Motor Core and Its Manufacturing Method

Abstract

The present invention provides a motor core having excellent fatigue characteristics, and also provides a method for manufacturing the motor core at low cost. In the motor core which is a laminate of electromagnetic steel sheets, the exposure rate of recrystallized grains having a diameter of 15 μm or less in the outer peripheral surface of the motor core is 70% or more of the plate thickness of the motor core.

Description

Technical Field

[0001] The present invention relates to a motor core excellent in fatigue characteristics formed by laminating electromagnetic steel sheets and a method for manufacturing the same. Background Art

[0002] With the increasing demand for energy conservation of electrical equipment globally in recent years, there is a requirement for more excellent magnetic characteristics and fatigue characteristics for non-oriented electromagnetic steel sheets used in the cores (motor cores) of rotating machines. In addition, recently, in drive motors for HEVs (hybrid electric vehicles) or EVs (electric vehicles), there is a strong demand for miniaturization and high output. To meet this requirement, research is being conducted to increase the rotational speed of motors.

[0003] More specifically, a motor core includes a stator core and a rotor core. Since the rotor core of an HEV or EV drive motor has a large outer diameter, a large centrifugal force acts on it. In addition, the rotor core has a very narrow portion (1 mm to 2 mm wide) called a rotor core bridge portion in its structure, and this portion becomes a state where the stress is particularly high during driving. Furthermore, since the motor repeatedly rotates and stops, a large repeated stress caused by centrifugal force acts on the rotor core. Therefore, the electromagnetic steel sheet used in the rotor core needs to have excellent fatigue characteristics.

[0004] On the other hand, regarding the electromagnetic steel sheet used in the stator core, in order to achieve miniaturization and high output of the motor, a high magnetic flux density and low iron loss are required. That is, as the characteristics of the electromagnetic steel sheet used as a motor core, high fatigue characteristics are necessary when used for the rotor core, and high magnetic flux density and low iron loss are necessary when used for the stator core.

[0005] Thus, even for the electromagnetic steel sheets used in the same motor core, the required characteristics for the rotor core and the stator core are quite different. However, in the manufacture of a motor core, in order to improve the yield and productivity, sometimes rotor core material and stator core material are taken simultaneously by blanking from the same base material steel sheet, and then each core material is laminated and assembled into a rotor core or a stator core.

[0006] In Patent Document 1, a technique is disclosed: rotor core material and stator core material are taken from a high-strength non-oriented electromagnetic steel sheet by blanking, and they are laminated to assemble a rotor core and a stator core. It is also disclosed that: thereafter, by performing stress relief annealing only on the stator core, a high-strength rotor core and a low-iron-loss stator core are manufactured from the same base material.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2008-50686 Summary of the Invention

[0010] However, in the technology disclosed in the above-mentioned Patent Document 1, the yield stress is increased by using a high-strength non-oriented electromagnetic steel sheet. However, the improvement of the fatigue characteristics, which is one of the most important characteristics, is not considered.

[0011] The present invention has been completed in view of the problems of the above-mentioned prior art, and its object is to provide a motor core and a manufacturing method thereof that are not only excellent in magnetic characteristics but also excellent in fatigue characteristics.

[0012] 1. A motor core, which is a laminate of electromagnetic steel sheets, and the exposure rate of recrystallized grains with a particle size of 15 μm or less in the outer peripheral surface of the motor core is 70% or more of the plate thickness of the motor core.

[0013] Here, the above-mentioned "outer peripheral surface" refers to the surface formed by laminating multiple layers of motor core materials taken out from electromagnetic steel sheets by blanking or the like, and is the outer peripheral side surface of the motor core. In addition, the above-mentioned "recrystallized grains" are grains with a GOS of 2.0° or less, and the GOS refers to the value obtained by averaging the orientation difference between the average orientation of the grain and the measurement points within the grain for all points within the grain.

[0014] 2. The motor core according to the above 1, wherein an unrecrystallized grain layer in which unrecrystallized grains account for 70% or more of the plate thickness of the motor core is provided inside the outer peripheral surface.

[0015] Here, the above-mentioned unrecrystallized grains are grains with a GOS greater than 2.0°.

[0016] 3. The motor core according to the above 1 or 2, wherein the electromagnetic steel sheet has the following composition: by mass%, it contains

[0017] C: 0.0100% or less,

[0018] Si: 2.0% - 7.0%,

[0019] Mn: 0.05% - 3.0%,

[0020] Al: 3.0% or less,

[0021] P: 0.2% or less,

[0022] S: 0.005% or less and

[0023] N: 0.0050% or less,

[0024] The balance is Fe and unavoidable impurities.

[0025] 4. The non-oriented electromagnetic steel sheet according to 3 above, wherein, in the above composition, in mass %, further contains one or more selected from

[0026] Cr: 0.1% to 5.0%,

[0027] Ca: 0.001% to 0.01%,

[0028] Mg: 0.001% to 0.01%,

[0029] REM: 0.001% to 0.01%,

[0030] Sn: 0.001% to 0.2%,

[0031] Sb: 0.001% to 0.2%,

[0032] Cu: 0.10% or less,

[0033] Ti: 0.010% or less,

[0034] Nb: 0.010% or less,

[0035] V: 0.20% or less,

[0036] Mo: 0.20% or less,

[0037] B: 0.0050% or less,

[0038] Co: 0.1% or less and

[0039] Ni: 0.1% or less

[0040] and one or more of the above.

[0041] 5. A method for manufacturing a motor core, which is the method for manufacturing a motor core according to any one of 1 to 4 above, having:

[0042] A blanking process of blanking the motor core material from the above electromagnetic steel sheet;

[0043] A stacking process of stacking multiple sheets of the motor core material; and

[0044] An annealing process of heating the stacked motor core material to a temperature of 550°C to 700°C at a heating rate of 3°C / min or more and holding at this temperature for 650 seconds to 36000 seconds.

[0045] 6. A method for manufacturing a motor core, which is the method for manufacturing a motor core according to any one of 1 to 4 above, having:

[0046] A blanking process of blanking the motor core material from the above electromagnetic steel sheet;

[0047] Annealing process: heating the motor core material at a heating rate of 3°C / min or more to a temperature of 550°C to 700°C and holding at this temperature for 650 seconds to 36000 seconds; and

[0048] Laminating process: laminating multiple pieces of the annealed motor core material.

[0049] 7. The method for manufacturing a motor core according to item 5 or 6 above, wherein the blanking gap in the above blanking process is set to 3% to 15% of the thickness of the electromagnetic steel sheet.

[0050] 8. The method for manufacturing a motor core according to any one of items 5 to 7 above, wherein the blanking speed in the above blanking process is set to 100 mm / s to 500 mm / s.

[0051] According to the present invention, a motor core with excellent fatigue characteristics can be provided at low cost. Description of the Drawings

[0052] Figure 1 It is a schematic diagram showing the cross-sectional structure of the bridge portion of the rotor core.

[0053] Figure 2 It is a graph showing the influence of the exposure rate of recrystallized grains with a particle size of 15 μm or less in the blanking end face. Detailed Description of the Invention

[0054] The motor core of the present invention will be described.

[0055] In the following description, as described above, recrystallized grains are grains with a GOS of 2.0° or less, and can be obtained by the EBSD measurement described later. As described above, non-recrystallized grains are grains with a GOS greater than 2.0°, and can be obtained by the EBSD measurement described later. In addition, generally speaking, the tensile strength is related to the fatigue limit. Therefore, excellent fatigue characteristics in the present invention mean that the fatigue limit obtained by performing a fatigue test on a motor core made of the motor core material is high with respect to a reference value obtained by adding a specified threshold value to half of the tensile strength of the motor core material. Therefore, it can be said that the larger the positive value of the difference between the fatigue limit and the reference value, the more excellent the fatigue characteristics. It should be noted that the specified threshold value is set to 70 MPa as described later, but the specified threshold value is a value set by the inventors and others, and is a value that can meet the requirements of future customers for the high fatigue characteristics of the motor core.

[0056] The motor core of the present invention is formed by laminating motor core materials obtained by blanking electromagnetic steel sheets according to each core shape. For example, 100 to 1000 motor core materials are laminated. Importantly, on the outer peripheral surface of the motor core at this time, that is, on the collective surface including the blanking end faces of the laminated multiple motor core materials, recrystallized grains with a diameter of 15 μm or less are exposed over 70% or more of the plate thickness of the motor core.

[0057] [The exposure rate of recrystallized grains with a diameter of 15 μm or less in the outer peripheral surface (blanking end face) of the motor core is 70% or more of the plate thickness of the motor core]

[0058] The inventors et al. found that: if unrecrystallized grains with residual strain are exposed on the blanking end face (the surface that becomes the outer peripheral surface of the motor core) of the motor core material blanked from the electromagnetic steel sheet as the base material, when repeated stress is applied to the motor core, stress concentration occurs at the residual strain part, and it easily becomes the starting point for the generation of fatigue cracks. Therefore, it is necessary to expose recrystallized grains without residual strain on the blanking end face of the motor core material. However, when the grains on the blanking end face are recrystallized grains but the grain size is large, when repeated stress is applied, the deformation will be uneven, stress concentration will occur, and fatigue cracks are likely to occur. On the other hand, if the recrystallized grains exposed on the blanking end face are controlled to be fine grains, the end face strength will increase through grain refinement strengthening, and the effect of suppressing the generation of fatigue cracks can be obtained.

[0059] Based on the above insights, the present inventors et al. conducted further research and found that, in order to sufficiently suppress the generation of fatigue cracks through the grain refinement of recrystallized grains, it is effective to set the exposure rate of recrystallized grains with a diameter of 15 μm or less on the blanking end face to 70% or more of the thickness of the blanking end face. Here, the exposure rate of recrystallized grains in the motor core refers to the ratio of recrystallized grains with a diameter of 15 μm or less exposed on the blanking end face to the plate thickness of the end face. Hereinafter, when simply referred to as "diameter", it means "grain size".

[0060] That is, by setting the above exposure rate to 70% or more, the fatigue limit of the motor core material can be made higher than the above reference value. By controlling the exposure rate of the recrystallized grains to preferably 80% or more, more preferably 90% or more, the fatigue characteristics will be further improved.

[0061] [Inside the recrystallized grains with a diameter of 15 μm or less, there is an unrecrystallized grain layer in which unrecrystallized grains extend over 70% or more of the plate thickness of the motor core]

[0062] As described above, the non-recrystallized grains are the starting points of fatigue cracking. On the other hand, there are fluctuations in the crystal orientation within the non-recrystallized grains, and the resistance to the development of fatigue cracks generated on the blanking end face into the interior is high. It is important to prevent the development of fatigue cracks generated on the blanking end face, and it is preferable to have a non-recrystallized grain layer present inside the steel sheet. To obtain such an effect, it is preferable that: on the inner side of the outer peripheral surface of the motor core (the inner side of the blanking end face), preferably in the adjacent region of the recrystallized grain layer with a grain size of 15 μm or less, there is a non-recrystallized grain layer in which the non-recrystallized grains exist over 70% or more of the plate thickness of the end face in the thickness direction (hereinafter also referred to as the existence rate). Here, the existence rate of the non-recrystallized grains refers to the ratio of the non-recrystallized grains present on the inner side of the blanking end face to the plate thickness of the same end face. That is, in the case where there are a plurality of separated non-recrystallized grain layers in the plate thickness direction, the total value of the lengths of these non-recrystallized grain layers in the plate thickness direction becomes the length of the non-recrystallized grain layer.

[0063] By setting the above-mentioned existence rate to 70% or more, the fatigue limit of the motor core material can be reliably made higher than the above-mentioned reference value. By controlling the existence rate of the non-recrystallized grains to be more preferably 80% or more and further preferably 90% or more, the effect of preventing the development of fatigue cracks will be further improved.

[0064] For the structure that satisfies the above conditions, with reference to Figure 1 which schematically shows the structure, a detailed description will be given.

[0065] Figure 1 Figure 12 shows the cross-sectional structure of the rotor core bridge part of the motor core material with a plate thickness of ST. In this cross-section, the grains represented by white are recrystallized grains with a diameter of 15 μm or less, and the grains represented by slashes are non-recrystallized grains. In the illustrated example, recrystallized grains with a diameter of 15 μm or less are exposed on the blanking end face, and non-recrystallized grains are exposed in part. In this case, as Figure 1 shown, the exposed length of the recrystallized grains with a diameter of 15 μm or less is L1 + L2, and the exposure rate (%) is (L1 + L2) / ST × 100. Therefore, the recrystallized grains P1 that are not exposed on the blanking end face are not included in the calculation of this exposure rate. Incidentally, in the illustrated example, non-recrystallized grains are exposed in part on the blanking end face, but preferably non-recrystallized grains are not exposed on the blanking end face.

[0066] In addition, on the inner side of the blanking end face, it is preferable to have an unrecrystallized grain layer Ly, which is an aggregate in which unrecrystallized grains are adjacent to each other in the plate thickness direction and continuously exist. The unrecrystallized grain layer Ly is a region where unrecrystallized grains adjacent to the above-mentioned recrystallized grain layer are continuous in the plate thickness direction. In the illustrated example, the length of the unrecrystallized grain layer Ly in the plate thickness direction is represented by L3. Moreover, the occupancy rate (%) of the unrecrystallized grain layer Ly is L3 / ST×100. Therefore, the unrecrystallized grains P2 separated by the recrystallized grains from this region are not included in the unrecrystallized grain layer Ly. In addition, when there are a plurality of separated unrecrystallized grain layers in the plate thickness direction, the sum of the lengths of these unrecrystallized grain layers in the plate thickness direction becomes the above-mentioned L3.

[0067] It should be noted that the remaining region other than the above-mentioned recrystallized grains with a diameter of 15 μm or less and the unrecrystallized grain layer Ly can be any structure. For example, it can be a structure composed of either or both of recrystallized grains containing recrystallized grains P1 and unrecrystallized grains that do not belong to the unrecrystallized grain layer Ly.

[0068] [Composition of the steel sheet]

[0069] Next, the preferred composition of the electromagnetic steel sheet used in the motor core of the present invention will be described. The unit of the content of elements in the composition is "mass%", and hereinafter, it will be simply represented by "%" unless otherwise specified.

[0070] C: 0.0100% or less

[0071] C is a harmful element that forms carbides during the use of the motor, causing magnetic aging and deteriorating the iron loss characteristics. In order to avoid magnetic aging, it is preferable to set the C contained in the steel sheet to 0.0100% or less. More preferably, it is 0.0050% or less. It should be noted that the lower limit of C is not particularly limited, but a steel sheet with an excessive reduction of C is very expensive. Therefore, it is preferably set to about 0.0001%.

[0072] Si: 2.0% - 7.0%

[0073] Si has the effect of increasing the inherent resistance of the steel and reducing the iron loss. In addition, it also has the effect of increasing the strength of the steel by solid solution strengthening. In order to reliably obtain such effects, it is preferable to set the Si addition amount to 2.0% or more. On the other hand, if it is greater than 7.0%, the toughness will decrease and cracks are likely to occur. Therefore, the upper limit is preferably set to 7.0%. Therefore, it is preferable to contain Si in the range of 2.0% - 7.0%. The lower limit of Si is more preferably 3.0%. Further preferably, it is 3.7% or more.

[0074] Mn: 0.05% - 3.0%

[0075] Mn, like Si, is an element useful for increasing the intrinsic resistance and strength of steel, so it is preferably contained in an amount of 0.05% or more. On the other hand, when the addition amount is more than 3.0%, the toughness will decrease and cracks are likely to occur during processing. Therefore, the upper limit is preferably set at 3.0%. Therefore, it is preferred to contain Mn in the range of 0.05% to 3.0%. More preferably, it is 0.1% or more. More preferably, it is 2.0% or less.

[0076] Al: 3.0% or less

[0077] Al, like Si, is a useful element having the effect of increasing the intrinsic resistance of steel and reducing iron loss. However, if it is more than 3.0%, the toughness will decrease and cracks are likely to occur during processing. Therefore, the upper limit is preferably set at 3.0%. More preferably, it is 2.0% or less.

[0078] It should be noted that in the range where the content of Al is greater than 0.01% and less than 0.1%, fine AlN precipitates and the iron loss is likely to increase. Therefore, Al is more preferably in the range of 0.01% or less or 0.1% or more. In particular, if Al is reduced, the grain structure is improved and the magnetic flux density is increased. Therefore, when emphasizing the magnetic flux density, it is preferably set that Al: 0.01% or less. More preferably, it is 0.003% or less.

[0079] P: 0.2% or less

[0080] P is a useful element for adjusting the strength (hardness) of steel. However, if it is more than 0.2%, the toughness will decrease and cracks are likely to occur during processing. Therefore, the upper limit is preferably set at 0.2%. It should be noted that the lower limit is not particularly limited, but steel plates with an excessive reduction in P are very expensive. Therefore, it is more preferably set at about 0.001%. Further preferably, it is in the range of 0.005% to 0.1%.

[0081] S: 0.005% or less

[0082] S is an element that forms fine precipitates and has an adverse effect on the iron loss characteristics. In particular, if it is more than 0.005%, its adverse effect becomes significant. Therefore, it is preferably set at 0.005% or less. More preferably, it is 0.003% or less.

[0083] N: 0.0050% or less

[0084] N is an element that forms fine precipitates and has an adverse effect on the iron loss characteristics. In particular, if it is more than 0.0050%, its adverse effect becomes significant. Therefore, it is preferably set at 0.0050% or less. More preferably, it is 0.003% or less.

[0085] In the electromagnetic steel sheet used in the present invention, the remaining part other than the above components is Fe and inevitable impurities. Further, according to the required characteristics, in addition to the above component composition, one or more selected from Cr, Ca, Mg, REM, Sn, Sb, Cu, Ti, Nb, V, Mo, B, Co, and Ni can be contained within the following ranges.

[0086] Cr: 0.1% to 5.0%

[0087] Cr has the effect of increasing the inherent resistance of the steel and reducing iron loss. To obtain such an effect, it is preferable to add 0.1% or more of Cr. On the other hand, if it is greater than 5.0%, the magnetic flux density will be significantly reduced due to the decrease in the saturation magnetic flux density. Therefore, when adding Cr, it is preferably added within the range of 0.1% to 5.0%.

[0088] Ca: 0.001% to 0.01%

[0089] Ca is an element that fixes S in the form of sulfide and helps reduce iron loss. To obtain such an effect, it is preferable to add 0.001% or more of Ca. On the other hand, if it is greater than 0.01%, the above effect will saturate and only lead to an increase in raw material costs. Therefore, the upper limit is preferably set at 0.01%.

[0090] Mg: 0.001% to 0.01%

[0091] Mg is an element that fixes S in the form of sulfide and helps reduce iron loss. To obtain such an effect, it is preferable to add 0.001% or more of Mg. On the other hand, if it is greater than 0.01%, the above effect will saturate and only lead to an increase in raw material costs. Therefore, the upper limit is preferably set at 0.01%.

[0092] REM: 0.001% to 0.01%

[0093] REM is an element that fixes S in the form of sulfide and helps reduce iron loss. To obtain such an effect, it is preferable to add 0.001% or more of REM. On the other hand, if it is greater than 0.01%, the above effect will saturate and only lead to an increase in raw material costs. Therefore, the upper limit is preferably set at 0.01%.

[0094] Sn: 0.001% to 0.2%

[0095] Sn is an element effective in increasing the magnetic flux density by improving the aggregation structure. To obtain such an effect, it is preferable to add 0.001% or more. On the other hand, if it is greater than 0.2%, the above effect will saturate and only lead to an increase in raw material costs. Therefore, the upper limit is preferably set at 0.2%.

[0096] Sb: 0.001% to 0.2%

[0097] Sb is an element effective in increasing the magnetic flux density by improving the collective structure. To obtain such an effect, it is preferably added in an amount of 0.001% or more. On the other hand, if it exceeds 0.2%, the above effect saturates, only resulting in an increase in raw material costs. Therefore, the upper limit is preferably set at 0.2%.

[0098] Cu: 0.10% or less

[0099] Cu precipitates finely in the steel by aging during the above annealing process, etc., and contributes to an increase in the strength of the steel sheet through precipitation strengthening. Therefore, it is preferably added in an amount of 0.005% or more. On the other hand, if it is added in an excessive amount exceeding 0.10%, the precipitated Cu will inhibit the recrystallization of the blanking end face during the annealing process and at the same time become the starting point of fatigue cracks, sometimes deteriorating the fatigue characteristics. Therefore, the content in the case of adding Cu is preferably 0.10% or less. Further, it is more preferably 0.05% or less.

[0100] Ti: 0.010% or less

[0101] Ti precipitates finely in the steel as carbides by aging during the above annealing process, etc., and contributes to an increase in the strength of the steel sheet through precipitation strengthening. Therefore, it is preferably added in an amount of 0.0005% or more. On the other hand, if it is added in an excessive amount exceeding 0.010%, the precipitated Ti carbides will inhibit the recrystallization of the blanking end face during the annealing process and at the same time become the starting point of fatigue cracks, sometimes deteriorating the fatigue characteristics. Therefore, the content in the case of adding Ti is preferably 0.010% or less. Further, it is more preferably 0.005% or less.

[0102] Nb: 0.010% or less

[0103] Nb precipitates finely in the steel as carbides by aging during the above annealing process, etc., and contributes to an increase in the strength of the steel sheet through precipitation strengthening. Therefore, it is preferably added in an amount of 0.0005% or more. On the other hand, if it is added in an excessive amount exceeding 0.010%, the precipitated Nb carbides will inhibit the recrystallization of the blanking end face during the annealing process and at the same time become the starting point of fatigue cracks, sometimes deteriorating the fatigue characteristics. Therefore, the content in the case of adding Nb is preferably 0.010% or less. Further, it is more preferably 0.005% or less.

[0104] V: 0.20% or less

[0105] V precipitates finely as carbides in the steel through aging during the annealing process and contributes to the increase in the strength of the steel sheet through precipitation strengthening. Therefore, it is preferably added in an amount of 0.0005% or more. On the other hand, if it is added in excess at more than 0.20%, the precipitated V carbides will inhibit the recrystallization of the blanking end face during the annealing process and at the same time become the starting point of fatigue cracks, sometimes deteriorating the fatigue characteristics. Therefore, the content when adding V is preferably 0.20% or less. Further, it is more preferably 0.05% or less.

[0106] Mo: 0.20% or less

[0107] Mo precipitates finely as carbides in the steel through aging during the annealing process and contributes to the increase in the strength of the steel sheet through precipitation strengthening. Therefore, it is preferably added in an amount of 0.0005% or more. On the other hand, if it is added in excess at more than 0.20%, the precipitated Mo carbides will inhibit the recrystallization of the blanking end face during the annealing process and at the same time become the starting point of fatigue cracks, sometimes deteriorating the fatigue characteristics. Therefore, the content when adding Mo is preferably 0.20% or less. Further, it is more preferably 0.10% or less.

[0108] B: 0.0050% or less

[0109] B has the effect of improving the workability of the steel sheet and inhibiting fracture during cold rolling. To obtain such an effect, B is preferably added in an amount of 0.0010% or more. On the other hand, if it is more than 0.0050%, a large amount of nitrides will be formed in the steel, sometimes deteriorating the iron loss. Therefore, the content when adding B is preferably 0.0050% or less.

[0110] Co: 0.1% or less

[0111] Co has the effect of increasing the magnetic flux density of the steel sheet. To obtain such an effect, Co is preferably added in an amount of 0.01% or more. On the other hand, if it is more than 0.1%, the effect will saturate. Therefore, the content when adding Co is preferably set to 0.1% or less.

[0112] Ni: 0.1% or less

[0113] Ni has the effect of increasing the magnetic flux density of the steel sheet. To obtain such an effect, Ni is preferably added in an amount of 0.01% or more. On the other hand, if it is more than 0.1%, the effect will saturate. Therefore, the content when adding Ni is preferably set to 0.1% or less.

[0114] Next, a preferred embodiment of the method for manufacturing a motor core of the present invention (hereinafter also simply referred to as "the manufacturing method of the present invention") will be described. Generally speaking, it is a method for obtaining a motor core with excellent fatigue characteristics through the following processes: a blanking process, in which a motor core material is taken from an electromagnetic steel sheet by blanking; a stacking process, in which the motor core materials are stacked; and an annealing process, in which heat treatment is performed on the motor core material or the motor core.

[0115] 〈Electromagnetic steel sheet〉

[0116] According to the present invention, in the case of using any electromagnetic steel sheet as the blank material of the motor core, a motor core with excellent fatigue characteristics can be obtained compared with existing products. Therefore, the electromagnetic steel sheet used in the manufacturing of the motor core of the present invention is not particularly limited. From the viewpoint of improving the performance of the motor core, it is desirable to use an electromagnetic steel sheet with high magnetic flux density, low iron loss, and high strength as much as possible.

[0117] 〈Blanking process〉

[0118] The blanking process is a process of blanking out the motor core materials (rotor core material and stator core material) that make up the rotor core and the stator core from the above-mentioned electromagnetic steel sheet.

[0119] The blanking process is not particularly limited as long as it is a process of obtaining a motor core material with a specified size from the above-mentioned electromagnetic steel sheet, and a common blanking process can be used.

[0120] In addition, by combining the blanking gap control and blanking speed control described below, a motor core with more excellent fatigue characteristics can be obtained.

[0121] [Blanking gap: 3% - 15% of the plate thickness]

[0122] If the gap between the punch and the die when blanking the motor core material from the electromagnetic steel sheet, that is, the blanking gap, is less than 3% of the plate thickness, secondary shear cross-sections, cracks, etc. are likely to occur on the blanking end face, which becomes the starting point of fatigue cracks, and the fatigue characteristics will deteriorate. Therefore, the blanking gap is preferably set to 3% or more of the plate thickness. On the other hand, if the blanking gap becomes larger than 15% of the plate thickness, it is easy to suppress the processing hardening of the blanking end face caused by blanking, and sometimes the recrystallization of the blanking end face is suppressed, resulting in a decrease in fatigue characteristics. Therefore, the blanking gap is preferably set to 15% or less of the plate thickness. Therefore, the blanking gap is preferably set to 3% - 15% of the plate thickness. More preferably, it is 5% - 12% of the plate thickness.

[0123] [Blanking speed: 100 mm / s - 500 mm / s]

[0124] If the blanking speed when blanking the motor core material from the electromagnetic steel sheet is less than 100 mm / s, stress concentration parts such as burrs are likely to be generated, which will become the starting point of fatigue cracks and the fatigue characteristics will deteriorate. Therefore, the blanking speed is preferably set to 100 mm / s or more. On the other hand, if the blanking speed is greater than 500 mm / s, stress concentration parts such as roughness and notches are likely to be generated on the blanking end face, and the fatigue characteristics will deteriorate. Therefore, the blanking speed is preferably set to 500 mm / s or less.

[0125] 〈Laminating process〉

[0126] The laminating process is a process of laminating the motor core material to manufacture the motor core. The laminating process is not particularly limited as long as it can laminate the motor core material within the specified dimensions, and common laminating processes can be used.

[0127] 〈Annealing process〉

[0128] The annealing process is a process of annealing the motor core material or the motor core obtained by laminating it. More specifically, the annealing process is a process of heating the motor core material or the motor core at a heating rate of 3°C / min or more to a temperature of 550°C to 700°C, holding for 650 seconds to 36000 seconds, and then cooling. It should be noted that the temperature here refers to the temperature of the steel sheet surface. In the case of annealing the laminated core, it sometimes takes a long time for the temperature inside the steel sheet to rise, but in the present invention, as long as the blanking end face reaches the specified heat process, all the temperatures described below are the steel sheet surface temperatures.

[0129] [Heating rate: 3°C / min or more]

[0130] If the heating rate is less than 3°C / min, it will be held at a temperature below the recrystallization start temperature for a long time, so excessive recovery will occur before recrystallization starts. Therefore, the blanking end face is not sufficiently recrystallized and cannot become the desired steel sheet structure (hereinafter also simply referred to as "desired steel sheet structure") in which recrystallized grains with a particle size of 15 μm or less are exposed over 70% of the plate thickness on the blanking end face. Therefore, the heating rate is limited to 3°C / min or more. Preferably it is 5°C / min or more. There is no particular limitation on the upper limit of the heating rate, but if the heating rate is greater than 50°C / min, the generation of recrystallization nuclei will be promoted, and as a result, there is a risk that the existence rate of the unrecrystallized grain layer inside the blanking end face is less than 70%. Therefore, the heating rate is preferably 50°C / min or less.

[0131] [Annealing temperature: 550°C to 700°C]

[0132] If the annealing temperature is less than 550 °C, recrystallization of the blanked end face caused by annealing cannot occur sufficiently, and the blanked end face of the manufactured motor core cannot become the desired steel plate structure. On the other hand, if the annealing temperature is greater than 700 °C, the recrystallized grains of the blanked end face grow excessively, so the grain size becomes coarse, and the blanked end face cannot become the desired steel plate structure. Therefore, the annealing temperature T is limited to the range of 550 °C to 700 °C. Preferably, it is in the range of 570 °C to 650 °C.

[0133] [Maintain for 650 seconds to 36000 seconds at the annealing temperature]

[0134] When the holding time at the above annealing temperature is less than 650 seconds, recrystallization caused by annealing cannot occur sufficiently, and the blanked end face of the manufactured motor core cannot become the desired steel plate structure. On the other hand, when the holding time at the above annealing temperature is greater than 36000 seconds, the recrystallized grains of the blanked end face grow excessively, so the grain size becomes coarse, and the blanked end face cannot become the desired steel plate structure. Therefore, the holding time at the above annealing temperature is set to 650 seconds to 36000 seconds. Preferably, it is 1200 seconds to 18000 seconds.

[0135] As described above, the obtained motor core has excellent fatigue characteristics. When using a high-strength steel plate as the motor core blank material, more excellent fatigue characteristics can be obtained. In this case, when there is a concern about deterioration of the iron loss of the stator core due to the use of a high-strength steel plate, stress relief annealing for improving the iron loss can also be performed only on the stator core.

[0136] Examples

[0137] <Manufacture of motor core>

[0138] By blanking processing that meets the above blanking conditions, stator core materials and rotor core materials are taken from electromagnetic steel plates with the plate thickness and composition shown in Table 1-1 and Table 1-2. 400 sheets of each core material are laminated, and the stator core and the rotor core are manufactured from the same blank. Furthermore, the above rotor core is heat-treated (annealing process) under the conditions shown in Table 2-1 and Table 2-2.

[0139] <Evaluation>

[0140] Take test pieces from the obtained rotor core and conduct the EBSD measurement described below. In addition, for the purpose of measuring fatigue characteristics, use the same electromagnetic steel sheet as the rotor core to fabricate tensile fatigue test pieces that are blanked under the same conditions and heat-treated under the same conditions. Furthermore, for tensile strength measurement and magnetic property evaluation, use steel sheets obtained by heat-treating the same electromagnetic steel sheet as the rotor core under the same conditions to fabricate tensile test pieces and test pieces for magnetic measurement. Use these test pieces to conduct magnetic property evaluation, tensile tests, and tensile fatigue tests. The test methods are as follows.

[0141] (EBSD Measurement)

[0142] Cut out a test piece for EBSD measurement from the bridge part of the rotor core in such a way that the plane perpendicular to the plate surface and the blanking end face becomes the observation surface. Embed this test piece with resin and mirror-polish the above-mentioned observation surface by grinding and chemical polishing. For this observation surface, conduct electron backscatter diffraction (EBSD) measurement in a field of view that includes the blanking end face and its vicinity. It should be noted that the above measurement conditions are set as follows: step size: 0.3 μm, measurement area: more than half of the total plate thickness in the plate thickness direction × the plate thickness in the direction orthogonal to the plate thickness, so as to conduct EBSD measurement. Then, use the analysis software: OIM Analysis 8 to analyze the local orientation data of the above measurement results. It should be noted that before the above data analysis, screen the measurement points under the condition of GSZ[&;5.000,20,0.100,0,0,8.0,1,1,1.0,0;]>0.000 (Minimum Size: 20 points, Minimum Confidence Index: 0.1, Grain Size>0) in PartitionProperties for analysis. It should be noted that all of this analysis is carried out under the condition that the Grain Tolerance Angle is 5°.

[0143] Extract the grains exposed on the blanking end face among the grains with a diameter of 15 μm or less and a GOS of 2.0° or less, and measure what percentage of the plate thickness this area (exposure rate) is on the blanking end face. This number is equivalent to: what percentage or more of the outer peripheral surface (blanking end face) of the rotor core throughout the plate thickness has recrystallized grains with a particle size of 15 μm or less exposed. Conduct the above measurement in 3 different fields of view on the blanking end face and take the average value as the exposure rate.

[0144] In the present embodiment, the exposure rate of recrystallized grains is calculated by the total length in the plate thickness direction of a plurality of recrystallized grains exposed on the blanking end face in the above-described observation field with respect to the plate thickness. The lengths of the exposed portions of the recrystallized grains are added together regardless of whether the respective recrystallized grains are adjacent to each other. In addition, even if adjacent to the recrystallized grains exposed on the blanking end face, the recrystallized grains not exposed on the blanking end face are not included in the exposure rate in the present embodiment.

[0145] That is, as shown previously Figure 1 as described, the length of the recrystallized grains exposed on the blanking end face in the present embodiment is the sum of the length L1 and the length L2. Moreover, when 0.7 × plate thickness ST ≤ L1 + L2 holds, it can be said that recrystallized grains with a crystal grain diameter of 15 μm or less are exposed over 70% or more of the plate thickness on the outer peripheral surface (blanking end face) of the motor core.

[0146] Next, in the inner layer portion (inside the blanking end face) of the rotor core, grains with a GOS greater than 2.0° are extracted, and the percentage of this region with respect to the plate thickness is measured. This figure corresponds to: over what percentage of the plate thickness in the inner layer portion (inside the blanking end face) of the rotor core has an unrecrystallized grain layer (whether there are unrecrystallized grains).

[0147] Here, as described above, the unrecrystallized grain layer in the present embodiment refers to a layer in which a plurality of unrecrystallized grains are integrated and continuous in the thickness direction, and specifically, is composed of an aggregate of a plurality of mutually adjacent unrecrystallized grains. The existence rate of the unrecrystallized grains is calculated by the length in the plate thickness direction of the unrecrystallized grain layer with respect to the plate thickness.

[0148] That is, as shown previously Figure 1 as described, the unrecrystallized grain layer in the present embodiment includes an aggregate of mutually adjacent unrecrystallized grain layers, and the length in the plate thickness direction of the unrecrystallized grain layer Ly is L3. Moreover, when 0.7 × plate thickness ST ≤ L3 holds, it can be said that the inner layer portion (inside the blanking end face) of the motor core has an unrecrystallized grain layer over 70% or more of the plate thickness. It should be noted that in the case where there are a plurality of separated unrecrystallized grain layers in the plate thickness direction, it is sufficient if the sum of the lengths in the plate thickness direction of these respective unrecrystallized grain layers is longer than 0.7 × plate thickness ST.

[0149] (Tensile test)

[0150] For an electromagnetic steel sheet having the same material source as the above-described rotor core material, after heat treatment under the same conditions as the above-described rotor core, a JIS No. 5 tensile test piece with the rolling direction as the tensile direction is taken, and a tensile test is conducted in accordance with JIS Z2241:2011 to measure the tensile strength (TS).

[0151] (Tensile fatigue test)

[0152] By blanking process, a tensile fatigue test piece with the rolling direction as the length direction is taken from the electromagnetic steel sheet having the same material source as the above rotor core material (the same shape as No. 1 test piece according to JIS Z2275:1978, b: 15 mm, R: 100 mm). After heat treatment under the same conditions as the above rotor core, it is supplied for fatigue test. The above fatigue test is carried out under the conditions of tension-tension (pulsation), stress ratio (= minimum stress / maximum stress): 0.1 and frequency: 20 Hz. The maximum stress that does not cause fatigue fracture in 10 7 cycles is taken as the fatigue limit (σmax). It should be noted that for the evaluation of test results, the results that satisfy the conditions of the following formula for the fatigue limit are evaluated as having excellent fatigue characteristics, and the results that do not satisfy are evaluated as having poor fatigue characteristics.

[0153] Fatigue limit ≥ 0.5 × Tensile strength (TS) + 70 (MPa)

[0154] In the above formula, generally speaking, the fatigue limit required in the relationship with the tensile strength is "0.5 × tensile strength", and the specified threshold value is 70 MPa added to the right side of the above formula. When the above formula is satisfied, in Table 2 described later, a positive value is recorded in the column of "B1: (fatigue limit) - 0.5 × TS + 70", and at the same time, the mark in the column of B2 (blanking fatigue characteristics) is △, ○ or ◎. On the other hand, when the above formula is not satisfied, a negative value is recorded in the B1 column, and at the same time, the mark in the B2 column is ×. In the B2 column, when the value in the B1 column is 0 to 19, the mark is △, when the value in the B1 column is 20 to 39 and the fatigue characteristics are more excellent, the mark is ○, and when the value in the B1 column is 40 or more and the fatigue characteristics are extremely excellent, the mark is ◎. It should be noted that △, ○, and ◎ are relatively marked for the purpose of easily recognizing the superiority of fatigue characteristics at a glance. Of course, this is not an absolute evaluation. For example, even if the same mark ○ is used, the example with a value of "30" in the B1 column is obviously more excellent in fatigue characteristics than the example with a value of "20". The absolute evaluation of fatigue characteristics is carried out through the numerical value in the B1 column.

[0155] (Magnetic property measurement)

[0156] From the electromagnetic steel sheet having the same material source as the above rotor core material, a magnetic measurement test piece with a width of 30 mm and a length of 180 mm in the rolling direction and the direction perpendicular to the rolling direction is taken. After heat treatment under the same conditions as the above rotor core, the iron loss W is measured by the Epstein method according to JIS C2550-1:2011 10 / 400 . For the iron loss values, excellent values are all shown.

[0157] The results of the above evaluation tests are all recorded in Tables 2-1 and 2-2. In addition, the influence of the exposure rate of recrystallized grains with a particle size of 15 μm or less in the blanking end face on the fatigue limit is sorted out and shown in Figure 2 . As shown in this figure, it can be seen that if the exposure rate is 70% or more, then (fatigue limit) -0.5×TS + 70 is 10 MPa or more.

[0158] From the results of No. 1 to No. 36 and No. 57 to No. 64 in Tables 1-1 to 2 and Tables 2-1 to 2, it can be seen that if the exposure rate is 70% or more, excellent fatigue characteristics and iron loss characteristics are exhibited regardless of the composition of the steel sheet. In addition, from the results of No. 1 and No. 37 to No. 56 in Tables 1-1 to 2 and Tables 2-1 to 2, by setting the blanking conditions in the blanking process and the annealing conditions in the annealing process to the above conditions, excellent fatigue characteristics and iron loss characteristics can be imparted. In addition, it can be seen that in order to improve the fatigue characteristics, compared with the blanking conditions, precisely controlling the annealing conditions contributes more to the improvement of the fatigue characteristics. Furthermore, under the annealing conditions, the annealing temperature T and the holding time t contribute greatly to the improvement of the fatigue characteristics.

[0159]

[0160]

[0161]

[0162]

[0163] Industrial application fields

[0164] The technology of the present invention is effective in improving the fatigue characteristics of the motor core. Therefore, it is not limited to the case where the rotor core material and the stator core material are taken from the same billet steel sheet, and can also be applied to the case where the rotor core material and the stator core material are taken from different billet steel sheets respectively.

Claims

1. A motor core is a laminate of electromagnetic steel sheets. On the outer peripheral surface of the motor core, that is, on the blanking end faces of the laminated plurality of motor core materials, the exposure rate of recrystallized grains with a particle size of 15 μm or less is 70% or more of the plate thickness of the motor core. The recrystallized grains are grains with a GOS of 2.0° or less. The GOS is a value obtained by averaging the orientation differences between the average orientation of the grain and the measurement points within the grain for all points within the grain.

2. The motor iron core according to claim 1, wherein, An unrecrystallized grain layer is provided inside the outer peripheral surface. In the unrecrystallized grain layer, the unrecrystallized grains account for 70% or more of the plate thickness of the motor core.

3. The motor core according to claim 1 or 2, wherein, The electromagnetic steel sheet has the following composition: by mass%, it contains C: 0.0100% or less, Si: 2.0% - 7.0%, Mn: 0.05% - 3.0%, Al: 3.0% or less, P: 0.2% or less, S: 0.005% or less, and N: 0.0050% or less, and the balance is iron and unavoidable impurities.

4. The motor core according to claim 3, wherein, In the above composition, by mass%, it further contains one or more selected from Cr：0.1％～5.0％、 Ca: 0.001% - 0.01%, Mg: 0.001% - 0.01%, REM: 0.001% - 0.01%, Sn: 0.001% - 0.2%, Sb: 0.001% - 0.2%, Cu: 0.10% or less, Ti: 0.010% or less, Nb: 0.010% or less, V: 0.20% or less, Mo: 0.20% or less, B: 0.0050% or less, Co: 0.1% or less, and Ni: 0.1% or less among them.

5. A method for manufacturing a motor core, which is a method for manufacturing the motor core according to any one of claims 1 to 4, and has the following steps: A blanking step of blanking motor core materials from the electromagnetic steel sheet; A lamination step of laminating a plurality of the motor core materials; and An annealing step of heating the laminated motor core materials to a temperature of 550°C to 700°C at a heating rate of 3°C / min or more and holding at this temperature for 650 seconds to 36000 seconds.

6. A method for manufacturing a motor core, which is a method for manufacturing the motor core according to any one of claims 1 to 4, and has the following steps: A blanking step of blanking motor core materials from the electromagnetic steel sheet; An annealing step of heating the motor core materials to a temperature of 550°C to 700°C at a heating rate of 3°C / min or more and holding at this temperature for 650 seconds to 36000 seconds; and A lamination step of laminating a plurality of the annealed motor core materials.

7. The manufacturing method of the motor iron core according to claim 5 or 6, wherein, Set the blanking gap in the blanking step to 3% - 15% of the thickness of the electromagnetic steel sheet.

8. The manufacturing method of the motor core according to any one of claims 5 to 7, wherein, Set the blanking speed in the blanking step to 100 mm / s - 500 mm / s.

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