JP7284383B2 - Non-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a non-oriented electrical steel sheet.

In recent years, in the field of electrical equipment (especially rotating machines, small and medium-sized transformers, electrical equipment, etc., where non-oriented electrical steel sheets are used as core materials), there has been a worldwide trend toward power and energy savings and _CO2 reduction. There is a movement to protect the global environment. In this situation, the demand for high efficiency and miniaturization is increasing more and more. Under such a social environment, it is of course an urgent task to improve the performance of non-oriented electrical steel sheets.

As is well known, many measures have been taken to improve the performance of non-oriented electrical steel sheets. Iron loss is roughly classified into two types: hysteresis loss and eddy current loss. In general, iron loss reduction has been achieved by increasing the content of Si, Al, etc., from the viewpoint of reducing eddy current loss due to increased specific resistance. However, if the contents of Si and Al are excessively increased, there is a problem that the steel sheet becomes embrittled and the productivity is lowered. Further, when Mn is added, the increase in the hardness of the steel sheet is small, but the effect of increasing the specific resistance is about half that of Si and Al. Furthermore, there is an upper limit to the amount of addition since it may cause red shortness problems in the hot rolling process.

Therefore, as another technique for increasing the specific resistance, for example, Patent Document 1 discloses a technique for increasing the specific resistance by adding 1.5% to 20% of Cr. The effect of increasing the specific resistance when Cr is added is about the same as that of Mn, but if the addition is 20% or less, the hardness of the steel sheet does not increase so much, and embrittlement is less likely to occur. Moreover, unlike Mn, there are few problems of red heat brittleness.

By the way, drive motors for electric vehicles and hybrid vehicles are used not only for high-speed running, but also for low-speed, high-torque running when starting up and when climbing hills. Something is possible. Therefore, electrical steel sheets for motor cores are required to reduce iron loss not only at high frequencies but also at low frequencies. Iron loss is good, but at low frequencies such as 800 Hz, there is a problem that iron loss deteriorates as the amount of Cr added increases. Moreover, the frequency at which core loss begins to deteriorate changes depending on the plate thickness of the product.

In addition, since Si and Al in the steel sheet are easily oxidized, when oxygen diffuses into the steel sheet at high temperature and internal oxidation occurs, domain wall movement is hindered and hysteresis loss is deteriorated. Furthermore, when internal oxidation occurs, the presence of the non-magnetic oxide layer reduces the effective cross-sectional area through which magnetic flux can pass, increasing the magnetic flux density and degrading eddy current loss. Moreover, at high frequencies, the magnetic flux concentrates near the surface of the steel sheet due to the skin effect, so the above effect becomes more pronounced. On the other hand, Cr oxide has a thin and very dense structure, and when formed on the surface of the steel sheet, it is thought that it prevents subsequent penetration of oxygen and suppresses internal oxidation of Si and Al.

In Patent Document 5, C: 0.005% by mass or less, S: 0.003% by mass or less, N: 0.003% by mass or less, Si: 2.0% by mass or more and less than 4.5% by mass, Al: It contains 0.15% by mass or more and less than 2.5% by mass, and Cr: 0.3% by mass or more and less than 5.0% by mass, the balance being Fe and unavoidable impurities, and the surface side has a thickness of 0.5%. A non-oriented electrical steel sheet characterized by having a layer containing Cr oxide of 01 μm or more and 0.5 μm or less, further satisfying the following formulas 1 and 2, and having a thickness of 0.3 mm or less, Si , Al and Cr, by satisfying a certain formula with the product thickness, it is possible to provide a non-oriented electrical steel sheet with excellent iron loss over a wide range of frequencies.

However, the increase in Cr content increases the specific resistance to the same extent as in the case of Si, Al, and Mn, and the amount of saturation magnetic flux density decrease at the content that reduces eddy current loss is large, and the magnetic flux density B50 decreases. There is also the problem that the generation is large.

As one of the techniques for improving the magnetic flux density, as described in Patent Document 6, a technique of adding P and causing segregation at grain boundaries is known. A method using rapid heating is also known, as described in Patent Document 7.

Moreover, as a means for improving the magnetic flux density, a method using rapid solidification is known as described in Patent Document 8. However, when rapid solidification is industrially performed, there is a problem that fine precipitates inhibit grain growth during finish annealing. As described in Patent Document 9, a method for solving this problem by including one or two of REM and Ca is also known.

Japanese Patent No. 5780013 Japanese Patent Application Laid-Open No. 2003-183788 JP-A-2002-317254 JP-A-2002-115035 Japanese Patent No. 5429411 Japanese Patent No. 5995002 Japanese Patent No. 5825494 JP-A-62-240714 Japanese Patent No. 4648910

However, the methods of Patent Documents 6 and 7 do not always provide a high magnetic flux density. In the method of Patent Document 8, grain growth during finish annealing is inhibited and a high magnetic flux density can be obtained, but it is not satisfactory in terms of low iron loss. The method of Patent Document 9 solves the grain growth inhibition problem of Patent Document 8, but has the problem of deterioration of hysteresis loss due to the Al content.

Here, low core loss and high magnetic flux density are required for motors, particularly non-oriented electrical steel sheets for stators. high strength is required. In particular, with the recent development of high-speed rotation and IPM (Interier Permanent Magnet, embedded magnet type), there is an increasing demand for higher strength of electromagnetic steel sheets for rotors. In addition to high alloying, grain refinement is effective in increasing the strength of steel sheets.

By the way, it is being considered to take both a stator steel plate and a rotor steel plate from the same electromagnetic steel plate. Specifically, high-strength non-oriented electrical steel sheets due to refinement of crystal grains are used as they are as steel sheets for rotors, while high-strength non-oriented electrical steel sheets due to refinement of crystal grains are used as steel sheets for stators. After punching, the punched material is annealed, and the iron loss is reduced by crystal grain growth before use.

However, in steel sheets for stators, due to the presence of fine precipitates in the steel during annealing of the punched material, sufficient grain growth does not occur, making it difficult to achieve low iron loss. may decrease.
In addition, regardless of whether the steel sheet is used for a rotor or a stator, oxidation of the surface of the steel sheet, especially internal oxidation, which occurs inevitably during the heat treatment process, may cause deterioration of the magnetic properties.

Therefore, in view of the above problems, the problem of the present invention is to provide a first non-oriented electrical steel sheet with low iron loss and high magnetic flux density, and a high strength steel sheet with no iron loss after annealing the punched material. A second object of the present invention is to provide a non-oriented electrical steel sheet having a low magnetic flux density and a high magnetic flux density.

The above problems are solved by the following means.

<1>
% by mass C: more than 0% to 0.0030%,
Si: 2.00% to 4.50%,
sol. Al: 0.15% to 2.50%,
Mn: 0.20% to 1.50%,
Cr: 0.30-5.00%
P: 0.005% to 0.200%,
S: 0.0010% to 0.0100%,
Ti: 0.0005% to 0.0100%,
Ca: 0.0005% to 0.0100%,
One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.0005% to 0.0200% in total, and
Balance: having a chemical composition containing Fe and impurities, and having an inverse pole figure with a {100} plane strength of 2.4 or more,
The area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) is 18% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The average crystal grain size is 55 μm to 200 μm,
The plate thickness is 0.10 mm to 0.30 mm,
Having a layer containing Cr oxide with a thickness of 0.01 μm or more and 0.5 μm or less on the surface of the steel plate,
The Si content (mass%) is [Si], the Al content (mass%) is [Al], the Cr content (mass%) is [Cr], and the thickness of the non-oriented electrical steel sheet A non-oriented electrical steel sheet that satisfies the following formulas 1 and 2 when (mm) is t.
10.00% ≤ 2 [Si] + 2 [Al] + [Cr] < 15.00% (Formula 1)
(2[Al]+[Cr])/2[Si]−10t ² ≦0.35 (Formula 2)
<2>
The Si content (mass%) is [Si], the Al content (mass%) is [Al], the Mn content (mass%) is [Mn], the Cr content (mass%) ) as [Cr], the non-oriented electrical steel sheet according to <1>, wherein R represented by the following formula 3 is 64.00 or more.
R = 9.9 + 12.4 x [Si] + 10.0 x [Al] + 6.6 x [Mn] + 5.0 x [Cr] (Formula 3)
<3>
<1> or <2> in which the area ratio of crystal grains having a crystal orientation of {411} orientation (within a tolerance of 20°) in the entire field of view is 70% or more when measured by electron beam backscatter diffraction (EBSD) The non-oriented electrical steel sheet according to .
<4>
<1> to <3> in which the area ratio of crystal grains having a crystal orientation of {111} orientation (within a tolerance of 20°) in the entire field of view is 25% or less when measured by electron beam backscatter diffraction (EBSD) The non-oriented electrical steel sheet according to any one of .
<5>
A non-oriented electrical steel sheet obtained by annealing at 750 ° C. for 120 minutes to obtain the non-oriented electrical steel sheet according to any one of <1> to <4>,
% by mass C: more than 0% to 0.0030%,
Si: 2.00% to 4.50%,
sol. Al: 0.15% to 2.5%,
Mn: 0.20% to 1.50%,
Cr: 0.30% to 5.0%
P: 0.005% to 0.200%,
S: 0.0010% to 0.0100%,
Ti: 0.0005% to 0.0100%,
Ca: 0.0005% to 0.0100%,
One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.0005% to 0.0200% in total, and
Balance: having a chemical composition containing Fe and impurities,
After annealing at 750°C for 120 minutes,
The {100} face strength of the inverse pole figure is 2.4 or more,
The area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) is 18% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The average crystal grain size is 20 μm or less,
The plate thickness is 0.10 mm to 0.30 mm,
A layer containing Cr oxide having a thickness of 0.01 μm or more and 0.5 μm or less on the surface of the steel sheet, wherein the Si content (mass%) is [Si], and the Al content (mass%) is A non-oriented electrical steel sheet that satisfies the above formulas 1 and 2, where [Al], the Cr content (% by mass) is [Cr], and the thickness (mm) of the non-oriented electrical steel sheet is t.

According to the present invention, a first non-oriented electrical steel sheet having low iron loss and high magnetic flux density, and a high strength non-oriented electrical steel sheet having low iron loss and high magnetic flux density after annealing the punched material. Two non-oriented electrical steel sheets can be provided.

An embodiment, which is an example of the present invention, will be described in detail below.

In addition, in this specification, "%" display of the content of each element in the chemical composition means "% by mass".
A numerical range represented using "to" means a range including the numerical values described before and after "to" as lower and upper limits.
Numerical ranges in which "greater" or "less than" are attached to numerical values written before and after "to" mean ranges that do not include these numerical values as lower or upper limits.
The term "process" includes not only independent steps, but also if the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps.
A non-oriented electrical steel sheet obtained through the steps of continuous casting and hot rolling is also called a “CC material”.
The "{100} plane strength of the inverse pole figure" may be simply referred to as "{100} plane strength".
"When measured by electron beam backscatter diffraction (EBSD)," area ratio of crystal grains having a crystal orientation of {100} orientation (within 20 ° tolerance) with respect to the entire field of view, "{411} orientation (tolerance The area ratio of crystal grains having a crystal orientation of {111} orientation (within 20 °) in the entire field of view, and the area ratio of crystal grains having a crystal orientation of {111} orientation (within a margin of , the area ratio of {100} oriented grains, the area ratio of {411} oriented grains, and the area ratio of {111} oriented grains.

<Non-oriented electrical steel sheet>
The non-oriented electrical steel sheet according to the first embodiment has a predetermined chemical composition and exhibits the following properties (1), (2), (3A), (4), (5) and (6). Fulfill.
On the other hand, the non-oriented electrical steel sheet according to the second embodiment is a non-oriented electrical steel sheet from which the non-oriented electrical steel sheet according to the first embodiment is obtained by annealing at 750° C. for 120 minutes, and It has a composition and satisfies the following properties (1), (2), (3B), (4), (5) and (6). That is, the non-oriented electrical steel sheet according to the second embodiment has an average grain size of 55 μm to 200 μm after annealing at 750° C. for 120 minutes, and satisfies the characteristics of the non-oriented electrical steel sheet according to the first embodiment. It is a steel plate that becomes like this.

(1) The {100} face strength of the inverse pole figure is 2.4 or more.
(2) The area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) is 18% or more in the entire visual field when measured by electron beam backscatter diffraction (EBSD).
(3A) The average crystal grain size is 55 μm to 200 μm.
(3B) The average crystal grain size is 20 μm or less.
(4) The plate thickness is 0.10 mm to 0.30 mm.
(5) A layer containing Cr oxide having a thickness of 0.01 μm or more and 0.5 μm or less (hereinafter, the “layer containing Cr oxide” is also referred to as “Cr oxide layer”) on the surface of the steel sheet.
(6) Si content (mass%) [Si], Al content (mass%) [Al], Cr content (mass%) [Cr], thickness of non-oriented electrical steel sheet When (mm) is t, the following formulas 1 and 2 are satisfied.
10.00% ≤ 2 [Si] + 2 [Al] + [Cr] < 15.00% (Formula 1)
(2[Al]+[Cr])/2[Si]−10t ² ≦0.35 (Formula 2)

The non-oriented electrical steel sheet according to the first embodiment is a non-oriented electrical steel sheet with low iron loss and high magnetic flux density due to the above configuration.
On the other hand, the non-oriented electrical steel sheet according to the second embodiment is a non-oriented electrical steel sheet with low core loss and high magnetic flux density after the punched material is annealed, while having high strength due to the above configuration.
These non-oriented electrical steel sheets according to the present embodiment were discovered based on the following findings.

Increasing the content of Si, Al, Mn and Cr raises the specific resistance of the steel sheet and reduces the eddy current loss. On the other hand, Si, Al, Mn and Cr lower the saturation magnetic flux density of the steel sheet. When comparing the contents that raise the specific resistance to the same extent, the saturation magnetic flux density reduction of Si and Mn is almost the same, but the saturation magnetic flux density reduction of Al is larger than that of Si and Mn, and the saturation magnetic flux density of Cr is reduced. is greater than Al. Furthermore, when the contents of Al and Cr are increased, the hysteresis loss deteriorates, so at frequencies where the ratio of hysteresis loss is large, the iron loss may not decrease as much as the specific resistance. It is known that Si and Mn have a smaller effect on hysteresis loss than Al and Cr, and the hysteresis loss is greatly reduced when the Si content is around 6.5%.
On the other hand, Si tends to embrittle the steel sheet more easily than Al, Mn and Cr, and excessive Si increases the concern of brittle fracture during production. Cr is less likely to embrittle the steel sheet than Si, Al and Mn.
Furthermore, Si, Al and Mn are strong oxide-forming elements, and may increase internal oxidation on the surface of the steel sheet during the heat treatment process, degrading the magnetic properties.
However, if the equations 1 and 2 are satisfied, the deterioration of the hysteresis loss and the decrease of the magnetic flux density B50 can be suppressed. Further, by forming a dense Cr oxide layer containing Cr so as to satisfy the formulas 1 and 2, the internal oxidation is suppressed and the deterioration of the magnetic properties due to the internal oxidation can be avoided.

In order to reduce core loss, the average grain size is increased to 55 μm to 200 μm by finish annealing.
However, when obtaining a high-strength steel sheet, the average grain size is suppressed to 20 μm or less by low-temperature finish annealing. When the average crystal grain size is suppressed to 20 μm or less, for example, after punching steel sheets by the user and laminating them to produce a motor core, high temperature annealing (for example, 750 to 850 ° C., 60 to 180 minutes) is performed for the purpose of strain relief. As a result, the average crystal grain size is increased (for example, the average crystal grain size is increased to 55 μm to 200 μm), and low iron loss can be achieved.

On the other hand, increasing the amount of Si and Mn usually lowers the saturation magnetic flux density. However, by improving the texture, a high magnetic flux density can be obtained. A crystal orientation near {100} is important as a texture that contributes to the improvement of the magnetic flux density.
By increasing the {100} plane strength and the existence probability of {100} oriented grains, the magnetic flux density is improved even if the Si content and the Mn content are increased, and low core loss and high magnetic flux density can be realized.

When the thickness of the non-oriented electrical steel sheet is set to 0.10 mm to 0.30 mm, the eddy current loss, which is one type of iron loss, is reduced. can be done.

Further, it is the presence of fine precipitates in the steel that inhibits the growth of grains during annealing of the punched material. However, due to the inclusion of at least one of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd (hereinafter these elements may be referred to as X), fine precipitates that inhibit grain growth Of these, sulfides such as MnS can be rendered harmless by coarsely precipitating as XS compounds and X-OS compounds.
On the other hand, among the fine precipitates that inhibit grain growth due to the inclusion of at least one of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd, fine Al-based Substances (AlN, Al ₂ O _3, etc.) can be rendered harmless by complex precipitation of precipitates.
In this way, by including at least one of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd, sufficient crystal grain growth occurs during annealing of the punched material (for example, the average crystal grain size is 55 μm to It grows up to 200 μm), and low iron loss is achieved.

Also, the decrease in the magnetic flux density due to the growth of crystal grains during the annealing of the punched material is mainly due to the grain growth of {111} orientation grains such as {111}<112> crystal grains. However, when the average crystal grain size is 20 μm or less, by suppressing the area ratio of {111} orientation grains (that is, suppressing {111} orientation grains such as {111}<112> crystal grains to a very small amount), Even if crystal grains grow (for example, crystal grains grow to an average crystal grain size of 55 μm to 200 μm) during annealing of the punched material, the magnetic flux density is less likely to decrease.

Further, by providing a Cr oxide layer having a thickness of 0.01 μm or more and 0.5 μm or less on the surface of the steel sheet, internal oxidation that deteriorates hysteresis loss and eddy current loss can be suppressed.

Based on the above findings, it was found that the non-oriented electrical steel sheet according to the first embodiment is a non-oriented electrical steel sheet with low core loss and high magnetic flux density due to the above configuration.
On the other hand, the non-oriented electrical steel sheet according to the second embodiment has high strength due to the above configuration, but after annealing the punched material, it becomes a non-oriented electrical steel sheet with low iron loss and high magnetic flux density. was found.
And the non-oriented electrical steel sheet according to the first embodiment is suitable as a steel sheet for a stator. On the other hand, the non-oriented electrical steel sheet according to the second embodiment is suitable as a steel sheet for the rotor, and also suitable as a steel sheet for co-coupling the steel sheet for the stator and the steel sheet for the rotor.

Hereinafter, the details of the non-oriented electrical steel sheets according to the first and second embodiments (common items are hereinafter referred to as "non-oriented electrical steel sheets according to the present embodiment") will be described.

The chemical composition of the non-oriented electrical steel sheet according to this embodiment will be described. In addition, "%" is "mass%" about the chemical composition of a steel plate.

The chemical composition of the non-oriented electrical steel sheet is
C: 0.0030% or less,
Si: 2.00% to 4.50%,
sol. Al: 0.15% to 2.5%,
Mn: 0.20% to 1.50%,
Cr: 0.30% to 5.00%
P: 0.005% to 0.200%,
S: 0.0010% to 0.0100%,
Ti: 0.0005% to 0.0100%,
Ca: 0.0005% to 0.0100%,
One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd (hereinafter also referred to as "specific element group"): 0.0005% to 0.0200% in total, and
Balance: contains Fe and impurities.

The non-oriented electrical steel sheet contains C, Si, sol. It may be a non-oriented electrical steel sheet having a chemical composition containing Al, Mn, P, S, Ti, Ca, and one or more elements selected from a specific element group, with the balance being Fe and impurities.

[C: more than 0% to 0.0030% or less]
C (carbon) is an element that is inevitably contained (that is, the content exceeds 0%), and is an element that causes iron loss deterioration. If the C content exceeds 0.0030%, core loss deterioration occurs in the non-oriented electrical steel sheet, making it difficult to obtain good magnetic properties. Therefore, the content of C is set to 0.0030% or less. The content of C is preferably 0.0020% or less, more preferably 0.0015% or less.
On the other hand, the lower limit of the C content is preferably more than 0%, and more preferably 0.0005% or more from the viewpoint of refining cost.

[Si: 2.00% to 4.50%]
Si (silicon) is an element that increases the specific resistance of steel, reduces eddy current loss, and improves iron loss. In addition, since Si has a large solid-solution strengthening ability, it is an element effective for increasing the strength of a non-oriented electrical steel sheet. Increasing the strength is important from the viewpoint of suppressing deformation and fatigue fracture during high-speed rotation of the motor. In order to sufficiently exhibit such effects, it is necessary to contain 2.00% Si. Therefore, the Si content is set to 2.00%.
On the other hand, if the Si content exceeds 4.50%, workability tends to deteriorate. Therefore, the content of Si is set to 4.50% or less.
The Si content is preferably 2.50% to 3.90%, more preferably 3.20% to 3.80%.

[Sol. Al: 0.15% to 2.50%]
Al (aluminum) is an element that, when dissolved in steel, increases the specific resistance of a non-oriented electrical steel sheet, thereby reducing eddy current loss and improving high-frequency iron loss. On the other hand, Al significantly lowers saturation magnetic flux density, lowers magnetic permeability, and increases hysteresis loss than Si. If it is less than 0.15%, the specific resistance cannot be sufficiently increased, and the effect of reducing iron loss cannot be sufficiently obtained. On the other hand, since Al lowers the saturation magnetic flux density of the steel sheet, when it exceeds 2.50%, the saturation magnetic flux density is significantly lowered, and the low magnetic flux density B50 becomes conspicuous. Therefore, the Al content is set to 0.15% to 2.50%.
The lower limit of the Al content is preferably 0.30%, more preferably 0.60% or more.
The upper limit of the Al content is preferably 1.80%, more preferably 1.20% or less.

[Mn: 0.20% to 1.50%]
Mn has the effect of increasing specific resistance and reducing eddy current loss. Furthermore, Mn has the effect of suppressing precipitation of fine sulfides such as MnS that are harmful to grain growth. In order to exhibit such an effect, the Mn content must be a certain amount or more, but if it is less than 0.20%, a sufficient eddy current loss reduction effect cannot be obtained and precipitation of fine sulfides cannot be suppressed. Therefore, the content of Mn is set to 0.20% or more.
On the other hand, if the Mn content exceeds 1.50%, the crystal grain growth itself during annealing deteriorates, and iron loss increases. Therefore, the Mn content is set to 1.50% or less.
The Mn content is preferably 0.25% or more and 1.30% or less, more preferably 0.50% or more and 1.10% or less.

[Cr: 0.30% to 5.00%]
Cr has the effect of increasing the specific resistance of the steel sheet and reducing the eddy current loss, although the effect is smaller than that of Si and Al. Moreover, Cr changes the oxidation behavior of the steel sheet during the heat treatment process, and forms an oxide mainly composed of Cr on the surface of the steel sheet. Furthermore, in steel sheets containing strong sulfide-forming elements such as Ca, Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd, Cr is converted into dense Cr in heat treatment, as described below. It becomes easy to form an oxide layer. And Cr suppresses internal oxidation by forming a dense Cr oxide layer, and exerts an effect of avoiding deterioration of magnetic properties. In order to exhibit such an effect, the Cr content must be a certain amount or more, but if it is less than 0.30%, a sufficient effect cannot be obtained. Therefore, the Cr content is set to 0.30% or more.
On the other hand, when the Cr content exceeds 5.00%, the saturation magnetic flux density of the steel sheet is significantly lowered, and the magnetic flux density B50 is significantly lowered. Therefore, the Cr content is set to 0.30% to 5.00%.
The Cr content is preferably 0.60% or more and 4.00% or less, more preferably 1.20% or more and 3.00% or less.

[P: 0.005% to 0.200%]
P (phosphorous) is an element that suppresses recrystallization from grain boundaries during annealing and suppresses the growth of {111} orientation grains, etc., which are inferior in magnetic properties. In order to exhibit such an effect, it is necessary to contain 0.005% or more of P. Therefore, the P content should be 0.005% or more.
On the other hand, when the P content exceeds 0.200%, the steel sheet becomes embrittled. Therefore, the content of P is set to 0.200% or less.
The P content is preferably 0.06% or more and 0.15% or less, more preferably 0.08% or more and 0.12% or less.

[S: 0.0010% to 0.0100%]
S (sulfur) is an element that increases iron loss by forming fine sulfides such as MnS and degrades magnetic properties. Also, fine sulfides such as MnS inhibit recrystallization and grain growth during annealing and the like.
Therefore, considering refining cost, S is set to 0.0010% to 0.0100%.
The S content is preferably 0.0080% or less, more preferably 0.0060% or less.

[Ti: 0.0005% to 0.0100%]
Ti (titanium) combines with C, N, O, etc. in the base iron to form fine precipitates such as TiN, TiC, Ti oxides, etc., which inhibit the growth of crystal grains during annealing and improve magnetic properties. It is an element that causes deterioration.
Therefore, considering refining cost, Ti is set to 0.0005% to 0.0100%.
The Ti content is preferably 0.0008% or more and 0.0080% or less, more preferably 0.0010% or more and 0.0060% or less.

[Ca: 0.0005% to 0.0100%]
Ca is an element that fixes S as a sulfide or oxysulfide, avoids fine precipitation of MnS and the like, smoothes domain wall movement, and reduces iron loss. In order to exhibit such an effect, it is necessary to contain 0.0005% or more of Ca. Therefore, the content of Ca is set to 0.0005% or more.
On the other hand, when the Ca content exceeds 0.0100%, sulfides or oxysulfides themselves become excessive, and iron loss tends to deteriorate. Therefore, the content of Ca is set to 0.0100% or less.
The Ca content is preferably 0.0010% or more and 0.0080% or less, more preferably 0.0015% or more and 0.0060% or less.

[One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: total 0.0005% to 0.0200%]
Mg, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd fix S as sulfides or oxysulfides, avoid fine precipitation of MnS and the like, smooth domain wall movement, and reduce iron loss. It has a lowering effect. Therefore, it is necessary to contain one or more selected from these specific elements. In order to exhibit such an effect, the total content of one or more elements selected from the specific element group should be 0.0005% or more.
On the other hand, if the total content of at least one element selected from the specific element group exceeds 0.0200%, the sulfide or oxysulfide itself becomes excessive, resulting in deterioration of iron loss. Therefore, the total content of at least one element selected from the specific element group is set to 0.0100% or less.
The total content of one or more selected from the specific element group is preferably 0.0010% or more and 0.0150% or less, more preferably 0.0020% or more and 0.0100% or less. .

In addition, the inclusion of Ca, which is a strong sulfide-forming element, and the above-mentioned specific element group are considered to refine the surface of the steel sheet in the process of heat treatment and affect the oxidation behavior of the steel sheet. It acts to favorably form a Cr oxide layer.

[Remainder]
The balance of the non-oriented electrical steel sheet is Fe and impurities. Here, the term "impurity" refers to a component contained in the raw material or a component mixed in during the manufacturing process and not intentionally included in the steel sheet. Further, the impurities also include components contained intentionally within a range that does not affect the performance of the steel sheet.

[(Formula 1) 10.00% ≤ 2 [Si] + 2 [Al] + [Cr] < 15.00%]
When the Si content (mass%) is [Si], the Al content (mass%) is [Al], and the Cr content (mass%) is [Cr], the conditions of the following formula 1 are satisfied. to
10.00% ≤ 2 [Si] + 2 [Al] + [Cr] < 15.00% (Formula 1)
If 2[Si]+2[Al]+[Cr] is less than 10%, the iron loss at 3000 Hz becomes too large. On the other hand, when it exceeds 15.00%, the saturation magnetic flux density of the steel sheet is significantly lowered, and the magnetic flux density B50 is significantly lowered. The reason why the specific gravities of Si and Al are doubled relative to Cr is that Cr has a small effect.
In addition, control of the total content of Si and Al, which are strong oxide-forming elements, is also necessary for preferably forming a dense Cr oxide layer, which will be described later.

[(Formula 2) (2[Al]+[Cr])/2[Si]−10t ² ≦0.35]
[Si] is the content (% by mass) of Si, [Al] is the content (% by mass) of Al, [Cr] is the content (% by mass) of Cr, and t (mm) is the plate thickness of the product. Sometimes the condition of the following expression 2 is satisfied.
(2[Al]+[Cr])/2[Si]−10t ² ≦0.35 (Formula 2)
As a result of repeated experiments by the present inventors, it was found that the hysteresis loss does not deteriorate so much even if the Si content is increased, but that the hysteresis loss deteriorates rapidly if the Al and Cr contents are increased. As a result, even if the specific resistance and plate thickness are the same, that is, even if the eddy current loss is the same, the iron loss deteriorates as the ratio of (2[Al]+[Cr])/2[Si] increases. , that is, the hysteresis loss deteriorates.
Furthermore, as a result of further experiments, it was found that the plate thickness also decreased in the low frequency region where the ratio of hysteresis loss increases or in the high frequency region, and this tendency became more pronounced when the eddy current loss decreased. The eddy current loss is proportional to the square of the frequency and the square of the plate thickness, and the hysteresis loss is proportional to the first power of the frequency but is not dependent on the plate thickness. Equation 2 was derived based on experimental data.
Further, in order to improve iron loss in a lower frequency range (eg, 400 Hz), it is preferable to further satisfy the conditions of the following formula.
(2[Al]+[Cr])/2[Si]−5t ² ≦0.35
Controlling the balance with Si and Al, which are strong oxide-forming elements, is a favorable condition for more preferably forming a dense Cr oxide layer, which will be described later.

[(Formula 3) R = 9.9 + 12.4 x [Si] + 10.0 x [Al] + 6.6 x [Mn] + 5.0 x [Cr]: 64.00 or more]
Si content (mass%) [Si], Al content (mass%) [Al], Mn content (mass%) [Mn], Cr content (mass%) [Cr ], R represented by the following formula 3 is preferably 64.00 or more.
R = 9.9 + 12.4 x [Si] + 10.0 x [Al] + 6.6 x [Mn] + 5.0 x [Cr] (Formula 3)

Here, increasing the Si content, Al content, Mn content and Cr content increases the specific resistance and decreases the eddy current loss as described above. On the other hand, since Si easily embrittles the steel sheet compared to Al, Mn and Cr, it is preferable to increase the amount of Cr, which is relatively hard to embrittle, to increase the resistivity.
Therefore, from the viewpoint of increasing the specific resistance and lowering the core loss, the R value (= 9.9 + 12.4 x [Si] + 10.0 x [Al] + 6.6 x [Mn] + 5.0 x [Cr ]) is preferably 64.00 or more, more preferably 66.00 or more.
On the other hand, if the Si content, Al content and Mn content are excessively increased, the tendency of the steel sheet to embrittle increases. Moreover, when the amount of Si, the amount of Al, the amount of Mn, and the amount of Cr are excessively increased, the saturation magnetic flux density is significantly lowered, and the magnetic flux density B50 is significantly lowered. Therefore, the R value is preferably 85.00 or less, more preferably 80.00 or less.
In addition, since Mn is also a strong oxide forming element next to Si and Al, control of the content including Mn is also necessary to preferably form a dense Cr oxide layer to be described later.

(Metal structure of non-oriented electrical steel sheet, etc.)
Next, the metal structure of the non-oriented electrical steel sheet according to this embodiment will be described.

[Thickness of layer containing Cr oxide: 0.01 μm or more and 0.5 μm or less]
Cr oxides formed under appropriate heat treatment conditions have a very dense structure, and when formed on the surface of the steel sheet, they are thought to prevent the subsequent penetration of oxygen and suppress the internal oxidation of Si and Al. Since Si and Al in the steel sheet are easily oxidized, when oxygen diffuses into the steel sheet at high temperature and internal oxidation occurs, domain wall motion is hindered and hysteresis loss is deteriorated. Furthermore, when internal oxidation occurs, the presence of the non-magnetic oxide layer reduces the effective cross-sectional area through which magnetic flux can pass, increasing the magnetic flux density and degrading eddy current loss. Moreover, at high frequencies, the magnetic flux concentrates near the surface of the steel sheet due to the skin effect, so the above effect becomes more pronounced.
In order to preferably obtain these effects, it is necessary to balance the Si and Al contents defined by formulas 1 and 2, the Mn content defined by formula 3, and the addition of strong sulfide-forming elements such as Ca. An appropriate amount of content is required.

Considering the above, the thickness of the Cr oxide layer formed on the surface of the steel sheet should be 0.01 μm or more and 0.5 μm or less. If the thickness of the Cr oxide layer is less than 0.01 μm, the effect of preventing the penetration of oxygen and suppressing the internal oxidation of Si and Al is insufficient. Also, when the thickness of the Cr oxide layer exceeds 0.5 μm, the magnetic properties begin to be adversely affected. When the oxygen potential in the final annealing after cold rolling is sufficiently low, the Cr oxide layer forms a thin and dense outer oxide film. It forms an internal oxide layer that is easy to remove. Reducing the Cr content in the steel lowers the upper limit of the oxygen potential for forming an outer oxide film. In particular, the oxygen potential at the time of temperature rise in finish annealing is important. and a low oxygen potential even when the temperature is raised. For example, when annealing steel containing 2% or more of Cr, 300 ° C. to 500 ° C. during temperature rise is set to P _H2O /P _H2 ≤ 5 × 10 ^-2 , and steel with a Cr content of 0.3% is annealed. In that case, 300° C. to 500° C. during temperature rise is set to P _H2O /P _H2 ≦10 ⁻² .
Note that P _H2O /P _H2 is the ratio of the H ₂ O partial pressure and the H ₂ partial pressure.

[{100} surface strength: 2.4 or more]
The {100} face strength ({100} face strength of an inverse pole figure) is 2.4 or more.

Here, the crystal orientation near {100} is a texture that contributes to the improvement of the magnetic flux density. As described above, when the amount of Si and Mn is increased, the saturation magnetic flux density decreases, but when the {100} plane strength is increased, the magnetic flux density B ₅₀ (when the steel sheet is magnetized with an exciting magnetizing force of 5000 A / m generated magnetic flux density) is improved. In order to achieve such a high magnetic flux density, a {100} plane strength of 2.4 or more is required. Therefore, the {100} face strength of the inverse pole figure is set to 2.4 or more.
The stronger the {100} plane intensity, the better the magnetic properties, and there is no need to specify the upper limit.
From the viewpoint of increasing the magnetic flux density, the {100} plane strength of the inverse pole figure is preferably 3.5 or more, more preferably 3.8 or more.

[{100} oriented grain area ratio: 18% or more]
The area ratio of {100} oriented grains (the area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) measured by electron beam backscatter diffraction (EBSD) with respect to the entire field of view) is 18. % or more.

Here, similarly to the above, the crystal orientation near {100} is a texture that contributes to the improvement of the magnetic flux density. As described above, increasing the amount of Si and Mn reduces the saturation magnetic flux density, but increasing the probability of existence of {100} oriented grains increases the magnetic flux density _B50 . In order to achieve such a high magnetic flux density, the area ratio of {100} oriented grains is required to be 18%. Therefore, the area ratio of {100} oriented grains is set to 18% or more.
The {100} area ratio of the {100} single crystal is 100%, and the higher the {100} area ratio, the better the magnetic properties, and there is no need to specify the upper limit.
From the viewpoint of increasing the magnetic flux density, the area ratio of {100} oriented grains is preferably 20% or more, more preferably 22% or more.

[Thickness]
The plate thickness is 0.10 mm to 0.30 mm. If the plate thickness is too thin, cold rolling becomes difficult and industrial production becomes impossible. On the other hand, if the plate thickness is too thick, eddy current loss increases and core loss deteriorates. Therefore, the plate thickness is set to 0.10 mm to 0.30 mm. The plate thickness is preferably 0.20 mm to 0.27 mm.

[Average grain size]
The average grain size of the electrical steel sheet according to the first embodiment is 55 μm to 200 μm. If the crystal grain size becomes finer, the hysteresis loss deteriorates. If the grain size is less than 55 μm, the deterioration of the hysteresis loss becomes remarkable, and the low iron loss required for non-oriented electrical steel sheets for stator cores cannot be achieved, so the lower limit is made 55 μm. If the average crystal grain size exceeds 200 μm, the abnormal eddy current loss increases and the low iron loss required for non-oriented electrical steel sheets for stator cores cannot be achieved, so the upper limit is made 200 μm. The average grain size is preferably 60 μm to 150 μm.

On the other hand, the average grain size of the electrical steel sheet according to the second embodiment is 20 μm or less. As the crystal grains coarsen, the strength decreases. Therefore, the average crystal grain size is set to 20 μm or less. The lower limit of the average grain size is not particularly limited, and a 100% non-recrystallized structure may be used. If no recrystallized grains are observed, the average grain size defined in the present invention shall be 0 (zero) μm. However, if the crystal grains are excessively refined and the average crystal grain size is too small, the shape of the product steel sheet may deteriorate depending on the steel composition, hot rolling and cold rolling conditions, and the shape accuracy at the time of punching will decrease. The average crystal grain size is preferably 10 μm or more because it may cause concern. The average crystal grain size is preferably 13 μm to 17 μm from the viewpoint of realizing the effects of the invention including increasing the strength of the steel sheet and achieving a high level of shape accuracy during punching.

The average grain size after annealing the magnetic steel sheet according to the second embodiment at 750° C. for 120 minutes is 55 μm to 200 μm. If the crystal grains do not coarsen and the average crystal grain size is too small, the user punches steel sheets, laminates them, and manufactures the motor core, then heats them at high temperature (for example, 750 to 850°C, 60 to 180 minutes) for the purpose of strain relief. The iron loss at the time of annealing is not sufficiently improved. On the other hand, if the crystal grains become excessively coarse and the average crystal grain size becomes too large, the user punches steel sheets, laminates them, and manufactures the motor core. 180 minutes) The eddy current loss during annealing worsens. Therefore, the average grain size after annealing the electrical steel sheet according to the second embodiment at 750° C. for 120 minutes is set to 55 μm to 200 μm. The average grain size is preferably 60 μm to 150 μm.

[Area ratio of {411} oriented grains: 70% or more]
The area ratio of {411} oriented grains (area ratio of crystal grains having a crystal orientation of {411} orientation (within a tolerance of 20°) measured by electron beam backscatter diffraction (EBSD) with respect to the entire field of view) is 70. % or more.
Furthermore, in order to improve the magnetic properties of a non-oriented electrical steel sheet and achieve low core loss and high magnetic flux density, it is preferable to increase the existence probability of {411} oriented grains, which are superior in magnetic properties. Therefore, the area ratio of {411} oriented grains is preferably 70% or more, more preferably 80% or more. Although the higher the area ratio of the {411} oriented grains, the better, but from the viewpoint of production, the upper limit of the area ratio of the {411} oriented grains is, for example, 95% or less.

[Area ratio of {111} oriented grains: 25% or less]
The area ratio of {111} oriented grains (the area ratio of crystal grains having a crystal orientation of {111} orientation (within a tolerance of 20°) as measured by electron beam backscatter diffraction (EBSD) in the entire field of view) is It is preferably 25% or less.
Furthermore, in order to improve the magnetic properties of the non-oriented electrical steel sheet and achieve low iron loss and high magnetic flux density, it is preferable to reduce the existence probability of {111} oriented grains, which are inferior in magnetic properties. Therefore, the area ratio of {111} oriented grains is preferably 25% or less, more preferably 15% or less, and even more preferably 10% or less. The area ratio of {111} oriented grains is most preferably 0%, but from the viewpoint of production, the lower limit of the area ratio of {111} oriented grains is, for example, 5% or more.

[Tensile strength]
The tensile strength of the electrical steel sheet according to the second embodiment is preferably 600 MPa or more. When the tensile strength is within the above range, the steel sheet is suitable as a non-oriented electrical steel sheet for rotors. Tensile strength is more preferably 600 MPa to 800 MPa, even more preferably 650 MPa to 800 MPa.
If the tensile strength is less than 600 MPa, deformation of the rotor core cannot be sufficiently suppressed. However, if the tensile strength exceeds 850 MPa, punching becomes difficult, and it may become difficult to obtain shape accuracy. Therefore, the upper limit of the tensile strength is preferably 850 MPa or less.

[others]
The non-oriented electrical steel sheet according to this embodiment may have an insulating coating on one side or both sides.
In order to improve the magnetic properties of non-oriented electrical steel sheets, it is important to reduce iron loss. Iron loss is composed of eddy current loss and hysteresis loss. By providing an insulating coating on the surface of the non-oriented electrical steel sheet, it is possible to suppress the conduction between the non-oriented electrical steel sheets laminated as the iron core and reduce the eddy current loss of the core. It is possible to further improve the practical magnetic properties of

Here, the insulating coating is not particularly limited as long as it is used as an insulating coating for non-oriented electrical steel sheets, and known insulating coatings can be used. As such an insulating coating, for example, a composite insulating coating containing an inorganic substance as a main component and an organic substance can be cited. Here, the composite insulating coating is mainly composed of, for example, at least one of inorganic substances such as metal chromate, metal phosphate, colloidal silica, Zr compound, Ti compound, etc., and fine organic resin particles are dispersed. It is an insulating film that has In particular, from the viewpoint of reducing the environmental impact during production, which has been in increasing demand in recent years, insulating coatings using metal phosphates, Zr or Ti coupling agents, or their carbonates or ammonium salts as starting materials. It is preferably used.

The amount of ^the insulating ^coating is not particularly limited ^. 0.8 g/m ² or less is more preferable. By forming the insulating film so as to have such an amount of adhesion, excellent uniformity can be maintained. In addition, when measuring the adhesion amount of this insulating film after the fact, it is possible to utilize various well-known measuring methods.
The amount of the insulating coating can be calculated by, for example, removing only the insulating coating by immersing the non-oriented electrical steel sheet on which the insulating coating is formed in a hot alkaline solution, and calculating the difference in mass before and after removing the insulating coating. It is possible.

Next, various measuring methods will be described.

[{100} surface strength]
The {100} face strength is measured as follows.
For example, the planar orientation can be obtained by comparing the integrated diffraction intensity of each crystal plane with the ideal intensity ratio in a randomly oriented material from a normal X-ray diffraction profile. The measurement can be performed using, for example, Rigaku's sample horizontal high-intensity X-ray diffractometer RINT-TTR3 or powder X-ray diffractometer RINT-2000, but the measurement results essentially do not depend on the measuring equipment. .

[Area ratio of each oriented grain]
The area ratio of each oriented grain ({100} oriented grain, {411} oriented grain, {111} oriented grain) is measured as follows.
Using OIM Analysis (manufactured by TSL), the area ratio of each oriented grain of interest is extracted (tolerance is set to 20°) from the field of view under the scanning electron microscope observed under the following measurement conditions. The extracted area is divided by the area of the observation field to obtain a percentage. Let this percentage be the area ratio of each oriented grain.

The details of the measurement conditions for obtaining the area ratio of each oriented grain are as follows.
・ Measuring device: Scanning electron microscope with electron beam backscatter diffraction device (SEM-EBSD) "SEM model number JSM-6400 (manufactured by JEOL) EBSD detector uses model number "HIKARI" (manufactured by TSL)"
・Step interval: 2 μm
・Measurement object: Center layer (1/2 plate thickness) of the Z plane of the steel plate (the cut surface of the steel plate cut in the plate thickness direction)
・Measurement area: 8000 μm × 2400 μm area ・Grain boundary: The angle difference in crystal orientation is 15 ° or more (a continuous region with an angle difference of less than 15 ° is regarded as one crystal grain)

[Average grain size]
In the data for determining the area ratio, the diameter of a circle equal to the area of each crystal grain is defined as the grain size of each crystal grain. Then, the arithmetic mean of the grain sizes of all the grains recognized as grains in the measurement area (the crystal orientation could be specified by the Kikuchi line pattern of EBSD) is taken as the average grain size defined in the present invention. . A region in which the EBSD Kikuchi line pattern is unclear and the crystal orientation cannot be identified is determined to be a non-recrystallized structure. A completely non-recrystallized structure is when the crystal orientation cannot be specified in the entire measurement area, and the average crystal grain size in this case is determined to be 0 (zero) μm in the present invention.

[Thickness of Cr oxide layer]
The thickness of the Cr oxide layer (layer containing Cr oxide) is measured as follows.
First, the cross section of the steel sheet is revealed, observed with an SEM without etching, and subjected to energy dispersive X-ray analysis (EDS) to identify a region with higher Cr and O concentrations than the base iron as a Cr oxide layer.
Then, the thickness of the Cr oxidized layer at the observed five points is measured, and the arithmetic mean is taken as the thickness of the Cr oxidized layer. An electron probe microanalyzer (EPMA) or Auger electron spectroscopy (AES) may be used to measure the thickness of the Cr oxide layer.

[Tensile strength]
Tensile strength is measured by a tensile test according to JIS Z 2241 (2011).

Next, an example of a method for manufacturing a non-oriented electrical steel sheet according to this embodiment will be described.

As the method for manufacturing the non-oriented electrical steel sheet according to the present embodiment, the following (1) strip casting method, (2) thin slab continuous casting method, (3) lubricating hot rolling method, and (4) high temperature hot rolled sheet annealing + cold rolling high reduction method, (5) multiple cold rolling method, and the like.

(1) Strip casting method The strip casting method manufactures a non-oriented electrical steel sheet as follows.
First, in the steelmaking process, a hot-rolled coil with a thickness of 1 to 3 mm is directly produced by strip casting.
In strip casting, molten steel is rapidly cooled between a pair of water-cooled rolls to directly obtain a steel sheet having a thickness equivalent to that of a hot-rolled coil. At this time, by sufficiently increasing the temperature difference between the outermost surface of the steel sheet in contact with the water-cooled roll and the molten steel, crystal grains solidified on the surface grow in the direction perpendicular to the steel sheet to form columnar crystals.
In steel with a BCC structure, columnar crystals grow such that the {100} planes are parallel to the steel plate surface. The {100} plane strength increases, and the probability of existence of {100} oriented grains increases. It is important not to change the {100} plane by transformation, working or recrystallization as much as possible. Specifically, by containing Si, which is a ferrite-promoting element, and limiting the content of Mn, which is an austenite-promoting element, a ferrite single phase is obtained from immediately after solidification to room temperature without undergoing austenite phase generation at high temperatures. It is important to
{100} planes are partially maintained even if austenite-ferrite transformation occurs, but the content of Si and Mn is adjusted within the above ranges to provide a component system in which austenite-ferrite transformation does not occur.

Next, the steel sheet of the hot-rolled coil obtained by strip casting is hot-rolled, and then the obtained hot-rolled sheet is annealed (hot-rolled sheet annealing).
In addition, the hot rolling may not be performed, and the post-process may be performed as it is.
Further, the post-process may be performed as it is without performing the hot-rolled sheet annealing. Here, when a strain of 30% or more is introduced into a steel sheet by hot rolling, if the hot-rolled steel sheet is annealed at a temperature of 550° C. or more, recrystallization may occur from the strain-introduced part and the crystal orientation may change. Therefore, when a strain of 30% or more is introduced by hot rolling, hot-rolled sheet annealing is not performed, or is performed at a temperature at which recrystallization does not occur.

Next, the steel plate is pickled before cold rolling.
Pickling is a process necessary to remove scales from the steel sheet surface. Pickling conditions are selected according to the descaling situation. Note that the scale may be removed with a grinder instead of pickling.

Next, cold rolling is implemented with respect to a steel plate.
Cold rolling is an essential step to obtain the desired product thickness. However, if the rolling reduction of cold rolling becomes excessive, the desired crystal orientation cannot be obtained in the product. Therefore, the rolling reduction in cold rolling is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less. Although it is not necessary to set a lower limit of the rolling reduction in cold rolling, the lower limit of the rolling reduction is determined from the thickness of the steel sheet before cold rolling and the desired product thickness. Cold rolling is also required when the surface properties and flatness required for laminated steel sheets are not obtained, and the minimum cold rolling for that purpose is required.
Cold rolling may be performed with a reverse mill or a tandem mill.

From the viewpoint of avoiding brittle fracture, instead of cold rolling, warm rolling may be performed at a temperature equal to or higher than the ductile/brittle transition temperature of the material.

Next, the steel plate is subjected to finish annealing.
The finish annealing conditions need to be determined in order to obtain a crystal grain size that provides the desired magnetic properties and strength, but the range of finish annealing conditions for ordinary non-oriented electrical steel sheets is sufficient.
Finish annealing may be continuous annealing or batch annealing. From the viewpoint of cost, it is preferable to carry out the finish annealing by continuous annealing.
The finish annealing is performed so that the thickness of the Cr oxide layer formed on the surface of the steel sheet is 0.01 μm or more and 0.5 μm or less. If the thickness of the Cr oxide layer is less than 0.01 μm, the effect of preventing the penetration of oxygen and suppressing the internal oxidation of Si and Al is insufficient. Also, when the thickness of the Cr oxide layer exceeds 0.5 μm, the magnetic properties begin to be adversely affected. When the oxygen potential in the final annealing after cold rolling is sufficiently low, the Cr oxide layer forms a thin and dense outer oxide film. On the other hand, when the oxygen potential is high, a thick, sparse, oxygen-permeable internal oxide layer is formed instead of the external oxide film. Reducing the Cr content in the steel lowers the upper limit of the oxygen potential for forming an outer oxide film. In particular, the oxygen potential at the time of temperature rise in finish annealing is important. and a low oxygen potential even when the temperature is raised. For example, when annealing steel containing 2% or more of Cr, 300 ° C. to 500 ° C. during temperature rise is set to P _H2O /P _H2 ≤ 5 × 10 ^-2 , and steel with a Cr content of 0.3% is annealed. In that case, 300° C. to 500° C. during temperature rise is set to P _H2O /P _H2 ≦10 ⁻² .
Especially in the strip casting method, columnar crystals developed by casting are processed by hot rolling and cold rolling, and crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) are regenerated by final annealing. crystallize. On the other hand, when the thickness of the Cr oxide layer formed on the surface of the steel sheet during the final annealing temperature rise is outside the specified range, the recrystallization of the crystal grains having the {100} orientation (within a margin of 20°) is impeded. Therefore, in the final annealing, it is important to set the entire annealing to a low oxygen potential and to keep the low oxygen potential even when the temperature is raised.

Through the above steps, (1) the strip casting method can obtain the intended non-oriented electrical steel sheet.

(2) Thin slab continuous casting method In the thin slab continuous casting method, a non-oriented electrical steel sheet is manufactured as follows.
In the thin slab continuous casting method, a slab with a thickness of 30 to 60 mm is produced in the steelmaking process, and rough rolling in the hot rolling process is omitted. It is desirable to sufficiently develop columnar crystals with the {100} plane parallel to the steel sheet surface in a thin slab, and leave the {100}<011> orientation obtained by processing the columnar crystals by hot rolling in the hot-rolled sheet. For this purpose, it is desirable not to implement electromagnetic stirring in continuous casting. In addition, it is desirable to reduce fine inclusions in molten steel that promote solidification nucleation as much as possible.
After the thin slab is heated in a reheating furnace, it is continuously finish-rolled in a hot-rolling process to obtain a hot-rolled coil having a thickness of about 2 mm.

After that, the steel sheet of the hot-rolled coil is subjected to hot-rolled sheet annealing, pickling, cold rolling, and finish annealing in the same manner as (1) strip casting method.

Through the above steps, (2) the thin slab continuous casting method can obtain the intended non-oriented electrical steel sheet.

(3) Lubrication Hot Rolling Method In the lubrication hot rolling method, a non-oriented electrical steel sheet is produced as follows.
First, a slab is manufactured in a steelmaking process. After heating the slab in a reheating furnace, the slab is continuously rough-rolled and finish-rolled in a hot-rolling process to obtain a hot-rolled coil.
Here, hot rolling is usually performed without lubrication, but hot rolling is performed under appropriate lubrication conditions. When hot rolling is performed under appropriate lubrication conditions, the shear deformation introduced near the surface layer of the steel sheet is reduced. As a result, a deformed structure having RD//<011> orientation called α-fiber, which normally develops in the center of the steel sheet, can be developed to the vicinity of the steel sheet surface layer. For example, as described in JP-A-10-36912, 0.5 to 20% oil is mixed in hot rolling roll cooling water as a lubricant during hot rolling, and the average friction coefficient between the finishing hot rolling roll and the steel sheet is 0.25 or less, the α-fiber can be developed.

After that, the steel sheet of the hot-rolled coil is subjected to hot-rolled sheet annealing, pickling, cold rolling, and finish annealing in the same manner as (1) strip casting method. When α-fibers are developed to the vicinity of the surface layer of the steel sheet of the hot-rolled coil, {h11} <1/h 1 2>, especially {100} <012> to {411} <148> are formed in the subsequent hot-rolled steel annealing. recrystallize. When this steel plate is pickled, cold-rolled, and finish-annealed, {100}<012> to {411}<148> are recrystallized. As a result, the {100} plane strength increases and the existence probability of {100} oriented grains increases.

Through the above steps, the desired non-oriented electrical steel sheet is obtained in (3) the lubricating hot rolling method.

(4) High-Temperature Hot-Rolled Sheet Annealing + Cold-Rolling Strong Reduction Method In the high-temperature hot-rolled sheet annealing + cold-rolling heavy reduction method, a non-oriented electrical steel sheet is manufactured as follows.
First, a slab is manufactured in a steelmaking process. After heating the slab in a reheating furnace, the slab is continuously rough-rolled and finish-rolled in a hot-rolling process to obtain a hot-rolled coil.
Next, the steel sheet of the hot-rolled coil is subjected to hot-rolled sheet annealing. The hot-rolled sheet is annealed to recrystallize and coarsely grow crystal grains to a crystal grain size of 300 to 500 μm.
Hot-rolled sheet annealing may be continuous annealing or batch annealing. From the viewpoint of cost, it is preferable to carry out hot-rolled sheet annealing by continuous annealing. In order to carry out continuous annealing, it is necessary to grow crystal grains at a high temperature in a short time. to implement. Here, the soaking time refers to the time during which the highest temperature reached −10° C. is maintained.

Next, the steel plate is subjected to pickling and then cold rolling.
Here, in a high-grade non-oriented electrical steel sheet with a high Si content, if the crystal grain size is excessively coarsened, the steel sheet becomes embrittled, and there is concern about brittle fracture during cold rolling. Therefore, the average grain size of the steel sheet before cold rolling is usually limited to 200 μm or less. On the other hand, in the present invention, the average grain size before cold rolling is set to 300 to 500 μm, and subsequent cold rolling is performed at a rolling reduction of 80 to 95%.
From the viewpoint of avoiding brittle fracture, instead of cold rolling, warm rolling may be performed at a temperature equal to or higher than the ductile/brittle transition temperature of the material.
After that, when finish annealing is performed, ND//<100> recrystallized grains grow. As a result, the {100} plane strength increases and the existence probability of {100} oriented grains increases.

Pickling and finish annealing are carried out in the same manner as in 1) strip casting method.

Through the above steps, (4) high-temperature hot-rolled sheet annealing + cold-rolling high reduction process yields the desired non-oriented electrical steel sheet.

(5) Multiple Cold Rolling Method In the multiple cold rolling method, a non-oriented electrical steel sheet is manufactured as follows.
First, a slab is manufactured in a steelmaking process. After heating the slab in a reheating furnace, hot rolling, hot-rolled sheet annealing, and pickling are performed.

Next, cold rolling is implemented with respect to the steel plate after pickling.
Here, high-grade non-oriented electrical steel sheets are usually hot rolled, hot-rolled sheet annealed, pickled, and then cold rolled once to obtain a desired product thickness. When the thickness of the product is reduced to 0.3 mm or less, the reduction ratio of cold rolling becomes high, and an ND//<111> texture called γ fiber, which is not preferable for magnetic properties, develops.
Therefore, cold rolling is carried out two or more times with one or more annealing intervening to achieve a final cold rolling reduction of 55 to 75%. As a result, the growth of γ fibers can be suppressed, and desired product characteristics can be obtained.
Furthermore, cold rolling is preferably performed three times or more with two or more annealing steps intervening, and the rolling reduction of the final cold rolling and the penultimate cold rolling is 55 to 75%. As a result, the growth of γ fibers can be further suppressed, the ND//<001> texture can be developed, and desired product properties can be obtained.
Cold rolling may be performed with a reverse mill or a tandem mill.

From the viewpoint of avoiding brittle fracture, instead of cold rolling, warm rolling may be performed at a temperature equal to or higher than the ductile/brittle transition temperature of the material.

After that, the steel sheet of the cold-rolled coil is subjected to finish annealing in the same manner as (1) strip casting method.

Through the above steps, (5) the multiple cold rolling method can obtain the intended non-oriented electrical steel sheet.

Here, (1) strip casting method, (2) thin slab continuous casting method, (3) lubrication hot rolling method, (4) high temperature hot rolled plate annealing + cold rolling strong reduction method, (5) multiple When the non-oriented electrical steel sheet according to the first embodiment is produced by a production method such as the rotary cold rolling method and, for example, the low iron loss required for the non-oriented electrical steel sheet for stator cores is achieved, finish annealing is performed. is carried out at elevated temperature. Specifically, for example, finish annealing is performed at a maximum temperature of 900° C. to 1100° C. and a soaking time of 10 seconds to 60 seconds. Here, the soaking time refers to the time during which the highest temperature reached −10° C. is maintained.
This high-temperature finish annealing causes crystal grains to grow to an average crystal grain size of 55 μm to 200 μm, thereby obtaining a non-oriented electrical steel sheet with low iron loss.

On the other hand, when manufacturing the non-oriented electrical steel sheet according to the second embodiment and realizing, for example, the high strength required for the non-oriented electrical steel sheet for rotor cores, the finish annealing is performed at a low temperature. Specifically, for example, finish annealing is performed at a maximum temperature of 750° C. to 850° C. and a soaking time of 10 seconds to 60 seconds. Here, the soaking time refers to the time during which the highest temperature reached −10° C. is maintained.
This low-temperature finish annealing suppresses the growth of crystal grains and makes the average crystal grain size 20 μm or less, thereby obtaining a high-strength non-oriented electrical steel sheet.

Then, when the obtained non-oriented electrical steel sheet according to the second embodiment is used as a steel sheet for a rotor, the obtained steel sheet is used as it is.
On the other hand, when the obtained non-oriented electrical steel sheet according to the second embodiment is used as a steel sheet for a stator, after punching the obtained steel sheet, the punched material is annealed (for example, the maximum reaching temperature of 750 to 850 ℃ and a soaking time of 60 to 180 minutes) before use.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. However, each of these examples does not limit the present invention.

(Example 1A: plate thickness 0.20 mm)
A steel having a chemical composition shown in Table 1 was melted and hot-rolled to prepare a hot-rolled sheet having a thickness of 1.7 mm. The hot-rolled sheet was annealed at 1,050° C. for 30 minutes and then pickled to remove surface scales. After that, it was finished by cold rolling to a thickness of 0.20 mm, and was subjected to final annealing at 750° C. for 15 seconds while controlling the thickness of the Cr oxide layer by _PH2O / _PH2 at 300° C. to 500° C. during temperature rise. Steel D1A and steel K1A fractured during cold rolling.
A non-oriented electrical steel sheet was obtained through the above steps.
In Table 1, "Total" indicates the total amount of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd.

The following measurements were performed on each obtained non-oriented electrical steel sheet. Table 2 shows the results.

- {100} surface strength, area ratio of grains in each orientation, average crystal grain size, thickness of Cr oxide layer, tensile strength -
According to the method described above, {100} plane strength, area ratio of each oriented grain ({100} oriented grain, {411} oriented grain, {111} oriented grain), average crystal grain size, thickness of Cr oxide layer, Tensile strength was measured.

－Iron loss and magnetic flux density－
A measurement sample was obtained by cutting a piece having a width of 55 mm and a length of 55 mm from the obtained non-oriented electrical steel sheet.
Then, the iron loss W _15/50 , iron loss W _10/400 , and magnetic flux density B ₅₀ of the measurement sample were measured. Each magnetic property was measured by a single-plate magnetic tester in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction), and the average value was evaluated.

-Characteristics after annealing at 750°C for 120 minutes-
The obtained non-oriented electrical steel sheet was punched to obtain a steel sheet for property evaluation. Then, the steel sheet for property evaluation was annealed at a temperature of 750° C. for 120 minutes.
The strength of the {{100} plane, the area ratio of grains in each orientation, and the average grain size of the steel sheets for property evaluation after annealing were measured according to the methods described above. Then, iron loss and magnetic flux density were measured.

As can be seen from the above results, steel A1A, steel B1A, steel C1A, steel E1A, steel F1A, steel H1A, steel L1A, steel M1A, steel N1A, steel O1A, and steel Y1A have a {100} surface strength of 2.4 or more. Although the magnetic flux density _B50 was high, the average crystal grain size after annealing was less than 50 μm, resulting in a structure in which coarse grains and fine grains were mixed, and the iron losses W15 _/50 and W10 _/400 deteriorated. Furthermore, steel C1A, steel E1A, and steel H1A had R of formula 3 of less than 64, and W _10/400 in particular deteriorated.
Steel G1A and steel I1A had a {100} plane strength of 2.4 or more, but each of Mn and Cr exceeded the upper limit, and B50 decreased.
Steel J1A had a crystal grain size of 55 μm or more, but the {100} plane strength was less than 2.4, and the magnetic flux density _B50 was deteriorated.
Steel Z1A had a crystal grain size of 55 μm or more and a {100} surface strength of 2.4 or more, but the thickness of the Cr oxide layer was almost 0 μm, and the iron loss W _15/50 , W _10/400 , and the magnetic flux density B ₅₀ deteriorated. Steel WW1A had a crystal grain size of 55 μm or more and a {100} surface strength of 2.4 or more, but the thickness of the Cr oxide layer was 1 μm, iron loss W _15/50 , W _10/400 , magnetic flux density B ₅₀ has deteriorated.

On the other hand, steels P1A to X1A, steels XX1A and ZZ1A improved in iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ after annealing at 750° C. for 120 minutes. Moreover, before annealing at 750° C. for 120 minutes, good iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were obtained while having high tensile strength.
However, in steels XX1A and ZZ1A, the {411} orientation grain area ratio was less than 70% and the {111} orientation grain area ratio was more than ₂₅ %. _10/400 was high and the magnetic flux density _B50 was low.
Steels T1A1 to T1A5 had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more as a result of changing the P _H2O /P _H2 at 300° C. to 500° C. during the temperature rise in the final annealing. , the thickness of the Cr oxide layer was 0 to 0.6 μm, and the iron losses W _15/50 , W _10/400 and the magnetic flux density B ₅₀ of steel T1A1 and steel T1A5 outside the specified range deteriorated.
Steel ZZ1A had a 100% non-recrystallized structure (described as having an average grain size of 0 μm) after finish annealing, and its tensile strength satisfied a suitable range for a non-oriented electrical steel sheet for rotors. After annealing at 750° C. for 120 minutes, the average grain size was 85 μm, the {100} plane strength was 5.2, and the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were all improved.
Steel PP1A had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 85 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good.
Steel PPP1A had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 40 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, both iron loss W _15/50 and W _10/400 improved.

(Example 1B: plate thickness 0.15 mm)
A steel having the chemical composition shown in Table 3 was melted and hot-rolled to produce a hot-rolled sheet having a thickness of 1.25 mm. The hot-rolled sheet was annealed at 1,050° C. for 30 minutes and then pickled to remove surface scales. After that, it was finished by cold rolling to a thickness of 0.15 mm, and the Cr oxide layer thickness was controlled by _PH2O / _PH2 at 300°C to 500°C during temperature rise, and finish annealing was performed at 750°C for 15 seconds. Steel D1B and steel K1B fractured during cold rolling.
A non-oriented electrical steel sheet was obtained through the above steps.
In Table 3, "Total" indicates the total amount of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd.

The following measurements were performed on each obtained non-oriented electrical steel sheet. Table 4 shows the results.

- {100} surface strength, area ratio of grains in each orientation, average crystal grain size, thickness of Cr oxide layer, tensile strength -
According to the method described above, {100} plane strength, area ratio of each oriented grain ({100} oriented grain, {411} oriented grain, {111} oriented grain), average crystal grain size, thickness of Cr oxide layer, Tensile strength was measured.

－Iron loss and magnetic flux density－
A measurement sample was obtained by cutting a piece having a width of 55 mm and a length of 55 mm from the obtained non-oriented electrical steel sheet.
Then, the iron loss W _15/50 , iron loss W _10/400 , and magnetic flux density B ₅₀ of the measurement sample were measured. Each magnetic property was measured by a single-plate magnetic tester in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction), and the average value was evaluated.

-Characteristics after annealing at 750°C for 120 minutes-
The obtained non-oriented electrical steel sheet was punched to obtain a steel sheet for property evaluation. Then, the steel sheet for property evaluation was annealed at a temperature of 750° C. for 120 minutes.
The strength of the {{100} plane, the area ratio of grains in each orientation, and the average grain size of the steel sheets for property evaluation after annealing were measured according to the methods described above. Then, iron loss and magnetic flux density were measured.

As can be seen from the above results, steel A1B, steel B1B, steel C1B, steel E1B, steel F1B, steel H1B, steel L1B, steel M1B, steel N1B, steel O1B, and steel Y1B have a {100} surface strength of 2.4 or more. Although the magnetic flux density _B50 was high, the average crystal grain size after annealing was less than 50 μm, resulting in a structure in which coarse grains and fine grains were mixed, and the iron losses W15 _/50 and W10 _/400 deteriorated. Furthermore, steel C1B, steel E1B, and steel H1B had R of Formula 3 less than 64, and W _10/400 was particularly degraded.
Steel G1B and steel I1B had a {100} plane strength of 2.4 or more, but each of Mn and Cr exceeded the upper limit, and B50 decreased.
Steel J1B had a crystal grain size of 55 μm or more, but the {100} plane strength was less than 2.4, and the magnetic flux density _B50 was deteriorated.
Steel Z1B had a crystal grain size of 55 μm or more and a {100} surface strength of 2.4 or more, but the thickness of the Cr oxide layer was almost 0 μm, and the iron loss W _15/50 , W _10/400 , and the magnetic flux density B ₅₀ deteriorated. Steel WW1B had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more, but the thickness of the Cr oxide layer was 1 μm, iron loss W _15/50 , W _10/400 , magnetic flux density B ₅₀ has deteriorated.

In contrast, steels P1B to X1B, steels XX1B, and ZZ1B improved in iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ after annealing at 750° C. for 120 minutes. Moreover, before annealing at 750° C. for 120 minutes, good iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were obtained while having high tensile strength.
However, steels XX1B and ZZ1B had a {411} orientation grain area ratio of less than 70% and a {111} orientation grain area ratio of more than ₂₅ %. _10/400 was high and the magnetic flux density _B50 was low.
Steels S1A1 to S1A5 had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more as a result of changing the P _H2O /P _H2 at 300° C. to 500° C. during the temperature rise in the final annealing. , the Cr oxide layer thickness was 0 to 0.6 μm, and the iron losses W _15/50 , W _10/400 and the magnetic flux density B ₅₀ were deteriorated in the steels S1A1 and S1A5 outside the specified range.
Steel ZZ1B had a 100% non-recrystallized structure (described as having an average crystal grain size of 0 μm) after finish annealing, and its tensile strength satisfied a suitable range for a non-oriented electrical steel sheet for rotors. After annealing at 750° C. for 120 minutes, the average grain size was 85 μm, the {100} plane strength was 5, and the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were all improved.
Steel PP1B had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 75 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good.
Steel PPP1B had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 35 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, both iron loss W _15/50 and W _10/400 improved.

(Example 1C: plate thickness 0.25 mm)
A steel having a chemical composition shown in Table 5 was melted and hot-rolled to produce a hot-rolled sheet having a thickness of 2.1 mm. The hot-rolled sheet was annealed at 1,050° C. for 30 minutes and then pickled to remove surface scales. After that, it was finished by cold rolling to a thickness of 0.25 mm, and was subjected to final annealing at 750° C. for 15 seconds while controlling the thickness of the Cr oxide layer by _PH2O / _PH2 at 300° C. to 500° C. during temperature rise. Steel D1C and steel K1C fractured during cold rolling.
A non-oriented electrical steel sheet was obtained through the above steps.
In Table 5, "Total" indicates the total amount of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd.

The following measurements were performed on each obtained non-oriented electrical steel sheet. Table 6 shows the results.

- {100} surface strength, area ratio of grains in each orientation, average crystal grain size, thickness of Cr oxide layer, tensile strength -
According to the method described above, {100} plane strength, area ratio of each oriented grain ({100} oriented grain, {411} oriented grain, {111} oriented grain), average crystal grain size, thickness of Cr oxide layer, Tensile strength was measured.

－Iron loss and magnetic flux density－
A measurement sample was obtained by cutting a piece having a width of 55 mm and a length of 55 mm from the obtained non-oriented electrical steel sheet.
Then, the iron loss W _15/50 , iron loss W _10/400 , and magnetic flux density B ₅₀ of the measurement sample were measured. Each magnetic property was measured by a single-plate magnetic tester in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction), and the average value was evaluated.

-Characteristics after annealing at 750°C for 120 minutes-
The obtained non-oriented electrical steel sheet was punched to obtain a steel sheet for property evaluation. Then, the steel sheet for property evaluation was annealed at a temperature of 750° C. for 120 minutes.
The strength of the {{100} plane, the area ratio of grains in each orientation, and the average grain size of the steel sheets for property evaluation after annealing were measured according to the methods described above. Then, iron loss and magnetic flux density were measured.

As can be seen from the above results, steel A1C, steel B1C, steel C1C, steel E1C, steel F1C, steel H1C, steel L1C, steel M1C, steel N1C, steel O1C, and steel Y1C have a {100} surface strength of 2.4 or more. Although the magnetic flux density _B50 was high, the average crystal grain size after annealing was less than 50 μm, resulting in a structure in which coarse grains and fine grains were mixed, and the iron losses W15 _/50 and W10 _/400 deteriorated. Furthermore, steel C1C, steel E1C, and steel H1C had R of Formula 3 less than 64, and W _10/400 was particularly degraded.
Steel G1C and steel I1C had a {100} plane strength of 2.4 or more, but each of Mn and Cr exceeded the upper limit, and B50 decreased.
Steel J1C had a crystal grain size of 55 μm or more, but the {100} plane strength was less than 2.4, and the magnetic flux density _B50 was deteriorated.
Steel Z1C had a crystal grain size of 55 μm or more and a {100} surface strength of 2.4 or more, but the thickness of the Cr oxide layer was almost 0 μm, and the iron loss W _15/50 , W _10/400 , and the magnetic flux density B ₅₀ deteriorated. Steel WW1C had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more, but the thickness of the Cr oxide layer was 1 μm, and the iron loss was W _15/50 , W _10/400 , and the magnetic flux density was B _{50 .} has deteriorated.

On the other hand, steels P1C to X1C, steels XX1C and ZZ1C improved in iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ . Moreover, before annealing at 750° C. for 120 minutes, good iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were obtained while having high tensile strength.
However, steels XX1C and ZZ1C had a {411} orientation grain area ratio of less than 70% and a {111} orientation grain area ratio of more than ₂₅ %. _10/400 was high and the magnetic flux density _B50 was low.
Steels T1A1 to T1A5 had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more as a result of changing the P _H2O /P _H2 at 300° C. to 500° C. during the temperature rise in the final annealing. , the thickness of the Cr oxide layer was 0 to 0.6 μm, and the iron losses W _15/50 , W _10/400 and the magnetic flux density B ₅₀ of steel T1A1 and steel T1A5 outside the specified range deteriorated.
Steel ZZ1C had a 100% non-recrystallized structure after finish annealing (described as having an average grain size of 0 μm), and its tensile strength satisfied a range suitable for a non-oriented electrical steel sheet for rotors. After annealing at 750° C. for 120 minutes, the average grain size was 85 μm, the {100} plane strength was 5.1, and the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were all improved.
Steel PP1C had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 80 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good.
Steel PPP1C had a {100} plane strength of 2.4 or more after finish annealing, but the grain size was 35 μm, so the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were good. However, the tensile strength deteriorated. After annealing at 750° C. for 120 minutes, both iron loss W _15/50 and W _10/400 improved.

(Example 2)
Molten steel having the chemical composition shown in Table 7 was rapidly cooled between a pair of water-cooled rolls to produce a 1 mm thick cast slab. After removing surface _{scales by} pickling, the cast slab was finished by cold rolling to a thickness of 0.20 mm. It was finish annealed at °C for 15 seconds. Note that Steel D2 and Steel K2 fractured during cold rolling.
A non-oriented electrical steel sheet was obtained through the above steps. Then, in the same manner as in Example 1, various measurements were performed on the obtained non-oriented electrical steel sheet. Table 8 shows the results.
In Table 7, "Total" indicates the total amount of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd.

As can be seen from the above results, by setting {100} plane strength ≥ 2.4 and {100} orientation grain area ratio ≥ 18% with the components in a predetermined range, while having high tensile strength, good good core losses W _15/50 , W _10/400 and magnetic flux density B ₅₀ were obtained.
Steel A2, Steel B2, Steel C2, Steel E2, Steel F2, Steel H2, Steel M2, Steel N2, Steel O2, and Y2 had a {100} surface strength of 2.4 or higher and a high magnetic flux density _B50 . However, the average grain size after annealing at 750° C. for 120 minutes was less than 50 μm, resulting in a structure in which coarse grains and fine grains coexist, and the iron losses W _15/50 and W _10/400 deteriorated. Furthermore, Steel C2, Steel E2, and Steel H2 had R of formula 3 of less than 64, and W _10/400 in particular deteriorated.
Steel G2 and steel I2 had a {100} surface strength of 2.4 or more, but each of Mn and Cr exceeded the upper limit, and the magnetic flux density B50 decreased.
Steel Z2 had a crystal grain size of 50 μm and a {100} surface strength of 2.4 or more, but the Cr oxide layer thickness was 1 μm, and the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were deteriorated.

In contrast, steels P2 to X2, steel ZZ2, and steel WW2 improved in iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ after annealing at 750° C. for 120 minutes. Moreover, before annealing at 750° C. for 120 minutes, good iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were obtained while having high tensile strength.
However, since Steel ZZ2 and Steel WW2 had {111} orientation grain area ratios exceeding 25%, compared to Steels P1A to X1A, iron losses W _15/50 and W _10/400 were higher, and magnetic flux densities B ₅₀ was low.
Steels S21 to S25 had a crystal grain size of 55 μm or more and a {100} plane strength of 2.4 or more as a result of changing the P _H2O /P _H2 at 300° C. to 500° C. during the temperature rise in the final annealing. , the thickness of the Cr oxide layer was 0 to 0.6 μm, and the iron losses W _15/50 and W _10/400 and the magnetic flux density B ₅₀ deteriorated in the steels S21 and S25 outside the specified range.
Steel WW2 had a 100% non-recrystallized structure (described as having an average crystal grain size of 0 μm) after finish annealing, and its tensile strength satisfied a suitable range for a non-oriented electrical steel sheet for rotors. After annealing at 750° C. for 120 minutes, the average grain size was 80 μm, the {100} surface strength was 5.4, and the iron loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ were all improved.

(Example 3)
Steel A having the chemical composition shown in Table 9 was melted and hot-rolled to produce a hot-rolled sheet with a thickness of 2.1 mm and a hot-rolled sheet with a thickness of 1.25 mm.
A hot-rolled sheet with a thickness of 2.1 mm is annealed under conditions 1) at 1,050°C for 30 minutes and under condition 2) at 1,050°C for 5 minutes, or under condition 3) after annealing a hot-rolled sheet with a thickness of 1.25 mm for 1,050°C. After annealing at 050°C for 30 minutes, condition 4) after annealing a hot-rolled sheet with a thickness of 1.8 mm at 1.050°C for 30 minutes, or condition 5) after annealing a hot-rolled sheet with a thickness of 1.8 mm at 1,050°C. After annealing for 30 minutes, surface scale was removed by pickling.
After that, it was finished by cold rolling to a thickness of 0.25 mm, and was finished annealed at 750° C. for 15 seconds while controlling P _H2O /P _H2 at 300° C. to 500° C. to 10 ⁻³ or less.
A non-oriented electrical steel sheet was manufactured through the above steps. In addition, the non-oriented electrical steel sheet Nos obtained by annealing the hot-rolled sheets under conditions 1), 2), 3), 4), and 5) are C-1, C-2, and C- 3, C-4, and C-5.
Then, in the same manner as in Example 1, various measurements were performed on the obtained non-oriented electrical steel sheet. Table 10 shows the results. For C-5, a steel sheet for characteristic evaluation obtained by punching the obtained non-oriented electrical steel sheet was annealed at a temperature of 750° C. for 60 minutes.
In Table 5, "Total" indicates the total amount of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd.

As can be seen from the above results, Steel C-2 and Steel C-3 had a {100} plane strength of less than 2.4 and a deteriorated magnetic flux density _B50 .
On the other hand, Steel C-1, Steel C-4, and Steel C-5 have high tensile strength before annealing at 750° C. for 120 minutes, but iron losses W _15/50 , W _10/400 , and Both the magnetic flux density _B50 improved. And Steel C-5 obtained good core loss W _15/50 , W _10/400 and magnetic flux density B ₅₀ after annealing at 750° C. for 120 minutes.

Claims (3)

% by mass C: more than 0% to 0.0030%,
Si: 2.00% to 4.50%,
sol. Al: 0.15% to 2.50%,
Mn: 0.20% to 1.50%,
Cr: 0.30% to 5.00%
P: 0.005% to 0.200%,
S: 0.0010% to 0.0100%,
Ti: 0.0005% to 0.0100%,
Ca: 0.0005% to 0.0100%,
One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.0005% to 0.0200% in total, and
Balance: having a chemical composition consisting of Fe and impurities,
The {100} face strength of the inverse pole figure is 2.4 or more,
The area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) is 18% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The area ratio of crystal grains having a crystal orientation of {411} orientation (within a tolerance of 20°) is 70% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The average crystal grain size is 55 μm to 200 μm,
The plate thickness is 0.10 mm to 0.30 mm,
A layer containing Cr oxide having a thickness of 0.01 μm or more and 0.5 μm or less on the surface of the steel sheet, and having a higher Cr content and O content than the base iron ,
The Si content (mass%) is [Si], the Al content (mass%) is [Al], the Cr content (mass%) is [Cr], and the thickness of the non-oriented electrical steel sheet When (mm) is t, the following formulas 1 and 2 are satisfied,
The Si content (mass%) is [Si], the Al content (mass%) is [Al], the Mn content (mass%) is [Mn], the Cr content (mass%) ) is [Cr], R represented by the following formula 3 is 64.00 or more .
10.00% ≤ 2 [Si] + 2 [Al] + [Cr] < 15.00% (Formula 1)
(2[Al]+[Cr])/2[Si]−10t ² ≦0.35 (Formula 2)
R = 9.9 + 12.4 x [Si] + 10.0 x [Al] + 6.6 x [Mn] + 5.0 x [Cr] (Formula 3) 2. The non-crystalline material according to claim 1, wherein the area ratio of crystal grains having a crystal orientation of {111} orientation (within a tolerance of 20°) in the entire field of view when measured by electron beam backscatter diffraction (EBSD) is 25% or less. Oriented electrical steel sheet. A non-oriented electrical steel sheet obtained by annealing at 750 ° C. for 120 minutes to obtain the non-oriented electrical steel sheet according to claim 1 or claim 2 ,
% by mass C: more than 0% to 0.0030%,
Si: 2.00% to 4.50%,
sol. Al: 0.15% to 2.5%,
Mn: 0.20% to 1.50%,
Cr: 0.30% to 5.00%
P: 0.005% to 0.200%,
S: 0.0010% to 0.0100%,
Ti: 0.0005% to 0.0100%,
Ca: 0.0005% to 0.0100%,
One or more selected from the group consisting of Mg, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: 0.0005% to 0.0200% in total, and
Balance: having a chemical composition consisting of Fe and impurities,
The average crystal grain size is 20 μm or less,
The area ratio of crystal grains having a crystal orientation of {111} orientation (within a tolerance of 20°) is 30% or less in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
After annealing at 750°C for 120 minutes,
The {100} face strength of the inverse pole figure is 2.4 or more,
The area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) is 18% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The area ratio of crystal grains having a crystal orientation of {411} orientation (within a tolerance of 20°) is 70% or more in the entire field of view when measured by electron beam backscatter diffraction (EBSD),
The average crystal grain size is 55 μm to 200 μm ,
The plate thickness is 0.10 mm to 0.30 mm,
A layer containing Cr oxide having a thickness of 0.01 μm or more and 0.5 μm or less on the surface of a steel sheet, having a higher Cr content and O content than the base iron , and containing the Si [Si] is the amount (% by mass), [Al] is the content (% by mass) of Al, [Cr] is the content (% by mass) of Cr, and the thickness (mm) t of the non-oriented electrical steel sheet When the above formulas 1 and 2 are satisfied,
The Si content (mass%) is [Si], the Al content (mass%) is [Al], the Mn content (mass%) is [Mn], the Cr content (mass%) ) is [Cr], R represented by the above formula 3 is 64.00 or more .