Non-oriented electromagnetic steel sheet

Abstract

To provide a non-oriented electrical steel sheet with low stress sensitivity and excellent magnetic properties in the direction of 45°.SOLUTION: A non-oriented electromagnetic steel sheet has a prescribed chemical composition satisfying (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≥1.50%. When Ahkl-uvw is defined to represent an area ratio to the entire field view, of crystal particles in a {hkl}<uvw> orientation obtained by measuring, by a SEM-EBSD, a face parallel to a rolled face with a depth, a half of a sheet thickness, from a surface thereof, A411-011 is 15.0% or more. B50D, which is an average magnetic flux density in a direction of 45 degrees and a direction of 135 degrees with respect of a rolling direction, is 1.70 T or more. W10D / 400D, which is an average core loss in the direction of 45 degrees and the direction of 135 degrees with respect to the rolling direction, is 12.0 W / kg or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet. [Background technology]

[0002] Electrical steel sheets are used as materials for the cores (iron cores) of electrical equipment. Examples of electrical equipment include drive motors installed in automobiles, various compressor motors such as those used in air conditioners and refrigerators, and even household or industrial generators. These electrical equipment require high energy efficiency, compactness, and high output. Therefore, the electrical steel sheets used as cores of electrical equipment must have low iron loss and high magnetic flux density. Iron loss can be reduced by reducing the thickness of the plate, but this reduces the production efficiency of motors, so there has been a demand for a method to reduce iron loss while maintaining the plate thickness. Texture control is one solution to these problems and to obtain low iron loss and high magnetic flux density. To date, technology has been proposed to develop a texture (α-fiber) that has an easy axis of magnetization within the steel sheet plane, is advantageous for improving magnetic properties, and can be relatively easily increased in concentration through rolling processes in hot rolling and cold rolling, which are essential processes in steel sheet manufacturing. Specifically, <110> A texture is formed whose direction is approximately parallel to the rolling direction (RD).

[0003] For example, Patent Document 1 describes that after hot rolling, the steel sheet is cooled to 250°C or less at a cooling rate of 200°C / sec or more within 3 seconds, that no annealing is performed between hot rolling and cold rolling, and that the cumulative reduction in cold rolling is 88% or more. <011> It is said that it is possible to manufacture magnetic steel sheets that are concentrated in a certain direction.

[0004] On the other hand, a technique for developing the {411} orientation, which is rotated 20° from the {100} orientation, has also been proposed to improve magnetic properties. Patent Documents 2 to 8 all disclose techniques for developing the {411} orientation, and describe optimizing the grain size in hot-rolled sheets and strengthening the α-fiber in the texture of the hot-rolled sheets.

[0005] Specifically, Patent Document 2 describes cold rolling a hot-rolled sheet in which the concentration of the {211} orientation is higher than that of the {411} orientation, and the cumulative reduction in the cold rolling is set to 80% or more. This makes it possible to produce an electrical steel sheet in which the {411} orientation is concentrated on the steel sheet surface.

[0006] Patent Documents 3 and 4 also describe that the slab heating temperature is 700°C or higher and 1150°C or lower, the start temperature of finish rolling is 650°C or higher and 850°C or lower, the end temperature of finish rolling is 550°C or higher and 800°C or lower, and further, the cumulative reduction rate in cold rolling is 85 to 95%. This makes it possible to produce electrical steel sheets with grains concentrated in the {100} and {411} orientations on the steel sheet surface.

[0007] Patent Document 5 describes a method for producing non-oriented electrical steel sheets in which α-fibers are developed in the vicinity of the surface layer of a hot-rolled coil steel sheet by strip casting or the like, and the {h11}<1 / h12> orientation, especially {100} <012> ~{411} <148> It is stated that the orientation is recrystallized.

[0008] Patent Document 6 describes a method in which the {100} plane intensity of the inverse pole figure is 2.4 or more, and the {100} orientation (within a tolerance of 20°) measured by electron backscatter diffraction (EBSD) is In a non-oriented electrical steel sheet having an area ratio of 18% or more of crystal grains with a crystal orientation relative to the entire field of view, an average crystal grain size of 20 μm or less, a sheet thickness of 0.10 mm to 0.30 mm, and a Q of 2.00 or more, expressed as Q = [Si] - 0.5 × [Mn] where [Si] is the Si content (mass%) and [Mn] is the Mn content (mass%), the invention discloses that, in order to improve magnetic properties and achieve low core loss and high magnetic flux density, the probability of the existence of {411} oriented grains, which are advantageous for magnetic properties, is increased. Patent Document 6 discloses that when α-fibers are grown to the vicinity of the surface layer of a hot-rolled coil steel sheet, the {h11}<1 / h12> orientation, especially {100} <012> ~{411} <148> It is stated that the orientation is recrystallized.

[0009] Patent Document 7 describes a steel sheet having an α-γ transformation system and a chemical composition, in mass%, of Si: 2.0 to 4.5%, Mn: more than 3.0 to 5.0%, and the balance: Fe, optional elements, and impurity elements. <011> The X-ray random intensity ratio of the crystal orientation is 0 to 15.0, and {411} <148> A non-oriented electrical steel sheet is disclosed in which the X-ray random intensity ratio of the crystal orientation is 4.0 to 200.

[0010] Patent Document 8 describes a non-oriented electrical steel sheet having an inverse pole figure {100} plane intensity of 2.4 or more, an area ratio of crystal grains having a crystal orientation of {100} orientation (within a tolerance of 20°) to the entire field of view of 18% or more when measured by electron backscatter diffraction (EBSD), an average crystal grain size of 55 μm to 200 μm, a sheet thickness of 0.10 mm to 0.30 mm, a layer containing Cr oxide having a thickness of 0.01 μm to 0.5 μm on the surface of the steel sheet, and a ratio of 10.00%≦2[Si]+2[Al]+[Cr]<15.00% and (2[Al]+[Cr]) / 2[Si]−10t 2It has been disclosed that in non-oriented electrical steel sheets satisfying the condition of 0.35, in order to achieve low core loss and high magnetic flux density, the probability of the existence of {411} oriented grains, which are advantageous for magnetic properties, is increased. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2017-145462 [Patent Document 2] Patent No. 4218077 [Patent Document 3] Patent No. 5256916 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-111658 [Patent Document 5] Japanese Patent Application Publication No. 2019-183185 [Patent Document 6] Japanese Patent Publication No. 2020-76138 [Patent Document 7] Japanese Patent Application Publication No. 2020-100860 [Patent Document 8] Japanese Patent Application Publication No. 2020-139198 Summary of the Invention [Problem to be solved by the invention]

[0012] The inventors of the present invention have studied the above technology and have found that <011> It has been found that if one attempts to improve the magnetic properties by strengthening the orientation, rapid cooling immediately after hot rolling is required, which poses a problem of high manufacturing load. <011> It was found that when orientation-strengthened steel sheets are used as materials for crimped cores, the core properties expected from the material may not be obtained. <011> It was thought that the orientation affected the change in magnetic properties in response to stress, specifically the deterioration of magnetic properties (stress sensitivity) when compressive stress was applied.

[0013] In addition, although the techniques disclosed in Patent Documents 2 to 8 develop the {411} orientation, the in-plane orientation <011> It was found that the magnetic properties at 45° from the rolling direction of the steel sheet, which is a characteristic of α-fiber, were not sufficiently high. <011> The lack of alignment, i.e., the large deviation from the α-fiber, is a factor that inhibits the accumulation of the {411} plane orientation, and may be the reason why the magnetic properties are not sufficiently improved.

[0014] In view of the above problems, the present invention aims to provide a non-oriented electrical steel sheet that has low stress sensitivity and excellent magnetic properties in the 45° direction, while using a manufacturing method that does not impose a heavy manufacturing load. [Means for solving the problem]

[0015] The inventors focused on the {411} plane, which is a plane orientation rotated 20° from the {100} plane, and further investigated. <011> It was discovered that by developing this special orientation, the magnetic properties (especially the magnetic properties in the direction at 45° from the rolling direction) can be further improved.

[0016] Based on this finding, the present inventors have conducted further intensive research and have come up with the following aspects of the invention.

[0017] [1] In mass%, C: 0.0100% or less, Si: 1.50% to 4.00%, sol.Al: 0.0001% to 1.00%, S: 0.0100% or less, N: 0.0100% or less, one or more selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total, Co: 0.000% to 1.000%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, P: 0.000% to 0.400%, and Mg, Ca, Sr, Ba, Ce, La, Nd, P The alloy contains one or more elements selected from the group consisting of r, Zn, and Cd in a total amount of 0.0000% to 0.0100%, and when the Mn content is [Mn], the Ni content is [Ni], the Cu content is [Cu], the Si content is [Si], the sol. Al content is [sol. Al], and the P content is [P], the alloy has a chemical composition that satisfies the following formula (1), with the balance consisting of Fe and impurities, and the {hkl} when measured by SEM-EBSD on a plane parallel to the rolled surface at a depth of 1 / 2 the plate thickness from the surface. <uvw>When the area ratio of the grain orientation to the entire field of view is expressed as Ahkl-uvw, A411-011 is 40.0 % or more, A non-oriented electrical steel sheet having an average magnetic flux density B50D in the directions of 45 degrees and 135 degrees relative to the rolling direction of 1.70 T or more, and an average iron loss W10D / 400D in the directions of 45 degrees and 135 degrees relative to the rolling direction of 12.0 W / kg or less. (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≧1.50% ···(1) [2] The non-oriented electrical steel sheet according to [1], wherein, when the average magnetic flux densities in the 0 degree direction and the 90 degree direction relative to the rolling direction are defined as B50L, the B50D and the B50L satisfy the following formula (2): B50D / B50L≧1.05 (2) [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a non-oriented electrical steel sheet that has low stress sensitivity and excellent magnetic properties in the 45° direction. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a non-oriented electrical steel sheet according to one embodiment of the present invention (non-oriented electrical steel sheet according to this embodiment) and a preferred method for producing the same will be described.

[0020] [Non-oriented electrical steel sheet] The non-oriented electrical steel sheet according to this embodiment is having a predetermined chemical composition, {hkl} when measured by SEM-EBSD on a plane parallel to the rolling surface at a depth of 1 / 2 the plate thickness from the surface <uvw>When the area ratio of the orientation grains to the entire field of view is expressed as Ahkl-uvw, A411-011 is 15.0% or more, The average magnetic flux density B50D in the 45 degree and 135 degree directions relative to the rolling direction is 1.70 T or more, The average iron loss W10D / 400D in the directions of 45 degrees and 135 degrees relative to the rolling direction is 12.0 W / kg or less.

[0021] <Chemical composition> First, the chemical composition of the non-oriented electrical steel sheet according to this embodiment will be described. In the following description, "%," which is the unit of content of each element, means "% by mass" unless otherwise specified. Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits.

[0022] The non-oriented electrical steel sheet according to this embodiment has a chemical composition in which ferrite-austenite transformation (hereinafter referred to as α-γ transformation) can occur to some extent (a chemical composition in which a certain amount of γ is produced when heated, even if the entire structure is not transformed into γ), and contains C: 0.0100% or less, Si: 1.50% to 4.00%, sol.Al: 0.0001% to 1.00%, S: 0.0100% or less, N: 0.0100% or less, and an amount selected from the group consisting of Mn, Ni, and Cu. The alloy has a chemical composition comprising a total of 2.50% to 5.00% of one or more elements selected from the group consisting of Co, 0.000% to 1.000%, Sn, 0.000% to 0.400%, Sb, 0.000% to 0.400%, P, and a total of 0.0000% to 0.0100% of one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd, with the balance being Fe and impurities. Furthermore, the contents of Mn, Ni, Cu, Si, sol. Al, and P satisfy the specified conditions described below. Examples of impurities include those contained in raw materials such as ore and scrap, and those contained during the manufacturing process.

[0023] (C: 0.0100% or less) C is an element that increases iron loss and causes magnetic aging by precipitating fine carbides and inhibiting grain growth. Therefore, the lower the C content, the better. This phenomenon becomes more pronounced when the C content exceeds 0.0100%. For this reason, the C content is set to 0.0100% or less. The C content is preferably 0.0050% or less, and more preferably 0.0025% or less. There is no particular lower limit for the C content, but considering the cost of decarburization during refining, the C content is preferably 0.0005% or more.

[0024] (Si: 1.50% to 4.00%) Silicon is an element that increases electrical resistance, reduces eddy current loss, reduces iron loss, and increases the yield ratio, improving the punching workability of iron cores. If the Si content is less than 1.50%, these effects cannot be fully achieved. Therefore, the Si content is set to 1.50% or more. On the other hand, if the Si content exceeds 4.00%, the magnetic flux density decreases, punching workability decreases due to an excessive increase in hardness, and cold rolling becomes difficult. Therefore, the Si content is set to 4.00% or less.

[0025] (sol.Al:0.0001%~1.00%) Sol. Al is an element that increases electrical resistance, reduces eddy current loss, and reduces iron loss. Sol. Al also contributes to improving the relative magnitude of magnetic flux density B50 relative to saturation magnetic flux density. Here, magnetic flux density B50 is the magnetic flux density in a magnetic field of 5000 A / m. If the sol. Al content is less than 0.0001%, these effects cannot be fully obtained. Furthermore, Al also has the effect of promoting desulfurization in steelmaking. Therefore, the sol. Al content is set to 0.0001% or more. The sol. Al content is preferably 0.001% or more, more preferably 0.10% or more. On the other hand, if the sol. Al content exceeds 1.00%, the magnetic flux density decreases, and therefore the sol. Al content is set to 1.00% or less.

[0026] (S:0.0100% or less) S is not an essential element, but is contained in steel as an impurity, for example. S precipitates as fine MnS and inhibits recrystallization and grain growth during annealing. Therefore, the lower the S content, the better. Such an increase in iron loss and a decrease in magnetic flux density due to the inhibition of recrystallization and grain growth become significant when the S content exceeds 0.0100%. For this reason, the S content is set to 0.0100% or less. There is no particular lower limit for the S content, but considering the cost of desulfurization treatment during refining, the S content is preferably set to 0.0003% or more.

[0027] (N:0.0100% or less) N is an element that deteriorates magnetic properties through the formation of fine precipitates such as TiN and AlN. Therefore, the lower the N content, the better. Such deterioration of magnetic properties becomes significant when the N content exceeds 0.0100%, so the N content is set to 0.0100% or less. There is no particular lower limit for the N content, but considering the cost of denitrification treatment during refining, the N content is preferably set to 0.0010% or more.

[0028] (One or more selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total) These elements are necessary for causing the α-γ transformation. The non-oriented electrical steel sheet according to this embodiment contains at least one of these elements in a total amount of 2.50% or more. On the other hand, if the total content of these elements exceeds 5.00%, not only will the cost increase, but the magnetic flux density may also decrease. Therefore, the total content of at least one of these elements is set to 5.00% or less.

[0029] There are no limitations on the respective contents of Mn, Ni, and Cu, but from the viewpoint of resistivity, the Mn content is preferably 1.50% or more.

[0030] Furthermore, the following condition is also satisfied in order to cause the α-γ transformation and obtain good magnetic properties: When the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], the sol. Al content (mass%) is [sol. Al], and the P content (mass%) is [P], the following formula (1) is satisfied: (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≧1.50% ···(1) If the above formula (1) is not satisfied, the α-γ transformation will not occur, or even if it does occur, the transformation point will be high, and therefore sufficient magnetic flux density will not be obtained even if the manufacturing method described below is applied.

[0031] The chemical composition of the non-oriented electrical steel sheet according to this embodiment basically contains the above elements, with the balance being Fe and impurities (impurities other than those mentioned above). However, instead of a portion of the balance Fe, Co, Sn, Sb, P, Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd may be contained in the ranges shown below. These elements do not necessarily have to be contained, so the lower limit is 0%. Furthermore, it is permissible for these elements to be contained as impurities without being intentionally added.

[0032] (Co: 0.000% to 1.000%) Co is an element that increases the magnetic flux density, and therefore may be contained as needed. On the other hand, excessive Co content increases costs, so the Co content is set to 1.000% or less.

[0033] (Sn:0.000%~0.400%, Sb:0.000%~0.400%) Sn and Sb are elements that improve the texture after cold rolling and recrystallization, thereby increasing the magnetic flux density. Therefore, these elements may be added as needed. To impart further effects such as magnetic properties, it is preferable to add one or more elements selected from the group consisting of 0.020% to 0.400% Sn and 0.020% to 0.400% Sb. On the other hand, excessive content of these elements makes the steel embrittle, so the Sn content and Sb content are both set to 0.400% or less.

[0034] (P: 0.000% to 0.400%) P is an element that is effective in ensuring the hardness of the steel sheet after recrystallization. P also has a favorable effect on magnetic properties. Therefore, P may be added. To obtain these effects, the P content is preferably 0.020% or more. On the other hand, excessive P embrittles the steel, so the P content is set to 0.400% or less.

[0035] (One or more selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.0000% to 0.0100% in total) Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd are elements that react with S in molten steel during casting to form precipitates of sulfides, oxysulfides, or both. Hereinafter, Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd may be collectively referred to as "coarse precipitate-forming elements." The particle size of the precipitates of the coarse precipitate-forming elements is approximately 1 μm to 2 μm, which is much larger than the particle size (approximately 100 nm) of fine precipitates such as MnS, TiN, and AlN. Therefore, these fine precipitates adhere to the precipitates of the coarse precipitate-forming elements and are less likely to inhibit recrystallization and grain growth during annealing, such as intermediate annealing. To fully obtain these effects, the total content of these elements is preferably 0.0005% or more, and more preferably 0.0010% or more. On the other hand, if the total content of these elements exceeds 0.0100%, the total amount of sulfides or oxysulfides, or both, becomes excessive, which inhibits recrystallization and grain growth during annealing such as intermediate annealing. Therefore, the total content of coarse precipitate forming elements is set to 0.0100% or less.

[0036] The chemical composition is determined by the following method. The chemical composition can be measured using standard steel analysis methods. For example, the chemical composition can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, the chemical composition can be determined by measuring test pieces taken from the steel plate using a specified measuring device under conditions based on a pre-created calibration curve. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method. If the non-oriented electrical steel sheet has an insulating coating on the surface, it may be subjected to analysis after mechanically removing the insulating coating using a minitor or the like.

[0037] <Collective organization> In the non-oriented electrical steel sheet according to this embodiment, the texture is controlled when a surface parallel to the rolled surface at a depth of half the sheet thickness from the surface (if an insulating coating is present on the surface, this refers to the surface of the steel sheet (base steel sheet) excluding the insulating coating; the same applies below) is measured using a scanning electron microscope with electron backscatter diffraction (SEM-EBSD). Specifically, {hkl} obtained by the above measurement <uvw>The area ratio of grains with orientation (within 10° tolerance) to the entire field of view is expressed as Ahkl-uvw. <011> The percentage of the total amount of the surplus (sometimes referred to as the "income tax rate") must be 15.0% or more. <011> If the ratio is less than 15.0%, excellent magnetic properties cannot be obtained. <011> The ratio is preferably 25.0% or more, more preferably 30.0% or more, further preferably 35.0% or more, and even more preferably 40.0% or more. There is no particular upper limit, but it may be 80.0% or less from the viewpoint of production load.

[0038] Furthermore, in the non-oriented electrical steel sheet according to this embodiment, it is preferable that the proportion of the {111} orientation is small. The {111} orientation is an orientation that hinders in-plane magnetization, and excellent magnetic properties can be obtained by keeping the proportion of the {111} orientation (sometimes referred to as the {111} ratio) at 10.0% or less. The {111} ratio is preferably 8.0% or less, more preferably 7.0% or less, and even more preferably 5.0% or less. There is no particular lower limit, but it may be 1.0% or more from the viewpoint of production load.

[0039] The area ratio of specific orientation grains in the non-oriented electrical steel sheet according to this embodiment can be measured by the following method. Specifically, the area ratio of specific orientation grains is measured by extracting the specific orientation of interest from a measurement area observed under the following measurement conditions using a scanning electron microscope (SEM) equipped with electron backscattering diffraction (EBSD) using OIM Analysis 7.3 (manufactured by TSL). (The tolerance is set to 10°, hereinafter referred to as "within 10° tolerance"). The extracted area is divided by the area of ​​the measurement area to obtain a percentage. This percentage is the area ratio of specific orientation grains. In this embodiment, "{hkl} <uvw>The area ratio of the crystal grains having a crystal orientation of {hkl} (within a tolerance of 10°) to the measured area, and the area ratio of the crystal grains having a crystal orientation of {hkl} (within a tolerance of 10°) to the measured area are simply referred to as "{hkl} <uvw>It is sometimes called the "{hkl} ratio" or "{hkl} ratio." The tolerance for describing the crystal orientation is within 10°.

[0040] The details of the measurement conditions for determining the area ratio of each orientation grain are as follows. Measurement equipment: SEM model number "JSM-6400 (manufactured by JEOL)", EBSD detector model number "HIKARI (manufactured by TSL)", or a similar device is used. Step spacing: 5.0μm ·Magnification: 100x Measurement target: Surface parallel to the rolled surface at a depth of 1 / 2 the plate thickness from the surface Measurement area: Rectangular area of ​​1000 μm or more x 1000 μm or more

[0041] <Average grain size> In the non-oriented electrical steel sheet according to this embodiment, if the average grain size is too small without the grains being coarsened, there is a concern that iron loss may increase. On the other hand, if the grains are excessively coarsened and the average grain size is too large, not only may workability be impaired but eddy current loss may also be impaired. Therefore, the average grain size of the non-oriented electrical steel sheet is preferably set to 50 μm to 150 μm. The average crystal grain size can be measured, for example, at any cross section by the cutting method of JIS G0551 (2020).

[0042] <Thickness> The thickness of the non-oriented electrical steel sheet according to this embodiment is not particularly limited. Usually, as the sheet thickness decreases, the iron loss decreases, but the magnetic flux density also decreases. In light of this, if the sheet thickness is 0.25 mm or more, the iron loss decreases and the magnetic flux density increases. Furthermore, if the sheet thickness is 0.50 mm or less, low iron loss can be maintained. Therefore, the sheet thickness of the non-oriented electrical steel sheet according to this embodiment is preferably 0.25 to 0.50 mm, and more preferably 0.30 to 0.50 mm.

[0043] <Magnetic properties> The non-oriented electrical steel sheet according to this embodiment has a controlled chemical composition and texture, and has an average magnetic flux density B50D of 1.70 T or more in the directions at 45 degrees and 135 degrees relative to the rolling direction, and an average iron loss W10D / 400D of 12.0 W / kg or less in the directions at 45 degrees and 135 degrees relative to the rolling direction. In general, the magnetic properties of non-oriented electrical steel sheets are often evaluated as the average value in the rolling direction (coil longitudinal direction, L direction) and the perpendicular direction (coil width direction, C direction). This is because the in-plane anisotropy of the sheet is taken into consideration, and many conventional non-oriented electrical steel sheets with low magnetic anisotropy have been proposed. However, these conventional non-oriented electrical steel sheets often have inferior magnetic properties in the direction at 45 degrees from the rolling direction (diagonal direction of the coil) compared to the two directions (L and C directions). This posed a challenge when using them as split cores, which are designed so that the main magnetization direction of the core is 45 degrees from the rolling direction of the steel sheet. In contrast, the non-oriented electrical steel sheet according to this embodiment has excellent magnetic properties in the 45-degree direction and the 135-degree direction (that is, directions of ±45 degrees from the rolling direction), as described above. Therefore, the non-oriented electrical steel sheet according to this embodiment is particularly suitable for use as a split core designed so that the main magnetization direction of the core is at an angle of 45° from the rolling direction of the steel sheet, and further suitable for split cores for drive motors of electric vehicles or hybrid vehicles, which are used in the high frequency range of 1000 Hz or more. B50D is preferably 1.73T or more, more preferably 1.76T or more. Also, W10D / 400D is preferably 11.5 W / kg or less.

[0044] In the non-oriented electrical steel sheet according to this embodiment, when the average magnetic flux densities in the directions of 0 degree and 90 degrees relative to the rolling direction are defined as B50L, B50D and B50L preferably satisfy the following formula (2), making the steel sheet more suitable for the above-mentioned applications. B50D / B50L≧1.05 (2)

[0045] Furthermore, the non-oriented electrical steel sheet according to this embodiment has a controlled chemical composition and texture as described above, and the deterioration of magnetic properties (stress sensitivity) when a compressive stress is applied is small. The stress sensitivity can be evaluated, for example, by the iron loss deterioration rate calculated from the iron loss W10 / 50 (45° direction) without stress and the iron loss W10 / 50 (45° direction) under a compressive stress of 10 MPa.

[0046] [Manufacturing method] Next, an example of a method for manufacturing a non-oriented electrical steel sheet according to this embodiment will be described. The non-oriented electrical steel sheet according to this embodiment can achieve its effects as long as it has the above-mentioned characteristics, regardless of the manufacturing method. However, it is preferable to use a manufacturing method including a hot rolling step, a cooling step, a cold rolling step, an intermediate annealing step, a second cold rolling (hereinafter referred to as a skin-pass rolling step), and a finish annealing step, which will be described later, because this method can be stably obtained. Preferred conditions for each step will be described below. For conditions not described, known conditions can be applied. Hereinafter, in this embodiment, the Ar3 temperature, Ar1 temperature, and Ac1 temperature (all in ° C. units) are determined by the following method. The Ar3 temperature and Ar1 temperature are determined from the change in thermal expansion of the steel material (steel plate) during cooling at an average cooling rate of 1°C / s, and the Ac1 temperature is determined from the change in thermal expansion of the steel material (steel plate) during heating at an average heating rate of 1°C / s.

[0047] <Hot rolling process> In the hot rolling process, hot rolling is performed on the steel material satisfying the above-mentioned chemical composition to produce a hot-rolled steel sheet. The hot rolling process includes a heating step and a rolling step.

[0048] The steel material is, for example, a slab produced by normal continuous casting, and steel material having the above-mentioned composition is produced by a well-known method. For example, molten steel is produced in a converter or electric furnace. The produced molten steel is subjected to secondary refining in a degassing facility or the like to produce molten steel having the above-mentioned chemical composition (the chemical composition does not change substantially in subsequent processes). The molten steel is cast into a slab by a continuous casting method or an ingot casting method. The cast slab may be bloomed.

[0049] In the heating process, it is preferable to heat the steel material having the above-mentioned chemical composition to 1000 to 1200°C. Specifically, the steel material is charged into a heating furnace or a soaking furnace and heated in the furnace. The holding time at the above heating temperature in the heating furnace or the soaking furnace is not particularly limited, but is, for example, 30 to 200 hours.

[0050] In the rolling process, the steel material heated in the heating process is subjected to multiple passes of rolling to produce a hot-rolled steel sheet. Here, "pass" means that the steel sheet passes through one rolling stand having a pair of work rolls and is subjected to rolling reduction. Hot rolling may be performed, for example, by tandem rolling using a tandem rolling mill including multiple rolling stands arranged in a row (each rolling stand having a pair of work rolls), or by reverse rolling using a pair of work rolls. From the viewpoint of productivity, it is preferable to perform multiple rolling passes using a tandem rolling mill.

[0051] The rolling process (rough rolling and finish rolling) is preferably carried out at a temperature in the γ range (Ar3 temperature or higher). In other words, hot rolling is preferably carried out so that the temperature at the time of passing the final pass of finish rolling (finish rolling temperature FT (°C)) is Ar3 temperature or higher.

[0052] The finish rolling temperature FT means the surface temperature (°C) of the steel sheet at the exit side of the rolling stand where the final pass is performed during the rolling process in the hot rolling step. The finish rolling temperature FT can be measured, for example, by a thermometer installed at the exit side of the rolling stand where the final pass is performed. For example, when the entire length of the steel sheet is divided into 10 equal sections in the rolling direction, the finish rolling temperature FT means the average value of the temperature measurement results for the sections excluding one section at the front end and one section at the rear end.

[0053] <Cooling process> In the cooling process, the steel sheet (hot-rolled steel sheet) is cooled after the hot rolling process (after the completion of finish rolling). This cooling transforms austenite to ferrite, resulting in high strain and moderately fine crystal grains. The cooling conditions are preferably such that cooling begins 0.10 seconds or more after the final pass of finish rolling (after 0.10 seconds or more have elapsed), and the surface temperature of the hot-rolled steel sheet is cooled to 300°C or higher and Ar1 temperature or lower after 3 seconds (no immediate rapid cooling). Avoiding immediate rapid cooling in this way eliminates the need for special rapid cooling equipment, which is also beneficial in terms of manufacturing (cost). Furthermore, when immediate rapid cooling is performed, the texture of the hot-rolled steel sheet becomes a structure in which unrecrystallized austenite is transformed, and the structure after the subsequent finish annealing has a {100} <011> On the other hand, if rapid cooling is not performed immediately after the initial annealing, the partially recrystallized austenite will be transformed into a structure, and the structure after the subsequent final annealing will have a texture concentrated in the {411} <011> It is assumed that the particles tend to accumulate in the {411} direction. <011> In order to increase the yield, it is important to transform the partially recrystallized austenite, and it is preferable not to perform rapid cooling immediately after the transformation. The cooling conditions are preferably such that the average grain size of the hot-rolled steel sheet before cold rolling is 3 to 10 μm. If the grain size is not excessively refined and cold rolling is then performed, α-fiber will develop after intermediate annealing, and {411} α-fiber, which is not normally developed after the subsequent skin pass and finish annealing, will develop. <011> On the other hand, if the grains become too coarse, it becomes difficult to develop α-fiber after cold rolling and intermediate annealing, and the desired {411} <011> The rate may not be available. In order to make the average grain size of the hot-rolled steel sheet before cold rolling 3 to 10 μm, the temperature should be lowered to Ar1 temperature or lower within 3 seconds after passing the final pass of finish rolling. On the other hand, if the cooling stop temperature is lower than 300°C, there is a concern that the average grain size of the hot-rolled steel sheet will be excessively refined. Therefore, it is preferable to set the cooling stop temperature to 300°C or higher.

[0054] The temperature of the hot-rolled steel sheet (particularly the finish rolling temperature), and the surface temperature of the hot-rolled steel sheet 3 seconds after passing the final pass of finish rolling, are measured by the following method. In a hot rolling equipment line used for manufacturing non-oriented electrical steel sheets, a cooling device and a conveying line (e.g., conveying rollers) are arranged downstream of the hot rolling mill, a thermometer for measuring the surface temperature of the hot-rolled steel sheet is arranged at the exit side of the rolling stand that performs the final pass of the hot rolling mill, and in the case where multiple thermometers are also arranged along the conveying line on the conveying rollers arranged downstream of the rolling stand, the hot rolling temperature and the surface temperature of the hot-rolled steel sheet 3 seconds after passing through the final pass of finish rolling can be measured by the thermometer arranged in the hot rolling equipment line. Cooling is performed using a cooling device arranged downstream of the rolling stand that performs the final pass. A plurality of water cooling devices are generally arranged, and a temperature gauge is arranged at the inlet side of each water cooling device. The cooling device may be, for example, a well-known water cooling device or a well-known forced air cooling device. Preferably, the cooling device is a water cooling device. The cooling liquid of the water cooling device may be water or a mixed fluid of water and air.

[0055] <Cold rolling process> In the cold rolling process, the hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet. In order to develop α-fiber after cold rolling, it is preferable that the hot-rolled steel sheet is not subjected to hot-rolled sheet annealing before the cold rolling process. The hot-rolled sheet annealing here means, for example, heat treatment in which the heating temperature is Ac1 temperature or lower and 300°C or higher. Cold rolling may be performed, for example, by tandem rolling using a tandem rolling mill including a plurality of rolling stands arranged in a row (each rolling stand having a pair of work rolls) to perform multiple passes. Alternatively, reverse rolling may be performed using a Sendzimir mill or the like having a pair of work rolls to perform single or multiple passes. From the viewpoint of productivity, it is preferable to perform multiple passes using a tandem rolling mill.

[0056] In cold rolling, cold rolling is performed without annealing treatment during the cold rolling. For example, when performing reverse rolling and performing cold rolling in multiple passes, multiple passes of cold rolling are performed without annealing treatment between passes of cold rolling. If annealing is performed between passes, it is not possible to develop the desired orientation in the process described below. Cold rolling may be performed in a single pass using a reverse rolling mill, or in a tandem rolling mill, cold rolling is performed in multiple passes (passes at each rolling stand) consecutively.

[0057] In this embodiment, in order to develop α-fiber, the reduction rate RR1 (%) in cold rolling is preferably set to 75 to 95%. The reduction rate RR1 is more preferably 78 to 92%. Here, the reduction rate RR1 is defined as follows. Reduction rate RR1 (%) = (1 - thickness after the final pass of cold rolling / thickness before the first pass of cold rolling) x 100

[0058] <Intermediate annealing process> In the intermediate annealing step, intermediate annealing is performed on the steel sheet (cold-rolled steel sheet) after the cold rolling step. In this embodiment, annealing is preferably performed by increasing (heating) the temperature to an annealing temperature (intermediate annealing temperature T1) (°C) between 600°C and the Ac1 temperature at a temperature increase rate of 300°C / sec or more. If the heating rate to the annealing temperature is less than 300°C / s, sufficient recovery will not occur, and there is a concern that the desired texture will not be obtained. The heating rate is preferably 400°C / s or more. A faster heating rate is preferable for texture formation, but a heating rate of more than 2000°C / s requires special equipment and control, which significantly increases costs, so the heating rate may be set to 2000°C / s. A heating rate of 1000°C / s or less is more preferable. The temperature rise rate is calculated by dividing the temperature change from room temperature (for example, 25° C.) to the annealing temperature by the time required for the temperature rise. Furthermore, if the annealing temperature of the intermediate annealing exceeds the Ac1 temperature, part of the structure of the steel sheet will transform to austenite, and due to the change in crystal orientation that accompanies the transformation, the {411} <011> Oriented grains may not grow sufficiently, resulting in an insufficient magnetic flux density. On the other hand, if the intermediate annealing temperature is too low, recrystallization will not occur, and the {411} <011> The oriented grains may not grow sufficiently, and the magnetic flux density may not be high. Therefore, it is preferable that the intermediate annealing temperature T1 (°C) is 600°C or higher. The intermediate annealing temperature T1 (°C) is the sheet temperature (surface temperature) near the extraction port of the annealing furnace. The holding time at the intermediate annealing temperature T1 (°C) in the intermediate annealing step may be a time known to those skilled in the art. The holding time at the intermediate annealing temperature T1 (°C) is, for example, 5 to 60 seconds, but is not limited to this. The atmosphere during intermediate annealing is not particularly limited, but for example, an atmospheric gas (dry) containing 20% ​​by volume of H2 and the remainder of N2 is used. The cooling rate of the steel sheet after intermediate annealing is not particularly limited, but is, for example, 5.0 to 60.0°C / sec.

[0059] <Skin pass rolling process> In the skin pass rolling process, the cold rolled steel sheet after the intermediate annealing process is rolled (cold rolling) at room temperature in the atmosphere. For the skin pass rolling here, for example, a reverse rolling mill typified by the above-mentioned Sendzimir rolling mill or a tandem rolling mill is used. In the skin pass rolling process, rolling is performed without performing an annealing treatment in between. For example, when performing skin pass rolling in multiple passes with reverse rolling, multiple passes are performed without annealing treatment between passes. Skin pass rolling may be performed in only one pass using a reverse rolling mill. Furthermore, when performing skin pass rolling using a tandem rolling mill, rolling is performed continuously in multiple passes (passes at each rolling stand). In this embodiment, after strain is introduced into the steel sheet by hot rolling and cold rolling, the strain introduced into the steel sheet is temporarily reduced by intermediate annealing. Then, skin-pass rolling is performed. By performing intermediate annealing while reducing the excessive strain introduced by cold rolling, preferential recrystallization of {111} grains in the steel sheet surface is suppressed, and {411} <011> The skin-pass rolling process introduces an appropriate amount of strain into each grain in the steel sheet, creating a state in which grain growth due to bulging is more likely to occur in the subsequent finish annealing process. The reduction ratio RR2 in skin-pass rolling is preferably 10 to 15%. If the reduction ratio RR2 is less than 10%, the amount of strain becomes too small, and the finish annealing time required for grain growth due to bulging becomes long. On the other hand, if the reduction ratio RR2 exceeds 15%, the amount of strain becomes too large, and normal grain growth occurs instead of bulging, and the {411} <148> and <112> grows.

[0060] Here, the rolling reduction RR2 is defined as follows. Reduction rate RR2 (%) = (1 - thickness after the final pass of skin pass rolling / thickness before the first pass of skin pass rolling) x 100

[0061] The number of passes in skin pass rolling may be only one pass (that is, only one rolling), or may be multiple passes. The skin-pass rolling performed in this embodiment has a significantly different effect from skin-pass rolling performed after finish annealing. A desired structure can be obtained by performing hot rolling, cooling, cold rolling, intermediate annealing, skin-pass rolling, and finish annealing in this order under predetermined conditions.

[0062] <Finishing annealing process> In the final annealing process, the steel sheet after the skin-pass rolling process is annealed at an annealing temperature T2 (°C) of 750°C or higher and Ac1 temperature or lower for 2 hours or more. If the final annealing temperature T2 (°C) is set to less than 750°C, there is a concern that grain growth due to bulging may not occur sufficiently. In this case, the {411} <011> The degree of orientation concentration decreases. On the other hand, if the final annealing temperature T2 (°C) exceeds the Ac1 temperature, part of the structure of the steel sheet will transform to austenite, and grain growth due to bulging will not occur, resulting in the desired {411} <011> The rate is not available. Furthermore, when the annealing time is less than 2 hours, even if the final annealing temperature T2 (°C) is 750°C or higher and the Ac1 temperature or lower, grain growth due to bulging does not occur sufficiently, and the {411} <011> There is a concern that the degree of orientation integration may decrease. On the other hand, the annealing time for the finish annealing is not particularly limited, but since the effect is saturated even if the annealing time exceeds 10 hours, it may be 10 hours or less.

[0063] The temperature increase rate TR2 up to the final annealing temperature T2 in the final annealing step may be any temperature increase rate known to those skilled in the art, and may be, for example, 40°C / hour or more and less than 200°C / hour, but is not limited to this range.

[0064] The temperature rise rate TR2 is determined by the following method. A thermocouple is attached to a steel sheet having the above chemical composition and obtained by carrying out the above steps from hot rolling to skin pass, to prepare a sample steel sheet. The sample steel sheet to which the thermocouple is attached is heated, and the time from the start of the heating until the temperature reaches the finish annealing temperature T2 is measured. The heating rate TR2 is calculated based on the measured time.

[0065] The atmosphere during the final annealing step is not particularly limited. For example, the atmosphere during the final annealing step may be an atmospheric gas (dry) containing 20% ​​H2 by volume and the remainder N2, or a 100% hydrogen (H2) atmosphere. The cooling rate of the steel sheet after final annealing is not particularly limited. The cooling rate is, for example, 5 to 20°C / second.

[0066] When the core is made from non-oriented electrical steel sheets, the steel sheets are punched and / or laminated. The punching and / or lamination of the steel sheets may be performed after the finish annealing step, or may be performed after the skin pass rolling step and before the finish annealing step. When punching and / or lamination is performed before the finish annealing step, the finish annealing (annealing temperature of 750° C. or higher and Ac1 temperature or lower for 2 hours or longer) may also be performed as stress relief annealing.

[0067] In the manufacturing method of a non-oriented electrical steel sheet according to this embodiment, for example, shot blasting and / or pickling may be performed after the cooling step and before the cold rolling step among the above manufacturing steps. In shot blasting, shot blasting is performed on the hot-rolled steel sheet to destroy and remove scale formed on the surface of the hot-rolled steel sheet. In pickling, pickling treatment is performed on the hot-rolled steel sheet. For example, the pickling treatment uses an aqueous hydrochloric acid solution as the pickling bath. Pickling removes scale formed on the surface of the steel sheet. Shot blasting may be performed after the cooling step and before the cold rolling step, and then pickling may be performed. Alternatively, pickling may be performed after the cooling step and before the cold rolling step, without shot blasting. Alternatively, shot blasting may be performed after the cooling step and before the cold rolling step, without pickling treatment. Shot blasting and pickling are optional steps. Therefore, it is not necessary to perform both the shot blasting step and the pickling step.

[0068] <Insulating film formation process> The method for producing an electrical steel sheet according to this embodiment may further include forming an insulating coating on the surface of the steel sheet (non-oriented electrical steel sheet) after the final annealing step by coating after the final annealing step. The insulating coating forming step is an optional step. Therefore, coating does not necessarily have to be performed after the final annealing.

[0069] The type of insulating coating is not particularly limited. The insulating coating may be made of either an organic or inorganic component, or the insulating coating may contain both an organic and an inorganic component. Examples of inorganic components include dichromate-boric acid, phosphoric acid, and silica-based resins. Examples of organic components include common acrylic, acrylic styrene, acrylic silicone, silicone, polyester, epoxy, and fluorine-based resins. Considering paintability, emulsion-type resins are preferred. An insulating coating that exhibits adhesive properties when heated and / or pressurized may also be applied. Examples of insulating coatings with adhesive properties include acrylic, phenolic, epoxy, and melamine-based resins. [Example]

[0070] Next, the non-oriented electrical steel sheet according to the embodiment of the present invention will be specifically described with reference to examples. The examples shown below are merely examples of the non-oriented electrical steel sheet according to the embodiment of the present invention, and the non-oriented electrical steel sheet according to the present invention is not limited to the examples below.

[0071] Molten steel was cast to produce ingots having the chemical compositions shown in Table 1 (units are mass%, the remainder being Fe and impurities). In Table 1, the left side of the formula represents the value of the left side of the formula (1) above. Furthermore, the total of elements that form coarse precipitates, such as Mg, represents the total of one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd. No. 8 was a component system in which α was stable and α-γ transformation did not occur. The produced ingot was heated to 1150° C. and held at this temperature for 1 hour, and then hot rolled to a finish rolling temperature FT shown in Table 2. After completion of hot rolling (after passing the final pass), the time until the start of cooling was set as shown in Table 2, and cooling was performed so that the temperature of the steel sheet 3 seconds after the start of cooling reached the temperature shown in Table 2. The hot-rolled steel sheets thus obtained were not subjected to hot-rolled sheet annealing, but were subjected to pickling to remove scale, and then cold-rolled at a rolling reduction RR1 shown in Table 2. Then, in an atmosphere consisting of 20% hydrogen and 80% nitrogen by volume, the steel was heated to an intermediate annealing temperature T1 shown in Table 2 at a temperature increase rate shown in Table 2, and intermediate annealing was performed by holding the steel at T1 for 30 seconds. For cold rolling after intermediate annealing, skin pass rolling was performed at a rolling reduction rate RR2 shown in Table 2. Next, the steel sheet after skin-pass rolling was subjected to finish annealing in a 100% hydrogen atmosphere at a temperature increase rate of 100°C / hour at the finish annealing temperature T2 shown in Table 2. At this time, the holding time at the finish annealing temperature T2 was 2 hours. Non-oriented electrical steel sheets were produced as described above. However, for No. 7, the sheet broke into two pieces during cold rolling, so the subsequent processes were not carried out.

[0072] In order to investigate the texture of the obtained non-oriented electrical steel sheets, a part of the steel sheet was cut off to obtain a test piece, which was then subjected to thickness reduction processing by reducing the pressure from the surface to half of the thickness. The measurement plane was a plane parallel to the rolled surface at a depth of half the plate thickness from the surface exposed by the thickness reduction of this test piece, and the {411} <011> The {111} ratio and {111} ratio were measured. In addition, the average crystal grain size was measured on the measurement surface by the cutting method of JIS G0551 (2020).

[0073] The magnetic properties of the obtained non-oriented electrical steel sheets were measured in the following manner.

[0074] <Magnetic flux density> As measurement samples, 55mm square single sheet magnetic property test samples were taken in two directions, 0° and 45° from the rolling direction.The magnetic flux density B50 of these two types of samples was then determined at angles of 0°, 45°, 90°, and 135° from the rolling direction in accordance with JISC2556 (2015). The average of the magnetic flux densities at angles of 45° and 135° to the rolling direction was defined as B50D, and the average of the magnetic flux densities at angles of 0° and 90° to the rolling direction was defined as B50L.

[0075] <Iron loss and iron loss degradation rate> For the iron loss W10 / 400, the above measurement samples were taken at an angle of 45° to the rolling direction, and the iron loss was calculated in the 45° and 135° directions relative to the rolling direction in accordance with JIS C2556 (2015), and the average was taken as W10D / 400D. Furthermore, with regard to the iron loss degradation rate Wx [%] of iron loss W10 / 50 under compressive stress, when the iron loss W10 / 50 (45° direction) without stress is set to W10 / 50(0) and the iron loss W10 / 50 (45° direction) under a compressive stress of 10 MPa is set to W10 / 50(10), the iron loss degradation rate Wx was calculated using the following formula. Wx={W10 / 50(10)-W10 / 50(0)} / W10 / 50(0) If the iron loss degradation rate of W10 / 50 under compressive stress in a direction at an angle of 45° to the rolling direction is 40% or less, it is determined that the iron loss degradation rate (stress sensitivity) is low.

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079] As can be seen from Tables 1 to 3, in the invention examples Nos. 1 to 5, the chemical compositions were within the ranges of the invention, the textures were also within the ranges of the invention, and the magnetic properties (magnetic flux density, iron loss, and iron loss degradation rate) were excellent. In contrast, in the comparative examples, No. 6 and Nos. 8 to 18, one or more of the chemical composition, manufacturing method, texture, and magnetic properties were outside the range of the present invention.< / uvw> < / uvw> < / uvw> < / uvw> < / uvw>

Claims

1. In mass%, C: 0.0100% or less, Si: 1.50% to 4.00%, sol. Al: 0.0001% to 1.00%, S: 0.0100% or less, N: 0.0100% or less, One or more elements selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total; Co: 0.000% to 1.000%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, P: 0.000% to 0.400%, and one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.0000% to 0.0100% in total; Contains When the Mn content is [Mn], the Ni content is [Ni], the Cu content is [Cu], the Si content is [Si], the sol. Al content is [sol. Al], and the P content is [P], the following formula (1) is satisfied: The balance is Fe and impurities, When a surface parallel to the rolled surface at a depth of 1 / 2 of the plate thickness from the surface is measured by SEM-EBSD, the area ratio of {hkl}<uvw> orientation crystal grains to the entire field of view is expressed as Ahkl-uvw, and A411-011 is 40.0% or more, B50D, which is the average magnetic flux density in the 45 degree direction and the 135 degree direction relative to the rolling direction, is 1.70 T or more, The average iron loss W10D / 400D in the 45 degree direction and the 135 degree direction relative to the rolling direction is 12.0 W / kg or less. A non-oriented electrical steel sheet characterized by: (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≧1.50% ... (1)

2. When the average magnetic flux density in the 0 degree direction and the 90 degree direction with respect to the rolling direction is B50L, The B50D and the B50L satisfy the following formula (2): The non-oriented electrical steel sheet according to claim 1 . B50D / B50L≧1.05...(2)

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