JP7849644B2 - Non-oriented electrical steel sheets, motor cores, and motors - Google Patents

Description

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

In recent years, global environmental issues have attracted increasing attention, and the demand for energy conservation efforts has grown 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.

Reducing iron loss, which is the main source of losses, is crucial for achieving high-efficiency motors. Reducing iron loss in the electrical steel sheet used as the motor core is an effective way to achieve this. While grain coarsening is effective in reducing iron loss, it is known that fine precipitates such as MnS are detrimental to grain growth (see, for example, Patent Document 1).

Japanese Patent Publication No. 2019-99854

MnS redissolves during the hot rolling process and then precipitates finely during the subsequent hot-rolled sheet annealing process, inhibiting grain growth during annealing. As a result, MnS inhibits magnetic domain wall movement when magnetized in the product, increasing iron loss. Therefore, operations are being 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 over the entire length and width of the slab and hot-rolled sheet, and variations in iron loss within the coil are contributing to factors such as reduced yield.

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

The present invention is essentially a non-oriented electrical steel sheet, a motor core, and a motor, as described below.

(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 remainder consists of Fe and impurities.
The following equation (i) is satisfied:
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 base material further satisfies the following formula (ii):
The non-oriented electrical steel sheet described in (1) above.
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 ratio 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.
Non-oriented electrical steel sheet as described in (1) or (2) above.

(4) Laminates the non-oriented electrical steel sheets described in any of (1) to (3) above,
Motor core.

(5) Including the motor core described in (4) above,
Motor.

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

Figure 1 is a diagram illustrating the sampling locations for the test specimens.

As a result of diligent research conducted by the inventors to solve the above problems, we have obtained 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. 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 in the high-temperature range than MnS, there is less risk of re-solution during the hot rolling process or the hot-rolled sheet annealing process.

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

Furthermore, if large amounts of Ti, Nb, and V are present, sulfides such as MnS tend to precipitate in combination with these carbonitrides, using them as nuclei. In addition, when 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.

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

1. Chemical composition of the base material. The reasons for limiting each element are as follows. In the following explanation, "%" for content refers to "mass%".

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. Note that 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.

Si: Over 1.20% and up to 4.00% Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves high-frequency iron loss in non-oriented electrical steel sheets. To obtain this effect, the Si content should be over 1.20%. Preferably, the Si content is 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 will decrease. Therefore, the Si content should be 4.00% or less. Preferably, the Si content is 3.70% or less, and more preferably 3.50% or less.

Al: greater than 0.12% and less than or equal to 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. In addition, Al also has the effect of improving iron loss by improving the texture. Furthermore, Al also has the effect of indirectly promoting the formation of _Zr₂S₃ by fixing N as AlN. To obtain these effects, the Al content should be greater than 0.12%. The _Al content is preferably 0.25% or more, and more preferably 0.40% or more. However, if the Al content is excessive, the toughness will decrease. Therefore, the Al content should be 2.50% or less. The Al content is preferably 2.00% or less, and more preferably 1.00% or less.

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 the present 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.

P: 0.20% or less. Phosphorus (P) is present in steel as an impurity, and if its content is excessive, the toughness of the non-oriented electrical steel sheet 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 an increase in 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.

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.

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.

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 an increase in 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.

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.

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.

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 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.

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 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 all be less than 0.0030%. Preferably, the content of Ti, Nb, and V should all be 0.0025% or less, and more preferably 0.0020% or less. For similar reasons, 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. While there are no particular lower limits to the content of Ti, Nb, and V, extreme reductions in their content may lead to increased manufacturing costs. Therefore, the content of Ti, Nb, and V is preferably 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. 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 impurity levels are 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. 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, the content of REM, Ca, and Mg is preferably greater 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 lanthanides, 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. 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.

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.

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 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 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.

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 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 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 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 even more preferably 0.010% or more.

Ni: 0.050% or less. Nickel (Ni) is an element that can be mixed into steel as an impurity. 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 the lower limit is 0%. However, an extreme reduction in Ni content may lead to an increase in manufacturing costs. For this reason, it is preferable that the Ni content is greater 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. 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.

B: 0.0030% or less Boron (B) is an element that can be mixed into steel as an impurity. 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 the lower limit is 0%. However, an extreme reduction in the B content may lead to an increase in manufacturing costs. For this reason, preferably, the B content is greater 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 remainder is Fe and impurities. Here, "impurities" means 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 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 contained in amounts of 0.005% or less of 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, 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 may be measured using inert gas combustion-thermal conductivity spectrometry, and O may be measured using inert gas fusion-non-dispersive infrared absorption spectrometry.

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

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.

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-section at t/4"), it is preferable that the number ratio 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 need to set an upper limit for the number ratio, 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.

While there is no particular limit to the number density of Zr-containing particles, it is preferable to set it to 40/ ^mm² or higher in order to more reliably obtain the fixation effect of S.

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.

First, a test specimen is cut out so that the Z-section at t/4 becomes the observation surface, and then mirror-polished. Then, using a SEM equipped with an automatic particle measurement function, a backscattered electron image is captured on the observation surface under ^the following conditions: magnification: 500x, acceleration voltage: 20 keV, beam diameter: 0.79 μm, work distance: 17 mm, and measurement area: 25 mm² or higher. Furthermore, a chemical analysis of coarse particles contained in the field of view is performed 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 used as the target elements, 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.

The above analysis is performed on multiple fields of view, and the analysis is terminated when the total number of coarse particles exceeds 1000 and the measurement area exceeds 25 ^mm² . The percentage of Zr-containing particles relative to the total number of coarse particles analyzed is then calculated. The number density of Zr-containing particles (/ ^mm² ) is determined by dividing the total number of Zr-containing particles observed in all analyzed fields by the total area of all fields.

3. Magnetic Properties The non-oriented electrical steel sheet according to this embodiment exhibits little variation in iron loss W _10/400 within the coil. Here, little 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. Furthermore, the iron loss W _10/400 shall be measured in accordance with the Single Sheet Tester (SST) method specified in JIS C 2556:2015. However, the SST measurement shall be performed on a 55 mm x 55 mm test piece using a corresponding small single sheet tester. Note that the iron loss W _10/400 refers to the iron loss that occurs under the conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz. Furthermore, when measuring iron loss, the excitation direction is set to two directions: one parallel to the rolling direction (hereinafter referred to as the L direction) and one perpendicular to the rolling direction (hereinafter referred to as the C direction). 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 be explained in detail. Figure 1 is a diagram illustrating the sampling location of the test specimens. First, a 55 mm x 55 mm test specimen is taken from the center of the coil in both the longitudinal and width directions. Furthermore, one 55 mm x 55 mm test specimen is taken from each of the adjacent positions on both sides of the coil in the longitudinal direction, with a spacing of no more than 1 cm between them. These three test specimens are designated as the width-direction center test specimens.

Furthermore, the sampling locations of the three widthwise central test specimens mentioned above coincide with their positions in the longitudinal direction of the coil. A total of six 55 mm x 55 mm test specimens are taken from positions 2 cm away from each end in the widthwise direction of the coil, and these are designated as widthwise end test specimens.

The obtained test specimens are subjected to stress-relieving annealing by heating at 800°C for 2 hours in an _H2 :100% atmosphere, and then the iron loss W _10/400 is measured using the method described above. If the following equation (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 in the central part of the specimen in the width direction (W/kg)
W _me : Average value of iron loss W _10/400 (W/kg) of the end specimen in the width direction.

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

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.

The obtained test specimens are subjected to stress-relieving annealing by heating at 800°C for 2 hours in an _H2 :100% atmosphere, and then the iron loss W _10/400 is measured using the method described above. If the following equation (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 in the longitudinal center of the test specimen (W/kg)
W _tc : Average value of iron loss W _10/400 of the longitudinal top section of the test specimen (W/kg)
W _bc : Average value of iron loss W _10/400 of the longitudinal bottom portion of the test specimen (W/kg)

4. Plate Thickness There are no particular restrictions on the plate 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 plate 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 plate thickness of the base material be 0.50 mm or less. It is more preferable that the plate thickness of the base material be 0.20 to 0.40 mm.

5. Insulating Coating In the non-oriented electrical steel sheet according to this embodiment, it is preferable to have an insulating coating on the surface of the base material. Since the non-oriented electrical steel sheet is used after being laminated after punching out the core blank, providing an insulating coating on the surface of the base material can reduce eddy currents between sheets, thereby reducing eddy current losses as a core.

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 impact 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.

The amount of insulating film applied is not particularly limited, but it is preferably about 200 to 3000 mg/ ^m² per side, and more preferably 300 to 2500 mg/ ^m² per side. By forming the insulating film with an application amount 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 applied afterward, various known measurement methods can be used, such as measuring the mass difference before and after immersion in a sodium hydroxide aqueous solution, or using a calibration curve method with X-ray fluorescence, as appropriate.

6. Motor Core and Motor The motor core according to one embodiment of the present invention is made by laminating the above-mentioned non-oriented electrical steel sheets. 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 are the above-mentioned non-oriented electrical steel sheets. Furthermore, the motor according to one embodiment of the present invention includes the above-mentioned 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 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.

<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.

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 more, the finish rolling start temperature in the hot rolling process should be 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 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.

Furthermore, 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 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.

There are no particular restrictions on the finish rolling completion temperature, but 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 to 600°C.

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, for example, to set the thickness after rough rolling to approximately 35 to 45 mm and the reduction ratio for finish rolling to 91% to 97%.

<Hot-rolled sheet annealing process>
Subsequently, hot-rolled sheet annealing is performed as needed, with the aim of reducing 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.

<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.

<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.

<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.

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.

<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.

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 prior pretreatment.

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.

<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.

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

<Stress Removal 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.

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.

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

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.

A test piece was cut from the center of the coil manufactured by the above process, with the Z-section at t/4 from the center in both the longitudinal and width directions serving as the observation surface, and then mirror-polished. Subsequently, a backscattered electron image was captured on the observation surface using an SEM equipped with an automatic particle measurement function under the ^following conditions: magnification: 500x, acceleration voltage: 20 keV, work distance: 17 mm, and measurement area: 25 mm². Furthermore, a 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 elements contained in the particles reached 2500 counts, or when it exceeded 1000 counts and the measurement time reached 0.5 seconds. Furthermore, if the Zr concentration of the coarse particles was 30 at% or higher, the coarse particles were determined to be Zr-containing particles.

The above analysis was performed on multiple fields of view, and the analysis was terminated when the total number of coarse particles exceeded 1000 and the measurement area was ²⁵ mm² or larger. The ratio of Zr-containing particles to the total number of coarse particles analyzed was then calculated. In addition, the number density of Zr-containing particles was determined by dividing the total number of Zr-containing particles observed in all analyzed fields of view by the total area of all fields of view.

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, following 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 _10/400 was measured. The iron loss W _10/400 was measured in accordance with the SST specified in JIS C 2556:2015. However, the SST measurement was performed on a 55 mm × 55 mm specimen 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 material's iron loss value.

The results are shown in Table 2. In this embodiment, it was determined that the variation in iron loss within the coil was small and that the coil had a consistently low iron loss when equations (I) and (II) described above were satisfied and W _mcc was 18.0 W/kg or less.

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 grade A, it can be seen that in Tests No. 1 and 2, where the manufacturing conditions satisfy the favorable conditions, the proportion of Zr-containing particles is higher compared to Tests No. 3 and 4, where the conditions do not meet the favorable conditions. As a result, variations in iron loss within the coil can be further reduced. Similarly, comparing Tests No. 9 to 11 using the same steel grade E, in Tests No. 9 and 10, where the manufacturing conditions satisfy the favorable conditions, the proportion of Zr-containing particles is higher compared to Test No. 11, where the conditions do not meet the favorable conditions. As a result, variations in iron loss within the coil are further reduced.

In contrast, tests No. 22 to 35, which deviated 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 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.

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 to 29, the content of at least one of Ti, Nb, and _V was excessive, making it easier for fine MnS and _Zr₂S₃ to precipitate, resulting in greater variability in iron loss.

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.

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.

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 (6)

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. 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. 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. 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. A laminate of non-oriented electrical steel sheets according to any one of claims 1 to 4,
Motor core. Including the motor core described in claim 5,
Motor.