Technical field
[0001]
The present disclosure relates to non-oriented electrical steel sheets and manufacturing methods thereof.
Background technology
[0002]
In recent years, global environmental issues have been attracting attention, and the demand for energy-saving initiatives is increasing. Above all, there is a strong demand for higher efficiency in electrical equipment. Therefore, even in non-oriented electrical steel sheets, which are widely used as iron core materials for motors, generators, etc., there is a growing demand for improved magnetic properties. This tendency is conspicuous in drive motors for electric vehicles and hybrid vehicles and in compressor motors for air conditioners.
[0003]
The motor cores of the various motors described above are composed of a stator, which is a stator, and a rotor, which is a rotor. The characteristics required for the stator and rotor that make up the motor core are different from each other. is required to have excellent mechanical properties (high strength).
[0004]
Since the properties required for the stator and rotor are different, the desired properties can be achieved by separately producing non-oriented magnetic steel sheets for the stator and non-oriented magnetic steel sheets for the rotor. However, preparing two types of non-oriented electrical steel sheets leads to a decrease in yield. Therefore, in order to achieve low iron loss while achieving high strength required for rotors, non-oriented electrical steel sheets having excellent strength and excellent magnetic properties have been studied.
[0005]
For example, Patent Documents 1 to 3 attempt to achieve excellent magnetic properties and high strength. Further, Patent Document 4 attempts to achieve high magnetic flux density and low iron loss over a wide frequency range.
[0006]
　　Patent Document 1: JP-A-2004-300535
　　Patent Document 2: JP-A-2007-186791
　　Patent Document 3: JP-A-2012-140676
　　Patent Document 4: JP-A-11-092891
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0007]
However, in recent years, in order to achieve the energy-saving characteristics required for motors of electric vehicles or hybrid vehicles, the technologies disclosed in Patent Documents 1 to 3 are insufficient in reducing iron loss as a stator material. rice field. Further, the technique disclosed in Patent Document 4 does not consider strength.
[0008]
The present disclosure has been made to solve such problems, and aims to stably obtain a non-oriented electrical steel sheet having high strength and excellent magnetic properties at low cost.
Means to solve problems
[0009]
The gist of the present disclosure is the following non-oriented electrical steel sheet and manufacturing method thereof.
[0010]
(1) The chemical composition of the base material is % by mass,
C: 0.0010 to 0.0040%,
Si: 3.5 to 4.9%,
Mn: 0.05-0.20%,
Al: 0.05-0.45%,
P: 0.030% or less,
S: 0.0030% or less,
N: 0.0030% or less,
O: 0.0100 to 0.0400%,
Ca: less than 0.0010%,
Ti: less than 0.0050%,
Nb: less than 0.0050%,
Zr: less than 0.0050%,
V: less than 0.0050%,
Cu: less than 0.20%,
Ni: less than 0.50%,
Sn: 0 to 0.05%,
Sb: 0 to 0.05%, and
The balance: Fe and impurities, and
satisfying the following formula (i),
The O content in the region excluding the position of 10 μm in the depth direction from the surface of the base material is less than 0.0050%,
　Non-oriented electrical steel sheet.
4.0 ≤ Si + Al ≤ 5.0 (i)
However, the element symbol in the above formula (i) is the content (% by mass) of each element in the base material.
[0011]
(2) Tensile strength is 600 MPa or more,
The non-oriented electrical steel sheet according to (1) above.
[0012]
(3) having an insulating coating on the surface of the base material;
The non-oriented electrical steel sheet according to (1) or (2) above.
[0013]
(4) A method for manufacturing a non-oriented electrical steel sheet according to any one of (1) to (3) above,
in % by mass,
C: 0.0020-0.0060%,
Si: 3.5 to 4.9%,
Mn: 0.05-0.20%,
Al: 0.05-0.45%,
P: 0.030% or less,
S: 0.0030% or less,
N: 0.0030% or less,
O: less than 0.0050%,
Ca: less than 0.0010%,
Ti: less than 0.0050%,
Nb: less than 0.0050%,
Zr: less than 0.0050%,
V: less than 0.0050%,
Cu: less than 0.20%,
Ni: less than 0.50%,
Sn: 0 to 0.05%,
Sb: 0 to 0.05%, and
The balance: Fe and impurities, and
For a steel ingot having a chemical composition that satisfies the following formula (i),
Manufacture of a non-oriented electrical steel sheet by sequentially performing a hot rolling process, a cold rolling process, and a finish annealing process with a soaking temperature of 750 to 1050°C, a soaking time of 1 to 300 seconds, and a dew point of 0 to 50°C. Method.
4.0 ≤ Si + Al ≤ 5.0 (i)
However, the element symbol in the above formula (i) is the content (% by mass) of each element in the steel ingot.
[0014]
(5) further comprising a hot-rolled sheet annealing step between the hot-rolling step and the cold-rolling step;
A method for manufacturing a non-oriented electrical steel sheet according to (4) above.
The invention's effect
[0015]
According to the present disclosure, it is possible to stably obtain a non-oriented electrical steel sheet having high strength and excellent magnetic properties at low cost.
MODE FOR CARRYING OUT THE INVENTION
[0016]
In order to solve the above problems, the disclosing parties have made intensive studies, and as a result, have obtained the following findings.
[0017]
When it is desired to increase the strength of steel, a method of incorporating a large amount of alloying elements such as Cu, Ni, Ti and V is often used. However, when alloying elements such as Cu, Ni, Ti and V are contained in large amounts, not only the cost increases but also the magnetic properties deteriorate.
[0018]
　In order to achieve high strength without containing expensive alloying elements as much as possible, it is effective to use Si and Al. In order to improve the magnetic properties of non-oriented electrical steel sheets, it is necessary to improve high-frequency iron loss, which mainly consists of hysteresis loss and eddy current loss. Si and Al also have the effect of increasing the electrical resistance of steel and reducing eddy current loss.
[0019]
On the other hand, an increase in the Si content deteriorates the toughness and causes embrittlement cracking during cold rolling, which makes manufacturing difficult. As a countermeasure, in order to suppress embrittlement cracking during cold rolling, it is conceivable to strengthen the grain boundaries by segregating C at the grain boundaries. However, C precipitates as a carbide in the environment of use, which hinders domain wall motion and causes an increase in hysteresis loss.
[0020]
Therefore, it is desired to reduce the C content in the final product by decarburizing after cold rolling, although C is contained to some extent during cold rolling. This makes it possible to achieve both an improvement in cold workability and a reduction in iron loss.
[0021]
It should be noted that the content of Mn, which has a relatively low contribution to high strength and a relatively low effect of increasing electrical resistance, is reduced.
[0022]
This disclosure has been made based on the above findings. Each requirement of the present disclosure will be described in detail below.
In the present disclosure, a numerical range represented using "~" means a range including the numerical values described before and after "~" as lower and upper limits.
A numerical range when "more than" or "less than" is attached to the numerical value described before and after "~" means a range that does not include these numerical values as the lower or upper limit.
The term "process" includes not only an independent process, but also if the intended purpose of the process is achieved, even if it cannot be clearly distinguished from other processes.
In the numerical ranges stated in stages in this disclosure, the upper limit stated in one numerical range is the upper limit of another numerical range stated in other stages, or the lower limit stated in one numerical range. may be replaced with the lower limit of the numerical range described in other steps.
In addition, in the numerical ranges described in the present disclosure, the upper limit or lower limit of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, a combination of preferred aspects is a more preferred aspect.
[0023]
1. overall structure
The non-oriented electrical steel sheet according to the present disclosure has high strength and excellent magnetic properties, and is therefore suitable for both stators and rotors. Moreover, the non-oriented electrical steel sheet according to the present disclosure preferably has an insulating coating on the surface of the base material described below.
[0024]
2. Chemical composition of base material
The reasons for limiting each element are as follows. In addition, "%" about content in the following description means "mass %."
[0025]
C: 0.0010-0.0040%
C (carbon) is an element that causes iron loss deterioration. If the C content exceeds 0.0040%, iron loss deterioration occurs in the non-oriented electrical steel sheet, and good magnetic properties cannot be obtained. On the other hand, C is an element effective for increasing the strength of steel sheets. Therefore, the C content should be 0.0010 to 0.0040%. The C content is preferably 0.0012% or more, more preferably 0.0015% or more. The C content is preferably 0.0035% or less, more preferably 0.0030% or less.
[0026]
Si: 3.5-4.9%
Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves high-frequency iron loss. In addition, since Si has a high solid-solution strengthening ability, it is an element effective for increasing the strength of steel sheets. On the other hand, if the Si content is excessive, workability is significantly degraded, making cold rolling difficult. Therefore, the Si content should be 3.5 to 4.9%. The Si content is preferably 3.6% or more, more preferably 3.7% or more. Also, the Si content is preferably 4.8% or less, more preferably 4.7% or less.
preferred.
[0027]
　Mn: 0.05 to 0.20%
　Mn (manganese) has the effect of increasing the electrical resistance of steel, reducing eddy current loss, and improving high-frequency iron loss, but it is less effective than Si and Al. On the other hand, as the Mn content increases, the magnetic flux density decreases. However, Mn has the effect of suppressing embrittlement during hot rolling due to S, which is unavoidably contained in steel. Therefore, the Mn content should be 0.05 to 0.20%. The Mn content is preferably 0.06 to 0.19% or less, more preferably 0.07 to 0.18% or less.
[0028]
Al: 0.05-0.45%
Al (aluminum) is an element that has the effect of reducing eddy current loss and improving high-frequency iron loss by increasing the electrical resistance of steel. Also, it is an element that contributes to high strength through solid-solution strengthening, though not as much as Si. On the other hand, in the case of high-Si steel having a Si content of 3.5% or more, if the Al content is excessive, the toughness is significantly deteriorated, resulting in embrittlement cracking during cold rolling. Therefore, the Al content should be 0.05 to 0.45%. The Al content is preferably 0.10% or more, more preferably 0.15% or more. Also, the Al content is preferably 0.40% or less, more preferably 0.38% or less, and even more preferably 0.35% or less.
[0029]
In the present disclosure, the electrical resistance of steel is ensured by appropriately controlling the Si and Al contents. Also, from the viewpoint of securing strength and toughness, appropriate control is necessary. Therefore, it is necessary to satisfy the following formula (i) in addition to the content of Si and Al being within the above ranges. Si+sol. The value of Al is preferably 4.2 or more and preferably 4.8 or less.
4.0 ≤ Si + Al ≤ 5.0 (i)
However, the above formula (P: 0.030% or less
P (phosphorus) is contained in steel as an impurity, and if the content is excessive, the toughness of the steel sheet is significantly reduced. Therefore, the P content should be 0.030% or less. The P content is preferably 0.025% or less, more preferably 0.020% or less. In addition, since an extreme reduction in the P content may lead to an increase in manufacturing costs, the P content may be 0.0005% or more, 0.0008% or more, or 0.001% or more.
[0031]
S: 0.0030% or less
S (sulfur) is an element that increases iron loss by forming fine precipitates of MnS and degrades the magnetic properties of the steel sheet. Therefore, the S content should be 0.0030% or less. The S content is preferably 0.0020% or less, more preferably 0.0015% or less. Note that an extreme reduction in the S content may lead to an increase in manufacturing costs, so the S content may be 0.0001% or more, 0.0003% or more, or 0.0005% or more.
[0032]
N: 0.0030% or less
　N (nitrogen) is an element that is unavoidably mixed, and is an element that forms nitrides, increases core loss, and deteriorates the magnetic properties of the steel sheet. Therefore, the N content should be 0.0030% or less. The N content is preferably 0.0025% or less, more preferably 0.0020% or less. Note that the N content may be 0.0005% or more because an extreme reduction in the N content may lead to an increase in manufacturing costs.
[0033]
O: 0.0100-0.0400%
　O (oxygen) is an element that is unavoidably mixed, and is an element that forms an oxide to increase iron loss and deteriorate the magnetic properties of the steel sheet. Therefore, the lower the O content is, the better. However, since O forms an oxide layer on the surface during decarburization, it is difficult to reduce its content. However, excessive oxidation of the surface layer of the base material also causes deterioration of the magnetic flux density. Therefore, the average O content in the entire thickness of the base material is set to 0.0100 to 0.0400%. The O content is preferably 0.0350% or less, more preferably 0.0300% or less.
[0034]
Also, as described above, although the formation of an oxide layer on the surface layer of the base material is unavoidable, it is desirable to reduce the O content in the region other than the surface layer as much as possible. Specifically, it is necessary to set the O content in a region excluding a position of 10 μm in the depth direction from the surface of the base material to less than 0.0050%. Oxygen in the center of the base material 10 μm or more from the surface of the base material is considered to be oxygen contained in oxides formed during solidification in the steelmaking process. That is, when the surface layer is oxidized by controlling the dew point in the final annealing process, the internal oxidation is about several μm, and the depth of 10 μm or more from the base metal surface corresponds to the O content during steel making. If the oxygen content is 0.0050% or more, a large amount of oxide is formed in the base material, increasing the hysteresis loss. Therefore, the O content in the region excluding the position of 10 μm in the depth direction from the surface of the base material should be less than 0.0050%. The O content in the region excluding the position 10 μm from the surface of the base material in the depth direction is preferably 0.0045% or less, more preferably 0.0040% or less.
The O content in the region excluding the position of 10 μm in the depth direction from the surface of the base material is chemically polished using a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide to the position of 10 μm from the front and back surfaces of the base material. can be measured by inert gas fusion-nondispersive infrared absorption method.
[0035]
　Ca: less than 0.0010%
　Ca (calcium) is added at the steelmaking stage as a desulfurizing agent. Ca remaining in the base material combines with S to form Ca-based sulfides. This sulfide may precipitate coarsely and degrade the fatigue strength of the product, making it unnecessary to add a large amount of Ca and increasing the cost. Therefore, the Ca content should be less than 0.0010%. The Ca content is preferably 0.0008% or less, more preferably 0.0005% or less. Note that the Ca content may be 0.0001% or more, since an extreme reduction in the Ca content may lead to an increase in manufacturing costs.
[0036]
　Ti: less than 0.0050%
Ti (titanium) is an element that is unavoidably mixed in, and can combine with carbon or nitrogen to form precipitates (carbides or nitrides). If carbides or nitrides are formed, these precipitates themselves degrade the magnetic properties. Furthermore, it inhibits the growth of crystal grains during the final annealing, degrading the magnetic properties. Therefore, the Ti content should be less than 0.0050%. The Ti content is preferably 0.0040% or less, more preferably 0.0030% or less, even more preferably 0.0020% or less. Note that the Ti content may be 0.0005% or more, since an extreme reduction in the Ti content may lead to an increase in manufacturing costs.
[0037]
Nb: less than 0.0050%
Nb (niobium) is an element that combines with carbon or nitrogen to form precipitates (carbides) that contribute to increased strength, but these precipitates themselves degrade the magnetic properties. Therefore, the Nb content should be less than 0.0050%. The Nb content is preferably 0.0040% or less, more preferably 0.0030% or less, even more preferably 0.0020% or less. The lower the Nb content, the better, preferably below the limit of measurement.
[0038]
Zr: less than 0.0050%
Zr (zirconium) is an element that combines with carbon or nitrogen to form precipitates (carbides, nitrides) that contribute to increased strength, but these precipitates themselves degrade the magnetic properties. Therefore, the Zr content should be less than 0.0050%. The Zr content is preferably 0.0040% or less, more preferably 0.0030% or less, even more preferably 0.0020% or less. The lower the Zr content, the better, preferably below the measurement limit.
[0039]
　V: less than 0.0050%
V (vanadium) is an element that combines with carbon or nitrogen to form precipitates (carbides, nitrides) that contribute to increased strength, but these precipitates themselves degrade the magnetic properties. Therefore, the V content should be less than 0.0050%. The V content is preferably 0.0040% or less, more preferably 0.0030% or less, even more preferably 0.0020% or less. The lower the V content, the better, preferably below the measurement limit.
[0040]
Cu: less than 0.20%
Cu (copper) is an element that is unavoidably mixed. Intentional addition of Cu increases the manufacturing cost of the steel sheet. Therefore, in the present disclosure, it is not necessary to actively add it, and an impurity level is sufficient. The Cu content is set to less than 0.20%, which is the maximum value that can be unavoidably mixed in the manufacturing process. The Cu content is preferably 0.15% or less, more preferably 0.10% or less. Although the lower limit of the Cu content is not particularly limited, an extreme reduction in the Cu content may lead to an increase in manufacturing costs. Therefore, the Cu content may be 0.001% or more, 0.003% or more, or 0.005% or more.
[0041]
Ni: less than 0.50%
Ni (nickel) is an element that is unavoidably mixed. However, since Ni is also an element that improves the strength of the steel sheet, it may be intentionally added. However, since Ni is expensive, its content should be less than 0.50% when it is intentionally added. The Ni content is preferably 0.40% or less, more preferably 0.30% or less. Although the lower limit of the Ni content is not particularly limited, an extreme reduction in the Ni content may lead to an increase in manufacturing costs. Therefore, the Ni content may be 0.001% or more, 0.003% or more, or 0.005% or more.
[0042]
Sn: 0-0.05%
Sb: 0-0.05%
Sn (tin) and Sb (antimony) segregate on the surface and suppress oxidation and nitridation during annealing, and are useful elements for ensuring low iron loss. In addition, it also has the effect of improving the texture by segregating at the grain boundaries and increasing the magnetic flux density. Therefore, at least one of Sn and Sb may be contained as necessary. However, if the content of these elements is excessive, the toughness of the steel may decrease, making cold rolling difficult. Therefore, the contents of Sn and Sb are each set to 0.05% or less. The contents of Sn and Sb are each preferably 0.03% or less. To obtain the above effects, the content of at least one of Sn and Sb is preferably 0.005% or more, more preferably 0.01% or more.
[0043]
In the chemical composition of the base material of the non-oriented electrical steel sheet of the present disclosure, the balance is Fe and impurities. Here, the term "impurities" refers to components mixed in by various factors in raw materials such as ore, scrap, etc., and in the manufacturing process when steel is manufactured industrially, to the extent that they do not adversely affect the effects of the present disclosure. means acceptable.
[0044]
The content of Cr and Mo as impurity elements is not particularly defined. In the non-oriented electrical steel sheet according to the present disclosure, even if these elements are contained at 0.5% or less, the effects of the present disclosure are not particularly affected. Further, even if Mg is contained in the range of 0.002% or less, the effect of the present disclosure is not particularly affected, and even if the rare earth element (REM) is contained in the range of 0.004% or less, the effect of the present disclosure has no particular effect on REM is a general term for a total of 17 elements of Sc, Y and lanthanoids, and the content of REM refers to the total content of one or more elements in REM.
[0045]
In addition to the above elements, elements such as Pb, Bi, As, B, and Se may be included, but if the content of each is in the range of 0.0050% or less, the effect of the present disclosure is impaired. not a thing
[0046]
3. Magnetic properties
In the non-oriented electrical steel sheet according to the present disclosure, excellent magnetic properties mean low iron loss W10/400 and high magnetic flux density B50. Here, the above magnetic properties are measured by the Epstein method specified in JIS C 2550-1 (2011). If it is difficult to measure by the Epstein method, such as when the test piece is small, the Epstein method according to the single sheet magnetic property measurement method (Single Sheet Tester: SST) specified in JIS C 2556 (2015) The measurement may be made after correction so that it is equivalent to the measured value. In the present disclosure, low iron loss W 10/400 means 30.0 W/kg or less for plate thicknesses of 0.26 mm or more, 22.0 W/kg or less for plate thicknesses of 0.21 to 0.25 mm, and 0.0 W/kg or less for plate thicknesses of 0.21 to 0.25 mm. At 20 mm or less, it is 18.0 W/kg or less. A high magnetic flux density B50 means 1.60 T or more regardless of the plate thickness.
[0047]
4. mechanical properties
In the non-oriented electrical steel sheet according to the present disclosure, having high strength means that the tensile strength is preferably 600 MPa or more. More preferably, the tensile strength is 610 MPa or higher, and even more preferably 630 MPa or higher. Here, the tensile strength is measured by performing a tensile test based on JIS Z 2241 (2011).
[0048]
5. insulating coating
As described above, the non-oriented electrical steel sheet according to the present disclosure preferably has an insulating coating formed on the surface of the base material. Non-oriented electrical steel sheets are laminated after punching core blanks, so by providing an insulating coating on the surface of the base material, it is possible to reduce eddy currents between the sheets and reduce eddy current loss as a core. can be reduced.
[0049]
The type of insulation coating is not particularly limited, and it is possible to use known insulation coatings used as insulation coatings for non-oriented electrical steel sheets. Insulation like thisAs the coating, for example, a composite insulating coating containing an inorganic substance as a main component and an organic substance can be used. 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.
[0050]
Here, although the amount of the insulating coating is not particularly limited, it is preferably about 200 to 1500 mg/m 2 per side, more preferably 300 to 1200 mg/m 2 per side. Excellent uniformity can be maintained by forming the insulating coating so that the coating amount is within the above range. In addition, when measuring the adhesion amount of the insulating film after the fact, it is possible to use various known measurement methods, for example, a method of measuring the difference in mass before and after immersion in an aqueous sodium hydroxide solution, A fluorescent X-ray method using a ray method may be used as appropriate.
[0051]
6. Production method
A method for manufacturing a non-oriented electrical steel sheet according to the present disclosure will be described. The non-oriented electrical steel sheet according to the present disclosure is, in mass%, C: 0.0020 to 0.0060%, Si: 3.5 to 4.9%, Mn: 0.05 to 0.20%, Al: 0.05 to 0.45%, P: 0.030% or less, S: 0.0030% or less, N: 0.0030% or less, O: less than 0.0050%, Ca: less than 0.0010%, Ti : less than 0.0050%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.20%, Ni: less than 0.50%, Sn: 0 0.05%, Sb: 0-0.05%, the balance: Fe and impurities, and a steel ingot having a chemical composition that satisfies the above formula (i) is subjected to a hot rolling process and a cold rolling process. It is possible to manufacture by sequentially performing a rolling process and a finish annealing process with a soaking temperature of 750 to 1050°C, a soaking time of 1 to 300 seconds, and a dew point of 0 to 50°C. A hot-rolled sheet annealing step may be further provided between the hot rolling step and the cold rolling step. Further, when an insulating coating is formed on the surface of the base material, the insulating coating is formed after the finish annealing. Each step will be described in detail below.
[0052]

　The chemical composition of the steel ingot is the same as the chemical composition of the steel plate except for C and O, so the explanation is omitted. The reasons for limiting C and O are described below.
[0053]
C: 0.0020-0.0060%
C has the effect of suppressing embrittlement cracking during cold rolling by segregating at grain boundaries. In order to obtain this effect, the C content in the steel ingot is preferably 0.0020% or more. However, as mentioned above, if the final product contains excessive C, good magnetic properties cannot be obtained. In the present disclosure, decarburization is performed in the final annealing step to reduce the C content in the final product. It becomes difficult to control the amount below 0.0040%. Therefore, the C content in the steel ingot is preferably 0.0020 to 0.0060%, more preferably 0.0025 to 0.0055%, and more preferably 0.0030 to 0.0050%. is more preferred.
[0054]
O: less than 0.0050%
O is an element that is unavoidably mixed in, and is an element that forms an oxide to increase iron loss and deteriorate the magnetic properties of the steel sheet. As described above, in order to make the O content in the final product less than 0.0050% in the region excluding the position of 10 μm in the depth direction from the surface of the base metal, the O content in the steel ingot must be 0. It is preferably less than 0.0050%.
[0055]

A steel ingot (slab) having the above chemical composition is heated, and the heated steel ingot is hot-rolled to obtain a hot-rolled sheet. Here, the heating temperature of the steel ingot for hot rolling is not particularly specified, but it is preferably 1050 to 1250° C., for example. Also, the thickness of the hot-rolled sheet after hot rolling is not particularly specified, but considering the final thickness of the base material, it is preferably about 1.5 to 3.0 mm, for example. .
[0056]

After that, for the purpose of increasing the magnetic flux density of the steel sheet, the hot-rolled sheet is annealed as necessary. The heat treatment conditions in the hot-rolled sheet annealing are not particularly specified, but, for example, heating at a temperature of 950° C. or less is preferable. Also, the heating time is preferably 1 to 300 seconds. Although the magnetic properties are inferior to those in the case where the hot-rolled sheet annealing process is performed, the hot-rolled sheet annealing process may be omitted for cost reduction.
[0057]

After the hot-rolled sheet annealing, pickling is carried out to remove the scale layer formed on the surface of the base material. Here, the pickling conditions such as the concentration of the acid used for pickling, the concentration of the accelerator used for pickling, and the temperature of the pickling solution are not particularly limited, and known pickling conditions may be used. can.
[0058]

After the pickling, cold rolling is performed. In the cold rolling, the pickled sheet from which the scale layer has been removed is rolled at a reduction rate such that the final sheet thickness of the base material is 0.10 to 0.35 mm.
[0059]

After the cold rolling, finish annealing is performed. In the method for manufacturing a non-oriented electrical steel sheet according to the present disclosure, a continuous annealing furnace is used for finish annealing. The finish annealing step is an important step for decarburizing and controlling the C content and grain size in the base material.
[0060]
Here, as for the final annealing conditions, the soaking temperature is 750 to 1050 ° C., the soaking time is 1 to 300 s, and the atmosphere is a mixed atmosphere of H 2 and N 2 in which the proportion of H 2 is 10 to 100% by volume. (ie, H 2 +N 2 =100% by volume), and the dew point of the atmosphere is preferably 0 to 50°C.
[0061]
If the soaking temperature is less than 750°C, the crystal grain size becomes finer, the ratio of the non-recrystallized region increases, and the iron loss deteriorates, which is not preferable. This is not preferable because the strength becomes insufficient and iron loss deteriorates. The soaking temperature is more preferably 770 to 1020°C, more preferably 800 to 1000°C. The proportion of H 2 in the atmosphere is more preferably 15-90% by volume. By setting the dew point of the atmosphere to 0° C. or higher, sufficient decarburization can be performed and the C content in the base material can be reduced. Further, by setting the dew point of the atmosphere to 50° C. or lower, excessive oxidation of the surface of the base material can be suppressed. The dew point of the atmosphere is more preferably 10 to 40°C, more preferably 15 to 35°C.
[0062]

After the finish annealing, a step of forming an insulating coating is carried out as necessary. Here, the process of forming the insulating coating is not particularly limited, and the coating and drying of the insulating coating may be performed by a known method using the known insulating coating treatment liquid as described above.
[0063]
The surface of the base material on which the insulating coating is formed may be subjected to any pretreatment such as degreasing treatment with alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc. before applying the treatment liquid. Alternatively, the surface may be left as it is after finish annealing without performing these pretreatments.
[0064]
The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

The scope of the claims
[Claim 1]
　The chemical composition of the base material is % by mass,
C: 0.0010 to 0.0040%,
Si: 3.5 to 4.9%,
Mn: 0.05-0.20%,
Al: 0.05-0.45%,
P: 0.030% or less,
S: 0.0030% or less,
N: 0.0030% or less,
O: 0.0100 to 0.0400%,
Ca: less than 0.0010%,
Ti: less than 0.0050%,
Nb: less than 0.0050%,
Zr: less than 0.0050%,
V: less than 0.0050%,
Cu: less than 0.20%,
Ni: less than 0.50%,
Sn: 0 to 0.05%,
Sb: 0 to 0.05%, and
The balance: Fe and impurities, and
satisfying the following formula (i),
The O content in the region excluding the position of 10 μm in the depth direction from the surface of the base material is less than 0.0050%,
　Non-oriented electrical steel sheet.
4.0 ≤ Si + Al ≤ 5.0 (i)
However, the element symbol in the above formula (i) is the content (% by mass) of each element in the base material.
[Claim 2]
The tensile strength is 600 MPa or more,
The non-oriented electrical steel sheet according to claim 1.
[Claim 3]
having an insulating coating on the surface of the base material,
The non-oriented electrical steel sheet according to claim 1 or claim 2.
[Claim 4]
A method for manufacturing the non-oriented electrical steel sheet according to any one of claims 1 to 3,
in % by mass,
C: 0.0020-0.0060%,
Si: 3.5 to 4.9%,
Mn: 0.05-0.20%,
Al: 0.05-0.45%,
P: 0.030% or less,
S: 0.0030% or less,
N: 0.0030% or less,
O: less than 0.0050%,
Ca: less than 0.0010%,
Ti: less than 0.0050%,
Nb: less than 0.0050%,
Zr: less than 0.0050%,
V: less than 0.0050%,
Cu: less than 0.20%,
Ni: less than 0.50%,
Sn: 0 to 0.05%,
Sb: 0 to 0.05%, and
The balance: Fe and impurities, and
For a steel ingot having a chemical composition that satisfies the following formula (i),
A hot rolling process, a cold rolling process, and a final annealing process with a soaking temperature of 750 to 1050°C, a soaking time of 1 to 300 seconds, and a dew point of 0 to 50°C are performed in order.
　Method for manufacturing non-oriented electrical steel sheets.
4.0 ≤ Si + Al ≤ 5.0 (i)
However, the element symbol in the above formula (i) is the content (% by mass) of each element in the steel ingot.
[Claim 5]
A hot-rolled sheet annealing step is further provided between the hot rolling step and the cold rolling step,
A method for manufacturing the non-oriented electrical steel sheet according to claim 4.