WO2025229787A1 - Non-oriented electromagnetic steel sheet, motor core, and motor - Google Patents

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

The present invention relates to non-oriented electrical steel sheets, motor cores, and motors.

In recent years, global environmental issues have received increasing attention, and demand for energy conservation efforts has grown even more. In particular, there is a strong demand for higher efficiency in electrical equipment. As a result, 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, and other devices. This trend is particularly evident in drive motors for electric and hybrid vehicles, and air conditioner compressor motors.

In order 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 in motor cores is an effective way to reduce iron loss. Coarsening crystal grains is an effective way to reduce iron loss, but it is known that fine precipitates such as MnS are harmful to grain growth (see, for example, Patent Document 1).

JP 2019-99854 A

MnS redissolves during 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 movement when the product is magnetized, causing increased iron loss. For this reason, operations are carried out to suppress the redissolution of MnS by lowering the heating temperature in the hot rolling and hot-rolled sheet annealing processes. However, it is difficult to properly control the temperature across 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.

The present invention was made to solve these problems, and aims to provide a non-oriented electrical steel sheet with little variation in iron loss within the coil.

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

(1) The chemical composition of the base material is, in mass%,
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: 0.0030 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 is Fe and impurities.
The following formula (i) is satisfied:
Non-oriented electrical steel sheet.
1.0≦Zr/S≦3.0...(i)
In the above formula, the element symbols indicate the content (mass %) of each element.

(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)
In the above formula, the element symbols indicate the content (mass %) of each element.

(3) In a cross section parallel to the surface of the base material at a quarter thickness position from the surface of the base material, the number ratio 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.
The non-oriented electrical steel sheet according to (1) or (2) above.

(4) A laminate comprising the non-oriented electrical steel sheets according to any one of (1) to (3) above.
Motor core.

(5) A motor including the motor core according to (4) above.
Motor.

According to the present invention, it is possible to obtain non-oriented electrical steel sheets with little variation in iron loss within the coil.

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

The inventors conducted extensive research to solve the above problems, and as a result, arrived at the following findings.

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. _Zr2S3 crystallizes _and precipitates at a higher temperature than MnS, so it is coarse and does not inhibit grain growth. Furthermore, _Zr2S3 exists more stably in a high temperature range than MnS, so _there is little risk of it re-forming into a solid solution during the hot rolling process or the hot-rolled sheet annealing process.

However, Zr has a high affinity not only with S but also with N, and there is a possibility that it may crystallize as Zr(N,C), so it is necessary to include a certain amount of Al or more and fix the N as AlN.

Furthermore, when large amounts of Ti, Nb, and V are contained, 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, fine _Zr2S3 also precipitates in combination with these _{carbonitrides} , which may adversely affect grain growth. Therefore, it is necessary to limit the contents of Ti, Nb, and V.

The present invention was made based on the above findings. Each of the requirements of the present invention will be explained in detail below.

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 %."

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.

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.

Al: More than 0.12% and Not More than 2.50% Al (aluminum) is an element that increases the electrical resistance of steel, thereby reducing eddy current loss and improving high-frequency iron loss in non-oriented electrical steel sheets. Al also improves the texture, thereby improving iron loss. Additionally, Al fixes N as AlN, thereby indirectly promoting the formation of Zr ₂ S ₃ . To achieve these effects, the Al content is set to more than 0.12%. The Al content is preferably 0.25% or more, more preferably 0.40% or more. However, excessive Al content reduces toughness. Therefore, the Al content is set to not more than 2.50%. The Al content is preferably 2.00% or less, more preferably 1.00% or less.

Mn: 0.10-1.00%
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 that 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.

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.

S: 0.0010-0.050%
S (sulfur) is an element that increases iron loss by forming fine precipitates of MnS, thereby degrading the magnetic properties of non-oriented electrical steel sheets. However, in this embodiment, Zr is used to fix S as _Zr2S3 , making it possible to suppress the precipitation of fine MnS. Therefore, from the perspective of cost reduction, the S content is not extremely reduced, 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 deteriorate significantly 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.

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.

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.

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 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 particles containing Zr 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.

In this embodiment, the Zr content needs to be adjusted according to the S content. Therefore, in addition to the S and Zr contents each being within the above ranges, the following formula (i) needs to be satisfied. If the value of the middle part of the formula (i) is less than 1.0, the S fixing effect of Zr becomes insufficient. On the other hand, if the value of the middle part of the formula (i) exceeds 3.0, fine ZrN, ZrC, _ZrO2, etc. will crystallize, increasing iron loss. The value of the middle part of the 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. Furthermore, the value of the middle part of the 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)
In the above formula, the element symbols indicate the content (mass %) of each element.

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 contents being within the above ranges, 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, and precipitation of ZrN can be suppressed. 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)
In the above formula, the element symbols indicate the content (mass %) of each element.

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 described above, excessive Ti, Nb, and V contents tend to cause sulfides such as MnS to precipitate in combination with these carbonitrides as nuclei. In addition, when Ti, Nb, and V carbonitrides precipitate finely, Zr ₂ S ₃ may also precipitate finely in combination with these carbonitrides, 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 preferably 0.0025% or less, and 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. The lower limits of the Ti, Nb, and V contents are not particularly limited, but excessive reductions in their contents may increase manufacturing costs. Therefore, the Ti, Nb, and V contents are preferably all greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

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.

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.

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.

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.

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.

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.

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.

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.

In the chemical composition of the base material of the non-oriented electrical steel sheet of the present invention, the balance is Fe and impurities. Here, "impurities" refers to components that are mixed in during the industrial production of steel due to various factors in the raw materials, such as ore and scrap, and in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention. Impurities include, for example, 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 contained in an amount of 0.005% or less each.

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, measurement can be performed using inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES) and inductively coupled plasma (ICP) mass spectrometry (ICP-MS). Furthermore, C and S can be measured using the combustion-infrared absorption method, N can be measured using the inert gas combustion-thermal conductivity method, and O can be measured using the inert gas fusion-non-dispersive infrared absorption method.

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.

In this specification, particles include compounds that crystallize in the liquid phase and compounds that precipitate in the solid phase, such as carbides, nitrides, carbonitrides, sulfides, oxides, and composites of these.

Specifically, in a cross section parallel to the surface of the base material at a position 1/4 the thickness from the surface of the base material (hereinafter also referred to as the "Z cross section at t/4"), among particles with an equivalent circle diameter of 1 μm or more (hereinafter also referred to as "coarse particles"), the number proportion of particles with a Zr concentration of 30 at% or more (hereinafter also referred to as "Zr-containing particles") is preferably 30% or more, and more preferably 35% or more. There is no particular need to set an upper limit to this number proportion, but it may be, for example, 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.

There is no particular need to limit the number density of the Zr-containing particles, but in order to more reliably obtain the fixing effect of S, it is preferable that the number density be 40/mm ² or more.

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.

First, a test piece is cut out so that the Z-section at t/4 becomes the observation surface and is mirror-polished. Then, using an SEM with an automatic particle measurement function, a backscattered electron image is taken of the observation surface under the following conditions: magnification: 500x, acceleration voltage: 20 keV, beam diameter: 0.79 μm, work distance: 17 mm, measurement area: 25 mm2 or more ^. Furthermore, 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. At this time, the ten elements C, Si, Mn, P, S, Al, Ti, N, O, and Zr are used as 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 more, the coarse particles are determined to be Zr-containing particles.

The above analysis is performed on multiple visual fields and is terminated when the total number of coarse particles reaches 1,000 or more and the measurement area reaches 25 mm2 or ^more . The percentage (%) of the number of Zr-containing particles relative to the total number of coarse particles analyzed is then calculated. The total number of Zr-containing particles confirmed in all visual fields analyzed is divided by the total area of all visual fields to determine the number density (/ ^mm2 ) of Zr-containing particles.

3. Magnetic Properties The non-oriented electrical steel sheet according to this embodiment has a small variation in iron loss W10/ ₄₀₀ within the coil. Here, a 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 that the difference in iron loss between the center and end portions in the longitudinal direction of the coil is small. The iron loss W10 _/400 is measured in accordance with the Single Sheet Tester (SST) method specified in JIS C 2556:2015. The SST measurement is performed on a 55 mm x 55 mm test piece using a corresponding small single sheet tester. The iron loss W10 _/400 refers to the iron loss occurring under conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz. When measuring the iron loss, the excitation direction is set to two directions: a direction parallel to the rolling direction (hereinafter referred to as the L direction) and a direction perpendicular to the rolling direction (hereinafter referred to as the C direction), and the average value of the values measured in each direction is calculated as the iron loss value of the material.

The method for evaluating the variation in iron loss within a coil will now be explained in detail. Figure 1 is a diagram illustrating the location of test specimen collection. First, a 55mm x 55mm test specimen is collected from the center of the coil in the longitudinal direction and the center in the width direction. Furthermore, two 55mm x 55mm test specimens are collected from positions adjacent to the collection position of the test specimen on both sides of the coil in the longitudinal direction, with an interval of no more than 1cm between each. These three test specimens are referred to as the width direction center test specimens.

Furthermore, a total of six 55 mm x 55 mm test pieces were taken from positions that were aligned with the longitudinal positions of the coil from the three widthwise center test pieces mentioned above, and 2 cm away from each end of the coil in the widthwise direction. These were designated as widthwise end test pieces.

The obtained test pieces were subjected to stress relief annealing by heating at 800°C for 2 hours in a 100% _H2 atmosphere, and then the iron loss W10 _/400 was measured using the method described above. If 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)
However, the meanings of the symbols in the above formula are as follows:
W _mcl : average value of iron loss W _10/400 of the test piece at the center in the width direction (W / kg)
W _me : average value of iron loss W _10/400 of width direction end test pieces (W / kg)

Next, a 55mm x 55mm test piece is taken from the center of the coil in the longitudinal direction and the center in the width direction. Furthermore, two 55mm x 55mm test pieces are taken from positions adjacent to the test piece taken on both sides of the coil in the width direction, with an interval of no more than 1cm between each. These three test pieces are called the longitudinal center test pieces.

Furthermore, three test pieces are taken from a position 5 m away from the innermost edge of the coil, where the positions in the width direction of the coil coincide with the positions of the three longitudinal center test pieces mentioned above, and these are designated as the longitudinal top test pieces. Similarly, three test pieces are taken from a position 5 m away from the outermost edge of the coil, where the positions in the width direction of the coil coincide with the positions of the three longitudinal center test pieces mentioned above, and these are designated as the longitudinal bottom test pieces.

The obtained test pieces were subjected to stress relief annealing by heating at 800°C for 2 hours in a 100% _H2 atmosphere, and then the iron loss W10 _/400 was measured using the method described above. 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)
However, the meanings of the symbols in the above formula are as follows:
W _mcc : average value of iron loss W _10/400 of the longitudinal center test piece (W / kg)
W _tc : average value of iron loss W _10/400 of the longitudinal top test piece (W / kg)
W _bc : average value of iron loss W _10/400 of the test piece at the bottom in the longitudinal direction (W/kg)

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.

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.

There are no particular restrictions on the type of insulating coating, and known insulating coatings used for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings that are primarily made of inorganic materials and also contain organic materials. Here, a composite insulating coating is an insulating coating that is primarily made of at least one of inorganic materials such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, and Ti compounds, with fine organic resin particles dispersed in it. In particular, given the growing need for reducing the environmental impact during manufacturing, insulating coatings that use metal phosphate salts, Zr or Ti coupling agents, or Zr or Ti carbonates or ammonium salts as starting materials are preferred.

The amount of the insulating coating applied is not particularly limited, but is preferably about 200 to 3,000 mg/ ^m² per side, and more preferably 300 to 2,500 mg/ ^m² per side. Forming the insulating coating so that the amount of coating falls within the above range makes it possible to maintain excellent insulating properties of the coating and uniformity when bonding the core. When measuring the amount of the insulating coating applied after the fact, various known measurement methods can be used, such as measuring the difference in mass before and after immersion in a sodium hydroxide aqueous solution, or fluorescent X-ray analysis using a calibration curve method.

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.

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.

<Hot rolling process>
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 when subjected to hot rolling is not particularly limited, but is preferably 1050 to 1250°C, for example.

However, when it is desired to set the number ratio of Zr-containing particles to coarse particles in the Z cross section at t/ ₄ to 30% or more, the heating temperature is set to 1150°C or higher from the viewpoint of sufficiently promoting the precipitation of _Zr2S3 . In addition, when it is desired to set the number ratio to 30% or more, the finish rolling start temperature in the hot rolling step is set to 950°C or lower. This is because by setting the heating temperature to 1150°C or higher and the finish rolling _start temperature to 950°C or lower, it is possible to promote the precipitation of a sufficient amount of _Zr2S3 before the start of finish rolling. There is no need to particularly set a lower limit for 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.

In the hot rolling process under the above-mentioned preferred conditions, it is necessary to increase the heating temperature before hot rolling and to control the start temperature of finish rolling low. Under such conditions, the hot-rolled sheet is allowed to cool naturally after the completion of rough rolling and before the _start of finish rolling. By performing the above-mentioned cooling, it is possible to further promote the precipitation of _Zr2S3 . There is no particular limitation on the cooling time, and it is sufficient to allow the sheet to cool appropriately until the finish rolling start temperature becomes 950°C or less.

There are no particular restrictions 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 lower limit to the finish rolling end temperature, but it may be 740°C, for example. After finish rolling is complete, coiling is performed. There are no particular restrictions on the coiling temperature, but it is preferably 500 to 600°C.

The thickness of the hot-rolled sheet after hot rolling is not particularly specified, but taking into account the final thickness of the base material, it is preferable to set it at, for example, approximately 1.5 to 3.0 mm. Although not particularly limited, it is preferable that the thickness after rough rolling be approximately 35 mm to 45 mm, and that the reduction rate in finish rolling be 91% to 97%.

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

<Acid washing process>
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 carried out 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.

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

<Finishing annealing process>
After the cold rolling, finish annealing is performed. A continuous annealing furnace is preferably used for the finish annealing. The finish annealing is performed under conditions of a soaking temperature of 880 to 1080°C and a soaking time of 1 second to 10 minutes. The atmosphere is preferably a mixed atmosphere of _H2 and _N2 with a _H2 ratio of 1 to 100% by volume (i.e., _H2 + _N2 = 100% by volume), and the dew point of the atmosphere is preferably -50 to +10°C.

If the soaking temperature is less than 880°C, the grain size will become finer and iron loss will increase, 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 also undesirable. Furthermore, if the soaking time is less than 1 second, the grains will not grow sufficiently. On the other hand, if the soaking time exceeds 10 minutes, this will result in increased manufacturing costs.

<Insulating film formation process>
After the above-mentioned finish annealing, an insulating coating formation 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.

The surface of the base material on which the insulating coating is to be formed may be subjected to any pretreatment, such as degreasing with alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc., before the treatment solution is applied. The treatment solution may also be applied to the surface of the base material immediately after finish annealing without undergoing these pretreatments.

Furthermore, motor cores and the like can be manufactured by sequentially performing a punching process and a lamination process on the obtained non-oriented electrical steel sheet under the conditions shown below, for example. Note that if low iron loss is more important for the obtained motor cores and the like, a stress relief annealing process may be further performed after the lamination process.

<Punching process>
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. There are no particular restrictions on the processing conditions, and any commonly used method can be used.

<Lamination process>
A number of punched non-oriented electrical steel sheets are laminated to form a motor core.

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

There are no particular restrictions on the conditions for stress relief annealing, but from the perspective 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, 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; the heating time and cooling time below 750°C can be set as appropriate.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

A slab having the chemical composition shown in Table 1 was heated to the temperature shown in Table 2, then hot-rolled to a finish thickness of 2.0 mm, and coiled at 600°C to obtain a hot-rolled steel sheet. The finish rolling start temperature was adjusted by allowing the sheet to cool naturally 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 pickled to remove scale, and then cold-rolled to a cold-rolled steel sheet having a thickness of 0.35 mm. Furthermore, the steel sheet was subjected to finish annealing under the conditions shown in Table 2 in a mixed atmosphere of 25% _H2 and 75% _N2 .

A test piece was cut out from the center of the coil manufactured by the above process in the longitudinal direction and the center in the width direction so that the Z cross section at t/4 was the observation surface, and mirror polishing was performed. Then, using an SEM with automatic particle measurement function, a backscattered electron image was taken of the observation surface under the ^following conditions: magnification: 500x, acceleration voltage: 20 keV, work distance: 17 mm, measurement area: 25 mm2. Furthermore, chemical analysis of the coarse particles contained in the field of view was performed using an EDS attached to the SEM. At this time, the 10 elements of 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 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 more, the coarse particles were determined to be Zr-containing particles.

The above analysis was performed on multiple visual fields and was terminated when the total number of coarse particles reached 1,000 or more and the measurement area reached 25 mm2 or ^more . The ratio of the number of Zr-containing particles to the total number of coarse particles analyzed was then calculated. The total number of Zr-containing particles confirmed in all visual fields analyzed was divided by the total area of all visual fields to determine the number density of Zr-containing particles.

Next, 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 collected using the procedure described above. The obtained test pieces were subjected to stress relief annealing by heating at 800°C for 2 hours in a 100% _H2 atmosphere, and then iron loss W10 _/400 was measured. Iron loss W10 _/400 was measured in accordance with the SST specified in JIS C 2556:2015. However, the SST measurement was performed on 55 mm x 55 mm test pieces using a corresponding small single plate tester. Note that when measuring iron loss, the excitation direction was set to two directions, the L direction and the C direction, and the average of the values measured in each direction was calculated as the iron loss value of the material.

The results are also shown in Table 2. In this example, when the above-mentioned formulas (I) and (II) are satisfied and W _mcc is 18.0 W/kg or less, it was determined that the variation in iron loss within the coil is small and that the iron loss is stably low.

As shown in Table 2, Tests No. 1 to 21, which satisfy all of the specifications of the present invention, have small variations in iron loss within the coil and consistently low iron loss. Furthermore, when comparing Tests No. 1 to 4, which use the same steel type A, it is clear that Tests No. 1 and 2, in which the manufacturing conditions satisfy the optimum conditions, have a higher proportion of Zr-containing particles than Tests No. 3 and 4, in which the manufacturing conditions deviate from the optimum conditions, and as a result, it is possible to further reduce the variation in iron loss within the coil. Similarly, when comparing Tests No. 9 to 11, which use the same steel type E, it is clear that Tests No. 9 and 10, in which the manufacturing conditions satisfy the optimum conditions, have a higher proportion of Zr-containing particles than Test No. 11, in which the manufacturing conditions deviate from the optimum conditions, and as a result, the variation in iron loss within the coil is reduced.

In contrast, Tests No. 22 to 35, which deviate from the provisions of this invention, resulted in either greater variation in iron loss within the coil or higher iron loss.

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, resulting in an excess amount of particles and increased 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.

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, which made it easier for fine MnS and _Zr2S3 to precipitate, resulting in a large variation _in iron loss.

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

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 some 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, _ZrO2 , etc. were crystallized, increasing the variation in iron loss.

As described above, the present invention makes it possible to obtain non-oriented electrical steel sheets with little variation in iron loss within the coil.

Claims (6)

The chemical composition of the base material is, in mass%,
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: 0.0030 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 is Fe and impurities.
The following formula (i) is satisfied:
Non-oriented electrical steel sheet.
1.0≦Zr/S≦3.0...(i)
In the above formula, the element symbols indicate the content (mass %) of each element. The chemical composition of the base material further satisfies the following formula (ii):
The non-oriented electrical steel sheet according to claim 1.
Al/Zr≧25.0...(ii)
In the above formula, the element symbols indicate the content (mass %) of each element. In a cross section parallel to the surface of the base material at a quarter thickness position from the surface of the base material, the number ratio 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.
The non-oriented electrical steel sheet according to claim 1. In a cross section parallel to the surface of the base material at a quarter thickness position from the surface of the base material, the number ratio 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.
The non-oriented electrical steel sheet according to claim 2. A laminate comprising the non-oriented electrical steel sheets according to any one of claims 1 to 4.
Motor core. A motor core comprising the motor core according to claim 5.
Motor.