Non-oriented electromagnetic steel sheet and method for manufacturing the same

Abstract

A non-oriented electrical steel sheet, a chemical composition of a base material of which is, in mass%, C: 0.0050% or less, Si: more than 3.50% and 4.50% or less, Mn: less than 0.60%, Al: 0.25 to 0.65%, P: 0.030% or less, S: 0.0020% or less, N: 0.0040% or less, Ti: less than 0.0040%, Nb: less than 0.0040%, Zr: less than 0.0040%, V: less than 0.0040%, Cu: less than 0.200%, Ni: less than 0.500%, a total of one or both of Sn and Sb: 0.030% or less, a remainder: Fe and impurities, and satisfies [4.3 ≤ Si + Al + 0.5 × Mn ≤ 5.0], an average crystal grain diameter of the base material is more than 40 µm and 140 µm or less, an aggregation degree of {111} orientation is 3.0 or more, an aggregation degree of {110} orientation is 0.15 or less, and a sheet thickness is 0.10 to 0.30 mm.

Description

Technical Field

[0001] This invention relates to a non-oriented electromagnetic steel sheet and its manufacturing method. Background Technology

[0002] In recent years, global environmental issues have garnered significant attention, leading to increased demands for energy conservation. This includes a strong expectation for higher efficiency in electrical equipment. Consequently, the demand for improved magnetic properties in non-oriented electromagnetic steel sheets, widely used as core materials for motors and generators, has intensified. This trend is particularly pronounced in drive motors for electric and hybrid vehicles, as well as compressor motors for air conditioners. Furthermore, there is a growing expectation for miniaturized and efficiently high-output drive and compressor motors.

[0003] To achieve high efficiency in motors, reducing iron losses and copper losses, which are the main sources of losses, becomes crucial. For reducing iron losses, improving the iron loss of the electromagnet used in the motor core is effective; for reducing copper losses, increasing the magnetic flux density of the electromagnet is effective. On the other hand, to achieve high output, high torque and high-speed rotation become important. For high torque, increasing the magnetic flux density of the electromagnet is effective; for high-speed rotation, increasing the strength of the electromagnet is effective. Furthermore, for high-speed rotation, the frequency needs to be increased, which increases iron losses, thus requiring electromagnets with low iron losses. Therefore, to promote high efficiency and high output in motors, electromagnets with low iron losses, high magnetic flux density, and high strength are needed. Among these three characteristics, low iron loss, which contributes significantly to both high efficiency and high output, is the most effective method. Considering the progress in high-speed rotation in recent years, increasing strength is the next important step.

[0004] As described above, the motor core of various motors consists of a stator as the stationary element and a rotor as the rotating element. The required characteristics of the stator and rotor constituting the motor core are not the same. For the stator, excellent magnetic properties (especially low iron loss) are required, while for the rotor, low iron loss and excellent mechanical properties (high strength) are required.

[0005] Because the stator and rotor require different characteristics, the desired properties can be achieved by manufacturing non-oriented electromagnetic steel sheets for the stator and rotor separately. However, preparing two types of non-oriented electromagnetic steel sheets complicates the core manufacturing process and reduces the yield rate. Therefore, in order to achieve the low iron loss and high strength required for the rotor, and the low iron loss required for the stator, research has been ongoing on a non-oriented electromagnetic steel sheet with low iron loss and high strength.

[0006] Furthermore, on the other hand, the dimensional accuracy of the iron core manufactured through punching is also important for improving the practical performance of the motor. Regarding the dimensional accuracy of the iron core, it is known that the anisotropy of the mechanical properties of the electromagnetic steel sheet has an impact; therefore, a method for improving dimensional accuracy has been studied.

[0007] For example, Patent Documents 1-4 present an attempt to achieve excellent magnetic properties and high strength. Patent Document 5 proposes adjusting the mold dimensions based on the anisotropy of the mechanical properties of the electromagnetic steel sheet.

[0008] Prior technology documents

[0009] Patent documents

[0010] Patent Document 1: International Publication No. 2019 / 017426

[0011] Patent Document 2: International Publication No. 2020 / 091039

[0012] Patent Document 3: International Publication No. 2020 / 091043

[0013] Patent Document 4: Japanese Patent Application Publication No. 2010-90474

[0014] Patent Document 5: International Publication No. 2022 / 210867 Summary of the Invention

[0015] The technical problem that the invention aims to solve

[0016] However, to achieve a non-oriented electromagnetic steel sheet that balances low iron loss and high strength, as disclosed in Patent Documents 1-4, it is necessary to incorporate a large amount of alloying elements, which leads to problems such as reduced toughness and susceptibility to breakage during cold rolling. Furthermore, to improve the dimensional accuracy during the punching process of the iron core, as disclosed in Patent Document 5, there is a problem: due to the anisotropic mechanical properties of the electromagnetic steel sheet, extremely complex methods such as adjusting the die dimensions are required each time.

[0017] This invention was made to solve such problems, and its purpose is to provide a non-oriented electromagnetic steel sheet with low iron loss, high strength, and excellent dimensional accuracy during punching.

[0018] Technical means for solving technical problems

[0019] The subject of this invention is the following non-oriented electromagnetic steel sheet and its manufacturing method.

[0020] (1) A non-oriented electromagnetic steel sheet, wherein the chemical composition of its base material, in mass percent, is:

[0021] C: Below 0.0050%,

[0022] Si: exceeding 3.50% but below 4.50%,

[0023] Mn: less than 0.60%,

[0024] Al: 0.25–0.65%,

[0025] P: below 0.030%,

[0026] S: Below 0.0020%,

[0027] N: below 0.0040%

[0028] Ti: less than 0.0040%,

[0029] Nb: less than 0.0040%,

[0030] Zr: less than 0.0040%,

[0031] V: Less than 0.0040%,

[0032] Cu: less than 0.200%,

[0033] Ni: less than 0.500%,

[0034] The total of one or two of Sn and Sb: less than 0.030%,

[0035] Remaining components: Fe and impurities.

[0036] And satisfy the following equation (i),

[0037] 4.3≤Si+Al+0.5×Mn≤5.0・・・(i)

[0038] In the above formula, the element symbols represent the content (mass%) of each element.

[0039] The average crystal grain size of the parent material is greater than 40 μm and less than 140 μm;

[0040] At a position 1 / 4 of the plate thickness from the surface of the base material, the degree of aggregation of the {111} orientation is 3.0 or more, and the degree of aggregation of the {110} orientation is 0.15 or less;

[0041] The plate thickness is 0.10 to 0.30 mm.

[0042] (2) The non-oriented electromagnetic steel sheet as described in (1) above, wherein,

[0043] The yield strength of 0.2% is above 450 MPa.

[0044] (3) The non-oriented electromagnetic steel sheet as described in (1) or (2) above, wherein,

[0045] The surface of the base material has an insulating film.

[0046] (4) A method for manufacturing a non-oriented electromagnetic steel sheet as described in any one of (1) to (3) above, wherein the method comprises, in sequence, a hot rolling process; a hot-rolled sheet annealing process with a soaking temperature of 760 to 880°C and a soaking time of 5 to 100 seconds; a descaling process based on pickling; a cold rolling process to a sheet thickness of 0.10 to 0.30 mm; and a final annealing process after heating to a temperature of 850°C or higher at a heating rate of 100°C / s or less in a temperature range of 500 to 850°C, with a soaking temperature of 850 to 1050°C and a soaking time of 1 to 300 seconds.

[0047] The steel ingot has the following chemical composition, in mass percent:

[0048] C: Below 0.0050%,

[0049] Si: exceeding 3.50% but below 4.50%,

[0050] Mn: less than 0.60%,

[0051] Al: 0.25–0.65%,

[0052] P: below 0.030%,

[0053] S: Below 0.0020%,

[0054] N: below 0.0040%

[0055] Ti: less than 0.0040%,

[0056] Nb: less than 0.0040%,

[0057] Zr: less than 0.0040%,

[0058] V: Less than 0.0040%,

[0059] Cu: less than 0.200%,

[0060] Ni: less than 0.500%,

[0061] The total of one or two of Sn and Sb: less than 0.030%,

[0062] Remaining components: Fe and impurities.

[0063] Satisfying the following equation (i),

[0064] 4.3≤Si+Al+0.5×Mn≤5.0・・・(i)

[0065] In the above formula, the element symbols represent the content (mass%) of each element.

[0066] Invention Effects

[0067] According to the present invention, a non-oriented electromagnetic steel sheet with excellent magnetic properties, high strength, and excellent dimensional accuracy during punching can be obtained. Detailed Implementation

[0068] In order to solve the above problems, the inventors conducted in-depth research and obtained the following understanding.

[0069] In order to obtain non-oriented electromagnetic steel sheets with low iron loss and high strength while ensuring toughness during cold rolling, the contents of Si, Mn and Al, which are the main alloying elements, need to be optimized.

[0070] Specifically, the Si content is set to be more than 3.50% and less than 4.50%, which has the highest solid solution strengthening ability and contributes the most to the increase in electrical resistance. Furthermore, to obtain good grain growth, the Al content is set to be 0.25% or more. On the other hand, to suppress the deterioration of toughness and to form a texture with good dimensional accuracy, the Al content is set to be 0.65% or less.

[0071] Furthermore, Mn has the lowest solid solution strengthening ability among the three elements, but suffers less toughness degradation and contributes to increased electrical resistance. It also has the effect of fixing S as MnS, thereby mitigating the adverse effects of S on magnetic properties and surface characteristics. However, through repeated research, the inventors found that when excessive amounts of Mn, which has a lower solid solution strengthening ability compared to Si and Al, are present, the increase in alloy cost is greater than the increase in strength, and the effect of mitigating the adverse effects of S also saturates. Therefore, the Mn content is set to less than 0.60%.

[0072] As described above, reducing the anisotropy of the mechanical properties of the electromagnetic steel sheet is effective in achieving excellent dimensional accuracy. The inventors have investigated methods to further reduce the anisotropy of mechanical properties. It was found that the anisotropy of mechanical properties can be reduced by controlling the texture.

[0073] In order to develop a texture that is beneficial to dimensional accuracy, the contents of Al, Sn and Sb are reduced, and the soaking temperature in the annealing of hot-rolled plates is lowered.

[0074] However, textures that are advantageous for dimensional accuracy are also detrimental to magnetic properties. Therefore, a certain degree of reduction in magnetic flux density is unavoidable. However, the inventors conducted detailed research and found that the impact on iron loss is slight.

[0075] This invention is based on the above understanding. The various elements of this invention will now be described in detail.

[0076] 1. Overall Composition

[0077] The non-oriented electromagnetic steel sheet of one embodiment of the present invention has low iron loss and high strength, and also exhibits excellent dimensional accuracy during punching, making it preferred for both stators and rotors. Furthermore, it is preferable that the non-oriented electromagnetic steel sheet of this embodiment has an insulating film on the surface of the base material described below.

[0078] 2. Chemical composition of the parent material

[0079] The reasons for the limitations of each element are as follows. Additionally, in the following explanation, "%" for content means "mass %".

[0080] C: Below 0.0050%

[0081] Carbon (C) is an element that causes deterioration of iron loss in non-oriented electromagnetic steel sheets. When the C content exceeds 0.0050%, the iron loss of the non-oriented electromagnetic steel sheet deteriorates, and good magnetic properties cannot be obtained. Therefore, the C content is set to 0.0050% or less. Preferably, the C content is 0.0040% or less, more preferably 0.0035% or less. A lower limit for the C content is not required, and it can be 0%. However, because C contributes to the high strength of non-oriented electromagnetic steel sheets, to achieve this effect, it is preferable that the C content is more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0082] Si: More than 3.50% and less than 4.50%

[0083] Silicon (Si) is an element that increases the electrical resistance of steel, thereby reducing eddy current losses and improving the iron loss of non-oriented electromagnetic steel sheets. Furthermore, Si has a high solid solution strengthening ability, thus it is also effective for increasing the strength of non-oriented electromagnetic steel sheets. To achieve these effects, the Si content is set to more than 3.50%. Preferably, the Si content is 3.60% or more, more preferably 3.70% or more, and even more preferably 3.80% or more. On the other hand, when the Si content is excessive, the processability deteriorates significantly, and cold rolling becomes difficult. Therefore, the Si content is set to 4.50% or less. Preferably, the Si content is 4.40% or less, more preferably 4.30% or less.

[0084] Mn: less than 0.60%

[0085] Manganese (Mn) is an element that increases the electrical resistance of steel and reduces eddy current losses, effectively improving the iron loss of non-oriented electromagnetic steel sheets. Furthermore, it also has the effect of mitigating the adverse effects of sulfur (S) on magnetic properties and surface characteristics by fixing sulfur (S) as part of MnS. However, compared to Si and Al, Mn has poor solid solution strengthening ability; therefore, to obtain high strength, a large content is required, which leads to a greater decrease in magnetic flux density and increases alloy costs. Moreover, even with excessive content, the effect of mitigating the adverse effects of S will saturate. Therefore, the Mn content is set to less than 0.60%. Regarding the Mn content, it is preferable to be 0.55% or less, more preferably 0.50% or less. A lower limit for the Mn content is not required, and it can be 0%. However, to obtain the above-mentioned effects, it is preferable that the Mn content is more than 0%, more preferably 0.10% or more, and even more preferably 0.20% or more.

[0086] Al: 0.25–0.65%

[0087] Al (aluminum) is an element that reduces eddy current losses by increasing the electrical resistance of steel and improves the iron loss of non-oriented electromagnetic steel sheets. Furthermore, while Al is not as strong as Si, it also contributes to the high strength of non-oriented electromagnetic steel sheets through solid solution strengthening. Moreover, the addition of an appropriate amount of Al suppresses the refinement of AlN that occurs due to its combination with N in the steel, improving grain growth during final annealing. To achieve these effects, the Al content is set to 0.25% or more. Preferably, the Al content is 0.30% or more, and more preferably 0.35% or more. On the other hand, when the Al content is excessive, the aggregation degree of the {111} orientation decreases, while the aggregation degree of the {110} orientation increases, which adversely affects the dimensional accuracy of the core during punching. Therefore, the Al content is set to 0.65% or less. Preferably, the Al content is 0.60% or less, and more preferably 0.55% or less.

[0088] In this embodiment, the electrical resistance of the steel is ensured by appropriately controlling the contents of Si, Al, and Mn. Furthermore, from the viewpoint of ensuring strength, it is also necessary to appropriately control the contents of Si, Al, and Mn. On the other hand, from the viewpoint of ensuring toughness, an upper limit is also required. Therefore, the contents of Si, Al, and Mn are within the aforementioned ranges, and furthermore, the following equation (i) needs to be satisfied. Regarding the value of the middle part of the following equation (i), it is preferably 4.4 or more, more preferably 4.5 or more, more preferably 4.9 or less, and even more preferably 4.8 or less.

[0089] 4.3≤Si+Al+0.5×Mn≤5.0・・・(i)

[0090] In the above formula, the element symbols represent the content (mass%) of each element.

[0091] P: below 0.030%

[0092] Phosphorus (P) is contained in steel as an impurity, and when its content is excessive, the toughness of the non-oriented electromagnetic steel sheet will be significantly reduced. Therefore, the P content is set to 0.030% or less. Preferably, the P content is 0.025% or less, more preferably 0.020% or less. It is not necessary to set a lower limit for the P content, and it can be 0%. However, extremely low P content can sometimes lead to increased manufacturing costs; therefore, preferably, the P content is more than 0%, more preferably more than 0.001%, further preferably more than 0.003%, and even more preferably more than 0.005%.

[0093] S: below 0.0020%

[0094] Sulfur (S) is an element that increases iron loss and degrades the magnetic properties of non-oriented electromagnetic steel sheets by forming fine precipitates of MnS. Therefore, the S content is set to 0.0020% or less. Preferably, the S content is 0.0018% or less, more preferably 0.0016% or less. A lower limit for the S content is not required, and it can be 0%. However, extremely low S content can sometimes increase manufacturing costs; therefore, preferably, the S content is more than 0%, more preferably 0.0001% or more, further preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0095] N: below 0.0040%

[0096] Nitrogen (N) is an element that inevitably mixes into steel and forms nitrides, increasing iron loss and degrading the magnetic properties of non-oriented electromagnetic steel sheets. Therefore, the N content is set to 0.0040% or less. Preferably, the N content is 0.0035% or less, more preferably 0.0030% or less. A lower limit for the N content is not required, and it can be 0%. However, drastic reductions in the N content can sometimes increase manufacturing costs. Therefore, preferably, the N content is greater than 0%, more preferably 0.0001% or more, further preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0097] Ti: less than 0.0040%

[0098] Titanium (Ti) is an element that inevitably mixes into steel, combining with carbon or nitrogen to form precipitates (carbides, nitrides). When carbides or nitrides are formed, these precipitates themselves degrade the magnetic properties of the non-oriented electromagnetic steel sheet. Furthermore, they hinder grain growth during final annealing, further degrading the magnetic properties of the non-oriented electromagnetic steel sheet. Therefore, the Ti content is set to be less than 0.0040%. Regarding the Ti content, it is preferable to be 0.0030% or less, more preferably 0.0025% or less. A lower limit is not required for the Ti content, and it can be 0%. However, drastic reductions in the Ti content can sometimes increase manufacturing costs; therefore, regarding the Ti content, it is preferable to be more than 0%, more preferably 0.0001% or more, further preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0099] Nb: less than 0.0040%

[0100] Niobium (Nb) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electromagnetic steel sheets. Therefore, the Nb content is set to be less than 0.0040%. Regarding the Nb content, it is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. A lower limit for the Nb content is not required, and it can be 0%. However, extremely low Nb content can sometimes increase manufacturing costs; therefore, regarding the Nb content, it is preferably more than 0%, more preferably more than 0.0001%, even more preferably more than 0.0003%, and even more preferably more than 0.0005%.

[0101] Zr: less than 0.0040%

[0102] Zirconium (Zr) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electromagnetic steel sheets. Therefore, the Zr content is set to less than 0.0040%. Regarding the Zr content, it is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. A lower limit for the Zr content is not required, and it can be 0%. However, drastic reductions in Zr content can sometimes increase manufacturing costs; therefore, regarding the Zr content, it is preferably more than 0%, more preferably more than 0.0001%, even more preferably more than 0.0003%, and even more preferably more than 0.0005%.

[0103] V: Less than 0.0040%

[0104] Vanadium (V) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electromagnetic steel sheets. Therefore, the V content is set to be less than 0.0040%. Regarding the V content, it is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. A lower limit for the V content is not required, and it can be 0%. However, drastic reductions in the V content can sometimes increase manufacturing costs; therefore, regarding the V content, it is preferably more than 0%, more preferably more than 0.0001%, even more preferably more than 0.0003%, and even more preferably more than 0.0005%.

[0105] Cu: less than 0.200%

[0106] Copper (Cu) is an element that inevitably mixes into steel. Intentionally including Cu increases the manufacturing cost of non-oriented electromagnetic steel sheets. Therefore, in this embodiment, it is not necessary to actively include Cu; the impurity level is sufficient. The Cu content is set to be less than the maximum value that may inevitably be mixed in during the manufacturing process, i.e., 0.200%. Preferably, the Cu content is 0.150% or less, more preferably 0.100% or less. Furthermore, the lower limit of the Cu content is not particularly limited and can also be 0%. However, drastic reductions in Cu content can sometimes increase manufacturing costs. Therefore, preferably, the Cu content is more than 0%, more preferably 0.001% or more, further preferably 0.003% or more, and even more preferably 0.005% or more.

[0107] Ni: less than 0.500%

[0108] Ni (Ni) is an element that inevitably mixes into steel. However, Ni is also an element that increases the strength of non-oriented electromagnetic steel sheets, so it can be intentionally included. However, because Ni is expensive, the Ni content is set to be less than 0.500%. Regarding the Ni content, it is preferable to be 0.400% or less, more preferably 0.300% or less. Furthermore, the lower limit of the Ni content is not particularly limited, and it can also be 0%. However, drastic reductions in Ni content can sometimes increase manufacturing costs. Therefore, regarding the Ni content, it is preferable to be more than 0%, more preferably 0.001% or more, further preferably 0.003% or more, and even more preferably 0.005% or more. Moreover, when intentionally included, it is preferable to set the Ni content to 0.200% or more.

[0109] The total of one or two of Sn and Sb: less than 0.030%.

[0110] Sn (tin) and Sb (antimony) can improve the magnetic flux density of non-oriented electromagnetic steel sheets, but they also hinder the development of textures that are beneficial to dimensional accuracy. Furthermore, when the combined content of Sn and Sb is excessive, the toughness of the steel decreases, making cold rolling difficult. Therefore, the combined content of one or both of Sn and Sb is set to 0.030% or less. Regarding the combined content of Sn and Sb, it is preferable to be 0.025% or less, more preferably 0.020% or less. Regarding the content of Sn and Sb, it is preferable that each is 0.025% or less, more preferably 0.020% or less, and even more preferably 0.015% or less.

[0111] Furthermore, there is no need to set a lower limit for the content of Sn and Sb; both can be 0%. On the other hand, Sn and Sb are elements useful for ensuring low iron loss in non-oriented electromagnetic steel sheets by segregating to the surface of the base material and suppressing oxidation and nitriding during annealing. To obtain this effect, regarding the total content of one or both of Sn and Sb, it is preferable to be more than 0%, more preferably more than 0.001%, further preferably more than 0.005%, more preferably more than 0.010%, and even more preferably more than 0.015%.

[0112] In the chemical composition of the base material of the non-oriented electromagnetic steel sheet of the present invention, the remaining part is Fe and impurities. Here, "impurities" refers to components that are mixed in during the industrial manufacturing of steel due to various factors such as raw materials (ore, waste, etc.) and manufacturing processes, and are therefore permissible within the range that will not adversely affect the present invention.

[0113] Furthermore, the contents of Cr and Mo, as impurity elements, are not specifically specified. In the non-oriented electromagnetic steel sheet of this embodiment, the presence of these elements in amounts of 0.5% or less does not particularly affect the properties of the non-oriented electromagnetic steel sheet. Similarly, the presence of Ca and Mg in amounts of 0.002% or less does not particularly affect the properties of the non-oriented electromagnetic steel sheet. The presence of rare earth elements (REM) in amounts of 0.004% or less does not particularly affect the properties of the non-oriented electromagnetic steel sheet. In this embodiment, REM refers to a total of 17 elements, consisting of Sc, Y, and lanthanides, and the aforementioned REM content refers to the total content of these elements.

[0114] O is also an impurity element, but even if it is present in the range of 0.035% or less, it does not affect the properties of the non-oriented electromagnetic steel sheet of this embodiment. O may sometimes be mixed into the steel during the annealing process, so even if it is present in the billet stage (i.e., ladle value) in the range of 0.010% or less, it will not particularly affect the properties of the non-oriented electromagnetic steel sheet of this embodiment.

[0115] In addition to the elements mentioned above, impurity elements such as Pb, Bi, As, B, and Se can be included, but when their respective contents are in the range of 0.0050% or less, they will not impair the characteristics of the non-oriented electromagnetic steel sheet of this embodiment.

[0116] The chemical composition of the base material of the non-oriented electromagnetic steel sheet of this embodiment can be determined by combining various known measurement methods. In this invention, the content of elements is determined using ICP emission spectrometry (ICP-AES) and ICP mass spectrometry (ICP-MS). Furthermore, C and S can be determined using combustion-infrared absorption spectroscopy, N can be determined using inert gas combustion-thermal conductivity spectroscopy, and O can be determined using inert gas melting-non-dispersive infrared absorption spectroscopy.

[0117] 3. Crystal grain size

[0118] In this embodiment, the average grain size of the base material is set to be greater than 40 μm and less than 140 μm. By setting the average grain size of the base material to be greater than 40 μm, the deterioration of hysteresis loss can be suppressed and iron loss can be improved. On the other hand, by setting the average grain size to be less than 140 μm, the strength of the steel can be improved, and the deterioration of iron loss due to the increase of eddy current loss can be suppressed. Regarding the average grain size, it is preferable to be 50 μm or more, and more preferably 60 μm or more. Furthermore, regarding the average grain size, it is preferable to be 130 μm or less, and more preferably 120 μm or less.

[0119] In addition, in this invention, the average grain size of the base material is determined according to JIS G 0551:2013 "Microscopic test method for grain size of steel".

[0120] 4. Texture

[0121] In this embodiment, to improve dimensional accuracy during punching, the {111} orientation is encouraged to develop while the {110} orientation is suppressed. Specifically, the aggregation degree of the {111} orientation, which is beneficial to dimensional accuracy, is set to 3.0 or higher, and the aggregation degree of the {110} orientation, which is detrimental to dimensional accuracy, is set to 0.15 or lower. Regarding the aggregation degree of the {111} orientation, it is preferable to be 3.5 or higher, and more preferably, to be greater than 4.0. Furthermore, regarding the aggregation degree of the {110} orientation, it is preferable to be 0.12 or lower, and more preferably, to be 0.10 or lower. While no upper limit is required for the aggregation degree of the {111} orientation, considering manufacturability, a practical upper limit of 7.0 is adopted. Furthermore, no lower limit is required for the aggregation degree of the {110} orientation; it can be 0. On the other hand, in order to sufficiently reduce the iron loss W10 / 400, the degree of aggregation of the {110} orientation is preferably 0.01 or more, and more preferably 0.02 or more.

[0122] Furthermore, the aggregation degree of the {111} and {110} orientations was determined using an X-ray diffraction apparatus. The aggregation degree is defined as the value obtained by measuring the X-ray intensity of a standard sample and the test material that do not exhibit aggregation towards a specific orientation under the same conditions using X-ray diffraction, and then dividing the X-ray intensity of the test material by the X-ray intensity of the standard sample. The specific measurement method is as follows: A 26mm diameter test piece was punched from the base material of the non-oriented electromagnetic steel sheet of the test material, and the measurement was performed on the surface after chemical grinding, removing material from one side to a depth of 1 / 4 of the sheet thickness. Furthermore, considering both measurement accuracy and experimental efficiency, the number of test pieces used for measurement was set to 10. Regarding the aggregation degree of the {111} and {110} orientations, the integral intensity of the diffraction of each crystal plane is calculated based on the X-ray diffraction pattern measured by an X-ray diffraction device, and the value obtained by dividing it by the integral intensity of the standard sample is defined as the aggregation degree of the {111} and {110} orientations.

[0123] <Determination Method>

[0124] A 26 mm diameter test piece was placed in the sample holder. At the same time, a standard sample provided by the manufacturer that does not have aggregation to a specific orientation was also placed. As the measurement conditions for reverse X-ray analysis, the measurement axis was set to 2θ / θ, the measurement method was set to FT, and the counting unit was set to CPS. In addition, the step size was set to 0.010°, the counting time to 0.6 s, the voltage to 50 kV, the voltage to 200 mA, the divergence and scattering slits to 1°, the divergence longitudinal slit to 10 mm, and the light-receiving slit to 0.15 mm. As the measurement range, it was set to (110): 2θ = 18.000~21.500°, (200): 2θ = 27.750~29.500°, and (222): 2θ = 49.750~52.000°.

[0125] <Analytical Methods>

[0126] The analysis software "Invpole.cnd" was used. A standard result needed to be selected, so the data was set to refer to the standard sample measured along with the test piece. Smoothing, peak correction, and background removal were not performed. The intensity calculation was performed using "integral intensity," and for crystallization, cubic crystals (α-axis: 2.866 Å) were selected.

[0127] 5.Magnetic properties

[0128] In the non-oriented electromagnetic steel sheet of this embodiment, the term "excellent magnetic properties" means that the iron loss W 10 / 400 Lower.

[0129] Here, the iron loss W is made 10 / 400 The iron loss W is determined according to the Epstein test method specified in JIS C 2550-1:2011. 10 / 400 This means the iron loss generated under conditions such as a maximum magnetic flux density of 1.0T and a frequency of 400Hz.

[0130] The density of the steel plate used for the measurement was set as a value calculated using [7.865 - 0.065 × (Si + 1.7 × Al)]. Here, Si and Al are their respective contents (mass%) in the steel plate. Furthermore, when measuring iron loss according to the Epstein test method, the excitation directions were set as two directions: one parallel to the rolling direction (hereinafter referred to as the L direction) and the other perpendicular to the rolling direction (hereinafter referred to as the C direction). Test pieces excited along the L direction and C direction were measured using half the amount of each direction.

[0131] Furthermore, it is impossible to extract a test piece as large as the Epstein test piece from the motor core. In evaluating the iron loss of the motor core, the stacked core is separated into steel plates, and a small test piece for single-sheet magnetic property measurement is fabricated using electrical discharge machining (EDM), the size of which can be extracted based on the size of the separated steel plates. Then, the iron loss value is measured using a small single-sheet tester corresponding to the aforementioned small test piece. At this time, the measurement principle is made according to the Single Sheet Tester (SST) method specified in JIS C 2556:2015. When measuring iron loss using the single-sheet magnetic property measurement method, the excitation directions are set to two directions: L and C, and the average value measured in each direction is used as the magnetic property value of the material.

[0132] Furthermore, Epstein test pieces and small test pieces were extracted from several types of non-oriented electromagnetic steel sheets beforehand. Iron loss values ​​were measured using the Epstein method and the single-plate magnetic property measurement method, and a conversion formula was derived beforehand based on the relationship between the two measured values. Then, the iron loss values ​​measured by the single-plate tester were corrected using the aforementioned conversion formula to make them equivalent to the iron loss values ​​measured by the Epstein method.

[0133] In the non-oriented electromagnetic steel sheet of this embodiment, the so-called iron loss W 10 / 400 Lower means that when the plate thickness is 0.26 mm or more, it is below 14.5 W / kg; when the plate thickness is 0.21–0.25 mm, it is below 12.5 W / kg; and when the plate thickness is 0.20 mm or less, it is below 11.2 W / kg. Preferably, regarding iron loss W... 10 / 400 When the plate thickness is above 0.26mm, it is below 14.3W / kg; when the plate thickness is between 0.21 and 0.25mm, it is below 12.3W / kg; and when the plate thickness is below 0.20mm, it is below 11.0W / kg.

[0134] 6. Mechanical properties

[0135] The non-oriented electromagnetic steel sheet of this embodiment has high strength. While there is no particular limitation on the 0.2% yield strength, it is preferable that the 0.2% yield strength is 450 MPa or more. More preferably, it is 470 MPa or more, and even more preferably, it is 490 MPa or more. Here, the 0.2% yield strength is determined by a tensile test in accordance with JIS Z 2241:2011, using the offset method.

[0136] For the test piece, the plate thickness is kept constant, the rolling direction is taken as the long side, and it is machined into the shape of a JIS 5 test piece. Alternatively, if the extraction of a JIS 5 test piece is difficult due to the size of the steel plate, a proportionally reduced shape can be used to perform the tensile test.

[0137] 7.Plate thickness

[0138] In the non-oriented electromagnetic steel sheet of this embodiment, from the viewpoint of reducing manufacturing costs associated with cold rolling and final annealing, the thickness of the base material is set to 0.10 mm or more. On the other hand, from the viewpoint of reducing iron loss, the thickness of the base material is set to 0.30 mm or less. Therefore, the thickness of the base material of the non-oriented electromagnetic steel sheet of this embodiment is 0.10 to 0.30 mm. Preferably, the thickness of the base material is 0.15 to 0.27 mm.

[0139] 8. Insulating film

[0140] In the non-oriented electromagnetic steel sheet of this embodiment, it is preferable that an insulating film is provided on the surface of the base material. The non-oriented electromagnetic steel sheet is used after being stacked from the core blank after being punched out. Therefore, by providing an insulating film on the surface of the base material, eddy currents between the sheets can be reduced, and it can be used as a core to reduce eddy current losses.

[0141] The type of insulating film is not particularly limited, and known insulating films used as insulating films for non-oriented electromagnetic steel sheets can be used. Examples of such insulating films include composite insulating films that are primarily inorganic and also contain organic materials. Here, a composite insulating film refers, for example, an insulating film primarily composed of at least one of inorganic materials such as metal chromate salts, metal phosphate salts, colloidal silica, Zr compounds, or Ti compounds, and in which fine organic resin particles are dispersed. In particular, from the viewpoint of reducing the environmental impact of manufacturing processes, which has been increasingly demanded in recent years, insulating films using metal phosphate salts, Zr or Ti coupling agents, or Zr or Ti carbonates or ammonium salts as starting materials are preferred.

[0142] There is no particular limitation on the amount of insulating film applied, but it is preferred, for example, to be 200-3000 mg / m² per single side. 2 More preferably, it is set at 300–2500 mg / m² per single surface. 2 By forming the insulating film with an adhesion amount within the aforementioned range, excellent uniformity can be maintained. Furthermore, when measuring the adhesion amount of the insulating film afterward, various known measurement methods can be used, such as methods that appropriately measure the mass difference before and after immersion in sodium hydroxide aqueous solution, or fluorescence X-ray methods using calibration curves, etc.

[0143] 9. Manufacturing method

[0144] The non-oriented electromagnetic steel sheet of this embodiment is not particularly limited in its manufacturing method, but for steel blocks having the above-mentioned chemical composition, it can be manufactured, for example, by sequentially performing a hot rolling process, a hot-rolled sheet annealing process, a descaling process, a cold rolling process, and a final annealing process under the conditions shown below. Furthermore, when an insulating film is formed on the surface of the base material, the insulating film forming process is performed after the aforementioned final annealing process. Each process will be described in detail below.

[0145] <Hot Rolling Process>

[0146] A steel block (billet) having the above-mentioned chemical composition is heated, and the heated steel block is hot-rolled to obtain a hot-rolled plate. There are no particular specifications for the heating temperature of the steel block during hot rolling, but it is preferably set to, for example, 1050–1250°C. Furthermore, there are no particular specifications for the thickness of the hot-rolled plate, but considering the final thickness of the base material, it is preferably set to, for example, approximately 1.5–3.0 mm.

[0147] <Hot-rolled sheet annealing process>

[0148] Then, hot-rolled sheet annealing is performed to reduce iron loss in the steel sheet. Preferably, a continuous annealing furnace is used for hot-rolled sheet annealing, which is more productive than intermittent annealing and produces a more homogeneous metal structure after annealing. The hot-rolled sheet annealing is performed at a soaking temperature of 760–880°C and a soaking time of 5 to 100 seconds. As mentioned above, by lowering the soaking temperature, a texture favorable to dimensional accuracy can be developed. On the other hand, to ensure lower iron loss W... 10 / 400 The heat spreader temperature is set to 760°C or higher. Furthermore, it is preferable that the lower the Si content of the base material, the higher the heat spreader temperature. Specifically, when the Si content is 4.40% or lower, it is preferable to set the heat spreader temperature to 770°C or higher; when the Si content is 4.30% or lower, it is preferable to set the heat spreader temperature to 780°C or higher.

[0149] <Descaling process>

[0150] For the steel sheet after annealing the aforementioned hot-rolled sheet, pickling is performed to remove the oxide scale layer formed on the surface of the base material. The pickling conditions, such as the concentration of the acid used for pickling, the concentration of the pickling accelerator used for pickling, and the temperature of the pickling solution, are not particularly limited and can be set to known pickling conditions. Furthermore, to improve the descaling properties, it is preferable to perform shot peening after annealing the hot-rolled sheet and before pickling.

[0151] <Cold rolling process>

[0152] The steel sheet after descaling is then subjected to cold rolling. During cold rolling, the sheet is rolled at a reduction rate that results in a final sheet thickness of 0.10 to 0.30 mm.

[0153] <Final Annealing Process>

[0154] After the aforementioned cold rolling, a final annealing is performed. In the manufacturing method of the non-oriented electromagnetic steel sheet of this embodiment, it is preferable to use a continuous annealing furnace for the final annealing. The final annealing is performed by heating to a temperature of 850°C or higher at a heating rate of 100°C / s or less within a temperature range of 500 to 850°C, and then annealing at a soaking temperature of 850 to 1050°C for a soaking time of 1 to 300 seconds. Preferably, the atmosphere is a mixture of H2 and N2 with a H2 content of 1 to 100 vol% (i.e., H2 + N2 = 100 vol%), and the dew point of the atmosphere is set to -50 to +10°C.

[0155] By setting the heating rate to below 100°C / s within the temperature range of 500–850°C, a texture favorable to dimensional accuracy can be developed. When the heating rate exceeds 100°C / s, there is a risk that the aggregation degree of the {111} orientation will be less than 3.0. Alternatively, the average heating rate can be set to 1–100°C / s throughout the entire heating process, including temperature ranges below 500°C and homogenization temperatures.

[0156] Furthermore, when the soaking temperature is below 850°C, the crystal grain size becomes finer and the iron loss deteriorates, which is not preferable. When the soaking temperature exceeds 1050°C, the strength is insufficient and the iron loss also deteriorates, which is also not preferable. In addition, when the soaking time is less than 1 second, sufficient grain growth cannot be achieved. On the other hand, when the soaking time exceeds 300 seconds, it will increase the manufacturing cost.

[0157] <Insulating film formation process>

[0158] After the final annealing described above, an insulating film forming process is performed as needed. The method for forming the insulating film is not particularly limited; a known processing solution for forming an insulating film, as described below, can be used, and the solution can be coated and dried using known methods. For example, a composite insulating film that is primarily inorganic and also contains organic matter can be cited as a known insulating film.

[0159] Composite insulating films, for example, refer to insulating films primarily composed of at least one of metal salts such as chromate and phosphate, or inorganic substances such as colloidal silica, Zr compounds, and Ti compounds, and containing dispersed fine organic resin particles. In particular, from the viewpoint of reducing the environmental burden during manufacturing, which has become increasingly important in recent years, insulating films using coupling agents of metal phosphate, Zr, or Ti as starting materials, or insulating films using carbonates or ammonium salts of metal phosphate, Zr, or Ti as starting materials, are preferred.

[0160] Before applying the coating solution, the surface of the base material to which the insulating film is formed can undergo any pretreatment, such as degreasing based on alkali or pickling based on hydrochloric acid, sulfuric acid, phosphoric acid, etc. Alternatively, these pretreatments can be omitted, and the coating solution can be applied directly to the surface of the base material after final annealing.

[0161] The non-oriented electromagnetic steel sheet of the present invention obtained as described above has the characteristics of low iron loss, high strength, and excellent dimensional accuracy during punching, and is therefore preferred as a raw material for either the rotor or the stator.

[0162] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments.

[0163] Example 1

[0164] A steel billet with the chemical composition shown in Table 1 was heated to 1150°C, then hot-rolled at a final temperature of 850°C and a final thickness of 2.0 mm, and coiled at 600°C to produce a hot-rolled steel sheet. The resulting hot-rolled steel sheet was then annealed in a continuous annealing furnace under the conditions shown in Table 2. After descaling the steel sheet by shot peening and pickling, it was cold-rolled to produce a cold-rolled steel sheet with a thickness of 0.25 mm.

[0165] Furthermore, final annealing was carried out in a mixed atmosphere of H2: 20%, N2: 80%, and dew point: -30°C, under the conditions shown in Table 2. An insulating film composed of aluminum phosphate and a styrene-acrylic acid copolymer resin emulsion with a particle size of 0.2 μm was coated onto the final annealed steel sheet, and sintering was performed at 350°C in atmospheric conditions.

[0166] [Table 1]

[0167]

[0168] [Table 2]

[0169]

[0170] For each test material obtained, the average grain size of the base material was measured according to JIS G 0551:2013 "Steel - Microscopic Test Method for Grain Size". Furthermore, Epstein test pieces were extracted from the rolling direction and width direction of each test material, and the iron loss W was measured according to the Epstein test in JIS C 2550-1:2011. 10 / 400 An evaluation was conducted.

[0171] After the parent material of each test material was chemically ground to a depth of 1 / 4 of the plate thickness, the aggregation degree of the {111} and {110} orientations was determined by X-ray diffraction using a Rigaku RINT-2500 apparatus. Next, JIS No. 5 tensile test specimens were extracted from each test material according to JIS Z 2241:2011, with the length direction aligned with the rolling direction of the steel plate. Tensile tests were then performed on these specimens according to JIS Z 2241:2011, and the 0.2% yield strength was determined.

[0172] Furthermore, in this embodiment, to evaluate the dimensional accuracy during the punching process, a 50mm diameter disc was punched, and the roundness of the punched steel sheet was measured. Additionally, the roundness of this invention is displayed according to JIS B 0621 (1984), which states that "roundness is expressed as the difference in radii when a circular object is held between two concentric geometric circles, minimizing the distance between the two concentric circles, and is displayed as roundness_mm or roundness_μm." In this embodiment, a roundness of 30μm or less is considered to indicate excellent dimensional accuracy during the punching process.

[0173] The results above are shown in Table 2.

[0174] In tests No. 1, 4, and 5 that meet the requirements of this invention, it can be seen that the iron loss W 10 / 400 It has a relatively low yield strength of over 450 MPa (0.2%) and good roundness. In contrast, in comparative tests No. 2, 3, and 6, the iron loss W was found to be... 10 / 400 The yield strength of 0.2% is equivalent to that of the example of the present invention, but the roundness is poorer.

[0175] Specifically, in Test No. 2, the Sn content was higher than the specified range, resulting in an aggregate degree of {110} orientation exceeding the specified range, leading to poor roundness. In Test No. 3, the Sn content was higher than the specified range, and the soaking temperature of the hot-rolled plate annealing exceeded the specified range. Therefore, the aggregate degree of {111} orientation was lower than the specified range, while the aggregate degree of {110} orientation was higher than the specified range, resulting in poor roundness.

[0176] In test number 6, the final annealing heating rate was higher than the specified range, resulting in a lower aggregation degree for the {111} orientation than the specified range, leading to poorer roundness. As mentioned above, it can be concluded that poor roundness occurs when the aggregation degree of the {111} orientation becomes lower than the specified range, or the aggregation degree of the {110} orientation becomes higher than the specified range, or the aggregation degrees of both orientations simultaneously deviate from the specified range.

[0177] Example 2

[0178] A steel billet with the chemical composition shown in Table 3 was heated to 1150°C, then hot-rolled at a final temperature of 850°C and a final thickness of 2.0 mm, and coiled at 600°C to produce a hot-rolled steel sheet. The resulting hot-rolled steel sheet was then annealed in a continuous annealing furnace under the conditions shown in Table 4. After descaling the steel sheet by shot peening and pickling, it was cold-rolled to produce a cold-rolled steel sheet with a thickness of 0.25 mm.

[0179] Subsequently, final annealing was carried out in a mixed atmosphere of H2: 20%, N2: 80%, and dew point: -30°C, under the conditions shown in Table 4. An insulating film composed of aluminum phosphate and a styrene-acrylic acid copolymer resin emulsion with a particle size of 0.2 μm was coated onto the final annealed steel sheet, and sintering was performed at 350°C in atmospheric conditions.

[0180] [Table 3]

[0181]

[0182] [Table 4]

[0183]

[0184] For each of the obtained test materials, the average grain size and iron loss W of the parent material were measured using the same method as in Example 1. 10 / 400 The aggregation degree of the {111} and {110} orientations, as well as the 0.2% yield strength, were measured. The results are shown in Table 4.

[0185] In tests No. 7, 9, 11, 13, 14, and 16 that meet the requirements of this invention, it can be seen that the iron loss W 10 / 400 It has a lower yield strength and a high yield strength of 0.2% exceeding 450 MPa. In contrast, in tests No. 8, 10, 12, 15, 17, and 18, which served as comparative examples, the iron loss W... 10 / 400 If the yield strength is less than 0.2% or the texture is poor, or it will break during cold rolling, the properties cannot be evaluated.

[0186] Specifically, in Test No. 8, the Si content was higher than the specified range, resulting in fracture during cold rolling. In Test No. 10, the Si content was lower than the specified range, resulting in a poor 0.2% yield strength. In Test No. 12, the Al content became higher than the specified range, resulting in a lower aggregation degree in the {111} orientation and a higher aggregation degree in the {110} orientation.

[0187] In Test No. 15, the S content was higher than the specified range, resulting in a smaller grain size and consequently, poorer iron loss. In Test No. 17, the Al content was lower than the specified range, leading to a smaller grain size and also poorer iron loss. In Test No. 18, the Si + Al + 0.5 × Mn ratio was higher than the specified range, causing fracture during cold rolling, making it impossible to evaluate the properties.

[0188] Industrial utilization potential

[0189] As described above, according to the present invention, a non-oriented electromagnetic steel sheet with excellent magnetic properties, high strength, and excellent dimensional accuracy during punching can be obtained.

Claims

1. A non-oriented electromagnetic steel sheet, wherein the chemical composition of its base material, in mass percent, is: C: Below 0.0050%, Si: exceeding 3.50% but below 4.50%, Mn: less than 0.60%, Al：0.25～0.65%， P: below 0.030%, S: below 0.0020%, N: below 0.0040%, Ti: less than 0.0040%, Nb: less than 0.0040%, Zr: less than 0.0040%, V: Less than 0.0040%, Cu: less than 0.200%, Ni: less than 0.500%, The total of one or two of Sn and Sb: less than 0.030%, Remaining components: Fe and impurities. And satisfy the following equation (i), 4.3≤Si+Al+0.5×Mn≤5.0・・・(i) in, In the above formula, the element symbols represent the content of each element in terms of mass%. The average crystal grain size of the parent material is greater than 40 μm and less than 140 μm; At a position 1 / 4 of the plate thickness from the surface of the base material, the degree of aggregation of the {111} orientation is 3.0 or higher, and the degree of aggregation of the {110} orientation is 0.15 or lower. The plate thickness is 0.10 to 0.30 mm.

2. The non-oriented electromagnetic steel sheet as described in claim 1, wherein, The yield strength of 0.2% is above 450 MPa.

3. The non-oriented electromagnetic steel sheet as described in claim 1 or 2, wherein, The surface of the base material has an insulating film.

4. A method for manufacturing a non-oriented electromagnetic steel sheet as described in any one of claims 1 to 3, comprising, for a steel ingot, the following steps in sequence: a hot rolling process; a hot-rolled sheet annealing process with a soaking temperature of 760–880°C and a soaking time of 5 to 100 seconds; a descaling process based on pickling; a cold rolling process to a sheet thickness of 0.10–0.30 mm; and a final annealing process after heating to a temperature of 850°C or higher at a heating rate of 100°C / s or less within a temperature range of 500–850°C, and then soaking at a temperature of 850–1050°C for a soaking time of 1 to 300 seconds. The steel ingot has the following chemical composition, in mass percent: C: Below 0.0050%, Si: exceeding 3.50% but below 4.50%, Mn: less than 0.60%, Al：0.25～0.65%， P: below 0.030%, S: Below 0.0020%, N: below 0.0040% Ti: less than 0.0040%, Nb: less than 0.0040%, Zr: less than 0.0040%, V: Less than 0.0040%, Cu: less than 0.200%, Ni: less than 0.500%, The total of one or two of Sn and Sb: less than 0.030%, Remaining components: Fe and impurities. Satisfying the following equation (i), 4.3≤Si+Al+0.5×Mn≤5.0・・・(i) in, The element symbols in the above formula represent the content of each element in terms of mass%.

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