80 ppm, with the balance being iron and unavoidable impurities, wherein B in the rolling direction ８ is 1.900T or more, and the hysteresis loss W at B = 1.7T ｈｙｓ Grain-oriented electrical steel sheet that satisfies the following formula (1). ｈｙｓ ≦-2.5×B ８ +5.15 ​​(1) 2. The grain-oriented electrical steel sheet according to claim 1, wherein the chemical composition further contains, in mass%, one or more elements selected from Ni: 1.50% or less, Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less, P: 0.50% or less, Cr: 1.50% or less, Mo: 0.50% or less, B: 0.0050% or less, Nb: 0.0100% or less, Co: 0.0100% or less, Ti: 0.0050% or less, Zn: 0.050% or less, Bi: 0.0200% or less, W: 0.0030% or less, Pb: 0.0010% or less, Ge: 0.0010% or less, As: 0.0010% or less, and Ag: 0.0010% or less.

3. A method for producing the grain-oriented electrical steel sheet according to claim 1 or 2, wherein, in mass%, C: 0.08% or less, Si: 2.0% to 4.5%, Mn: 0.01% to 0.5%, and in mass ppm, Se, Te, and O: less than 50 ppm each, acid-soluble Al: 20 ppm to less than 100 ppm, S: less than 50 ppm, N: 80 ppm or less, and Ga: the concentration of acid-soluble Al satisfies the following formula (2), i.e., 0.030×Al×2.58≦Ga≦1.000×Al×2.58 (2) In a method for producing a grain-oriented electrical steel sheet, a steel slab is cast from molten steel having a composition satisfying the formula (I) above, with the remainder being Fe and unavoidable impurities, and the resulting slab is hot-rolled to form a hot-rolled sheet, which is then annealed and rolled to form a cold-rolled sheet of a final thickness, which is then subjected to primary recrystallization annealing, further subjected to secondary recrystallization annealing, and then an insulating coating is formed, ２ atmosphere, Ar atmosphere, or N ２ and Ar, and the temperature range of 800°C to 900°C was maintained for 35 hours or more. ２ % or more of ammonium nitrate, and then soaking the steel sheet at a maximum temperature exceeding 1150°C for 3 hours or more in an atmosphere containing 5 volume % or more of ammonium nitrate, and then cooling the steel sheet for 10 hours or more in a temperature range of 1100°C or less and 900°C or more.

4. A method for producing a grain-oriented electrical steel sheet according to claim 3, wherein the chemical composition further contains, in mass%, one or more elements selected from Ni: 1.50% or less, Sn: 0.50% or less, Sb: 0.50% or less, Cu: 0.50% or less, P: 0.50% or less, Cr: 1.50% or less, Mo: 0.50% or less, B: 0.0050% or less, Nb: 0.0100% or less, Co: 0.0100% or less, Ti: 0.0050% or less, Zn: 0.050% or less, Bi: 0.0200% or less, W: 0.0030% or less, Pb: 0.0010% or less, Ge: 0.0010% or less, As: 0.0010% or less, and Ag: 0.0010% or less.

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