Title of invention: Non-oriented electrical steel sheet
Technical field
[0001]
　The present invention relates to non-oriented electrical steel sheets.
　The present application claims priority based on Japanese Patent Application No. 2018-206970 filed in Japan on November 2, 2018, the contents of which are incorporated herein by reference.
Background technology
[0002]
　In recent years, global environmental problems have been attracting attention, and the demand for energy conservation efforts is increasing. Among the demands for energy saving efforts, there is a strong demand for higher efficiency of electrical equipment. Therefore, even in non-oriented electrical steel sheets widely used as iron core materials for motors, generators, etc., there is an increasing demand for improvement of magnetic characteristics. This tendency is remarkable in drive motors for electric vehicles and hybrid vehicles and compressor motors for air conditioners.
[0003]
　The motor core of various motors as described above is composed of a stator which is a stator and a rotor which is a rotor. The characteristics required for the stator and rotor that make up the motor core are different from each other. The stator is required to have excellent magnetic properties (low iron loss and high magnetic flux density), especially low iron loss, while the rotor is required to have excellent mechanical properties (high strength).
[0004]
　Since the characteristics required for the stator and the rotor are different, the desired characteristics can be realized by separately producing the non-oriented electrical steel sheet for the stator and the non-oriented electrical steel sheet for the rotor. However, preparing two types of non-oriented electrical steel sheets causes a decrease in yield. Therefore, in order to realize the high strength required for the rotor and the low iron loss required for the stator without performing strain annealing and annealing, the non-oriented electrical steel sheet has excellent strength and magnetic characteristics. However, it has been studied conventionally.
[0005]
　For example, in Patent Documents 1 to 3, attempts have been made to realize excellent magnetic properties and high strength. Further, in Patent Document 4, an attempt is made to realize excellent magnetic characteristics and high strength, and to further reduce characteristic variations.
Prior art literature
Patent documents
[0006]
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-300535
Patent Document 2: Japanese Patent Application Laid-Open No. 2007-186791
Patent Document 3: Japanese Patent Application Laid-Open No. 2012-140676
Patent Document 4: Japanese Patent Application Laid-Open No. 2010-90474 Gazette
Outline of the invention
Problems to be solved by the invention
[0007]
　However, in recent years, in order to realize the energy-saving characteristics required for motors of electric vehicles or hybrid vehicles, the technologies disclosed in Patent Documents 1 to 3 are insufficient to reduce iron loss as a stator material. It was. Further, in Patent Document 4, since the recrystallized grains are refined by performing finish annealing in a low temperature region, the hysteresis loss becomes large, and as in Patent Documents 1 to 3, low iron loss cannot be achieved as a stator material. There was a problem that it was enough.
[0008]
　The present invention has been made to solve such a problem, and an object of the present invention is to provide a non-oriented electrical steel sheet having high strength and excellent magnetic properties.
Means to solve problems
[0009]
　The gist of the present invention is the following non-oriented electrical steel sheets.
[0010]
(1) The non-oriented electrical steel sheet according to one aspect of the present invention has a chemical composition of a base material in mass% of
　C: 0.0050% or less,
　Si: 3.7% or more and 5.0% or less. ,
　Mn: more than 0.2% and less than 1.5%,
　sol. Al: 0.05 to 0.45%,
　P: 0.030% or less,
　S: 0.0030% or less,
　N: 0.0030% or less,
　Ti: less than 0.0050%,
　Nb: less than 0.0050% ,
　Zr: less than 0.0050%,
　V: less than 0.0050%,
　Cu: less than 0.200%,
　Ni: less than 0.500%,
　Sn: 0 to 0.100%,
　Sb: 0 to 0.100% , And the
　balance: Fe and impurities,
　satisfying the following formula (i) , and
　the average crystal grain size of the base metal is more than 40 μm and 120 μm or less.
　Si + sol. Al + 0.5 × Mn ≧ 4.3 (i)
　However, the element symbol in the above formula is the content (mass%) of each element.
(2) The non-oriented electrical steel sheet according to (1) above may have a tensile strength of 600 MPa or more.
(3) The non-oriented electrical steel sheet according to (1) or (2) above has a chemical composition of% by mass,
　Sn: 0.005 to 0.100%, and
　Sb: 0.005 to 0. It
　may contain one or two selected from .100% .
(4) The non-oriented electrical steel sheet according to any one of (1) to (3) above may have an insulating film on the surface of the base material.
Effect of the invention
[0011]
　According to the above aspect according to the present invention, a non-oriented electrical steel sheet having high strength and excellent magnetic properties can be obtained.
Mode for carrying out the invention
[0012]
　As a result of diligent studies to solve the above problems, the present inventors have obtained the following findings.
[0013]
　Si, Mn and Al are elements that have the effect of increasing the electrical resistance of steel and reducing eddy current loss. In addition, these elements are elements that also contribute to increasing the strength of steel.
[0014]
　Among Si, Mn and Al, Si is the element that most efficiently contributes to the increase in electrical resistance. Like Si, Al also has the effect of efficiently increasing the electrical resistance. On the other hand, Mn has a slightly lower effect of increasing electrical resistance than Si and Al.
[0015]
　From these facts, in this embodiment, by adjusting the contents of Si, Al and Mn within an appropriate range, high strength and improvement of magnetic properties are achieved.
[0016]
　Further, in the present embodiment, control of the crystal grain size is also important for increasing the strength and improving the magnetic properties. From the viewpoint of increasing strength, it is desirable that the crystal grains in the steel are fine grains.
[0017]
　Further, in order to improve the magnetic properties of the non-oriented electrical steel sheet, it is necessary to improve the high frequency iron loss. Iron loss mainly consists of hysteresis loss and eddy current loss. Here, in order to reduce the hysteresis loss, it is preferable to make the crystal grains coarser, and in order to reduce the eddy current loss, it is preferable to make the crystal grains finer. That is, there is a trade-off relationship between the two.
[0018]
　Therefore, as a result of further studies, the present inventors have found that there is a range of suitable particle sizes for achieving high strength and improvement of magnetic properties.
[0019]
　The present invention has been made based on the above findings. Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0020]
　1. 1. Overall configuration
　The non-oriented electrical steel sheet according to this embodiment has high strength and excellent magnetic properties, and is therefore suitable for both a stator and a rotor. Further, the non-oriented electrical steel sheet according to the present embodiment preferably has an insulating film on the surface of the base material described below.
[0021]
　2. Chemical Composition of Base Material In the chemical composition of the base material of the
　non-oriented electrical steel sheet according to the present embodiment, the reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%". The numerical limit range described with "~" in between includes the lower limit value and the upper limit value.
[0022]
　C: 0.0050% or less
　C (carbon) is an element that causes iron loss deterioration of non-oriented electrical steel sheets. If the C content exceeds 0.0050%, the iron loss of the non-oriented electrical steel sheet deteriorates, and good magnetic characteristics cannot be obtained. Therefore, the C content is set to 0.0050% or less. The C content is preferably 0.0040% or less, more preferably 0.0035% or less, and even more preferably 0.0030% or less. Since C contributes to increasing the strength of the non-oriented electrical steel sheet, the C content is preferably 0.0005% or more, preferably 0.0010% or more, when the effect is desired. Is more preferable.
[0023]
　Si: More than 3.7% and 5.0% or less
　Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves high-frequency iron loss of non-oriented electrical steel sheets. .. Further, Si is an element effective for increasing the strength of non-oriented electrical steel sheets because it has a large solid solution strengthening ability. In order to obtain these effects, the Si content is set to more than 3.7%. The Si content is preferably 3.8% or more, more preferably 3.9% or more, and even more preferably more than 4.0%. On the other hand, if the Si content is excessive, the workability is remarkably deteriorated and it becomes difficult to carry out cold rolling. Therefore, the Si content is 5.0% or less. The Si content is preferably 4.8% or less, more preferably 4.5% or less.
[0024]
　Mn: More than 0.2% and 1.5% or less
　Mn (manganese) is effective for increasing the electrical resistance of steel, reducing eddy current loss, and improving high-frequency iron loss of non-oriented electrical steel sheets. Element. Further, when the Mn content is too low, the effect of increasing the electric resistance is small, and fine sulfides (MnS) are precipitated in the steel, so that the grains may not grow sufficiently at the time of finish annealing. Therefore, the Mn content is set to more than 0.2%. The Mn content is preferably 0.3% or more, and more preferably 0.4% or more. On the other hand, if the Mn content is excessive, the magnetic flux density of the non-oriented electrical steel sheet is significantly reduced. Therefore, the Mn content is set to 1.5% or less. The Mn content is preferably 1.4% or less, more preferably 1.2% or less.
[0025]
　sol. Al: 0.05 to 0.45%
　Al (aluminum) is an element that has the effect of reducing eddy current loss by increasing the electrical resistance of steel and improving high-frequency iron loss of non-oriented electrical steel sheets. .. Further, Al is an element that contributes to increasing the strength of the non-oriented electrical steel sheet by solid solution strengthening, though not as much as Si. In order to obtain these effects, sol. The Al content is 0.05% or more. sol. The Al content is preferably 0.10% or more, and more preferably 0.15% or more. On the other hand, sol. When the Al content is excessive, the decrease in the magnetic flux density of the non-oriented electrical steel sheet becomes remarkable. Therefore, sol. The Al content is 0.45% or less. sol. The Al content is preferably 0.40% or less, more preferably 0.35% or less, and even more preferably 0.30% or less. In addition, in this embodiment, sol. The Al content is sol. It means the content of Al (acid-soluble Al).
[0026]
　In the present embodiment, the electrical resistance of steel is ensured by appropriately controlling the contents of Si, Al and Mn. Further, from the viewpoint of ensuring strength, it is necessary to appropriately control the contents of Si, Al and Mn. Therefore, in addition to the contents of Si, Al, and Mn being within the above ranges, it is necessary to satisfy the following formula (i). The value on the left side of the following equation (i) is preferably 4.4 or more, and more preferably 4.5 or more.
[0027]
　Si + sol. Al + 0.5 × Mn ≧ 4.3 (i)
　However, the element symbol in the above formula is the content (mass%) of each element.
[0028]
　P: 0.030% or less
　P (phosphorus) is contained in steel as an impurity, and if the content is excessive, the ductility of the non-oriented electrical steel sheet is significantly lowered. Therefore, the P content is 0.030% or less. The P content is preferably 0.025% or less, more preferably 0.020% or less. The P content is preferably 0%, but the P content may be 0.003% or more because an extreme reduction in the P content may cause an increase in manufacturing cost.
[0029]
　S: 0.0030% or less
　S (sulfur) is an element that increases iron loss by forming fine precipitates of MnS and deteriorates the magnetic properties of non-oriented electrical steel sheets. Therefore, the S content is set to 0.0030% or less. The S content is preferably 0.0020% or less, more preferably 0.0015% or less. Since an extreme reduction in the S content may cause an increase in manufacturing cost, the S content is preferably 0.0001% or more, more preferably 0.0003% or more, and 0. It is even more preferable that it is 0005% or more.
[0030]
　N: 0.0030% or less
　N (nitrogen) is an element that is inevitably mixed in steel, and is an element that forms nitrides to increase iron loss and deteriorate the magnetic properties of non-oriented electrical steel sheets. is there. Therefore, the N content is set to 0.0030% or less. The N content is preferably 0.0025% or less, more preferably 0.0020% or less. The N content is preferably 0.0005% or more because an extreme reduction in the N content may cause an increase in manufacturing cost.
[0031]
　Ti: Less than 0.0050%
　Ti (titanium) is an element that is inevitably mixed in steel and can combine with carbon or nitrogen to form precipitates (carbides, nitrides). When carbides or nitrides are formed, these precipitates themselves deteriorate the magnetic properties of grain-oriented electrical steel sheets. Furthermore, it inhibits the growth of crystal grains during finish annealing and deteriorates the magnetic properties of non-oriented electrical steel sheets. Therefore, the Ti content is set to less than 0.0050%. The Ti content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. The Ti content is preferably 0.0005% or more because an extreme reduction in the Ti content may cause an increase in manufacturing cost.
[0032]
　Nb: Less than 0.0050%
　Nb (niobium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides), but these precipitates themselves are non-directional. Deteriorates the magnetic properties of electrical steel sheets. Therefore, the Nb content is set to less than 0.0050%. The Nb content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. Further, the Nb content is more preferably not less than the measurement limit, and more preferably less than 0.0001%. Since the lower the Nb content is, the more preferable it is, the Nb content may be 0%.
[0033]
　Zr: Less than 0.0050%
　Zr (zirconium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves are Deteriorates the magnetic properties of non-directional electromagnetic steel sheets. Therefore, the Zr content is set to less than 0.0050%. The Zr content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. Further, the Zr content is more preferably not more than the measurement limit, and more preferably 0.0001% or less. Since the lower the Zr content is, the more preferable it is, the Zr content may be 0%.
[0034]
　V: Less than 0.0050%
　V (vanadium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves are Deteriorates the magnetic properties of non-oriented electrical steel sheets. Therefore, the V content is set to less than 0.0050%. The V content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. The V content is more preferably not less than the measurement limit, and more preferably 0.0001% or less. Since the lower the V content is, the more preferable it is, the V content may be 0%.
[0035]
　Cu: Less than 0.200%
　Cu (copper) is an element that is inevitably mixed in steel. If Cu is intentionally contained, the manufacturing cost of the non-oriented electrical steel sheet increases. Therefore, in the present embodiment, Cu does not need to be positively contained, and may be at the impurity level. The Cu content shall be less than 0.200%, which is the maximum value that can be unavoidably mixed in the manufacturing process. The Cu content is preferably 0.150% or less, more preferably 0.100% or less. The lower limit of the Cu content is not particularly limited, but an extreme reduction in the Cu content may cause an increase in manufacturing cost. Therefore, the Cu content is preferably 0.001% or more, more preferably 0.003% or more, and even more preferably 0.005% or more.
[0036]
　Ni: Less than 0.500%
　Ni (nickel) is an element that is inevitably mixed in steel. However, since Ni is also an element that improves the strength of the non-oriented electrical steel sheet, it may be intentionally contained. However, since Ni is expensive, the Ni content is set to less than 0.500%. The Ni content is preferably 0.400% or less, more preferably 0.300% or less. The lower limit of the Ni content is not particularly limited, but an extreme reduction in the Ni content may cause an increase in manufacturing cost. Therefore, the Ni content is preferably 0.001% or more, more preferably 0.003% or more, and even more preferably 0.005% or more.
[0037]
　Sn: 0 to 0.100%
　Sb: 0 to 0.100%
　Sn (tin) and Sb (antimony) segregate on the surface of the base metal and suppress oxidation and nitriding during annealing to prevent grain-oriented electrical steel sheets. It is an element useful for ensuring low iron loss in. In addition, Sn and Sb also have the effect of segregating at the grain boundaries to improve the texture and increasing the magnetic flux density of the non-oriented electrical steel sheet. Therefore, at least one of Sn and Sb may be contained if 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 set to 0.100% or less, respectively. The contents of Sn and Sb are preferably 0.060% or less, respectively. When the above effect is to be surely obtained, the content of at least one of Sn and Sb is preferably 0.005% or more, and more preferably 0.010% or more.
[0038]
　In the chemical composition of the base material of the non-oriented electrical steel sheet according to the present embodiment, the balance is Fe and impurities. Here, the "impurity" is a component mixed with raw materials such as ore and scrap, and various factors in the manufacturing process when steel is industrially manufactured, and is a component of the non-oriented electrical steel sheet according to the present embodiment. It means what is allowed as long as it does not adversely affect the characteristics.
[0039]
　The contents of Cr and Mo as impurity elements are not particularly specified. In the non-oriented electrical steel sheet according to the present embodiment, even if each of these elements is contained in the range of 0.5% or less, the characteristics of the non-oriented electrical steel sheet according to the present embodiment are not particularly affected. Further, even if Ca and Mg are contained in the range of 0.002% or less, the characteristics of the non-oriented electrical steel sheet according to the present embodiment are not particularly affected. Even if the rare earth element (REM) is contained in the range of 0.004% or less, there is no particular effect on the characteristics of the non-oriented electrical steel sheet according to the present embodiment. In the present embodiment, REM refers to a total of 17 elements composed of Sc, Y and lanthanoid, and the content of REM refers to the total content of these elements.
[0040]
　O is also an impurity element, but even if it is contained in the range of 0.05% or less, it does not affect the characteristics of the non-oriented electrical steel sheet according to the present embodiment. Since O may be mixed in the steel in the annealing step, even if it is contained in the range of 0.01% or less in the content of the slab stage (that is, the ladle value), it is non-directional according to the present embodiment. There is no particular effect on the characteristics of electrical steel sheets.
[0041]
　In addition to the above elements, elements such as Pb, Bi, As, B, and Se may be included as impurity elements, but if the content of each is in the range of 0.0050% or less, the present embodiment It does not impair the characteristics of the non-oriented electrical steel sheet according to the above.
[0042]
　The chemical composition of the base material of the non-oriented electrical steel sheet according to the present embodiment may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrum). In addition, sol. Al may be measured by ICP-AES using a filtrate obtained by heat-decomposing the sample with an acid. Further, C and S may be measured by using the combustion-infrared absorption method, and N may be measured by using the inert gas melting-thermal conductivity method.
[0043]
　3. 3. Grain size
　from the standpoint of increasing the strength of non-oriented electrical steel sheet, it is desirable that the crystal grains in the steel is fine. In addition, it is preferable to coarsen the crystal grains in order to reduce the hysteresis loss, and it is preferable to make the crystal grains finer in order to reduce the eddy current loss.
[0044]
　When the average crystal grain size of the base metal is 40 μm or less, the hysteresis loss is remarkably deteriorated, and it becomes difficult to improve the magnetic properties of the non-oriented electrical steel sheet. On the other hand, when the average crystal grain size of the base metal exceeds 120 μm, not only the strength of the steel is lowered, but also the eddy current loss is remarkably deteriorated, and it becomes difficult to improve the magnetic properties of the non-oriented electrical steel sheet. .. Therefore, the average crystal grain size of the base material is set to more than 40 μm and 120 μm or less. The average crystal grain size of the base material is preferably 45 μm or more, more preferably 50 μm or more, and even more preferably 55 μm or more. The average crystal grain size of the base metal is preferably 110 μm or less, and more preferably 100 μm or less.
[0045]
　In the present embodiment, the average crystal grain size of the base material is determined according to JIS G 0551 (2013) “Steel-Crystal Particle Size Microscopic Test Method”. Specifically, first, a test piece is collected from a position 10 mm or more away from the end of the non-oriented electrical steel sheet so that the plate thickness cross section parallel to the rolling direction becomes the observation surface. Using an optical microscope having an imaging function, an observation surface at which the crystal grain boundaries can be clearly observed by etching with a corrosive liquid is photographed at a magnification of 100 times. Using the obtained observation photograph, the average crystal grain size of the observed crystal grains is measured by the cutting method described in JIS G 0551 (2013). In the cutting method, five or more straight lines with a length of 2 mm in the rolling direction are drawn at equal intervals in the plate thickness direction, and the number of captured crystal grains captured by a straight line of 10 mm or more in total and the plate thickness direction orthogonal to the straight line in the rolling direction. Five or more straight lines parallel to the above are drawn at equal intervals in the rolling direction, and evaluation is performed using two types of supplementary crystal grain numbers: the supplementary crystal grain number supplemented by a straight line with a total (plate thickness x 5) mm or more. ..
[0046]
　4. Magnetic characteristics In the
　non-oriented electrical steel sheet according to the present embodiment, excellent magnetic characteristics means that the iron loss W 10/400 is low and the magnetic flux density B 50 is high. Specifically, when the thickness of the non-directional electromagnetic steel plate is more than 0.30 mm and 0.35 mm or less, the iron loss W 10/400 is 16.0 W / kg or less and the magnetic flux density B 50 is excellent. 15.0 W / kg or less and magnetic flux density B 50 of 1.60 T or more, 0.20 mm or more, 0.25 mm or less and 13.0 W / kg or less and magnetic flux density of 1.60 T or more and 0.25 mm or more and 0.30 mm or less. When the density B 50 is 1.60 T or more and 0.20 mm or less, it means 12.0 W / kg or less and the magnetic flux density B 50 is 1.59 T or more. Here, in the present embodiment, the above magnetic characteristics (iron loss W 10/400 and magnetic flux density B 50 ) are measured by the Epstein test specified in JIS C 2550-1 (2011). The iron loss W 10/400 means the iron loss generated under the condition that the maximum magnetic flux density is 1.0 T and the frequency is 400 Hz, and the magnetic flux density B 50 means the magnetic flux density in a magnetic field of 5000 A / m.
[0047]
　5. Mechanical properties In the
　non-oriented electrical steel sheet according to the present embodiment, having high strength means that the tensile (maximum) strength is 600 MPa or more. The non-oriented electrical steel sheet according to this embodiment has a tensile strength of 600 MPa or more. The tensile strength is preferably 610 MPa or more. The upper limit of the tensile strength is not particularly limited, but may be 720 MPa or less. Here, the tensile strength is measured by performing a tensile test in accordance with JIS Z 2241 (2011).
[0048]
　6. Insulating film In the
　non-oriented electrical steel sheet according to the present embodiment, it is preferable to have an insulating film on the surface of the base metal. Since non-oriented electrical steel sheets are used after the core blank is punched out and laminated, the eddy current between the plates can be reduced by providing an insulating film on the surface of the base metal, and the eddy current as the core. It is possible to reduce the loss.
[0049]
　In the present embodiment, the type of the insulating coating is not particularly limited, and a known insulating coating used as the insulating coating of the non-oriented electrical steel sheet can be used. Examples of such an insulating film include a composite insulating film mainly composed of an inorganic substance and further containing an organic substance. Here, the composite insulating coating is mainly composed of at least one of a metal salt such as a chromic acid metal salt and a phosphoric acid metal salt, or an inorganic substance such as colloidal silica, a Zr compound, and a Ti compound, and is a fine organic substance. It is an insulating film in which resin particles are dispersed. In particular, from the viewpoint of reducing the environmental load during manufacturing, which has been in increasing demand in recent years, an insulating coating using a metal phosphate, a Zr or Ti coupling agent as a starting material, or a metal phosphate, Zr or Ti. An insulating coating using a carbonate or ammonium salt of the coupling agent as a starting material is preferably used.
[0050]
　The amount of the insulating coating adhered is not particularly limited, but is preferably about 200 to 1500 mg / m 2 per side, and more preferably 300 to 1200 mg / m 2 per side . By forming the insulating film so that the amount of adhesion is within the above range, it is possible to maintain excellent uniformity. When the amount of the insulating film adhered is measured after the fact, various known measuring methods can be used. For example, a method of measuring the mass difference before and after immersion in the sodium hydroxide aqueous solution, or a calibration curve. A fluorescent X-ray method using a linear method or the like may be appropriately used.
[0051]
　7. Manufacturing Method
　The manufacturing method of the non-directional electromagnetic steel sheet according to the present embodiment is not particularly limited, but for example, a hot rolling step and a hot rolling plate annealing step are performed on a steel ingot having the above-mentioned chemical composition. , Pickling step, cold rolling step and finish annealing step can be carried out in order. When the insulating film is formed on the surface of the base material, the insulating film forming step is performed after the finishing annealing step. Hereinafter, each step will be described in detail.
[0052]
　
　A steel ingot (slab) having the above chemical composition is heated, and the heated steel ingot is hot-rolled to obtain a hot-rolled steel sheet. Here, the heating temperature of the ingot when subjected to hot rolling is not particularly specified, but is preferably 1050 to 1250 ° C., for example. Further, the thickness of the hot-rolled steel sheet after hot rolling is not particularly specified, but it is preferably about 1.5 to 3.0 mm in consideration of the final thickness of the base metal. ..
[0053]
　 After hot rolling, hot rolled sheet annealing is carried out as necessary for the purpose of increasing the magnetic flux density of the non-oriented electrical steel sheet. Regarding the heat treatment conditions in the hot-rolled sheet annealing, for example, in the case of continuous annealing, it is preferable to perform annealing in which the hot-rolled steel sheet is held at 700 to 1000 ° C. for 10 to 150 s. The heat treatment conditions are more preferably 10 to 150 s at 800 to 980 ° C., and even more preferably 10 to 150 s at 850 to 950 ° C.
[0054]
　In the case of box annealing, it is preferable to hold the hot-rolled steel sheet at 600 to 900 ° C. for 30 minutes to 24 hours. More preferably, the heat is equalized from 1 h to 20 h at 650 to 850 ° C. Although the magnetic characteristics are inferior to those in which the hot-rolled plate annealing step is performed, the above-mentioned hot-rolled plate annealing step may be omitted in order to reduce costs.
[0055]
　
　After the hot-rolled plate annealing, pickling is performed to remove the scale layer formed on the surface of the base metal. 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. it can. When the hot-rolled plate is annealed in a box, the pickling step is preferably performed before the hot-rolled plate is annealed from the viewpoint of descalability. In this case, it is not necessary to perform pickling after annealing the hot-rolled plate.
[0056]
　
　After the pickling (when the hot-rolled plate annealing is carried out by box annealing, it may be after the hot-rolled plate annealing step), cold rolling is carried out. In cold rolling, the pickling plate from which the scale layer has been removed is rolled at a rolling reduction ratio such that the final plate thickness of the base metal is 0.10 to 0.35 mm.
[0057]
　
　After the cold rolling, finish annealing is performed. In the method for manufacturing non-oriented electrical steel sheets according to the present embodiment, a continuous annealing furnace is used for finish annealing. The finish annealing step is an important step for controlling the average crystal grain size of the base metal.
[0058]
　Here, the finishing annealing conditions are a mixed atmosphere of H 2 and N 2 (that is, a soaking temperature of 850 to 1050 ° C., a soaking time of 1 to 300 s, and a proportion of H 2 of 10 to 100% by volume ). , H 2 + N 2 = 100% by volume), and the dew point of the atmosphere is preferably 30 ° C. or lower.
[0059]
　When the soaking temperature is less than 850 ° C., the crystal grain size becomes fine and the iron loss of the non-oriented electrical steel sheet deteriorates, which is not preferable. If the soaking temperature exceeds 1050 ° C., the strength of the non-oriented electrical steel sheet becomes insufficient and the iron loss also deteriorates, which is not preferable. The soaking temperature is more preferably 875 to 1025 ° C, even more preferably 900 to 1000 ° C. If the soaking time is less than 1 s, the crystal grains cannot be sufficiently coarsened. If the soaking time exceeds 300 s, the manufacturing cost will increase. The proportion of H 2 in the atmosphere is more preferably 15-90% by volume. The dew point of the atmosphere is more preferably 10 ° C. or lower, and even more preferably 0 ° C. or lower.
[0060]
　
　After the finish annealing, an insulating film forming step is carried out as necessary. Here, the method for forming the insulating coating is not particularly limited, and the treatment liquid may be applied and dried by a known method using a treatment liquid for forming a known insulating coating as shown below. .. Examples of known insulating coatings include composite insulating coatings mainly composed of inorganic substances and further containing organic substances. The composite insulating film is mainly composed of at least one of a metal salt such as a chromic acid metal salt and a phosphate metal salt, or an inorganic substance such as colloidal silica, a Zr compound, and a Ti compound, and is a fine organic resin particle. Is a dispersed insulating film. In particular, from the viewpoint of reducing the environmental load during manufacturing, which has been in increasing demand in recent years, an insulating coating using a metal phosphate, a Zr or Ti coupling agent as a starting material, or a metal phosphate, Zr or Ti. An insulating coating using a carbonate or ammonium salt of the coupling agent as a starting material is preferably used.
[0061]
　The surface of the base material on which the insulating film is formed may be subjected to any pretreatment such as degreasing treatment with alkali or the like or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid or the like before applying the treatment liquid. The treatment liquid may be applied to the surface of the base material as it is after finish annealing without performing these pretreatments.
Example
[0062]
　Hereinafter, the present invention will be described in more detail with reference to Examples, but the conditions in the Examples are merely examples adopted for confirming the feasibility and effect of the present invention, and the present invention is limited to this Condition Example. It is not something that is done. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.
[0063]
　After heating the slab having the composition shown in Table 1 to 1150 ° C., hot rolling was performed at a finishing temperature of 850 ° C. and a finishing plate thickness of 2.0 mm, and the slab was wound at 650 ° C. to obtain a hot-rolled steel sheet. The obtained hot-rolled steel sheet was subjected to the test No. 1 shown in Table 2. In Nos. 1 to 16, 22, 23, 25 and 26, hot-rolled plates were annealed at 900 ° C. for 50 s in a continuous annealing furnace, and surface scale was removed by pickling. Further, the obtained hot-rolled steel sheet was subjected to the test No. 1 shown in Table 2. In Nos. 17 to 21, after removing the scale on the surface by pickling, hot-rolled plate annealing at 750 ° C. × 10 h was performed in a box annealing furnace. Furthermore, the test Nos. In No. 24, hot-rolled plate was annealed at 1000 ° C. for 50 s in a continuous annealing furnace, and surface scale was removed by pickling. The steel sheet thus obtained was cold-rolled to obtain a cold-rolled steel sheet having a plate thickness of 0.25 mm.
[0064]
　Further, in a mixed atmosphere of H 2 : 30%, N 2 : 70%, and dew point 0 ° C., the annealing temperature: 850 to 1050 ° C. and soaking heat so as to have the average crystal grain size as shown in Table 2 below. Time: Within the range of 1 to 300 s, the finish annealing conditions were changed and annealing was performed. Specifically, when the average crystal grain size was controlled to be large, the finish annealing temperature was made higher and / or the soaking time was made longer. When the average crystal grain size was controlled to be small, the opposite was true. Then, an insulating film was applied to produce a non-oriented electrical steel sheet, which was used as a test material.
[0065]
　Further, the above-mentioned insulating film is coated with an insulating film composed of aluminum phosphate and an acrylic-styrene copolymer resin emulsion having a particle size of 0.2 μm so as to have a predetermined adhesion amount, and baked in the air at 350 ° C. Formed.
[0066]
[table 1]

[0067]
[Table 2]

[0068]
　For each of the obtained test materials, the average crystal grain size of the base material was measured according to JIS G 0551 (2013) “Steel-Crystal Particle Size Microscopic Test Method”. In addition, Epstein test pieces were collected from the rolling direction and width direction of each test material, and the magnetic characteristics (iron loss W 10/400 and magnetic flux density B 50 ) were determined by the Epstein test in accordance with JIS C 2550-1 (2011). evaluated. When the iron loss W 10/400 was 13.0 W / kg or less and the magnetic flux density B 50 was 1.60 T or more, it was judged to be acceptable as having excellent magnetic characteristics. If this condition is not satisfied, it is judged to be inferior in magnetic characteristics and rejected. The pass condition was set because the plate thickness of each test material was more than 0.20 mm and 0.25 mm or less.
[0069]
　Further, from each test material, JIS No. 5 tensile test pieces were taken according to JIS Z 2241 (2011) so that the longitudinal direction coincided with the rolling direction of the steel sheet. Then, a tensile test was performed using the above test piece according to JIS Z 2241 (2011), and the tensile strength was measured. When the tensile strength was 600 MPa or more, it was judged to be acceptable as having high strength. When the tensile strength was less than 600 MPa, it was judged to be inferior in strength and rejected.
[0070]
　The results of the Epstein test and the tensile test are also shown in Table 2.
[0071]
　Test No. in which the chemical composition of the steel sheet and the average grain size after finish annealing satisfy the provisions of the present invention. In 2, 4, 5, 7, 10, 12, 15, 16, 18 to 20, 25 and 26, the iron loss is low, the magnetic flux density is high, and the tensile strength is as high as 600 MPa or more. I found out.
[0072]
　On the other hand, Test No. which is a comparative example. In 1, 3, 6, 8, 9, 11, 13, 14, 17, 21 to 24, at least one of the magnetic properties and the tensile strength is inferior, or the toughness is significantly deteriorated, which makes the production difficult.
[0073]
　Specifically, the test No. In No. 1, since the Si content was lower than the specified range, the tensile strength was inferior. In addition, Test No. in which the chemical composition satisfies the regulation. Comparing 3 to 6, the test No. In No. 3, the average crystal grain size was smaller than the specified range, so that the iron loss was inferior. In No. 6, the tensile strength was inferior because the average crystal grain size was larger than the specified range.
[0074]
　In addition, the test No. In No. 8, the Si content exceeded the specified range, and Test No. In 13, sol. The Al content exceeded the specified range, and Test No. In No. 22, since the P content exceeded the specified range, the toughness deteriorated and fracture occurred during cold rolling, and the average crystal grain size, tensile strength, and magnetic properties could not be measured.
　Test No. In No. 11, since the equation (i) was not satisfied, the iron loss and the tensile strength were inferior.
[0075]
　Test No. In 9, sol. The Al content was below the specified range, and Test No. In No. 14, since the S content exceeded the specified range, the iron loss was inferior. Then, the test No. in which the chemical composition satisfies the regulation. Comparing 17 to 21, Test No. In No. 17, the average crystal grain size was smaller than the specified range, so that the iron loss was inferior. In No. 21, the tensile strength was inferior because the average crystal grain size was larger than the specified range.
[0076]
　Test No. In 23 and 24, since the Si content was lower than the specified range, a tensile strength of 600 MPa or more could be obtained by setting the average crystal grain size lower than the specified range, but the iron loss was inferior.
Industrial applicability
[0077]
　As described above, according to the present invention, a non-oriented electrical steel sheet having high strength and excellent magnetic properties can be obtained.
The scope of the claims
[Claim 1]
　The chemical composition of the base
　metal is C: 0.0050% or less,
　Si: 3.7% or more and 5.0% or less,
　Mn: 0.2% or more and 1.5% or less,
　sol. .. Al: 0.05 to 0.45%,
　P: 0.030% or less,
　S: 0.0030% or less,
　N: 0.0030% or less,
　Ti: less than 0.0050%,
　Nb: less than 0.0050% ,
　Zr: less than 0.0050%,
　V: less than 0.0050%,
　Cu: less than 0.200%,
　Ni: less than 0.500%,
　Sn: 0 to 0.100%,
　Sb: 0 to 0.100% , And the
　balance: Fe and impurities, which
　satisfy the following formula (i) , and
　the average crystal grain size of the base metal is more than 40 μm and 120 μm or less
　.
　Si + sol. Al + 0.5 × Mn ≧ 4.3 (i)
　However, the element symbol in the above formula is the content of each element in mass%.
[Claim 2]

　The non-oriented electrical steel sheet according to claim 1, 　which has a tensile strength of 600 MPa or more .
[Claim 3]
　1 or claim 1 　, 　wherein the chemical composition contains one or two selected from
　Sn: 0.005 to 0.100% and
　Sb: 0.005 to 0.100% in mass%. The non-directional electromagnetic steel plate according to claim 2.

[Claim 4]

　The non-oriented electrical steel sheet according to any one of claims 1 to 3 　, which has an insulating film on the surface of the base material .