Non-oriented electrical steel sheets, motor cores, and motors

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

[Technical Field]

[0001] This invention relates to non-oriented electrical steel sheets, motor cores, and motors. [Background technology]

[0002] In recent years, global environmental issues have attracted attention, and the demand for energy conservation efforts has increased significantly. In particular, there is a strong demand for increased efficiency in electrical equipment. Therefore, the need for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as core materials for motors and generators, is becoming even stronger. This trend is particularly pronounced in drive motors for electric and hybrid vehicles, as well as in motors for air conditioner compressors.

[0003] Reducing iron loss, which is the main source of losses, is crucial for achieving high efficiency in motors. Reducing iron loss in the electrical steel sheets used as the motor core is an effective way to achieve this. Coarsening the crystal grains is effective in reducing iron loss, but it is known that fine precipitates such as MnS are detrimental to crystal grain growth (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-99854 [Overview of the project] [Problems that the invention aims to solve]

[0005] MnS redissolves during the hot rolling process and precipitates finely during the subsequent annealing process of the hot-rolled sheet, thereby inhibiting grain growth during annealing. As a result, in the product, when magnetized, MnS becomes a factor that inhibits domain wall movement and increases iron loss. Therefore, operations are carried out to suppress the redissolution of MnS, such as lowering the heating temperature in the hot rolling process and the annealing process of the hot-rolled sheet. However, it is difficult to appropriately control the temperature over the entire length and width of the slab and the hot-rolled sheet, and the variation in iron loss within the coil has become a factor such as a decrease in yield.

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

Means for Solving the Problems

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

[0008] (1) The chemical composition of the base material is, in mass%, C: 0.010% or less, Si: more than 1.20% and 4.00% or less, Al: more than 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, 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, The balance: Fe and impurities, satisfying the following formula (i), Non-oriented electrical steel sheet. 1.0 ≦ Zr / S ≦ 3.0 ···(i) However, the element symbols in the above formula represent the content (% by mass) of each element.

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

[0010] (3) At the 1 / 4 thickness position from the surface of the base material, in a cross-section parallel to the surface of the base material, among the particles with an equivalent circle diameter of 1 μm or more, the number ratio of the particles with a Zr concentration of 30 at% or more is 30% or more, The non-oriented electrical steel sheet according to (1) or (2) above.

[0011] (4) Stacked with the non-oriented electrical steel sheet according to any one of (1) to (3) above, Motor core.

[0012] (5) A motor including the motor core according to (4) above, Motor. [Effect of the Invention]

[0013] According to the present invention, a non-oriented electrical steel sheet with less variation in iron loss in the coil can be obtained. [Brief Description of the Drawings] <000012??>

[0014] [Figure 1] Figure 1 is a diagram for explaining the sampling position of the test piece. It should be noted that there seems to be a formatting issue in the original text where "図1は、試験片の採取位置を説明するための図である。" has an incorrect placeholder "??" in the translated text. It should be corrected to "Figure 1 is a diagram for explaining the sampling position of the test piece." without the incorrect placeholder. Also, it's assumed that the "<000012??>" in the original is a typo and should be something like " " which is then translated as " ". These are likely errors in the original text that are carried over in the translation for accuracy comparison purposes.[Modes for carrying out the invention]

[0015] As a result of diligent research conducted by the inventors to solve the above problems, we have obtained the following findings.

[0016] By including a predetermined amount or more of Zr, which has a high affinity for S, it is possible to fix S as Zr2S3 and suppress the precipitation of fine MnS. Since Zr2S3 crystallizes at a higher temperature than MnS, it is coarser and has the characteristic of not inhibiting grain growth. In addition, since Zr2S3 exists more stably at high temperatures than MnS, there is less risk of resolution during the hot rolling process or the hot rolled sheet annealing process.

[0017] However, since Zr has a high affinity not only for S but also for N, it may crystallize as Zr(N,C). Therefore, it is necessary to include more than a certain amount of Al and fix the N as AlN.

[0018] Furthermore, if large amounts of Ti, Nb, and V are present, these carbonitrides will act as nuclei, making it easier for sulfides such as MnS to precipitate in combination. In addition, if Ti, Nb, and V carbonitrides precipitate in fine particles, Zr2S3 may also precipitate in combination with them, potentially adversely affecting grain growth. Therefore, it is necessary to limit the content of Ti, Nb, and V.

[0019] This invention is based on the above findings. The requirements of this invention will be described in detail below.

[0020] 1. Chemical composition of the base material The reasons for the limitations on each element are as follows. Note that in the following explanation, "%" for content refers to "mass%".

[0021] C: 0.010% or less Carbon (C) 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 sheet increases, and good magnetic properties cannot be obtained. Therefore, the C content should be 0.010% or less. Preferably, the C content is 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0040% or less. There is no lower limit to the C content, and it may be 0%. However, since C contributes to increasing the strength of non-oriented electrical steel sheets, if this effect is to be obtained, it is preferable that the C content is greater than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0022] Si: more than 1.20% and less than 4.00% Silicon (Si) is an element that increases the electrical resistance of steel, reduces eddy current losses, and improves high-frequency iron loss in non-oriented electrical steel sheets. To obtain this effect, the Si content should be greater than 1.20%. Preferably, the Si content should be 1.50% or more, more preferably 2.00% or more, and even more preferably 2.50% or more. On the other hand, if the Si content is too high, the workability decreases. Therefore, the Si content should be 4.00% or less. Preferably, the Si content should be 3.70% or less, and more preferably 3.50% or less.

[0023] Al: more than 0.12% and less than 2.50% Aluminum (Al) is an element that reduces eddy current loss by increasing the electrical resistance of steel, thereby improving high-frequency iron loss in non-oriented electrical steel sheets. Al also improves iron loss by improving the texture. Furthermore, Al indirectly promotes the formation of Zr2S3 by fixing N as AlN. To obtain these effects, the Al content should be greater than 0.12%. Preferably, the Al content is 0.25% or more, and more preferably 0.40% or more. However, excessive Al content reduces toughness. Therefore, the Al content should be 2.50% or less. Preferably, the Al content is 2.00% or less, and more preferably 1.00% or less.

[0024] Mn: 0.10~1.00% Manganese (Mn) is an effective element for increasing the electrical resistance of steel, reducing eddy current losses, and improving high-frequency iron loss in non-oriented electrical steel sheets. To obtain this effect, the Mn content should be 0.10% or more. Preferably, the Mn content should be 0.15% or more, and more preferably 0.20% or more. On the other hand, if the Mn content is excessive, the formation of MnS cannot be suppressed even in this invention which utilizes Zr, and iron loss may increase. Therefore, the Mn content should be 1.00% or less. Preferably, the Mn content should be 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 Phosphorus (P) is present in steel as an impurity, and if its content is excessive, the toughness of non-oriented electrical steel sheets will be significantly reduced. Therefore, the P content should be 0.20% or less. Preferably, the P content is 0.10% or less, and more preferably 0.030% or less. There is no lower limit for the P content, and the lower limit is 0%. However, since extreme reduction of the P content may lead to increased manufacturing costs, it is preferable that the P content be greater than 0%, more preferably 0.003% or more, and even more preferably 0.005% or more.

[0026] S: 0.0010~0.050% S (sulfur) is an element that increases iron loss by forming fine MnS precipitates, thereby degrading the magnetic properties of non-oriented electrical steel sheets. However, in this embodiment, it is possible to fix S as Zr2S3 using Zr, thereby suppressing the precipitation of fine MnS. Therefore, from the viewpoint of cost reduction, the S content is not reduced to an extreme degree, and 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 degradation of magnetic properties becomes significant even in this invention that 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 Oxygen (O) is an element that reduces the magnetic properties of non-oriented electrical steel sheets by forming oxide inclusions. Therefore, the O content should be 0.0050% or less. Preferably, the O content is 0.0040% or less, and more preferably 0.0020% or less. There is no lower limit for the O content, and the lower limit is 0%. However, since extreme reduction of the O content may lead to increased manufacturing costs, it is preferable that the O content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0028] N: Less than 0.0040% Nitrogen (N) is an element that is inevitably mixed into steel, and it forms fine nitrides, increasing iron loss and degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the N content should be less than 0.0040%. Preferably, the N content is 0.0030% or less, and more preferably 0.0020% or less. There is no lower limit for the N content, and the lower limit is 0%. However, since extreme reduction of the N content may lead to increased manufacturing costs, it is preferable that the N content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0029] Zr: 0.0030~0.10% Zr (zirconium) is an element that has the effect of suppressing the precipitation of fine MnS by fixing S as Zr2S3. To obtain this effect, the Zr content should be 0.0030% or more. Preferably, the Zr content should be 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 particles containing Zr will be excessive, which may increase iron loss. Therefore, the Zr content should be 0.10% or less. Preferably, the Zr content should be 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 content being within the above ranges, the following equation (i) must be satisfied. If the value of the middle side of equation (i) is less than 1.0, the fixing effect of S by Zr will be insufficient. On the other hand, if the value of the middle side of equation (i) exceeds 3.0, fine ZrN, ZrC, ZrO2, etc. will crystallize, and iron loss will increase. The value of the middle side of equation (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. Furthermore, the value of the middle side of equation (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 formula represent the content (mass %) of each element.

[0031] In addition, in this embodiment, it is preferable to adjust the Al content according to the Zr content. Specifically, in addition to the Al and Zr content being within the above ranges, it is preferable that the following equation (ii) is satisfied. By satisfying the following equation (ii), even when the N content is high, it is possible to fix N with Al and suppress the precipitation of ZrN. The value on the left side of the following equation (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 on the value on the left side of the following equation (ii), and the practical upper limit is 833.3. The value on the left side of the following equation (ii) is more preferably 500.0 or less, more preferably less than 250.0, and even more preferably 200.0 or less. Al / Zr≧25.0 ···(ii) However, 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% Titanium (Ti), niobium (Nb), and vanadium (V) are elements that inevitably become mixed into steel. As mentioned above, if the content of Ti, Nb, and V is excessive, sulfides such as MnS tend to precipitate in combination with these carbonitrides, using them as nuclei. In addition, if carbonitrides of Ti, Nb, and V precipitate finely, Zr2S3 may also precipitate finely in combination with them, potentially adversely affecting grain growth. For this reason, the content of Ti, Nb, and V should each be less than 0.0030%. Preferably, the content of Ti, Nb, and V should each be 0.0025% or less, and more preferably 0.0020% or less. For the same reason, the total content of Ti, Nb, and V should preferably be 0.0060% or less, more preferably 0.0055% or less, and even more preferably 0.0050% or less. While there are no particular limitations on the lower limits of the Ti, Nb, and V content, extreme reductions in their content may lead to increased manufacturing costs. Therefore, it is preferable that the Ti, Nb, and V content be greater than 0%, more preferably 0.0001% or higher, and even more preferably 0.0005% or higher.

[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. Intentionally including these elements increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include REM, Ca, and Mg, and their presence at impurity levels is sufficient. For this reason, the content of REM, Ca, and Mg is set to 0.0050% or less for each. Preferably, the content of REM, Ca, and Mg is 0.0030% or less for each, and more preferably 0.0010% or less for each. The lower limit of the content of REM, Ca, and Mg is not particularly limited, and the lower limit is 0%. However, extreme reduction of these contents may lead to an increase in manufacturing costs. Therefore, preferably, the content of REM, Ca, and Mg is greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more for each. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanides, and the REM content refers to the total content of these elements.

[0034] Cu: 0.50% or less Copper (Cu) is an element that can be mixed into steel as an impurity. Intentionally including Cu increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include Cu, and an impurity level is sufficient. For this reason, the Cu content is set to 0.50% or less. Preferably, the Cu content is 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 Cu content may lead to an increase in manufacturing costs. For this reason, it is preferable that the Cu content is greater than 0%, and more preferably 0.0005% or more.

[0035] Mo: 0.050% or less Molybdenum (Mo) is an element that can be mixed into steel as an impurity. Intentionally including Mo increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include Mo, and an impurity level is sufficient. For this reason, the Mo content is set to 0.050% or less. Preferably, the Mo content is 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 its lower limit is 0%. However, an extreme reduction in the Mo content may lead to an increase in manufacturing costs. For this reason, it is preferable that the Mo content is greater 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 favorable for improving magnetic properties, but if it is included in excess, the effect saturates and manufacturing costs increase. Therefore, in this embodiment, the Sn content is set to 0.20% or less. Preferably, the Sn content is 0.15% or less, more preferably 0.10% or less, even more preferably 0.050% or less, and still 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 to be obtained, the Sn content is more preferably 0.0005% or more, even more preferably 0.0010% or more, and still more preferably 0.010% or more.

[0037] Sb: 0.20% or less Antimony (Sb) is an element that can be mixed into steel as an impurity. Sb has the effect of developing a texture favorable for improving magnetic properties, but if it is included in excess, the effect saturates and manufacturing costs increase. Therefore, in this embodiment, the Sb content is set to 0.20% or less. Preferably, the Sb content is 0.15% or less, more preferably 0.10% or less, even more preferably 0.050% or less, and still 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 to be obtained, the Sb content is preferably greater than 0%, more preferably 0.0005% or more, even more preferably 0.0010% or more, and still more preferably 0.010% or more.

[0038] Ni: 0.050% or less Nickel (Ni) is an element that can be present as an impurity in steel. Intentionally including Ni increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include Ni, and an impurity level is sufficient. For this reason, the Ni content is set to 0.050% or less. Preferably, the Ni content is 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 its lower limit is 0%. However, an extreme reduction in Ni content may lead to an increase in manufacturing costs. Therefore, it is preferable that the Ni content is greater 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. Intentionally including Cr increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include Cr, and an impurity level is sufficient. For this reason, the Cr content is set to 0.50% or less. Preferably, the Cr content is 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, an extreme reduction in Cr content may lead to an increase in manufacturing costs. For this reason, it is preferable that the Cr content is greater than 0%, and more preferably 0.0005% or more.

[0040] B: 0.0030% or less Boron (B) is an element that can be present as an impurity in steel. Intentionally including B increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, it is not necessary to actively include B, and an impurity level is sufficient. For this reason, the B content is set to 0.0030% or less. Preferably, the B content is 0.0020% or less, and more preferably 0.0010% or less. The lower limit of the B content is not particularly limited, and its lower limit is 0%. However, an extreme reduction in the B content may lead to an increase in manufacturing costs. Therefore, preferably, the B content is greater than 0%, preferably 0.0001% or more, and more preferably 0.0003% or more.

[0041] In the chemical composition of the base material of the non-oriented electrical steel sheet of the present invention, the remainder is Fe and impurities. Here, "impurities" means components that are mixed in during the industrial production of steel due to raw materials such as ore and scrap, and various factors 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, and one or more elements selected from these may be present in amounts of 0.005% or less of each.

[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. Depending on the element content, it may be measured using ICP emission spectrometry (ICP-AES) and ICP mass spectrometry (ICP-MS). Furthermore, C and S may be measured using combustion-infrared absorption spectrometry, N using inert gas combustion-thermal conductivity spectrometry, and O using inert gas fusion-nondispersive infrared absorption spectrometry.

[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 in which the particles exist within 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 later, so that the number ratio of Zr-containing particles to coarse particles is above a certain amount.

[0044] In this specification, particles include compounds crystallized in the liquid phase and compounds precipitated in the 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 thickness of 1 / 4 from the surface of the base material (hereinafter also referred to as the "Z cross-section at t / 4"), it is preferable that the number proportion of particles with a Zr concentration of 30 at% or more (hereinafter also referred to as "Zr-containing particles") among particles with an equivalent circle diameter of 1 μm or more (hereinafter also referred to as "coarse particles") is 30% or more, and more preferably 35% or more. There is no particular upper limit to the number proportion, but for example, it may be 65% or less, or 55% or less. Here, "equivalent circle diameter" means the diameter of a circle having an area equal to the area of ​​the particle.

[0046] There is no particular need to limit the number density of Zr-containing particles, but to more reliably obtain the fixation effect of S, 40 / mm 2 It is preferable to keep the above in place.

[0047] In this invention, the number ratio of Zr-containing particles to 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 specimen is cut out so that the Z-section at t / 4 becomes the observation surface, and then mirror-polished. Then, using a SEM with an automatic particle measurement function, the above observation surface is measured with the following settings: magnification: 500x, acceleration voltage: 20keV, beam diameter: 0.79μm, work distance: 17mm, measurement area: 25mm. 2 Under the above conditions, backscattered electron images are captured, and then the coarse particles contained in the field of view are chemically analyzed using an energy-dispersive X-ray analyzer (EDS) attached to the SEM. In this process, ten elements—C, Si, Mn, P, S, Al, Ti, N, O, and Zr—are selected as the elements to be measured, and the content of each element is determined so that the total content of these elements equals 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 performed on multiple fields of view, and the total number of coarse particles was 1000 or more and the field size was 25 mm. 2 The measurement is terminated when the above measurement area is reached. Then, the percentage of Zr-containing particles relative to the total number of coarse particles analyzed is calculated. Additionally, the number density of Zr-containing particles ( / mm²) is calculated by dividing the total number of Zr-containing particles observed in the entire field of view by the total area of ​​the entire field of view. 2 )

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

[0051] The evaluation method for the variation of iron loss in the coil will be described in detail. Figure 1 is a diagram for explaining the sampling positions of the test pieces. First, a 55 mm × 55 mm test piece is sampled from the center in the longitudinal direction of the coil and from the center in the width direction. Further, from the positions adjacent to both sides in the longitudinal direction of the coil at the sampling position of the test piece, one 55 mm × 55 mm test piece is sampled at intervals within 1 cm each. These three test pieces are used as the center test pieces in the width direction.

[0052] Furthermore, a total of six 55 mm × 55 mm test pieces are sampled from the positions where the sampling positions of the above three center test pieces in the width direction coincide and from positions 2 cm away from both ends in the width direction of the coil, and these are used as the end test pieces in the width direction.

[0053] The obtained test pieces are subjected to stress relief annealing by heating at 800°C for 2 hours in an atmosphere of H2: 100%, and then the iron loss W 10 / 400 is measured. And when the following formula (I) is satisfied, it is determined that the variation of iron loss in the width direction is small. (|W mcl -W me |) / W mcl <0.080 ···(I) However, the meanings of the symbols in the above formula are as follows. W mclIron loss W in the central part of the specimen in the width direction 10 / 400 Average value (W / kg) W me Iron loss W of the end specimen in the width direction 10 / 400 Average value (W / kg)

[0054] Next, a 55mm x 55mm test specimen is taken from the center of the coil in both its longitudinal and widthwise directions. Furthermore, one 55mm x 55mm test specimen is taken from each of the adjacent positions in the widthwise direction of the coil, with a spacing of no more than 1cm between each. These three test specimens are designated as the longitudinal center test specimens.

[0055] Furthermore, three test specimens are taken from a position where the sampling locations of the three longitudinal center test specimens described above coincide with their positions in the width direction of the coil, and are located 5 m away from the innermost end of the coil. These specimens are designated as the longitudinal top test specimens. Similarly, three test specimens are taken from a position where the sampling locations of the three longitudinal center test specimens described above coincide with their positions in the width direction of the coil, and are located 5 m away from the outermost end of the coil. These specimens are designated as the longitudinal bottom test specimens.

[0056] The obtained specimens were subjected to stress-relieving annealing by heating at 800°C for 2 hours in an H2:100% atmosphere, and then the iron loss W was measured using the method described above. 10 / 400 The following is measured. If equation (II) below 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) However, the meanings of the symbols in the above formula are as follows: W mcc Iron loss W of the specimen at the longitudinal center 10 / 400 Average value (W / kg) W tc Iron loss W of the longitudinal top portion of the test specimen 10 / 400 Average value (W / kg) W bcIron loss W of the longitudinal bottom portion of the test specimen 10 / 400 Average value (W / kg)

[0057] 4. Plate 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 cost, 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. It is more preferable that the thickness of the base material be 0.20 to 0.40 mm.

[0058] 5. Insulating coating In the non-oriented electrical steel sheet according to this embodiment, it is preferable that the base material surface has an insulating coating. Since the non-oriented electrical steel sheet is used after the core blank has been punched out and then laminated, providing an insulating coating on the surface of the base material can reduce eddy currents between the sheets, thereby reducing eddy current losses as a core.

[0059] The type of insulating coating is not particularly limited, and known insulating coatings used as insulating coatings for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings mainly composed of inorganic materials and further containing organic materials. Here, a composite insulating coating is an insulating coating mainly composed of at least one of the following: metal chromate salts, metal phosphate salts, or inorganic materials such as colloidal silica, Zr compounds, or Ti compounds, with fine organic resin particles dispersed within it. In particular, from the viewpoint of reducing the environmental burden during manufacturing, which has been a growing need 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 insulating coating applied is not particularly limited, but for example, 200-3000 mg / m² per side. 2 It is preferable to use a concentration of approximately 300-2500 mg / m² per side. 2It is more preferable to do so. By forming the insulating film so that the amount of adhesion falls within the above range, it is possible to maintain excellent insulating properties of the film and uniformity during core adhesion. When measuring the amount of insulating film adhesion afterward, various known measurement methods can be used, for example, a method of measuring the mass difference before and after immersion in a sodium hydroxide aqueous solution, or a fluorescence X-ray method using a calibration curve can be used as appropriate.

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

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

[0063] <Hot rolling process> A steel ingot having the above chemical composition is heated, and the heated steel ingot is hot-rolled to obtain a hot-rolled sheet. There is no particular requirement for the heating temperature of the steel ingot when subjecting it to hot rolling, but it is preferably, for example, 1050 to 1250°C.

[0064] However, if the ratio of Zr-containing particles to coarse particles in the Z cross-section at t / 4 is to be 30% or more, the heating temperature should be 1150°C or higher from the viewpoint of sufficiently promoting the precipitation of Zr2S3. In addition, if the ratio of Zr-containing particles is to be 30% or higher, the finish rolling start temperature in the hot rolling process should be 950°C or lower. This is because setting the heating temperature to 1150°C or higher and the finish rolling start temperature to 950°C or lower promotes the precipitation of a sufficient amount of Zr2S3 before the start of finish rolling. There is no particular need to limit the lower limit of the finish rolling start temperature, but it may be set to, for example, 910°C or higher from the viewpoint of preventing excessive hot rolling load.

[0065] Furthermore, in the hot rolling process under the above-described preferred conditions, it is necessary to increase the heating temperature before hot rolling and to control the start temperature of finish rolling at a low level. Under these conditions, the hot-rolled sheet is allowed to cool between the end of rough rolling and the start of finish rolling. This cooling process can further promote the precipitation of Zr2S3. There are no particular restrictions on the cooling time; it is sufficient to allow the sheet to cool as needed until the start temperature of finish rolling falls below 950°C.

[0066] There are no particular restrictions on the finish rolling completion temperature, however, if the finish rolling start temperature is 950°C or lower, the finish rolling completion temperature will be less than 800°C. The finish rolling completion temperature may be 790°C or lower, and even 780°C or lower. There is no particular need to limit the lower limit of the finish rolling completion temperature, but for example, it may be 740°C. After the finish rolling is completed, winding is performed. There are no particular restrictions on the winding temperature, but it is preferable to set it to 500-600°C.

[0067] While there are no specific requirements for the thickness of the hot-rolled sheet after hot rolling, it is preferable to set it to approximately 1.5 to 3.0 mm, taking into account the final thickness of the base material. Although not particularly limited, it is preferable to set the thickness after rough rolling to approximately 35 mm to 45 mm and the reduction ratio for finish rolling to 91% to 97%.

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

[0069] <Acid washing process> After hot rolling or hot-rolled sheet annealing, the steel sheet is subjected to pickling to remove the scale layer formed on the surface of the base material. If the hot-rolled sheet annealing is box annealing, it is preferable to perform the pickling process before hot-rolled sheet annealing from the viewpoint of descaling. Here, the pickling conditions, such as the concentration of the acid used, the concentration of the accelerator used, and the temperature of the pickling solution, are not particularly limited and can be those of known pickling conditions.

[0070] <Cold rolling process> Cold rolling is performed on the steel sheet after annealing the hot-rolled sheet described above. In cold rolling, the sheet is rolled at a reduction ratio such that the final thickness of the base material is 0.10 to 0.50 mm.

[0071] <Finishing Annealing Process> Following the cold rolling described above, finish annealing is performed. For finish annealing, it is preferable to use a continuous annealing furnace. Finish annealing is carried out under conditions of a soaking temperature of 880 to 1080°C and a soaking time of 1 second to 10 minutes. It is preferable to use a mixed atmosphere of H2 and N2 with an H2 content of 1 to 100 volume percent (i.e., H2 + N2 = 100 volume percent) and a dew point of the atmosphere of -50 to +10°C.

[0072] If the soaking temperature is below 880°C, the grain size becomes finer and iron loss increases, which is undesirable. If the soaking temperature exceeds 1080°C, not only is the strength insufficient, but nitriding occurs in the surface layer, increasing iron loss, which is also undesirable. Furthermore, if the soaking time is less than 1 second, sufficient grain growth cannot occur. On the other hand, if the soaking time exceeds 10 minutes, it leads to an increase in manufacturing costs.

[0073] <Insulating film formation process> Following the above-mentioned finish annealing, an insulating coating formation process is carried out as needed. Here, the method for forming the insulating coating is not particularly limited, and the treatment solution may be applied and dried using a known method using a known insulating coating forming solution as shown below. Examples of known insulating coatings include composite insulating coatings mainly composed of inorganic materials and further containing organic materials.

[0074] The surface of the base material on which the insulating coating is formed may be subjected to any pretreatment before applying the treatment solution, such as degreasing with an alkali or pickling with hydrochloric acid, sulfuric acid, or phosphoric acid. Alternatively, the treatment solution may be applied to the surface of the base material directly after finish annealing without any of these pretreatments.

[0075] Furthermore, motor cores and the like can be manufactured from the obtained non-oriented electrical steel sheet by sequentially performing a punching process and a lamination process under the conditions shown below. If lower iron loss is a greater consideration for the obtained motor cores and the like, a stress-relieving annealing process may be further performed after the lamination process.

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

[0077] <Lamination process> Multiple sheets of non-oriented electrical steel, which have undergone a punching process, are laminated together to form a motor core.

[0078] <Stress Relief Annealing Process> The stacked motor cores are subjected to stress-relieving annealing as needed. Stress-relieving annealing promotes recrystallization and grain growth in the motor cores, reducing iron loss and significantly improving 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, it is preferable to set the annealing temperature in the range of 750 to 900°C. There are also no restrictions on the annealing time, but for example, it is preferable to set it to 0.5 to 5.0 hours. Note that the annealing time is the time during which the motor core is at 750°C or higher, and the heating time below 750°C and the cooling time may be set as appropriate.

[0080] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0081] Slabs having the chemical composition shown in Table 1 were heated to the temperatures shown in Table 2, then hot-rolled to a finished thickness of 2.0 mm, and wound at 600°C to obtain hot-rolled steel sheets. The starting temperature for finish rolling was adjusted by allowing cooling as needed after rough rolling, resulting in the temperatures shown in Table 2. The obtained hot-rolled steel sheets were then subjected to hot-rolled sheet annealing in a continuous annealing furnace at 1000°C for 1 minute. After removing scale from the resulting steel sheets by pickling, they were cold-rolled to a thickness of 0.35 mm. Furthermore, finish annealing was performed in a mixed atmosphere of H2:25% and N2:75% under the conditions shown in Table 2.

[0082] [Table 1]

[0083] [Table 2]

[0084] A test piece was cut from the center of the coil manufactured by the above process, both longitudinally and widthwise, so that the Z-section at t / 4 would be the observation surface, and then mirror-polished. Subsequently, using a SEM with an automatic particle measurement function, the above observation surface was measured with the following settings: magnification: 500x, acceleration voltage: 20keV, work distance: 17mm, measurement area: 25mm. 2 Under these conditions, backscattered electron images were captured, and further chemical analysis of coarse particles contained in the field of view was performed using an EDS attached to the SEM. In this process, ten elements—C, Si, Mn, P, S, Al, Ti, N, O, and Zr—were selected as the target elements, and the content of each element was determined so that the total content of these elements equaled 100%. The measurement was terminated when the peak intensity of the element contained in the particle reached 2500 counts, or when it exceeded 1000 counts and the measurement time reached 0.5 seconds. If the Zr concentration of a coarse particle was 30 at% or higher, the particle was determined to be a Zr-containing particle.

[0085] The above analysis was performed on multiple fields of view, and the total number of coarse particles was 1000 or more and the field size was 25 mm. 2 The measurement was terminated when the measurement area reached the specified limit. The ratio of Zr-containing particles to the total number of coarse particles analyzed was then calculated. Furthermore, the number density of Zr-containing particles was determined by dividing the total number of Zr-containing particles observed in the entire field of view by the total area of ​​the entire field of view.

[0086] Next, to evaluate the variation in iron loss of the above coil, specimens were taken from the center in the width direction, the ends in the width direction, the center in the longitudinal direction, the top in the longitudinal direction, and the bottom in the longitudinal direction using the procedure described above. The obtained specimens were subjected to stress-relieving annealing by heating at 800°C for 2 hours in an H2:100% atmosphere, and then the iron loss W was measured. 10 / 400 Measurements were taken. Iron loss W 10 / 400The measurements were performed in accordance with the SST method specified in JIS C 2556:2015. However, the SST measurements were performed on 55 mm x 55 mm test specimens using a corresponding small single-sheet 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 shown in Table 2. In this embodiment, equations (I) and (II) described above are satisfied, and W mcc When the value is 18.0 W / kg or less, it is determined that the variation in iron loss within the coil is small and that it has consistently low iron loss.

[0088] As shown in Table 2, Tests No. 1 to 21, which satisfy all the provisions of the present invention, exhibit small variations in iron loss within the coil and consistently low iron loss. Furthermore, comparing Tests No. 1 to 4 using the same steel type A, it can be seen that in Tests No. 1 and 2, where the manufacturing conditions are favorable, the proportion of Zr-containing particles is higher compared to Tests No. 3 and 4, where the conditions are not favorable, resulting in a greater reduction in variations in iron loss within the coil. Similarly, comparing Tests No. 9 to 11 using the same steel type E, in Tests No. 9 and 10, where the manufacturing conditions are favorable, the proportion of Zr-containing particles is higher compared to Test No. 11, where the conditions are not favorable, resulting in even less variation in iron loss within the coil.

[0089] In contrast to these, tests No. 22 to 35, which deviated from the provisions of the present invention, resulted in either greater variation in iron loss within the coil or higher iron loss.

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

[0091] In test No. 25, the value of the middle side of equation (i) was excessive, resulting in an excess of particles and increased iron loss. In tests No. 26-29, the excessive content of at least one of Ti, Nb, and V made it easier for fine MnS and Zr2S3 to precipitate, leading to greater variability in iron loss.

[0092] In Test No. 30, the Al content was below the specified value, so iron loss could not be reduced. In addition, N could not be sufficiently fixed as AlN, and the formation of Zr2S3 could not be promoted, resulting in a large variation in iron loss. In Test No. 31, the Mn content was excessive, so the formation of MnS could not be suppressed, resulting in increased iron loss and an even larger variation in iron loss.

[0093] In Test No. 32, the Si content was below the specified value, so the iron loss could not be reduced. In Test No. 33, the Al content was excessive, causing cracks to occur during cold rolling. In Test No. 34, the N content was excessive, so some of the Zr was consumed as ZrN, resulting in insufficient fixing effect of S by Zr and a large variation in iron loss. In Test No. 35, the S content was below the specified value, and as a result the value of the middle side of equation (i) was excessive, causing fine ZrN, ZrC, ZrO2, etc. to crystallize and a large variation in iron loss. [Industrial applicability]

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

Claims

1. The chemical composition of the base material is, in mass percent, C: 0.010% or less, Si: more than 1.20% and less than 4.00%, Al: more than 0.12% and less than 2.50%, Mn: 0.10-1.00%, P: 0.20% or less, S: 0.0010-0.050%, O: 0.0050% or less, N: Less than 0.0040% Zr: 0.0035 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 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, The remainder consists of Fe and impurities. The following equation (i) is satisfied, In a cross-section parallel to the surface of the base material at a position 1 / 4 thickness from the surface of the base material, among particles with an equivalent circular diameter of 1 μm or more, the number proportion of particles with a Zr concentration of 30 at% or more is 15% or more, and the number density is 20 / mm² or more. Non-oriented electrical steel sheet. 1.0≦Zr / S≦3.0...(i) However, the element symbols in the above formula represent the content (mass %) of each element.

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

3. In a cross-section parallel to the surface of the base material at a position 1 / 4 thickness from the surface of the base material, the number proportion of particles with a circular equivalent diameter of 1 μm or more that have a Zr concentration of 30 at% or more is 30% or more. The non-oriented electrical steel sheet according to claim 1.

4. In a cross-section parallel to the surface of the base material at a position 1 / 4 thickness from the surface of the base material, the number proportion of particles with a circular equivalent diameter of 1 μm or more that have a Zr concentration of 30 at% or more is 30% or more. The non-oriented electrical steel sheet according to claim 2.

5. A laminate of non-oriented electrical steel sheets according to any one of claims 1 to 4, Motor core.

6. Including the motor core described in claim 5, Motor.

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