JP2021031714A - Non-oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

To provide a non-oriented electrical steel sheet that is excellent in magnetic property and film adhesion property, and to provide a method for manufacturing the same.SOLUTION: Provided is a non-oriented electrical steel sheet having: a mother steel sheet having a chemical composition containing, in mass%, C: 0.004% or less, Si: 2.0% or more and 4.0% or less, Al: 0.20 or more and 3.00% or less, Mn: 0.05% or more and 4.00% or less, S: 0.005% or less, N: 0.004% or less, P: 0.20% or less, and at least one of Sn and Sb: 0.001% or more and 0.200% or less in total, and in which the balance is Fe and impurities; and an insulation coating film formed on the surface of the mother steel sheet, and in which an Al-based oxide is present on the surface of the mother steel sheet on the insulation coating film side, and the coverage percentage of the Al-based oxide on the surface of the mother steel sheet is 30% or more and 95% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties and high strength and a method for producing the same. More specifically, the present invention relates to the iron core of an electric device such as a compressor motor of an air conditioner, a hybrid vehicle, an electric vehicle, and a drive motor mounted on a fuel cell vehicle, which are required to have high energy efficiency and small size and high output at the same time. The present invention relates to a non-oriented electrical steel sheet suitable for a material and a method for producing the same.

Due to the growing global environmental problems in recent years, small size, high output, and high energy efficiency are required for electrical equipment, and non-oriented electrical steel sheets, which are core materials, are strongly required to have both low iron loss and high magnetic flux density. ing.

In particular, in drive motors of hybrid vehicles and electric vehicles, measures are taken to increase the number of revolutions in order to compensate for the decrease in torque due to miniaturization. When the number of revolutions is increased, the frequency of the magnetic field applied to the steel sheet increases and the iron loss increases. Therefore, the non-oriented electrical steel sheet, which is the core material, suffers iron loss (high frequency iron loss) at a high frequency. It is required to reduce. Further, in order to increase the number of rotations, strength that does not deform or fatigue fracture even at high speed rotation is required. Further, in order to increase the efficiency of the drive motor of a hybrid vehicle, an electric vehicle, or the like, sufficient cooling of the drive motor is required.

As means for reducing high-frequency iron loss, thinning the plate thickness, increasing the specific resistivity by increasing the content of alloying elements such as Si and Al, controlling the texture by adding Sb and Sn, and increasing the purity of the steel sheet. Etc. have been adopted. However, if Sb or Sn is added to the mother steel sheet in order to reduce iron loss, the film adhesion of the mother steel sheet may decrease after strain removal and quenching for the purpose of removing strain due to punching or processing. .. As a result, the insulating coating may be peeled off from the surface of the mother steel plate and mixed with the refrigerant used for cooling the drive motor, thereby deteriorating the cooling performance.

On the other hand, in Patent Document 1, in order to improve the adhesion of the insulating film, the amount of subscale under the insulating film is set to 1.3 g / m ² or less in terms of oxygen basis weight, and the basis weight of the insulating film is set to be insulated. 0.1~4.0g / ^{m 2} if the type of coating is an inorganic or organic-inorganic composite film has been disclosed that in the case of the organic coating is effective to 0.1~12g / ^{m 2} ..

Further, in Patent Document 2, in order to improve the film adhesion in the non-oriented electrical steel sheet containing a small amount of Sb and Sn to improve the magnetic characteristics, the concentration of Sb and Sn on the surface of the mother steel sheet, Sb + 1 /. It is disclosed that it is effective to suppress 2Sn to 20 wt% or less. As a result, it is possible to prevent the insulating film from peeling off from the surface of the mother steel sheet and being mixed with the refrigerant to deteriorate the cooling performance.

Further, in Patent Document 3, if Cu and Ni are segregated on the surface of the mother steel sheet together with Sb and Sn, the effect of Sb and Sn segregated on the surface of the mother steel sheet to reduce the adhesion of the insulating coating is canceled out, and the surface of the mother steel sheet A technique for improving the adhesion of the insulating coating formed on the steel sheet is disclosed.

However, the non-oriented electrical steel sheets described in Patent Documents 1 and 2 are sufficient to prevent the insulating coating from peeling from the surface of the mother steel sheet during long-term operation of a drive motor of a hybrid vehicle, an electric vehicle, or the like. The film adhesion was not excellent. Therefore, during long-term operation of a drive motor of a hybrid vehicle, an electric vehicle, or the like, there is still a possibility that the insulating film is peeled off from the surface of the mother steel plate and mixed with the refrigerant, resulting in deterioration of cooling performance.

Further, in Patent Document 4, an Al-concentrated layer is formed on the surface of the mother steel sheet, and the Sb and Sn contents on the outermost surface of the mother steel sheet are the Si content in the mother steel sheet and [Sb] + 1/2 [Sn]. ] ≤40 / [Si] can be satisfied to suppress deterioration of corrosion resistance due to oxidation during pure strain removal and quenching, and non-directional electromagnetic steel having excellent corrosion resistance and magnetic properties after purely strain removal and quenching. We provide steel sheets. It is said that this avoids the occurrence of rust on the mother steel sheet, but the effect on the adhesion of the coating film is not sufficient.

Japanese Unexamined Patent Publication No. 2001-279400 Japanese Unexamined Patent Publication No. 8-291375 Japanese Unexamined Patent Publication No. 2017-82276 Japanese Unexamined Patent Publication No. 2003-293101

The present invention has been made in view of the above circumstances, and when Sb and Sn are added to the base steel sheet in order to reduce high-frequency iron loss, Sb and Sn segregate on the surface of the base steel sheet and onto the surface of the base steel sheet. By detoxifying the action of reducing the adhesion of the formed insulating coating, it is sufficient to prevent the insulating coating from peeling off from the surface of the base steel plate during long-term operation of a drive motor such as a hybrid vehicle or an electric vehicle. An object of the present invention is to provide a non-oriented electrical steel sheet having excellent film adhesion and a method for producing the same.

In order to solve the above problems, the present inventors have conducted diligent research on the change in the adhesion of the insulating film depending on the oxide coating state on the surface of the mother steel sheet when Sb and Sn are segregated on the surface of the mother steel sheet. It was. As a result, if an Al-based oxide is present on the surface of the mother steel sheet at a predetermined coverage, it is formed on the surface of the mother steel sheet by canceling the effect of Sb and Sn segregated on the surface of the mother steel sheet to reduce the adhesion of the insulating film. It was found that the adhesiveness of the insulating coating can be improved. The present invention has been made based on these findings, and the gist thereof is as follows.

That is, in the present invention, in terms of mass%, C: 0.004% or less, Si: 2.0% or more and 4.0% or less, Al: 0.20 or more and 3.00% or less, Mn: 0.05% or more. 4.00% or less, S: 0.005% or less, N: 0.004% or less, P: 0.20% or less, and at least one of Sn and Sb: 0.001% or more and 0.200 in total A non-directional electromagnetic steel sheet containing% or less and having a chemical composition in which the balance is composed of Fe and impurities, and an insulating film formed on the surface of the mother steel sheet, wherein the mother steel sheet is the above-mentioned. Provided is a non-directional electromagnetic steel sheet in which an Al-based oxide is present on the surface on the insulating coating side and the coverage of the Al-based oxide on the surface of the mother steel sheet is 30% or more and 95% or less.

Further, the present invention is a method for producing a non-directional electromagnetic steel sheet, wherein the slab having the above-mentioned chemical composition is heated to a temperature of 1000 ° C. or higher and 1250 ° C. or lower in a heating furnace. It is obtained by the slab heating step, the hot rolling step in which the heated slab is hot-rolled, water-cooled after the final rolling pass, and wound into a coil at a temperature of 650 ° C. or lower, and the hot rolling step. A hot-rolled sheet annealing / pickling step in which a hot-rolled steel sheet is annealed and pickled, and a cold-rolled sheet obtained by the above-mentioned hot-rolled sheet annealing / pickling step is cold-rolled. There are a step, a finish annealing step of applying finish annealing to the cold-rolled steel sheet obtained by the cold rolling step, and an insulating film forming step of forming an insulating film on the surface of the steel sheet obtained by the finish annealing step. However, in the finish annealing step, the atmosphere in the temperature range of 500 ° C. or higher and 900 ° C. or lower before first reaching 900 ° C. is the partial pressure ratio P (H _{2 ) of water vapor (H 2} O) and hydrogen (H _2). Provided is a method for producing a non-directional electromagnetic steel sheet, wherein O) / P (H ₂ ) is 0.002 or more and 0.100 or less, and the residence time in the above temperature range is 40 seconds or less.

According to the present invention, omnidirectional electromagnetic steel having excellent film adhesion is sufficient to prevent the insulating film from peeling off from the surface of the mother steel plate during long-term operation of a drive motor of a hybrid vehicle, an electric vehicle, or the like. A steel plate and a method for manufacturing the same can be provided. The non-oriented electrical steel sheet obtained by the present invention is extremely effective in improving the small size, high output, and high energy efficiency of electrical equipment, and its industrial value is extremely high.

It is a figure which shows the example of the element mapping image by EPMA.

Hereinafter, the non-oriented electrical steel sheet of the present invention and its manufacturing method will be described in detail.

A. Non-oriented electrical steel sheet Hereinafter, each configuration of the non-oriented electrical steel sheet of the present invention will be described.

1. 1. Mother steel plate a. Chemical Composition First, the reason for limiting the chemical composition of the grain steel sheet in the non-oriented electrical steel sheet of the present invention will be described. In the following, the content of each component is a value in% by mass.

(1) C
C is contained as an impurity, and when the content exceeds 0.004%, fine carbides are precipitated and the iron loss increases remarkably. Therefore, the C content is set to 0.004% or less. From this viewpoint, the C content is preferably 0.003% or less, more preferably 0.002% or less.

(2) Si
Since Si has an action of increasing specific resistance, it is contained in order to reduce iron loss. It is also effective in improving the strength of the steel sheet. However, excessive Si content reduces the saturation magnetic flux density, causing embrittlement of the steel and an increase in the finish annealing temperature, further increasing the cost. From these viewpoints, the Si content is set to 2.0% or more and 4.0% or less. From these viewpoints, the Si content is preferably 2.5% or more, more preferably 3.0% or more, and the Si content is preferably 3.5% or less.

(3) Al
Since Al has an action of increasing specific resistance like Si, it is contained in order to reduce iron loss. Further, in the present invention, Al is an essential element in the present invention because the adhesion of the insulating film formed on the surface of the mother steel sheet is improved by utilizing the Al-based oxide. In order to improve the adhesion of the insulating film, the Al content is 0.20% or more. The Al content is preferably 0.6% or more, more preferably 0.9% or more, still more preferably 1.4% or more. However, if Al is excessively contained, the coverage of the Al-based oxide on the surface of the mother steel sheet becomes excessive, which not only lowers the adhesion of the insulating film but also reduces the saturation magnetic flux density, which is disadvantageous in terms of magnetic flux density. It becomes. From these viewpoints, the Al content is set to 3.00% or less.

(4) Mn
Since Mn has an action of increasing specific resistance like Si and Al, it is contained in order to reduce iron loss. However, if Mn is excessively contained, the saturation magnetic flux density is reduced, which is disadvantageous in terms of magnetic flux density. From these viewpoints, the Mn content is 0.05% or more and 4.00% or less. From these viewpoints, the Mn content is preferably 3.00% or less, more preferably 2.00% or less.

(5) S
When the content of S exceeds 0.005%, a large amount of sulfides such as MnS are precipitated and the iron loss increases remarkably. Therefore, the S content is set to 0.005% or less. From these viewpoints, the S content is preferably 0.003% or less, more preferably 0.002% or less.

(6) N
When the content of N exceeds 0.004%, the increase in iron loss becomes remarkable due to the increase in nitride. Therefore, the N content is set to 0.004% or less.

(7) P
Like Si, P is an element effective for improving the strength of the steel sheet. However, excessive content causes embrittlement of steel. From this point of view, the P content is 0.20% or less. Since the segregation site of P competes with Sn and Sb when segregating on the surface of the mother steel sheet, segregation of Sn and Sb on the surface of the mother steel sheet is suppressed by segregating P on the surface of the mother steel sheet, and the surface of the mother steel sheet is suppressed. It is possible to obtain the effect of suppressing a decrease in the adhesiveness of the insulating coating formed on the steel sheet. Therefore, in order to improve the adhesion of the insulating film formed on the surface of the mother steel sheet, it is preferable to contain P so that P segregates on the surface of the mother steel sheet. From this viewpoint, the P content is preferably 0.05% or more and 0.20% or less.

(8) Sn and Sb
Since Sn and Sb have the effect of improving the texture of the electrical steel sheet and reducing iron loss, at least one of Sn and Sb is contained. Further, when heated to a high temperature in a nitrogen atmosphere containing hydrogen, there is also an iron loss reducing effect by preventing the invasion of nitrogen from the surface of the steel and suppressing the formation of AlN. When Sn or Sb is contained, it segregates and thickens on the surface of the mother steel sheet, thereby lowering the adhesion of the insulating film formed on the surface of the mother steel sheet, but due to the action of the Al-based oxide described later, The effect of suppressing the decrease in film adhesion can be obtained. However, if Sn or Sb is excessively contained, the decrease in film adhesion cannot be avoided despite the effect of suppressing the decrease in film adhesion due to the Al-based oxide described later. Further, if Sn or Sb is excessively contained, the crystal grain growth will be inhibited. From these viewpoints, the total content of Sn and Sb is 0.001% or more and 0.200% or less. From these viewpoints, the total content is preferably 0.003% or more, more preferably 0.010% or more, still more preferably 0.030% or more. The total content is preferably 0.100% or less.

(9) Ca, Mg, and REM
Ca, Mg, and REM are elements effective in controlling the morphology of inclusions, and effectively reduce iron loss through the action of promoting the growth of crystal grains. Therefore, at least one selected from the group consisting of Ca, Mg, and REM may be contained in place of a part of Fe. However, even if the content of any of the elements exceeds 0.01%, the effect of the above action is saturated and it is disadvantageous in terms of cost. Therefore, it is preferable that the Ca content is 0.01% or less, the Mg content is 0.01% or less, and the REM content is 0.01% or less. More preferably, the Ca content is 0.005% or less, the Mg content is 0.005% or less, and the REM content is 0.005% or less. In order to obtain the effect of the above action more reliably, the content of any of the elements is preferably 0.001% or more.

Here, REM is a general term for a total of 17 elements of Sc, Y, and lanthanoids. The REM may contain one or more of the 17 elements in total. The content of REM refers to the total content of these elements.

(10) Cu, Cr and Ni
Cu, Cr, and Ni, together with Sn and Sb, segregate and thicken on the surface of the mother steel sheet, thereby having an effect of canceling the decrease in film adhesion due to the segregated Sn and Sb on the surface. Therefore, at least one of Cu, Cr and Ni may be contained in place of a part of Fe. However, since the addition of Cu, Cr, and Ni causes an increase in alloy cost, the Cu content, Cr content, and Ni content are preferably 1.0% or less, respectively. In order to obtain the effect of the above action, it is preferable to contain at least one of Cu, Cr and Ni in a total of 0.02% or more.

(11) Remaining portion The remaining portion is Fe and impurities. Of the impurities, Ti, V, Nb, Zr, and Se, which adversely affect the grain growth, are preferably reduced as much as possible, and the content of each is preferably 0.008% or less. Further, B may be contained in an amount of 0.0010% or less.

Here, the chemical composition of the grain steel sheet is measured by removing the insulating film from the non-oriented electrical steel sheet and using the steel sheet from which the insulating film has been removed as the grain steel sheet, and measuring the master steel sheet. The method for removing the insulating film will be described later.

b. Al-based oxide In the present invention, Al-based oxide is present on the surface of the mother steel sheet on the insulating coating side, that is, at the interface between the mother steel plate and the insulating coating, and the coverage of the Al-based oxide on the surface of the mother steel sheet is 30. It is characterized by being% or more and 95% or less. It is not clear why the decrease in adhesion of the insulating coating due to Sn and / or Sb can be suppressed by the presence of the Al-based oxide on the surface of the base steel sheet on the insulating coating side at a predetermined coating ratio. It can be considered as follows. That is, in the mother steel sheet, Sn and / or Sb, which cause a decrease in film adhesion, segregate in the inner layer rather than the Al oxide. Therefore, when the Al oxide is present on the surface of the mother steel sheet at a predetermined coverage, Sn and / or Sb are segregated. Segregation of and / or Sb on the surface of the mother steel sheet can be suppressed, and Sb and / or Sn segregate on the surface of the mother steel sheet to substantially reduce the adhesion of the insulating film formed on the surface of the mother steel sheet. It is thought that this is because it can be detoxified. Regarding the oxide formed on the surface of the mother steel sheet, although it depends on the chemical composition of the mother steel sheet and the oxidation conditions such as the oxidizing atmosphere and temperature, in the non-directional electromagnetic steel sheet, Al, Mn, Si, Cr and the like are used. It is known that oxides are formed. Of these, the Al-based oxide has a lower crystal lattice consistency with the mother steel plate than other oxides such as Si-based oxides, so that the segregation element is present at the interface between the Al-based oxide and the mother steel plate. Easy to be trapped. As a result, it is presumed that the presence of the Al-based oxide on the surface of the mother steel sheet at a predetermined coating ratio can suppress the segregation of Sn and Sb at the interface between the insulating film and the mother steel sheet.

Here, there is also a document that the formation of Al-based oxides should be avoided in order to avoid deterioration of film adhesion. On the other hand, in the present invention, the Al-based oxide acts effectively for ensuring the film adhesion. This difference is not clear, but it can be considered as follows. That is, it is considered that conventionally, since the oxidation of the steel sheet proceeds on the entire surface of the steel sheet, the steel sheet is covered with a film-like Al-based oxide, and the oxygen supply to the inside of the steel sheet is cut off. To. In this situation, the internal oxide existing in the surface layer region of the steel sheet is reduced and decomposed, and voids are formed in the surface layer region of the steel sheet in the decomposition process. Then, it is presumed that this void became the starting point of the film peeling and lowered the film adhesion. On the other hand, in the present invention, the surface of the steel sheet is kept in a state where oxidation does not proceed on the entire surface due to the chemical composition of the steel sheet, heat treatment conditions, etc., and the coverage of the Al-based oxide on the surface of the steel sheet is controlled within an appropriate range. There is. Therefore, the formation of voids in the surface layer region of the steel sheet is suppressed, and the non-uniformity of the coating by the Al-based oxide complicates the interface structure between the insulating film and the steel sheet, which is advantageous for ensuring the film adhesion. It is thought that it has become.

The coverage of the Al-based oxide on the surface of the base steel sheet is 30% or more and 95% or less, preferably 40% or more and 90% or less, and more preferably 50% or more and 80% or less. The higher the coverage, the more trap sites Sn and Sb are, and the more the surface segregation can be suppressed. On the other hand, the higher the coating ratio, the better the film adhesion, but if the coating ratio is too high, the Al-based oxide becomes thicker, so that the peeling at the interface between the Al-based oxide and the mother steel plate has a mechanical effect. May occur. Therefore, the coverage is preferably within the above range.

In the present invention, the coverage of Al-based oxides on the surface of the above-mentioned grain steel sheet is measured with respect to the grain steel sheet in which the insulating film is removed in the non-oriented electrical steel sheet and the steel sheet from which the insulating film is removed is used as the grain steel sheet. To carry out. Specifically, the coverage of Al-based oxides on the surface of the mother steel sheet is determined by performing mapping analysis on Al and O on the surface of the mother steel sheet using an electron probe microanalyzer (EPMA). Typical test conditions are an acceleration voltage of 15 kV, an irradiation current of 100 nA, an irradiation time of 50 ms, an observation field of view of 200 μm × 200 μm, and a number of divisions of 400 × 400. Here, a region having an Al concentration of 5% or more and an O concentration of 5% or more determined by EPMA measurement is defined as a coating region with an Al-based oxide. An example of measuring the distribution of Fe, Si, Al, and O by the above method is shown in FIG. In the example shown in FIG. 1, the coverage of the Al-based oxide on the surface of the mother steel sheet is 90%.

The insulating coating is removed by the following method. That is, the non-oriented electrical steel sheet having an insulation coating, NaOH: _10% by _weight, H 2 O: 90 wt% aqueous sodium hydroxide, 5 minutes at 80 ° C., immersion.

2. Insulating film The non-oriented electrical steel sheet of the present invention further has an insulating film formed on the surface of the base steel sheet in order to insulate between the laminated steel sheets in the iron core.

It is necessary to secure a film thickness of the insulating film formed on the surface of the base steel sheet in order to insulate between the laminated steel sheets in the iron core, but if it is too thick, the film adhesion is lowered and it is easy to peel off. From these viewpoints, the film thickness of the insulating film is preferably 0.1 μm or more and 0.5 μm or less. If the film thickness of the insulating film is too thick, the film adhesion will decrease. When the electromagnetic steel sheet is punched into the motor steel core and then strain-removed and annealed, the oxygen contained in the insulating film reacts with the surface of the mother steel sheet to cause new oxidation. It is presumed that the cause is the formation of a film.

3. 3. Plate Thickness The present invention is essentially premised on achieving high frequency low iron loss. Therefore, the thickness of the non-oriented electrical steel sheet is preferably 0.30 mm or less. On the other hand, excessive thinning may lead to an extreme decrease in space factor and a decrease in productivity of the iron core due to deterioration of flatness. Therefore, the thickness of the non-oriented electrical steel sheet is preferably 0.10 mm or more.

4. Manufacturing Method The non-oriented electrical steel sheet of the present invention is preferably manufactured by the non-oriented electrical steel sheet manufacturing method described later.

B. Method for manufacturing grain-oriented electrical steel sheet Next, each step in the method for manufacturing grain-oriented electrical steel sheet of the present invention will be described.
The process conditions required to identify the present invention relate to a slab heating process, a hot rolling process and a finish annealing process. The following description of the conditions of the steps other than these shows general conditions for reference, and even if the conditions are not satisfied, the effect of the present invention can be obtained.

1. 1. Slab heating step In the slab heating step, a slab having the above-mentioned chemical composition is heated to a temperature of 1000 ° C. or higher and 1250 ° C. or lower in a heating furnace. If the heating temperature is less than 1000 ° C., scale formation on the slab surface is insufficient, the surface texture of the steel sheet deteriorates, and there is a risk of causing breakage in the cold rolling process. Further, if the heating temperature exceeds 1250 ° C., the sulfide in the slab may be solid-solved and finely precipitated during hot spreading to deteriorate the iron loss. The heating temperature is preferably 1050 ° C or higher and 1200 ° C or lower.

2. Hot rolling step In the hot rolling step, the slab after heating is hot-rolled, and after the final rolling pass, it is water-cooled and wound into a coil at a temperature of 650 ° C. or lower.

In the present invention, the temperature specified here means the surface temperature of the steel sheet after hot rolling, and the surface temperature of the steel sheet after hot rolling means the temperature measured by a contact thermometer or a radiation thermometer. To do.

If the temperature at which the coil is wound after the final rolling pass exceeds 650 ° C., the scale layer on the surface of the mother steel sheet becomes thick and internal oxidation may occur, which may cause deterioration of magnetic properties. Furthermore, when pickling is strengthened to remove scale, Al is removed from the surface layer of the mother steel sheet as a large amount of oxide, which causes a decrease in the Al concentration on the surface layer of the mother steel sheet, resulting in the formation of Al-based oxides in the finish annealing step described later. It can also be a hindrance factor.

Further, the conditions of the hot rolling process other than this are not particularly limited.

3. 3. Hot-rolled plate annealing / pickling step In the hot-rolled plate annealing / pickling step, the hot-rolled steel sheet obtained by the hot rolling step is annealed and pickled. Pickling and hot-rolled plate annealing are in no particular order, and hot-rolled plate annealing may be performed after pickling, or pickling may be performed after hot-rolled plate annealing.

The conditions for hot-rolled sheet annealing are not particularly limited, but when hot-rolled sheet is annealed, the hot-rolled steel sheet is held in a temperature range of 700 ° C. or higher and 1100 ° C. or lower for 1 minute or longer and 24 hours or shorter. Is preferable. This is because when the hot-rolled sheet annealing temperature is lower than the above range, the strain accumulated in the hot-rolled steel sheet is not released and the possibility of fracture in the cold rolling in the subsequent process increases, and the hot-rolled sheet annealing time is described above. If it falls below the range, the possibility of breaking in cold rolling increases for the same reason. Further, when the hot-rolled plate annealing temperature exceeds the above range, the addition to the equipment becomes large, and when the hot-rolled plate annealing time exceeds the above range, the productivity is deteriorated.

Further, the annealing atmosphere preferably contains hydrogen from the viewpoint of suppressing scale growth on the surface of the mother steel sheet, and more preferably the hydrogen concentration is 10% by volume or more. Further, the annealing atmosphere preferably contains nitrogen as a main gas from the viewpoint of cost.

The hot-rolled plate annealing method may be a continuous annealing method or a batch annealing method. The hot-rolled sheet annealing conditions are preferably adjusted in order to control the crystal structure of the mother steel sheet after annealing according to the required magnetic properties and production efficiency. For example, in order to improve the magnetic flux density, it is preferable to adjust the annealing temperature and annealing time so that the crystal grain size of the mother steel sheet after annealing is 40 μm or more.

On the other hand, the pickling conditions are not particularly limited, and for example, the main component of the pickling solution can be hydrochloric acid and the temperature can be 80 ° C. or higher.

4. Cold rolling step In the cold rolling step, the hot-rolled annealed sheet obtained by the above-mentioned hot-rolled sheet annealing / pickling step is cold-rolled. Cold rolling conditions such as cold rolling reduction are not particularly limited and may be normal conditions. For example, the cold spreading reduction rate can be 70% or more.

5. Finish Annealing Step In the finish annealing step, the cold-rolled steel sheet obtained by the cold rolling step is subjected to finish annealing to form an Al-based oxide on the surface of the steel sheet. In the finish annealing step, Al-based oxides are formed on the surface of the mother steel sheet in an appropriate form by controlling the atmosphere and residence time in the temperature range of 500 ° C. or higher and 900 ° C. or lower before first reaching 900 ° C. be able to.

The atmosphere in the above temperature range is preferably such that the partial pressure ratio of _{water vapor (H 2} O) and hydrogen (H _{2 ) and P (H 2} O) / P (H ₂ ) are 0.002 or more and 0.100 or less. .. If P (H ₂ O) / P (H ₂ ) is less than 0.002, a reducing atmosphere may be formed and it may be difficult to form an Al-based oxide. P (H ₂ O) / P (H ₂ ) is preferably 0.01 or more, more preferably 0.03 or more. On the other hand, if P (H ₂ O) / P (H ₂ ) exceeds 0.100, internal oxidation may proceed and the magnetic characteristics may be deteriorated.

The residence time in the above temperature range is preferably 40 seconds or less. If the residence time exceeds 40 seconds, internal oxidation may proceed and the magnetic characteristics may deteriorate. The residence time is preferably 20 seconds or less, more preferably 10 seconds or less. If the residence time is short, it becomes difficult to form a sufficient Al-based oxide depending on the above atmosphere. Therefore, the residence time is appropriately adjusted in consideration of the above atmosphere. However, such adjustment is not difficult for those skilled in the art who routinely carry out heat treatment in which the surface oxidation state of the steel sheet is controlled.

Here, if only the Al-based oxide is formed on the surface of the steel sheet, it can be carried out by adjusting the atmosphere and the residence time in a temperature range exceeding 900 ° C., for example. And such adjustment is also relatively easy for those skilled in the art as described above. However, in the temperature range of 900 ° C. or higher, the diffusion rate of oxygen in the steel becomes high, and it becomes difficult to control the formation of oxides in an appropriate form. In particular, in the present invention, since it is necessary to control the growth and morphology of the oxide in consideration of the surface segregation of Sn and Sb generated during high temperature holding, the Al-based oxide first reaches 900 ° C. in the finish annealing step. When the film is formed in a temperature range of 500 ° C. or higher and 900 ° C. or lower before annealing, and then the temperature is raised to 900 ° C. or higher, it is preferable to create an atmosphere that suppresses the formation of Al-based oxides in the temperature range of 900 ° C. or higher. .. Specifically, in the temperature range of 900 ° C. or higher, _{it is preferable that P (H 2} O) / P (H ₂ ) is less than 0.002 for the atmosphere.

Further, although it is possible to control the formation of oxides on the surface of the steel sheet even in the cooling process of finish annealing, the present invention determines the growth and morphology of oxides in consideration of the surface segregation of Sn and Sb generated during high temperature holding. Since it is controlled, in order to obtain the effect of the invention, it is necessary to control the formation of oxides before reaching the high temperature region for the first time in the finish annealing step, specifically, before reaching 900 ° C. preferable.

Further, in the temperature range over 900 ° C., the maximum temperature reached and the residence time may be appropriately determined in consideration of the target magnetic properties through recrystallization and grain growth of the steel sheet structure. As a general condition, the maximum temperature reached can be 950 ° C. or higher and 1200 ° C. or lower, and the residence time can be 10 seconds or longer and 300 seconds or lower.

The atmosphere and residence time in the temperature range of 500 ° C. or higher and 900 ° C. or lower are preferable conditions for producing the non-oriented electrical steel sheet having excellent magnetic properties and film adhesion of the present invention. As a matter of course, the formation behavior of Al-based oxides on the surface of the steel sheet is influenced not only by the chemical composition of the steel sheet, especially the Al content, but also by elements competing in oxide formation, such as Si, Mn, Cr, etc. Furthermore, it is affected by Sn, Sb, Cu, Ni, P, B, S, etc., which tend to segregate on the surface of the steel sheet. Therefore, even if the conditions deviate from the preferable conditions of the atmosphere and the residence time in the above temperature range, the finish annealing is performed so as to satisfy the coverage of the Al-based oxide on the surface of the mother steel sheet specified in the present invention. Is included in the scope of the present invention. Some adjustment is required depending on the chemical composition of the steel sheet, but it is appropriate to form an Al-based oxide on the surface of the steel sheet by several trials as necessary with reference to the preferable conditions of the atmosphere and residence time in the above temperature range. It is not difficult for a person skilled in the art who routinely performs heat treatment in which the surface oxidation state of the steel sheet is controlled.

6. Insulating film forming step In the insulating film forming step, an insulating film is formed on the surface of the steel sheet obtained by the above finish annealing step. The insulating film can be formed by applying a coating liquid to the surface of the steel sheet obtained by the above finish annealing step and baking it. The insulating film forming conditions and the coating liquid may be the same as usual.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

[Example 1]
(Manufacturing of non-oriented electrical steel sheet)
Sample No. shown in Table 1. Steels having a chemical composition of A01 to A19 were melted in vacuum, cast into a 25 kg ingot, heated to 1150 ° C., and then forged into a steel piece having a thickness of 40 mm. Next, the steel pieces were heated to 1150 ° C. in a heating furnace and hot-rolled to a plate thickness of 2.0 mm. The hot rolling was completed at a surface temperature of 850 ° C., which is the end temperature of the hot rolling. Next, the hot-rolled steel sheet was water-cooled to a surface temperature of 650 ° C. for 1 hour, and then air-cooled. Next, the air-cooled steel sheet was held at 950 ° C. for 30 seconds in a nitrogen atmosphere for 30 seconds to perform hot-rolled sheet baking, and then allowed to cool in the air. Next, the steel sheet after hot-rolling and pure was pickled and then cold-rolled to a thickness of 0.25 mm. Next, the steel sheet after cold rolling was degreased and then subjected to finish quenching in a nitrogen / hydrogen mixed atmosphere at 1000 ° C. for 30 seconds. At this time, in the temperature range of 500 ° C. or higher and 900 ° C. or lower in the heating process _{, Al-based oxidation is performed by adjusting the atmosphere P (H 2} O) / P (H ₂ ) and the residence time as shown in Table 1. Controlled the morphology of things. _{The P (H 2} O) / P (H ₂ ) in the atmosphere after reaching 900 ° C. was set to less than 0.002. Next, an organic-inorganic composite coating liquid was applied to the surface of the steel sheet after finish baking and baked to form an insulating film having a thickness of 0.5 μm.

(Coating rate of Al-based oxide on the surface of the mother steel sheet)
With respect to the non-oriented electrical steel sheet obtained as described above, after removing the insulating film by the above-mentioned method, the coverage of Al-based oxide on the surface of the mother steel sheet was measured. The results are shown in Table 1 below.

(Film adhesion)
The film adhesion was evaluated for the non-oriented electrical steel sheets obtained as described above. First, the first peeling test was performed on the insulating film formed on the surface of the base steel sheet of the non-oriented electrical steel sheet obtained as described above. In the first peeling test, after bending 180 degrees so as to wrap it around a stainless steel rod with a diameter of 10 mm, and then applying cellophane tape to the surface of the mother steel plate (inner surface during bending) that was bent back, the presence or absence of peeling of the insulating film was checked. It was evaluated visually, and the ratio of the area where the insulating film was peeled off was measured as the peeling rate [%]. Further, as a result of the first peeling test, the non-oriented electrical steel sheet in which the insulating film was not peeled was subjected to the second peeling test after the heat treatment held at 600 ° C. for 2 hours in a nitrogen atmosphere. In the second peeling test as well, after bending 180 degrees so as to wrap it around a stainless steel rod with a diameter of 10 mm, and then applying cellophane tape to the surface of the mother steel plate (inner surface during bending) that was bent back, the presence or absence of peeling of the insulating film was checked. It was evaluated visually. Further, as a result of the second peeling test, the non-oriented electrical steel sheet in which the insulating film was not peeled was subjected to the third peeling test after the heat treatment held at 600 ° C. for 2 hours in a nitrogen atmosphere. In the third peeling test as well, after bending 180 degrees so as to wrap it around a stainless steel rod with a diameter of 10 mm, and then applying cellophane tape to the surface of the mother steel plate (inner surface during bending) that was bent back, the presence or absence of peeling of the insulating film was checked. It was evaluated visually. From this, the film adhesion of the insulating film formed on the surface of the mother steel sheet was evaluated. The results are shown in Table 1 below. The evaluation criteria for the film adhesion of the insulating film formed on the surface of the base steel sheet are as follows.

2: No peeling in the 3rd peeling test 1: No peeling in the 2nd peeling test No peeling in the 3rd peeling test 0: No peeling in the 1st peeling test and peeling in the 2nd peeling test -1 1: Peeling rate in the first peeling test 10% or less -2: Peeling rate in the first peeling test more than 10% 20% or less -3: Peeling rate in the first peeling test more than 20% 30% or less- 4: Peeling rate over 30% in the first peeling test 40% or less -5: Peeling rate over 40% in the first peeling test

(Strength and magnetic properties)
A JIS No. 5 tensile test piece was taken from the non-oriented electrical steel sheet obtained as described above, and a tensile test was performed to evaluate the yield stress (YS) [MPa]. Further, a 55 mm square single plate test piece is punched from the non-oriented electrical steel sheet obtained as described above, and using a single plate magnetic measuring instrument, iron loss W _10/400 [W / kg] (maximum at 400 Hz). The average value of the iron loss in the rolling direction and the iron loss in the direction perpendicular to the rolling when the magnetic flux density was alternately excited to 1.0 T) was measured. The results are shown in Table 1 below.

(Evaluation)
Sample No. in which the steel plate components are substantially the same. In A01 to A05, sample No. in which Al-based oxide was not substantially formed. Sample No. A01, which has a low coverage even if Al-based oxides are formed. A02, Sample No. with excessive coverage. Sample No. in which Al-based oxide is appropriately formed with respect to A05. The film adhesion of A03 and A04 was good.

In addition, sample No. which further utilized Cu and Ni for surface modification of the mother steel sheet. In A06 to A10, the effect of Al-based oxide was confirmed. Sample No. In A06 and A07, the formation of the Al oxide film was insufficient, but the film adhesion was good due to the effects of Cu and Ni. Sample No. Since the characteristics of A06 are not inferior, it was used as a reference example in this example. Sample No. A07 is the sample No. Al-based oxide was formed on A06, but the coverage was insufficient, and sample No. Since the effect did not appear as compared with A06, it was used as a comparative example. For these, sample No. Comparing A08 and A09, it was confirmed that the Al-based oxide had the effect of further improving the film adhesion. In addition, the sample No. in which the Al-based oxide is excessive. The film adhesion of A10 is the sample No. It was inferior to A06 and A07, suggesting that excess Al-based oxide significantly deteriorates the adhesion.

In addition, sample No. A11 to A19 are sample No. having a high Al content. A similar study was conducted on steel grades having a lower Al content than A01 to A10. Sample No. The same effect as A01 to A10 could be confirmed.

In addition, sample No. In A15, the finish annealing conditions are the above-mentioned preferable conditions, but the coverage of the Al-based oxide is not sufficient because the Al content of the steel sheet is low. Sample No. It can be judged that A15 secures the film adhesion due to the effects of Cu and Ni, and the sample No. Similar to A06, this example was used as a reference example. On the other hand, sample No. Although A17 is manufactured under conditions where the residence time under the finish annealing conditions does not meet the above-mentioned preferable conditions, the Al content of the steel sheet is low and the formation of Al-based oxides tends to be suppressed, resulting in the result on the surface of the steel sheet. The coverage of the Al-based oxide remained within the range of the present invention, and the effect of improving the film adhesion was exhibited.

[Example 2]
Sample No. having the chemical composition shown in Table 2 below. The steels B01 to D08 were melted in vacuum, cast into a piece of steel having a thickness of 40 mm, heated to 1150 ° C., and then hot-rolled to a plate thickness of 2.0 mm. The hot rolling was completed at a surface temperature of 850 ° C., which is the end temperature of the hot rolling. Next, the hot-rolled steel sheet was water-cooled to a surface temperature of 650 ° C. for 1 hour, and then air-cooled. Next, the air-cooled steel sheet was kept at 1000 ° C. for 30 seconds in a nitrogen atmosphere for 30 seconds to perform hot-rolled sheet baking, and then allowed to cool in the air. Next, the steel sheet after hot-rolling and pure was pickled and then cold-rolled to a thickness of 0.20 mm. Next, the steel sheet after cold rolling was degreased and then finish-baked. At this time, in the temperature range of 500 ° C. or higher and 900 ° C. or lower in the heating process, the atmosphere P (H ₂ O) / P (H ₂ ) was 0.03 and the residence time was 40 seconds, which were fixed conditions. In this example, the morphology of the Al-based oxide was controlled mainly by the steel sheet component, particularly the Al content. _{The P (H 2} O) / P (H ₂ ) in the atmosphere after reaching 900 ° C. was set to less than 0.002. Next, an organic-inorganic composite coating liquid was applied to the surface of the steel sheet after finish baking and baked to form an insulating film having a thickness of 0.3 μm.

(Coating rate of Al-based oxide on the surface of the mother steel sheet)
With respect to the non-oriented electrical steel sheet obtained as described above, the coverage of Al-based oxide on the surface of the grain steel sheet was measured in the same manner as in Example 1. The results are shown in Table 2 below.

(Film adhesion)
With respect to the non-oriented electrical steel sheet obtained as described above, the film adhesion was evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

(Strength and magnetic properties)
With respect to the non-oriented electrical steel sheet obtained as described above, the yield stress (YS) and the iron loss W _10/400 were measured in the same manner as in Example 1. The results are shown in Table 2 below.

(Evaluation)
Sample No. in which the steel sheet components other than Al were substantially the same and the Al content was changed. In B01 to B06 and B07 to B10, sample No. in which Al-based oxide was not substantially formed. Sample No. which has a low coverage even if B01, B07, and Al oxides are formed. B02, sample No. with excessive coverage. Sample No. in which Al-based oxides are appropriately formed with respect to B06 and B10. The film adhesion of B03 to B05, B08, and B09 was good.

Sample No. C01 to C11 are examples in which the effects of Al-based oxides are confirmed according to the Sn and Sb contents in steel sheets having the same Al content. Sample No. in which Al-based oxide was appropriately formed. It was confirmed that C02 to C04, C06, C07, and C09 to C11 exhibited good film adhesion in the steel sheet containing Sn and Sb within the range specified by the present invention. Sample No. Since C01 does not contain Sn and Sb, the film adhesion is not so bad, but the film adhesion is not particularly preferable even though it forms an Al-based oxide. In addition, sample No. Since C05 and C08 contain an excess of Sn and Sb, sufficient film adhesion could not be obtained even if the Al-based oxide of the present invention was applied.

In addition, sample No. D02, D03 and D05 to D08 are sample Nos. Based on the chemical composition of the steel sheets of B02, B03 and B05 to B08, Cu and Ni are further added to each of them for surface modification of the mother steel sheet. Sample No. B-series film adhesion and sample No. Comparing the film adhesion of the D series, only when the Al-based oxide is formed in an appropriate range, the film adhesion improving effect of the Al-based oxide is superimposed on the film adhesion ensuring effect of Cu and Ni. It was.

By comparing Table 1 and Table 2 as a whole, the effect of improving the film adhesion by the Al-based oxide of the present invention is that the steel sheet containing Sn or Sb at the same time is more effective than the steel sheet containing Sn or Sb alone. It was confirmed that a more remarkable effect appears in.

Claims (2)

By mass%, C: 0.004% or less, Si: 2.0% or more and 4.0% or less, Al: 0.20 or more and 3.00% or less, Mn: 0.05% or more and 4.00% or less, S: 0.005% or less, N: 0.004% or less, P: 0.20% or less, and at least one of Sn and Sb: 0.001% or more and 0.200% or less in total. A non-directional electromagnetic steel plate having a mother steel plate having a chemical composition in which the balance is composed of Fe and impurities and an insulating film formed on the surface of the mother steel plate.
Al-based oxide is present on the surface of the mother steel sheet on the insulating coating side,
A non-oriented electrical steel sheet having a coverage of the Al-based oxide on the surface of the mother steel sheet of 30% or more and 95% or less. A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet is manufactured.
A slab heating step of heating the slab having the chemical composition according to claim 1 to a temperature of 1000 ° C. or higher and 1250 ° C. or lower in a heating furnace.
A hot rolling step in which the heated slab is hot-rolled, water-cooled after the final rolling pass, and wound into a coil at a temperature of 650 ° C. or lower.
A hot-rolled sheet annealing / pickling step in which the hot-rolled steel sheet obtained by the hot rolling step is annealed and pickled.
A cold rolling step of cold-rolling the hot-rolled annealed plate obtained by the hot-rolled sheet annealing / pickling step, and a cold rolling step.
A finish annealing step of applying finish annealing to the cold-rolled steel sheet obtained by the cold rolling step, and
It has an insulating coating forming step of forming an insulating coating on the surface of the steel sheet obtained by the finish annealing step.
In the finish annealing step, the atmosphere in the temperature range of 500 ° C. or higher and 900 ° C. or lower before first reaching 900 ° C. is the partial pressure ratio P (H ₂ O) of _{water vapor (H 2} O) and hydrogen (H _2). A method for producing a non-directional electromagnetic steel plate, wherein / P (H ₂ ) is 0.002 or more and 0.100 or less, and the residence time in the temperature range is 40 seconds or less.