Non-oriented electromagnetic steel sheet, motor core, and motor

Abstract

In this non-oriented electromagnetic steel sheet, the chemical composition of the base material thereof contains, in mass%, not more than 0.010% of C, more than 1.20% but not more than 4.00% of Si, more than 0.12% but not more than 2.50% of Al, 0.10-1.00% of Mn, not more than 0.20% of P, 0.0010-0.050% of S, not more than 0.0050% of O, less than 0.0040% of N, 0.0030-0.10% of Zr, less than 0.0030% of Ti, less than 0.0030% of Nb, less than 0.0030% of V, not more than 0.0050% of REM, not more than 0.0050% of Ca, not more than 0.0050% of Mg, not more than 0.50% of Cu, not more than 0.050% of Mo, not more than 0.20% of Sn, not more than 0.20% of Sb, not more than 0.050% of Ni, not more than 0.50% of Cr, and not more than 0.0030% of B, the balance being Fe and impurities, and satisfies [1.0≤Zr / S≤3.0].

Description

Non-oriented electrical steel sheets, motor cores and motors

[0001] The present invention relates to a non-oriented electrical steel sheet, a motor core, and a motor.

[0002] In recent years, global environmental issues have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there is a strong demand for higher efficiency in electrical equipment. Therefore, there is an increasing demand for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as iron core materials for motors, generators, etc. This trend is particularly evident in drive motors for electric and hybrid vehicles and air conditioner compressor motors.

[0003] To achieve high motor efficiency, it is important to reduce iron loss, which is the main cause of loss. Reducing iron loss in the electromagnetic steel sheets used as the iron core of the motor is an effective way to reduce iron loss. Coarsening of crystal grains is an effective way to reduce iron loss, but fine precipitates such as MnS are known to be harmful to grain growth (see, for example, Patent Document 1).

[0004] JP 2019-99854 A

[0005] MnS redissolves in the hot rolling process and precipitates finely in the subsequent hot-rolled sheet annealing process, inhibiting grain growth during annealing. As a result, MnS inhibits domain wall motion when the product is magnetized, causing increased iron loss. Therefore, operations are being carried out to suppress the redissolution of MnS by lowering the heating temperature in the hot rolling process and the hot-rolled sheet annealing process. However, it is difficult to appropriately control the temperature over the entire length and width of the slab and hot-rolled sheet, and variations in iron loss within the coil are a factor in reduced yields, etc.

[0006] The present invention has been made to solve such problems, and has an object to provide a non-oriented electrical steel sheet with less variation in iron loss within the coil.

[0007] The present invention relates to the following non-oriented electrical steel sheet, motor core, and motor.

[0008] (1) The chemical composition of the base metal is, in mass%, C: 0.010% or less, Si: over 1.20% and 4.00% or less, Al: over 0.12% and 2.50% or less, Mn: 0.10 to 1.00%, P: 0.20% or less, S: 0.0010 to 0.050%, O: 0.0050% or less, N: less than 0.0040%, Zr: 0.0030 to 0.10%, Ti: less than 0.0030%, Nb: less than 0.0030%, V: less than 0.0030%, REM: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, Cu: 0.50% or less, Mo: 0.050% or less, A non-oriented electrical steel sheet having Sn: 0.20% or less, Sb: 0.20% or less, Ni: 0.050% or less, Cr: 0.50% or less, B: 0.0030% or less, and the balance: Fe and impurities, which satisfies the following formula (i): 1.0≦Zr / S≦3.0 (i) where the element symbols in the formula indicate the content (mass%) of each element.

[0009] (2) The non-oriented electrical steel sheet according to (1) above, wherein the chemical composition of the base material further satisfies the following formula (ii): Al / Zr≧25.0 (ii), where the element symbols in the formula indicate the content (mass%) of each element.

[0010] (3) The non-oriented electrical steel sheet according to (1) or (2) above, wherein, in a cross section parallel to the surface of the base material at a position one-quarter thickness from the surface of the base material, the proportion by number of particles having a Zr concentration of 30 at% or more among particles having a circle equivalent diameter of 1 μm or more is 30% or more.

[0011] (4) A motor core in which the non-oriented electrical steel sheets according to any one of (1) to (3) above are laminated.

[0012] (5) A motor including the motor core described in (4) above.

[0013] According to the present invention, a non-oriented electrical steel sheet with little variation in iron loss within the coil can be obtained.

[0014] FIG. 1 is a diagram for explaining the position where the test piece is collected.

[0015] As a result of extensive research conducted by the present inventors to solve the above problems, the present inventors have come to the following findings.

[0016] By including a certain amount or more of Zr, which has a high affinity with S, S can be absorbed into Zr. ２ S ３ It is possible to fix Zr as Zr and suppress the precipitation of fine MnS. ２ S ３ Since Zr crystallizes at a higher temperature than MnS, it is coarse and does not inhibit grain growth. ２ S ３ Since Mn exists more stably in a high temperature range than MnS, there is little risk of re-dissolving Mn in the hot rolling process or the hot-rolled sheet annealing process.

[0017] However, Zr has a high affinity not only with S but also with N, and may crystallize out as Zr(N,C), so it is necessary to contain a predetermined amount or more of Al and fix N as AlN.

[0018] Furthermore, when Ti, Nb, and V are contained in large amounts, sulfides such as MnS tend to precipitate in combination with these carbonitrides as nuclei. In addition, when Ti, Nb, and V carbonitrides are finely precipitated, Zr ２ S ３ Therefore, it is necessary to limit the contents of Ti, Nb and V.

[0019] The present invention was made based on the above findings. Each of the features of the present invention will be described in detail below.

[0020] 1. Chemical composition of the base material The reasons for limiting the content of each element are as follows: In the following description, "%" for the content means "mass %."

[0021] C: 0.010% or less C (carbon) is an element that causes an increase in iron loss in non-oriented electrical steel sheets. If the C content exceeds 0.010%, the iron loss of the non-oriented electrical steel sheets increases, making it impossible to obtain good magnetic properties. Therefore, the C content is set to 0.010% or less. The C content is preferably 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0040% or less. Note that there is no need to set a lower limit for the C content; it may be 0%. However, since C contributes to increasing the strength of non-oriented electrical steel sheets, if this effect is desired, the C content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0022] Si: more than 1.20% and not more than 4.00% Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves the high-frequency iron loss of non-oriented electrical steel sheets. To achieve this effect, the Si content is set to more than 1.20%. The Si content is preferably 1.50% or more, more preferably 2.00% or more, and even more preferably 2.50% or more. On the other hand, excessive Si content reduces workability. Therefore, the Si content is set to 4.00% or less. The Si content is preferably 3.70% or less, more preferably 3.50% or less.

[0023] Al: more than 0.12% and not more than 2.50% Al (aluminum) is an element that has the effect of increasing the electrical resistance of steel, thereby reducing eddy current loss and improving high-frequency iron loss of non-oriented electrical steel sheets. Al also has the effect of improving iron loss by improving the texture. In addition, Al fixes N as AlN, thereby improving the iron loss of Zr ２ S ３ It also has the effect of indirectly promoting the formation of Al. To obtain these effects, the Al content is set to more than 0.12%. The Al content is preferably 0.25% or more, and more preferably 0.40% or more. However, if the Al content is excessive, toughness decreases. Therefore, the Al content is set to 2.50% or less. The Al content is preferably 2.00% or less, and more preferably 1.00% or less.

[0024] Mn: 0.10 to 1.00% Mn (manganese) is an element that increases the electrical resistance of steel, reduces eddy current loss, and is effective in improving the high-frequency iron loss of non-oriented electrical steel sheets. To achieve this effect, the Mn content is set to 0.10% or more. The Mn content is preferably 0.15% or more, and more preferably 0.20% or more. On the other hand, excessive Mn content may not suppress the formation of MnS, even in the present invention, which utilizes Zr, and may increase iron loss. Therefore, the Mn content is set to 1.00% or less. The Mn content is preferably less than 1.00%, more preferably 0.90% or less, even more preferably 0.80% or less, even more preferably 0.70% or less, even more preferably 0.60% or less, even more preferably 0.50% or less, and even more preferably 0.40% or less.

[0025] P: 0.20% or less P (phosphorus) is contained in steel as an impurity, and if its content is excessive, the toughness of the non-oriented electrical steel sheet is significantly reduced. Therefore, the P content is set to 0.20% or less. The P content is preferably 0.10% or less, and more preferably 0.030% or less. There is no need to set a lower limit for the P content, and the lower limit is 0%. However, since an extreme reduction in the P content may increase manufacturing costs, the P content is preferably more than 0%, more preferably 0.003% or more, and even more preferably 0.005% or more.

[0026] S: 0.0010 to 0.050% S (sulfur) is an element that increases iron loss by forming fine precipitates of MnS, thereby degrading the magnetic properties of the non-oriented electrical steel sheet. However, in this embodiment, S is replaced by Zr. ２ S ３It is possible to fix the S content as 0.0010% or more, thereby suppressing the precipitation of fine MnS. Therefore, from the viewpoint of cost reduction, the S content is not reduced excessively, but is set to 0.0010% or more. The S content is preferably 0.0020% or more, and more preferably 0.0050% or more. However, if the S content exceeds 0.050%, the magnetic properties will be significantly reduced even in the present invention, which utilizes Zr. Therefore, the S content is set to 0.050% or less. The S content is preferably 0.040% or less, and more preferably 0.030% or less.

[0027] O: 0.0050% or less O (oxygen) is an element that forms oxide-based inclusions, thereby degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the O content is set to 0.0050% or less. The O content is preferably 0.0040% or less, and more preferably 0.0020% or less. There is no need to set a lower limit for the O content, and the lower limit is 0%. However, since an extreme reduction in the O content may increase manufacturing costs, the O content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0028] N: Less than 0.0040% N (nitrogen) is an element that is inevitably mixed into steel and forms fine nitrides, increasing iron loss and degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the N content is less than 0.0040%. The N content is preferably 0.0030% or less, and more preferably 0.0020% or less. There is no need to set a lower limit for the N content, and the lower limit is 0%. However, since an extreme reduction in the N content may increase manufacturing costs, the N content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0029] Zr: 0.0030 to 0.10% Zr (zirconium) is used to replace S with Zr ２ S ３Zr is an element that has the effect of suppressing the precipitation of fine MnS by fixing it as Zr. To achieve this effect, the Zr content is set to 0.0030% or more. The Zr content is preferably 0.0035% or more, more preferably 0.0040% or more, and even more preferably 0.0045% or more. On the other hand, if the Zr content is excessive, the amount of Zr-containing particles may become excessive, which may increase iron loss. Therefore, the Zr content is set to 0.10% or less. The Zr content is preferably 0.080% or less, more preferably 0.050% or less, even more preferably 0.030% or less, and even more preferably 0.010% or less.

[0030] In this embodiment, the Zr content needs to be adjusted according to the S content. Therefore, in addition to the S and Zr contents being within the above ranges, the following formula (i) needs to be satisfied. If the value of the middle part of the following formula (i) is less than 1.0, the effect of Zr in fixing S becomes insufficient. On the other hand, if the value of the middle part of the following formula (i) exceeds 3.0, fine ZrN, ZrC, and ZrO particles are formed. ２ etc. crystallize out, resulting in an increase in iron loss. The value of the middle part of the following formula (i) is preferably 1.2 or more, more preferably 1.3 or more, even more preferably 1.4 or more, and even more preferably 1.5 or more. The value of the middle part of the following formula (i) is preferably 2.8 or less, more preferably 2.7 or less, even more preferably 2.6 or less, and even more preferably 2.5 or less. 1.0≦Zr / S≦3.0 (i) However, the element symbols in the above formulas represent the content (mass%) of each element.

[0031] Additionally, in this embodiment, it is preferable to adjust the Al content according to the Zr content. Specifically, in addition to the Al and Zr contents being within the respective ranges described above, it is preferable to satisfy the following formula (ii). By satisfying the following formula (ii), even when the N content is high, N can be fixed by Al, thereby suppressing the precipitation of ZrN. The value of the left side of the following formula (ii) is more preferably 30.0 or more, and even more preferably 35.0 or more. There is no need to set an upper limit to the value of the left side of the following formula (ii), and the substantial upper limit is 833.3. The value of the left side of the following formula (ii) is preferably 500.0 or less, more preferably less than 250.0, and even more preferably 200.0 or less. Al / Zr≧25.0 (ii) where the element symbols in the above formula represent the content (mass%) of each element.

[0032] Ti: less than 0.0030% Nb: less than 0.0030% V: less than 0.0030% Ti (titanium), Nb (niobium) and V (vanadium) are elements that are inevitably mixed into steel. As mentioned above, when the contents of Ti, Nb and V are excessive, sulfides such as MnS tend to precipitate in combination with these carbonitrides as nuclei. In addition, when fine carbonitrides of Ti, Nb and V precipitate, they are combined with Zr ２ S ３ Also, Ti, Nb, and V may precipitate finely, which may adversely affect grain growth. Therefore, the contents of Ti, Nb, and V are all less than 0.0030%. The contents of Ti, Nb, and V are each preferably 0.0025% or less, more preferably 0.0020% or less. For the same reason, the total content of Ti, Nb, and V is preferably 0.0060% or less, more preferably 0.0055% or less, and even more preferably 0.0050% or less. Note that the lower limits of the contents of Ti, Nb, and V are not particularly limited, but excessive reduction in these contents may increase manufacturing costs. Therefore, the contents of Ti, Nb, and V are each preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0033] REM: 0.0050% or less Ca: 0.0050% or less Mg: 0.0050% or less REM (rare earth elements), Ca (calcium), and Mg (magnesium) are elements that can be mixed into steel as impurities. Intentional inclusion of these elements increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, REM, Ca, and Mg do not need to be actively included; impurity levels are sufficient. Therefore, the contents of REM, Ca, and Mg are all set to 0.0050% or less. The contents of REM, Ca, and Mg are preferably 0.0030% or less, and more preferably 0.0010% or less. The lower limits of the REM, Ca, and Mg contents are not particularly limited, and the lower limit is 0%. However, excessive reductions in these contents may result in increased manufacturing costs. Therefore, the contents of REM, Ca, and Mg are each preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the REM content refers to the total content of these elements.

[0034] Cu: 0.50% or less Cu (copper) is an element that can be mixed into steel as an impurity. Intentional inclusion of Cu increases the manufacturing cost of the non-oriented electrical steel sheet. Therefore, in this embodiment, it is not necessary to actively include Cu; impurity levels are sufficient. Therefore, the Cu content is set to 0.50% or less. The Cu content is preferably 0.30% or less, more preferably 0.10% or less, and even more preferably 0.050% or less. The lower limit of the Cu content is not particularly limited, and the lower limit is 0%. However, an extreme reduction in the Cu content may increase manufacturing costs. Therefore, the Cu content is preferably more than 0%, and more preferably 0.0005% or more.

[0035] Mo: 0.050% or less Mo (molybdenum) is an element that can be mixed into steel as an impurity. Intentional inclusion of Mo increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Mo does not need to be actively added; impurity levels are sufficient. Therefore, the Mo content is set to 0.050% or less. The Mo content is preferably 0.030% or less, more preferably 0.010% or less, and even more preferably 0.0050% or less. The lower limit of the Mo content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the Mo content may increase manufacturing costs. Therefore, the Mo content is preferably more than 0%, and more preferably 0.0005% or more.

[0036] Sn: 0.20% or less Sn (tin) is an element that can be mixed into steel as an impurity. Sn has the effect of developing a texture that is favorable for improving magnetic properties, but if it is contained in excess, the effect saturates and manufacturing costs increase. Therefore, in this embodiment, the Sn content is set to 0.20% or less. The Sn content is preferably 0.15% or less, more preferably 0.10% or less, even more preferably 0.050% or less, and even more preferably 0.025% or less. The lower limit of the Sn content is not particularly limited, and the lower limit is 0%. However, if the above-mentioned effects of Sn are desired to be obtained, the Sn content is preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.010% or more.

[0037] Sb: 0.20% or less Sb (antimony) is an element that can be mixed into steel as an impurity. Sb has the effect of developing a texture that is favorable for improving magnetic properties, but if it is contained in excess, the effect saturates and manufacturing costs increase. Therefore, in this embodiment, the Sb content is set to 0.20% or less. The Sb content is preferably 0.15% or less, more preferably 0.10% or less, even more preferably 0.050% or less, and even more preferably 0.025% or less. The lower limit of the Sb content is not particularly limited, and the lower limit is 0%. However, if the above-mentioned effects of Sb are desired to be obtained, the Sb content is preferably more than 0%, more preferably 0.0005% or more, even more preferably 0.0010% or more, and even more preferably 0.010% or more.

[0038] Ni: 0.050% or less Ni (nickel) is an element that can be mixed into steel as an impurity. Intentional inclusion of Ni increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Ni does not need to be actively added; impurity levels are sufficient. Therefore, the Ni content is set to 0.050% or less. The Ni content is preferably 0.030% or less, more preferably 0.010% or less, and even more preferably 0.0050% or less. The lower limit of the Ni content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the Ni content may increase manufacturing costs. Therefore, the Ni content is preferably more than 0%, and more preferably 0.0005% or more.

[0039] Cr: 0.50% or less Cr (chromium) is an element that can be mixed into steel as an impurity. Intentional inclusion of Cr increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Cr does not need to be actively added; impurity levels are sufficient. Therefore, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, more preferably 0.10% or less, and even more preferably 0.050% or less. The lower limit of the Cr content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the Cr content may increase manufacturing costs. Therefore, the Cr content is preferably more than 0%, and more preferably 0.0005% or more.

[0040] B: 0.0030% or less B (boron) is an element that can be mixed into steel as an impurity. Intentional inclusion of B increases the manufacturing cost of the non-oriented electrical steel sheet. Therefore, in this embodiment, it is not necessary to actively include B; impurity-level B is sufficient. Therefore, the B content is set to 0.0030% or less. The B content is preferably 0.0020% or less, and more preferably 0.0010% or less. The lower limit of the B content is not particularly limited, and the lower limit is 0%. However, an extreme reduction in the B content may increase manufacturing costs. Therefore, the B content is preferably more than 0%, preferably 0.0001% or more, and more preferably 0.0003% or more.

[0041] The chemical composition of the base material of the non-oriented electrical steel sheet of the present invention is such that the balance is Fe and impurities. Here, "impurities" refer to components that are mixed in during industrial steel production due to various factors in raw materials such as ores and scrap, or in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention. Examples of impurities include Bi, As, Te, Pb, Zn, W, Co, Ba, Cd, Pt, Au, In, Ga, Ge, Sc, and Hf. The steel sheet may contain one or more elements selected from these elements in an amount of 0.005% or less.

[0042] The chemical composition of the base material of the non-oriented electrical steel sheet according to this embodiment can be measured by combining various known measurement methods. Inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES) and / or ICP mass spectrometry (ICP-MS) may be used depending on the element content. Furthermore, carbon and sulfur may be measured using a combustion-infrared absorption method, nitrogen may be measured using an inert gas combustion-thermal conductivity method, and oxygen may be measured using an inert gas fusion-non-dispersive infrared absorption method.

[0043] 2. Particles In this embodiment, by controlling the chemical composition of the base material, it is possible to suppress the precipitation of fine MnS and reduce the variation in iron loss within the coil. Therefore, there are no particular restrictions on the state of particles present in the steel. However, from the viewpoint of more reliably reducing the variation in iron loss, it is preferable to optimize the hot rolling conditions as described below so that the number ratio of Zr-containing particles to the coarse particles is equal to or greater than a certain amount.

[0044] In this specification, particles include compounds crystallized in a liquid phase and compounds precipitated in a solid phase, such as carbides, nitrides, carbonitrides, sulfides, oxides, and composites thereof.

[0045] Specifically, in a cross section parallel to the surface of the base material at a quarter thickness position from the surface of the base material (hereinafter also referred to as a "Z cross section at t / 4"), among particles having a circle-equivalent diameter of 1 μm or more (hereinafter also referred to as "coarse particles"), the number ratio of particles having a Zr concentration of 30 at% or more (hereinafter also referred to as "Zr-containing particles") is preferably 30% or more, more preferably 35% or more. There is no particular need to set an upper limit to the number ratio, but it may be, for example, 65% or less or 55% or less. Here, "circle-equivalent diameter" means the diameter of a circle having an area equal to the area of ​​the particle.

[0046] The number density of the Zr-containing particles does not need to be particularly limited, but in order to more reliably obtain the fixing effect of S, it is preferable that the number density be 40 / mm ２ It is preferable that the above is set.

[0047] In the present invention, the ratio of the number of Zr-containing particles to the number of coarse particles and the number density of Zr-containing particles are measured using a scanning electron microscope (SEM) equipped with an automatic particle measurement function.

[0048] First, a test piece is cut out so that the Z cross section at t / 4 becomes the observation surface, and is mirror-polished. Then, using an SEM with an automatic particle measurement function, the observation surface is measured at a magnification of 500 times, an acceleration voltage of 20 keV, a beam diameter of 0.79 μm, a work distance of 17 mm, and a measurement area of ​​25 mm. ２ A backscattered electron image is taken under the above conditions, and then a chemical analysis of the coarse particles contained in the field of view is performed using an energy dispersive X-ray analyzer (EDS) attached to the SEM. Ten elements, namely, C, Si, Mn, P, S, Al, Ti, N, O, and Zr, are selected as the measurement target elements, and the content of each element is determined so that the total content of these elements is 100%. If the Zr concentration of the coarse particles is 30 at% or higher, the coarse particles are determined to be Zr-containing particles.

[0049] The above analysis was carried out for multiple fields of view, and the total number of coarse particles was 1000 or more and 25 mm ２ The measurement is completed when the area measured reaches this value. Then, the ratio (%) of the number of Zr-containing particles to the total number of coarse particles analyzed is calculated. The total number of Zr-containing particles confirmed in the entire analyzed visual field is divided by the total area of ​​the entire visual field to determine the number density ( / mm ２ ) is required.

[0050] 3. Magnetic properties The non-oriented electrical steel sheet according to this embodiment has low iron loss W １０／４００ Here, the small variation in iron loss within the coil means that the difference in iron loss between the center and end portions in the width direction of the coil is small, and the difference in iron loss between the center and end portions in the longitudinal direction of the coil is small. １０／４００The iron loss W is measured in accordance with the Single Sheet Tester (SST) method specified in JIS C 2556:2015. However, the SST measurement is performed on a 55 mm x 55 mm test piece using a corresponding small single sheet tester. １０／４００ means the iron loss that occurs under the conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz. When measuring iron loss, the excitation direction is set to two directions: a direction parallel to the rolling direction (hereinafter referred to as L direction) and a direction perpendicular to the rolling direction (hereinafter referred to as C direction), and the average value of the values ​​measured in each direction is calculated as the iron loss value of the material.

[0051] The method for evaluating the variation in iron loss within a coil will now be described in detail. FIG. 1 is a diagram illustrating the location of test specimens. First, a 55 mm x 55 mm test specimen is taken from the center of the coil in the longitudinal direction and the center in the width direction. Furthermore, two 55 mm x 55 mm test specimens are taken from positions adjacent to both sides of the test specimen taking position in the longitudinal direction of the coil, with an interval of 1 cm or less between each of the test specimens. These three test specimens are referred to as width direction center test specimens.

[0052] Furthermore, a total of six 55 mm x 55 mm test pieces were taken from positions that were the same as the positions in the longitudinal direction of the coil for the above three widthwise center test pieces and were 2 cm away from each end of the coil in the width direction, and these were used as widthwise end test pieces.

[0053] For the obtained test piece, H ２ After stress relief annealing by heating at 800 ° C for 2 hours in a 100% atmosphere, the iron loss W １０／４００ Then, when the following formula (I) is satisfied, it is determined that the variation in iron loss in the width direction is small. (|W ｍｃｌ -W ｍｅ |) / W ｍｃｌ <0.080 (I) where the symbols in the above formula have the following meanings: W ｍｃｌ : Iron loss W of test piece at center of width direction １０／４００ Average value of (W / kg) W ｍｅ: Iron loss W of test piece at end in width direction １０／４００ Average value (W / kg)

[0054] Next, a 55 mm x 55 mm test piece was taken from the center of the coil in the longitudinal direction and the center in the width direction. Furthermore, two 55 mm x 55 mm test pieces were taken from positions adjacent to the test piece taken on both sides of the coil in the width direction, with an interval of 1 cm or less between each of the test pieces. These three test pieces were designated as longitudinal center test pieces.

[0055] Furthermore, three test pieces were taken from positions 5 m away from the innermost end of the coil, which were the same as the positions of the three longitudinal center test pieces in the width direction of the coil, and these were designated as longitudinal top test pieces. Similarly, three test pieces were taken from positions 5 m away from the outermost end of the coil, which were the same as the positions of the three longitudinal center test pieces in the width direction of the coil, and these were designated as longitudinal bottom test pieces.

[0056] For the obtained test piece, H ２ After stress relief annealing by heating at 800 ° C for 2 hours in a 100% atmosphere, the iron loss W １０／４００ Then, if the following formula (II) is satisfied, it is determined that the variation in iron loss in the longitudinal direction is small. (|W ｍｃｃ - (W ｔｃ +W ｂｃ ) / 2|) / W ｍｃｃ <0.080 (II) where the symbols in the above formula have the following meanings: W ｍｃｃ : Iron loss W of test piece at center of longitudinal direction １０／４００ Average value of (W / kg) W ｔｃ : Iron loss W of the test piece at the top in the longitudinal direction １０／４００ Average value of (W / kg) W ｂｃ : Iron loss W of the test piece at the bottom in the longitudinal direction １０／４００ Average value (W / kg)

[0057] 4. Sheet Thickness There are no particular restrictions on the thickness of the base material of the non-oriented electrical steel sheet according to this embodiment. However, from the viewpoint of manufacturing costs, it is preferable that the thickness of the base material be 0.10 mm or more. On the other hand, from the viewpoint of reducing iron loss, it is preferable that the thickness of the base material be 0.50 mm or less. The thickness of the base material is more preferably 0.20 to 0.40 mm.

[0058] 5. Insulating Coating The non-oriented electrical steel sheet according to this embodiment preferably has an insulating coating on the surface of the base material. Because the non-oriented electrical steel sheet is used after being punched into a core blank and then laminated, providing an insulating coating on the surface of the base material can reduce eddy currents between the sheets, thereby making it possible to reduce eddy current loss in the core.

[0059] The type of insulating coating is not particularly limited, and known insulating coatings used for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings primarily composed of inorganic materials and further containing organic materials. Here, a composite insulating coating is an insulating coating primarily composed of at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during manufacturing, which has become increasingly important in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or Zr or Ti carbonates or ammonium salts as starting materials are preferably used.

[0060] The amount of the insulating coating is not particularly limited, but is, for example, 200 to 3000 mg / m per side. ２ The coating amount is preferably about 300 to 2500 mg / m per side. ２ It is more preferable to set the coating weight within the above range. By forming the insulating coating so that the coating weight falls within the above range, it is possible to maintain excellent insulating properties of the coating and uniformity during core bonding. When measuring the coating weight of the insulating coating afterward, various known measurement methods can be used. For example, a method of measuring the difference in mass before and after immersion in a sodium hydroxide aqueous solution, or a fluorescent X-ray method using a calibration curve method may be used as appropriate.

[0061] 6. Motor Core and Motor A motor core according to one embodiment of the present invention is formed by laminating the above-described non-oriented electromagnetic steel sheets. The motor core is obtained by laminating a plurality of non-oriented electromagnetic steel sheets punched into a predetermined shape and, if necessary, performing stress relief annealing. Some or all of the plurality of laminated non-oriented electromagnetic steel sheets may be the above-described non-oriented electromagnetic steel sheets. A motor according to one embodiment of the present invention includes the above-described motor core.

[0062] 7. Manufacturing Method The non-oriented electrical steel sheet according to this embodiment can be manufactured by sequentially carrying out a hot rolling step, a hot-rolled sheet annealing step, a cold rolling step, and a finish annealing step. It is preferable to carry out a pickling step either before or after the hot-rolled sheet annealing step. Furthermore, when an insulating coating is formed on the surface of the base material, an insulating coating forming step is carried out after the finish annealing step.

[0063] <Hot Rolling Step> A steel ingot having the above chemical composition is heated and hot rolled to obtain a hot-rolled sheet. The heating temperature of the steel ingot during hot rolling is not particularly limited, but is preferably 1050 to 1250°C, for example.

[0064] However, if it is desired to make the ratio of the number of Zr-containing particles to the number of coarse particles in the Z cross section at t / 4 30% or more, Zr ２ S ３ In order to sufficiently promote the precipitation of Zr, the heating temperature is set to 1150°C or higher. In addition, if it is desired to set the number ratio to 30% or higher, the finish rolling start temperature in the hot rolling step is set to 950°C or lower. By setting the heating temperature to 1150°C or higher and the finish rolling start temperature to 950°C or lower, a sufficient amount of Zr can be precipitated before the start of finish rolling. ２ S ３ The lower limit of the finish rolling start temperature does not need to be particularly limited, but it may be set to, for example, 910°C or higher in order to prevent excessive hot rolling load.

[0065] In the hot rolling process under the above-mentioned preferable conditions, it is necessary to control the heating temperature before hot rolling to be high and the start temperature of finish rolling to be low. Under such conditions, after the completion of rough rolling, the hot rolled sheet is allowed to cool naturally before the start of finish rolling. By cooling naturally, Zr ２ S ３ There is no particular limitation on the cooling time, and the steel may be cooled appropriately until the finish rolling start temperature reaches 950°C or less.

[0066] There is no particular restriction on the finish rolling end temperature, but if the finish rolling start temperature is 950°C or less, the finish rolling end temperature will be less than 800°C. The finish rolling end temperature may be 790°C or less, or even 780°C or less. There is no particular restriction on the lower limit of the finish rolling end temperature, but it may be 740°C, for example. After the finish rolling is completed, coiling is performed. There is no particular restriction on the coiling temperature, but it is preferably 500 to 600°C.

[0067] The thickness of the hot-rolled sheet after hot rolling is not particularly specified, but is preferably about 1.5 to 3.0 mm, for example, taking into consideration the final thickness of the base material. Although not particularly limited, it is preferable that the thickness after rough rolling is about 35 mm to 45 mm, and the reduction ratio of finish rolling is 91% to 97%.

[0068] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is performed as necessary for the purpose of reducing iron loss of the steel sheet. In the case of continuous annealing, the hot-rolled sheet may be annealed, for example, by soaking at 750 to 1200°C for 10 seconds to 10 minutes. In the case of box annealing, the hot-rolled steel sheet may be annealed, for example, by soaking at 650 to 950°C for 30 minutes to 24 hours. Note that although the magnetic properties will be inferior compared to when the hot-rolled sheet annealing process is performed, in order to reduce costs, the hot-rolled sheet may be subjected to self-annealing or the hot-rolled sheet annealing process may be omitted.

[0069] <Pickling step> The steel sheet after the hot rolling or after the hot-rolled sheet annealing is subjected to pickling to remove the scale layer formed on the surface of the base material. When the hot-rolled sheet annealing is box annealing, the pickling step is preferably performed before the hot-rolled sheet annealing from the viewpoint of descaling properties. Here, the pickling conditions, such as the concentration of the acid used in the pickling, the concentration of the accelerator used in the pickling, and the temperature of the pickling solution, are not particularly limited, and known pickling conditions can be used.

[0070] <Cold Rolling Step> The steel sheet after the hot-rolled sheet annealing is subjected to cold rolling, for example, at a reduction ratio such that the final thickness of the base material is 0.10 to 0.50 mm.

[0071] <Finish annealing step> After the cold rolling, finish annealing is carried out. For the finish annealing, it is preferable to use a continuous annealing furnace. The finish annealing is carried out under the conditions of a soaking temperature of 880 to 1080°C and a soaking time of 1 second to 10 minutes. ２ The ratio of H is 1 to 100% by volume. ２ and N ２ A mixed atmosphere of H ２ +N ２ = 100% by volume), and the dew point of the atmosphere is preferably -50 to +10°C.

[0072] If the soaking temperature is less than 880°C, the grain size becomes small and iron loss increases, which is undesirable. If the soaking temperature exceeds 1080°C, not only will the strength be insufficient, but nitriding will occur in the surface layer, which will also increase iron loss, which is undesirable. Also, if the soaking time is less than 1 second, sufficient grain growth will not occur. On the other hand, if the soaking time exceeds 10 minutes, the manufacturing cost will increase.

[0073] <Insulating Coating Forming Step> After the above-mentioned finish annealing, an insulating coating forming step is carried out as necessary. Here, the method for forming the insulating coating is not particularly limited, and a known insulating coating forming treatment liquid such as that described below may be used, and the treatment liquid may be applied and dried by a known method. An example of a known insulating coating is a composite insulating coating that is mainly made of an inorganic material and further contains an organic material.

[0074] Before applying the treatment liquid to the surface of the base material on which the insulating coating is to be formed, any pretreatment may be performed, such as degreasing with an alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc. The treatment liquid may also be applied to the surface of the base material as is after finish annealing without performing these pretreatments.

[0075] Furthermore, the obtained non-oriented electrical steel sheet can be subjected to a punching step and a laminating step in this order under the conditions shown below, thereby manufacturing a motor core or the like. Note that, when low iron loss is more important for the obtained motor core or the like, a stress relief annealing step may be further carried out after the laminating step.

[0076] <Punching Step> The non-oriented electrical steel sheet obtained as described above is subjected to punching to form the shape required for the rotor core or stator core material. There are no particular restrictions on the processing conditions, and a general method can be used.

[0077] <Laminating Process> A plurality of punched non-oriented electrical steel sheets are laminated to form a motor core.

[0078] <Stress relief annealing step> The laminated motor core is subjected to stress relief annealing as necessary. A motor core that has been subjected to stress relief annealing undergoes recrystallization and grain growth, reducing iron loss and enabling a significant improvement in motor efficiency.

[0079] There are no particular restrictions on the conditions for stress relief annealing, but from the viewpoint of improving magnetic properties, it is preferable to perform stress relief annealing at a high temperature, specifically, the annealing temperature is preferably in the range of 750 to 900°C. There are also no restrictions on the annealing time, and it is preferable to set it, for example, to 0.5 to 5.0 hours. Note that the annealing time is the time during which the motor core reaches 750°C or higher, and the heating time and cooling time below 750°C may be set appropriately.

[0080] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0081] A slab having the chemical composition shown in Table 1 was heated to the temperature shown in Table 2, and then hot-rolled to a finish thickness of 2.0 mm. The slab was then coiled at 600°C to obtain a hot-rolled steel sheet. The finish rolling start temperature was adjusted by allowing the slab to cool after rough rolling as necessary, to the temperature shown in Table 2. The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing by heating at 1000°C for 1 minute in a continuous annealing furnace. The steel sheet thus obtained was subjected to pickling to remove scale, and then cold-rolled to a cold-rolled steel sheet having a thickness of 0.35 mm. Furthermore, H ２ : 25%, N ２ Finish annealing was carried out in a mixed atmosphere of 100% ammonium hydroxide, ...75% ammonium hydroxide, and 75% ammonium hydroxide under the conditions shown in Table 2.

[0082]

[0083]

[0084] A test piece was cut out from the center of the coil in the longitudinal direction and the center of the coil in the width direction, so that the Z cross section at t / 4 was the observation surface, and the test piece was mirror-polished. Then, using an SEM with an automatic particle measurement function, the observation surface was measured at a magnification of 500x, an acceleration voltage of 20 keV, a working distance of 17 mm, and a measurement area of ​​25 mm. ２ A backscattered electron image was taken under the conditions of (a) and (b). Furthermore, chemical analysis of the coarse particles contained in the field of view was performed using an EDS attached to the SEM. Ten elements, namely, C, Si, Mn, P, S, Al, Ti, N, O, and Zr, were used as measurement target elements, and the content of each element was determined so that the total content of these elements was 100%. The measurement was terminated when the peak intensity of the elements contained in the particles reached 2500 counts or exceeded 1000 counts and the measurement time reached 0.5 seconds. If the Zr concentration of the coarse particles was 30 at% or higher, the coarse particles were determined to be Zr-containing particles.

[0085] The above analysis was carried out for multiple fields of view, and the total number of coarse particles was 1000 or more and 25 mm ２The measurement was terminated when the area reached this value. Then, the ratio of the number of Zr-containing particles to the total number of coarse particles analyzed was calculated. In addition, the total number of Zr-containing particles confirmed in the entire analyzed field of view was divided by the total area of ​​the entire field of view to determine the number density of the Zr-containing particles.

[0086] Next, in order to evaluate the variation in iron loss of the above coil, widthwise center test pieces, widthwise end test pieces, longitudinal center test pieces, longitudinal top test pieces, and longitudinal bottom test pieces were taken according to the above-mentioned procedure. ２ : After stress relief annealing by heating at 800 ° C for 2 hours in a 100% atmosphere, iron loss W １０／４００ The iron loss W １０／４００ was measured in accordance with the SST specified in JIS C 2556:2015. However, the SST measurement was performed on a 55 mm x 55 mm test piece using a corresponding small single plate tester. When measuring the iron loss, the excitation direction was set to two directions, the L direction and the C direction, and the average value of the values ​​measured in each direction was calculated as the iron loss value of the material.

[0087] The results are also shown in Table 2. In this example, the above formulas (I) and (II) are satisfied and W ｍｃｃ When the wattage is 18.0 W / kg or less, it is determined that the variation in iron loss within the coil is small and that the iron loss is stably low.

[0088] As shown in Table 2, Test Nos. 1 to 21, which satisfy all of the requirements of the present invention, have small variations in iron loss within the coil and consistently low iron loss. Comparing Test Nos. 1 to 4, which use the same steel type A, shows that Test Nos. 1 and 2, which satisfy the preferred manufacturing conditions, have a higher percentage of Zr-containing particles than Test Nos. 3 and 4, which deviate from the preferred manufacturing conditions. As a result, it can be seen that the variation in iron loss within the coil can be further reduced. Similarly, comparing Test Nos. 9 to 11, which use the same steel type E, shows that Test Nos. 9 and 10, which satisfy the preferred manufacturing conditions, have a higher percentage of Zr-containing particles than Test No. 11, which deviates from the preferred manufacturing conditions. As a result, the variation in iron loss within the coil is further reduced.

[0089] In contrast, Test Nos. 22 to 35, which do not comply with the provisions of the present invention, resulted in either a large variation in iron loss within the coil or high iron loss.

[0090] Specifically, in Test No. 22, the Zr content was less than the specified value, so the precipitation of fine MnS could not be suppressed, resulting in large variations in iron loss. In Test No. 23, the Zr content was excessive, so the amount of particles was excessive, resulting in an increase in iron loss. In Test No. 24, the value of the middle part of equation (i) was less than the specified value, so the precipitation of fine MnS could not be suppressed, resulting in large variations in iron loss.

[0091] In Test No. 25, the value of the middle part of equation (i) was excessive, resulting in an excessive amount of particles and an increase in iron loss. In Test Nos. 26 to 29, the content of at least one of Ti, Nb, and V was excessive, resulting in the formation of fine MnS and Zr ２ S ３ became more likely to precipitate, resulting in greater variations in iron loss.

[0092] In Test No. 30, the Al content was less than the specified value, so the iron loss could not be reduced. In addition, N could not be sufficiently fixed as AlN, and Zr ２ S ３In Test No. 31, the Mn content was excessive, so the formation of MnS could not be suppressed, increasing the iron loss and further increasing the iron loss variation.

[0093] In Test No. 32, the Si content was less than the specified value, so iron loss could not be reduced. In Test No. 33, the Al content was excessive, so cracks occurred during cold rolling. In Test No. 34, the N content was excessive, so part of the Zr was consumed as ZrN, which made the S fixing effect of Zr insufficient and increased the variation in iron loss. In Test No. 35, the S content was less than the specified value, so the value of the middle part of equation (i) was excessive, so fine ZrN, ZrC, and ZrO ２ etc. crystallized out, and the variation in iron loss increased.

[0094] As described above, according to the present invention, a non-oriented electrical steel sheet with little variation in iron loss within the coil can be obtained.

Claims

1. The chemical composition of the base material is, in mass%, C: 0.010% or less, Si: over 1.20% and up to 4.00%, Al: over 0.12% and up to 2.50%, Mn: 0.10 to 1.00%, P: 0.20% or less, S: 0.0010 to 0.050%, O: 0.0050% or less, N: less than 0.0040%, Zr: 0.0030 to 0.10%, Ti: less than 0.0030%, Nb: less than 0.0030%, V: less than 0.0030%, REM: 0.0050% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, Cu: 0.50% or less, Mo: 0.050% or less, A non-oriented electrical steel sheet having Sn: 0.20% or less, Sb: 0.20% or less, Ni: 0.050% or less, Cr: 0.50% or less, B: 0.0030% or less, and the balance: Fe and impurities, which satisfies the following formula (i): 1.0≦Zr / S≦3.0 (i) where the element symbols in the formula indicate the content (mass%) of each element.

2. The non-oriented electrical steel sheet according to claim 1, wherein the chemical composition of the base material further satisfies the following formula (ii): Al / Zr≧25.0 (ii), where the element symbols in the formula indicate the content (mass%) of each element.

3. The non-oriented electrical steel sheet according to claim 1, wherein, in a cross section parallel to the surface of the base material at a position 1 / 4 of the thickness from the surface of the base material, the proportion of particles having a Zr concentration of 30 at% or more among particles having a circle equivalent diameter of 1 μm or more is 30% or more.

4. The non-oriented electrical steel sheet according to claim 2, wherein, in a cross section parallel to the surface of the base material at a position 1 / 4 of the thickness from the surface of the base material, the proportion of particles having a Zr concentration of 30 at% or more among particles having a circle equivalent diameter of 1 μm or more is 30% or more.

5. A motor core in which the non-oriented electrical steel sheets according to any one of claims 1 to 4 are laminated.

6. A motor comprising the motor core according to claim 5.