JP7640827B2 - Manufacturing method of grain-oriented electrical steel sheet and grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing grain-oriented electrical steel sheet and grain-oriented electrical steel sheet.

Grain-oriented electrical steel sheets generally contain 2% to 5% by mass of Si as a steel sheet component, and the orientation of the crystal grains of the steel sheet is highly concentrated in the {110}<001> orientation, known as the Goss orientation. Grain-oriented electrical steel sheets have excellent magnetic properties and are used, for example, as iron core materials for stationary inductors such as transformers.

Various technologies have been developed to improve the magnetic properties of such grain-oriented electrical steel sheets. In particular, with the recent demand for energy conservation, there is a demand for even lower iron loss in grain-oriented electrical steel sheets. To reduce iron loss in grain-oriented electrical steel sheets, it is effective to increase the concentration of crystal grains in the Goss orientation in the steel sheet to improve magnetic flux density and reduce hysteresis loss.

Grain-oriented electrical steel sheets used as the base material for wound transformers are required to reduce noise as well as reduce iron loss. Magnetic domain refinement is carried out on electrical steel sheets to reduce iron loss. Magnetic domain refinement to reduce iron loss is generally carried out by introducing distortion near the surface of the electrical steel sheet using laser irradiation or other methods.

As an example of a magnetic domain refinement method that introduces strain near the surface of an electrical steel sheet by laser irradiation, Patent Document 1 discloses that the iron loss of the resulting grain-oriented electrical steel sheet is reduced by suppressing the N content in the forsterite coating formed after final annealing to 3.0 mass% or less and performing a magnetic domain refinement process by laser irradiation. It also discloses that the iron loss improvement effect is further improved by suppressing compositional fluctuations of each forsterite by controlling the Al and Ti amounts in the forsterite coating and setting the standard deviation of the forsterite grain size to 1.0 times or less the average grain size.

Patent Document 2 discloses that by controlling the amount of crystalline forsterite in the glass coating applied to the surface of the steel sheet and the distribution of forsterite grains with a specific average crystal grain size within the steel sheet surface, a grain-oriented electrical steel sheet for laser magnetic domain control is provided that has a high magnetic domain control effect even with low laser power, and that the grain-oriented electrical steel sheet achieves a high level of low iron loss and low magnetostriction.

Patent documents 1 and 2 propose various techniques for refining magnetic domains to reduce iron loss, but make no proposals regarding achieving both low noise and low iron loss effects.

JP 2012-31512 A JP 2019-002039 A

The closure domains introduced to the surface of the magnetic steel sheet by the magnetic domain refining process have a negative effect on noise. Transformers require both low noise and low iron loss, and there is a particular demand for a magnetic domain refining method that has a minimal effect on noise.

In the present invention, the finish annealed sheet prior to the magnetic domain refinement process is lightly pickled using a special light pickling solution, thereby increasing the heat transfer coefficient of precipitates such as MnS present on the surface of the steel sheet, concentrating the effects of the magnetic domain refinement process only on the surface of the steel sheet, and reducing the total amount of distortion, i.e., suppressing the amount of closure domains generated and suppressing the increase in hysteresis loss, thereby reducing the iron loss of the resulting grain-oriented electrical steel sheet, and also achieving further noise reduction.

The gist of the present invention is
(1) In order,
a step of hot rolling the slab containing, in mass% , 2.5% to 4.5% Si, 0.01% to 0.15% Mn, 0.020 to 0.100% C, 0.001 to 0.050% of one or two of S and Se in total, 0.010 to 0.050% acid-soluble Al, 0.002 to 0.015% N, 0.300% or less Cr, 0.400% or less Cu, 0.500% or less P, 0.300% or less Sn, 0.300% or less Sb, 1.000% or less Ni, 0.020% or less Bi , with the balance being Fe and impurities, to obtain a hot-rolled steel sheet;
A step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot- rolled annealed sheet;
A step of cold rolling the hot-rolled annealed sheet to obtain a cold-rolled steel sheet;
A step of subjecting the cold-rolled steel sheet to decarburization annealing;
A step of applying an annealing separator containing MgO to the surface of the cold-rolled steel sheet after decarburization annealing, and then performing finish annealing to obtain a finish annealed sheet;
A step of subjecting the finish annealed sheet to light pickling to remove the annealing separator;
A process of applying an insulating coating liquid to the steel sheet from which the annealing separator has been removed, and performing flattening annealing;
a step of subjecting the obtained flattened annealed sheet to a magnetic domain refining treatment by a thermal distortion imparting means;
A method for producing a grain-oriented electrical steel sheet comprising:
The light pickling solution contains one or more elements selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, and the total concentration of each element is 0.0001 to 0.1000 mass % ,
The pH is -1 or more and 5 or less,
The liquid temperature is 15°C or higher and 100°C or lower,
The method for producing a grain-oriented electrical steel sheet, wherein the finish annealed sheet is immersed in the light pickling solution for a time period of 5 seconds or more and 200 seconds or less.
(2) The method for producing a grain-oriented electrical steel sheet according to (1) above, wherein the thermal distortion imparting means is selected from a laser and an electron beam.
(3) An electrical steel sheet containing, by mass% , Si : 2.50 to 4.50%, Mn: 0.01 to 0.15% , C: 0.085% or less, acid-soluble Al: 0.065% or less, N: 0.012% or less, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S and Se being 0.001 to 0.050% in total, Bi: 0.02% or less , the balance being Fe and impurities, and having magnetic domain refinement performed by thermal distortion imparting means, wherein eddy current loss is reduced by 0.07 W/kg or more compared to before the magnetic domain refinement treatment is performed,
The increase in hysteresis loss is 0.02 W/kg or less,
A grain-oriented electrical steel sheet, characterized in that the change in magnetostriction λp-p when excited to 1.7 T is 0.2 μm/m or less.
(4) The grain-oriented electrical steel sheet according to (3) above, wherein the thermal distortion imparting means is selected from a laser and an electron beam.

According to the present invention, the effect of the magnetic domain refining process during manufacturing is concentrated only on the surface layer of the steel sheet, reducing the total amount of distortion and suppressing the occurrence of closure domains, thereby suppressing the increase in hysteresis loss, reducing the iron loss of the directional electrical steel sheet, and reducing noise.

The preferred embodiment of the present invention will be described in detail below. Unless otherwise specified, the notation "A-B" for numerical values A and B means "greater than or equal to A and less than or equal to B." In such notation, when a unit is added only to numerical value B, the unit is also applied to numerical value A.

One embodiment of the present invention is a method for producing a grain-oriented electrical steel sheet having the following configuration.
a step of hot rolling the slab containing, in order, by mass% , Si : 2.5% to 4.5%, Mn: 0.01% to 0.15%, C: 0.020 to 0.100%, S and Se: 0.001 to 0.050%, acid-soluble Al: 0.010 to 0.050%, N: 0.002 to 0.015%, Cr: 0.300% or less, Cu: 0.400% or less, P: 0.500% or less, Sn: 0.300% or less, Sb: 0.300% or less, Ni: 1.000% or less, Bi: 0.020% or less , with the balance being Fe and impurities, to obtain a hot-rolled steel sheet;
A step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot- rolled annealed sheet;
A step of cold rolling the hot-rolled annealed sheet to obtain a cold-rolled steel sheet;
A step of subjecting the cold-rolled steel sheet to decarburization annealing;
A step of applying an annealing separator containing MgO to the surface of the cold-rolled steel sheet after decarburization annealing, and then performing finish annealing to obtain a finish annealed sheet;
A step of subjecting the finish annealed sheet to light pickling to remove the annealing separator;
A process of applying an insulating coating liquid to the steel sheet from which the annealing separator has been removed, and performing flattening annealing;
a step of subjecting the obtained flattened annealed sheet to a magnetic domain refining treatment by a thermal distortion imparting means;
A method for producing a grain-oriented electrical steel sheet comprising:
The light pickling solution contains one or more elements selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, and the total concentration of each element is 0.0001 to 0.1000 mass % ,
The pH is -1 or more and 5 or less,
The liquid temperature is 15°C or higher and 100°C or lower,
The method for producing a grain-oriented electrical steel sheet, wherein the finish annealed sheet is immersed in the light pickling solution for a time period of 5 seconds or more and 200 seconds or less.

The manufacturing method for the grain-oriented electrical steel sheet according to this embodiment will be described in detail below.

[Slab composition]
First, the composition of the slab used in the grain-oriented electrical steel sheet according to this embodiment will be described. In the following, unless otherwise specified, the notation "%" will represent "mass %". The remainder of the slab other than the elements described below is Fe and impurities. Here, the impurities refer to components contained in the raw materials or components mixed in during the manufacturing process, and components that are not intentionally contained in the steel sheet. In addition, the chemical composition of the slab, which is the material for the grain-oriented electrical steel sheet, is basically similar to the composition of the grain-oriented electrical steel sheet. However, in the manufacture of general grain-oriented electrical steel sheets, some of the contained elements are discharged outside the system by decarburization annealing and purification annealing during the manufacturing process, so that the chemical composition of the slab, which is the material, and the grain-oriented electrical steel sheet, which is the final product, are different. In order to obtain the desired characteristics of the grain-oriented electrical steel sheet, the slab composition can be appropriately adjusted taking into account the effects of decarburization annealing and purification annealing during the manufacturing process.

The components of the slab used in the production of the grain-oriented electrical steel sheet according to the present invention contain Si : 2.50 to 4.50%, Mn: 0.01 to 0.15%.

The Si (silicon) content is 2.5-4.5%. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the Si content is less than 2.5%, it is not preferable because it becomes difficult to sufficiently suppress eddy current loss in the final grain-oriented electrical steel sheet. If the Si content is more than 4.5%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. Therefore, the Si content is 2.5%-4.5%, and preferably 2.7-4.0%.

The Mn (manganese) content is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that affect secondary recrystallization. If the Mn content is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the Mn content is more than 0.15%, it is not preferable because it becomes difficult for Mn to form a solid solution during slab heating. Also, if the Mn content is more than 0.15%, it is not preferable because the precipitate size of MnS and MnSe, which are inhibitors, tends to become coarse, which impairs the optimal size distribution as an inhibitor. Therefore, the Mn content is 0.01 to 0.15%, and preferably 0.03 to 0.13%.

The components other than Si and Mn can be the following components.
For example, as components other than Si and Mn, the alloy may contain, in mass%, C: 0.020 to 0.100%, the total of one or two of S and Se: 0.001 to 0.050%, acid-soluble Al: 0.010 to 0.050%, N: 0.002 to 0.015%, Cr : 0.300 % or less, Cu : 0.400 % or less, P : 0.500 % or less, Sn : 0.300% or less, Sb: 0.300% or less, Ni : 1.000% or less, and Bi : 0.020% or less.

The C (carbon) content is 0.02-0.10%. C has various roles, but if the C content is less than 0.02%, the grain size becomes excessively large when the slab is heated, which increases the iron loss value of the final grain-oriented electrical steel sheet, which is not preferable. If the C content exceeds 0.10%, the decarburization time becomes long during decarburization after cold rolling, which increases the manufacturing cost, which is not preferable. Also, if the C content exceeds 0.10%, decarburization is likely to be incomplete, which is not preferable because it may cause magnetic aging in the final grain-oriented electrical steel sheet. Therefore, the C content is 0.02-0.10%, and preferably 0.05-0.09%.

The total content of S (sulfur) and Se (selenium) is 0.001-0.050%. S and Se form inhibitors together with the above-mentioned Mn. Both S and Se may be contained in the slab, but it is sufficient that at least one of them is contained in the slab. If the total content of S and Se is outside the above range, it is not preferable because a sufficient inhibitor effect cannot be obtained. Therefore, the total content of S and Se is 0.001-0.050%, and preferably 0.001-0.040%.

The content of acid-soluble Al (acid-soluble aluminum) is 0.01 to 0.05%. Acid-soluble Al constitutes an inhibitor necessary for producing grain-oriented electrical steel sheets with high magnetic flux density. If the content of acid-soluble Al is less than 0.01%, the amount of acid-soluble Al is insufficient, and the inhibitor strength is insufficient, which is not preferable. If the content of acid-soluble Al is more than 0.05%, the AlN precipitated as an inhibitor becomes coarse, which is not preferable, as it reduces the inhibitor strength. Therefore, the content of acid-soluble Al is 0.01 to 0.05%, and preferably 0.01 to 0.04%.

The N (nitrogen) content is 0.002-0.015%. N forms AlN, an inhibitor, together with the acid-soluble Al mentioned above. If the N content is outside the above range, it is not preferable because a sufficient inhibitor effect cannot be obtained. Therefore, the N content is 0.002-0.015%, and preferably 0.002-0.012%.

In addition, in order to improve magnetic properties, the slab used in the manufacture of the grain-oriented electrical steel sheet according to this embodiment may contain, in addition to the above-mentioned elements, one or more elements selected from the group consisting of Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1.0% or less, and Bi: 0.02% or less, in mass%, in place of a portion of the remaining Fe. In the slab according to one embodiment, the Cr content may be 0.02% or more, the Bi content may be 0.0005% or more, the Sb content may be 0.005% or more, and the Mo content may be 0.005% or more, in mass%.

A slab is formed by casting molten steel adjusted to the composition described above. The method for casting the slab is not particularly limited. In research and development, even if a steel ingot is formed in a vacuum melting furnace or the like, the same effects can be confirmed for the above-mentioned components as when a slab is formed.

[Process for producing hot-rolled steel sheet]
The cast slab is heated at a predetermined temperature, and the heated slab is hot-rolled to be processed into a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet after processing may be, for example, 1.8 mm to 3.5 mm. If the thickness of the hot-rolled steel sheet is less than 1.8 mm, the steel sheet temperature after hot rolling becomes low, and the amount of AlN precipitation in the steel sheet increases, making secondary recrystallization unstable, which is not preferable because the magnetic properties of the grain-oriented electrical steel sheet with a final thickness of 0.23 mm or less are reduced. If the thickness of the hot-rolled steel sheet is more than 3.5 mm, the rolling load in the cold rolling process becomes large, which is not preferable.

[Annealing process]
The hot-rolled steel sheet may be subjected to normal hot-rolled annealing to obtain a hot-rolled annealed sheet. By subjecting the hot-rolled steel sheet to hot-rolled annealing, the grain structure of the hot-rolled steel sheet can be adjusted, and more stable secondary recrystallization can be obtained.

[Process for producing cold-rolled steel sheet]
The hot-rolled steel sheet is subjected to pickling and then rolled by one cold rolling or multiple cold rolling with intermediate annealing therebetween, thereby being processed into a cold-rolled steel sheet.
In addition, the steel sheet may be heat-treated at about 300° C. or less between passes of cold rolling, between rolling roll stands, or during rolling. In such a case, the magnetic properties of the final grain-oriented electrical steel sheet can be improved. The hot-rolled steel sheet may be rolled by three or more cold rolling passes, but since multiple cold rolling passes increase the manufacturing cost, it is preferable to roll the hot-rolled steel sheet by one or two cold rolling passes. When cold rolling is performed by reverse rolling such as a Sendzimir mill, the number of passes in each cold rolling pass is not particularly limited, but is preferably 9 or less from the viewpoint of manufacturing cost.

[Decarburization annealing process]
Next, decarburization annealing is performed. The cold-rolled steel sheet is subjected to heat treatment (i.e., decarburization annealing) under a predetermined temperature condition (for example, heating at 700 to 900°C for 1 to 3 minutes). When the decarburization annealing is performed, the carbon in the cold-rolled steel sheet is reduced to a predetermined amount or less, and a primary recrystallization structure is formed. In addition, in the decarburization annealing, an oxide layer containing silica (SiO ₂ ) as a main component is formed on the surface of the cold-rolled steel sheet.

Next, the annealing separator is applied. In this process, an annealing separator containing magnesia (MgO) as its main component is applied to the surface of the cold-rolled steel sheet (the surface of the oxide layer).

[Finish annealing process]
Next, the cold-rolled steel sheet coated with the annealing separator is subjected to heat treatment (i.e., finish annealing) under a predetermined temperature condition (for example, heating at 1100 to 1300°C for 20 to 24 hours). When the finish annealing is performed, secondary recrystallization occurs in the cold-rolled steel sheet, and the cold-rolled steel sheet is purified. As a result, a cold-rolled steel sheet is obtained that has the above-mentioned chemical composition of the steel sheet and has a crystal orientation controlled so that the magnetization easy axis of the crystal grains coincides with the rolling direction X.

Furthermore, when the above-mentioned final annealing treatment is performed, the oxide layer containing silica as a main _component reacts with the annealing separator containing magnesia as a main component to form a glass film containing composite oxides such as forsterite ( _Mg2SiO4 ) on the surface of the steel sheet. In the final annealing process, the final annealing treatment is performed with the steel sheet wound in a coil shape. By applying the annealing separator to the surface of the steel sheet, it is possible to prevent seizure from occurring on the coiled steel sheet.

[Light pickling process]
Subsequently, the finish annealed steel sheet is lightly pickled to remove any annealing separator remaining on the surface.

The light pickling solution contains one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni, the total concentration of each element is 0.0001-0.1000%, and the pH is -1 or more and 5 or less. The temperature of the pickling solution is 15°C or more and 100°C or less, and the steel sheet is immersed in the light pickling solution for 5 seconds or more and 200 seconds or less.

If the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the light pickling solution is less than 0.0001%, the effect of modifying the residual MnS/Se surface in the thickness direction will be insufficient, which is not preferred. If the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the light pickling solution is more than 0.1000%, the effect of improving magnetic properties will saturate and the cost of the light pickling solution will increase, which is not preferred. Therefore, the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the light pickling solution is 0.0001 to 0.1000%.

If the pH of the light pickling solution is less than -1, it is not preferable because the acidity becomes too strong and the glass film on the steel sheet surface is removed. If the pH of the light pickling solution is more than 5, the effect of modifying the residual MnS/Se surface by the light pickling process becomes insufficient, which is also not preferable. Therefore, the pH of the light pickling solution is from -1 to 5.

If the temperature of the light pickling solution is less than 15°C, the effect of modifying the residual MnS/Se surface by the light pickling process will be insufficient, which is not preferable. If the temperature of the light pickling solution is more than 100°C, it will be difficult to handle the pickling solution, which is not preferable. Therefore, the temperature of the light pickling solution is 15°C or higher and 100°C or lower.

If the time during which the steel sheet is immersed in the light pickling solution during the light pickling process is less than 5 seconds, the effect of modifying the residual MnS/Se surface by the light pickling process will be insufficient, which is not preferable. If the time during which the steel sheet is immersed in the light pickling solution during the light pickling process exceeds 200 seconds, the equipment will become long and large, which is not preferable. Therefore, the time during which the steel sheet is immersed in the light pickling solution during the light pickling process is 5 seconds or more and 200 seconds or less.

When light pickling is performed under the above conditions, the precipitates in the steel, MnS, are replaced by sulfides such as Cu on the surface of the steel sheet, or are coated with Cu, etc., which increases the heat transfer coefficient of these precipitates themselves, and also increases the heat transfer coefficient of the surface of the steel sheet containing these precipitates. Here, the "surface of the steel sheet" refers to a depth of about 10 μm from the surface of the steel sheet. In addition, "replacement" refers to the Mn portion of the originally formed MnS being replaced by Cu, etc. derived from the light pickling solution, and MnS being replaced with sulfides such as Cu, and "coated" refers to the new precipitation of Cu, etc. derived from the pickling solution around the originally formed MnS. Since such a phenomenon in the present invention is not affected by the precipitation method of Cu, etc., it does not matter whether the phenomenon of replacement with sulfides such as Cu, or coating with Cu, etc. occurs during the pickling treatment. This makes it possible to increase the heat propagation effect of laser irradiation, etc., which imparts thermal distortion, on the surface of the steel sheet.

[Application of insulating coating liquid ~ Flattening annealing process]
An insulating coating containing, for example, aluminum phosphate or colloidal silica as a main component is applied to the surface of the steel sheet that has been lightly pickled. The components of the insulating coating are not particularly limited as long as the steel sheet is provided with insulation and tension. Thereafter, planarization annealing is performed under a predetermined temperature condition (for example, 840 to 920°C), and finally, a grain-oriented electrical steel sheet is obtained.

[Magnetic domain subdivision processing]
The flattened annealed sheet is subjected to a magnetic domain refinement treatment by a thermal strain imparting means, which uses a laser or an electron beam to irradiate the steel sheet surface at a direction substantially perpendicular to the rolling direction to locally impart plastic strain.

When a laser is used as a heat applying means, the laser light source may be a high-power laser generally used for industrial purposes, such as a fiber laser, a YAG laser, a semiconductor laser, or a _CO2 laser. A pulsed laser or a continuous wave laser may also be used as the laser light source. As the laser light, it is preferable to use a single mode laser with high focusing ability.

As the conditions for the laser light irradiation, for example, it is preferable to set the laser output to 200 W to 3000 W, the focused spot diameter of the laser light in the rolling direction (i.e. the diameter including 86% of the laser output, hereinafter abbreviated as 86% diameter) to 10 μm to 200 μm, the focused spot diameter of the laser light in the plate width direction (86% diameter) to 10 μm to 1000 μm, and the laser scanning speed to 5 m/s to 50 m/s. These laser irradiation conditions are adjusted appropriately so that both low iron loss and low magnetostriction can be achieved.

When an electron beam is used as the heat application means, the electron beam irradiation device may be, for example, a conventional electron beam irradiation device using a filament, a grid, an electron gun, an electromagnetic lens, and a deflection coil.

The irradiation conditions for the electron beam irradiation are preferably, for example, acceleration voltage: 50 kV to 350 kV, beam current: 0.3 mA to 50 mA, beam irradiation diameter: 10 μm to 500 μm, irradiation interval: 3 mm to 20 mm, and scan speed: 5 m/sec to 80 m/sec. These electron beam irradiation conditions are adjusted appropriately so that low iron loss and low magnetostriction can be achieved at the same time.

Another embodiment of the present invention is a grain-oriented electrical steel sheet obtained by the above-mentioned method for producing a grain-oriented electrical steel sheet of the present invention. , C: 0.085% or less, acid-soluble Al: 0.065% or less, N: 0.012% or less, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S and Se are 0.001 to 0.050% in total, Bi: 0.02% or less , the balance being Fe and impurities, and the grain-oriented electrical steel sheet has been subjected to a magnetic domain refinement treatment by a thermal distortion imparting means, characterized in that the eddy current loss is reduced by 0.07 W/kg or more compared to before the magnetic domain refinement treatment, the increase in hysteresis loss is 0.02 W/kg or less, and the change in magnetostriction λp-p when excited to 1.7 T is 0.2 μm/m or less.

[Steel plate composition]
First, the chemical composition of the steel sheet used in the grain-oriented electrical steel sheet according to the present invention will be described.
In the following, unless otherwise specified, the notation "%" represents "mass %." The balance of the steel sheet other than the elements described below is Fe and impurities.

The steel sheet used in the grain-oriented electrical steel sheet according to the present invention has a composition preferable for controlling the crystal orientation to a Goss texture concentrated in the {110}<001> orientation , and contains Si : 2.50-4.50% and Mn: 0.01-0.15%.

(Si: 2.50-4.50%)
The content of Si (silicon) is 2.50 to 4.50%. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the content of Si is less than 2.50%, it is not preferable because it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet. If the content of Si is more than 4.50%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. Therefore, the content of Si is 2.50 to 4.50%, and preferably 2.70 to 4.00%.

(Mn: 0.01-0.15%)
The content of Mn (manganese) is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that influence secondary recrystallization. If the content of Mn is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the content of Mn is more than 0.15%, it is not preferable because it becomes difficult to dissolve Mn during slab heating. In addition, if the content of Mn is more than 0.15%, the precipitation size of MnS and MnSe, which are inhibitors, tends to become coarse, which is not preferable because the optimal size distribution as an inhibitor is impaired. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

The components other than Si and Mn may be the components contained in ordinary grain-oriented electrical steel sheets.
For example, components other than Si and Mn may contain, in mass%, C : 0.085% or less, acid-soluble Al : 0.065% or less, N : 0.012% or less, Cr : 0.3 % or less, Cu : 0.4 % or less, P : 0.5% or less, Sn : 0.3 % or less, Sb : 0.3 % or less, Ni : 1 % or less, S and Se in total 0.001 to 0.050%, and Bi : 0.02 % or less.

The remainder of the steel plate other than the above components is Fe and impurities. Here, impurity elements refer to components contained in the raw materials or components mixed in during the manufacturing process, but not intentionally included in the steel plate.

[Total iron loss]
The total energy loss that occurs in a grain-oriented electrical steel sheet when it is excited with an alternating current is called iron loss (here, it is called "total iron loss" because it is the sum of eddy current loss and hysteresis loss, which will be described later). Usually, total iron loss is measured by a method using an Epstein tester in JIS C 2550-1 or a method using a single sheet tester in JIS C 2556:2015. Both measuring instruments have the same measurement principle, and an excitation force is applied to the test piece by passing an AC excitation current through an excitation winding (primary winding) that surrounds the test piece, and the magnetization (magnetic polarization) of the test piece that is caused by this is measured by measuring the induced electromotive force generated in a search coil (secondary winding) that also surrounds the test piece, thereby measuring the magnetic polarization (magnetic flux density) in the test piece. The total iron loss is measured by inputting the magnetic polarization signal and the excitation force signal into a power meter.

[Eddy current loss]
The "eddy current loss" in the present invention refers to the iron loss caused by eddy currents generated in a steel sheet by induced electromotive force during AC excitation, and is calculated by subtracting hysteresis loss from total iron loss. Alternatively, there is a method of calculating it from the slope of the change in the value obtained by dividing the total iron loss by the excitation frequency (frequency separation).

The grain-oriented electrical steel sheet according to the present invention has eddy current loss reduced by 0.07 W/kg or more compared to the electrical steel sheet before being subjected to the magnetic domain refinement treatment.
The reason why the eddy current loss is reduced by 0.07 W/kg or more is believed to be that the amount of closure domains formed by the residual strain introduced by the magnetic domain refinement treatment is sufficient, resulting in a significant magnetic domain refinement effect.
For this reason, in the grain-oriented electrical steel sheet according to the present invention, the amount of closure domains generated is controlled.

The eddy current loss was measured in the following manner.
The iron loss is measured by AC magnetic measurement using the Epstein test method specified in JIS C 2550-1 or the single sheet magnetic measurement method specified in JIS C 2556, and the iron loss is calculated by subtracting the hysteresis loss described below.

[Hysteresis loss]
The "hysteresis loss" in the present invention refers to an iron loss component that is not dependent on the excitation frequency, and is determined by multiplying the loss determined by DC magnetic measurement by the excitation frequency.

The grain-oriented electrical steel sheet according to the present invention has an increase in hysteresis loss of 0.02 W/kg or less compared to the electrical steel sheet before being subjected to the magnetic domain refinement treatment.
The reason why the increase in hysteresis loss is 0.02 W/kg or less is believed to be that the residual strain introduced by the magnetic domain refining treatment is localized near the surface, and the closure domains formed are also localized near the surface, so as not to impede the magnetic domain wall motion necessary for the magnetization process.
For this reason, in the grain-oriented electrical steel sheet according to the present invention, the amount of closure domains generated is controlled.

The hysteresis loss was measured as follows.
It is calculated by multiplying the iron loss obtained by DC magnetic measurement using the Epstein test method specified in JIS C 2550-1 or the single sheet magnetic measurement method specified in JIS C 2556 by the excitation frequency.

[Magnetostriction λp-p]
In the present invention, "magnetostriction λp-p" refers to the absolute value of the difference between the minimum and maximum values of magnetostriction deformation when excited with an alternating current. In other words, it is |λmax-λmin|. However, the value used is converted to the value of magnetostriction deformation when the reference sample length is set to 1 m.

The grain-oriented electrical steel sheet according to the present invention has a change in magnetostriction λp-p of 0.2 μm/m or less when excited at 1.7 T.
The reason why the change in magnetostriction λp-p is 0.2 μm/m or less is believed to be that the residual strain introduced by the magnetic domain refinement process is localized near the surface and is not large as a total volume fraction of the closure domains, so that the amount of magnetostrictive deformation when the closure domains disappear during magnetization is small.
For this reason, when the grain-oriented electrical steel sheet according to the present invention is used in a transformer, noise generation is reduced.

The magnetostriction λp-p was measured as follows.
A rectangular sample cut so that its longitudinal direction is parallel to the rolling direction is inserted into an excitation frame, and magnetostriction deformation when excited with AC is measured using a non-contact optical measuring device such as a laser Doppler method. The measured waveform of magnetostriction deformation is stored in a transient memory, and magnetostriction λp-p can be calculated from the maximum and minimum values of magnetostriction deformation within one period of the excitation waveform of the sample measured separately with a search coil.

Plate Thickness
The thickness of the grain-oriented electrical steel sheet of the present invention is preferably 0.1 to 0.5 mm, and more preferably 0.15 to 0.35 mm.

The magnetic steel sheet according to the present invention has reduced iron loss (eddy current loss, hysteresis loss), and when used in a transformer, reduces noise generation. This effect is believed to be due to the light pickling applied to the finish annealed sheet during the production of the grain-oriented magnetic steel sheet.

When light pickling is performed on a finish annealed sheet under the above-mentioned light pickling conditions, the precipitates in the steel, MnS, are replaced by sulfides such as Cu on the surface of the steel sheet, or are coated with Cu, etc., which increases the heat transfer coefficient of these precipitates themselves and also increases the heat transfer coefficient of the surface layer of the steel sheet containing these precipitates. This makes it possible to increase the heat transfer effect of laser irradiation, etc., which imparts thermal distortion, on the surface layer of the steel sheet. In the present invention, the strain induced by irradiation with a laser or the like is concentrated only on the surface layer by increasing the heat transfer coefficient only on the surface of the steel sheet, thereby reducing the total amount of strain. In other words, the magnetic domain refinement effect is achieved while suppressing the amount of closure domains generated. In addition, by reducing the total amount of strain, the increase in hysteresis loss due to irradiation with a laser or the like is also suppressed.

The grain-oriented electrical steel sheet obtained using the manufacturing method of the present invention will be described in more detail below, with reference to examples. Note that the examples shown below are merely examples of the grain-oriented electrical steel sheet according to this embodiment, and the grain-oriented electrical steel sheet according to this embodiment is not limited to the examples shown below.

The slab contained, by mass fraction, 3.0% Si, 0.08% C, 0.05% acid-soluble Al, 0.01% N, 0.12% Mn, 0.05% Cr, 0.04% Cu, 0.01% P, 0.02% Sn, 0.01% Sb, 0.005% Ni, 0.007% S, 0.001% Se, with the remainder being Fe and impurities. Hot rolling was performed on the slab, and a hot-rolled steel sheet with a thickness of 2.3 mm was obtained.

Next, the above hot-rolled steel sheets were subjected to an annealing treatment under temperature conditions of heating at 1000° C. for 1 minute.
After the annealing treatment, cold rolling was performed to obtain a cold-rolled steel sheet having a thickness of 0.23 mm. Subsequently, the cold-rolled steel sheet was subjected to a decarburization annealing treatment under a temperature condition of heating at 800° C. for 2 minutes, and then an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the cold-rolled steel sheet.

Then, the cold-rolled steel sheet coated with the annealing separator was subjected to a final annealing treatment under the temperature conditions of heating at 1200°C for 20 hours. As a result, a steel sheet was obtained with the above-mentioned chemical composition, a glass film formed on the surface, and a crystal orientation controlled so that the magnetization easy axis of the crystal grains coincided with the rolling direction.

The surface of the finish annealed sheet was subjected to light pickling treatment using the light pickling solution and light pickling conditions shown in Table 1. After that, an insulating coating solution containing colloidal silica and phosphate was applied onto the glass film, and then flattening annealing was performed under temperature conditions of heating at 850°C for 1 minute, and finally, a grain-oriented electrical steel sheet with a glass film and an insulating film was obtained.

As an example (invention example), light pickling was performed using a light pickling solution within the scope of the present invention, and as a comparative example, light pickling was performed using a light pickling solution outside the scope of the present invention. The components, concentration, pH value, and immersion time of the light pickling solutions used in the examples and comparative examples are shown in Table 1.

After light pickling, the eddy current loss and hysteresis loss values of the electromagnetic steel sheets of the above examples and comparative examples were measured using the measurement method described above.

Next, the surface of the steel plate was irradiated with a laser and an electron beam, respectively, to impart thermal distortion to the surface of the steel plate.

The laser light irradiation device used was a fiber laser manufactured by IPG. The laser light irradiation conditions were adjusted to a laser output of 300 W, a focused spot diameter (86% diameter) of 50 μm in the rolling direction of the laser light, a focused spot diameter (86% diameter) of 100 μm in the plate width direction of the laser light, a laser scanning speed of 50 m/s, and a laser scanning pitch (spacing PL) of 3 mm.

The electron beam irradiation device used was a Mitsubishi Electric electron beam irradiation device. The electron beam irradiation conditions were an acceleration voltage of 150 kV, a beam current of 3.0 mA, a beam irradiation diameter of Φ200 μm, a scanning speed of 20 m/s, and an irradiation interval of 4 mm.

The total iron loss, eddy current loss, and hysteresis loss of the obtained magnetic steel sheets of the examples and comparative examples were measured using the measurement methods described above, and compared with the eddy current loss and hysteresis loss values after magnetic domain refinement processing. The eddy current loss and hysteresis loss values are those at a sinusoidal excitation with an excitation frequency of 50 Hz and a maximum magnetic flux density of 1.7 T. The magnetostriction λp-p was also measured when excited to 1.7 T with an excitation frequency of 50 Hz. Table 2 shows the results before and after the magnetic domain refinement processing by laser light irradiation, and the difference before and after the processing. Table 3 shows the results before and after the magnetic domain refinement processing by electron beam irradiation, and the difference before and after the processing.

As shown in Tables 2 and 3, if the light pickling solution and pickling conditions after the final annealing are not within the range of the present invention, the grain-oriented electrical steel sheet subjected to the magnetic domain refinement treatment will have an improvement in eddy current loss of less than 0.07 W/kg, an increase in hysteresis loss of more than 0.02 W/kg, or a change in magnetostriction λp-p when excited at 1.7 T of more than 0.2 μm/m, or all of these will occur, resulting in a grain-oriented electrical steel sheet with desirable magnetic properties. The eddy current loss indicates the degree of the effect of the magnetic domain refinement treatment, and in order to obtain a low iron loss material, it is preferable that the eddy current loss is larger. However, the increase in hysteresis loss due to the magnetic domain refinement treatment is a contradictory event that can be said to be a side effect of the magnetic domain refinement treatment, and it is preferable that the eddy current loss is smaller in order to obtain a low iron loss material. The change in the magnetostriction peak value due to the magnetic domain refinement treatment is an amount that indicates the magnitude of modulation of the magnetostriction waveform, and it is preferable that the change is smaller in order to obtain a low-noise transformer.

These results show that by performing pickling treatment under light pickling conditions within the range of the present invention, noise was reduced even further than in the comparative example.

Claims (2)

In order,
By mass%, Si: 2.5% to 4.5%,
Mn: 0.01% to 0.15%,
C: 0.020-0.100%,
S and Se: 0.001 to 0.050% in total,
Acid-soluble Al: 0.010 to 0.050%,
N: 0.002-0.015%,
Cr: 0.300% or less,
Cu: 0.400% or less,
P: 0.500% or less,
Sn: 0.300% or less,
Sb: 0.300% or less,
Ni: 1.000% or less,
A step of hot rolling a slab containing Bi: 0.020% or less and the balance being Fe and impurities to obtain a hot rolled steel sheet;
A step of subjecting the hot-rolled steel sheet to hot-rolled sheet annealing to obtain a hot-rolled annealed sheet;
A step of cold rolling the hot-rolled annealed sheet to obtain a cold-rolled steel sheet;
A step of subjecting the cold-rolled steel sheet to decarburization annealing;
A step of applying an annealing separator containing MgO to the surface of the cold-rolled steel sheet after decarburization annealing, and then performing finish annealing to obtain a finish annealed sheet;
A step of subjecting the finish annealed sheet to light pickling to remove the annealing separator;
A process of applying an insulating coating liquid to the steel sheet from which the annealing separator has been removed, and performing flattening annealing;
a step of subjecting the obtained flattened annealed sheet to a magnetic domain refining treatment by a thermal distortion imparting means;
A method for producing a grain-oriented electrical steel sheet comprising:
The light pickling solution contains one or more elements selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, and the total concentration of each element is 0.0001 to 0.1000 mass%,
The pH is -1 or more and 5 or less,
The liquid temperature is 15°C or higher and 100°C or lower,
The method for producing a grain-oriented electrical steel sheet, wherein the finish annealed sheet is immersed in the light pickling solution for a time period of 5 seconds or more and 200 seconds or less. The method for producing grain-oriented electrical steel sheet according to claim 1, wherein the thermal distortion imparting means is selected from a laser or an electron beam.