Non-oriented electrical steel sheet, its manufacturing method, and rotating electrical machine including the same

Abstract

(Problem) To provide a novel non-oriented electromagnetic steel sheet that has excellent magnetic aging resistance and does not tend to develop stretcher strain, a method for producing the same, and a rotary electric machine containing the same. (Solution) A non-oriented electromagnetic steel sheet comprising a chemical composition of, in mass%, C: 0.0100% or less, Si: 2.6-4.5% inclusive, Mn: 0.10-3.00% inclusive, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10-2.00% inclusive, one or more selected from Sn and Sb: 0-0.200%, Cr: 0.001-5.000%, predetermined amounts of optionally added elements (Ni, Cu, Ca, Mg, REM, Ti, B, O), and remainder: Fe and impurities, the non-oriented electromagnetic steel sheet being characterized in that the difference: A.I. in the lower yield point before and after aging when aged for one hour at 100°C after application of 8% strain is less than 40 MPa; a method for producing the same; and a rotary electric machine containing the same.

Description

[Technical field]

[0001] The present invention relates to a non-oriented electrical steel sheet, a method for producing the same, and a rotating electric machine including the same. [Background technology]

[0002] Recently, global environmental issues have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there has been a strong demand in recent years for high efficiency electrical equipment. For this reason, there has been an increasing demand for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as iron core materials for motors and the like. This trend is particularly evident in motors for electric and hybrid vehicles, where the efficiency of motors has been increasing in recent years, and in motors for compressors.

[0003] The temperature of automobile drive motors and the like can rise during use, and if magnetic aging occurs in that temperature range, naturally the magnetic properties will deteriorate over time from those at the time of delivery of the material.

[0004] Furthermore, in the case of automobile drive motors and the like, stretcher strain can occur when the core is crimped or bent into a helical shape, which can reduce the dimensional accuracy of the product and, as a result, the magnetic properties designed may not be achieved.

[0005] Patent Document 1 aims to provide a core material for rotating machines that has excellent bending workability and iron loss characteristics, and specifically describes that by adding 0.01 to 0.1% Ti to ultra-low C steel, C is completely fixed, improving aging resistance and resulting in a material with excellent bending workability.

[0006] Patent Document 2 aims to provide a low-cost non-oriented electrical steel sheet with excellent strength and magnetic properties suitable as an iron core material for electric vehicle motors. Specifically, it proposes punching a rotor and stator from a non-oriented electrical steel sheet with a specific chemical composition and then stress relief annealing only the stator, thereby achieving both high strength for the rotor and low iron loss for the stator. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4325235 [Patent Document 2] Patent No. 5228379 Summary of the Invention [Problem to be solved by the invention]

[0008] Various studies have been conducted so far on non-oriented electrical steel sheets with excellent magnetic properties, workability, or strength. However, Patent Document 1 requires the addition of Ti, which can have a detrimental effect on magnetic properties. In addition, Patent Document 2 punches out the rotor and stator from the same steel sheet and only the stator is stress relief annealed, but if the rotor and stator are obtained from different steel sheets and combined, or if it is possible to appropriately select whether or not to stress relief anneal the rotor and stator, the latitude in product design will be expanded.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel non-oriented electrical steel sheet which has excellent magnetic aging resistance and is less likely to cause stretcher strain, a method for manufacturing the same, and a rotating electric machine including the same. [Means for solving the problem]

[0010] The present invention provides the following aspects. [1] The chemical composition is as follows: C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, C A non-oriented electrical steel sheet comprising: a: 0-0.020%, Mg: 0-0.0200%, rare earth elements (REM): 0-0.020%, Ti: less than 0.0100%, B: 0%-0.0050%, O: 0%-0.0200%, and the balance: Fe and impurities, wherein when an 8% strain is applied and then aging treatment is performed at 100°C for 1 hour, the difference in lower yield point before and after aging treatment: AI is less than 40 MPa. [2] The non-oriented electrical steel sheet according to [1], wherein the chemical composition further includes Mo: 0% to 0.0200%. [3] The non-oriented electrical steel sheet according to [1] or [2], characterized in that the following formula satisfies Cev≦0.0055%. Cev=12×([C(mass%)] / 12+[N(mass%)] / 14-[B(mass%)] / 11-[Ti(mass%)] / 48-[Cr(mass%)] / 104-[Mo(mass%)] / 192) In the above formula, [element symbol (mass%)] indicates the content (mass%) of the corresponding element in the chemical composition, and if the corresponding element is not included, 0 is substituted. [4] The chemical composition is, in mass%, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0. 1. A method for producing a non-oriented electrical steel sheet according to any one of [1] to [3], characterized in that when a non-oriented electrical steel sheet consisting of 0.020%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance: Fe and impurities is produced through processes including steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and overaging treatment, the overaging temperature in the overaging treatment is 50°C to 500°C, and the temperature range of 50°C or higher is 10 seconds or longer. [5] The method for producing a non-oriented electrical steel sheet according to [4], wherein the chemical composition further contains Mo: 0% to 0.0200%. [6] The method for producing a non-oriented electrical steel sheet according to [4] or [5], characterized in that during the overaging treatment, in at least a part of the step of holding the temperature in the 50°C to 500°C range, bending is performed by pressing the steel sheet against a roll having a diameter of less than 500 mm. [7] The method for producing a non-oriented electrical steel sheet according to any one of [4] to [6], characterized in that after the overaging treatment, the steel sheet is pressed against a roll having a diameter of less than 500 mm to perform bending. [8] The chemical composition is, in mass%, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 1. A method for producing a non-oriented electrical steel sheet according to any one of [1] to [3], characterized in that when a non-oriented electrical steel sheet consisting of 0.020%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance: Fe and impurities is produced through steps including steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing, and bending, the bending is performed by pressing the steel sheet against a roll having a diameter of less than 500 mm. [9] The method for producing a non-oriented electrical steel sheet according to [8], wherein the chemical composition further contains Mo: 0% to 0.0200%.

[10] A rotating electric machine comprising a stator, a rotor, and a housing that houses the stator and the rotor, wherein a core material of the stator or a core material of the rotor is the non-oriented electrical steel sheet according to any one of [1] to [3]. Effect of the Invention

[0011] The non-oriented electrical steel sheet provided by the present invention has excellent magnetic aging resistance and is less susceptible to stretcher strain. The non-oriented electrical steel sheet can be obtained by the manufacturing method provided by the present invention. Furthermore, the rotating electrical machine provided by the present invention has excellent magnetic aging resistance and is less susceptible to stretcher strain during processing. Here, excellent magnetic aging resistance typically means that the iron loss deterioration rate is less than 0.9. The iron loss deterioration rate is the value obtained by dividing the increase in iron loss before and after aging treatment at 200°C for 24 hours by the iron loss before aging treatment. The fact that it is difficult to cause stretcher strain, although details will be described later, corresponds to the A.I. being less than 40 MPa.

Brief Explanation of Drawings

[0012] [Figure 1] Figure 1 is a schematic diagram for explaining how to obtain the A.I.

Embodiments for Carrying Out the Invention

[0013] The present invention will be described in detail for each constituent element.

[0014] The reasons for limiting the component composition of the steel are as follows. In the following description, unless otherwise specified, the content of each element is expressed in mass%, and the description of mass is omitted.

[0015] <C: 0.0100% or less> C exhibits the effect of increasing iron loss and causing magnetic aging. Therefore, C is set to 0.0100 mass% or less. Preferably, it is 0.001 to 0.004 mass%.

[0016] <Si: 2.6% or more and 4.5% or less> Si increases the specific resistance of the steel and exhibits the effect of reducing iron loss. In order to obtain this effect, 2.6% or more is required. On the other hand, when Si exceeds 4.5%, the steel becomes brittle and the rollability decreases. Therefore, Si is set to 2.6 to 4.5%. Preferably, it is 3.0 to 3.5 mass%.

[0017] <Mn: 0.10% or more and 3.00% or less> Mn increases the specific resistance of the steel and exhibits the effect of coarsening and detoxifying sulfides. In order to obtain this effect, 0.10% or more is required. On the other hand, when Mn exceeds 3.00 mass%, it causes a decrease in magnetic flux density and an increase in cost, and also makes it easier to crack during cold rolling. Therefore, Mn is set to 0.10 to 3.00%. Preferably, it is 0.1 to 0.5 mass%.

[0018] <P: Below 0.15%> P is an element necessary for increasing the hardness of the steel sheet and also for improving the punchability. However, if added in excess of 0.15%, the steel sheet will embrittle, so it is set to 0.15% or less. Preferably, it is 0.01 - 0.10%.

[0019] <S: Below 0.0040%> S is limited to 0.0040% or less. S precipitates as sulfide in the steel, deteriorating the grain growth property and iron loss. If it exceeds 0.0040%, the deterioration of grain growth property and iron loss becomes significant, so it is limited to 0.004% or less. The lower limit is not particularly limited, but it is difficult to make it 0.0005% or less by ordinary manufacturing methods. Preferably, it is 0.0010 - 0.0030%.

[0020] <N: Below 0.0040%> When N is contained in a large amount, it forms nitrides and deteriorates the magnetic properties, so its upper limit needs to be set to 0.0040%. Its lower limit is not particularly specified, but considering the current steelmaking technology, in fact, 0.0001% is the lower limit. Preferably, it is 0.0003 - 0.0020%.

[0021] <Al: 0.10% or more, 2.00% or less> Al is effective as a deoxidizer and can also coarsen nitrides to make them harmless. Also, like Si, it increases the specific resistance of the steel and reduces iron loss. To obtain these effects, 0.10% or more is required. However, if it exceeds 2.00%, the steel will embrittle and the rollability will decrease. Therefore, Al is set to 0.10 - 2.00%. Preferably, it is 0.20 - 1.50%.

[0022] <Sn and Sb: A total of 0% or more and 0.200% or less for one or both> Sn and Sb are effective in improving the microstructure and suppressing nitridation and oxidation during annealing. Also, when the content is 0.005% or more, Sn and Sb suppress the movement of C, improving the aging resistance. If the amount is too large, the effect saturates, and furthermore, it has an adverse effect on embrittlement of the steel and suppression of grain growth, so the content is set to 0.200% or less. Preferably, it is 0.030 - 0.150%.

[0023] <Cr: 0.001% or more, 5.000% or less> Cr has the ability to form carbides and nitrides, fixes solid - solution C and solid - solution N, and has an effect of suppressing stretcher strain. Therefore, the lower limit is set to 0.001% or more. On the other hand, Cr decreases the saturation magnetic flux density of the steel plate. If it exceeds 5.000%, the problem of addition cost also becomes large, so it is limited to 5.000% or less. Preferably, it is 0.100 - 4.000%.

[0024] <Ni: 0% or more, 5.000% or less> Ni is an effective element that can increase the strength of the steel plate without significantly embrittling it. However, since it is expensive, it is added according to the required strength. When adding, the upper limit is set to 5.000% considering the cost. Preferably, it is 1.000 - 4.000%.

[0025] <Cu: 0% or more, 5.000% or less> Cu increases the hardness of the steel plate. If it exceeds 5.000%, the problem of addition cost also becomes large, so it is limited to 5.0% or less. Preferably, it is 0.100 - 4.000%.

[0026] <Ca: 0% or more, 0.020% or less> Ca is intentionally added from the viewpoint of improving grain growth property. However, since it is expensive, it is added as needed. When adding, the upper limit is set to 0.020% or less considering the cost. Preferably, it is 0.008% or less.

[0027] <Mg: 0% or more, 0.0200% or less> Mg is intentionally added from the perspective of improving grain growth properties. However, due to its high cost, it is added as needed. When added, the upper limit is set to 0.0200% or less considering the cost. Preferably, it is 0.0080% or less.

[0028] <Rare earth element (REM): 0% or more, 0.020% or less> Rare earth elements are added for the purpose of improving grain growth properties by suppressing impurity precipitation. However, due to their high cost, they are added as needed. When added, the upper limit is set to 0.020% considering the cost. Preferably, it is 0.001 - 0.008%.

[0029] <Ti: less than 0.0100%> Ti has the ability to form carbides and nitrides, fix solid - solution C and solid - solution N, and has an effect of suppressing stretcher strain. However, Ti forms fine nitrides or carbides, significantly deteriorates the grain growth during strain relief annealing, and degrades magnetic properties. Therefore, it is specified to be less than 0.0100%. Preferably, it is 0.0030% or less. Ti may be 0%, but it may be unavoidably mixed in, and it may also be 0.0020% or less.

[0030] <B: 0% or more, 0.0050% or less> When Al is added, it may precipitate as fine AlN and cause deterioration of magnetic properties. Therefore, B is added simultaneously. If it exceeds 0.0050%, there is a risk of magnetic property deterioration due to excessive B. Therefore, the upper limit is set to 0.0050%. Preferably, it is 0.0030 - 0.0040%.

[0031] <O: 0% or more, 0.0200% or less> O forms precipitates, hinders grain growth during annealing, and degrades magnetic properties Therefore, it is set to 0.0200% or less. Preferably, it is 0.0030% or less. O may be 0%, but it may be unavoidably mixed in, and it may also be 0.0020% or less.

[0032] <Mo: 0% or more and 0.0200% or less> Mo has the ability to form carbides and nitrides, fix solid-solution C and solid-solution N, and has an effect of suppressing stretcher strain. Therefore, Mo may be 0% or more, or may be 0.0030% or more. However, Mo is specified to be 0.0200% or less because it forms precipitates, hinders grain growth during annealing, and deteriorates magnetic properties.

[0033] In addition to the above elements, the chemical composition of the non-oriented electrical steel sheet according to this embodiment may contain Nb, V, Zr, Ce, Bi, and W each at 0.10% or less within a range that does not affect the various properties of the non-oriented electrical steel sheet.

[0034] <Balance: Fe and impurities> The balance is Fe and impurities. Impurities mean elements mixed in from ore, scrap, or the manufacturing environment, etc. as raw materials when industrially manufacturing slabs or steel. Also, it does not exclude replacing and adding Fe with known elements within a range that does not eliminate the effects of the present invention while expecting known effects.

[0035] <cev> Stretcher strain is caused by dissolved C and dissolved N. Cev defined by the following formula is an index related to dissolved C and dissolved N, and if it is too large, stretcher strain is likely to occur. Therefore, it is desirable that Cev ≤ 0.0055%. Cev may be 0.0054% or less, preferably 0.0025 or less, more preferably 0.0015 or less, and even more preferably 0.0000 or less. The lower limit value of Cev is not limited, but it may be -0.5861 or more. Cev = 12 × ([C (mass%)] / 12 + [N (mass%)] / 14 - [B (mass%)] / 11 - [Ti (mass%)] / 48 - [Cr (mass%)] / 104 - [Mo (mass%)] / 192) In the above formula, [element symbol (mass%)] indicates the content (mass%) of the element in the chemical composition of the non-oriented electrical steel sheet. For example, [C (mass%)] indicates the content (mass%) of C in the chemical composition of the non-oriented electrical steel sheet. Also, when the element is not included in the chemical composition of the non-oriented electrical steel sheet, 0 is substituted.

[0036] <A.I. less than 40 MPa> The non-oriented electrical steel sheet according to this embodiment has an A.I. of less than 40 MPa. Here, AI is an abbreviation of Aging Index, and is also called aging index. AI is obtained by processing a JIS No. 13 B tensile sample from a steel plate, applying 8% strain, and then aging at 100°C for 1 hour, and calculating the difference between the stress at 8% strain before aging and the lower yield point after aging. The original gauge length is used as the reference, and the elongation from there is expressed as a percentage. The test speed at this time is 7.2 mm / min. (equivalent to a strain rate of 0.002 / s with an original gauge length of 60 mm) with stroke control. Figure 1 is a diagram that explains the outline of how to calculate AI. First, a tensile test is performed on the sample, applying 8% strain at room temperature (23°C). The stress at the time of applying 8% strain (i.e., the stress at 8% strain before aging) is recorded. After that, the sample after the tensile test is subjected to aging treatment at 100°C for 1 hour, cooled to room temperature (23°C), and then tensile testing is performed again to break the sample. The lower yield point after aging treatment is obtained from the stress-strain curve in this tensile test, and the difference with the stress at 8% strain before aging treatment is obtained. At this time, if a clear yield phenomenon and work hardening are observed in the stress-strain curve, the minimum value of the stress after the yield phenomenon and before work hardening is taken as the lower yield point. If work hardening is not clear as in Figure 1, the point with the lowest stress between the point of the yield phenomenon and the point of elongation 2% lower than the elongation at break is taken as the lower yield point. Other measurement items are in accordance with JIS Z 2241 (2011). If the AI ​​is 40 MPa or more, stretcher strain occurs during core processing, and dimensional accuracy deteriorates. In addition, magnetic aging occurs, and magnetic properties deteriorate over time. Generally, the smaller the AI, the better the stretcher strain suppression effect and aging resistance. Therefore, the AI ​​is preferably 35 MPa or less, and more preferably 30 MPa or less.

[0037] <Manufacturing conditions> Next, the reasons for limiting the manufacturing conditions in this invention and the preferred manufacturing conditions will be described. In general, the manufacturing method of a non-oriented electrical steel sheet includes the steps of steelmaking, slab casting, slab reheating, hot rolling, hot rolled sheet annealing, pickling, cold rolling, final annealing (finish annealing), overaging treatment and / or bending processing, and application of an insulating coating. Each step may be performed in the order described, or the order of the steps may be adjusted as appropriate.

[0038] (Steelmaking) The above-mentioned composition is adjusted by a conventional steelmaking method such as converter steelmaking and degassing treatment.

[0039] (Slab Casting) The slab casting for obtaining the steel having the above chemical composition is performed by conventional continuous casting. Although it is not prohibited to apply blooming method to the continuous cast slab to facilitate heating of the slab, it should be avoided as much as possible because it increases the cost.

[0040] In producing the slabs, a known continuous casting method is used to produce slabs having an initial thickness, which is not particularly limited, in the range of approximately 150 mm to 300 mm, preferably 200 mm to 250 mm.

[0041] (Slab reheating) The condition of the slab reheating temperature prior to hot rolling is very important for the production of non-oriented electrical steel sheets. This is because it is related to the solid solution and precipitation of impurity elements. In order to prevent the fine precipitation of compounds containing impurity elements, the slab reheating temperature is preferably 1250°C or less. Of course, if the absolute value of the content of the main harmful elements such as S and N can be reduced, it is possible to raise the slab heating temperature, but this is not realistic for industrial production.

[0042] (Hot Rolling) The hot rolling conditions for slabs for non-oriented electrical steel sheets are basically low temperature extraction and high temperature rolling, but by performing intermediate annealing, the coiling temperature does not need to be extremely high, and high temperature rolling is not preferable from the viewpoint of descalability. That is, it is sufficient to apply the following conditions in the finish hot rolling: the finish inlet temperature is 900°C to 1000°C, the outlet temperature is 830°C to 900°C, and the coiling temperature is 600°C to 700°C.

[0043] (Hot rolled sheet annealing) It is possible to anneal the hot-rolled sheet, but even if this annealing is applied, the magnetic properties in the rolling direction are improved, but not significantly, and the cost increases significantly. Therefore, the need for annealing should be determined based on the desired properties.

[0044] (pickling) Hot-rolled or hot-rolled annealed sheets can optionally undergo a descaling treatment before cold rolling or finish annealing to remove the layer of oxides, i.e. scale, that form on the steel sheet. Pickling is the most common descaling method, and involves chemical cleaning of the steel sheet surface by using an aqueous solution of one or more inorganic acids. Although descaling is not prevented, pickling may be unnecessary if the annealing atmosphere is good and the surface scale layer is rare.

[0045] (Cold Rolling) Cold rolling is performed once, or in two or more passes with annealing in between. One cold rolling pass means performing one or more cold rolling passes without annealing in between. In any cold rolling, the final reduction is preferably 70 to 95%.

[0046] When cold rolling is carried out in two steps with annealing in between, the annealing is preferably carried out at 750 to 1200° C. for 30 seconds to 10 minutes.

[0047] When cold rolling with intermediate annealing is performed in two or more steps, the magnetic properties tend to become uniform. The number of cold rolling steps is appropriately selected taking into consideration the desired magnetic properties and production costs.

[0048] The thickness of the final product is obtained at this stage. Generally, the product thickness may be less than 0.35 mm. Taking into account the capacity and handling of each production facility, the minimum thickness may be practically set at 0.20 mm. Once the final product thickness is determined, the thickness of the hot rolled steel strip is automatically determined by the cold rolling reduction ratio.

[0049] (Final annealing: finish annealing) Finish annealing is greatly affected by time and temperature, and a higher temperature is better for shortening the annealing time, but currently the maximum temperature is stipulated in the continuous annealing furnace equipment specifications as 1075°C. On the low temperature side, if it is less than 950°C, a slightly longer heating time is required. Furthermore, in order to improve the texture, a patent document (JP Patent Publication No. 06-051889) proposes heating to a temperature of 750 to 1150°C at a rate of 133°C / second or more. This technique is not precluded from being applied. If the holding time of the final annealing is less than 20 seconds, the grain growth is insufficient, whereas if it exceeds 90 seconds, no further grain growth occurs, so the holding time is set in the range of 20 to 90 seconds.

[0050] (Overaging treatment) By performing overaging treatment after the final annealing or during cooling of the final annealing, the solute C in the steel sheet is bonded with Fe atoms to form cementite, and the fixation of the solute C is promoted, thereby improving the effect of suppressing magnetic aging and stretcher strain. The overaging temperature of the overaging treatment is 50°C or higher and 500°C or lower. If the temperature is lower than 50°C, the effect may not be sufficiently obtained, and if the temperature exceeds 500°C, the fixation of the solute C may not be maintained. The upper limit of the overaging temperature is preferably 300°C or lower. The lower limit may be 100°C or higher, and is preferably 200°C or higher. The time of the overaging treatment is 10 seconds or more. If the time is less than 10 seconds, the effect of the overaging treatment may not be sufficiently obtained. The upper limit of the time of the overaging treatment is not particularly limited, but since the effect is saturated, it is preferable to set it to 60 minutes or less.

[0051] (Bending processing) By performing bending processing after the finish annealing, the solute C and solute N in the steel sheet penetrate into the dislocations of the Fe atomic arrangement, and the fixation of the solute C and solute N progresses, improving the effect of suppressing magnetic aging and stretcher strain. The bending processing is performed by winding the steel sheet around a roll with a diameter of less than 500 mm. That is, the bending processing is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm. With a roll with a diameter of 500 mm or more, the steel sheet cannot be bent sufficiently, and the effect may not be fully obtained. The lower limit of the roll diameter is not particularly limited, but since the smaller the diameter, the larger the bending becomes, and there is a risk of the steel sheet breaking, etc., it may be 300 mm or more. In addition, the bending angle of the steel sheet may be 5 degrees or more and 20 degrees or less, with the tangent direction (the horizontal direction of the sheet surface of the steel sheet in a flat state) at the contact point between the roll cross-sectional circle and the steel sheet as the reference (0 degrees). If it is less than 5 degrees, the steel sheet cannot be bent sufficiently, and the effect may not be fully obtained. If the bending angle is too large, there is a risk of the steel plate breaking, etc., so it may be set to 20 degrees or less. The upper limit of the bending angle may be set to 15 degrees or less. The lower limit may be set to 8 degrees or more, or 10 degrees or more. Skin pass processing differs from bending processing in the way that the Fe atomic arrangement in the steel is disturbed and the way in which dislocations are introduced is different, so it is difficult to obtain the same effects as bending processing. Also, bending processing is advantageous in terms of cost. However, bending processing can obtain the above effects by performing it only once. The leveling process involves winding a steel sheet around a roll. The purpose of this process is to straighten the coiled roll, eliminate any warping or bending of the coil, and make it flat. Generally, the roll diameter is small, typically 100 mm or less. Therefore, the leveling process is different from the bending process of this embodiment.

[0052] The overaging treatment and the bending treatment may be used in combination. The overaging treatment and the bending may be performed simultaneously, or the bending may be performed after the overaging treatment. By using them in combination, the effect of suppressing magnetic aging and stretcher strain can be synergistically improved.

[0053] (insulating coating) Since electrical steel sheets are laminated for use, an insulating coating may be applied to the surface to ensure interlayer resistance. Traditionally, coatings containing Cr have been used, but Cr-free coatings have been developed in recent years, so either can be used. EXAMPLES

[0054] Molten steel was continuously cast to prepare a 250 mm thick slab for obtaining a steel having the chemical composition shown in Table 1 below. Next, the slab was hot rolled to produce a hot rolled sheet. The slab reheating temperature at that time was 1200 ° C, the finishing temperature in the finish rolling was 850 ° C, the coiling temperature in the coiling was 650 ° C, and the finished sheet thickness was 2.0 mm. Next, the hot rolled sheet was annealed at 900 ° C for 1 minute as hot rolled sheet annealing, scale was removed by pickling, and cold rolled to a thickness of 0.25 mm. Then, finish annealing was performed at 800 ° C for 30 seconds. After that, overaging treatment as shown in Table 1 was performed. In addition, some samples were bent by winding them around a φ400 mm roll and passing them through the roll at a bending angle of 10 degrees (the tangent direction of the roll cross-sectional circle is set to 0 degrees). That is, bending was performed by pressing the steel sheet against the roll. The bending was performed during or after the overaging treatment when the overaging treatment was performed, and after the finish annealing when the overaging treatment was not performed. It was confirmed that the steel sheet (reference number 127) manufactured under the same conditions as reference number 101, except that the overaging treatment was performed during the cooling of the finish annealing, had the same magnetic properties and AI as reference number 101.

[0055] Next, the magnetic properties of iron loss W10 / 400 (iron loss at maximum magnetic flux density 1.0T, frequency 400Hz) and magnetic flux density B50 (magnetic flux density at magnetizing force 5000A / m) were measured. 55mm square specimens were taken as measurement samples, and the average values ​​of the properties in the rolling direction and width direction were calculated. Magnetic measurements were performed using a device that can measure 55mm square test pieces and even smaller test pieces conforming to the electromagnetic circuit described in JIS C 2556 (2015). The measurement results are shown in Table 1. For the samples after magnetic measurement, aging treatment for magnetic measurement was performed at 200 ° C for 24 hours, and iron loss W10 / 400 was measured. The increase in iron loss was divided by the iron loss W10 / 400 before aging treatment to determine the iron loss deterioration rate after aging treatment, which is shown in Table 1. AI was also measured, and the results are shown in Table 1.

[0056] [Table 1]

[0057] Reference numbers 101 to 122 and 127 have good components and AI. Reference number 123 has high AI because it has not been subjected to either overaging or bending. Reference numbers 124 and 126 do not contain Cr and have high AI. Reference number 125 has high iron loss because Ti is outside the upper limit. In addition, the comparative examples with high AI also tend to have high iron loss degradation rates after aging.

[0058] To evaluate stretcher strain, the yield elongation (specified in JIS Z2241) in tensile test (8% strain) before aging in the AI ​​test was investigated. When yield elongation occurs, stretcher strain, which is a visible surface defect, occurs. In all cases where the AI ​​was less than 40 MPa, yield elongation did not occur, but in cases where the AI ​​was 40 MPa or more, yield elongation did occur. This shows that stretcher strain can be suppressed by lowering the AI ​​(to less than 40 MPa). Note that "---" in the "Yield elongation" column in the table indicates that yield elongation did not occur.< / cev>

Claims

1. The chemical composition is, in mass%, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%. , Cu: 0-5.000%, Ca: 0-0.020%, Mg: 0-0.0200%, rare earth elements (REM): 0-0.020%, Ti: less than 0.0100%, B: 0%-0.0050%, O: 0%-0.0200%, and the balance: Fe and impurities, wherein the difference in lower yield point before and after aging treatment at 100 ° C. for 1 hour after imparting 8% strain: A.I. is less than 40 MPa.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that the chemical composition further contains Mo: 0% to 0.0200%.

3. The non-oriented electrical steel sheet according to claim 1 or 2, characterized in that the following formula satisfies Cev≦0.0055%. Cev=12×([C(mass%)] / 12+[N(mass%)] / 14-[B(mass%)] / 11-[Ti(mass%)] / 48-[Cr(mass%)] / 104-[Mo(mass%)] / 192) In the above formula, [element symbol (mass%)] indicates the content (mass%) of the corresponding element in the chemical composition, and 0 is substituted if the corresponding element is not contained.

4. The chemical composition is, in mass %, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more types selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM): 0 to 0.0 4. A method for producing the non-oriented electrical steel sheet according to any one of claims 1 to 3, comprising the steps of steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing and overaging treatment, the method comprising the steps of: producing a non-oriented electrical steel sheet consisting of Cu 20%, Ti: less than 0.0100%, B: 0% to 0.0050%, O: 0% to 0.0200%, and the balance: Fe and impurities, the method being characterized in that the overaging temperature in the overaging treatment is 50°C to 300°C, and the temperature range of 50°C or higher is 10 seconds to 60 minutes.

5. The method for producing a non-oriented electrical steel sheet according to claim 4, wherein the chemical composition further contains Mo: 0% to 0.0200%.

6. 6. The method for producing a non-oriented electrical steel sheet according to claim 4 or 5, characterized in that, during the overaging treatment, in at least a part of the step of holding the temperature in a range of 50°C to 300°C, bending is performed by pressing the steel sheet against a roll having a diameter of less than 500 mm.

7. The method for producing a non-oriented electrical steel sheet according to any one of claims 4 to 6, characterized in that after the overaging treatment, bending is performed by pressing the steel sheet against a roll with a diameter of less than 500 mm.

8. The chemical composition is, in mass%, C: 0.0100% or less, Si: 2.6% to 4.5%, Mn: 0.10% to 3.00%, P: 0.15% or less, S: 0.0040% or less, N: 0.0040% or less, Al: 0.10% to 2.00%, one or more selected from Sn and Sb: 0 to 0.200%, Cr: 0.001 to 5.000%, Ni: 0 to 5.000%, Cu: 0 to 5.000%, Ca: 0 to 0.020%, Mg: 0 to 0.0200%, and rare earth elements (REM):

0.

4. A method for producing the non-oriented electrical steel sheet according to any one of claims 1 to 3, comprising the steps of steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, finish annealing and bending, characterized in that in the bending, the steel sheet is pressed against a roll having a diameter of less than 500 mm.

9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the chemical composition further contains Mo: 0% to 0.0200%.

10. A rotating electric machine comprising a stator, a rotor, and a housing for accommodating the stator and the rotor, wherein a core material of the stator or a core material of the rotor is the non-oriented electrical steel sheet according to any one of claims 1 to 3.

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