JP6794705B2 - Manufacturing method of non-oriented electrical steel sheet, non-oriented electrical steel sheet and manufacturing method of motor core - Google Patents

Description

The present invention relates to a non-oriented electrical steel sheet, a method for manufacturing a non-oriented electrical steel sheet, and a method for manufacturing a motor core.

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. For this reason, even in non-oriented electrical steel sheets that are widely used as iron core materials for motors, transformers, etc., there is an increasing demand for improvement in magnetic characteristics. In recent years, this tendency is remarkable in motors for electric vehicles and hybrid vehicles, and motors for compressors, for which the efficiency of motors has been improved.

The motor core of various motors as described above is composed of a stator which is a stator and a rotor which is a rotor. When such a motor core is manufactured, the non-oriented electrical steel sheet is punched into the shape of the motor core and laminated, and then core annealing (also referred to as "strain relief annealing") is performed. Such core annealing is generally carried out in an atmosphere containing nitrogen, but there is a problem that the steel sheet is nitrided during such core annealing and iron loss is deteriorated.

Deterioration of iron loss due to nitriding of a steel sheet is caused by the combination of N incorporated into the steel sheet by nitriding and Al in the steel to form an AlN precipitate, which hinders the movement of the domain wall. It is believed that it is occurring. Therefore, for example, in Patent Document 1 below, a technique of concentrating Al on the surface of a steel sheet and covering the surface of the steel sheet with an Al oxide to prevent nitriding of the steel sheet during strain relief annealing and suppress deterioration of iron loss. Has been proposed.

Japanese Unexamined Patent Publication No. 10-18310

Here, in the motor core of a motor used for various purposes as described above, a circular blank is usually punched out from the same steel plate for a rotor, and a ring-shaped blank is punched out from the outer circumference of the circular blank. Is punched out for the stator. Here, as a result of studies by the present inventors in order to further increase the output and reduce the loss of the motor core, it has become clear that the following problems exist.

First, regarding the stator, the emphasis is mainly on reducing the loss during rotor rotation, and various studies have been conducted. However, distortion occurs during punching and the loss increases. Strain relief annealing is required to reduce the loss of the steel sheet and remove processing strain. However, when the grain size of the steel sheet is larger than the plate thickness, strain relief annealing is required to eliminate the strain existing at the grain boundaries. It was necessary to raise the temperature.

Further, it is important to further increase the mechanical strength of the rotor so that it can withstand the centrifugal force accompanying the rotation, mainly when the rotation speed increases. Here, when the grain size of the steel sheet is larger than the thickness of the steel sheet, the solid solution strengthening of the steel sheet is the main means for increasing the strength, but it can be controlled only by adjusting the alloy component of the steel sheet. However, there is a limit to the types and amounts of additive elements to be added to the steel sheet for solid solution strengthening due to the cold workability of the steel sheet, and it is difficult to increase the strength.

As described above, in view of economic efficiency, when manufacturing the rotor and the member for the stator of the motor core from the same non-oriented electrical steel sheet, both the low iron loss required for the stator and the high strength required for the rotor are compatible. It was difficult. In particular, when the grain size of the steel sheet is larger than the sheet thickness, it is required to raise the temperature of strain relief annealing to a higher temperature, but by setting the temperature higher, the adhesion of the insulating coating of the non-oriented electrical steel sheet is also improved. It will drop. If the insulating film is peeled off, an interlayer short circuit will occur and the core iron loss will increase, and if peeling occurs inside the motor case, foreign matter will be present in the operating area, causing damage to the motor core. There is a possibility that it will end up.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to realize further improvement of iron loss and strength while maintaining cost performance and adhesion of an insulating coating. It is an object of the present invention to provide a non-oriented electrical steel sheet, a method for manufacturing a non-oriented electrical steel sheet, and a method for manufacturing a motor core, which are possible.

As a result of diligent studies on the above problems, the present inventors set the average crystal grain size of the base iron to a predetermined value or less in the non-oriented electrical steel sheet in the previous stage to be processed as a motor core, and then determine the motor core. I came up with the idea of implementing a manufacturing process. This makes it possible to achieve both the low iron loss required for the stator and the high strength required for the rotor. Further, in such non-oriented electrical steel sheets, a layer having a lower Al concentration than that of the base material is intentionally provided in the vicinity of the surface, and the layer and the insulating coating are reacted to raise the strain-removing annealing temperature. However, it was found that the adhesion of the insulating film after strain removal and annealing can be improved.
The gist of the present invention based on such findings is as follows.

[1] In terms of mass%, C: 0.0010% to 0.0050%, Si: 2.5% to 4.0%, Al: 0.1% to 2.0%, Mn: 0.05% to 2.0%, P: 0.005% to 0.15%, S: 0.0001% to 0.0030%, Ti: 0.0005 to 0.0030%, N: 0.0010 to 0.0030% The balance is composed of Fe and impurities, the plate thickness of the base iron is 0.10 mm or more and 0.35 mm or less, the average crystal grain size in the base iron is 50 μm or less, and from the surface of the base iron. Regarding the Al concentration in the depth direction, a steel plate satisfying the relational expression shown in the following formula (1) and an insulating coating located on the surface of the steel plate are provided, and the amount of the insulating coating adhered is 400 mg / m. ^A non-directional electromagnetic steel sheet having a content of ² or more and 1200 mg / m ² or less and a divalent and trivalent Fe content in the insulating coating of 10 mg / m ² or more and 250 mg / m ² or less.
[2] The non-directional electromagnetic steel according to [1], which further contains at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. Steel plate.
[3] In [1] or [2], which further contains at least one of Ni, Cu, and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. The non-oriented electrical steel sheet described.
[4] Instead of a part of Fe in the balance, at least one of Ca of 0.0005% by mass or more and 0.0025% by mass or less, or REM of 0.0005% by mass or more and 0.0050% by mass or less. The non-oriented electrical steel sheet according to any one of [1] to [3], which contains.
[5] A method for producing a non-directional electromagnetic steel plate by sequentially performing hot rolling, hot rolling plate annealing, pickling, cold rolling, and finish annealing on a steel ingot having a predetermined chemical composition. The steel ingot is C: 0.0010% to 0.0050%, Si: 2.5% to 4.0%, Al: 0.1% to 2.0%, Mn: in mass%. 0.05% to 2.0%, P: 0.005% to 0.15%, S: 0.0001% to 0.0030%, Ti: 0.0005 to 0.0030%, N: 0.0010 It contains ~ 0.0030%, the balance is Fe and impurities, and the dew point in the annealing atmosphere is set to -40 ° C or higher and 60 ° C or lower, and the annealing temperature is set to 900 ° C or higher without removing the scale after the hot rolling. The hot-rolled sheet was annealed at 1100 ° C. or lower and the soaking time was 1 second or more and 300 seconds or less. By the pickling, the Al concentration in the depth direction from the surface of the base steel in the pickling board was measured. The scale layer including the internal oxide layer was removed while controlling the pickling weight loss so as to satisfy the relational expression shown in the following formula (2), and the final plate thickness of the base steel was reduced to 0 by the cold rolling. In the finish annealing, the finish annealing temperature was set to 950 ° C. or lower, and after the finish annealing, the amount of adhesion to the surface of the base steel was 400 mg / m ² or more and 1200 mg / m ² or less . In addition , the insulating film is formed so that the content of divalent and trivalent Fe in the insulating film is 10 mg / m ² or more and 250 mg / m ² or less, and the average crystal grain size of the base steel after the finish annealing is increased. A method for producing a non-directional electromagnetic steel sheet having a thickness of 50 μm or less .
[ 6 ] The steel ingot contains at least 0.01% by mass or more and 0.2% by mass or less of Sn or Sb, respectively, in place of a part of the remaining Fe, according to [5 ]. Manufacturing method of non-oriented electrical steel sheet.
[ 7 ] The steel ingot further contains at least one of Ni, Cu, and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. [5] Alternatively, the method for manufacturing a non-oriented electrical steel sheet according to [6] .
[ 8 ] The steel ingot is replaced with a part of Fe in the balance, and further, Ca of 0.0005% by mass or more and 0.0025% by mass or less, or 0.0005% by mass or more and 0.0050% by mass or less. The method for producing a non-oriented electrical steel sheet according to any one of [5] to [ 7 ], which contains at least one of REM.
[ 9 ] In mass%, C: 0.0010% to 0.0050%, Si: 2.5% to 4.0%, Al: 0.1% to 2.0%, Mn: 0.05% to 2.0%, P: 0.005% to 0.15%, S: 0.0001% to 0.0030%, Ti: 0.0005 to 0.0030%, N: 0.0010 to 0.0030% The balance is composed of Fe and impurities, the plate thickness of the base iron is 0.10 mm or more and 0.35 mm or less, the average crystal grain size in the base iron is 50 μm or less, and from the surface of the base iron. Regarding the Al concentration in the depth direction, a steel plate satisfying the relational expression shown in the following formula (1) and an insulating coating located on the surface of the steel plate are provided, and the amount of the insulating coating adhered is 400 mg / m. ^A non-directional electromagnetic steel plate having a core shape of ² or more and 1200 mg / m ² or less and having a divalent and trivalent Fe content in the insulating coating of 10 mg / m ² or more and 250 mg / m ² or less. A method for producing a motor core, which comprises punching and laminating the iron, and then performing strain removal and annealing at a temperature of 750 ° C. or higher and 900 ° C. or lower in an atmosphere containing 70% by volume or more of nitrogen.
[ 10 ] The non-oriented electrical steel sheet further contains at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. [ 9] ] The method for manufacturing a motor core described in.
[ 11 ] The non-oriented electrical steel sheet further contains at least one of Ni, Cu, and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. The method for manufacturing a motor core according to [ 9 ] or [ 10 ].
[ 12 ] The non-oriented electrical steel sheet has Ca of 0.0005% by mass or more and 0.0025% by mass or less, or 0.0005% by mass or more and 0.0050% by mass, in place of a part of Fe in the balance. The method for producing a motor core according to any one of [ 9 ] to [ 11 ], which contains at least one of REM of% or less.

0.1 0 ≤ Al (x ≤ 2 μm) / Al (x = 10 μm) <1.0 ... (1)

Here, in the above equation (1),
x: Depth from the surface of the ground iron [μm]
Al (x ≦ 2 μm): Mean value of Al concentration from the surface of the base metal to a depth of 2 μm Al (x = 10 μm): Indicates the Al concentration at a depth of 10 μm.

0.1 ≤ Al (x ≤ 5 μm) / Al (x = 10 μm) <1.0 ... (2)

Here, in the above equation (2),
x: Depth from the surface of the ground iron [μm]
Al (x ≦ 5 μm): Mean value of Al concentration from the surface of the base metal to a depth of 5 μm Al (x = 10 μm): Indicates the Al concentration at a depth of 10 μm.

As described above, according to the present invention, it is possible to realize further improvement in iron loss and strength while maintaining cost performance and adhesion of the insulating coating.

It is explanatory drawing which showed typically the structure of the non-oriented electrical steel sheet which concerns on embodiment of this invention. It is explanatory drawing for demonstrating the base steel of the non-oriented electrical steel sheet which concerns on this embodiment. It is explanatory drawing which showed typically the distribution of Al concentration in the base iron which concerns on this embodiment. It is a flow chart which showed an example of the flow of the manufacturing method of the non-oriented electrical steel sheet which concerns on the same embodiment. It is explanatory drawing for demonstrating the manufacturing method of the non-oriented electrical steel sheet which concerns on this embodiment. It is a flow chart which showed an example of the flow of the manufacturing method of the motor core which concerns on this embodiment. It is a flow chart which showed an example of the flow of the manufacturing method of the motor core which concerns on this embodiment.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

(About non-oriented electrical steel sheets)
First, the non-oriented electrical steel sheet according to the embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.
FIG. 1 is an explanatory view schematically showing the structure of a non-oriented electrical steel sheet according to an embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining the base steel of the non-oriented electrical steel sheet according to the present embodiment. FIG. 3 is an explanatory diagram schematically showing the distribution of Al concentration in the ground iron according to the present embodiment.

As schematically shown in FIG. 1, the non-oriented electrical steel sheet 10 according to the present embodiment contains a predetermined chemical component and has an uneven distribution of Al in the vicinity of the surface. It has an insulating coating 13 provided on the surface of the base iron 11.

In the following, first, the base steel 11 of the non-oriented electrical steel sheet 10 according to the present embodiment will be described in detail.

<Chemical composition of base iron>
The base iron 11 of the non-oriented electrical steel sheet 10 according to the present embodiment is C: 0.0010% to 0.0050%, Si: 2.5% to 4.0%, Al: 0.1 in mass%. % To 2.0%, Mn: 0.05% to 2.0%, P: 0.005% to 0.15%, S: 0.0001% to 0.0030%, Ti: 0.0005% to It contains 0.0030%, N: 0.0010% to 0.0030%, and the balance consists of Fe and impurities.

Further, the base iron 11 according to the present embodiment further contains at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. It may contain at least one of Ni, Cu and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, and at least one of Ca or REM in an amount of 0.0005% by mass or more. It may be contained in an amount of 0.0050% by mass or less.

In the following, the reason why the chemical composition of the base iron 11 according to the present embodiment is defined as described above will be described in detail. In the following, unless otherwise specified, "%" shall represent "mass%".

[C: 0.0010% to 0.0050%]
C (carbon) is an element that causes iron loss deterioration. When the C content exceeds 0.0050%, iron loss deterioration occurs in the non-oriented electrical steel sheet, and good magnetic characteristics cannot be obtained. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, the C content is set to 0.0050% or less. On the other hand, when the C content is less than 0.0010%, the magnetic flux density of the non-oriented electrical steel sheet decreases, and good magnetic characteristics cannot be obtained. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, the C content is set to 0.0010% or more. In the non-oriented electrical steel sheet according to the present embodiment, the C content is preferably 0.0010% or more and 0.0040% or less, and more preferably 0.0015% or more and 0.0030% or less. ..

[Si: 2.5% to 4.0%]
Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves high-frequency 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. 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 4.0%, the workability is significantly deteriorated and it becomes difficult to carry out cold rolling. Therefore, the Si content is set to 4.0% or less. The Si content is preferably 2.7% or more and 3.7% or less, and more preferably 3.0% or more and 3.5% or less.

[Al: 0.1% to 2.0%]
Al (aluminum) is an element effective for reducing eddy current loss and improving high-frequency iron loss by increasing the electrical resistance of non-oriented electrical steel sheets. When the Al content is less than 0.1%, the effect of increasing the electrical resistance is small, and AlN is finely deposited in the electromagnetic steel sheet, so that the crystal grains become fine and the iron loss is reduced. Adversely affect. Therefore, the Al content is set to 0.1% or more. On the other hand, when the Al content exceeds 2.0%, the magnetic flux density of the non-oriented electrical steel sheet is remarkably lowered. Therefore, the Al content is set to 2.0% or less. The Al content is preferably 0.25% or more and 1.5% or less, and more preferably 0.3% or more and 1.2% or less.

[Mn: 0.05% to 2.0%]
Mn (manganese) is an element effective for increasing the electrical resistance of steel, reducing eddy current loss, and improving high-frequency iron loss. 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 2.0%, the decrease in magnetic flux density becomes remarkable. Therefore, the Mn content is set to 2.0% or less. The Mn content is preferably 0.2% or more and 1.5% or less, and more preferably 0.5% or more and 1.3% or less.

[P: 0.005% to 0.15%]
P (phosphorus) has a large solid-dissolving ability and also has an effect of increasing the {100} texture, which is advantageous for improving magnetic properties, and is therefore extremely effective in achieving both high strength and high magnetic flux density. It is an element. Further, since the increase of {100} texture also contributes to the reduction of the anisotropy of the mechanical properties in the plate surface of the non-oriented electrical steel sheet, P is used during the punching process of the non-oriented electrical steel sheet. It also has the effect of improving dimensional accuracy. In order to obtain the effect of improving such strength, magnetic characteristics, and dimensional accuracy, it is necessary to set the P content to 0.005% or more. On the other hand, when the P content exceeds 0.15%, the ductility of the non-oriented electrical steel sheet is remarkably lowered. Therefore, the content of P is 0.15% or less. The content of P is preferably 0.01% or more and 0.10% or less, and more preferably 0.04% or more and 0.08% or less.

[S: 0.0001% to 0.0030%]
S (sulfur) 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 0.0030% or less. On the other hand, if an attempt is made to reduce the S content to less than 0.0001%, the cost will only increase unnecessarily. Therefore, the content of S is set to 0.0001% or more. The content of S is preferably 0.0003% or more and 0.0020% or less, and more preferably 0.0005% or more and 0.0010% or less.

[N: 0.0010% to 0.0030%]
N (nitrogen) is an element that causes magnetic aging, increases iron loss, and deteriorates the magnetic properties of non-oriented electrical steel sheets. Therefore, the content of N needs to be 0.0030% or less. On the other hand, if an attempt is made to reduce the N content to less than 0.0001%, the cost will only increase unnecessarily. Therefore, the content of N is set to 0.0001% or more. The content of N is preferably 0.0010% or more and 0.0025% or less, and more preferably 0.0010% or more and 0.0020% or less.

[Ti: 0.0005% to 0.0030%]
Ti (titanium) is an element that combines with C, N, Mn, etc. to form inclusions, inhibits the growth of crystal grains during strain relief annealing, and deteriorates the magnetic properties. Therefore, the Ti content is set to 0.0030% or less. On the other hand, if the Ti content is reduced to less than 0.0005%, the cost will be unnecessarily increased. Therefore, the Ti content is set to 0.0005% or more. The Ti content is preferably 0.0005% or more and 0.0015% or less, and more preferably 0.0005% or more and 0.0020% or less.

[Sn: 0.01% to 0.2%]
[Sb: 0.01% to 0.2%]
Sn (tin) and Sb (antimony) are optional additive elements that are useful for ensuring low iron loss by segregating on the surface and suppressing oxidation during annealing. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, at least one of Sn and Sb may be contained in the ground iron as an optional additive element in order to obtain such an effect. In order to fully exert such an effect, the content of Sn or Sb is preferably 0.01% or more, respectively. On the other hand, when the Sn or Sb content exceeds 0.2%, the ductility of the base iron may decrease, making cold rolling difficult. Therefore, the content of Sn or Sb is preferably 0.2% or less, respectively. When Sn or Sb is contained in the base iron, the content of Sn or Sb is more preferably 0.03% or more and 0.10% or less, respectively.

[Ni: 0.01% to 0.2%]
[Cu: 0.01% to 0.2%]
[Cr: 0.01% to 0.2%]
Ni (nickel), Cu (copper), and Cr (chromium) are optional additive elements that are effective in increasing specific resistance and reducing iron loss. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, at least one of Ni, Cu, and Cr may be contained in the ground iron as an optional additive element in order to obtain such an effect. In order to fully exert such an effect, the content of Ni, Cu or Cr is preferably 0.01% or more, respectively. On the other hand, if the contents of Ni, Cu or Cr each exceed 0.2%, the magnetic flux density may deteriorate. Therefore, the content of Ni, Cu or Cr is preferably 0.2% or less, respectively. When Ni, Cu or Cr is contained in the base iron, the content of Ni, Cu or Cr is more preferably 0.03% or more and 0.10% or less, respectively.

[Ca: 0.0005% to 0.0025%]
[REM: 0.0005% to 0.0050%]
Ca (calcium) and REM (Rare Earth Metal: rare earth element) are optional additive elements effective for promoting grain growth during finish annealing, respectively. Therefore, in the non-oriented electrical steel sheet according to the present embodiment, at least one of Ca and REM may be contained in the ground steel as an optional additive element in order to obtain such an effect. In order to fully exert such an effect, the content of Ca or REM is preferably 0.0005% or more, respectively. On the other hand, when the Ca content exceeds 0.0025%, or when the REM content exceeds 0.0050%, the effect is saturated and the cost is only increased. Therefore, the Ca content is preferably 0.0025% or less, and the REM content is preferably 0.0050% or less. When Ca or REM is contained in the ground iron, the Ca content is more preferably 0.0010% or more and 0.0025% or less, and the REM content is more preferably 0.0010%. More than 0.0030% or less.

In addition to the above elements, even if elements such as Pb, Bi, V, As, and B are contained in the range of 0.0001% to 0.0050%, the present invention is not impaired.

The chemical composition of the base iron in the non-oriented electrical steel sheet according to the present embodiment has been described in detail above.
In addition, when the chemical composition of the base iron in the non-directional electromagnetic steel plate is measured after the fact, various known measurement methods can be used, for example, ICP-MS (inductively coupled plasma mass spectrometry). The law, etc. may be used as appropriate.

<About the average crystal grain size of ground iron>
The grain steel 11 of the non-oriented electrical steel sheet according to the present embodiment has an average crystal grain size of 50 μm or less in metal structure. By setting the average crystal grain size of the base iron 11 to 50 μm or less, it is possible to realize both the high strength required for the rotor core and the low iron loss required for the stator that can be achieved by strain relief annealing.

That is, when manufacturing a rotor core, the non-oriented electrical steel sheet 10 is punched out to obtain a rotor blank having a predetermined shape, and the obtained rotor blanks are laminated and joined to manufacture the rotor core. Here, by setting the average crystal grain size of the base iron 11 after the finish annealing to 50 μm or less, the mechanical strength of the manufactured rotor core can be further increased as compared with the conventional mechanical strength. ..

Further, when manufacturing the stator core, similarly to the rotor core, the non-oriented electrical steel sheet 10 is punched out to obtain a staple steel blank having a predetermined shape, and the obtained stator blanks are laminated and joined, and then strain-removed and annealed. Is done. At this time, it is more cost-effective to punch the stator core blank from the outer peripheral portion of the same steel plate from which the rotor core blank has been punched. Here, by setting the average crystal grain size of the base steel 11 of the non-oriented electrical steel sheet 10 to 50 μm or less, the machining strain generated during the punching process can be sufficiently suppressed without raising the annealing temperature in the strain removing annealing. It can be removed. Further, since the ground iron 11 has a recrystallized structure having an average crystal grain size of 50 μm or less, grain growth of the recrystallized structure occurs even if the annealing temperature at the time of strain removal annealing is not raised, and the iron of the stator core It is possible to further reduce the loss.

Here, when the average crystal grain size of the base iron 11 exceeds 50 μm, it is required to set the annealing temperature of the strain removing annealing performed when manufacturing the motor core higher, and it is difficult to reduce the iron loss of the stator core. At the same time, it becomes difficult to improve the mechanical strength of the rotor core. On the other hand, when the average crystal grain size of the base iron 11 is less than 10 μm, the magnetic characteristics are deteriorated, and the grain growth of the recrystallized structure becomes non-uniform at the time of strain removal annealing of the stator core, so that the magnetic characteristics are improved. It is not preferable because the cost is small. Therefore, the average crystal grain size of the base iron 11 is preferably 10 μm or more. The average crystal grain size of the base iron 11 is preferably 10 μm to 50 μm, and more preferably 15 μm to 40 μm.

The method for measuring the average crystal grain size of the base iron 11 is not particularly limited, and it can be measured by a known method. For example, after polishing the cross section of the steel plate and then etching the grain boundaries by nital corrosion, the obtained test piece is observed with an optical microscope or SEM (Scanning Electron Microscope), and is generally known. It is possible to measure the average grain size of the base iron 11 by the conventional linear method or the like.

<About the thickness of the base iron>
The plate thickness of the base steel 11 (thickness t in FIG. 1) in the non-oriented electrical steel sheet 10 according to the present embodiment needs to be 0.35 mm or less in order to reduce high-frequency iron loss. On the other hand, when the plate thickness t of the base iron 11 is less than 0.10 mm, it may be difficult to pass the annealing line because the plate thickness is thin. Therefore, the plate thickness t of the base steel 11 in the non-oriented electrical steel sheet 10 is 0.10 mm or more and 0.35 mm or less. The plate thickness t of the base steel 11 in the non-oriented electrical steel sheet 10 is preferably 0.15 mm or more and 0.30 mm or less.

<Regarding the distribution of Al in the depth direction>
Subsequently, the distribution of Al in the base steel 11 of the non-oriented electrical steel sheet 10 according to the present embodiment will be described.
As mentioned briefly earlier, when manufacturing a motor core, it is manufactured after laminating and joining blanks punched from non-oriented electrical steel sheets, and strain relief annealing is performed as necessary. Here, the strain-removing annealing is often performed in nitrogen as a non-oxidizing atmosphere, but at that time, deterioration of iron loss occurs due to the progress of nitriding of the base iron and the precipitation of AlN accompanying the nitriding. Nitriding can be suppressed by using argon or helium instead of nitrogen in the inert atmosphere, but it is costly. Therefore, it is industrially essential to use nitrogen as the main atmosphere for strain relief annealing. Here, the present inventors have found that if the amount of Al to which N is bound is small, the precipitation of AlN can be suppressed and the deterioration of iron loss can be suppressed.

The increase in N concentration due to nitriding is limited to the vicinity of the surface of the base iron 11. Therefore, if the Al concentration near the surface of the base iron 11 in which N is dissolved can be reduced, the precipitation of AlN can be suppressed. Further, if the amount of Al having a high affinity for N on the outermost surface of the base iron can be reduced, it is possible to suppress the reaction itself in which the N molecule decomposes and dissolves into the base iron as an atom. Based on this finding, the present inventors unevenly distribute the Al distribution near the surface of the base iron 11 (more specifically, form a de-Al layer having a relatively low Al concentration near the surface of the base iron 11). By doing so, it was conceived that good magnetic characteristics can be obtained by suppressing the deterioration of iron loss during strain removal annealing.

FIG. 2 schematically shows the vicinity of the surface of the base iron 11 according to the present embodiment. In the following, for convenience, the x-axis positive direction is set in the direction from the surface of the base iron 11 toward the center in the thickness direction (depth direction), and the description will be given using such coordinate axes.

The base steel 11 of the non-oriented electrical steel sheet 10 according to the present embodiment has a base material portion 101 and a de-Al layer 103, as schematically shown in FIG.

The base material portion 101 is a portion in which Al is distributed substantially uniformly inside the base metal portion 11, and the Al concentration of the base material portion 101 is a value substantially equal to the Al content of the base metal portion 11. It has become. Further, the de-Al layer 103 is a layer located on the surface side of the base iron 11, and the Al concentration of the de-Al layer 103 is relatively lower than the Al concentration of the base material portion 101. ..

Specifically, when the surface of the base iron 11 is the origin of the x-axis (that is, the position of x = 0 μm), the following equation (101) is established in the de-Al layer 103. By establishing the relationship as shown in the following equation (101), the non-oriented electrical steel sheet 10 according to the present embodiment can suppress the deterioration of iron loss during strain relief annealing and obtain good magnetic characteristics. It will be possible.

0.1 ≤ Al (x ≤ 2 μm) / Al (x = 10 μm) <1.0 ... Equation (101)

Here, in the above formula (101),
x: Depth from the surface of the base iron 11 [μm]
Al (x ≦ 2 μm): Mean value of Al concentration from the surface of the base metal to a depth of 2 μm [mass%]
Al (x = 10 μm): Al concentration at a depth of 10 μm [mass%]
Represents.

As schematically shown in FIG. 3, when the de-Al layer 103 does not exist in the base iron 11 and the distribution of Al in the depth direction (x direction) is uniform, the Al concentration is Al ( The value of x = 10) (in other words, the value of the average Al concentration of the entire base iron 11) should be substantially constant. Further, in the technique for forming the Al-concentrated layer as in Patent Document 1, as shown by the broken line in FIG. 3, the Al concentration near the surface of the base iron is higher than the average Al concentration value of the entire base iron 11. Is also getting higher. However, in the ground iron 11 according to the present embodiment, a state opposite to that of Patent Document 1 is realized.

That is, in the base iron 11 according to the present embodiment, the de-Al layer 103 is formed, so that the depth is 2 μm (x = 2 μm) from the base iron surface (x = 0 μm) as shown by the solid line in FIG. The average Al concentration up to the position of is smaller than the Al concentration at the position (x = 10 μm) at a depth of 10 μm. Therefore, the inequality as shown on the rightmost side of the above equation (101) is established. The fact that such a state is realized means that the Al concentration of the de-Al layer 103 is relatively lower than the average Al concentration of the base material portion 101.

On the other hand, when the Al concentration of the de-Al layer 103 becomes too low and the concentration ratio represented by Al (x ≦ 2 μm) / Al (x = 10 μm) is less than 0.1, the vicinity of the surface of the base iron 11 Since the Al content of the aluminum becomes too low and the specific resistance in the vicinity of the surface layer decreases, the eddy current loss, which is important for high-frequency iron loss, deteriorates. Therefore, the concentration ratio represented by Al (x ≦ 2 μm) / Al (x = 10 μm) is set to 0.1 or more as shown in the inequality on the leftmost side of the above formula (101).

In the base iron 11 according to the present embodiment, the concentration ratio represented by Al (x ≦ 2 μm) / Al (x = 10 μm) is preferably 0.2 or more and 0.9 or less, and more preferably. It is 0.5 or more and 0.7 or less.

Here, the Al concentration of the base iron 11 along the depth direction as described above is determined along the depth direction from the surface of the base iron 11 using a glow discharge emission analyzer (Glow Discharge Spectroscopy: GDS). It can be specified by measuring the Al concentration. The measurement conditions for GDS are not particularly specified, but for example, a DC mode, a high frequency mode, a pulse mode, etc. are prepared depending on the material to be analyzed, but mainly the ground iron which is a conductor is used. Within the scope of this embodiment to be analyzed, there is no significant difference in any mode. Therefore, the measurement time may be set as a condition that the sputtering marks are uniform and the depth can be analyzed at 10 μm or more, and the analysis may be performed as appropriate.

The method of realizing the ground iron 11 in which Al is unevenly distributed in the depth direction as described above will be described in detail below.

In the non-oriented electrical steel sheet 10 according to the present embodiment, the de-Al layer 103 as described above is present on the surface layer of the base iron 13, so that Fe contained in the de-Al layer 103 is contained when the insulating coating 13 is provided. It becomes easy to be oxidized, and Fe becomes easy to diffuse toward the insulating film 13. As a result, in the non-oriented electrical steel sheet 10 according to the present embodiment, a predetermined amount of divalent and trivalent Fe is present in the insulating coating 13. In the non-oriented electrical steel sheet 10 according to the present embodiment, the presence of a predetermined amount of divalent and trivalent Fe in the insulating coating 13 makes it possible to suppress the permeation of oxygen and the like during strain relief annealing. It is possible to improve the adhesion of the insulating coating 13 after strain removal annealing.

As described above, the distribution of Al in the ground iron 11 according to the present embodiment in the depth direction has been described in detail with reference to FIGS. 2 and 3.

<Insulation film>
Returning to FIG. 1 again, the insulating coating 13 included in the non-oriented electrical steel sheet 10 according to the present embodiment will be described in detail.

Since the non-oriented electrical steel sheet is used by being laminated after punching the core blank, the eddy current between the plates can be reduced by providing the insulating coating 13 on the surface of the base steel 11, and the eddy current loss as the core. Can be reduced.

Here, the insulating coating 13 according to the present embodiment is not particularly limited as long as it is used as the insulating coating of the non-oriented electrical steel sheet, and a known insulating coating can be used. Examples of such an insulating film include a composite insulating film mainly composed of an inorganic substance and further containing an organic substance. Here, the composite insulating coating is mainly composed of, for example, at least one of a chromic acid metal salt, a phosphoric acid metal salt, and an inorganic substance such as colloidal silica, Zr compound, and 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 in increasing demand in recent years, an insulating film using a metal phosphate, 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 coating 13 adhered as described above is 400 mg / m ² or more and 1200 mg / m ² or less per side. If the amount of adhesion per side is less than 400 mg / m ² , the insulating film becomes thin, so oxygen and the like may permeate through the film during strain relief annealing, and the film adhesion may deteriorate. Further, when the non-oriented electrical steel sheets 10 are punched into a desired shape and laminated, it becomes difficult to sufficiently insulate between the laminated steel sheets, which is not preferable. On the other hand, when the adhesion amount per one side exceeds 1200 mg / m ² , the space factor is lowered and the film adhesion after strain removal annealing is deteriorated, which is not preferable. By setting the amount of adhesion of the insulating coating 13 per side to 400 mg / m ² or more and 1200 mg / m ² or less per side, the above characteristics are realized and the adhesion of the insulating coating 13 after strain removal and annealing is improved. It becomes possible to secure it. The amount of the insulating coating 13 adhered to one side is preferably 600 mg / m ² or more and 1200 mg / m ² or less, and more preferably 800 mg / m ² or more and 1000 mg / m ² or less.

Further, in the insulating coating 13 according to the present embodiment, the content of divalent and trivalent Fe in the insulating coating 13 is 10 mg / m ² or more and 250 mg / m ² or less in terms of metal Fe. When the content of divalent and trivalent Fe is less than 10 mg / m ² , the permeation of oxygen and the like that are inevitably present in the atmosphere in the strain annealing performed when manufacturing the motor core is sufficient. It cannot be suppressed, it becomes difficult to improve the adhesion of the insulating film 13, and it becomes difficult to raise the annealing temperature in the strain removing annealing. On the other hand, when the content of divalent and trivalent Fe exceeds 250 mg / m ² , it takes a long time to bake a normal insulating film, which is disadvantageous in terms of cost. The content of divalent and trivalent Fe in the insulating coating 13 is preferably 50 mg / m ² or more and 200 mg / m ² or less in terms of metal Fe.

When the amount of the insulating coating 13 adhered is measured after the fact, various known measuring methods can be used, for example, a method of measuring the weight difference before and after immersion in the sodium hydroxide aqueous solution. , The fluorescent X-ray method using the calibration curve method or the like may be appropriately used. Further, the content of divalent and trivalent Fe in the insulating coating 13 can be measured by using various known measurement methods. For example, the coating is dissolved by immersion in an aqueous sodium hydroxide solution, and the coating is dissolved. ICP (Inductively Coupled Plasma) emission spectroscopy of the Fe component contained in the aqueous solution (when sodium hydroxide is used, Fe in the steel plate is not dissolved, so the total amount of Fe2 valence and Fetrivalent can be quantified. ), And by combining the ICP emission spectroscopic measurement with the Mesbauer spectroscopy, the Fe2 valence content and the Fe3 valence content can be quantified separately from each other.

<Measurement method of magnetic properties of non-oriented electrical steel sheets>
The non-oriented electrical steel sheet 10 according to the present embodiment exhibits excellent magnetic characteristics by having the above-mentioned structure. Here, various magnetic properties indicated by the non-oriented electrical steel sheet 10 according to the present embodiment are described by the Epstein method specified in JIS C2550 and the single plate magnetic property measurement method (Single Sheet Tester: SST) specified in JIS C2556. ), It is possible to measure.

As described above, the non-oriented electrical steel sheet 10 according to the present embodiment has been described in detail with reference to FIGS. 1 to 3.

(About manufacturing method of non-oriented electrical steel sheet)
Subsequently, with reference to FIGS. 4 and 5, the method for manufacturing the non-oriented electrical steel sheet 10 according to the present embodiment as described above will be described in detail.
FIG. 4 is a flow chart showing an example of the flow of the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment, and FIG. 5 is for explaining the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment. It is explanatory drawing.

In the method for producing grain-oriented electrical steel sheet 10 according to the present embodiment, first, hot rolling, hot rolling sheet annealing, pickling, and cold rolling are performed on a steel ingot having a predetermined chemical component as described above. , Finish annealing is carried out in order. Then, in order to form the insulating film 13 on the surface of the base iron 11, the insulating film is formed after the finish annealing. Hereinafter, each step carried out by the method for manufacturing the non-oriented electrical steel sheet 10 according to the present embodiment will be described in detail.

<Hot rolling process>
In the method for producing non-oriented electrical steel sheet 10 according to the present embodiment, first, a steel ingot (slab) having the above chemical composition is heated, and the heated steel ingot is hot-rolled to obtain a hot-rolled plate. Obtain (step S101). Here, the heating temperature of the ingot during hot rolling is not particularly specified, but is preferably 1050 ° C. or higher and 1200 ° C. or lower, for example. Further, the plate thickness of the hot-rolled plate after hot rolling is not particularly specified, but it is preferably about 1.5 mm to 3.0 mm in consideration of the final plate thickness of the base iron. ..

By performing the above hot rolling on the steel ingot, as shown in the upper left figure of FIG. 5, a scale mainly composed of Fe oxide is generated on the surface of the base iron 11. Will be done. Further, in such a hot rolling step, it is considered that Al is almost uniformly dispersed in the base iron.

<Hot rolled plate annealing process>
After the hot rolling, hot rolled sheet annealing is performed (step S103). Here, in the method for manufacturing non-oriented electrical steel sheets according to the present embodiment, hot-rolled sheet annealing is carried out without removing the scale formed on the surface of the ground steel by hot rolling. As described below, by performing annealing without removing the scale generated by hot rolling, it is possible to form the de-Al layer 103 characteristic of the non-oriented electrical steel sheet 10 according to the present embodiment. It will be possible.

Specifically, the dew point in the annealing atmosphere is -40 ° C or more and 60 ° C or less, the annealing temperature is 900 ° C or more and 1100 ° C or less, and the soaking time is 1 second or more and 300 seconds or less, and the scale remains attached. Annealing is carried out on the hot-rolled plate.

If the dew point is less than −40 ° C., it is not preferable because the oxidation source is only the surface layer scale and it may not be possible to form a sufficient de-Al layer 103. On the other hand, when the dew point exceeds 60 ° C., the oxidation of Fe in the base iron progresses, resulting in deterioration of the yield due to pickling reduction, and the Al-concentrated layer and the de-Al layer as described below are formed. It is not preferable because it may disappear due to the oxidation of Fe. The dew point in the annealing atmosphere is preferably −30 ° C. or higher and 40 ° C. or lower, and more preferably −20 ° C. or higher and 30 ° C. or lower.

Further, when the annealing temperature is less than 900 ° C. or the soaking time is less than 1 second, the crystal grains of the ground iron are not sufficiently coarsened by annealing and good magnetic characteristics cannot be obtained. Therefore, it is not preferable. On the other hand, if the annealing temperature exceeds 1100 ° C. or the soaking time exceeds 300 seconds, the ground iron may break in the cold rolling step in the subsequent stage, which is not preferable. The annealing temperature is preferably 930 ° C. or higher and 1070 ° C. or lower, and more preferably 950 ° C. or higher and 1050 ° C. or lower. The soaking time is preferably 10 seconds or more and 150 seconds or less, and more preferably 30 seconds or more and 90 seconds or less.

In the cooling process in the hot-rolled plate annealing, the cooling rate in the temperature range of 800 ° C. to 500 ° C. is preferably 20 ° C./sec to 100 ° C./sec. By setting the cooling rate within such a range, it is possible to obtain better magnetic characteristics.

In the hot-rolled plate annealing step according to the present embodiment, as shown in the upper center of FIG. 5, annealing is carried out with the scale generated by hot rolling attached. Due to both the scale of the surface of the hot-rolled plate and the atmosphere at the time of annealing, Al contained in the ground iron is oxidized while diffusing in the scale direction. As a result, an Al-concentrated layer containing Al oxide is formed near the surface of the base iron, and de-Al is removed on the inner layer side (center side in the thickness direction of the base iron) of the Al-concentrated layer by several μm. Layers are formed.

At the time of such hot-rolled plate annealing, both the Al-concentrated layer and the de-Al-depleted layer are formed, but in the production method according to the present embodiment, Al is concentrated under a situation where Al is more easily oxidized as compared with the conventional case. Since the layers are formed, the Al concentration of the de-Al layer, which is the source of Al to the Al-concentrated layer, becomes even lower than in the conventional case. As a result, a de-Al layer having an Al concentration distribution as schematically shown in FIG. 3 is formed. On the other hand, even if the hot-rolled sheet is annealed under the above-mentioned annealing conditions after removing the scale generated by hot rolling, Al in the vicinity of the surface layer in the ground iron is not sufficiently oxidized, and the present embodiment It is not possible to form such a de-Al layer.

<Pickling process>
After the hot-rolled plate annealing, pickling is carried out (step S105). In the pickling step according to the present embodiment, the pickling weight loss of the pickling plate in the depth direction from the surface of the ground iron is controlled so as to satisfy the relational expression shown in the above formula (1). The scale layer including the internal oxide layer (that is, the Al concentrated layer) is removed.

That is, as shown in the upper right figure of FIG. 5, in the pickling step according to the present embodiment, the scale and the Al-concentrated layer, which is an internal oxide layer located on the outermost layer of the ground iron, are removed. Pickling is controlled so that the de-Al layer is the outermost layer. At this time, with respect to the steel sheet during or after pickling, the Al concentration in the depth direction is measured at any time by GDS, and the finally obtained non-oriented electrical steel sheet 10 satisfies the relational expression shown in the above formula (101). Control the pickling weight loss so that it does. The pickling weight loss can be controlled by changing at least one of the concentration of the acid used for pickling, the concentration of the accelerator used for pickling, and the temperature of the pickling solution.

Specifically, it is preferable to control the pickling weight loss so as to satisfy the relational expression shown in the following formula (103). By controlling the pickling weight loss so as to satisfy the relational expression shown in the following formula (103), the non-oriented electrical steel sheet 10 finally obtained satisfies the relational expression shown in the above formula (101). become.

0.1 ≤ Al (x ≤ 5 μm) / Al (x = 10 μm) <1.0 ... Equation (103)

Here, in the above equation (103),
x: Depth from the surface of the base iron 11 [μm]
Al (x ≦ 5 μm): Mean value of Al concentration from the surface of the base metal to a depth of 5 μm [mass%]
Al (x = 10 μm): Al concentration at a depth of 10 μm [mass%]
Represents.

<Cold rolling process>
After the pickling, cold rolling is carried out (step S107). In such cold rolling, the pickling plate from which the scale and the Al-concentrated layer have 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 0.35 mm or less. As shown in the lower right figure of FIG. 5, by such cold rolling, the metal structure of the base metal portion becomes a cold rolled structure obtained by cold rolling.

<Finishing annealing process>
After the cold rolling, finish annealing is performed (step S109). In the method for producing a non-directional electromagnetic steel plate according to the present embodiment, the de-Al layer is formed in the hot-rolled sheet annealing step, and the de-Al layer is maintained in the subsequent steps. In the finish annealing step, when the finish annealing temperature exceeds 950 ° C., there is a high possibility that Al diffuses from the base metal portion to the de-Al layer and the de-Al layer disappears. Therefore, in such finish annealing, the finish annealing temperature is set to 950 ° C. or lower. By carrying out finish annealing at a finish annealing temperature of 950 ° C. or lower, grain growth of a recrystallized structure is suitably caused in the structure of the base metal portion and the de-Al layer in the strain removing annealing carried out in the production of the stator core. A fine recrystallized structure having an average crystal grain size of 50 μm or less is produced. On the other hand, when the finishing annealing temperature is less than 750 ° C., there is a high possibility that the annealing time becomes too long and the productivity is lowered. Therefore, in such finish annealing, the finish annealing temperature is preferably 750 ° C. or higher. The finish annealing temperature is more preferably 775 ° C. or higher and 900 ° C. or lower.

Here, the annealing time for performing the finish annealing may be appropriately set according to the finish annealing temperature, and may be, for example, 1 second to 150 seconds. If the annealing time is less than 1 second, sufficient finish annealing may not be possible, and it may be difficult to properly form a recrystallized structure in the base metal portion. On the other hand, when the annealing time exceeds 150 seconds, there is a high possibility that the annealing time becomes too long and the productivity is lowered. The annealing time is more preferably 5 seconds to 100 seconds.

The heating rate in the temperature range of 950 ° C. or lower and 700 ° C. or higher in the finish annealing is preferably 10 ° C./s to 800 ° C./s. By setting the heating rate to 10 ° C./s to 800 ° C./s, it is possible to further improve the magnetic characteristics of the non-oriented electrical steel sheet, and the heating rate exceeds 800 ° C./s. This is because even if it is raised, the effect of improving the magnetic characteristics is saturated. The heating rate in the temperature range of 950 ° C. or lower and 700 ° C. or higher in the finish annealing is more preferably 100 ° C./s to 400 ° C./s.

The cooling rate in the temperature range of 900 ° C. or lower and 500 ° C. or higher is preferably 10 ° C./s to 100 ° C./s. This is because by setting the cooling rate to 10 ° C./s to 100 ° C./s, it is possible to further improve the magnetic characteristics of the non-oriented electrical steel sheet, and the cooling rate exceeds 100 ° C./s. This is because even if it is raised, the effect of improving the magnetic characteristics is saturated. The cooling rate in the temperature range of 900 ° C. or lower and 500 ° C. or higher in the finish annealing is more preferably 20 ° C./s to 70 ° C./s.

<Insulation film forming process>
After the finish annealing, a step of forming an insulating film is carried out (step S111). Here, 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 the known insulating coating treatment liquid as described above.

At this time, the amount of the insulating coating treatment liquid adhered is controlled so that the amount of the insulating coating adhered after drying is 400 mg / m ² or more and 1200 mg / m ² or less per side. The control of the amount of adhesion is not particularly limited, and the coating and drying may be carried out by a known method using an insulating coating treatment liquid having an appropriately adjusted solid content concentration.

By applying the insulating coating treatment liquid and heating the steel sheet to a temperature corresponding to the solvent of the insulating coating treatment liquid, the insulating coating treatment liquid and / or the solid content react with each other due to the presence of the de-Al layer in the base iron. As a result, a predetermined amount of divalent and trivalent Fe is easily introduced into the insulating coating.

Before applying the treatment liquid, the surface of the base iron on which the insulating film is formed is degreased with alkali or the like to the extent that it does not significantly affect the state and thickness of the de-Al layer, and hydrochloric acid, sulfuric acid, etc. Any pretreatment such as pickling treatment with phosphoric acid may be performed, or the surface may be left as it is after finish annealing without these pretreatments.

As described above, the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment has been described in detail with reference to FIGS. 4 and 5.

(About the manufacturing method of the motor core)
Subsequently, with reference to FIGS. 6A and 6B, a method of manufacturing a motor core using the non-oriented electrical steel sheet according to the present embodiment as described above will be briefly described.
6A and 6B are flow charts showing an example of the flow of the method for manufacturing the motor core according to the present embodiment.

First, among the methods for manufacturing the motor core according to the present embodiment, the method for manufacturing the rotor core will be described with reference to FIG. 6A.
In the method for manufacturing a rotor core according to the present embodiment, first, the non-oriented electrical steel sheets 10 according to the present embodiment are punched into a core shape and then laminated (step S201) to form a desired rotor core shape. That is, after the rotor blank is punched from the non-oriented electrical steel sheet 10 according to the present embodiment, the rotor blank is laminated and joined to form the shape of the rotor core.

Since the rotor core has a small average crystal grain size after finish annealing, it has high strength while maintaining the core shape, and thus can be preferably used as it is.

Next, among the methods for manufacturing the motor core according to the present embodiment, the method for manufacturing the stator core will be described with reference to FIG. 6B.
In the method for manufacturing a stator core according to the present embodiment, first, the non-oriented electrical steel sheets 10 according to the present embodiment are punched into a core shape and then laminated (step S211) to form a desired stator core shape. That is, after the stator blank is punched from the non-oriented electrical steel sheet 10 according to the present embodiment, the stator core shape is formed by laminating and joining the stator blanks.

Subsequently, strain relief annealing (core annealing) is performed on the non-oriented electrical steel sheets laminated in the stator core shape (step S213). Such strain-removing annealing is carried out in an atmosphere containing 70% by volume or more of nitrogen. The annealing temperature of the strain removing annealing is 750 ° C. or higher and 900 ° C. or lower. By performing strain relief annealing under such annealing conditions, as described above, the strain accumulated in the non-oriented electrical steel sheet 10 is released and is present in the base metal portion of the non-oriented electrical steel sheet 10. Grain growth proceeds from the recrystallized structure. As a result, it becomes possible to realize a stator core exhibiting desirable magnetic characteristics.

Here, when the ratio of nitrogen in the atmosphere is less than 70% by volume, the steel sheet is oxidized by the residual oxygen, and when a contaminant other than oxygen (for example, argon or helium) is used, the steel sheet is oxidized. The cost is high, which is not preferable. The proportion of nitrogen in the atmosphere is more preferably 80% by volume or more, further preferably 90% by volume to 100% by volume, and particularly preferably 97% by volume to 100% by volume. The atmospheric gas other than nitrogen is not particularly specified, but generally, a reducing mixed gas composed of hydrogen, carbon dioxide, carbon monoxide, water vapor, methane, or the like can be used. In order to obtain these gases, a method obtained by burning propane gas or natural gas is generally adopted.

Further, when the annealing temperature of the strain removing annealing is less than 750 ° C., the strain accumulated in the non-oriented electrical steel sheet 10 cannot be sufficiently released, which is not preferable. On the other hand, when the annealing temperature of the strain removing annealing exceeds 900 ° C., the adhesion of the insulating film is lowered, which is not preferable. Further, when the annealing temperature of strain relief annealing exceeds 900 ° C., the grain growth of the recrystallized structure progresses too much and the hysteresis loss decreases, but the eddy current loss increases, so that the total iron loss increases. To do. The annealing temperature of the strain removing annealing is preferably 775 ° C. or higher and 850 ° C. or lower.

The annealing time for performing strain relief annealing may be appropriately set according to the annealing temperature, but can be, for example, 10 minutes to 180 minutes. If the annealing time is less than 10 minutes, it may not be possible to sufficiently release the strain. On the other hand, when the annealing time exceeds 180 minutes, there is a high possibility that the annealing time becomes too long and the productivity is lowered. The annealing time is more preferably 30 minutes to 150 minutes. The annealing time refers to the holding time at the set temperature for strain relief annealing.

Further, the heating rate in the temperature range of 500 ° C. or higher and 750 ° C. or lower in the strain removing annealing is preferably 10 ° C./h to 300 ° C./h. By setting the heating rate to 0 ° C./h to 300 ° C./h, it is possible to further improve not only the magnetic characteristics but also various characteristics of the stator core including securing the shape of the core. This is because even if the heating rate is increased to exceed 300 ° C./h, the effect of improving various characteristics is saturated. The heating rate in the temperature range of 500 ° C. or higher and 750 ° C. or lower in the strain-removing annealing is more preferably 80 ° C./h to 150 ° C./h.

The cooling rate in the temperature range of 750 ° C. or lower and 500 ° C. or higher is preferably 50 ° C./h to 500 ° C./h. This is because by setting the cooling rate to 50 ° C./h to 500 ° C./h, it is possible to further improve various characteristics of the motor core, and even if the cooling rate exceeds 500 ° C./h. On the contrary, due to uneven cooling, strain due to thermal stress is likely to be introduced, which may cause deterioration of iron loss. The cooling rate in the temperature range of 750 ° C. or lower and 500 ° C. or higher in the strain removing annealing is more preferably 80 ° C./h to 200 ° C./h.

A motor core can be manufactured by going through each of the above steps.

As described above, the method of manufacturing the motor core according to the present embodiment has been briefly described with reference to FIG.

Hereinafter, the method for manufacturing the non-oriented electrical steel sheet and the non-oriented electrical steel sheet and the method for manufacturing the motor core 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 sheet, the method for manufacturing the non-oriented electrical steel sheet, and the method for manufacturing the motor core according to the present invention, and the non-oriented electrical steel sheet according to the present invention. The manufacturing method of non-oriented electrical steel sheets and the manufacturing method of motor cores are not limited to the following examples.

(Example 1)
A slab having the composition shown in Table 1 below was prepared in a laboratory, heated to 1150 ° C, hot-rolled to a finishing temperature of 850 ° C and a finished plate thickness of 1.6 mm, and wound at 650 ° C. It was made into a hot rolled plate. Regarding the surface scale, hot-rolled sheet annealing at 1000 ° C for 50 seconds in a nitrogen atmosphere with an atmospheric dew point of 10 ° C is performed from cooling before hot rolling winding to hot-rolled sheet annealing without going through the scale removal process. It was applied and pickled with hydrochloric acid. At this time, by changing the acid concentration, temperature, and time of hydrochloric acid during pickling, various Al (x ≦ 5 μm) / Al (x = 10 μm) values as shown in Table 2 below can be obtained. A pickling board was created. These pickled plates were cold-rolled to obtain a cold-rolled plate having a plate thickness of 0.20 mm. Further, after annealing under the finishing annealing conditions as shown in Table 2 in a mixed atmosphere of 20% hydrogen, 80% nitrogen, and 0 ° C., the acrylic-styrene copolymer resin emulsion having an aluminum phosphate and a particle size of 0.2 μ is used. The insulating coating was applied to a predetermined amount and baked in the air at 350 ° C. to obtain a non-directional electromagnetic steel plate. The cooling rate in the temperature range of 800 ° C. to 500 ° C. during hot-rolled sheet annealing is 40 ° C./sec, and the heating rate in the temperature range of 950 ° C. or lower and 700 ° C. or higher during finish annealing and 900 ° C. The cooling rates in the temperature range of ° C. or lower and 500 ° C. or higher were set to 100 ° C./sec and 30 ° C./sec, respectively. The following surveys were conducted on each of the obtained samples, and the obtained results are shown in Table 2.

In addition, the production of the stator core was simulated, and the No. 1 shown in Table 2 was shown. 1-No. For 50 non-oriented electrical steel sheets, some strains are annealed for 2 hours after reaching 700 ° C, 750 ° C, 800 ° C, 850 ° C, 900 ° C, and 950 ° C in a 99.99% nitrogen atmosphere with a dew point of -40 ° C. Annealed. The magnetic properties and film adhesion shown below were investigated for each of the obtained samples, and the results obtained are shown in Table 3 below.

<Strength (before strain removal annealing)>
The yield stress was determined according to JISZ2241. The obtained yield stress was evaluated as follows. When the yield stress is 450 MPa or more, it can be preferably used as a rotor core.
◯: Yield stress 450 MPa or more ×: Yield stress less than 450 MPa

<Magnetic characteristics (before and after strain removal annealing)>
The excitation frequency of 400 Hz and the magnetic flux density of 1.0 T (hereinafter referred to as W10 / 400) were measured with a single plate magnetic property tester. The iron loss value is the average of the value measured when the excitation direction is parallel to the rolling direction (L direction) and the value measured when the excitation direction is 90 ° (C direction) with respect to the rolling direction. The value was taken. Here, the iron loss value W10 / 400 ≦ 12.0 after strain removal annealing was evaluated as having excellent magnetic characteristics.

<Average crystal grain size (before and after strain removal annealing)>
After polishing the cross section of each of the obtained samples, they were corroded with nital, and the average crystal grain size was determined by the line segment method.

<Film adhesion after strain removal annealing>
After strain removal annealing, the sample was wound around a round bar having a diameter of 30 mm, and the residual state of the coating film on the outside of the wound portion was visually judged as follows. The sample evaluated as ◯ was judged to have excellent film adhesion after strain relief annealing.
◯: Peeling area ratio 20% or less Δ: Peeling area ratio more than 20% 50% or less ×: Peeling area ratio more than 50%

<De-Al layer (before strain removal annealing)>
After immersing the sample in a 20% aqueous sodium hydroxide solution to remove the insulating coating on the surface, the Al concentration distribution in the region 10 μm deep from the surface layer was examined by GDS, and the formulas (101) and (103) were used. I asked for a number.

<Amount of insulation film adhered (before strain removal annealing)>
The sample was immersed in a 20% aqueous sodium hydroxide solution, and the insulating film on the surface was determined from the mass difference before and after removal and the area of the sample.

<Fe2 valent and Fetrivalent contents contained in the insulating film (before strain removal annealing)>
The sample was immersed in a 20% aqueous sodium hydroxide solution, ICP analysis was performed on the obtained aqueous solution, the amount of Fe contained was quantified, and the amount of Fe adhered per area was converted. Fe does not elute from the steel sheet in the alkaline aqueous solution, and only the insulating film of the non-oriented electrical steel sheet is dissolved in the alkaline aqueous solution. Therefore, it is clear that the amount of Fe quantified by ICP analysis does not include metal Fe (zero-valent Fe). Further, since Fe has divalent and trivalent valences and is stable in the atmosphere, the above Fe adhesion amount can be rephrased as the total adhesion amount of divalent and trivalent Fe.

Further, as an example of a method for directly confirming that Fe contained in the insulating film is divalent or trivalent, the following method can be mentioned. First, a sample of a non-directional electromagnetic steel sheet having an insulating film having a certain area is immersed in a 5% bromine-methanol solution to dissolve the steel sheet in the solution, and an insoluble insulating film is raised and collected. The abundance ratio of Fe at each valence (including 0 valence) such as Fe ³⁺ and Fe ²⁺ can be determined from the collected coating film by using the female bower spectroscopy shown below.

Specifically, the following method is performed.
The collected film is spread on the surface of the filter paper to prepare a sample piece. Using a ⁵⁷ Co / Rh matrix as the radiation source, the sample development surface is irradiated with γ-rays taken out from the radiation source, the intensity of the γ-rays emitted from the back surface of the sample development surface is measured, and the Doppler shift with respect to pure iron is obtained. , Fe ³⁺ and Fe ²⁺ can be identified respectively.

In the examples shown below, no results showing the state of Fe other than the presence of Fe ³⁺ and Fe ²⁺ were observed. Therefore, all the Fe adhesion amounts analyzed and quantified using the above 20% sodium hydroxide aqueous solution are Fe. It was reconfirmed that it was due to ³⁺ and Fe ²⁺ .

No. 1 and No. As is clear from Table 2, the sample No. 2 had a low surface Al concentration defined by the formula (101), so that the magnetic properties (iron loss) after strain removal annealing deteriorated as shown in Table 3. It is considered that this is because the eddy current loss, which is important for high-frequency iron loss, deteriorates as the surface Al concentration decreases.

No. 3 and No. As is clear from Table 2, the sample No. 6 has a high surface Al concentration defined by the formula (101) and a crystal grain size of more than 50 μm, so that the strength is low. In addition, as is clear from Table 3, No. 3 and No. In the sample No. 6, the adhesion of the insulating film did not show an excellent value, and both the iron loss and the strength could not be improved. No. 16-No. As is clear from Table 2, the sample of 21 has a high surface Al concentration defined by the formula (101), and the Fe2 valence and Fe3 valence contents in the insulating coating are low. By strain-removing and annealing the sample, the adhesion of the insulating coating did not show an excellent value as shown in Table 3.

No. 25 and No. As is clear from Table 2, the sample 29 corresponds to the example of the present invention as a non-oriented electrical steel sheet, and has a strength that can be used as a rotor core. However, as is clear from Table 3, since the annealing temperature was too high during the strain-removing annealing, the adhesion of the insulating film deteriorated and the excellent magnetic characteristics were not exhibited. It is considered that this is because the annealing temperature at the time of strain removal annealing was too high, so that the recrystallized structure grew too much and the hysteresis loss increased.

No. 30 and No. As is clear from Table 2, the sample of No. 31 has a small amount of adhesion of the insulating film and a low content of Fe divalent and trivalent in the insulating film. Therefore, as shown in Table 3, even if the strain was removed and annealed under appropriate conditions, the adhesion of the insulating film deteriorated and the excellent magnetic characteristics were not exhibited.

No. As is clear from Table 2, the 36 samples had too high a total content of Fe2 valence and Fe3 valence in the insulating coating, and therefore, even if strain removing and annealing were performed under appropriate conditions, as shown in Table 3. The adhesion of the insulating film deteriorated.

On the other hand, the non-oriented electrical steel sheet corresponding to the example of the present invention has a strength that can be used as a rotor core, and by performing strain relief annealing under appropriate conditions, it also has excellent magnetic properties and insulation as a stator core. It can be seen that it shows the adhesion of the coating film.

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

10 Non-oriented electrical steel sheet 11 Base steel 13 Insulation coating 101 Base material 103 De-Al layer

Claims (12)

By mass%
C: 0.0010% to 0.0050%
Si: 2.5% to 4.0%
Al: 0.1% to 2.0%
Mn: 0.05% to 2.0%
P: 0.005% to 0.15%
S: 0.0001% to 0.0030%
Ti: 0.0005 to 0.0030%
N: 0.0010 to 0.0030%
The balance is composed of Fe and impurities, the plate thickness of the base iron is 0.10 mm or more and 0.35 mm or less, the average crystal grain size in the base iron is 50 μm or less, and the surface of the base iron is from the surface. With respect to the Al concentration in the depth direction, a steel sheet satisfying the relational expression shown in the following equation (1),
The insulating coating located on the surface of the steel sheet and
With
The amount of the insulating coating adhered is 400 mg / m ² or more and 1200 mg / m ² or less.
A non-oriented electrical steel sheet having a divalent and trivalent Fe content in the insulating coating of 10 mg / m ² or more and 250 mg / m ² or less.

0.1 0 ≤ Al (x ≤ 2 μm) / Al (x = 10 μm) <1.0 ... (1)

Here, in the above equation (1),
x: Depth from the surface of the ground iron [μm]
Al (x ≦ 2 μm): Mean value of Al concentration from the surface of the base metal to a depth of 2 μm Al (x = 10 μm): Indicates the Al concentration at a depth of 10 μm. The non-oriented electrical steel sheet according to claim 1, further containing at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. The non-directionality according to claim 1 or 2, further containing at least one of Ni, Cu, and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. Electromagnetic steel plate. Instead of a part of the remaining Fe, it further contains at least one of Ca of 0.0005% by mass or more and 0.0025% by mass or less, or REM of 0.0005% by mass or more and 0.0050% by mass or less. , The non-oriented electrical steel sheet according to any one of claims 1 to 3. A method for producing non-oriented electrical steel sheets by sequentially performing hot rolling, hot rolling plate annealing, pickling, cold rolling, and finish annealing on a steel ingot having a predetermined chemical composition.
The ingot is by mass%
C: 0.0010% to 0.0050%
Si: 2.5% to 4.0%
Al: 0.1% to 2.0%
Mn: 0.05% to 2.0%
P: 0.005% to 0.15%
S: 0.0001% to 0.0030%
Ti: 0.0005 to 0.0030%
N: 0.0010 to 0.0030%
Containing, the balance consists of Fe and impurities,
Without removing the scale after the hot rolling, the dew point in the annealing atmosphere is set to -40 ° C or higher and 60 ° C or lower, the annealing temperature is set to 900 ° C or higher and 1100 ° C or lower, and the soaking time is set to 1 second or higher and 300 seconds or lower. The hot-rolled plate was annealed as described above.
By the pickling, the internal oxide layer was formed while controlling the pickling weight loss so as to satisfy the relational expression shown in the following formula (2) with respect to the Al concentration in the depth direction from the surface of the ground iron in the pickling plate. Remove the including scale layer and
By the cold rolling, the final plate thickness of the base iron was made 0.10 mm or more and 0.35 mm or less.
In the finish annealing, the finish annealing temperature is set to 950 ° C. or lower.
After the finish annealing, the amount of adhesion to the surface of the base iron is 400 mg / m ² or more and 1200 mg / m ² or less , and the content of divalent and trivalent Fe in the insulating film is 10 mg / m ² or more. An insulating film is formed so that the content is 250 mg / m ² or less .
A method for producing a non-oriented electrical steel sheet, wherein the average crystal grain size of the ground steel after finish annealing is 50 μm or less .

0.1 ≤ Al (x ≤ 5 μm) / Al (x = 10 μm) <1.0 ... ( 2 )

Here, in the above equation (2),
x: Depth from the surface of the ground iron [μm]
Al (x ≦ 5 μm): Mean value of Al concentration from the surface of the base metal to a depth of 2 μm Al (x = 10 μm): Indicates the Al concentration at a depth of 10 μm. The non-directional according to claim 5, wherein the steel ingot further contains at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. Manufacturing method of electrical steel sheet. According to claim 5 or 6 , the steel ingot further contains at least one of Ni, Cu and Cr in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. The method for manufacturing a non-oriented electrical steel sheet described. The steel ingot is at least one of Ca of 0.0005% by mass or more and 0.0025% by mass or less, or REM of 0.0005% by mass or more and 0.0050% by mass or less instead of a part of Fe in the balance. The method for producing a non-oriented electrical steel sheet according to any one of claims 5 to 7 , which comprises. By mass%
C: 0.0010% to 0.0050%
Si: 2.5% to 4.0%
Al: 0.1% to 2.0%
Mn: 0.05% to 2.0%
P: 0.005% to 0.15%
S: 0.0001% to 0.0030%
Ti: 0.0005 to 0.0030%
N: 0.0010 to 0.0030%
The balance is composed of Fe and impurities, the plate thickness of the base iron is 0.10 mm or more and 0.35 mm or less, the average crystal grain size in the base iron is 50 μm or less, and from the surface of the base iron. Regarding the Al concentration in the depth direction, a steel plate satisfying the relational expression shown in the following formula (1) and an insulating coating located on the surface of the steel plate are provided, and the amount of the insulating coating adhered is 400 mg / m. ^A non-directional electromagnetic steel plate having a divalent and trivalent Fe content of ² or more and 1200 mg / m ² or less and a divalent and trivalent Fe content of 10 mg / m ² or more and 250 mg / m ² or less in the insulating coating.
A method for manufacturing a motor core, in which strain is removed and annealed at a temperature of 750 ° C. or higher and 900 ° C. or lower in an atmosphere containing 70% by volume or more of nitrogen after punching into a core shape and laminating.

0.1 0 ≤ Al (x ≤ 2 μm) / Al (x = 10 μm) <1.0 ... (1)

Here, in the above equation (1),
x: Depth from the surface of the ground iron [μm]
Al (x ≦ 2 μm): Mean value of Al concentration from the surface of the base metal to a depth of 2 μm Al (x = 10 μm): Indicates the Al concentration at a depth of 10 μm. The ninth aspect of the present invention, wherein the non-oriented electrical steel sheet further contains at least one of Sn and Sb in an amount of 0.01% by mass or more and 0.2% by mass or less, respectively, in place of a part of the remaining Fe. Motor core manufacturing method. The non-oriented electrical steel sheet, instead of the part of the remainder of Fe, further, Ni, at least one of Cu or Cr, containing 0.2 wt% 0.01 wt%, respectively, claim 9 Alternatively , the method for manufacturing a motor core according to 10 . In the non-oriented electrical steel sheet, in place of a part of the remaining Fe, Ca of 0.0005% by mass or more and 0.0025% by mass or less, or 0.0005% by mass or more and 0.0050% by mass or less. The method for manufacturing a motor core according to any one of claims 9 to 11 , which comprises at least one of REM.

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