JP2022060749A - Production method of directional electromagnetic steel sheet - Google Patents

Abstract

To provide a production method of a directional electromagnetic steel sheet, by which a directional electromagnetic steel sheet having little film defect and low iron loss can be produced.SOLUTION: To solve the problem, according to one aspect of the present invention, provided is a method for producing a directional electromagnetic steel sheet, which includes: a cold rolling step for producing a cold rolled steel sheet; a finish annealing step for performing finish annealing to induce secondary recrystallization on the cold rolled steel sheet; a groove forming step for forming grooves in a linear shape in a direction crossing the rolling direction of the cold rolled steel sheet before or after the finish annealing step; and a tension imparting step for forming a tensile film on the groove formed surface of the cold rolled steel sheet by applying and baking a coating solution containing a compound of phosphoric acid, phosphate, chromic anhydride, chromate, alumina or silica while the groove formed surface of the cold rolled steel sheet is directed downward.SELECTED DRAWING: Figure 1

Description

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

Electrical steel sheets are used in many electrical devices as magnetic steel cores. The grain-oriented electrical steel sheet is a steel sheet containing 0.8% to 4.8% of Si and whose crystal orientation of the product is highly concentrated in the {110} <001> orientation. As its magnetic characteristics, it is required that the magnetic flux density represented by the B8 value is high and the iron loss represented by _W17 / 50 is low. In particular, recently, there is an increasing demand for reduction of power loss from the viewpoint of energy saving.

In response to this demand, a technique for subdividing magnetic domains has been developed as a means for reducing iron loss in grain-oriented electrical steel sheets. Hereinafter, such a technique, that is, a technique for subdividing a magnetic domain, may be referred to as a "magnetic domain control technique", and the effect of the magnetic domain control technique may also be referred to as a "magnetic domain control effect".
For example, Patent Document 1 discloses a method of subdividing magnetic domains and reducing iron loss by irradiating a steel sheet after finish annealing with a laser beam. However, since the reduction of iron loss by this method is due to the strain introduced by laser irradiation, it cannot be used for a wound core transformer that requires strain relief annealing (SRA) after molding the transformer.

That is, the wound core transformer mainly used for small and medium-sized transformers is often manufactured by, for example, a method of manufacturing an iron core by mechanical bending. In this manufacturing method, strain removing annealing (for example, about 2 to 4 hours at 800 ° C.) is generally performed in order to eliminate the deterioration of iron loss due to the processing strain introduced by the bending process. By such strain removing annealing, the strain introduced for the subdivision of the magnetic domain disappears. Therefore, the method of subdividing the magnetic domain by introducing strain cannot be applied to the wound iron core transformer.

As the SRA magnetic domain control technology that does not lose the magnetic domain control effect even if the strain removal annealing as described above is performed, the "groove introduction type magnetic domain control technology" that periodically forms linear grooves in the direction intersecting the rolling direction. Is widely known. As such a groove-introduced magnetic domain control technique, a groove forming technique by machining, a groove forming technique by etching, a groove forming technique by laser irradiation, and the like are known. For example, Patent Document 2 discloses a groove forming technique by laser irradiation. However, these groove forming methods alone do not sufficiently meet the increasing demand for iron loss improvement in recent years.

On the other hand, as disclosed in Patent Document 3, a technique for forming an insulating film on the surface (that is, the groove-forming surface) of a steel sheet in which a groove is formed has been proposed. Specifically, Patent Document 3 describes that an insulating film made of colloidal silica and magnesium phosphate is formed on the groove-forming surface of a steel sheet.

Special Publication No. 58-26405 Japanese Patent No. 4384451 Japanese Patent No. 5742294

However, it has been found that when an insulating film is formed as in the technique disclosed in Patent Document 3, insulation may be insufficient due to film defects and iron loss may not be sufficiently improved.

The present invention has been made in view of the above problems, and an object of the present invention is to produce a grain-oriented electrical steel sheet having few film defects and low iron loss. The purpose is to provide a manufacturing method.

Aspects of the present invention are as follows.
(1) One aspect of the present invention is a cold rolling step for manufacturing a cold-rolled steel sheet, a finish-baking step for performing a finish-brinking of the cold-rolled steel sheet with secondary recrystallization, and a pre- or post-finish baking step. A groove forming step of forming a linear groove in a direction intersecting the rolling direction of the cold-rolled steel sheet with respect to the cold-rolled steel sheet, and phosphoric acid in a state where the groove-forming surface of the cold-rolled steel sheet is directed downward. A tension film applying step of forming a tension film on a groove-forming surface by applying and baking a coating solution containing a compound of a phosphate, chromic anhydride, chromate, alumina, or silica. This is a method for manufacturing a directional electromagnetic steel sheet.

(2) In the method for manufacturing a grain-oriented electrical steel sheet according to (1) above, in the tension coating applying step, the thickness of the tension coating formed inside the groove is 1/2 or less of the depth of the groove, and The thickness of the tension film may be adjusted so as to be at least twice the thickness of the tension film formed on the flat surface of the cold-rolled steel sheet.

(3) In the method for manufacturing a directional electromagnetic steel sheet according to (1) or (2) above, an annealing separator is applied to the cold-rolled steel sheet after the cold rolling step and before the finish annealing step. The annealing separating agent may further include a step of applying the annealing separating agent, and the annealing separating agent may contain magnesia.

According to the above aspect of the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having few film defects and low iron loss.

It is a flowchart for demonstrating an example of the manufacturing method of the grain-oriented electrical steel sheet which concerns on this Embodiment. It is a top view which shows the groove formed in the finished annealed steel sheet. It is a schematic cross-sectional view for demonstrating the structure in the vicinity of the groove of the grain-oriented electrical steel sheet. It is a schematic cross-sectional view for demonstrating the structure in the vicinity of the groove of the grain-oriented electrical steel sheet which concerns on the modification. It is a schematic cross-sectional view for demonstrating the manufacturing method of the grain-oriented electrical steel sheet which concerns on this Embodiment, particularly the tension film applying process. It is a schematic cross-sectional view for demonstrating the problem of the manufacturing method of the conventional grain-oriented electrical steel sheet. It is an SEM photograph for demonstrating the problem of the manufacturing method of the conventional grain-oriented electrical steel sheet.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value. "%" Means mass% unless otherwise specified.

The present inventors have repeatedly studied techniques for forming an insulating film on the groove-forming surface of a steel sheet. Here, the insulating coating is intended to reduce iron loss by applying tension to the surface of the steel sheet. From this point of view, the insulating coating in this embodiment may also be referred to as a tension coating.

For example, as disclosed in Patent Document 3, a technique itself for forming an insulating film on a groove-forming surface of a steel sheet already exists. However, with the techniques proposed so far, insulation may be insufficient due to film defects of grain-oriented electrical steel sheets, and iron loss cannot be sufficiently reduced.

The present inventors considered that the reason was the process of forming the insulating film. Details will be described later, but in the past, the coating solution was applied to the groove-forming surface with the groove-forming surface of the steel sheet "facing upward" and baked. Therefore, the coating solution tends to collect in the groove. That is, a part of the coating solution applied to the groove forming surface stays inside the groove in a liquid pooled state. When baking is performed in this state, the insulating film inside the groove is formed thicker than the insulating film on the other portion (so-called flat surface).

As described above, the insulating film inside the groove tends to be formed excessively thicker than the insulating film on the flat surface. Then, the insulating film formed excessively thick is easily peeled off from the steel plate which is the base material. That is, it is considered that the insulating film formed inside the groove is easily peeled off, and as a result, the insulation is insufficient and the iron loss cannot be sufficiently reduced.

By the way, in the directional electromagnetic steel plate in which the groove is formed, the magnetic flux that reaches one of the groove walls through the steel plate leaks from the magnetic domain wall (that is, due to the leakage of the magnetic flux), so that the static magnetic energy increases, and this static energy. The subdivision of the main magnetic domain in order to reduce the magnetic flux is the cause of the magnetic domain control effect. However, in a state where tension is not applied to the steel sheet, a reflux type magnetic domain is generated in the vicinity of the groove wall surface, the increase in the static magnetic energy described above is suppressed, and a sufficient magnetic domain control effect is not exhibited. Since the reflux magnetic domain becomes energetically unstable due to the isotropic tension due to the insulating film (due to the adverse effect of magnetostriction), the leakage of magnetic flux is restored and the magnetic domain control effect is improved. It is considered that the insulating film formed thickly in the groove cannot give a sufficient tension effect to the steel sheet because it is easily peeled off, or it cannot give a stress in the direction of destabilizing the reflux magnetic domain to the steel sheet.

In particular, when the coating solution is applied to the groove-forming surface of the steel sheet, gravity causes the steel sheet to have a concave (in other words, downwardly convex) catenary on the upper surface side. In this case, a liquid pool is likely to be formed in the groove, and a thicker insulating film is formed inside the groove. Therefore, the insulating film formed inside the groove is easily peeled off, and the effect of reducing iron loss is greatly impaired.

Based on the above study, the present inventors can apply a coating solution to the groove-forming surface with the groove-forming surface of the steel sheet "downward" and perform baking, which is formed inside the groove. It has been found that it is effective for thinning the insulating coating to be formed, thereby producing a grain-oriented electrical steel sheet having few coating defects and low iron loss.

Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described with reference to the flowchart shown in FIG.
The flowchart shown in FIG. 1 is merely an example of the method for manufacturing grain-oriented electrical steel sheets according to the present embodiment, and may be arbitrarily changed as long as the effects of the present embodiment are not impaired.
That is, the method for manufacturing a directional electromagnetic steel sheet according to the present embodiment is at least a cold rolling step for manufacturing a cold-rolled steel sheet and a finish shrinking step for performing finish annealing with secondary recrystallization on the cold-rolled steel sheet. A groove forming step of forming a linear groove in a direction intersecting the rolling direction of the cold-rolled steel sheet with respect to the cold-rolled steel sheet before or after the finish annealing step, and a groove forming surface of the cold-rolled steel sheet downward. A tension film is formed on the groove-forming surface by applying a coating solution containing a compound of phosphoric acid, phosphate, anhydrous chromic acid, chromate, alumina, or silica and baking it. It suffices to include a film applying step.

(Casting process S1)
In the casting step S1, a slab is prepared. An example of a method for manufacturing a slab is as follows. First, molten steel is manufactured (melted). Then, the slab is manufactured using molten steel. The method for producing the slab is not particularly limited, but the slab may be produced by, for example, a continuous casting method. The ingot may be manufactured using molten steel, and the ingot may be lump-rolled to produce a slab. The thickness of the slab is not particularly limited. The thickness of the slab may be, for example, 150 mm to 350 mm. The thickness of the slab is preferably 220 mm to 280 mm. As the slab, a so-called thin slab having a thickness of 10 mm to 70 mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling step S2.

The component composition of the slab may be any component composition that causes secondary recrystallization. The basic components and optional elements of the slab are as follows. The notation of% used for the component means mass%.

Si is an important element for increasing electrical resistance and reducing iron loss. If the content exceeds 4.8%, the material tends to crack during cold rolling, making rolling impossible. On the other hand, if the amount of Si is lowered, α → γ transformation occurs during finish annealing and the directionality of the crystal is impaired. Therefore, 0.8%, which does not affect the directionality of the crystal during finish annealing, may be set as the lower limit. Therefore, the Si content may be 0.8 to 4.8%.

Although C is an element effective in controlling the primary recrystallization structure in the manufacturing process, if the content in the final product is excessive, it may adversely affect the magnetic properties. Therefore, the C content may be 0.085% or less. The preferred upper limit of the C content is 0.080%. C is purified in the decarburization annealing step S5 and the finish annealing step S8 described later, and becomes 0.005% or less after the finish annealing step S8. When the slab contains C, the lower limit of the C content may be more than 0% or 0.001% in consideration of productivity in industrial production.

Acid-soluble Al is an element that functions as an inhibitor in the state of being combined with N to become AlN or (Al, Si) N. The content of the acid-soluble Al may be 0.012% to 0.050%, which increases the magnetic flux density.

If N is added in an amount of 0.01% or more during steelmaking, pores in the steel sheet called blister will be formed, so the upper limit of the N content may be 0.01%. Since N can be contained by nitriding in the middle of the manufacturing process, the lower limit is not particularly limited and may be 0%. However, since the detection limit of N is 0.0001%, the practical lower limit is 0.0001%.

Mn and S are precipitated as MnS and serve as inhibitors. If the Mn content is less than 0.02% and the S content is less than 0.005%, a predetermined amount of effective MnS inhibitor may not be secured. Further, if the Mn content is more than 0.3% and the S content is more than 0.04%, the solutionification at the time of slab heating becomes insufficient, and secondary recrystallization may not be performed stably. .. Therefore, the Mn content may be 0.02 to 0.3%, and the S content may be 0.005 to 0.04%.

B, Bi, Se, Pb, Sn, Ti and the like can also be added to the slab as other inhibitor constituent elements. The addition amount may be appropriately adjusted, the upper limit of the B content is 0.080%, the upper limit of the Bi content is 0.010%, the upper limit of the Se content is 0.035%, and the Pb content. The upper limit may be 0.10%, the upper limit of Sn content may be 0.10%, and the upper limit of Ti content may be 0.015%. Since these optional additive elements may be contained in the slab according to a known purpose, it is not necessary to set a lower limit value for the content of the optional additive element, and for example, the lower limit value may be 0%.

The rest of the chemical composition of the slab consists of Fe and impurities. The "impurity" referred to here is a component mixed in the slab due to raw materials such as ore and scrap, and various factors in the manufacturing process when the slab is industrially manufactured, and is a direction according to the present embodiment. It means that it is permissible as long as it does not substantially affect the electromagnetic steel sheet.

In addition to solving manufacturing problems, the slab may contain (add) any known element instead of a part of Fe in consideration of the enhancement of the inhibitor function by compound formation and the influence on the magnetic properties. good. Examples of the optional element contained in the slab instead of a part of Fe include Cu, P, Sb, Cr, Ni and the like. Any one or more of these may be added to the slab. The upper limit of Cu content is 0.40%, the upper limit of P content is 0.50%, the upper limit of Sb content is 0.10%, the upper limit of Cr content is 0.30%, and Ni content. The upper limit of the amount may be 1.00%. Since these optional additive elements may be contained in the slab according to a known purpose, it is not necessary to set a lower limit value for the content of the optional additive element, and the lower limit value may be 0%.

The chemical composition of the slab can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrum). Specifically, the chemical composition is specified by measuring a 35 mm square test piece collected from a slab with an ICPS-8100 manufactured by Shimadzu Corporation (measuring device) under conditions based on a calibration curve prepared in advance. .. In addition, C and S can be measured by using the combustion-infrared absorption method, and N can be measured by using the inert gas melting-heat conductivity method.

(Hot rolling step S2)
The hot rolling step S2 is a step of hot rolling a slab heated to a predetermined heating temperature (for example, 1100 ° C. to 1400 ° C.) to obtain a hot-rolled steel sheet. The heating temperature during hot rolling may be, for example, 1100 ° C. or higher from the viewpoint of ensuring the temperature during hot rolling, and further, 1280 ° C. or lower from the viewpoint of not completely dissolving AlN, which is an inhibitor component. You may. When AlN and MnS are the main inhibitors, the heating temperature during hot rolling may be 1300 ° C. or higher at which these inhibitor components are completely dissolved.

(Hot-rolled steel sheet annealing process S3)
The hot-rolled steel sheet annealing step S3 is a step of immediately or in a short time annealing the hot-rolled steel sheet obtained in the hot-rolling step S2 to obtain an annealed steel sheet. Annealing may be carried out in a temperature range of 750 ° C to 1200 ° C for 30 seconds to 30 minutes. This annealing is effective for enhancing the magnetic properties of the product.

(Cold rolling step S4)
In the cold rolling step S4, the annealed steel sheet obtained in the hot-rolled steel sheet annealing step S3 is cold-rolled once or cold-rolled a plurality of times (twice or more) via annealing (intermediate annealing) (for example). It is a process of obtaining a cold-rolled steel sheet by a total cold-rolling rate of 80% to 95%). The thickness of the cold-rolled steel sheet may be, for example, 0.10 mm to 0.50 mm.

(Decarburization annealing step S5)
In the decarburization annealing step S5, the cold-rolled steel sheet obtained in the cold rolling step S4 is decarburized and annealed to obtain a decarburized annealed steel sheet (cold-rolled steel sheet subjected to the decarburization annealing step) in which primary recrystallization has occurred. Is. Decarburization annealing may be performed, for example, at 700 ° C to 900 ° C for 1 to 3 minutes.

By decarburizing and annealing the cold-rolled steel sheet, the C component contained in the cold-rolled steel sheet is removed. The decarburization annealing is preferably performed in a moist atmosphere in order to remove the C component contained in the cold-rolled steel sheet.

(Nitriding process S6)
The nitriding treatment step S6 is a step carried out as necessary in order to adjust the strength of the inhibitor in the secondary recrystallization. The nitriding treatment is a treatment for increasing the nitrogen content of the cold-rolled steel sheet by about 40 ppm to 200 ppm from the start of the decarburization annealing step to the start of secondary recrystallization in the finish annealing step. The nitriding treatment includes, for example, a treatment of annealing a decarburized annealed steel sheet in an atmosphere containing a nitriding gas such as ammonia, and an annealing separating agent containing a nitriding powder such as MnN, which will be described later. Examples thereof include a process of applying to a decarburized annealed steel sheet in step S7.

(Annealing Separator Coating Step S7)
The annealing separation agent application step S7 is a step of applying the annealing separation agent to the decarburized and annealed steel sheet. As the annealing separator, for example, an annealing separator containing alumina (Al ₂ O ₃ ) as a main component can be used. The decarburized annealed steel sheet after the annealing separating agent is applied is finished-annealed in the next finish-annealing step S8 in a coiled state.
When forming a glass film containing Mg ₂ SiO ₄ , an annealing separator containing magnesia (MgO) as a main component is used.

(Finishing annealing step S8)
The finish annealing step S8 is a step of subjecting the decarburized annealed steel sheet coated with the annealing separator to finish annealing to generate secondary recrystallization. In the finish annealing step S8 accompanied by this secondary recrystallization, the {100} <001> oriented grains are preferentially grown and the magnetic flux is generated by advancing the secondary recrystallization in a state where the growth of the primary recrystallized grains is suppressed by the inhibitor. Dramatically improve the density.
When magnesia (MgO) is applied in the above-mentioned annealing separator application step S7, a glass film containing Mg ₂ SiO ₄ is formed by this finish annealing step S8. In this embodiment, such a glass coating is also included in the base steel sheet (finished annealed steel sheet described later). Therefore, for example, when a glass film is formed on a finished annealed steel sheet, the "surface of the finished annealed steel sheet" means the surface of the glass film. By forming the glass film, it is expected that the characteristics of the grain-oriented electrical steel sheet 200 will be further enhanced.

(Groove forming step S9)
The groove forming step S9 is a step of forming a groove in the steel sheet (finished annealed steel sheet) after the finish annealing step S8 for the purpose of magnetic domain control (magnetic domain subdivision). The groove can be formed by a known method such as laser, electron beam, plasma, mechanical method, or etching.

An example of the groove forming step S9 will be described with reference to FIGS. 2, 3, and 4. 2 is a plan view showing a groove G formed in the finished annealed steel sheet (base steel sheet) 110, and FIG. 3 is a schematic cross section for explaining a configuration in the vicinity of the groove G of the grain-oriented electrical steel sheet 200. It is a figure. FIG. 4 is a schematic cross-sectional view showing a modified example of the grain-oriented electrical steel sheet 200. The cross section of FIGS. 3 and 4 is a cross section perpendicular to the extending direction of the groove G.

In FIG. 2, the rolling direction of the finish-annealed steel sheet 110 is the X-axis, the width direction of the finish-annealed steel sheet 110 is the Y-axis, and the plate thickness direction of the finish-annealed steel sheet 110 is the Z-axis. The direction from the groove-forming surface 110a (the surface on which the groove G is formed; details will be described later) of the finished annealed steel sheet 110 to the other surface is the positive direction in the Z-axis direction. The same applies to the definitions of the XYZ axes shown in the other figures.

In FIG. 3, a finished annealed steel sheet 110 and an insulating coating (tension coating) 130 are drawn. That is, the grain-oriented electrical steel sheet 200 according to the present embodiment includes a finish-annealed steel sheet 110 and an insulating coating 130. The insulating coating 130 is formed on the groove forming surface 110a of the finished annealed steel sheet 110 by the tension coating applying step S10 described later.

As described above, the groove G is formed on the finished annealed steel sheet 110 by a known method such as laser, electron beam, plasma, mechanical method, and etching. Of the front and back surfaces of the finished annealed steel sheet 110, the surface on which the groove G is formed is also referred to as a groove forming surface 110a. Of the groove forming surface 110a, the portion where the groove G is not formed is referred to as a flat surface 110F.

The groove G is formed on the upper surface (upper surface) of the finished annealed steel sheet 110, not on the lower surface. However, in the tension film applying step S10, which will be described later, the coating solution is applied to the groove forming surface 110a with the groove G facing “downward”. Therefore, the groove G may be formed on the lower surface (lower surface) of the finished annealed steel sheet 110.

The form of the groove G is preferably in the following range in relation to the effect of the present embodiment. In order to specify the form of the groove G, it is necessary to observe the cross section of the groove G. In this case, an arbitrary cross section perpendicular to the stretching direction of the groove G may be formed into a mirror surface by machining, and this cross section may be observed as an observation cross section with a scanning electron microscope or the like.

From the viewpoint of reducing iron loss, the stretching direction of the groove G in the plan view is preferably in the range of 90 ° to 60 ° with respect to the X-axis direction (rolling direction), and is preferably in the range of 90 ° to 75 °. Is even more preferable.

If the stretching direction of the groove G is 60 ° or more with respect to the rolling direction X, the angle between the wall surface (groove wall surface) 110G of the groove G and the rolling direction becomes large, so that the effect of this embodiment can be achieved. The need to act increases. That is, since a larger amount of magnetic flux leaks from the groove G, it is necessary to make it easier for these magnetic fluxes to leak. That is, there is an increasing need to thin the insulating coating 130G inside the groove.

The pitch in the rolling direction of the groove G (rolling direction pitch) is preferably set in the range of 1 to 20 mm according to the necessity of subdividing the magnetic domain. It is more preferable to set the rolling direction pitch of the groove G in the range of 2 to 10 mm. It is more preferable that the upper limit of the rolling direction pitch of the groove G is 8 mm. It is more preferable that the upper limit of the rolling direction pitch of the groove G is 5 mm.

The rolling direction pitch may be measured by, for example, the following method. That is, attention is paid to a set of arbitrary grooves G adjacent to each other in a plan view. Then, the distance in the rolling direction between the center points in the width direction of the grooves G may be measured at several points, and the average value thereof may be used as the rolling direction pitch of the set of the grooves G. In the present embodiment, it is preferable that the arbitrary rolling direction pitch measured in this way is a value in the range of 2 to 10 mm.

The width w of the groove G is preferably 20 μm or more, and more preferably 30 μm or more. This is because when the width w is 20 μm or more, it is technically easy to control the thickness of the insulating coating 130G inside the groove.
The width w is the separation distance between the two flat surfaces 110F adjacent to each other in the rolling direction via the groove G in the direction perpendicular to the stretching direction of the groove G and the plate thickness direction (Z-axis direction).

The width w of the groove G is preferably 150 μm or less, and more preferably 90 μm or less. When the width w of the groove G is 150 μm or less, it is suitable from the viewpoint of subdividing the magnetic domain. Further, although it depends on the depth D of the groove G, the smaller the width w, the iron loss due to the angle difference between the magnetization direction of the grain-oriented electrical steel sheet 200 and the tension direction along the groove wall surface 110G due to the insulating coating 130G inside the groove. The problem of increase becomes remarkable. Therefore, the need for thinning the insulating coating 130 increases. Therefore, the width w of the groove G is preferably 150 μm or less.

The depth D of the groove G is preferably 5 μm or more, more preferably 15 μm or more. If the depth D is 5 μm or more, the iron loss increases due to the angle difference between the magnetization direction of the grain-oriented electrical steel sheet 200 and the tension direction along the groove wall surface 110G due to the insulating coating 130G inside the groove, although it depends on the width w. The problem becomes noticeable. Therefore, the need for thinning the insulating coating 130 increases. Therefore, the depth D of the groove G is preferably 5 μm or more.
The depth D is the distance (depth direction distance) in the plate thickness direction (Z-axis direction) from the bottom surface 110Ga of the groove G (the deepest part of the observation cross section of the groove G) to the flat surface 110F adjacent to the groove G. ).

The depth D of the groove G is preferably 50 μm or less, more preferably 30 μm or less. This is because when the depth D of the groove G is 50 μm or less, it is technically easy to control the thickness t2 of the insulating coating 130G inside the groove. Further, if the depth D of the groove G is more than 50 μm, the thickness of the finished annealed steel sheet 110 may be partially significantly reduced and the iron loss reducing effect may not be obtained.

The groove forming step S9 is performed after the finish annealing step S8 in the example shown in the flowchart of FIG. However, the groove forming step S9 may be performed on a steel sheet (that is, a cold-rolled steel sheet) that has undergone the cold rolling step S4. Even in this case, the cross-sectional shape of the linear groove G, which is ideal for subdividing the magnetic domain, can be maintained. Therefore, the timing of performing the groove forming step S9 may be before or after the finish annealing step S8. However, it is necessary to perform the groove forming step 9 at least before the tension film applying step S10.

In the modified example shown in FIG. 4, the finished annealed steel sheet 110 has a glass coating 150. The glass coating 150 contains Mg ₂ SiO ₄ . However, even in this case, the definition and determination method of the parameters (width w, depth D, etc.) related to the groove G do not change.

(Tension film applying step S10)
In the tension film applying step S10, the coating solution is applied and baked with the groove-forming surface 110a of the finished annealed steel sheet 110 facing “downward” to form an insulating film (tension film) 130 on the groove-forming surface 110a. It is a process to do.

Here, the coating solution contains, for example, a compound of phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or silica. The baking may be performed, for example, at 350 ° C to 1150 ° C for 5 seconds to 300 seconds.

In explaining the tension film applying step S10 of the present embodiment in detail, first, the problems of the conventional tension film applying process will be described with reference to FIGS. 6 and 7.

FIG. 6 shows an example of a conventional tension film applying process. In the example shown in FIG. 6, the finish-annealed steel sheet 110 is conveyed by the conveying roller 1000. Here, the groove forming surface 110a is directed upward. Then, the coating solution is applied to the groove-forming surface 110a from above the finish-annealed steel sheet 110 to perform baking. Therefore, it tends to accumulate in the coating solution in the groove G. That is, a part of the coating solution applied to the groove forming surface 110a stays inside the groove G in a liquid pooled state. When baking is performed in this state, the insulating coating 130G inside the groove is formed thicker than the insulating coating 130F of another portion (so-called flat surface 110F). FIG. 7 is an SEM photograph showing the cross-sectional structure of the grain-oriented electrical steel sheet 200 manufactured in the conventional tension film applying process. As can be seen from this SEM photograph, it can be seen that the insulating coating 130G inside the groove is formed thicker than the insulating coating 130F of the other portion (so-called flat surface 110F).

The insulating coating 130G inside the groove tends to be formed to be excessively thicker than the insulating coating 130F of the flat surface 110F, and such an excessively thick insulating coating 130G is easily peeled off from the finish annealed steel sheet 110 which is the base material. That is, it is considered that the insulating coating 130G formed inside the groove is easily peeled off, and as a result, the effect of reducing the iron loss of the grain-oriented electrical steel sheet 200 is impaired.

By the way, in the directional electromagnetic steel plate 200 in which the groove G is formed, the magnetic flux that reaches one of the groove walls through the steel plate leaks from the groove wall (that is, due to the leakage of the magnetic flux), so that the static magnetic energy increases. The subdivision of the main magnetic domain in order to reduce the static energy is the cause of the magnetic domain control effect.

However, in a state where tension is not applied to the steel sheet, a reflux type magnetic domain is generated in the vicinity of the groove wall surface, the increase in the static magnetic energy described above is suppressed, and a sufficient magnetic domain control effect is not exhibited.
Since the reflux magnetic domain becomes energetically unstable due to the isotropic tension due to the insulating film (due to the adverse effect of magnetostriction), the leakage of magnetic flux is restored and the magnetic domain control effect is improved.
It is considered that the insulating film formed thickly in the groove cannot give a sufficient tension effect to the steel sheet because it is easily peeled off, or it cannot give a stress in the direction of destabilizing the reflux magnetic domain to the steel sheet.

In particular, when the coating solution is applied to the groove-forming surface 110a of the finish-annealed steel sheet 110, gravity causes the finish-annealed steel sheet 110 to have a concave (in other words, downwardly convex) catenary on the upper surface side. In this case, the insulating coating 130G inside the groove tends to be formed excessively thicker than the insulating coating 130F on the flat surface 110F. That is, as shown in FIG. 6, when the coating solution is applied in the “upward” state, a liquid pool is likely to be formed in the groove G, and a thicker insulating film 130G is formed inside the groove. Therefore, the insulating coating 130G formed inside the groove is easily peeled off, and further impairs the effect of reducing iron loss.

On the other hand, in the tension film applying step S10 according to the present embodiment, as shown in FIG. 5, the coating solution is applied to the groove forming surface 110a with the groove forming surface 110a of the finished annealed steel sheet 110 facing downward. And anneal. The point that the finish-annealed steel sheet 110 is conveyed by the transfer roller 1000 is the same as in the conventional case.

Also in this embodiment, the point that the coating solution easily collects in the groove G and the point that the finished annealed steel sheet 110 has a concave catenary on the upper surface side due to gravity are the conventional tension film applying steps (that is, the groove forming surface faces upward). The process of applying the coating solution) is the same.

However, since the groove G faces downward, a part of the coating solution accumulated inside the groove will be dropped by gravity. Since the catenary has a downwardly convex shape, it is considered that the coating solution accumulated inside the groove is more likely to be dropped. As a result, after baking, it is considered that the insulating coating 130G inside the groove becomes thinner than the conventional tension coating applying step. That is, as a result of the insulating coating 130G inside the groove becoming thinner, the insulating coating 130G is less likely to peel off inside the groove, and the effect of reducing the iron loss of the grain-oriented electrical steel sheet 200 can be obtained. Further, since the insulating coating 130G inside the groove can leak more magnetic flux, it can be expected to improve the effect of reducing iron loss. As shown in Examples described later, when the coating solution is applied and baked with the groove forming surface 110a facing downward, the groove film peeling rate of the grain-oriented electrical steel sheet 200 can be reduced, resulting in iron loss. It was greatly reduced.

Here, in the tension film applying step S10, the thickness t2 of the insulating film 130G formed inside the groove is ½ or less of the depth D of the groove G, and the finished annealed steel sheet 110 (that is, the base steel sheet) is flat. It is preferable that the thickness is twice or less the thickness t1 of the insulating coating 130F formed on the surface 110F. Hereinafter, this requirement is also referred to as "additional requirement of thickness t2". The depth D and the thicknesses t1 and t2 are shown in FIG. Here, t1 is assumed to measure the thickness in the vertical direction with respect to the tangential direction of the steel plate surface at the thickness measurement point. Similarly, t2 also measures the thickness in the vertical direction with respect to the tangential direction along the groove surface.

Here, the thickness t2 of the insulating coating 130G inside the groove is an average value of the thickness t2 measured at a plurality of observation cross sections of the groove G.

Similarly, the thickness t1 of the insulating coating 130F on the flat surface 110F is also an average value of the thickness t1 measured at a plurality of points on the observation cross section.
The specific value of the thickness t1 of the insulating film 130F is not particularly limited and may be appropriately set according to the characteristics required for the grain-oriented electrical steel sheet 200, but is preferably 1 μm or more, for example, 2 μm or more. Is more preferable. This is because when the thickness t1 of the insulating film 130F is 1 μm or more, the corrosion resistance of the grain-oriented electrical steel sheet 200 and the insulating property can be further improved.

The thickness t1 of the insulating coating 130F is preferably 10 μm or less, and more preferably 5 μm or less. This is because when the thickness t1 of the insulating coating 130F is 10 μm or less, it is possible to prevent the space factor of the finished annealed steel sheet 110 from being significantly reduced.

It is preferable that the thickness t1, the thickness t2, and the depth D measured (determined) by the above method satisfy the above-mentioned "additional requirements for the thickness t2". In the tension film applying step S10, as described above, the thickness t2 is thinner than that of the conventional tension film applying step in which the groove forming surface is directed upward. Therefore, for example, the coating amount and viscosity of the coating solution to be applied are determined. And one or more of the concentrations, application method (application method includes application by roll coater, etc.), time from application to baking, air blowing to remove part of the coating solution, etc. By changing it, the above-mentioned "additional requirement of thickness t2" may be achieved.

The tension film applying step S10 may be performed on a separate line (that is, offline) from other steps, or may be performed on the same line (that is, online). When the groove G is formed on the lower surface of the finish-annealed steel sheet 110 in the above-mentioned groove forming step S9, the finish-annealed steel sheet 110 can be directly subjected to the tension film applying step S10. That is, the tension film applying step S10 can be performed in-line.

On the other hand, when the groove G is formed on the upper surface of the finish-annealed steel sheet 110 in the groove forming step S9, the finish-annealed steel sheet 110 is once wound up and then turned upside down to turn the finish-annealed steel sheet 110 upside down. May be subjected to the tension film applying step S10. In this case, the tension film applying step S10 may be performed offline or in-line.

In this embodiment, the effect of the method for manufacturing grain-oriented electrical steel sheets according to the above-described embodiment was verified. Of course, the present invention is not limited to the examples described below. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

First, by performing the above-mentioned casting step S1 to finish annealing step S8, a high magnetic flux density finish annealed steel sheet having a plate thickness of 0.23 mm and a magnetic flux density B8 value of 1.93 T at ₈₀₀ A / m. 110 was manufactured.

Then, the finished annealed steel sheet 110 has an elliptical beam shape of 20 μm in the rolling direction and 40 μm in the width direction of the steel sheet, and is irradiated with a fiber laser having a beam power of 2.5 kW to form the finished annealed steel sheet 110. A groove G was formed on the surface. Here, the scanning speed was set to 15 m / s, and linear grooves G having a width w of about 50 μm and a depth D of about 20 μm were formed at intervals of 3 mm in the direction perpendicular to the rolling direction.

Then, the coating solution was applied and baked in the manner shown in Table 1. Here, the coating solution contained a mixture containing aluminum phosphate and magnesium phosphate, and a coating solution containing 40 to 70 parts by mass of colloidal silica was used with respect to 100 parts by mass of the mixture in terms of solid content.
In Table 1, "direction of the groove forming surface at the time of baking" indicates the direction (upper side or lower side) of the groove forming surface 110a when the coating solution is applied. The coating solution was dropped from above the steel sheet and coated with a normal natural coater.

The coating solution application amount indicates the mass (g / m ² ) of the solid content of the coating solution applied per unit area of the groove forming surface 110a in a plan view. When it is desired to measure the coating solution coating amount from the dried insulating film, the insulating film is dissolved in the alkaline solution by immersing the directional electromagnetic steel plate in a heated alkaline solution (NaOH solution or the like). Then, the coating solution coating amount can be specified from the mass of the insulating film dissolved in the alkaline solution.

Next, the depth D (μm) of the groove G, the thickness t2 (μm) of the insulating film 130G inside the groove, the thickness t1 (μm) of the insulating film 130F of the flat surface 110F, and the peeling rate of the insulating film in the groove (area%). , The magnetic flux density B ₈ (T) and the iron loss W17 / 50 (W / kg) were measured. The method for measuring the depth D (μm) of the groove G, the thickness t2 (μm) of the insulating coating 130G inside the groove, and the thickness t1 (μm) of the insulating coating 130F on the flat surface 110F is as described above. The results are shown in Table 1.

Here, the "groove insulating film peeling rate" refers to the area ratio of the portion where the insulating film is peeled off with respect to the total area of the groove G in a plan view. Whether or not the insulating film was peeled off was determined by the area ratio of the exposed steel plate surface. Specifically, a case where the area ratio was 10% was determined to be unacceptable.

As is clear from Table 1, in the grain-oriented electrical steel sheets (Experiments Nos. 1 to 4) manufactured by the method for manufacturing grain-oriented electrical steel sheets according to the present embodiment, the groove-forming surface of the finished annealed steel sheet faces downward. By applying the coating solution and baking it in, there were few film defects and the iron loss was low.
On the other hand, in the grain-oriented electrical steel sheet (Experiment Nos. 5 to 7) manufactured by the conventional method for manufacturing grain-oriented electrical steel sheet, the coating solution is applied with the groove-forming surface of the finished annealed steel sheet facing upward. Due to the baking, there were many film defects and the iron loss was high.

In addition, the experiment No. 1 to 3 satisfy the "additional requirement of thickness t2". In this respect as well, Experiment No. In the examples of the inventions 1 to 3, it is considered that the iron loss is low.
However, since the thickness of the coating film inside the groove is more than twice the thickness formed on the flat surface of the steel sheet, it does not satisfy the "additional requirement of thickness t2"). Experiment No. No. 4 is the experiment No. Compared with 1 to 3, the iron loss was slightly higher.

As described above, according to the present embodiment, phosphoric acid, phosphate, chromic anhydride, chromic acid salt, with the groove forming surface 110a of the finished baked steel sheet 110 (or cold-rolled steel sheet) facing downward. An insulating film is formed on the groove-forming surface 110a by applying a coating solution containing an alumina or a compound of silica and baking the mixture. In the grain-oriented electrical steel sheet 200 manufactured by this manufacturing method, the insulating coating 130G inside the groove becomes thin, so that it is difficult to peel off. Therefore, there are few film defects and iron loss is reduced.

Here, in the tension coating applying step S10, the thickness t2 of the insulating coating 130G formed inside the groove is halved or less than the depth D of the groove G, and the finished annealed steel sheet 110 (or cold-rolled steel sheet) is formed. The thickness t2 of the insulating coating 130G may be adjusted so as to be less than twice the thickness t1 of the insulating coating 130F formed on the flat surface 110F. In this case, since the insulating coating 130G inside the groove is further thinned, the iron loss of the grain-oriented electrical steel sheet 200 is further reduced.

Further, after the cold rolling step and before the finish annealing step, the annealing separator coating step of applying the annealing separator to the cold-rolled steel sheet may be further performed. Then, the annealing separator may contain magnesia. In this case, the characteristics of the grain-oriented electrical steel sheet 200 are further improved.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

200 Directional electrical steel sheet 110 Finish-annealed steel sheet 110F Flat surface 110G Groove wall surface 130 Insulation coating (tension coating)
130F Insulation film on a flat surface 130G Insulation film inside a groove

Claims (3)

The cold rolling process for manufacturing cold-rolled steel sheets and
A finish annealing step of performing finish annealing with secondary recrystallization on the cold-rolled steel sheet, and
A groove forming step of forming a linear groove in a direction intersecting the rolling direction of the cold-rolled steel sheet with respect to the cold-rolled steel sheet before or after the finish annealing step.
With the groove-forming surface of the cold-rolled steel plate facing downward, a coating solution containing a compound of phosphoric acid, phosphate, chromic anhydride, chromic acid, alumina, or silica is applied and baked to obtain the above. A method for manufacturing a directional electromagnetic steel plate, which comprises a tension film applying step of forming a tension film on a groove forming surface. In the tension film applying step, the thickness of the tension film formed inside the groove is ½ or less of the depth of the groove, and the tension film is formed on the flat surface of the cold-rolled steel sheet. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the thickness of the tension film is adjusted so as to be twice or less the thickness of the above-mentioned tension film. After the cold rolling step and before the finish annealing step, the annealed separator coating step of applying the annealing separator to the cold-rolled steel sheet is further provided.
The method for producing grain-oriented electrical steel sheets according to claim 1 or 2, wherein the annealing-separating agent contains magnesia.

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