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

Abstract

This non-oriented electromagnetic steel sheet comprises a base material having a chemical composition, in terms of mass%, of C: 0.010% or less, Si: more than 1.20% but no more than 4.00%, Al: more than 0.10% but no more than 3.00%, Mn: 0.10%-1.00%, P: 0.20% or less, S: 0.0010% or less, O: 0.005% or less, N: 0.0040-0.015%, Zr: 0.0026-0.10%, Ti: 0.020% or less, Nb: 0.020% or less, V: 0.020% or less, REM: 0.0010% 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, and the balance being Fe and impurities. The non-oriented electromagnetic steel satisfies [0.10 ≤ Zr / (6.5 × N) ≤ 2.0], and has a Z cross-section taken at t / 4, in which the number ratio of particles having a Zr concentration of 30 at% or more among large particles having equivalent circle diameters of at least 1 μm is 30% or more.

Description

Non-oriented electrical steel sheets, motor cores and motors

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

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

[0003] To achieve high motor efficiency, it is important to reduce iron loss, which is the main cause of loss. Reducing iron loss in the electromagnetic steel sheets used as the iron core of the motor is an effective way to reduce iron loss. It is known that increasing the grain size is effective in reducing iron loss, but because fine precipitates such as AlN are harmful to grain growth, it is common to reduce the N content in the steel as much as possible (see, for example, Patent Document 1).

[0004] International Publication No. 2022 / 113264

[0005] In recent years, as one of the measures to achieve carbon neutrality, the steelmaking process has been converted to an electric furnace method. However, this has raised concerns about the contamination of N in the steelmaking process. Therefore, there is a need for a technology that can suppress the formation of fine precipitates such as AlN and reduce iron loss, even when the N content in steel is high.

[0006] The present invention has been made to solve such problems, and has an object to provide a non-oriented electrical steel sheet that has low iron loss even when the N content in the steel is high.

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

[0008] (1) The chemical composition of the base metal is, in mass%, C: 0.010% or less, Si: over 1.20% and 4.00% or less, Al: over 0.10% and 3.00% or less, Mn: 0.10 to 1.00%, P: 0.20% or less, S: 0.0010% or less, O: 0.005% or less, N: 0.0040 to 0.015%, Zr: 0.0026 to 0.10%, Ti: 0.020% or less, Nb: 0.020% or less, V: 0.020% or less, REM: 0.0010% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, Cu: 0.50% or less, Mo: 0.050% or less, A non-oriented electrical steel sheet having Sn: 0.20% or less, Sb: 0.20% or less, Ni: 0.050% or less, Cr: 0.50% or less, B: 0.0030% or less, balance: Fe and impurities, and satisfying the following formula (i): 0.10≦Zr / (6.5×N)≦2.0 (i) where the element symbols in the formula above represent the content (mass%) of each element.

[0009] (2) The number density of particles having a Zr concentration of 30 at% or more is 50 / mm ２ The non-oriented electrical steel sheet according to (1) above.

[0010] (3) The non-oriented electrical steel sheet according to (1) or (2) above, wherein an insulating coating is provided on the surface of the base material.

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

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

[0013] According to the present invention, even when the N content in the steel is high, it is possible to suppress the precipitation of fine AlN, and therefore it is possible to obtain a non-oriented electrical steel sheet having low iron loss.

[0014] Figure 1 is an electron micrograph taken using a TEM of a sample containing no Zr, and Figure 2 is an electron micrograph taken using a TEM of a sample containing 0.0045% Zr.

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

[0016] One method for suppressing the precipitation of AlN is to reduce the amount of Al, but since Al has the effect of improving magnetic properties, the content of Al must be kept at a certain level or more.

[0017] Therefore, the inventors conducted further studies and focused on Zr, which has a high affinity with N. Zr crystallizes as Zr(N,C) during solidification and fixes N. Generally, particles that crystallize in the molten steel stage are coarser than particles that precipitate after solidification, so they have less adverse effect on grain growth. Therefore, by adding Zr in an amount greater than or equal to a certain amount depending on the N content and fixing N, the precipitation of fine AlN is suppressed.

[0018] However, if the steel contains a large amount of S, when Zr is added, fine Zr(O,S) is generated, and the effect of fixing N is lost. Therefore, the S content needs to be sufficiently reduced.

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

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

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

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

[0023] Al: More than 0.10% and Not More than 3.00% Al (aluminum) is an element that has the effect of increasing the electrical resistance of steel, thereby reducing eddy current loss and improving high-frequency iron loss in non-oriented electrical steel sheets. Al also has the effect of improving iron loss by improving the texture. To achieve these effects, the Al content is set to more than 0.10%. The Al content is preferably 0.25% or more, and more preferably 0.40% or more. However, excessive Al content reduces toughness. Therefore, the Al content is set to 3.00% or less. The Al content is preferably 2.00% or less, and more preferably 1.00% or less.

[0024] Mn: 0.10 to 1.00% Mn (manganese) is an element that increases the electrical resistance of steel, reduces eddy current loss, and is effective in improving the high-frequency iron loss of non-oriented electrical steel sheets. To achieve this effect, the Mn content is set to 0.10% or more. The Mn content is preferably 0.15% or more, and more preferably 0.20% or more. On the other hand, excessive Mn content may increase iron loss. Therefore, the Mn content is set to 1.00% or less. The Mn content is preferably less than 1.00%, more preferably 0.90% or less, even more preferably 0.80% or less, even more preferably 0.70% or less, even more preferably 0.60% or less, even more preferably 0.50% or less, and even more preferably 0.40% or less.

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

[0026] S: 0.0010% or less S (sulfur) is an element that increases iron loss by forming fine MnS precipitates and reduces the magnetic properties of non-oriented electrical steel sheets. In addition, when Zr is added, it forms fine Zr(O,S) particles, which reduces the N-fixing effect of Zr. This effect is particularly pronounced in high-quality steels with a Si content of more than 1.20%. Therefore, the S content is set to 0.0010% or less. The S content is preferably 0.0008% or less, and more preferably 0.0006% or less. Since excessive reduction in the S content can increase manufacturing costs, the S content is preferably 0.0001% or more, and more preferably 0.0003% or more.

[0027] O: 0.005% or less O (oxygen) is an element that forms oxide-based inclusions, thereby reducing the magnetic properties of non-oriented electrical steel sheets. Therefore, the O content is set to 0.005% or less. The O content is preferably 0.004% or less, and more preferably 0.003% or less. There is no need to set a lower limit for the O content, and the lower limit is 0%. However, since an extreme reduction in the O content may increase manufacturing costs, the O content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0028] N: 0.0040 to 0.015% N (nitrogen) is an element that is inevitably mixed into steel. It forms fine nitrides, which increase iron loss and degrade the magnetic properties of non-oriented electrical steel sheets. However, as mentioned above, N contamination may be unavoidable during the steelmaking process. Therefore, this embodiment targets steel with an N content of 0.0040% or more. However, if the N content exceeds 0.0150%, the magnetic properties will deteriorate significantly even in the present invention, which utilizes Zr. Therefore, the N content is set to 0.015% or less. The N content is preferably 0.012% or less, and more preferably 0.0080% or less.

[0029] Zr: 0.0026 to 0.10% Zr (zirconium) is an element that crystallizes as Zr(N,C) during solidification and fixes N, thereby suppressing the precipitation of fine AlN. To achieve this effect, the Zr content is set to 0.0026% or more. The Zr content is preferably 0.0030% or more, and more preferably 0.0035% 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.

[0030] In this embodiment, the Zr content needs to be adjusted according to the N content. Therefore, in addition to the N 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 following formula (i) is less than 0.10, the N fixing effect of Zr becomes insufficient. On the other hand, if the value of the middle part of the following formula (i) exceeds 2.0, fine Zr(O, S) and the like crystallize, increasing iron loss. The value of the middle part of the following formula (i) is preferably 0.30 or more, more preferably 0.50 or more, and preferably 1.7 or less, and more preferably 1.5 or less. 0.10≦Zr / (6.5×N)≦2.0 (i) where the element symbols in the above formula represent the content (mass%) of each element.

[0031] Ti: 0.020% or less Ti (titanium) is an element that is inevitably mixed into steel. Intentional inclusion of Ti increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Ti does not need to be actively added; impurity levels are sufficient. Therefore, the Ti content is set to 0.020% or less. The Ti content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0020% or less. The lower limit of the Ti content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the Ti content may increase manufacturing costs. Therefore, the Ti content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0032] Nb: 0.020% or less Nb (niobium) is an element that can be mixed into steel as an impurity. Intentional inclusion of Nb increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Nb does not need to be actively added; impurity levels are sufficient. Therefore, the Nb content is set to 0.020% or less. The Nb content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0020% or less. The lower limit of the Nb content is not particularly limited, and the lower limit is 0%. However, an extreme reduction in the Nb content may increase manufacturing costs. Therefore, the Nb content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0033] V: 0.020% or less V (vanadium) is an element that can be mixed into steel as an impurity. Intentional inclusion of V increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, V does not need to be actively added; impurity levels are sufficient. Therefore, the V content is set to 0.020% or less. The V content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0020% or less. The lower limit of the V content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the V content may increase manufacturing costs. Therefore, the V content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0034] REM: 0.0010% or less REM (rare earth element) is an element that can be mixed into steel as an impurity. Intentional inclusion of REM increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, REM does not need to be actively added; impurity levels are sufficient. Therefore, the REM content is set to 0.0010% or less. The REM content is preferably 0.0008% or less, more preferably 0.0006% or less. The lower limit of the REM content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the REM content may increase manufacturing costs. Therefore, the REM content 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.

[0035] Ca: 0.0050% or less Mg: 0.0050% or less 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, Ca and Mg do not need to be actively included; impurity levels are sufficient. Therefore, the contents of Ca and Mg are both set to 0.0050% or less. The contents of Ca and Mg are preferably 0.0030% or less, more preferably 0.0010% or less, more preferably less than 0.0010%, and even more preferably less than 0.0005%. The lower limits of the 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 Ca and Mg are each preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0036] 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 0.10% or less, and more preferably 0.050% or less. The lower limit of the Cu content is not particularly limited, and the lower limit is 0%. However, excessive reduction of the Cu content may increase manufacturing costs. Therefore, the Cu content is preferably more than 0%, and more preferably 0.0005% or more.

[0037] 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.

[0038] 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, the Sn content is preferably more than 0%, more preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.010% or more.

[0039] 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, more preferably 0.0010% or more, and even more preferably 0.010% or more.

[0040] 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.

[0041] 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.

[0042] 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 non-oriented electrical steel sheets. Therefore, in this embodiment, B does not need to be actively added; impurity levels are 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, excessive reduction of the B content may increase manufacturing costs. Therefore, the B content is preferably more than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0043] The chemical composition of the base material of the non-oriented electrical steel sheet of the present invention is made up of the balance Fe and impurities, where "impurities" refer to components that are mixed in during industrial steel production due to various factors in raw materials such as ores and scraps, and in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention.

[0044] The chemical composition of the base material of the non-oriented electrical steel sheet according to this embodiment can be measured by combining various known measurement methods. Inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES) and / or ICP mass spectrometry (ICP-MS) may be used depending on the element content. Furthermore, carbon and sulfur may be measured using a combustion-infrared absorption method, nitrogen may be measured using an inert gas combustion-thermal conductivity method, and oxygen may be measured using an inert gas fusion-non-dispersive infrared absorption method.

[0045] 2. Particles In this embodiment, in a cross section parallel to the surface of the base material at a quarter thickness position (hereinafter also referred to as a "Z cross section at t / 4"), among particles having a circle-equivalent diameter of 1 μm or more (hereinafter also referred to as "coarse particles"), the number ratio of particles having a Zr concentration of 30 at% or more (hereinafter also referred to as "Zr-containing particles") is 30% or more. Here, the "circle-equivalent diameter" means the diameter of a circle having an area equal to the area of ​​the particle.

[0046] As a result of investigations conducted by the present inventors, it was found that by adjusting the Zr content in accordance with the N content and optimizing the manufacturing conditions, N is crystallized as coarse Zr(N,C), and the ratio of the number of Zr-containing particles to the number of coarse particles is set to 30% or more, thereby making it possible to suppress the precipitation of fine AlN.

[0047] In this specification, particles include compounds crystallized in a liquid phase and compounds precipitated in a solid phase, such as carbides, nitrides, carbonitrides, sulfides, oxides, and composites thereof.

[0048] Fig. 1 is an electron micrograph taken using a transmission electron microscope (TEM) of a sample containing no Zr, and Fig. 2 is an electron micrograph taken using a TEM of a sample containing 0.0045% Zr. As shown in Fig. 1, when no Zr is contained, countless fine AlN particles are precipitated, whereas as shown in Fig. 2, it can be seen that the precipitation of fine AlN particles can be significantly suppressed by including a trace amount of Zr.

[0049] The number density of the Zr-containing particles does not need to be particularly limited, but in order to more reliably obtain the fixing effect of N, it is preferable that the number density be 50 / mm ２ It is preferable that the thickness is 100 mm or more. ２ Furthermore, there is no particular need to limit the upper limit of the number density of the Zr-containing particles, and it is more preferable that it be 500 / mm ２ is the practical upper limit.

[0050] 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 by a Metal Quality Analyzer (MQA).

[0051] First, a test piece was cut out so that the Z cross section at t / 4 became the observation surface, and was mirror-polished. Then, using a scanning electron microscope (SEM) equipped in the MQA, the observation surface was observed at a magnification of 500x, an acceleration voltage of 20 kV, a work distance of 17 mm, a pixel size of 0.49 μm × 0.49 μm, and a measurement area of ​​25 mm. ２A backscattered electron image is taken under the above conditions, and then a chemical analysis of the coarse particles contained in the field of view is performed using an energy dispersive X-ray analyzer (EDS) attached to the SEM. Ten elements, namely, C, Si, Mn, P, S, Al, Ti, N, O, and Zr, are selected as the measurement target elements, and the content of each element is determined so that the total content of these elements is 100%. If the Zr concentration of the coarse particles is 30 at% or higher, the coarse particles are determined to be Zr-containing particles.

[0052] The above analysis was carried out for multiple fields of view, and the total number of coarse particles was 1000 or more and 25 mm ２ The measurement is completed when the area measured reaches this value. Then, the ratio (%) of the number of Zr-containing particles to the total number of coarse particles analyzed is calculated. The total number of Zr-containing particles confirmed in the entire analyzed visual field is divided by the total area of ​​the entire visual field to determine the number density ( / mm ２ ) is required.

[0053] 3. Magnetic Properties The non-oriented electrical steel sheet according to this embodiment has low iron loss W １５／５０ Here, the iron loss W １５／５０ The iron loss W is measured in accordance with the Single Sheet Tester (SST) method specified in JIS C 2556:2015. However, the SST measurement is performed on a 55 mm x 55 mm test piece using a corresponding small single sheet tester. １５／５０ means the iron loss that occurs under the conditions of a maximum magnetic flux density of 1.5 T and a frequency of 50 Hz. When measuring 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 of the values ​​measured in each direction is calculated as the iron loss value of the material. The number of small 55 mm x 55 mm test pieces is set to 10 from the viewpoint of achieving both measurement accuracy and test efficiency.

[0054] The magnetic property values ​​obtained by SST are obtained using correction factors. Specifically, Epstein test pieces and the above-mentioned small test pieces are taken in advance from several types of non-oriented electrical steel sheets, and the magnetic property values ​​are measured by the Epstein method specified in JIS C 2550-1:2011 and the above-mentioned SST, and a conversion formula is derived from the relationship between the two measured values. Then, the magnetic property values ​​measured by the single sheet tester are corrected using the above-mentioned conversion formula so that they are equivalent to the magnetic property values ​​measured by the Epstein method.

[0055] The density of the steel sheet as measured by the Epstein method was 7.65 g / cm ３ In addition, when measuring magnetic property values ​​in accordance with the Epstein test method, the excitation directions are two directions, L direction and C direction, and measurements are carried out using half of each test piece excited in the L direction and C direction.

[0056] 4. Sheet Thickness There are no particular restrictions on the sheet thickness of the non-oriented electrical steel sheet according to this embodiment. However, from the viewpoint of manufacturing costs, the sheet thickness is preferably 0.10 mm or more. On the other hand, from the viewpoint of reducing iron loss, the sheet thickness is preferably 0.50 mm or less. The sheet thickness is more preferably 0.20 to 0.40 mm.

[0057] 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.

[0058] The type of insulating coating is not particularly limited, and known insulating coatings used for insulating non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings primarily composed of inorganic materials and further containing organic materials. Here, a composite insulating coating is an insulating coating primarily composed of at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during manufacturing, which has become increasingly important in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or carbonates or ammonium salts thereof as starting materials are preferably used.

[0059] The amount of the insulating coating is not particularly limited, but is, for example, 200 to 3000 mg / m per side. ２ The coating amount is preferably about 300 to 2500 mg / m per side. ２ It is more preferable to set the range as follows. By forming the insulating coating so that the coating weight falls within the above range, it is possible to maintain excellent uniformity. When measuring the coating weight of the insulating coating afterward, various known measurement methods can be used. For example, a method of measuring the difference in mass before and after immersion in a sodium hydroxide aqueous solution, or a fluorescent X-ray method using a calibration curve method may be used as appropriate.

[0060] 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.

[0061] 7. Manufacturing Method The non-oriented electrical steel sheet according to this embodiment can be manufactured by sequentially carrying out a refining step, a casting step, 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.

[0062] In the present invention, in order to crystallize N as coarse Zr(N,C), it is particularly important to optimize the refining and casting processes. Each process will be described below.

[0063] <Refining Process> The refining process is a process for producing molten steel. In this process, Zr is added. Zr is an element that forms compounds not only with N but also with O and S. In order to crystallize Zr(N,C), it is necessary to suppress the crystallization of ZrO and ZrS. As described above, the crystallization of ZrS can be suppressed by reducing the S content. S can also be fixed as CaS or MgS by adding Ca or Mg. However, excessive amounts of CaS and MgS cause an increase in iron loss, especially in high-quality steel with a Si content of more than 1.20%. Therefore, it is necessary to reduce the S content. On the other hand, the crystallization of ZrO can be suppressed by adding Al before adding Zr.

[0064] <Casting Process> The casting process is a process of casting molten steel to produce a steel ingot (slab) having the above-mentioned chemical composition. There are no particular limitations on the casting method used in the casting process. For example, continuous casting may be used, in which the molten steel is primarily cooled in a mold, followed by secondary cooling by spraying a cooling spray. To crystallize coarse Zr(N,C), the cooling rate during casting must be reduced so that ZrN grows sufficiently during solidification. In particular, in high-quality steel with a Si content of more than 1.20%, fine Zr(N,C) particles must be sufficiently grown, as they may actually deteriorate the magnetic properties. When performing continuous casting, specifically, the cooling rate from 1600°C to 1000°C must be 30 K / min or less during secondary cooling by controlling the amount and temperature of the cooling spray.

[0065] In the present invention, the cooling rate from 1600°C to 1000°C is controlled by the following method. For steel ingots obtained under various casting conditions, the secondary dendrite arm spacing is measured at the 1 / 4 thickness position. Based on the following formula described in T. Edvardson, H. Fredriksson, and I. Svensson; Metal Science, 10 (1976), p. 298, if the measured secondary dendrite arm spacing is 95.3 μm or more, it is determined that the cooling rate from 1600°C to 1000°C was 30 K / min or less, and the casting conditions that will produce such a steel ingot are adopted. ２ = 140 x V －０．１１３ The symbols in the above formula have the following meanings: ２ : Secondary dendrite arm spacing (μm) V: Cooling rate from 1600°C to 1000°C (K / min)

[0066] <Hot Rolling Step> A steel ingot having the above chemical composition is heated and hot rolled to obtain a hot-rolled sheet. The heating temperature of the steel ingot when subjected to hot rolling is not particularly specified, but is preferably, for example, 1050 to 1250°C. The thickness of the hot-rolled sheet after hot rolling is also not particularly specified, but is preferably, for example, about 1.5 to 3.0 mm, taking into account the final thickness of the base material.

[0067] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is performed as necessary for the purpose of reducing iron loss of the steel sheet. In the case of continuous annealing, the hot-rolled sheet may be annealed, for example, by soaking at 750 to 1200°C for 10 seconds to 10 minutes. In the case of box annealing, the hot-rolled steel sheet may be annealed, for example, by soaking at 650 to 950°C for 30 minutes to 24 hours. Note that although the magnetic properties will be inferior compared to when the hot-rolled sheet annealing process is performed, in order to reduce costs, the hot-rolled sheet may be subjected to self-annealing or the hot-rolled sheet annealing process may be omitted.

[0068] <Pickling step> The steel sheet after the hot rolling or after the hot-rolled sheet annealing is subjected to pickling to remove the scale layer formed on the surface of the base material. When the hot-rolled sheet annealing is box annealing, the pickling step is preferably performed before the hot-rolled sheet annealing from the viewpoint of descaling properties. Here, the pickling conditions, such as the concentration of the acid used in the pickling, the concentration of the accelerator used in the pickling, and the temperature of the pickling solution, are not particularly limited, and known pickling conditions can be used.

[0069] <Cold Rolling Step> The steel sheet after the hot-rolled sheet annealing is subjected to cold rolling, for example, at a reduction ratio such that the final thickness of the base material is 0.10 to 0.50 mm.

[0070] <Finish annealing step> After the cold rolling, finish annealing is carried out. For the finish annealing, it is preferable to use a continuous annealing furnace. The finish annealing is carried out under the conditions of a soaking temperature of 880 to 1080°C and a soaking time of 1 second to 10 minutes. ２ The ratio of H is 1 to 100% by volume. ２ and N ２ A mixed atmosphere of H ２ +N ２ = 100% by volume), and the dew point of the atmosphere is preferably -50 to +10°C.

[0071] If the soaking temperature is less than 880°C, the grain size becomes small and iron loss increases, which is undesirable. If the soaking temperature exceeds 1080°C, not only will the strength be insufficient, but nitriding will occur in the surface layer, which will also increase iron loss, which is undesirable. Also, if the soaking time is less than 1 second, sufficient grain growth will not occur. On the other hand, if the soaking time exceeds 10 minutes, the manufacturing cost will increase.

[0072] <Insulating Coating Forming Step> After the above-mentioned finish annealing, an insulating coating forming step is carried out as necessary. Here, the method for forming the insulating coating is not particularly limited, and a known insulating coating forming treatment liquid such as that described below may be used, and the treatment liquid may be applied and dried by a known method. An example of a known insulating coating is a composite insulating coating that is mainly made of an inorganic material and further contains an organic material.

[0073] Before applying the treatment liquid to the surface of the base material on which the insulating coating is to be formed, any pretreatment may be performed, such as degreasing with an alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc. The treatment liquid may also be applied to the surface of the base material as is after finish annealing without performing these pretreatments.

[0074] Furthermore, the obtained non-oriented electrical steel sheet can be subjected to a punching step and a laminating step in this order under the conditions shown below, thereby manufacturing a motor core or the like. Note that, when low iron loss is more important for the obtained motor core or the like, a stress relief annealing step may be further carried out after the laminating step.

[0075] <Punching Step> The non-oriented electrical steel sheet obtained as described above is subjected to punching to form the shape required for the rotor core or stator core material. There are no particular restrictions on the processing conditions, and a general method can be used.

[0076] <Laminating Process> A plurality of punched non-oriented electrical steel sheets are laminated to form a motor core.

[0077] <Stress relief annealing step> The laminated motor core is subjected to stress relief annealing as necessary. A motor core that has been subjected to stress relief annealing undergoes recrystallization and grain growth, reducing iron loss and enabling a significant improvement in motor efficiency.

[0078] There are no particular restrictions on the conditions for stress relief annealing, but from the viewpoint of improving magnetic properties, it is preferable to perform stress relief annealing at a high temperature, specifically, the annealing temperature is preferably in the range of 750 to 900°C. There are also no restrictions on the annealing time, and it is preferable to set it, for example, to 0.5 to 5.0 hours. Note that the annealing time is the time during which the motor core reaches 750°C or higher, and the heating time and cooling time below 750°C may be set appropriately.

[0079] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0080] Steels having the chemical compositions shown in Table 1 were produced using a vacuum melting furnace. Except for Test No. 2, Al was added first, followed by Zr. For Test No. 2, Zr was added first, followed by Al. The steels were then cooled in a mold at various cooling rates to produce steel ingots. The cooling rate during the casting process was estimated by measuring the secondary dendrite arm spacing at a quarter-thickness position of the resulting steel ingot. Specifically, if the measured secondary dendrite arm spacing was 95.3 μm or greater, it was determined that the cooling rate from 1600°C to 1000°C was 30 K / min or less.

[0081] Subsequently, the obtained steel ingot was subjected to ２ After heating to 1100°C or 1200°C in a 100% N atmosphere, the steel sheet was hot-rolled to a finishing temperature of 850°C and a finishing thickness of 2.0 mm to obtain a hot-rolled steel sheet. ２ The steel sheets were subjected to hot-rolled sheet annealing by heating at 1000°C for 1 minute in a continuous annealing furnace under a 100% atmosphere. The steel sheets thus obtained were pickled to remove scale, and then cold-rolled to obtain cold-rolled steel sheets having a thickness of 0.35 mm. ２ : 25%, N ２The steel sheets were subjected to finish annealing in a mixed atmosphere of 75% SiO2, ...

[0082]

[0083]

[0084] From each of the obtained test materials, a test piece was cut out so that the Z cross section at t / 4 was the observation surface, and the test piece was mirror-polished. Then, using an SEM equipped with MQA (Metal Quality Analyser manufactured by FEI), the observation surface was observed at a magnification of 500x, an acceleration voltage of 20 kV, a work distance of 17 mm, a pixel size of 0.49 μm × 0.49 μm, and a measurement area of ​​25 mm. ２ A backscattered electron image was taken under the above conditions, and the coarse particles contained in the field of view were chemically analyzed using an EDS attached to the SEM. If the Zr concentration of the coarse particles was 30 at% or more, the coarse particles were determined to be Zr-containing particles.

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

[0086] Next, for each of the above test materials, a stress relief annealing was simulated. ２ After heat treatment at 800°C for 2 hours in a 100% atmosphere, iron loss W １５／５０ The iron loss W １５／５０was measured in accordance with the SST specified in JIS C 2556:2015. However, the SST measurement was performed on a 55 mm x 55 mm test piece using a corresponding small single plate tester. When measuring the iron loss, the excitation direction was set to two directions, the L direction and the C direction, and the average value of the values ​​measured in each direction was calculated as the iron loss value of the material. The number of small 55 mm x 55 mm test pieces was set to 10 from the viewpoint of achieving both measurement accuracy and test efficiency.

[0087] The magnetic property values ​​obtained by SST were obtained using correction factors. Specifically, Epstein test pieces and the above-mentioned small test pieces were taken in advance from several types of non-oriented electrical steel sheets, and the magnetic property values ​​were measured by the Epstein method specified in JIS C 2550-1:2011 and the above-mentioned SST, and a conversion formula was derived from the relationship between the two measured values. The magnetic property values ​​measured by the single sheet tester were then corrected using the above-mentioned conversion formula so that they were equivalent to the magnetic property values ​​measured by the Epstein method.

[0088] The density of the steel sheet as measured by the Epstein method was 7.65 g / cm ３ In addition, when measuring the magnetic property values ​​in accordance with the Epstein test method, the excitation directions were two directions, L direction and C direction, and measurements were carried out using half of each test piece excited in the L direction and C direction.

[0089] The results are also shown in Table 2. In this example, the iron loss W after the heat treatment simulating the stress relief annealing was performed. １５／５０ When the iron loss was 2.30 W / kg or less, it was determined that the iron loss was low.

[0090] As shown in Table 2, in Test Nos. 1, 6 to 15, 18, 20 and 22 to 26, which satisfy the provisions of the present invention, the iron loss W １５／５０ On the other hand, in Test Nos. 2 to 5, 16, 17, 19, 21, 27 and 28, which are comparative examples, the iron loss W １５／５０ The result was that the power consumption exceeded 2.30 W / kg.

[0091] Specifically, in Test No. 2, because Zr was added before Al was added in the refining process, the crystallization of ZrO could not be suppressed, the number ratio of Zr-containing particles decreased, and iron loss was poor. In Test No. 3, because the cooling rate in the casting process was excessive, the growth of ZrN could not be sufficiently promoted during solidification, and the number ratio of Zr-containing particles decreased, and iron loss was poor.

[0092] In Test Nos. 4, 17, 19, and 21, the Zr content and the value of the middle part of equation (i) were lower than the specified ranges, resulting in a decrease in the number ratio of Zr-containing particles and poor iron loss. In Test Nos. 5 and 16, the Zr content or the value of the middle part of equation (i) exceeded the specified ranges, resulting in an excessive amount of particles and an increase in iron loss.

[0093] In Test No. 27, the S content was excessive, so the crystallization of fine ZrS could not be suppressed, and the effect of Zr in fixing N was reduced, resulting in poor iron loss. In Test No. 28, the excess S was fixed with Ca, but the amount of CaS became excessive, resulting in poor iron loss.

[0094] As described above, according to the present invention, even when the N content in the steel is high, it is possible to suppress the precipitation of fine AlN, and therefore it is possible to obtain a non-oriented electrical steel sheet having low iron loss.

Claims

1. The chemical composition of the base material is, in mass%, C: 0.010% or less, Si: over 1.20% and up to 4.00%, Al: over 0.10% and up to 3.00%, Mn: 0.10 to 1.00%, P: 0.20% or less, S: 0.0010% or less, O: 0.005% or less, N: 0.0040 to 0.015%, Zr: 0.0026 to 0.10%, Ti: 0.020% or less, Nb: 0.020% or less, V: 0.020% or less, REM: 0.0010% or less, Ca: 0.0050% or less, Mg: 0.0050% or less, Cu: 0.50% or less, Mo: 0.050% or less, A non-oriented electrical steel sheet having Sn: 0.20% or less, Sb: 0.20% or less, Ni: 0.050% or less, Cr: 0.50% or less, B: 0.0030% or less, balance: Fe and impurities, and satisfying the following formula (i): 0.10≦Zr / (6.5×N)≦2.0 (i) where the element symbols in the formula above represent the content (mass%) of each element.

2. The number density of particles having a Zr concentration of 30 at% or more is 50 / mm ２ The non-oriented electrical steel sheet according to claim 1 , wherein 3. The non-oriented electrical steel sheet according to claim 1 or 2, wherein an insulating coating is provided on the surface of the base material.

4. A motor core in which the non-oriented electrical steel sheets according to any one of claims 1 to 3 are laminated.

5. A motor comprising the motor core according to claim 4.

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