BR112020014283B1 - GRAIN ORIENTED ELECTRIC STEEL SHEET - Google Patents

Abstract

A grain-oriented electrical steel sheet includes: a base steel sheet; a lower layer which is disposed in contact with the base steel plate; and an insulating coating which is disposed in contact with the bottom layer and which includes a phosphate and a colloidal silica as major components. The base steel sheet includes the predetermined chemical composition and includes a compound B whose major axis length is from 1 to 20 µm and whose number density is from 1^10 to 1^106 pieces/mm3. The bottom layer is a glassy film that includes a forsterite as a major component or an intermediate layer includes a silicon oxide as a major component.

Description

technical field

[001] The present invention relates to a grain-oriented electrical steel sheet with high magnetic flux density and extremely low iron loss, which is used as an iron core material for a transformer or a generator. Priority is claimed over Japanese Patent Application No. 2018-010203, filed on January 25, 2018, the contents of which are incorporated herein by reference.

Background Technique

[002] Grain-oriented electrical steel sheet is a soft magnetic material and is used for an iron core and the like of electrical equipment such as a transformer. Grain oriented electrical steel sheet includes approximately 7 wt% or less Si and has grains that align highly in the {110}<001> orientation as the milling index. When grain-oriented electrical steel sheet is produced, it is important to control the orientation of the grains in a process, and the orientation is controlled by an abnormal grain growth phenomenon called secondary recrystallization.

[003] To properly control secondary recrystallization, it is important to properly form a structure (primary recrystallized structure) by primary recrystallization before secondary recrystallization, and to properly control elements segregated at grain boundaries or fine precipitates called inhibitors.

[004] The inhibitor has the functions of suppressing the growth of grains other than grains that have the orientation {110}<001> in the primary recrystallized structure and promote the preferential growth of grains that have the orientation {110}<001> during recrystallization secondary. Thus, in particular, it is important to control the type and amount of inhibitors.

[005] Much research has been described in relation to inhibitors. Among them, as a technical feature, there is the technique of using B as the inhibitor. For example, patent documents 1 and 2 describe that the solid solute B has the function of the inhibitor and is effective in the development of the {110}<001> orientation.

[006] Patent documents 3 and 4 describe that fine BN is made to form by nitriding a material including B in a process after cold rolling, the fine BN formed acts as the inhibitor, and thus the orientation {110}< 001> is developed.

[007] Patent document 5 describes that, although the BN is not made to precipitate as much as possible during hot rolling, extremely fine BN is made to precipitate during the subsequent annealing heating step, and the BN formed acts as an inhibitor.

[008] Patent documents 6 and 7 describe a method in which, by controlling the morphology of the precipitation of B in the hot rolling process, the precipitate is made to act as an inhibitor.

[009] These documents describe the techniques of adding B as a steel composition and using B as the inhibitor. These documents describe that, by the techniques, the {110}<001> orientation is significantly developed after secondary recrystallization, the hysteresis loss is reduced, and thus the grain-oriented electrical steel sheet with low iron loss can be obtained. However, these documents do not describe that, by controlling the B morphology after secondary recrystallization, it is possible to achieve both a high magnetic flux density and an extremely low iron loss.

Related Art Documents Patent Documents

[0010] [Patent Document 1] - US Patent No. 3905842

[0011] [Patent Document 2] - US Patent No. 3905843

[0012] [Patent Document 3] - Japanese Unexamined Patent Application, First Publication No. H01-230721

[0013] [Patent Document 4] - Japanese Unexamined Patent Application, First Publication No. H01-283324

[0014] [Patent Document 5] - Japanese Unexamined Patent Application, First Publication No. H10-140243

[0015] [Patent Document 6] - PCT International Publication No. WO2011/007771

[0016] [Patent Document 7] - PCT International Publication No. WO2011/007817

Summary of the invention Technical problem to be solved

[0017] By the conventional techniques described in the related art documents, since it is difficult to sufficiently control the precipitation morphology of B in the steel sheet after secondary recrystallization, the hysteresis loss increases due to the precipitates of B. Thus, it is difficult obtain the grain-oriented electrical steel sheet with extremely low iron loss.

[0018] The present invention has been made in consideration of situations of conventional techniques. An object of the invention is to provide a grain oriented electrical steel sheet with which it is possible to solve the problems such that high magnetic flux density and extremely low iron loss are achieved in grain oriented electrical steel sheet using a B compound. as an inhibitor.

Solution to the problem

[0019] In order to stably produce grain-oriented electrical steel sheet with high magnetic flux density and extremely low iron loss by adding B as the steel composition, it is important to properly control the morphology of B precipitation in the steel sheet, in addition to increased magnetic flux density by highly aligning the {110}<001> orientation with respect to the grains after secondary recrystallization.

[0020] In a case where BN is used as the inhibitor and the precipitation morphology of B is fine after final annealing, fine BN is precipitated on the steel sheet, and thus, it is difficult to achieve both high magnetic flux density and extremely low iron loss. In particular, hysteresis loss increases due to thin BN, and thus it is difficult to achieve extremely low iron loss.

[0021] Based on the above, the present inventors have made a thorough investigation to solve the above-mentioned problems. As a result, it was found that by controlling the precipitation morphology of B after final annealing to be Fe2B and/or Fe3B, the influence on the hysteresis loss can be minimized, and thus it is possible to obtain the electric steel sheet of fine grain oriented in which both high magnetic flux density and extremely high iron loss are achieved.

[0022] The present invention is made on the basis of the above findings. One aspect of the present invention employs the following:

[0023] (1) A grain oriented electrical steel sheet according to an aspect of the present invention includes: a base steel sheet; a lower layer which is disposed in contact with the base steel plate; and an insulating coating that is disposed in contact with the bottom layer and that includes a phosphate and a colloidal silica as main components, where

[0024] the base steel sheet includes: as chemical composition, in % by mass,

[0025] 0.085% or less of C;

[0026] 0.80 to 7.00% Si;

[0027] 0.05 to 1.00% Mn;

[0028] 0.010 to 0.065% Al;

[0029] 0.0040% or less of N;

[0030] 0.015% or less of Seq = S + 0.406 ■ If;

[0031] 0.0005 to 0.0080% B; It is

[0032] the balance consisting of Fe and impurities,

[0033] the base steel sheet includes a composite B whose main axis length is 1 to 20 μm and whose numerical density is 1x10 to 1x106 parts/mm3, and

[0034] The bottom layer is a glassy film that includes a forsterite as a main component or an intermediate layer includes a silicon oxide as a main component.

[0035] (2) In the grain-oriented electrical steel sheet according to item (1),

[0036] the bottom layer may be the vitreous film, and

[0037] when a glow discharge emission spectroscopy is conducted after removing the insulating coating and the glassy film, when the region that is the glassy film side from the center of the thickness of the base steel sheet is divided into two regions which are the surface region on the glass-film side and a central region between the surface region and the center of the thickness, when a sputtering time to reach the central region is referred to as t (center), when a spraying time to reach the surface region is referred to as t (surface), when the emission intensity of B at time t (center) is referred to as IB_t (center), and when an emission intensity of B at time t ( surface) is referred to as I B_t (surface),

[0038] The IB_t (center) and the IB_t (surface) can satisfy expression (1) below.

[0039] I B_t (center) > I B_t (surface) •••(I)

[0040] (3) In the grain-oriented electrical steel sheet according to item (1),

[0041] the bottom layer can be the middle layer, and

[0042] when a total thickness of the base steel sheet and the intermediate layer is referred to as d, when the emission intensity of B at a depth of d/2 from the surface of the intermediate layer in a case where the intensity of emission of B is measured by glow discharge emission spectroscopy (GDS) from the surface of the buffer layer is referred to as IB (d/2), and when an emission intensity of B at a depth of d/10 from the surface of the middle layer is referred to as IB (d/10),

[0043] the IB (d/2) and the IB (d/10) can satisfy expression (2) below.

[0044] IB (d/2) > IB (d/10) •••(2)

[0045] (4) In the grain-oriented electrical steel sheet according to any one of items (1) to (3), compound B may be at least one selected from the group consisting of Fe2B and Fe3B. Effects of the invention

[0046] According to the above aspects of the present invention, in the grain-oriented electrical steel sheet using compound B as the inhibitor, it is possible to industrially and stably supply the grain-oriented electrical steel sheet in which the hysteresis loss can be be reduced by properly controlling the precipitation morphology of compound B, and thus both high magnetic flux density and low iron loss are achieved.

Brief description of the drawings

[0047] Fig. 1 is a schematic illustrating the layer structure of the grain-oriented electrical steel sheet according to the first embodiment.

[0048] Fig. 2 is a graph, for example, showing the result of conducting the GDS for the grain-oriented electric steel sheet according to the first modality. Detailed description of preferred modalities

[0049] A grain-oriented electrical steel sheet according to one embodiment (hereinafter, it shall be referred to as “the present electrical steel sheet”) includes: a base steel sheet; a bottom layer which is formed in contact with the base steel plate; and an insulating coating that is formed in contact with the bottom layer and that includes a phosphate and a colloidal silica as major components, where

[0050] the base steel sheet includes as chemical composition, in % by mass,

[0051] 0.085% or less of C;

[0052] 0.80 to 7.00% Si;

[0053] 0.05 to 1.00% Mn;

[0054] 0.010 to 0.065% Al;

[0055] 0.012% or less of N;

[0056] 0.015% or less of Seq = S + 0.406 ■ If;

[0057] 0.0005 to 0.0080% B; It is

[0058] the balance consisting of Fe and impurities,

[0059] the base steel sheet includes a composite B whose average length of the main axis is from 1 to 20 μm and whose numerical density is from 1x10 to 1x106 parts/mm3, and

[0060] The bottom layer is a glassy film that includes a forsterite as a main component or an intermediate layer includes a silicon oxide as a main component.

[0061] In addition, in the present electrical steel sheet,

[0062] the bottom layer may be the vitreous film, and

[0063] when the emission intensity of B measured by glow discharge emission spectroscopy (GDS) from a steel sheet without the glassy film on the grain-oriented electric steel sheet is referred to as IB, when a spray time to achieve the center is referred to as t (center), when a spray time for the surface of a steel sheet without the glassy film is referred to as t (surface), when an emission intensity of B at t (center) is referred to as I B_t (center), and when an emission intensity of B at surface t (surface) is referred to as IB_t (surface),

[0064] the IB_t (center) and the IB_t (surface) can satisfy expression (1) below.

[0065] I B_t (center) > I B_t (surface) •••(I)

[0066] In addition, in the present electrical steel sheet,

[0067] the bottom layer can be the middle layer, and

[0068] when a total thickness of the base steel sheet and the intermediate layer is referred to as d, when the emission intensity of B at a depth of d/2 from the surface of the intermediate layer in a case where an intensity of emission of B is measured by glow discharge emission spectroscopy (GDS) from the surface of the buffer layer is referred to as IB (d/2), and when an emission intensity of B at a depth of d/10 from the surface of the middle layer is referred to as IB (d/10),

[0069] the IB (d/2) and the IB (d/10) can satisfy expression (2) below.

[0070] IB (d/2) > IB (d/10) •••(2)

[0071] In addition, in the present electrical steel sheet, compound B can be Fe2B and/or Fe3B.

[0072] Hereinafter the present electrical steel plate is explained.

[0073] First modality

[0074] A grain-oriented electrical steel sheet according to the first embodiment includes: a base steel sheet; a glassy film which is disposed in contact with the base steel sheet and which includes forsterite as a main component; and an insulating coating which is disposed in contact with the glass film and which includes a phosphate and a colloidal silica as major components.

[0075] The base steel sheet includes, as chemical composition, in, % by mass,

[0076] 0.085% or less of C;

[0077] 0.80 to 7.00% Si;

[0078] 0.05 to 1.00% Mn;

[0079] 0.010 to 0.065% Al;

[0080] 0.012% or less of N;

[0081] 0.015% or less of Seq = S + 0.406 ■ If;

[0082] 0.0005 to 0.0080% B; It is

[0083] the balance consisting of Fe and impurities, and

[0084] The base steel sheet includes a composite B whose average length of the main axis is from 1 to 20 μm and whose numerical density is from 1x10 to 1x106 parts/mm3.

[0085] In addition, in the grain-oriented electric steel sheet according to the present embodiment,

[0086] when a region that is the glassy film side from the base steel plate thickness center is divided into two regions that are the surface region and the thickness center on the glassy film side and the center region between the surface region and the center of the thickness, when an emission intensity of B measured by glow-discharge emission spectroscopy (GDS) of the base steel sheet without the insulating coating and the glassy film is referred to as IB, when a spray time to reach the center region is referred to as t (center), when a spray time to reach the surface region is referred to as t (surface), when an emission intensity of B at time t (center) is referred as I B_t (center), and when an emission intensity of B at time t (surface) is referred to as I B_t (surface),

[0087] the IB_t (center) and the IB_t (surface) can satisfy expression (3) below.

[0088] I B_t (center) > lB_t (surface) •••(3) Chemical composition of base steel plate

[0089] The reasons for limiting the chemical composition of the base steel sheet are explained. Hereinafter, unless otherwise noted, “%” of chemical composition represents “% by mass”. Chemical composition 0.085% or less of C

[0090] C is an effective element for controlling the primary recrystallized structure, but negatively effective for the magnetic characteristics. Thus, C is the element to be removed by the decarburizing annealing before the final annealing. When the C content is greater than 0.085%, the time for decarburizing annealing needs to be prolonged, and the productivity decreases, which is not referable. The C content is preferably 0.070% or less, and more preferably 0.050% or less.

[0091] Although the lower limit of C includes 0%, the production cost drastically decreases to reduce the C content to be less than 0.0001%. Thus, the lower limit of C is substantially 0.0001% in practical steel sheet. 0.80 to 7.00% Si

[0092] Si is an element that increases the electrical resistance of steel sheet and improves the iron loss characteristics. When the Si content is less than 0.80%, the Y transformation occurs during the final annealing and the crystal orientation of the steel sheet is impaired, which is not preferable. The Si content is preferably 1.50% or more, and more preferably 2.50% or more.

[0093] On the other hand, when the Si content is greater than 7.00%, the workability deteriorates and cracks occur during rolling, which is not preferable. The Si content is preferably 5.50% or less, and more preferably 4.50% or less. 0.05 to 1.00% Mn

[0094] Mn is an element to suppress cracking during hot rolling and to form MnS and/or MnSe which acts as the inhibitor by binding to S and/or Se. When the Mn content is less than 0.05%, the addition effect is not obtained sufficiently, which is not preferable. The Mn content is preferably 0.07% or more, and more preferably 0.09% or more.

[0095] On the other hand, when the Mn content is greater than 1.00%, the dispersion state of the MnS and/or MnSe precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the density of magnetic flux decreases, which is not preferable. The Mn content is preferably 0.80% or less, and more preferably 0.60% or less. 0.010 to 0.065% acid-soluble Al

[0096] Acid-soluble Al is an element to form (Al, Si)N that acts as an inhibitor by binding with N. When the amount of acid-soluble Al is less than 0.010%, the addition effect is not sufficient obtained, secondary recrystallization does not take place sufficiently, which is not preferable. The amount of acid-soluble Al is preferably 0.015% or more, and more preferably 0.020% or more.

[0097] On the other hand, when the amount of acid-soluble Al is greater than 0.065%, the dispersion state of (Al, Si)N precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases, which is not preferable. The amount of acid-soluble Al is preferably 0.050% or less, and more preferably 0.040% or less. 0.012% or less of N

[0098] Since the risk of deterioration from iron loss due to nitride formation may increase, the N content should be 0.012% or less. As described later, N as a board composition is an element to form AlN which acts as an inhibitor by binding with Al. However, N is also an element to form bubbles (gaps) in the steel sheet during cold rolling. When the N content is less than 0.004%, AlN formation becomes insufficient, which is not preferable. The N content is preferably 0.006% or more, and more preferably 0.007% or more.

[0099] On the other hand, when the N content is greater than 0.012%, bubbles (gaps) may be formed in the steel sheet during cold rolling, which is not preferable. The N content is preferably 0.010% or less, and more preferably 0.009% or less. 0.015% or less of Seq = S + 0.406-Se

[00100] Since the risk of deterioration from iron loss due to the formation of sulfides may increase, the content should be 0.015% or less. As described later, S and Se as plaque composition are elements to form MnS and/or MnSe which acts as the inhibitor by binding with Mn. Its content is specified by Seq = S + 0.406-Se in consideration of the atomic weight ratio of S and Se.

[00101] When the Seq is less than 0.003%, the addition effect is not sufficiently obtained, which is not preferable. The Seq is preferably 0.005% or more, and most preferably 0.007% or more. On the other hand, when Seq is greater than 0.015%, the dispersion state of MnS and/or MnSe precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases, which does not it's preferable. The Seq is preferably 0.013% or less, and most preferably 0.011% or less. 0.0005 to 0.0080% of B

[00102] B is an element to form BN that acts as an inhibitor by binding with N and by complexly precipitating with MnS or MnSe.

[00103] When the content of B is less than 0.0005%, the addition effect is not obtained sufficiently, which is not preferable. The B content is preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand, when the B content is greater than 0.0080%, the dispersion state of the BN precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases, which does not it's preferable. The B content is preferably 0.0060% or less, and more preferably 0.0040% or less.

[00104] In the base steel sheet, the balance excluding the above elements and Fe are impurities. Impurities correspond to elements that are inevitably contaminated from steel raw materials and/or production processes. In the present electrical steel sheet, impurities are acceptable when they are contained within a range that does not deteriorate the characteristics.

[00105] In addition, the present electrical steel sheet may include at least one element selected from the group consisting of 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less Ni, 0.30% or less Sn, 0.30% or less Sb, and 0.01% or less Bi, which are in the range that can increase other characteristics without deteriorating characteristics magnetic.

[00106] Next, the characteristics of compound B in the present electrical steel sheet is explained.

Compound B morphology

[00107] Although the type of compound B is not limited, the average length of the main axis as a morphology should be from 1 to 20 μm.

[00108] When the length of the main axis is less than 1 μm, the precipitation frequency increases and the hysteresis loss increases, which is not preferable. The average length of the major axis is preferably 4 µm or more, and most preferably 8 µm or more.

[00109] On the other hand, it is preferable that the morphology of compound B is crude to reduce the frequency of precipitation. However, it is necessary to significantly reduce the cooling rate in purification annealing to precipitate compound B with the major axis length of 20 μm or more, which are difficult in industrial production and which are not preferable. Thus, the average principal axis length of compound B should be 20 µm or less. The average length of the major axis is preferably 17 µm or less, and more preferably 10 µm or less.

Numerical density of compound B

[00110] The numerical density of compound B must be 1x10 to 1x106 parts/mm3. When the number density is greater than 1x106 pieces/mm3, compound B becomes small, the frequency of precipitation of compound B with the main axis length of less than 1 μm increases, and the iron loss increases, which is not preferable. The number density is preferably 0.5x106 parts/mm3 or less, and more preferably 1x105 parts/mm3 or less.

[00111] On the other hand, when the number density of compound B is less than 1x10 pieces/mm3, the precipitate of B becomes significantly irregular and does not act as an inhibitor to control secondary recrystallization, which is not preferable. The number density of compound B is preferably 1x10 pieces/mm3 or more, and more preferably 1x102 pieces/mm3 or more.

[00112] For example, the numerical density of compound B is quantitatively evaluated by conducting the mapping of B by EPMA in the Z plane (plane perpendicular to the lamination direction) of the specimen, which is the polished steel sheet to the center of the thickness. Alternatively, EPMA B mapping can be conducted on the polished cross section of the specimen.

Compound B : Fe2B or Fe3B

[00113] Compound B is preferably Fe2B or Fe3B. Compound B is the compound reprecipitated during the purification annealing cooling, which originates from the BN that acted as an inhibitor and dissolved during the purification annealing.

[00114] When the N which is solid solute at high temperature is not released into the atmosphere and remains supersaturated in the steel sheet, the solid B solute binds to the solid solute N during purification annealing cooling, BN is reprecipitated finely and very frequently, and thus the hysteresis loss increases. When the annealing temperature is high and solid solute N is released out of the system during purification annealing, Fe2B or Fe3B is precipitated coarsely and with low frequency, which reduces the negative influence of iron loss.

[00115] The identification of Fe2B and/or Fe3B can be conducted by electron beam diffraction using a transmission electron microscope in addition to analysis using EPMA. The Fe2B and/or Fe3B crystal system is the tetragonal system, and its characteristics are 562.1 pm > a = b > 459.9 pm and 467.4 pm > c > 382.4 pm.

B distribution identified by GDS

[00116] In the distribution of B in the direction of the depth of the steel sheet, the fact that the concentration of B (intensity) in the surface region of the base steel sheet is greater than the concentration of B (intensity) in the central region of the base steel plate indicates that the thin BN exists in the surface region of the base steel plate. In the above case, iron loss increases, which is not preferable.

[00117] Fig. 1 is a schematic illustrating the layer structure of the grain-oriented electrical steel sheet according to the present embodiment. As shown in Fig. 1, the grain oriented electrical steel sheet 100 according to the present embodiment includes: base steel sheet 10; the vitreous film 20; and the insulating film 30. Furthermore, when the region which is the surface side (interface between the glass film 20 and the base steel sheet 10) from the center of the thickness C of the base steel sheet 10 is divided into two regions, the surface side region is referred to as the surface region 12 and the thickness center side region C is referred to as the center region 14.

[00118] When an emission intensity of B measured by glow discharge emission spectroscopy (GDS) of the steel sheet without the insulating coating and the glassy film is referred to as IB, when a spray time to reach the central region 14 is referred to as t (center), while a spray time to reach surface region 12 is referred to as t (surface),

[00119] It is preferable that the I B_t (center) and the IB_t (surface) satisfy expression (4) below:

[00120] I B_t (center) > IB_t (surface) •••(4)

[00121] IB_t (center) : emission intensity of B at t (center)

[00122] IB_t (surface) : emission intensity of B at t (surface)

[00123] When conducting the above measurement, the insulating coating 30 is removed using an aqueous alkaline solution such as sodium hydroxide, and the glassy film 20 is removed using hydrochloric acid, nitric acid, sulfuric acid, etc.

[00124] The t (surface) indicates the position immediately below the vitreous film, and the t (center) above is defined as the position that is from the position immediately below the vitreous film to the center of the thickness.

[00125] Fig. 2 is an example showing the GDS measurement result in the present mode. Specifically, t (surface) is defined as 300 to 400 seconds with the start of the measurement as the reference, and t (center) is defined as the time corresponding to a position of 400 seconds or more.

[00126] Furthermore, the IB_t (surface) is defined as the average of the emission intensities of B over 300 to 400 seconds with the beginning of the measurement as a reference. The IB_t (center) is defined as the average of the emission intensities of B over 400 to 900 seconds (to end the measurement) with the beginning of the measurement as a reference. However, the times above I B_t (surface) and IB_t (center) are examples because the time can be changed arbitrarily depending on the glass film thickness, GDS measurement conditions and the like.

[00127] In a case where IB_ (center) ^ IB_ (surface), the concentration (intensity) of B in the surface region of the base steel sheet becomes equal to or greater than the concentration (intensity) of B in the region core of the base steel sheet, fine BN exists in the surface region of the base steel sheet, and thus iron loss increases, which is not preferable.

glassy film

[00128] In the oriented grain electrical steel sheet of the present embodiment, the glassy film is formed in contact with the base steel sheet. The glassy skin includes complex oxides such as forsterite (Mg2SiO4). A glassy film is formed during the final annealing as described below, in which an oxide layer including silica as a major component reacts with an annealing separator including magnesia as a major component.

Insulation coating

[00129] In the grain-oriented electrical steel sheet according to the present embodiment, the insulating coating is formed in contact with the glassy film and includes phosphate and colloidal silica as main components.

[00130] Next, a method of producing the present electrical steel sheet from the present silicon steel will be described.

Composition of silicon steel plate

[00131] In the present electrical steel sheet, the silicon steel sheet includes, as a chemical composition, in % by mass, 0.085% or less of C; 0.80 to 7.00% Si; 0.05 to 1.00% Mn; 0.010 to 0.065% acid soluble Al; 0.004 to 0.012% N; 0.003 to 0.015% Seq = S + 0.406-Se; and 0.0005 to 0.0080% B. 0.085% or less C

[00132] C is an effective element to control the primary recrystallized structure, but it negatively affects the magnetic characteristics. Thus, C is the element to be removed by the decarburizing annealing before the final annealing. When the C content is greater than 0.085%, the time for decarburizing annealing needs to be prolonged, and the productivity decreases. Thus, the C content should be 0.085% or less. The C content is preferably 0.070% or less, and more preferably 0.050% or less.

[00133] Although the lower limit of C includes 0%, the cost of production increases dramatically to reduce the C content to less than 0.0001%. Thus, the lower limit of C is substantially 0.0001% as a practical steel sheet. In grain-oriented electrical steel sheet, C is generally reduced to approximately 0.001% or less in the decarburizing annealing. 0.80 to 7.00% Si

[00134] Si is an element that increases the electrical resistance of the steel sheet and improves the iron loss characteristics. When the Si content is less than 0.80%, the Y transformation occurs during the final annealing and the crystal orientation of the steel sheet is impaired. So the Si content should be 0.80% or more. The Si content is preferably 1.50% or more, and more preferably 2.50% or more.

[00135] On the other hand, when the Si content is greater than 7.00%, the workability deteriorates and cracks occur during rolling. Thus, the Si content should be 7.00% or less. The Si content is preferably 5.50% or less, and more preferably 4.50% or less. 0.05 to 1.00% Mn

[00136] Mn is an element to suppress cracks during hot rolling and form MnS which acts as an inhibitor by binding with S and/or Se. When the Mn content is less than 0.05%, the addition effect is not obtained sufficiently. Thus, the Mn content should be 0.05% or more. The Mn content is preferably 0.07% or more, and more preferably 0.09% or more.

[00137] On the other hand, when the Mn content is greater than 1.00%, the dispersion state of the MnS precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. Thus, the Mn content should be 1.00% or less. The Mn content is preferably 0.80% or less, and more preferably 0.06% or less. 0.010 to 0.065% acid-soluble Al

[00138] Acid-soluble Al is an element to form (Al, Si)N that acts as the inhibitor by binding with N. When the amount of acid-soluble Al is less than 0.010%, the effect of addition is not obtained sufficiently, secondary recrystallization does not take place sufficiently. Thus, the amount of acid-soluble Al should be 0.010% or more. The amount of acid-soluble Al is preferably 0.015% or more, and more preferably 0.020% or more.

[00139] On the other hand, when the amount of acid-soluble Al is greater than 0.065%, the dispersion state of the precipitation of (Al, Si)N becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. Thus, the amount of acid-soluble Al should be 0.065% or less. The amount of acid-soluble Al is preferably 0.050% or less, and more preferably 0.040% or less. 0.004 to 0.012% N

[00140] N is an element to form AlN that acts as an inhibitor by binding with Al. However, N is also an element that forms bubbles (gaps) in the steel sheet during cold rolling. When the N content is less than 0.004%, AlN formation becomes insufficient. Thus, the N content should be 0.004% or more. The N content is preferably 0.006% or more, and more preferably 0.007% or more.

[00141] On the other hand, when the N content is greater than 0.012%, bubbles (gaps) may be formed in the steel sheet during cold rolling. Thus, the N content should be 0.012% or less. The N content is preferably 0.010% or less, and more preferably 0.009% or less. 0.003 to 0.015% of Seq = S + 0.406-Se

[00142] S and Se as the plaque composition are elements to form MnS and/or MnSe which act as the inhibitor by binding with Mn. Its content is specified by Seq = S + 0.406 -Se in consideration of the atomic weight ratio of S and Se.

[00143] When the Seq is less than 0.003%, the addition effect is not obtained sufficiently. So the Seq must be 0.003% or more. The Seq is preferably 0.005% or more, and most preferably 0.007% or more. On the other hand, when the Seq is greater than 0.015%, the dispersion state of the MnS and/or MnSe precipitation becomes irregular, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. So the Seq must be 0.015% or less. The Seq is preferably 0.013% or less, and more preferably is 0.011% or less. 0.0005 to 0.0080% of B

[00144] B is an element to form BN which acts as the inhibitor by binding to N and by complexly precipitating with MnS.

[00145] When the content of B is less than 0.0005%, the addition effect is not obtained sufficiently. Thus, the B content must be 0.0005% or more. The B content is preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand, when the B content is greater than 0.0080%, the dispersion state of the BN precipitation becomes uneven, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. Thus, the B content should be 0.0080% or less. The B content is preferably 0.0060% or less, and more preferably 0.0040% or less.

[00146] In silicon steel plate, the balance excluding the above elements is Fe and the inevitable impurities. Impurities correspond to elements that are inevitably contaminated from steel raw materials and/or production processes. In the present electrical steel sheet, the unavoidable impurities are acceptable when they are contained within a range that does not deteriorate its characteristics.

[00147] In addition, the present electrical steel sheet may include at least one element selected from the group consisting of 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less Ni, 0.30% or less Sn, 0.30% or less Sb, and 0.01% or less Bi, which are in the range that can increase other characteristics without deteriorating characteristics silicon steel plate magnets.

silicon steel plate

[00148] This plate (silicon steel plate) is obtained by continuous casting or by conventional casting of ingots or blocks of molten steel with a predetermined chemical composition, which is done by a converter or an electric furnace and which is subjected to to a vacuum degassing treatment if necessary. The silicon steel plate is generally a piece of steel whose thickness is from 150 to 350 mm and preferably from 220 to 280 mm. The silicon steel plate can be a thin plate whose thickness is from 30 to 70 mm. In the case of a thin plate, there is the advantage that it is not necessary to conduct roughing processing to control the thickness to be an intermediate thickness to obtain the hot-rolled plate.

Silicon steel plate heating temperature

[00149] The steel plate is heated to 1250°C or less and subjected to hot rolling. When the heating temperature is higher than 1250°C, an amount of molten scale increases, MnS and MnSe are completely solute-solid and are finely precipitated in subsequent processes, the temperature for decarburizing annealing needs to be raised to 900°C or more to obtain the desired grain size after primary recrystallization, which is not preferable. The plate heating temperature is preferably 1250°C or less.

[00150] The lower limit of heating temperature is not particularly limited. To ensure the workability of the silicon steel plate, the heating temperature is preferably 1100°C or more.

Hot rolling, hot strip annealing

[00151] The silicon steel plate heated to 1250°C or less is subjected to hot rolling to obtain the hot rolled steel sheet. The hot-rolled steel sheet is heated and recrystallized to 1000 to 1150°C (first stage temperature), and subsequently heated and annealed to 850 to 1100°C (second stage temperature), which is lower than the first stage temperature. step, to homogenize the uneven structure after hot rolling. Annealing of the hot strip is preferably conducted one or more times to homogenize the hot rolled structure before the hot rolled sheet is subjected to final cold rolling.

[00152] In hot strip annealing, the temperature of the first stage significantly influences the precipitation of the inhibitor in subsequent processes. When the temperature of the first stage is higher than 1150°C, the inhibitor is finely precipitated in subsequent processes, the temperature for decarburizing annealing needs to be increased to 900°C or more to obtain the desired grain size after primary recrystallization, which is not preferable. The temperature of the first stage is preferably 1120°C.

[00153] On the other hand, when the temperature of the first stage is less than 1000°C, recrystallization becomes insufficient, the hot-rolled structure is not homogenized, which is not preferable. The temperature of the first stage is preferably 1030°C or more.

[00154] As with the temperature of the first stage, when the temperature of the second stage is greater than 1100°C, the inhibitor is finely precipitated in subsequent processes, which is not preferable. The temperature of the second stage is preferably 1070°C or less. On the other hand, when the temperature of the second stage is less than 850°C, the Y-phase is not transformed, the hot-rolled structure is not homogenized, which is not preferable. The temperature of the second stage is preferably 880°C or more.

cold rolling

[00155] The steel sheet after annealing the hot-rolled strip is cold-rolled once or cold-rolled two or more times with intermediate annealing, to obtain the steel sheet with the final thickness. Cold lamination can be conducted at room temperature or at a temperature higher than room temperature. For example, rolling between hot rolling and cold rolling (“warm rolling”) can be conducted after the steel sheet has been heated to approximately 200°C.

Decarburizing annealing

[00156] The steel sheet with the final thickness is subjected to decarburizing annealing in a humid atmosphere, to remove the C in the steel sheet and control the grain of the primary recrystallization to be the desired grain size. For example, it is preferable that the decarburizing annealing is conducted at the temperature of 770°C to 950°C for such a time that the grain size after primary recrystallization becomes 15 μm or more.

[00157] When the temperature for the decarburizing annealing is lower than 770°C, the desired grain size is not obtained. Thus, the temperature for the decarburizing annealing is preferably 700°C or more, and more preferably 800°C or more. On the other hand, when the temperature for decarburizing annealing is greater than 950°C, the grain size exceeds the desired grain size, which is not preferable. The temperature for decarburizing is preferably 920°C or less.

nitriding

[00158] The steel sheet after decarburizing annealing is subjected to nitriding before the final annealing, in order to control the N content of the steel sheet to be 40 to 1000 ppm. When the N content of the steel sheet after nitriding is less than 40 ppm, AlN is not precipitated sufficiently, and it does not act as an inhibitor, which is not preferable. The N content of the steel sheet after nitriding is preferably 80 ppm or more.

[00159] On the other hand, when the N content of the steel sheet is greater than 1000 ppm, AlN remains excessively after the end of the secondary recrystallization in the following final annealing, the iron loss increases, which is not preferable. The N content of the steel sheet is preferably 970 ppm or less.

Application of annealing separator

[00160] The annealing separator is applied to the steel sheet after nitriding, and the same is subjected to the final annealing. As the annealing separator, it is possible to use the common annealing separator.

final annealing Secondary recrystallization annealing

[00161] In the secondary recrystallization annealing of the final annealing, since the inhibitor is increased by BN, the heating rate in the temperature range of 1000 to 1100°C is preferably 15°C/hour or less, and more preferably 10°C/hour or less. Instead of controlling the heating rate, the steel sheet can be kept in the temperature range of 1000 to 1100°C for 10 hours or more.

purification annealing

[00162] The steel sheet after secondary recrystallization annealing is subjected to purification annealing which is followed by secondary recrystallization annealing. By conducting purification annealing for the steel sheet after completion of secondary recrystallization, the precipitates which were used as inhibitors are rendered harmless, and the hysteresis loss decreases as the magnetic characteristics of the final product, which is preferable. The purification annealing atmosphere is not particularly limited, but could be a hydrogen atmosphere, for example. Furthermore, purification annealing is conducted at the temperature of approximately 1200°C for 10 to 30 hours. The purification annealing temperature is not particularly limited, but is preferably 1180 to 1220°C from a productivity point of view. When the purification annealing temperature is 1180°C or less, it takes an excessive time to diffuse the elements, the annealing time needs to be extended, which is not preferable. On the other hand, when the purification annealing temperature is 1220°C or more, the maintenance (durability) of the annealing furnace becomes difficult, which is not preferable.

cooling condition

[00163] The steel sheet after purification annealing is cooled under predetermined cooling conditions (cooling rate).

[00164] To control the length of the main shaft of compound B to be in the desired range, the cooling rate in the temperature range from 1200 to 1000°C must be less than 50°C/hour. In addition, the cooling rate in the temperature range of 1000 to 600°C should be 30°C/hour.

[00165] The reason for controlling the cooling rate as described above is as follows.

[00166] BN is dissolved in solid solute B and solid solute N in the high temperature region, and N which is not solid solute is released into the atmosphere during cooling. On the other hand, B which is not a solid solute is not released out of the system during cooling, and is precipitated as a B compound such as BN, Fe2B, or Fe3B within the glass film or base steel sheet. In a case where solid solute B does not exist sufficiently in the base steel sheet, BN does not precipitate, but Fe2B or Fe3B precipitates.

[00167] When the cooling rate is adequate during cooling from the high temperature region, the solid solute N is released out of the system, and Fe2B or Fe3B precipitates on the base steel sheet. Furthermore, the precipitated Fe2B or Fe3B undergoes Ostwald ripening and is coalesced.

[00168] When the cooling rate is fast, the solid solute N is not released into the atmosphere, BN is finely precipitated in the base steel sheet, and Fe2B or Fe3B does not undergo Ostwald ripening and is finely precipitated. Compound B that is finely precipitated on the base steel sheet results in increased hysteresis loss and iron loss in the final product.

[00169] When the cooling rate is less than 10°C/hour, productivity is significantly affected. Thus, the cooling rate is preferably 10°C/hour or more. In other words, the cooling rate in the temperature range 1200 to 1000°C is preferably 10 to 50°C/hour, and the cooling rate in the temperature range 1000°C to 600°C is preferably 10 to 30°C/hour.

[00170] The atmosphere during annealing is preferably 100% H2 in the temperature range of at least 1200 to 600°C, and 100% N2 in the temperature range of less than 600°C. When the atmosphere during cooling is 100% N2 in the temperature range of 1200 to 600°C, the steel sheet is nitrided during cooling, and the formation of nitrides causes the hysteresis loss to deteriorate, which is not preferable. Air can be replaced by H2 during cooling in the temperature range of 1200 to 600°C, which is not preferable from an economy point of view.

Magnetic domain refining treatment

[00171] The grain-oriented electrical steel sheet after the final annealing can be subjected to the magnetic domain refining treatment. By the refining treatment of the magnetic domain, grooves are made, the width of the magnetic domain decreases, and as a result, the iron loss decreases, which is preferable. The specific treatment method of refining the magnetic domain is not particularly limited, but it can be groove making such as laser irradiation, electron beam irradiation, chemical etching, and toothed gearing.

[00172] While it is preferable that the magnetic domain refining treatment is conducted after the final annealing, the magnetic domain refining treatment can be conducted before the final annealing or after the formation of the insulating coating.

Formation of the insulating coating

[00173] The insulating coating is formed by applying and baking the solution for forming the insulating coating to the surface of the steel sheet after secondary recrystallization or after purification annealing. The type of insulating coating is not particularly limited, but it can be the conventionally known insulating coating. For example, the insulating coating can be formed by applying an aqueous solution including phosphate and colloidal silica.

[00174] The above phosphate is preferably the phosphate of Ca, Al, Sr, and the like, for example. Among these, aluminum phosphate is the most preferable. The type of colloidal silica is not particularly limited, and its particle size (average diameter) can be selected accordingly. However, when its particle size is greater than 200 nm, the particles can settle in the solution. Thus, the particle size (average diameter) of colloidal silica is preferably 200 nm or less, and more preferably 170 nm.

[00175] When the particle size of colloidal silica is less than 100 nm, although the dispersion is not affected, the production cost increases. Thus, the colloidal silica particle size is preferably 100 nm or more, more preferably 150 nm or more, from an economic point of view.

[00176] The insulating film is formed by the following. For example, the solution for forming the insulating coating is applied to the surface of the steel sheet by the dry application method such as roller coating, and it is baked at 800 to 900°C for 10 to 60 seconds in the air atmosphere.

Second modality

[00177] Next, an oriented grain electrical steel sheet according to the second embodiment and its production method are explained. Explanation of the same characteristics as those of the oriented grain electrical steel sheet according to the first embodiment is omitted in detail.

[00178] The grain-oriented electrical steel sheet according to the second embodiment includes: a base steel sheet; an intermediate layer which is disposed in contact with the base steel sheet and which includes a silicon oxide as a main component; and an insulating coating that is disposed in contact with the intermediate layer and that includes a phosphate and a colloidal silica as main components, where

[00179] the base steel sheet includes: as a chemical composition, in % by mass,

[00180] 0.085% or less of C;

[00181] 0.80 to 7.00% Si;

[00182] 0.05 to 1.00% Mn;

[00183] 0.010 to 0.065% Al;

[00184] 0.012% or less of N;

[00185] 0.015% or less of Seq = S + 0.406 ■ If;

[00186] 0.0005 to 0.0080% of B; It is

[00187] the balance consisting of Fe and impurities, and

[00188] The base steel sheet includes a composite B whose main axis length is from 1 to 20 μm and whose numerical density is from 1x10 to 1x106 parts/mm3.

[00189] In the grain oriented electric steel sheet according to the present modality,

[00190] when the total thickness of the base steel sheet and the intermediate layer is referred to as d, when an emission intensity of B at a depth of d/2 from a surface of the intermediate layer in a case where an intensity emission intensity of B is measured by glow discharge emission spectroscopy (GDS) from the surface of the buffer layer is referred to as IB (d/2), and when an emission intensity of B at a depth of d/10 from of the surface of the middle layer is referred to as IB (d/10),

[00191] the IB (d/2) and the IB (d/10) can satisfy expression (5) below.

[00192] I B (d/2) > IB (d/10) •••(5)

[00193] Although the grain-oriented electrical steel sheet according to the first embodiment includes the glassy film between the base steel sheet and the insulating coating, the grain-oriented electrical steel sheet according to the second embodiment includes the layer intermediate between the base steel sheet and the insulating coating.

middle layer

[00194] The grain-oriented electrical steel sheet according to the present embodiment includes the intermediate layer that is formed in contact with the base steel sheet and which includes silicon oxide as the main component.

[00195] The silicon oxide which is the main component of the intermediate layer is preferably SiOα (α = 1.0 to 2.0). When α = 1.5 to 2.0, silicon oxide becomes more stable, which is preferable. It is possible to form SiO2 with α ~ 2.0 by conducting sufficient oxidation annealing to form silicon oxide on the surface of the steel sheet.

Distribution of B identified by GDS

[00196] In the distribution of B in the direction of the depth of the steel sheet, the fact that the concentration of B (intensity) in the surface region of the base steel sheet is greater than the concentration of B (intensity) in the central region of the base steel plate indicates that the thin BN exists in the surface region of the base steel plate. In the above case, iron loss increases, which is not preferable.

[00197] Thus, when a total thickness of the base steel sheet and the intermediate layer is referred to as d, when an emission intensity of B at a depth of d/2 from the surface of the intermediate layer in a case where a emission intensity of B is measured by glow discharge emission spectroscopy (GDS) from the surface of the buffer layer is referred to as IB (d/2), and an emission intensity of B at a depth d/10 from of the surface of the middle layer is referred to as IB (d/10),

[00198] It is preferred that the IB (d/2) and the IB (d/10) satisfy expression (6) below.

[00199] IB (d/2) > IB (d/10) •••(6)

[00200] The total thickness d of the base steel plate and the intermediate layer is measured as follows. For grain-oriented electrical steel sheet that is produced by the production method described below, the insulating coating is removed using an alkaline aqueous solution such as sodium hydroxide. By removal as described above, the steel sheet becomes the state that only the middle layer is disposed on the base steel sheet, and then the total thickness d of the base steel sheet and the middle layer is measured with a micrometer or a thickness gauge.

production method

[00201] In the method for producing grain-oriented electrical steel sheet according to the first embodiment, the annealing separator that includes magnesia as the main component is applied to the steel sheet after nitriding, final annealing is conducted, and thus the glassy film which includes forsterite is formed on the surface of the base steel sheet. On the other hand, in the method for producing the grain-oriented electrical steel sheet according to the second embodiment, the glassy film which is formed by the above method is removed by pickling, grinding, and the like. After the above removal, it is preferred that the surface of the steel sheet be smoothed by chemical polishing or electrochemical polishing.

[00202] Alternatively, instead of magnesia, it is possible to use the annealing separator that includes alumina as the main component. The above annealing separator can be applied and dried, the steel sheet can be coiled after drying, and the final annealing (secondary recrystallization) can be conducted. By the above final annealing, it is possible to produce grain-oriented electrical steel sheet in which the formation of inorganic film such as forsterite is suppressed. After the above production, it is preferable that the surface of the steel sheet be smoothed by chemical polishing or electrochemical polishing.

Intermediate layer formation annealing

[00203] In the grain-oriented electrical steel sheet production method according to the second embodiment, the final annealing is conducted by the method mentioned above, and subsequently the intermediate layer forming annealing is conducted.

[00204] Annealing is conducted to the grain-oriented electrical steel sheet on which the inorganic film such as forsterite is removed or the grain-oriented electrical steel sheet on which the formation of the inorganic film such as forsterite is suppressed, and thus , the intermediate layer which includes silicon oxide as the main component is formed on the surface of the base steel sheet.

[00205] The annealing atmosphere is preferably a reducing atmosphere so that the inside of the steel sheet is not oxidized. In particular, an atmosphere of nitrogen mixed with hydrogen is preferable. For example, an atmosphere in which the hydrogen : nitrogen ratio is 75% : 25% and the dew point is -20 to 0°C is preferable.

[00206] Except for the production conditions described above, the method for producing the grain-oriented electrical steel sheet according to the second embodiment is the same as the method for producing the grain-oriented electrical steel sheet according to the first modality. Also the treatment of refining the magnetic domain is the same as that of the first embodiment. The magnetic domain refining treatment can be conducted before final annealing, after final annealing, or after forming the insulating coating.

Examples

[00207] Hereinafter, the examples of the present invention are explained. However, the conditions in the examples is an example condition employed to confirm the operability and effects of the present invention, so the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

Example 1

[00208] The steel plate whose chemical composition was shown in Table 1-1 was heated to 1150°C. The steel plate was hot-rolled to obtain the hot-rolled steel plate whose thickness was 2.6 mm. The hot rolled steel sheet was subjected to hot strip annealing in which the hot rolled steel sheet was annealed at 1100°C and then annealed at 900°C. The steel sheet after hot strip annealing was cold rolled once or it was cold rolled several times with intermediate annealing to obtain the cold rolled steel sheet whose thickness was 0.22mm. Table 1-1

[00209] The cold-rolled steel sheet with a final thickness of 0.22 mm was subjected to decarburizing annealing in which the immersion was conducted at 860°C in a humid atmosphere. Nitriding (annealing to increase the nitrogen content of the steel sheet) was conducted for the steel sheet after the decarburizing annealing. The annealing separator which included magnesia as the main component was applied to the steel sheet after nitriding, and then the steel sheet was kept at 1200°C for 20 hours in an atmosphere of hydrogen gas. The steel sheet after being maintained was cooled at 40°C/hour in the temperature range of 1200 to 1000°C and at 20°C/hour in the temperature range of 1000°C to 600°C. At that time, the atmosphere during cooling was 100% H2 in the temperature range of 1200 to 600°C, and was 100% N2 in the temperature range of less than 600°C.

[00210] Excess magnesia was removed from the steel sheet after being annealed, and then the insulating coating which included phosphate and colloidal silica as the main components was formed on the forsterite film (glass film) to obtain the final product.

[00211] The chemical composition of the base steel sheet in the product is shown in Table 1-2. Table 1-2

Magnetic domain control

[00212] To control the magnetic domain, mechanical treatment, laser irradiation, electron beam irradiation and the like were conducted. Some steel sheets were subjected to control of the magnetic domain in which the groove was made by chemical etching and laser irradiation.

B compound type

[00213] A flat specimen was taken by FIB from a region that includes compound B observed in section C of the steel plate, and then the precipitate was identified based on the diffraction pattern of electron beams from the transmission electron microscope . As a result it was identified from JCPDS cards that the precipitate was either Fe2B or Fe3B.

Numerical density of compound B

[00214] The number density of compound B was determined by analysis of mapping the concentration of B with EPMA at a step size of 1 μm in a region of 2 mm in the lamination direction x 2 mm in the width direction in a parallel plane to the rolling direction of the steel sheet.

[00215] The numerical density of compound B was determined by mapping the concentration of B with EPMA in the plane parallel to the rolling direction of the steel sheet. For example, the number density was determined by analyzing the region of 2 mm in the roll direction x 2 mm in the width direction at a step size of 1 µm.

Composite B main shaft length

[00216] Compound B identified by the above mapping was observed directly by SEM at a magnification of 1000 times to 5000 times, for example, and then the average principal axis length was determined from the principal axis lengths of B compounds of 20 parts or more. GDS (IB_t (center) / IB_t (surface))

[00217] Before conducting the GDS measurement, the insulating coating was removed using an aqueous alkaline solution such as sodium hydroxide, and the glassy film was removed using hydrochloric acid, nitric acid, and the like. The steel sheet after the above removal was subjected to glow discharge emission spectroscopy (GDS). When a measured emission intensity of B was referred to as IB, when a spray time to reach the central region was referred to as t (center), when a spray time to reach the surface region was referred to as t (surface), when an emission intensity of B at time t (center) was referred to as I B_t (center), and when an emission intensity of B at time t (surface) was referred to as I B_t (surface), IB_t (center) and IB_t (surface) were measured, and then the ratio I B_t (center) / IB_t (surface) was calculated. At that time, t (surface) was 300 to 400 seconds, and t (center) was 400 to 900 seconds.

magnetic characteristics Magnetic Flux Density B8

[00218] As the grain-oriented electrical steel sheet obtained by the above production method, the B8 magnetic flux density (magnetized magnetic flux density at 800 A/m) was measured by the single sheet tester (SST) method.

Iron loss W17/50

[00219] The test specimens (for example, 100 mm x 500 mm test specimen) were taken from the grain-oriented electric steel sheets before the magnetic domain control and after the magnetic domain control, and then the loss of W17/50 iron (unit : W/kg) which was the energy loss per unit weight was measured under excitation conditions such as a magnetic flux density of 1.7 T and a frequency of 50 Hz.

[00220] The structural characteristics and characteristics of the examples of the invention and the comparative examples are shown in Table 2. In the examples of the invention C1 to C15, which satisfy the conditions of the invention, the grain-oriented electrical steel sheets with excellent magnetic characteristics were obtained compared to the comparative examples. Table 2

Example 2

[00221] The grain-oriented electrical steel sheet (final product) was produced by the same method as in Example 1. To control the magnetic domain, mechanical treatment, laser irradiation, electron beam irradiation, and the like were conducted for the product.

[00222] In D6, the control of the magnetic domain was conducted before the final annealing. In D7, the magnetic domain control was conducted after the final annealing and before the formation of the insulating coating. In D8, the steel sheet was held at 1200°C for 20 hours, cooled at 5°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. In D9, the steel sheet was held at 1200°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 5°C/hour in the temperature range from 1000 to 600°C. In D10, the steel sheet was held at 120°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. In addition, the cooling atmosphere from D6 to D9 was the same as that from D1 to D5. In D10, the cooling atmosphere in the temperature range 1200 to 600°C was 100% Ar, and the cooling atmosphere in the temperature range less than 600°C was 100% N2. Except for the above conditions, D6 to D10 were produced by the same production method as D1 to D5.

[00223] In d1, the plate was heated to 1270°C, and then subjected to hot rolling. At d2, the plate was heated to 1300°C and then subjected to hot rolling. At d3, the annealing separator was applied, and then annealing was conducted at 1200°C for 3 hours in an atmosphere of hydrogen gas. At d4, the annealing separator was applied, and then annealing was conducted at 1200°C for 5 hours in an atmosphere of hydrogen gas. At d5, the steel sheet was held at 1200°C for 20 hours, cooled at 60°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. At d6, the steel sheet was held at 1200°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 40°C/hour in the temperature range from 1000 to 600°C.

[00224] Except for the above conditions, d1 to d6 were produced by the same production method as D1 to D5.

[00225] The structural characteristics and characteristics of the examples of the invention and comparative examples are shown in Table 3. At that time, t (surface) was 300 to 400 seconds, and t (center) was 400 to 900 seconds. Table 3

[00226] In the examples of the invention D1 to D10 in which the emission intensity of B IB_t (center) to the central region and the emission intensity of B IB_t (surface) to the surface region satisfied expression (1) above, Grain-oriented electrical steel sheets with excellent magnetic characteristics were obtained. On the other hand, in d1 to d6 in which any production condition was outside the range described above, the magnetic characteristics were insufficient.

Example 3

[00227] The steel plate whose chemical composition was shown in Table 4-1 was heated to 1150°C. The steel plate was hot-rolled to obtain the hot-rolled steel plate whose thickness was 2.6 mm. The hot rolled steel sheet was subjected to hot strip annealing in which the hot rolled steel sheet was annealed at 1100°C and then annealed at 900°C. The steel sheet after hot strip annealing was cold rolled once or cold rolled several times with intermediate annealing to obtain the cold rolled steel sheet whose thickness was 0.22mm. Table 4-1

[00228] The cold-rolled steel sheet with a final thickness of 0.22 mm was subjected to decarburizing annealing in which the immersion was conducted at 860°C in a humid atmosphere. Nitriding (annealing to increase the nitrogen content in the steel sheet) was conducted for the steel sheet after the decarburizing annealing. The annealing separator which included alumina as the main component was applied to the steel sheet after nitriding, and then the steel sheet was kept at 1200°C for 20 hours in an atmosphere of hydrogen gas. The steel sheet after being maintained was cooled at 40°C/hour in the temperature range of 1200 to 1000°C and by 20°C/hour in the temperature range of 1000 to 600°C. At that time, the atmosphere during cooling was 100% H2 in the temperature range of 1200 to 600°C and 100% N2 in the temperature range of less than 600°C.

[00229] Excess alumina was removed from the steel sheet after being annealed, and then the insulating coating which included phosphate and colloidal silica as the main components was formed on the steel sheet to obtain the final product.

[00230] The chemical composition of the base steel sheet in the product is shown in Table 4-2. Table 4-2

Magnetic domain control

[00231] To control the magnetic domain, mechanical treatment, laser irradiation, electron beam irradiation and the like were conducted. Some steel sheets were subjected to control of the magnetic domain in which the groove was made by chemical etching and laser irradiation.

[00232] As for the examples of the invention and comparative examples, the type, numerical density, and length of the main axis of compound B were determined by the same methods as in Examples 1 and 2. In addition, the magnetic characteristics were measured by the same methods as in the Examples 1 and 2. GDS (I B (d/2) / IB (d/10))

[00233] When a total thickness of the base steel sheet and the intermediate layer was referred to as d, when an emission intensity of B at a depth of d/2 from the surface of the intermediate layer in a case where an intensity of emission of B is measured by a glow discharge emission spectroscopy (GDS) from the surface of the buffer layer was referred to as IB (d/2), and when an emission intensity of B at a depth of d/10 from of the surface of the intermediate layer was referred to as IB (d/10), IB (d/2) and IB (d/10) were measured, and then the ratio IB (d/2) / IB (d/10) was calculated .

[00234] The total thickness d of the base steel plate and the intermediate layer was measured with a micrometer or a thickness gauge.

[00235] To determine “the depth d/2 from the surface of the intermediate layer”, and “the depth d/10 from the surface of the intermediate layer”, the point at which the spraying of Ar was stable between 1 to 10 seconds was defined as the surface of the middle layer. Subsequently, based on the d determined by the above method using the surface of the intermediate layer defined above, “the depth d/2 from the surface of the intermediate layer” and “the depth d/10 from the surface of the intermediate layer” were determined .

[00236] The structural characteristics and characteristics of the examples of the invention and the comparative examples are shown in Table 5. In the examples of the invention G1 to G15 that satisfied the conditions of the invention, the grain-oriented electric steel sheets with excellent magnetic characteristics were obtained in comparison to the comparative examples. Table 5

Example 4

[00237] The grain oriented electrical steel sheet (final product) was produced by the same method as in Example 3. To control the magnetic domain, mechanical treatment, laser irradiation, electron beam irradiation, and the like were conducted to the product.

[00238] In H6, the control of the magnetic domain was conducted before the final annealing. In H7, the control of the magnetic domain was carried out after the final annealing and before the formation of the insulating coating. In H8, the steel sheet was held at 1200°C for 20 hours, cooled at 5°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. In H9, the steel sheet was held at 1200°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 5°C/hour in the temperature range from 1000 to 600°C. In H10, the steel sheet was held at 1200°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. In addition, the cooling atmosphere from H6 to H9 was the same as that from H1 to H5. In H10, the cooling atmosphere in the temperature range 1200 to 600°C was 100% Ar, and the cooling atmosphere in the temperature range less than 600°C was 100% N2. Except for the above conditions, H6 to H10 were produced by the same production method as H1 to H5.

[00239] In h1, the plate was heated to 1270°C and then subjected to hot rolling. In h2, the plate was heated to 1300°C and then subjected to hot rolling. In h3, the annealing separator was applied, and then the annealing was conducted at 1200°C for 3 hours in an atmosphere of hydrogen gas. In h4, the annealing separator was applied, and then the annealing was conducted at 1200°C for 5 hours in a hydrogen gas atmosphere. In h5, the steel sheet was held at 1200°C for 20 hours, cooled at 60°C/hour in the temperature range 1200 to 1000°C, and then cooled at 20°C/hour in the temperature range from 1000 to 600°C. In h6, the steel sheet was held at 1200°C for 20 hours, cooled at 40°C/hour in the temperature range 1200 to 1000°C, and then cooled at 40°C/hour in the temperature range from 1000 to 600°C.

[00240] Except for the above conditions, h1 to h6 were produced by the same production method as H1 to H5.

[00241] The structural characteristics and characteristics of the examples of the invention and the comparative examples are shown in Table 6. Table 6

[00242] In H1 to H10, grain-oriented electrical steel sheets with excellent magnetic characteristics were obtained. On the other hand, in h1 to h6 in which some production condition was outside the range described above, the magnetic characteristics were insufficient.

Industrial applicability.

[00243] According to the above aspects of the present invention, it is possible to industrially and stably supply the grain oriented electrical steel sheet in which hysteresis loss and iron loss are reduced by proper control of the precipitation morphology of compound B , in grain-oriented electrical steel sheet (final product) that uses B as an inhibitor and that has a high magnetic flux density. Consequently, the present invention has applicability in the industrial field of grain-oriented electrical steel sheet.

Claims (3)

1. Grain-oriented electrical steel sheet, characterized in that it comprises: a base steel sheet; a lower layer which is disposed in contact with the base steel plate; and an insulating coating which is disposed in contact with the bottom layer and which includes a phosphate and a colloidal silica as major components, wherein the base steel sheet includes, as a chemical composition, by mass %, 0.085% or less of C ; 0.80 to 7.00% Si; 0.05 to 1.00% Mn; 0.010 to 0.065% Al; 0.0040% or less N; 0.015% or less of Seq = S + 0.406-Se; 0.0005 to 0.0080% B; and the balance consisting of Fe and impurities, wherein the base steel sheet includes a compound B whose major axis length is from 1 to 20 μm and whose number density is from 1x10 to 1x106 pieces/mm3, wherein the bottom layer is a glassy film comprising a forsterite as a major component or an intermediate layer comprising a silicon oxide as a major component, and wherein compound B is at least one selected from the group consisting of Fe2B and Fe3B. 2. Grain-oriented electrical steel sheet according to claim 1, characterized in that the lower layer is the glassy layer, and when a glow discharge emission spectroscopy is conducted after removing the insulating coating and the glassy film , when a region that is one side of the glassy film from the center of the thickness of the base steel sheet is divided into two regions that are the surface region of the on the glassy film side and the central region between the surface region and the thickness center, when a spray time to reach the center region is referred to as t (center), when a spray time to reach the surface region is referred to as t (surface), when an emission intensity of B at t (center) is referred to as IB_t (center), and when an emission intensity of B at t (surface) is referred to as IB_t (surface), the IB_t (center) and the IB_t (surface) satisfy expression (1) a then lB_t (center) > lB_t (surface) •••(1). 3. Grain-oriented electrical steel sheet according to claim 1, characterized in that the lower layer is the middle layer, and when a total thickness of the base steel sheet and the middle layer is referred to as d, when a emission intensity of B at a depth of d/2 from the surface of the buffer layer in a case where an emission intensity of B is measured by glow discharge emission spectroscopy from the surface of the buffer layer is referred to as IB (d/2), and when an emission intensity of B at a depth of d/10 from the surface of the intermediate layer is referred to as IB (d/10), the IB (d/2) and the IB ( d/10) satisfy expression (2) below, IB (d/2) > IB (d/10) •••(2).