JP2022074677A - Non-oriented electromagnetic steel plate excellent in magnetic characteristics and its manufacturing method - Google Patents

Abstract

To provide a manufacturing method of a novel and improved non-oriented electromagnetic steel sheet capable of manufacturing a non-oriented magnetic steel sheet excellent in magnetic characteristics while improving productivity by improving cold fragility, and a non-oriented electromagnetic steel sheet obtained thereby.SOLUTION: A non-oriented magnetic steel sheet characterized by containing by mass%, C: over 0% to 0.0050% or smaller, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: over 0% to smaller than 0.030%, S: over 0% to 0.0050% or smaller, Sol. Al: over 0% to 0.0040% or smaller; N: over 0% to 0.0040%; Cu: 0.00% to 1.0% or smaller, Sn: 0.000% to 0.10%, Sb: 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, and the remainder is Fe and impurity, Mn2SiO4 complex precipitated with SiO2 in the surface layer of base steel is 0.000001 piece/μm2 or larger, and 10.000 pieces/μm2, and its manufacturing method..SELECTED DRAWING: Figure 3

Description

The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing the same.

In recent years, global environmental problems have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there has been a strong demand for higher efficiency of electrical equipment in recent years. Therefore, even in non-oriented electrical steel sheets widely used as iron core materials for motors, transformers, etc., there is an increasing demand for improvement of magnetic characteristics. In recent years, the tendency is remarkable in motors for electric vehicles and hybrid vehicles, and motors for compressors, for which the efficiency of motors has been improved.

In order to improve the magnetic properties of non-oriented electrical steel sheets, it is effective to increase the electrical resistance of the steel sheets by adding alloying elements to the steel and reduce the eddy current loss. Therefore, for example, as disclosed in Patent Document 1 and Patent Document 2 below, it is possible to improve the magnetic properties by adding an element having an effect of increasing electric resistance such as Si, Al, Mn or P. It is done. Further, Patent Documents 3 and 4 disclose that the combined addition of Mn and Si not only improves the magnetic properties but also improves the cold rollability.

Japanese Unexamined Patent Publication No. 2000-129409 Japanese Unexamined Patent Publication No. 2015-131993 Japanese Unexamined Patent Publication No. 2018-66033 JP-A-2019-99854

High alloying (increasing Si concentration or increasing Al concentration) is effective for improving the magnetic properties of non-oriented electrical steel sheets (NO). On the other hand, since increasing the Si concentration or increasing the Al concentration significantly deteriorates the cold brittleness, it is generally difficult to achieve both productivity and magnetic properties. In response to this, various efforts as disclosed in Patent Documents 3 and 4 have been proposed, but further improvement and improvement in both productivity and magnetic characteristics are still required.

Therefore, an object of the present invention is a new and improved non-oriented electrical steel sheet capable of producing non-oriented electrical steel sheets having excellent magnetic properties while improving cold brittleness and increasing productivity. It is an object of the present invention to provide a method for manufacturing an electromagnetic steel sheet and a non-oriented electrical steel sheet obtained thereby.

As a result of diligent studies by the present inventors in order to solve the above problems, Mn having an Al content of a predetermined value or less and a small decrease in cold rollability was added in combination with Si, and By controlling the pickling conditions,
We have completed the present invention based on the finding that it is possible to improve both cold rollability and magnetic properties.

The present invention obtained from the above findings provides the following aspects.
[1]
By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Cu: 0.00% to 1.0% or less, Sn: 0.000% to 0.10%, Sb: Mn ₂ SiO ₄ which contains 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, the balance is Fe and impurities, and is compositely precipitated with SiO ₂ in the surface layer of the base steel plate. A non-directional electromagnetic steel sheet containing 0.000001 pieces / μm ² or more and 10.000 pieces / μm ² or less.
[2]
By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. A steel piece containing Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Ca: 0.0000% to 0.0050%, and the balance consisting of Fe and impurities was heated. A hot rolling process to obtain a hot-rolled steel sheet by hot rolling later,
The hot-rolled plate annealing step of annealing the hot-rolled plate, and
The pickling step of pickling the hot-rolled annealed plate and
A cold rolling step of obtaining a cold-rolled steel sheet by performing one cold rolling or a plurality of cold rolling sandwiching intermediate annealing after the pickling.
The finish annealing step of applying the finish annealing to the cold-rolled steel sheet and
It has an insulating coating process that applies an insulating coating, and has an insulating coating process.
In the pickling solution, the liquid temperature is 15 ° C. or higher and 100 ° C. or lower, the time for the steel plate to be immersed in the pickling liquid is 5 seconds or longer and 200 seconds or shorter, pH −1.5 or higher and lower than 7, and the above. A method for producing a non-directional electromagnetic steel plate, wherein the pickling solution contains Mn at 0.01 g / L or more and 2.00 g / L or less.
[3]
The method for manufacturing a non-oriented electrical steel sheet according to [2], wherein the steel piece contains REM: 0.0001 to 0.0100% in mass%.
[4]
The method for producing a non-oriented electrical steel sheet according to [3], wherein the pickling solution contains Cu and Mn of 0.01 g / L or more and 5.00 g / L or less in the pickling solution.
[5]
The soaking temperature of the finish annealing is 800 ° C. or higher, and the heating rate of 500 to 800 ° C. in the heating step is 100 ° C./sec to 2000 ° C./sec [3] or. The method for manufacturing a non-directional electromagnetic steel plate according to [4].
[6]
The soaking temperature of the finish annealing is 800 ° C. or higher, and the atmospheric dew point of 500 to 800 ° C. in the heating step is set to −50 ° C. or higher and 10 ° C. or lower [3] to [5]. The method for manufacturing a non-oriented electrical steel sheet according to any one of the above.
[7]
Any one of [3] to [6], wherein the soothing annealing temperature of the finish annealing is carried out at 800 ° C. or higher, and the oxygen potential at the soaking annealing temperature of the finish annealing is 0.2 or less. The method for manufacturing a non-directional electromagnetic steel sheet according to the above.
[8]
The steel piece is replaced with a part of Fe in the balance, and further, in mass%, at least one selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10%. The method for producing a non-oriented electrical steel sheet according to any one of [3] to [7], which contains seeds.

The method for manufacturing grain-oriented electrical steel sheets according to the present invention is novel, which can improve cold brittleness to increase productivity and can manufacture grain-oriented electrical steel sheets having excellent magnetic properties. It is an improved method for manufacturing grain-oriented electrical steel sheets, and the grain-oriented electrical steel sheets obtained by the above-mentioned manufacturing method are grain-oriented electrical steel sheets having excellent magnetic properties.

FIG. 1 is a flow chart showing an example of a flow of a method for manufacturing a non-oriented electrical steel sheet according to the present embodiment. FIG. 2 is a schematic view for explaining the surface layer portion of the steel plate base material. FIG. 3 is a schematic diagram for explaining a composite precipitate of SiO ₂ and Mn ₂ SiO ₄ .

First, the gist of the present invention will be described.

(About manufacturing method)
In order to improve the magnetic properties of non-oriented electrical steel sheets, as disclosed in Patent Document 1 and Patent Document 2, an element having an effect of increasing electric resistance such as Si, Al, Mn or P is added. Therefore, improvements are being made to the magnetic properties.
In particular, Al has an action of increasing electric resistance like Si, and reduces eddy current loss, which is one of the causes of iron loss, but on the other hand, it significantly deteriorates cold brittleness.
Therefore, when the present inventors examined the composite addition of Mn, which has an Al content of a predetermined value or less and a small decrease in cold rollability, together with Si, they recognized the harmful effects caused by Mn.
The harmful effect is that the oxide film in the finish annealing becomes porous. When the oxide film is porous, the gas (particularly N) in a neutralized atmosphere easily invades the surface layer of the steel sheet and reacts with the component elements in the steel sheet to react with the nitride (also called inclusions), for example (Si). , Mn) N, MnSiN ₂ and AlN) are precipitated and good magnetic properties cannot be obtained. When Al (instead of Mn) is added, a relatively tight film is formed, so that the gas (particularly N) in an annealed atmosphere does not easily penetrate into the surface layer of the steel sheet, and (Si, Mn) N or MnSiN. It is possible to avoid the formation of precipitates (magnetic deterioration factors) such as ₂ and AlN.
In order to prevent gas (particularly N) in the annealing atmosphere from entering the surface layer of the steel sheet, for example, measures such as lowering (drying) the dew point of the atmosphere at the time of temperature rise and the atmosphere at the time of soaking in the finishing annealing step are taken. There are methods, but they alone were not sufficient to prevent the oxide film from becoming porous.
On the other hand, the present inventors have conceived that by controlling the Mn concentration of the pickling solution, a tight film can be formed.
Specifically, when the Mn concentration of the pickling solution is at least a predetermined value, a Mn segregation layer is formed on the surface of the steel sheet after pickling.
Since the Mn segregation layer is a tight film, it leads to avoiding the formation of precipitates during finish annealing. That is, good magnetic properties can be obtained.
In the above, Mn was added to the pickling solution, but this effect can be enjoyed as long as it forms a segregation layer other than Mn. For example, the Cu concentration of the pickling solution may be set to a predetermined value or higher.
Further, by controlling the rate of temperature rise of the finish annealing and the annealing atmosphere, the magnetic characteristics tend to be more preferable.
On the other hand, in the aspect of the present invention, since Al is restricted, deterioration of cold brittleness due to Al can be avoided.

(About product)
Further, the non-oriented electrical steel sheet obtained by the manufacturing method of the present invention has the following characteristic structure. Its characteristic structure is that a part of the Mn segregation layer formed on the surface layer of the steel sheet derived from the pickling solution is bonded to SiO ₂ in the steel during finish annealing to form Mn ₂ SiO ₄ . Specifically, it is a structure (Core / Thin shell structure) in which Mn ₂ SiO ₄ surrounds the spherical SiO ₂ . Since the normal non-oriented electrical steel sheet is annealed after finishing and an insulating film is applied, no trace of this technique remains on the product surface. However, the above characteristic structure can be confirmed by removing the insulating film and observing the surface layer portion of the steel sheet.
Therefore, by measuring the number of Core / Shell type Mn ₂ SiO ₄ , it is possible to determine whether or not the effect of the present invention is enjoyed, that is, it is certified as a non-oriented electrical steel sheet according to the aspect of the present invention. It is possible.

The present inventors have come up with the present invention by considering the above findings. One embodiment of the present invention is a method for manufacturing a non-oriented electrical steel sheet having the following configuration.

By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Ca: 0.0000% to 0.0050%, and the balance was heated from a piece of steel consisting of Fe and impurities. A hot rolling step of hot rolling to obtain a hot-rolled steel plate, a hot-rolled plate annealing step of annealing the hot-rolled plate, a pickling step of pickling the hot-rolled plate, and the acid. After washing, a single cold-rolling process or a plurality of cold-rolling with intermediate annealing is performed to obtain a cold-rolled steel sheet, and a finish-rolling process is performed on the cold-rolled steel sheet. It has a finish rolling step and an insulating coating step of applying an insulating coating. In the pickling solution, the liquid temperature is 15 ° C. or higher and 100 ° C. or lower, and the time for the steel plate to be immersed in the pickling solution is 200 seconds or longer. Manufacture of non-directional electromagnetic steel sheet having a second or less, ph-1.5 or more and less than 7, and the pickling solution containing Mn at 0.01 g / L or more and 2.00 g / L or less. Method.

Hereinafter, the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment will be specifically described.

<Component composition of steel pieces>
First, the component composition of the steel piece (slab) of the non-oriented electrical steel sheet according to the present embodiment will be described. In the following, unless otherwise specified, the notation "%" means "mass%". Further, the balance other than the elements described below is Fe and impurities. Here, the impurity refers to a component contained in the raw material or a component mixed in the manufacturing process and not intentionally contained in the steel sheet. Further, the chemical composition of the steel piece, which is the material of the non-oriented electrical steel sheet, basically conforms to the composition of the non-oriented electrical steel sheet. However, in the production of general non-oriented electrical steel sheets, some of the contained elements are discharged to the outside of the system by the finish annealing process and the insulating film forming process in the manufacturing process, so it is a steel piece as a raw material and a final product. The chemical composition of non-oriented electrical steel sheets will be different. The composition of the steel pieces can be appropriately adjusted in consideration of the influence of the finish annealing step and the insulating film forming step in the manufacturing process so that the characteristics of the non-oriented electrical steel sheet become desired. Further, the notation of "electrical steel sheet" in the present invention means an electromagnetic steel sheet in any process from the steel piece to the final product in the manufacturing process of the electrical steel sheet, unless otherwise specified. That is, unless otherwise specified, the notation of "electrical steel sheet" in the manufacturing process of the non-oriented electrical steel sheet of the present invention is an electromagnetic steel sheet in any process from the steel piece in the manufacturing process of the electrical steel sheet to before the insulating film coating process. It shall mean.

[C: More than 0% to 0.0050% or less]
C (carbon) is an element that is inevitably contained and also causes iron loss deterioration. When the C content exceeds 0.0050%, magnetic aging (a phenomenon in which carbides precipitate over time and the magnetic properties deteriorate) occurs in the non-oriented electrical steel sheet, and good magnetic properties can be obtained. Can not. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, the content of C is set to 0.0050% or less. The content of C is preferably 0.0040% or less, and more preferably 0.0030% or less. The smaller the C content, the better, but if an attempt is made to reduce the C content to less than 0.0005%, it will only unnecessarily increase the cost. Therefore, the content of C is preferably 0.0005% or more.

[Si: 2.5% -5.0%]
Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves iron loss. Further, Si is an element effective for increasing the strength of non-oriented electrical steel sheets because it has a large solid solution strengthening ability. Higher strength is important from the viewpoint of suppressing deformation during high-speed rotation of the motor and suppressing fatigue fracture due to fluctuating stress associated with starting and stopping. In order to fully exert such an effect, it is necessary to contain 2.5% or more of Si. On the other hand, when the Si content exceeds 5.0%, the workability is significantly deteriorated and it becomes difficult to carry out cold rolling (that is, the cold rollability is lowered). Therefore, the Si content is 5.0% or less. The Si content is preferably 3.0% or more and 4.5% or less, and more preferably 3.2% or more and 3.8% or less.

[Mn: 0.05% to 4.0%]
Mn (manganese) is an element effective for reducing eddy current loss and improving iron loss by increasing electrical resistance without deteriorating the workability of steel. Further, Mn is an element that can contribute to high strength without deteriorating processability, although it has a smaller solid solution strengthening ability than Si. In order to fully exert such an effect, it is necessary to contain Mn of 0.05% or more. On the other hand, when the Mn content exceeds 4.0%, the decrease in magnetic flux density becomes remarkable. Therefore, the Mn content is set to 4.0% or less. The Mn content is preferably 0.07% or more and 3.0% or less, and more preferably 0.1% or more and 2.0% or less.

[P: Over 0% -0.030% or less]
P (phosphorus) is an element that is inevitably contained (that is, the content is more than 0%), and is remarkably high in the high alloy steel having a high content of Si and Mn, which is the subject of this embodiment. It is an element that deteriorates workability and makes cold rolling difficult. Such deterioration in workability becomes remarkable when the P content exceeds 0.030%. Therefore, the content of P is 0.030% or less. The content of P is preferably 0.001% or more and 0.020% or less, and more preferably 0.002% or more and 0.010% or less.

[S: More than 0% to 0.0050% or less]
S (sulfur) is an element that is inevitably contained and is an element that increases iron loss by forming fine precipitates of MnS and deteriorates the magnetic properties of non-oriented electrical steel sheets. Therefore, the content of S needs to be 0.0050% or less. The smaller the S content, the better, but if an attempt is made to reduce the S content to less than 0.0001%, it will only unnecessarily increase the cost. Therefore, the content of S is preferably 0.0001% or more. The content of S is preferably 0.0040% or less, and more preferably 0.0030% or less.

[Sol. Al: More than 0% to 0.0040% or less]
Al (aluminum) is an element that, when solid-solved in steel, increases the electrical resistance of non-oriented electrical steel sheets to reduce eddy current loss and improve iron loss. However, in the present embodiment, since Mn, which is an element that increases the electric resistance without deteriorating the workability as compared with Al, is positively contained, it is not positively contained. In this case, if the Al content exceeds 0.0040%, fine nitrides are deposited in the steel, which hinders the growth of crystal grains in hot-rolled sheet annealing and finish annealing, and deteriorates the magnetic properties. Therefore, the Al content is 0.0040% or less. On the other hand, if an attempt is made to reduce the Al content to more than 0.0001%, the cost will only increase unnecessarily. Therefore, the Al content is preferably 0.0001% or more and 0.0030% or less, and more preferably 0.0001% or more and 0.0020% or less. Since Al is limited to the above range, deterioration of cold brittleness due to Al can be avoided.

[N: More than 0% to 0.0040% or less]
N (nitrogen) is an element that is inevitably contained and is an element that causes magnetic aging to increase iron loss and deteriorate the magnetic properties of non-oriented electrical steel sheets. Therefore, the content of N needs to be 0.0040% or less. The smaller the N content, the better, but trying to reduce the N content to less than 0.0001% will only unnecessarily increase the cost. Therefore, the content of N is preferably 0.0001% or more. The content of N is preferably 0.0001% or more and 0.0030% or less, and more preferably 0.0001% or more and 0.0020% or less.

[Cu: 0.00% to 1.0%]
Cu (copper) is an optional additive element useful for improving the magnetic flux density. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, in order to obtain such an effect, Cu may be contained in the ground iron as an optional additive element instead of a part of Fe in the balance. In order to fully exert such an effect, the Cu content is preferably 0.05% or more. On the other hand, when the Cu content exceeds 1.0%, the effect of adding Cu is saturated, which only unnecessarily leads to an increase in cost. Therefore, the Cu content is preferably 1.0% or less. When Cu is contained in the base iron, the content of Cu is preferably 0.05% or more and 0.25% or less, and more preferably 0.07% or more and 0.20% or less.

[Sn: 0.000% to 0.10%]
[Sb: 0.000% to 0.10%]
Sn (tin) and Sb (antimony) are optional additive elements useful for ensuring low iron loss by segregating on the surface and suppressing oxidation and nitriding during annealing. In addition to this effect, it has an texture improving effect (magnetic property improving effect). Therefore, in the non-oriented electrical steel sheet according to the present embodiment, in order to obtain such an effect, at least one of Sn or Sb is contained in the ground iron as an optional additive element instead of a part of the remaining Fe. You may let me. In order to fully exert such an effect, it is preferable that the Sn or Sb content is 0.005% or more, respectively. On the other hand, when the Sn or Sb content exceeds 0.10%, the ductility of the base metal may decrease, making cold rolling difficult. Therefore, the content of Sn or Sb is preferably 0.10% or less, respectively. When Sn or Sb is contained in the ground iron, the content of Sn or Sb is more preferably 0.01% or more and 0.05% or less, respectively.

[Ca: 0.0000% to 0.0050%]
Ca (calcium) is an element that suppresses the precipitation of fine MnS by binding with S to form a coarse compound and promotes crystal grain growth during annealing. Furthermore, it is an effective element for avoiding nozzle blockage due to oxides during continuous casting by compoundly containing one or more of REM such as La, Ce, Pr, and Nd. In order to obtain such an effect, the Ca content is preferably 0.0001% or more, more preferably 0.0002% or more.
On the other hand, when the Ca content exceeds 0.0050%, the above-mentioned effect of improving crystal grain growth and the effect of suppressing nozzle blockage are saturated, which is economically disadvantageous. Therefore, the Ca content is set to 0.0050% or less. The Ca content is preferably 0.0040% or less, more preferably 0.0030% or less.
[REM: 0.0001% to 0.0100% in total]
REM is an abbreviation for Rare Earth Metal and includes La, Ce, Pr, Nd and the like. REM is an element that suppresses the precipitation of fine MnS by combining with S to form coarse sulfides, sulfates, or both, and promotes crystal grain growth during annealing. Further, it is an element effective for avoiding nozzle blockage due to oxides during continuous casting due to the composite content with Ca. In order to obtain such an effect, the total content of one or more of REM is preferably 0.0001% or more. On the other hand, when the content of one or more of REM exceeds 0.0100% in total, the effect of coarsening the fine precipitates as described above is saturated and it is economically disadvantageous, which is preferable. not. Therefore, the total content of one or more of REM is preferably 0.0100% or less. The content of one or more of REM is preferably 0.0010% or more and 0.0090% or less in total.

In the non-oriented electrical steel sheet according to this embodiment, the content of elements such as Ni (nickel) and Cr (chromium) other than the above-mentioned elements is not particularly specified. In the non-oriented electrical steel sheet according to the present embodiment, even if these elements are contained in an amount of 0.5% or less, the effect of the present invention is not particularly affected. Further, even if Mg (magnesium) is contained in the range of 0.002% or less, the effect of the present invention is not particularly affected.

Further, even if an element such as B (boron) is contained in the range of 0.0001% to 0.0050% in addition to the above elements, the effect of the present invention is not impaired.

The chemical composition of the non-oriented electrical steel sheet according to the present embodiment has been described in detail above.
Subsequently, in the method for manufacturing a non-oriented electrical steel sheet according to the present embodiment, hot rolling, hot rolling, annealing, pickling, and pickling are performed on a steel piece (slab) having a predetermined chemical component as described above. Cold rolling, finish annealing, and insulation coating steps are carried out in order. FIG. 1 is a flow chart showing an example of a flow of a method for manufacturing a non-oriented electrical steel sheet according to the present embodiment. Hereinafter, each step carried out by the method for manufacturing non-oriented electrical steel sheets according to the present embodiment will be described in detail with reference to FIG. 1.

<Hot rolling process>
In the method for manufacturing non-oriented electrical steel sheets according to the present embodiment, first, a steel piece (slab) having the above chemical composition is heated, and the heated steel piece is hot-rolled to obtain a hot-rolled sheet. (Step S101). Here, the heating temperature of the steel pieces when subjected to hot rolling is not particularly specified, but is preferably 1050 ° C to 1250 ° C, for example. Further, the plate thickness of the hot-rolled plate after hot rolling is not particularly specified, but it is preferably about 1.6 mm to 3.5 mm in consideration of the final plate thickness of the base iron. .. The hot rolling step is preferably completed while the temperature of the steel sheet is in the range of 700 ° C. to 1000 ° C. The heating temperature of the steel pieces is more preferably 1050 ° C to 1150 ° C, and the end temperature of hot rolling is more preferably 750 ° C to 950 ° C.

<Hot rolled sheet annealing process>
After the hot rolling, hot-rolled sheet annealing is optionally additionally performed (step S103). In the case of continuous annealing, the hot-rolled steel sheet may be annealed by soaking for 10 seconds to 10 minutes at, for example, 750 ° C to 1200 ° C. Further, in the case of box annealing, the hot-rolled steel sheet may be annealed by soaking heat for 30 minutes to 24 hours at, for example, 650 ° C to 950 ° C. Although the magnetic characteristics are inferior to those in which the hot-rolled plate annealing process is performed, in order to reduce the cost, the hot-rolled plate self-annealing or the like is performed, or the hot-rolled plate annealing step is omitted. You may.

<Pickling process>
After the hot rolling or hot rolling plate annealing, pickling is performed (step S105). As a result, the scale layer mainly composed of oxides formed on the surface of the steel sheet by hot rolling or hot rolling sheet annealing is removed. When the hot-rolled sheet is annealed in a box, the pickling step is preferably performed before the hot-rolled sheet is annealed from the viewpoint of descaling property.

The pickling step of the non-oriented electrical steel sheet according to the present embodiment is performed under the following pickling conditions. That is, in the pickling solution, the liquid temperature is 15 ° C. or higher and 100 ° C. or lower, the time for the steel plate to be immersed in the pickling liquid is 5 seconds or longer and 200 seconds or shorter, ph-1.5 or higher and lower than 7, and the pH is 1.5 or higher and lower than 7. The pickling solution contains Mn at 0.01 g / L or more and 2.00 g / L or less.

The liquid temperature of the pickling solution is 15 ° C. or higher and 100 ° C. or lower in this embodiment. When the temperature of the pickling solution is less than 15 ° C., the scale removing effect by pickling is insufficient, which is not preferable. If the temperature of the pickling solution exceeds 100 ° C., it becomes difficult to handle the pickling solution, which is not preferable. The fact that the liquid temperature of the pickling solution is 15 ° C. or higher and 100 ° C. or lower is also advantageous in that Mn contained in the pickling solution satisfactorily forms a Mn segregated layer on the surface of the steel sheet. The liquid temperature is preferably 50 ° C. or higher and 90 ° C. or lower, and more preferably 60 ° C. or higher and 90 ° C. or lower.

The time for the steel sheet to be immersed in the pickling solution is 5 seconds or more and 200 seconds or less in this embodiment. When the steel sheet is immersed in the pickling solution for less than 5 seconds, the scale removing effect by pickling becomes insufficient, which is not preferable. If the time for the steel sheet to be immersed in the pickling solution is more than 200 seconds, the equipment becomes long, which is not preferable. The immersion time is preferably 10 seconds or more and 150 seconds or less, and more preferably 20 seconds or more and 150 seconds or less.

The pH of the pickling solution is −1.5 or more and less than 7.0 in this embodiment. If it is 7.0 or more, the scale removing effect is insufficient, which is not preferable. On the other hand, the solution that can be actually prepared is pH-1.5 or higher. The pH is preferably less than 2.0, more preferably less than 1.0. Examples of the acid component contained in the pickling solution include sulfuric acid, hydrochloric acid, nitric acid and the like.

In this embodiment, the pickling solution contains Mn at 0.01 g / L or more and 2.00 g / L or less. By pickling the steel sheet with a pickling solution containing Mn at a predetermined concentration, a Mn segregation layer is formed on the surface of the steel sheet after pickling. Since the Mn segregation layer is a tight film, it is possible to avoid the formation of precipitates in the subsequent finish annealing. Since the precipitate is a factor that deteriorates the magnetic property, good magnetic property can be obtained by avoiding the formation of such a precipitate. In order to fully exert such an effect, it is necessary to contain Mn of 0.01 g / L or more. On the other hand, when the Mn content exceeds 2.00 g / L, the effect may be saturated and the magnetic characteristics may be deteriorated, and the scale removal effect may also be lowered. Therefore, the upper limit of Mn in the pickling solution is 2.00 g / L or less. The Mn content in the pickling solution is preferably 0.05 g / L or more and 1.00 g / L or less, more preferably 0.1 g / L or more and 0.50 g / L or less.

Further, when Cu is contained in the pickling solution, a Cu segregation layer is formed on the surface of the steel sheet after pickling, similar to Mn. Since this Cu segregation layer is also a tight film, it is possible to avoid the formation of precipitates in the subsequent finish annealing. That is, when the pickling solution contains Cu, it is possible to avoid the formation of precipitates that cause deterioration of the magnetic properties and obtain good magnetic properties. Therefore, Cu may be optionally added to the pickling solution. In order to fully exert such an effect, it is preferable that the total amount of Cu and Mn is 0.01 g / L or more. On the other hand, if the Cu content is excessive, the effect may be saturated and the scale removing effect may be reduced. Therefore, it is preferable that the total amount of Cu and Mn is 5.00 g / L or less. The total content of Mn and Cu in the pickling solution is preferably 0.02 g / L or more and 4.00 g / L or less, more preferably 0.03 g / L or more and 2.00 g / L or less.

<Cold rolling process>
After the pickling (when the hot-rolled plate annealing is carried out by box annealing, it may be after the hot-rolled plate annealing step), cold rolling is carried out (step S107). In such cold rolling, the pickled plate from which the scale has been removed is rolled at a rolling reduction ratio such that the final plate thickness of the base iron is 0.10 mm or more and 0.50 mm or less.

<Finishing annealing process>
After the cold rolling, finish annealing is performed (step S109). Here, the finish annealing conditions are not particularly specified, and known conditions (for example, continuous annealing) used in the finish annealing of non-oriented electrical steel sheets can be adopted. The soaking temperature, the rate of temperature rise, the dew point of the atmosphere, the oxygen potential of the atmosphere, and the like may be appropriately adjusted so that a recrystallized texture advantageous for the magnetic characteristics is formed.

Specifically, it is preferable that the soaking temperature of the finish annealing is 800 ° C. or higher, and the heating rate of 500 to 800 ° C. in the heating step is 100 ° C./sec to 2000 ° C./sec. The lower limit of the temperature rising rate is more preferably 200 ° C./sec or more, and more preferably 400 ° C./sec or more. The upper limit of the temperature rise rate is not limited, but is set to 2000 ° C./sec because if the temperature rise rate is too high, distortion may be introduced and the magnetic characteristics may be deteriorated.
For the above heating rate, for example, in the case of heating by gas combustion, direct heating or indirect heating using a radiant tube may be used, or a known heating method such as energization heating or induction heating may be used. By doing so, it is possible to realize it.

Further, it is preferable that the soaking temperature is carried out at 800 ° C. or higher, and the atmospheric dew point at 500 to 800 ° C. in the temperature raising step is −50 ° C. or higher and 10 ° C. or lower. The lower limit of the atmospheric dew point is more preferably −40 ° C. or higher, still more preferably −30 ° C. or higher. The upper limit of the atmospheric dew point is more preferably 5 ° C. or lower, still more preferably 1 ° C. or lower.

Further, it is preferable that the soaking temperature is carried out at 800 ° C. or higher and the oxygen potential at the soaking temperature is 0.2 or less. The oxygen potential is the ratio of the partial pressure of water vapor to the partial pressure of hydrogen (PH ₂ O / PH ₂ ) in a blunted atmosphere. The upper limit of the oxygen potential is more preferably 0.1 or less, still more preferably 0.01 or less.

In the temperature raising step in the finish annealing step, the average temperature rising rate may be set to 1 ° C./sec to 2000 ° C./sec.
The lower limit of the soaking temperature is preferably 700 ° C. or higher, more preferably 800 ° C. or higher, further preferably 900 ° C. or higher, and the upper limit of the soaking temperature is preferably 1200 ° C. or lower, more preferably 1100 ° C. ° C or lower, more preferably 1050 ° C or lower.
Further, in the cooling process after the soaking process, the average cooling rate may be cooled to 200 ° C. or lower at 1 ° C./sec to 100 ° C./sec. The average cooling rate is more preferably 5 ° C./sec to 50 ° C./sec, and even more preferably 5 ° C./sec to 30 ° C./sec.

<Insulation film forming process>
After the finish annealing, a step of forming an insulating film is carried out (step S111). The insulating film according to the present embodiment is not particularly limited as long as it is used as the insulating film of the non-oriented electrical steel sheet, and a known insulating film can be used. The step of forming the insulating coating is not particularly limited, and the treatment liquid may be applied and dried by a known method using a known insulating coating treating liquid.

As the insulating film, for example, a composite insulating film containing mainly an inorganic substance and further containing an organic substance can be mentioned. Here, the composite insulating film is mainly composed of at least one of an inorganic substance such as a metal chromium acid salt, a metal phosphate salt or a colloidal silica, a Zr compound, and a Ti compound, and fine organic resin particles are dispersed. It is an insulating film. In particular, from the viewpoint of reducing the environmental load during manufacturing, which has been increasing in demand in recent years, an insulating film using a metal phosphate salt, a Zr or Ti coupling agent, or these carbonates or ammonium salts as a starting material is used. It is preferably used.

Here, the amount of the insulating film adhered as described above is not particularly limited, but is preferably, for example, 0.1 g / m ² or more and 2.0 g / m ² or less per one side, and is 0 per one side. It is more preferably .3 g / m ² or more and 1.5 g / m ² or less. By forming the insulating film so as to have such an adhesion amount, it is possible to maintain excellent uniformity. When the amount of the insulating film adhered is measured after the fact, various known measuring methods can be used. The amount of the insulating film adhered can be calculated from, for example, the mass difference before and after the removal of the insulating film by immersing the non-oriented electrical steel sheet on which the insulating film is formed in a thermal alkaline solution to remove only the insulating film. It is possible.

In addition, the surface of the base iron on which the insulating film is formed may be subjected to any pretreatment such as degreasing treatment with alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc. before applying the treatment liquid. Alternatively, the surface may be the surface as it is after finish baking without performing these pretreatments.

By going through each of the steps as described above, the non-oriented electrical steel sheet according to the present embodiment can be manufactured.

One embodiment of the present invention is a non-oriented electrical steel sheet having the following configuration.

By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Cu: 0.00% to 1.0% or less, Sn: 0.000% to 0.10%, Sb: Mn ₂ SiO ₄ which contains 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, the balance is Fe and impurities, and is compositely precipitated with SiO ₂ in the surface layer of the base steel plate. A non-directional electromagnetic steel sheet containing 0.000001 pieces / μm ² or more and 10.000 pieces / μm ² or less.

Hereinafter, the non-oriented electrical steel sheet according to the present embodiment will be specifically described.

<Component composition of steel sheet>
The non-oriented electrical steel sheet according to the present embodiment can be manufactured by the above-mentioned manufacturing method, and its component composition conforms to the component composition of the steel piece (slab) of the non-oriented electrical steel sheet used in the manufacturing method. become.

<Composite precipitate of SiO ₂ and Mn ₂ SiO ₄ >
The non-oriented electrical steel sheet according to the present embodiment contains Mn ₂ SiO ₄ composite-precipitated with SiO ₂ in the surface layer portion of the base steel sheet at 0.000001 pieces / μm ² or more and 10.000 pieces / μm ² or less.

SiO ₂ is precipitated by internal oxidation of Si, which is a component composition of the steel sheet. The Mn ₂ SiO ₄ is formed by partially combining the Mn segregation layer formed on the surface layer of the steel sheet derived from Mn in the pickling solution with the SiO ₂ in the steel during finish annealing. Therefore, the Mn ₂ SiO ₄ composite-precipitated with the SiO ₂ is formed on the surface layer portion of the steel sheet base material as shown in the schematic diagram of FIG. The surface layer portion of the steel sheet refers to a region having a depth of 1 μm in the inner direction of the steel sheet from the interface between the steel plate base material (base metal) and the insulating coating. The composite precipitate has a structure (Core / Thin shell structure) in which Mn ₂ SiO ₄ surrounds the spherical SiO ₂ as shown in the schematic diagram of FIG.

Tracing the origin of the above composite precipitate, the composite precipitate confirmed on the surface layer of the non-oriented electrical steel sheet of the product is evidence that the Mn segregation layer was present on the surface of the steel sheet after pickling. I can say. As described above, the Mn segregation layer after pickling is a tight film, which avoids the formation of precipitates that deteriorate the magnetic properties during finish annealing and brings about good magnetic properties. .. Therefore, it is possible to determine the presence or absence of the above effect by observing Mn ₂ SiO ₄ which is compositely precipitated with SiO ₂ and measuring the number density thereof. In order to enjoy such an effect, 0.000001 pieces / μm ² or more of Mn ₂ SiO ₄ complex-precipitated with SiO ₂ is required. On the other hand, if the number of composite precipitates exceeds 10.000 pieces / μm ² , the effect is saturated and the magnetic properties may deteriorate. Therefore, the upper limit of the number density of the composite precipitate is 10.000 / μm ² or less. The number density of the composite precipitate is preferably 0.000005 / μm ² or more and 1.000 / μm ² or less, and more preferably 0.000010 / μm ² or more and 0.100 / μm ² or less. Is.

Here, the number density of the composite precipitates of SiO ₂ and Mn ₂ SiO ₄ appropriately adjusts the composition of the steel pieces and the pickling conditions when manufacturing the non-oriented electrical steel sheet according to the present embodiment. By doing so, it can be controlled.

The verification of the precipitates present on the surface layer of the steel sheet can be carried out by using the following measurement method.
That is, in the cross section (L cross section) parallel to the rolling direction of the product plate (finished annealed plate) subjected to Focused Ion Beam (FIB) processing, the morphology is observed by a transmission electron microscope (TEM) according to a known method. The precipitate present on the surface layer of the base steel plate is evaluated by performing composition analysis or crystal structure analysis by electron beam diffraction with the energy dispersive X-ray analyzer (EDS) attached to the TEM. be able to.

Further, the number of composite precipitates of SiO ₂ and Mn ₂ SiO ₄ existing on the surface layer of the base steel sheet per predetermined area can be measured as follows. That is, at the time of the TEM observation, the number of the composite precipitates is counted for any field of view having a total area of 1 mm ² or more in the above L cross section, and the number of the composite precipitates per 1 mm ² is counted. Just do it.

In the EDS analysis of the precipitate, the element content obtained by the EDS analysis is different between the SiO ₂ portion and the Mn ₂ SiO ₄ portion. Specifically, in the SiO ₂ portion, the peak height of the Si Kα line of EDS and the peak height of Mn Kα are 1.0 times or more and 0.5 times or less, respectively, with respect to the peak height of the OKα line. Any precipitate may be used. Since the SiO ₂ portion is amorphous, an electron diffraction pattern cannot be obtained. Therefore, more accurate analysis can be performed by combining the EDS and the electron diffraction pattern. The Mn ₂ SiO ₄ moiety has a crystal structure. By collating the electron diffraction pattern with the JCPDS card, it is possible to determine whether or not it is Mn ₂ SiO ₄ . For example, JCPDS No. 35-048 can be mentioned. When EDS analysis was performed on Mn ₂ SiO ₄ , the peak height of Si Kα line and the peak height of Mn Kα were 0.5 times or more and 1.0, respectively, with respect to the peak height of OKα line. More than double the EDS spectrum can be obtained.

<Insulation coating>
Subsequently, the insulating coating preferably possessed by the non-oriented electrical steel sheet according to the present embodiment will be briefly described.

Here, the insulating film according to the present embodiment can be obtained by the insulating film forming step of the method for manufacturing a non-oriented electrical steel sheet described above.
In order to improve the magnetic properties of non-oriented electrical steel sheets, it is important to reduce iron loss, and such iron loss is composed of eddy current loss and hysteresis loss. By providing an insulating film on the surface of the steel sheet base material, it is possible to suppress the conduction between the electromagnetic steel sheets laminated as the iron core and reduce the eddy current loss of the iron core, and the practical magnetism of the non-oriented electrical steel sheet. It is possible to further improve the characteristics.

<Measurement method of magnetic properties of non-oriented electrical steel sheets>
The non-oriented electrical steel sheet according to this embodiment has an excellent magnetic property by having the above-mentioned structure. Here, various magnetic properties exhibited by the non-oriented electrical steel sheet according to the present embodiment can be measured by the Epstein method specified in JIS C2550.

Hereinafter, the non-oriented electrical steel sheet according to the present invention will be specifically described with reference to Examples and Comparative Examples. The examples shown below are merely examples of the non-oriented electrical steel sheets according to the present invention, and the non-oriented electrical steel sheets according to the present invention are not limited to the following examples.

(Example 1)
A steel slab containing the composition shown in Table 1 and having the balance of Fe and impurities was heated to 1150 ° C. and then rolled to a thickness of 2.0 mm by hot rolling. Subsequently, the hot-rolled plates of test numbers 1 to 14 and 27 to 34 were subjected to continuous annealing of hot-rolled plates at 1000 ° C. for 40 seconds. The hot-rolled plates of test numbers 15 to 26 were not annealed. Then, the hot-rolled plate and the hot-rolled plate annealed plate were immersed in a pickling solution (pH <1) at 80 ° C. containing 0.25 ± 0.05 g / L of Mn for 30 seconds. Then, the thickness was 0.25 mm by cold rolling, and finish annealing was performed at 1000 ° C. for 15 seconds. After that, a solution containing a metal phosphate as a main component and an acrylic resin emulsion was applied and baked on both sides of the steel sheet to form a composite insulating film, thereby producing a non-oriented electrical steel sheet.
Here, the temperature rising rate of 500 to 800 ° C. in the temperature raising step of the finish annealing was set to 400 ° C./s, and the dew point of the atmosphere was set to −30 ° C. The oxygen potential at the soaking temperature was set to 0.01.
In addition, in Table 1 below, "Tr" means that the corresponding element was not intentionally added.
Then, the magnetic flux density _{B50 and the iron loss W 10/400 were} evaluated for each of the manufactured non-oriented electrical steel sheets by the Epstein method specified in JIS C2550. The obtained results are shown in Table 1 below.
Further, the cross section of the obtained non-oriented electrical steel sheet was observed with a transmission electron microscope (TEM) and measured in 10 fields at a magnification of 10000. The average number of composite precipitates of Mn ₂ SiO ₄ and SiO ₂ was measured. The density was counted. The obtained results are also shown in Table 1.
In the evaluation column, those with an iron loss of 11.5 or less are VG: Very Good (very good), those with an iron loss of more than 11.5 and 12.5 or less are G: Good (good), and those with an iron loss of more than 12.5 are 13.0. The following are defined as F: Fine (effective), and those that cannot be evaluated due to over 13.0 or breakage are defined as NG: Not Good (defective).

(Example 2)
The steel slabs shown in Table 1, whose balance is Fe and impurities, were heated to 1160 ° C. and then rolled to a thickness of 2.0 mm by hot rolling. Subsequently, the hot-rolled plates of test numbers A1 to 15 and a1-2 were annealed at 1000 ° C. for 40 seconds by continuous annealing. The hot-rolled plates of test numbers A16 to A20 were not annealed. Next, the hot-rolled plate and the annealed hot-rolled plate were pickled under the conditions shown in Table 2. Then, the thickness was 0.25 mm by cold rolling, and finish annealing was performed for 15 seconds under the conditions shown in Table 2. After that, a solution containing a metal phosphate as a main component and an acrylic resin emulsion was applied and baked on both sides of the steel sheet to form a composite insulating film, thereby producing a non-oriented electrical steel sheet. Then, the magnetic flux density _{B50 and the iron loss W 10/400 were} evaluated for each of the manufactured non-oriented electrical steel sheets by the Epstein method specified in JIS C2550. The obtained results are shown in Table 2 below.
Further, the cross section of the obtained non-oriented electrical steel sheet was observed with a transmission electron microscope (TEM) and measured in 10 fields at a magnification of 10000. The average number of composite precipitates of Mn ₂ SiO ₄ and SiO ₂ was measured. The density was counted. The obtained results are shown in Table 2 below.
In the evaluation column, as in Table 1, VG: Very Good (very good) with an iron loss of 11.5 or less, G: Good (good) with an iron loss of more than 11.5 and 12.5 or less, 12 If it is more than 5.5 and 13.0 or less, it is F: Fine (effective), and if it is more than 13.0 or cannot be evaluated due to breakage or the like, it is NG: Not Good (defective).

Claims (8)

By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Cu: 0.00% to 1.0% or less, Sn: 0.000% to 0.10%, Sb: Mn ₂ SiO ₄ which contains 0.000% to 0.10%, Ca: 0.0000% to 0.0050%, the balance is Fe and impurities, and is compositely precipitated with SiO ₂ in the surface layer of the base steel plate. A non-directional electromagnetic steel sheet containing 0.000001 pieces / μm ² or more and 10.000 pieces / μm ² or less. By mass%, C: more than 0% to 0.0050% or less, Si: 2.5% to 5.0%, Mn: 0.05% to 4.0%, P: more than 0% to 0.030%. Less than, S: more than 0% to 0.0050% or less, Sol. Al: more than 0% to 0.0040% or less, N: more than 0% to 0.0040%, Ca: 0.0000% to 0.0050%, and the balance was heated from a piece of steel consisting of Fe and impurities. A hot rolling step of later hot rolling to obtain a hot rolled steel plate, a hot rolling plate annealing step of optionally additionally annealing the hot rolled plate, and pickling on the hot rolled plate or the hot rolled plate annealed plate. A cold rolling step of obtaining a cold-rolled steel sheet by performing a single cold rolling or a plurality of cold rolling sandwiching intermediate quenching after the pickling step, and the cold rolling step. It has a finish annealing step of applying a finish annealing to a rolled steel sheet and an insulating coating step of applying an insulating film. The immersion time is 5 seconds or more and 200 seconds or less, ph-1.5 or more and less than 7, and the pickling solution is characterized by containing Mn at 0.01 g / L or more and 2.00 g / L or less. A method for manufacturing a non-directional electromagnetic steel sheet. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein the steel piece contains REM: 0.0001 to 0.0100% in mass%. The method for producing a non-directional electromagnetic steel plate according to claim 3, wherein the pickling solution has a total Cu and Mn content of 0.01 g / L or more and 5.00 g / L or less in the pickling solution. .. 3. 4. The method for manufacturing a non-directional electromagnetic steel plate according to 4. Any of claims 3 to 5, wherein the soaking temperature of the finish annealing is 800 ° C. or higher, and the atmospheric dew point of 500 to 800 ° C. in the heating step is −50 ° C. or higher and 10 ° C. or lower. The method for manufacturing a non-directional electromagnetic steel plate according to item 1. The present invention according to any one of claims 3 to 6, wherein the soothing annealing temperature of the finish annealing is carried out at 800 ° C. or higher, and the oxygen potential at the soaking annealing temperature of the finish annealing is 0.2 or less. The method for manufacturing a non-directional electromagnetic steel sheet according to the description. The steel piece is replaced with a part of Fe in the balance, and further, in mass%, at least one selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10%. The method for producing a grain-containing non-oriented electrical steel sheet according to any one of claims 3 to 7.

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