แผ่นเหล็กกล้าทางไฟฟ้าชนิดไม่จัดเรียงตัว แกนมอเตอร์ และวิธีการผลิตของสิ่งเหล่านั้น

Abstract

ในการผลิตของแผ่นเหล็กกล้าสำหรับงานทางไฟฟ้าชนิดไม่จัดเรียงตัวโดยการรีดร้อนสแล็บเหล็กกล้าที่มีSi:2.8ถึง6.5%โดยมวลและZn:0.0005ถึง0.0050%โดยมวลที่ต่อตามมาโดยการรีดเย็นและการอบอ่อนขั้นสำเร็จสารการเคลือบที่มีอย่างน้อยที่สุดหนึ่งธาตุที่ได้รับการเลือกมาจากSn,Sb,P,S,Se,As,Te,B,PbและBiจะได้รับการใส่ลงที่พื้นผิวแผ่นเหล็กกล้าหลังการอบอ่อนขั้นสำเร็จเพื่อก่อรูปสารเคลือบที่เป็นฉนวนที่มีความสามารถการยับยั้งไนไทรดิงอย่างเป็นทางเลือกชั้นระหว่างกลางที่มีอย่างน้อยที่สุดหนึ่งธาตุที่ได้รับการเลือกมาจากSn,Sb,P,S,Se,As,Te,B,PbและBiและที่มีความสามารถการยับยั้งในไทรดิงจะได้รับการก่อรูปขึ้นบนเมทริกซ์เหล็กของแผ่นเหล็กกล้าหลังการอบอ่อนขั้นสำเร็จและก่อรูปสารเคลือบที่เป็นฉนวนที่ไม่มีธาตุข้างบนนี้จะได้รับการก่อรูปขึ้นบนชั้นระหว่างกลางซึ่งทำให้ได้มาซึ่งแผ่นเหล็กกล้าสำหรับงานทางไฟฟ้าชนิดไม่จัดเรียงตัวซึ่งแกนโรเตอร์ที่มีความแข็งแรงสูงและแกนสเตเตอร์ที่มีสมบัติทางแม่เหล็กที่ดีเยี่ยมหลังการอบอ่อนคลายความเค้นสามารถได้รับการทำให้ได้มาณเวลาเดียวกันและแกนมอเตอร์ที่ประกอบรวมด้วยแกนสเตเตอร์และแกนโรเตอร์จะได้รับการผลิตจากแผ่นเหล็กกล้านั้น;

Description

Non-oriented electrical steel sheet, motor core, and manufacturing method thereof

[0001] The present invention relates to a non-oriented electrical steel sheet suitable for use in the iron core of a small, high-power motor, a motor core, and a method for manufacturing the same.

[0002] In recent years, with the increasing demand for energy conservation in electrical equipment, non-oriented electrical steel sheets used in the iron cores (motor cores) of rotating machines are being required to have better magnetic properties than before. In particular, drive motors for hybrid electric vehicles (HEVs) need to be small and high-output, and therefore non-oriented electrical steel sheets used as the material for motor cores are being required to have better magnetic properties (high magnetic flux density and low iron loss).

[0003] Motor cores are divided into a fixed stator core and a rotating rotor core. To achieve smaller sizes and higher output, HEV drive motors tend to operate at higher rotation speeds. This means that the rotor cores of HEV drive motors, which have larger outer diameters, are subjected to large centrifugal forces. Furthermore, depending on the motor's structure, the rotor cores may contain very narrow sections (1 to 2 mm) called bridge sections. Therefore, there is a strong demand for non-oriented electrical steel sheets used in the rotor cores of HEV drive motors to have higher strength than conventional steel sheets.

[0004] Therefore, the properties required for non-oriented electrical steel sheets used in motor cores for HEV drive motors are not only excellent magnetic properties, but also high strength for rotor cores and higher magnetic flux density and lower iron loss for stator cores. Thus, even for the same motor core, the properties required for rotor cores and stator cores differ significantly. From the perspective of motor core manufacturing, it is desirable to simultaneously obtain rotor core material and stator core material from the same base steel sheet, particularly in order to increase material yield and reduce raw material inventory.

[0005] As described above, as a non-oriented electrical steel sheet having high strength and excellent magnetic properties, for example, Patent Document 1 discloses a method in which a rotor material and a stator material are simultaneously punched out from a non-oriented electrical steel sheet having a thickness of 0.15 to 0.35 mm and a yield strength of the steel sheet of 600 MPa or more before stress relief annealing, and then these are laminated to assemble a rotor core and a stator core, and further, stress relief annealing is performed only on the stator core, thereby reducing the iron loss W after stress relief annealing. １０／４００ A method for manufacturing a motor core with a strength of 20 W / kg or less has been proposed.

[0006] Japanese Patent Application Laid-Open No. 2008-50686

[0007] However, the technology of Patent Document 1 requires the addition of 0.5 mass% or more of expensive Ni to increase the strength of the steel sheet, which results in high manufacturing costs. Furthermore, when the steel sheet of Patent Document 1 is subjected to stress relief annealing, the magnetic properties of the steel sheet, particularly the iron loss properties, deteriorate, which leads to a serious problem of reduced motor efficiency.

[0008] The present invention has been made in view of the above-mentioned problems associated with the conventional technology, and its object is to provide a non-oriented electrical steel sheet that allows a high-strength rotor core and a stator core that has excellent magnetic properties after stress relief annealing to be manufactured from the same material, without using expensive Ni, and a motor core made from the above-mentioned steel sheet, and to propose a method for manufacturing the above-mentioned non-oriented electrical steel sheet and motor core at low cost.

[0009] In order to solve the above problems, particularly to prevent deterioration of magnetic properties after stress relief annealing, the inventors conducted extensive research focusing on the effect of surface properties on the magnetic properties of non-oriented electrical steel sheets. As a result, they discovered that the deterioration of magnetic properties due to stress relief annealing is caused by nitriding of the surface layer of the steel sheet during stress relief annealing, and that in order to suppress nitriding of the surface layer of the steel sheet, it is effective to include a predetermined amount of Zn in the steel material (slab) and to form a coating with appropriate nitriding suppression ability on the surface of the steel sheet before stress relief annealing, which led to the development of the present invention.

[0010] That is, the present invention provides a non-oriented electrical steel sheet having a component composition containing C: 0.0050 mass% or less, Si: 2.8 to 6.5 mass%, Mn: 0.1 to 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.3 to 2.0 mass%, N: 0.0050 mass% or less, Zn: 0.0005 to 0.0050 mass%, Ti: 0.0030 mass% or less, Nb: 0.0030 mass% or less, and O: 0.0050 mass% or less, with the balance being Fe and unavoidable impurities, and having on the surface of the steel sheet a coating layer containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi.

[0011] The non-oriented electrical steel sheet of the present invention is characterized in that, in addition to the above-mentioned chemical composition, it further contains at least one element selected from the following groups A to D. Group A: One or two elements selected from 0.005 to 0.20 mass% of Sn and 0.005 to 0.20 mass% of Sb; Group B: One or more elements selected from Ca, Mg, and REM in a total amount of 0.0005 to 0.020 mass%; Group C: One or more elements selected from Cu, Ni, Cr, and Co in a total amount of 0.01 to 1.0 mass%; Group D: One or two elements selected from 0.001 to 0.1 mass% of Mo and 0.001 to 0.1 mass% of W.

[0012] The coating layer in the non-oriented electrical steel sheet of the present invention is characterized in that it is an insulating coating formed on the surface of the steel sheet substrate.

[0013] The coating layer in the non-oriented electrical steel sheet of the present invention comprises an insulating coating formed on the uppermost layer of the steel sheet surface, and an intermediate layer formed between the insulating coating and the surface of the steel sheet substrate, and the intermediate layer contains at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi.

[0014] The present invention also provides a method for producing a non-oriented electrical steel sheet by hot rolling a steel slab, cold rolling the same, and finish annealing the same, wherein the steel slab contains C: 0.0050 mass% or less, Si: 2.8 to 6.5 mass%, Mn: 0.1 to 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.3 to 2.0 mass%, N: 0.0050 mass% or less, Zn: 0.0005 to 0.0050 mass%, and mass%, Ti: 0.0030 mass% or less, Nb: 0.0030 mass% or less, and O: 0.0050 mass% or less, with the balance being Fe and unavoidable impurities, and a coating layer containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is formed on the steel sheet surface after the above-mentioned finish annealing.

[0015] The steel slab used in the method for producing non-oriented electrical steel sheet is characterized in that it further contains, in addition to the above-mentioned chemical composition, at least one element selected from the following groups A to D: Group A: One or two elements selected from 0.005 to 0.20 mass% of Sn and 0.005 to 0.20 mass% of Sb; Group B: One or more elements selected from Ca, Mg, and REM in a total amount of 0.0005 to 0.020 mass%; Group C: One or more elements selected from Cr, Co, Ni, and Cu in a total amount of 0.01 to 1.0 mass%; Group D: One or two elements selected from 0.001 to 0.1 mass% of Mo and 0.001 to 0.1 mass% of W.

[0016] The method for producing a non-oriented electrical steel sheet is characterized in that a coating agent containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is applied as the coating layer to the base steel surface of the steel sheet after the finish annealing, to form an insulating coating having nitriding suppression ability.

[0017] The method for producing a non-oriented electrical steel sheet is characterized in that a treatment agent containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is applied to the surface of the steel sheet substrate after the finish annealing to form an intermediate layer having nitriding suppression ability, and an insulating coating not containing any of the above elements is formed on the intermediate layer.

[0018] The present invention also provides a motor core comprising a rotor core formed by laminating core materials processed into a core shape from any of the non-oriented electrical steel sheets described above, and a stator core formed by laminating core materials processed into a core shape from the same non-oriented electrical steel sheets as described above and then performing stress relief annealing, wherein the steel sheets constituting the stator core have an iron loss W １０／８００ (W / kg) is related to the plate thickness t (mm) by the following formula (1); W １０／８００ ≦15+80×t (1) and the amount of N present as AlN (Na as AlN) in a layer from one surface of the steel sheet to 1 / 20 of the sheet thickness after the stress relief annealing is 0.0100 mass% or less.

[0019] The present invention also proposes a method for manufacturing a motor core comprising a stator core and a rotor core, in which non-oriented electrical steel sheets manufactured by any of the methods described above are processed into a core shape, stacked, and assembled into a stator core and a rotor core, and then stress relief annealing is performed on the stator core, characterized in that the stress relief annealing is performed in an atmosphere consisting of one gas or a mixed gas of two or more gases selected from nitrogen, hydrogen, and a rare gas, under conditions of a soaking temperature of 800 to 950°C and a soaking time of 0.5 to 3.0 hours.

[0020] The method for manufacturing a motor core of the present invention is to reduce the iron loss W of the steel sheet after the stress relief annealing. １０／８００ (W / kg) is related to the plate thickness t (mm) by the following formula (1); W １０／８００ ≦15+80×t (1) and the N present as AlN (Na as AlN) in a layer from one surface of the steel sheet to 1 / 20 of the sheet thickness after the strain relief annealing is 0.0100 mass% or less.

[0021] According to the present invention, rotor cores, which require high strength, and stator cores, which require low iron loss after stress relief annealing, can be produced from the same steel sheet material. Therefore, the non-oriented electrical steel sheet of the present invention can greatly contribute to the miniaturization and high output of motors used in hybrid vehicles, electric vehicles, vacuum cleaners, high-speed generators, air compressors, machine tools, etc.

[0022] Iron loss W after stress relief annealing due to tapping charge １０／８００ 1 is a graph showing the variation in the N concentration in the 1 / 20 layer of the sheet thickness and the Zn content in the steel material and the iron loss W after stress relief annealing. １０／８００ 1 is a graph showing the relationship between the N concentration in the 1 / 20 layer after stress relief annealing and the iron loss W １０／８００ 10 is a graph showing the relationship between the plate thickness and the iron loss W １０／８００ FIG. 10 is an example diagram showing the relationship between

[0023]

[0023] The first embodiment of the present invention is characterized in that a coating made of a composite compound such as an oxide containing Zn and Al is formed on the surface of the steel sheet after finish annealing by adding an appropriate amount of Zn to a steel material (slab), and further, at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is added to the insulating coating formed on the surface of the steel sheet after finish annealing, thereby imparting nitriding suppression ability to both of the above coatings, thereby suppressing nitriding of the surface layer of the steel sheet during stress relief annealing.

[0024] First, the experiment that led to the development of the invention of the first embodiment will be described. Two charges (charges A and B) of steel having a composition containing C: 0.0025 mass%, Si: 3.5 mass%, Mn: 0.6 mass%, P: 0.01 mass%, S: 0.0015 mass%, Al: 0.9 mass%, N: 0.0023 mass%, Ti: 0.0011 mass%, Nb: 0.0009 mass%, and O: 0.0021 mass%, with the balance being Fe and inevitable impurities, were melted and produced into a steel material (slab) by a continuous casting method. The slab was then hot-rolled to a hot-rolled sheet having a thickness of 1.9 mm, annealed at 950°C for 30 seconds, pickled, and cold-rolled to a cold-rolled sheet having a final thickness of 0.30 mm.２ :N ２ After the steel sheet was subjected to finish annealing at 800°C for 10 seconds in an atmosphere of SiO2 = 20:80, an insulating coating was formed on the front and back surfaces of the steel sheet after the finish annealing to obtain a finished steel sheet. ２ P.O. ４ ) ２ A coating solution was prepared by mixing acrylic resin (manufactured by Taihei Chemical Industry Co., Ltd.) and acrylic resin (EFD-5560 manufactured by DIC) in a mass % solids ratio of 90:10, and adjusting the solids concentration to 10 mass % with deionized water. The coating was then baked to a coating weight of 0.5 g / m per side. ２ The coating was applied to both sides of the steel sheet using a roll coater so that the coating became as follows: and the sheet was baked in a hot air furnace under conditions such that the sheet reached a maximum temperature of 280°C in 30 seconds (with a soaking time of 0 seconds).

[0025] Next, test pieces of 280 mm in length and 30 mm in width were cut out from the product plate coated with the insulating coating in the rolling direction (L direction) and in the direction perpendicular to the rolling direction (C direction). ２ After heat treatment simulating stress relief annealing at 850°C for 1 hour in an atmosphere of 100vol%, the high frequency iron loss W in the (L+C) direction was measured in an Epstein test. １０／８００ As a result, the measured iron loss values ​​varied, and as shown in Figure 1(a), the iron loss characteristics of a specific charge (charge B) after stress relief annealing were superior. To investigate the cause of this, the concentration of N (Na as AlN) present as AlN in the steel sheet surface layer, specifically in the layer extending from one surface of the steel sheet to 1 / 20 of the sheet thickness (hereinafter, the "layer extending from one surface of the steel sheet to 1 / 20 of the sheet thickness" will also be simply referred to as the "1 / 20 sheet thickness layer") was confirmed. As shown in Figure 1(b), in the steel sheet produced by charge A, which has high iron loss, nitriding occurred in the steel sheet surface layer, whereas in the steel sheet produced by charge B, which has low iron loss, the N concentration in the steel sheet surface layer was not significantly different from the value at tapping, indicating that nitriding was suppressed. Therefore, further investigation of trace elements in the steel material revealed that the steel material produced by charge B contained approximately 0.0020 mass% Zn.

[0026] <Experiment 2> Therefore, the following experiment was conducted to investigate the effect of Zn content on the nitriding behavior on the steel sheet surface during stress relief annealing and the iron loss characteristics after stress relief annealing. A steel sheet containing C: 0.0027 mass%, Si: 3.6 mass%, Mn: 0.8 mass%, P: 0.01 mass%, S: 0.0018 mass%, Al: 1.1 mass%, N: 0.0021 mass%, Ti: 0.0012 mass%, Nb: 0.0008 mass%, and O: 0.0022 mass% was used. Steel having a composition containing various amounts of Cu in the range of 0.001 to 0.01 mass%, with the balance being Fe and unavoidable impurities, was melted in a vacuum melting furnace, cast into a steel ingot, hot rolled into a hot rolled sheet having a thickness of 2.0 mm, annealed at 940°C for 30 seconds, pickled, and cold rolled into a cold rolled sheet having a final thickness of 0.25 mm. ２ :N ２ After finish annealing at 780°C for 10 seconds in an atmosphere of SiO2 = 20:80, an insulating coating was formed on the front and back surfaces of the steel sheets under the same conditions as in Experiment 1 above to obtain finished steel sheets.

[0027] Next, test pieces of 280 mm in length and 30 mm in width were cut out from the product plate coated with the insulating coating in the rolling direction (L direction) and in the direction perpendicular to the rolling direction (C direction). ２ After heat treatment simulating stress relief annealing at 830°C for 1 hour in an atmosphere of 100vol%, the high frequency iron loss in the (L+C) direction was measured in an Epstein test. １０／８００ The results are shown in Figure 2. From this figure, it can be seen that the iron loss after stress relief annealing is reduced when the Zn content is within a predetermined range, and in particular, when the Zn content is in the range of 0.0005 to 0.005 mass%, the iron loss is reduced as expressed by the following formula (2): W １０／８００ It was found that the iron loss was lower than the iron loss reference value defined by the following equation: = 15 + 80 × t (2).

[0028] Here, the "reference iron loss value" defined by the above formula (2) is the iron loss W that is considered necessary to reduce heat generation in the stator core and prevent a decrease in motor efficiency. １０／８００The iron loss value is highly dependent on the sheet thickness, and even for steel sheets with the same characteristics, the thicker the sheet, the greater the eddy current loss, as shown in Figure 4. Therefore, in the present invention, the iron loss reference value is set as shown in the above formula (2) in relation to the sheet thickness. Incidentally, Figure 4 shows the relationship between sheet thickness and iron loss in an example of the present invention described in the Examples section below.

[0029] Next, in order to investigate the cause of the decrease in iron loss due to the addition of Zn, the thickness cross section of the steel sheet after stress relief annealing was observed with a SEM (scanning electron microscope). As a result, in the steel sheets whose iron loss exceeded the above-mentioned iron loss reference value, a large number of finely precipitated AlN were found in the surface layer of the steel sheet, specifically in the layer from one surface of the steel sheet to 1 / 20 of the sheet thickness, and it was presumed that the iron loss increased due to these finely precipitated nitrides.

[0030] Therefore, after removing the insulating coating from the steel sheet after the stress relief annealing, the concentration of N (N as AlN) present as AlN in the 1 / 20 layer of the sheet thickness was analyzed by electrolytic extraction, and the N concentration and the iron loss W １０／８００ The relationship between these is shown in Figure 3. From this figure, it was found that in steel sheets to which Zn was added within the appropriate range, the N concentration present as AlN in the 1 / 20 sheet thickness layer after strain relief annealing was 100 mass ppm (0.0100 mass%) or less. The reason why nitriding during strain relief annealing is suppressed by adding Zn to the steel sheet is thought to be because a coating made of a complex compound such as an oxide containing Zn or Al was formed on the steel sheet surface during strain relief annealing. Therefore, in the present invention, it was made an essential requirement that the N concentration in the 1 / 20 sheet thickness layer of the steel sheet after strain relief annealing be 0.0100 mass% or less.

[0031] Next, the inventors investigated methods other than adding Zn to the steel material as a method for suppressing nitriding of the surface layer of a steel sheet during stress relief annealing, and found that adding at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi to an insulating coating formed on the surface of a steel sheet before stress relief annealing can impart nitriding suppression properties to the insulating coating. In other words, by including any of these elements in the insulating coating and mixing compounds containing these elements in the insulating coating, the density and adhesion of the insulating coating can be improved, resulting in a significant improvement in the nitriding suppression properties of the insulating coating.

[0032] While stress relief annealing, particularly stress relief annealing performed at a high soaking temperature of 800°C or higher, is expected to have the effect of improving iron loss by eliminating processing strain and coarsening crystal grains, it also has the problem of nitriding occurring in the surface layer of the steel sheet, resulting in deterioration of magnetic properties. However, by adding an appropriate amount of Zn to the steel material (slab) and adding an element with a nitriding suppression effect to the insulating coating, it is possible to more effectively suppress nitriding during stress relief annealing. In other words, it has been found that the effects of adding Zn to the steel material and adding an element with a nitriding suppression effect to the insulating coating described above in suppressing nitriding during stress relief annealing are not sufficient when used alone, and that the nitriding suppression effect can be greatly enhanced by using both methods together.

[0033] [Embodiment 2] As described above, the first embodiment of the present invention is characterized in that the steel material contains an appropriate amount of Zn and the insulating coating contains an element that has a nitriding-suppressing effect, i.e., the insulating coating is imparted with nitriding-suppressing ability, thereby suppressing nitriding of the surface layer of the steel sheet during stress relief annealing at high temperatures. However, the second embodiment of the present invention is characterized in that, instead of the insulating coating of the first embodiment, an intermediate layer containing an element that has a nitriding-suppressing effect is formed between the insulating coating and the surface of the steel sheet substrate (and therefore the insulating coating does not contain an element that has a nitriding-suppressing effect), thereby suppressing nitriding of the surface layer of the steel sheet during stress relief annealing at high temperatures.

[0034] The inventors immersed the steel sheet after finish annealing produced in the above-mentioned <Experiment 1> in a treatment bath of zinc phosphate (PB-L47 manufactured by Nippon Parkerizing) for 30 seconds, rinsed with water, and dried with hot air to form an intermediate layer on the front and back surfaces of the steel sheet. An insulating coating was then applied on the intermediate layer to produce a finished steel sheet. The coating weight of the intermediate layer was set to 30 nm on one side. The insulating coating was prepared by mixing silica sol (ST-C manufactured by Nissan Chemical Industries, Ltd.) and acrylic resin (EFD-5560 manufactured by DIC Corporation) at a solids ratio of 90:10 by mass, and adjusting the solids concentration to 10 mass% with deionized water. The coating weight was 0.5 g / m on one side. ２ The coating was applied to both sides of the steel sheet using a roll coater so that the coating became as follows: and the sheet was baked in a hot air furnace under conditions such that the sheet reached a maximum temperature of 280°C in 30 seconds (heating time: 0 seconds).

[0035] Next, test pieces of 280 mm in length and 30 mm in width were cut out from the product plate coated with the insulating coating in the rolling direction (L) and in the direction perpendicular to the rolling direction (C). ２ After heat treatment simulating stress relief annealing at 830°C for 1 hour in an atmosphere of 100vol%, the high frequency iron loss in the (L+C) direction was measured in an Epstein test. １０／８００ As a result, similar to Fig. 2 obtained in <Experiment 2>, it was confirmed that when the Zn content in the steel material was in the range of 0.0005 to 0.005 mass%, the iron loss decreased and was below the aforementioned iron loss standard value.

[0036] Next, after removing the insulating coating from the surface of the steel sheet after the stress relief annealing, the concentration of N (N as AlN) present as AlN in the layer 1 / 20 of the sheet thickness was analyzed by electrolytic extraction. As a result, the iron loss W １０／８００ It was found that the steel sheets in which the N as AlN content was equal to or less than the reference value all had N as AlN levels of 100 ppm by mass (0.0100% by mass), as in Figure 4. These results show that the same nitriding suppression effect can be obtained by forming an intermediate layer between the surface of the steel sheet substrate and the insulating coating, the intermediate layer containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi that has a nitriding suppression effect.

[0037] In the second embodiment, the intermediate layer has the ability to suppress nitriding, so the insulating coating can be provided with functions other than the nitriding suppression function, such as an insulating effect. To improve the adhesion and scratch resistance of the insulating coating, it is necessary to strengthen the bond of the insulating coating itself. However, if the insulating coating contains many elements, as in the first embodiment, the bond tends to be weak. However, in the second embodiment, it is not necessary to impart the insulating coating with the new function of suppressing nitriding, and the elements contained in the insulating coating can be limited, so the bond of the coating itself can be maintained strong.

[0038] In the second embodiment, the coating layer on the surface of the steel sheet has a multi-layer structure consisting of an intermediate layer and an insulating coating between the surface of the steel sheet substrate and the insulating coating, which has the secondary effects of improving corrosion resistance and moisture resistance. Furthermore, the intermediate layer is expected to have an insulating effect in addition to suppressing nitriding, so the total thickness of the intermediate layer and the insulating coating can be made thinner than the thickness of the insulating coating alone in the first embodiment, which also has the effect of increasing the space factor (core magnetic flux).

[0039] Next, the chemical composition of the steel material (slab) used to manufacture the non-oriented electrical steel sheet of the present invention will be described. Note that there is no difference in the chemical composition of the steel material used between the first embodiment and the second embodiment of the present invention.

[0040] C: 0.0050 mass% or less C contained in the product sheet is a harmful element that forms carbides, causes magnetic aging, and deteriorates iron loss characteristics. Therefore, the upper limit of C contained in the material is limited to 0.0050 mass%, preferably 0.0040 mass% or less. Note that there is no particular lower limit for C, but from the viewpoint of reducing decarburization costs in the refining process, it is preferable to set it to about 0.0001 mass%.

[0041] Si: 2.8 to 6.5 mass% Si has the effect of increasing the resistivity of steel and reducing iron loss, and also has the effect of increasing the strength of steel by solid solution strengthening, so it is contained in an amount of 2.8 mass% or more. On the other hand, if it exceeds 6.5 mass%, the steel becomes embrittled and rolling becomes difficult, so the upper limit is set to 6.5 mass%. The range is preferably 3.0 to 6.0 mass%.

[0042] Mn: 0.1 to 2.0 mass% Like Si, Mn is a useful element for increasing the resistivity and strength of steel, and also fixes S to improve hot brittleness, so it is contained in an amount of 0.1 mass% or more. On the other hand, addition of more than 2.0 mass% causes slab cracking and deteriorates the operability of the steelmaking process, so the upper limit is set to 2.0 mass%. A preferable range is 0.2 to 1.5 mass%. In particular, when Mn is contained in an amount of 0.2 mass% or more, MnS is preferentially formed and the formation of ZnS is suppressed, thereby promoting the formation of a coating made of a complex compound containing Zn oxide and the like.

[0043] P: 0.10 mass% or less P is an element that increases the resistivity of steel and has a significant effect of reducing eddy current loss. It also has a high solid solution strengthening ability, so it can be added appropriately. However, excessive addition of P embrittles the steel and deteriorates its cold rolling properties, so the upper limit is set to 0.10 mass%. It is preferably 0.05 mass% or less.

[0044] S: 0.0050 mass% or less S becomes sulfide and forms precipitates and inclusions, which reduces manufacturability (hot rolling ability) and the magnetic properties of the finished sheet, so the lower the content, the better. Therefore, the upper limit of S is 0.0050 mass%, preferably 0.0030 mass% or less.

[0045] Al: 0.3 to 2.0 mass% Like Si, Al has the effect of increasing the resistivity of steel and reducing iron loss. However, if the Al content exceeds 2.0 mass%, the steel becomes embrittled and difficult to roll, so the upper limit is set to 2.0 mass%. On the other hand, if the Al content is less than 0.3 mass%, fine nitrides are formed and precipitated, which actually worsens the iron loss characteristics, so the lower limit is set to 0.3 mass%. The preferred range is 0.4 to 1.5 mass%.

[0046] N: 0.0050 mass% or less N is an element that forms nitrides and precipitates, deteriorating the magnetic properties, so its content is limited to 0.0050 mass% or less, preferably 0.0040 mass% or less.

[0047] Ti: 0.0030 mass% or less, Nb: 0.0030 mass% or less Ti and Nb are elements that form fine precipitates and precipitate, increasing iron loss. If either of them exceeds 0.0030 mass%, the above-mentioned adverse effects become significant, so the upper limit of each is set to 0.0030 mass%. Preferably, each is 0.0020 mass% or less.

[0048] O: 0.0050 mass% or less O is an element that forms oxides and exists as inclusions in steel, deteriorating magnetic properties, so its content is limited to 0.0050 mass% or less, preferably 0.0040 mass% or less.

[0049] Zn: 0.0005 to 0.0050 mass% Zn is one of the most important elements in the present invention and has the effect of suppressing nitriding during stress relief annealing, so it is contained in an amount of 0.0005 mass% or more. On the other hand, if added in excess of 0.0050 mass%, sulfides are formed, increasing iron loss, so the content is limited to 0.0050 mass% or less. The preferred range is 0.001 to 0.004 mass%.

[0050] The steel material used in the present invention contains the remainder, other than the above-mentioned components, of Fe and unavoidable impurities. In addition to the above-mentioned components, the steel material may further contain at least one of the following groups A to D: Group A: One or two selected from Sn: 0.005 to 0.20 mass% and Sb: 0.005 to 0.20 mass%. Sn and Sb have the effect of improving the recrystallization texture and improving the magnetic flux density and core loss characteristics. To achieve this effect, it is preferable to contain 0.005 mass% or more of these elements. However, even if added in amounts exceeding 0.20 mass%, the effect saturates. Therefore, when Sn and Sb are added, it is preferable to add them in the range of 0.005 to 0.20 mass% each. More preferably, each is in the range of 0.01 to 0.1 mass%.

[0051] Group B: 0.0005 to 0.020 mass% of one or more elements selected from Ca, Mg, and REM. Ca, Mg, and REM form stable sulfides and have the effect of improving grain growth during stress relief annealing. To achieve this effect, it is preferable to add the above elements in a total amount of 0.0005 mass% or more. On the other hand, even if the amount exceeds 0.020 mass%, the above effect saturates. Therefore, when adding the above elements, it is preferable to add them in a total amount of 0.0005 to 0.020 mass%. More preferably, it is in the range of 0.001 to 0.008 mass%.

[0052] C group: 0.01 to 1.0 mass% total of one or more elements selected from Cu, Ni, Cr, and Co. Cu, Ni, Cr, and Co have the effect of increasing the resistivity of steel, reducing iron loss, and increasing the strength of steel. To achieve this effect, it is preferable to add Cu, Ni, Cr, and Co in a total amount of 0.01 mass% or more. However, adding more than 1 mass% increases raw material costs. Therefore, when adding the above elements, it is preferable to add them in a total amount of 0.01 to 1.0 mass%. More preferably, it is in the range of 0.1 to 0.5 mass%.

[0053] Group D: One or two elements selected from Mo: 0.001 to 0.1 mass% and W: 0.001 to 0.1 mass%. Mo and W are both elements effective in suppressing surface defects (scavenging). Because the steel sheet of the present invention is a high-alloy steel, its surface is easily oxidized, raising concerns about the occurrence of scavenging due to surface cracking. However, adding trace amounts of Mo and W, elements that enhance high-temperature strength, can suppress cracking. The above effect is insufficient when the Mo and W contents are below 0.001 mass%, respectively. On the other hand, adding more than 0.1 mass% saturates the effect and simply increases raw material costs. Therefore, when adding Mo and W, it is preferable to keep them within the above ranges. A more preferred content is 0.0050 to 0.050 mass%, respectively.

[0054] Next, a method for manufacturing the non-oriented electrical steel sheet of the present invention will be described. The non-oriented electrical steel sheet of the present invention can be manufactured by a manufacturing process consisting of a series of steps: producing a steel material (slab) having the above-mentioned chemical composition, hot-rolling the slab to form a hot-rolled sheet, optionally subjecting the slab to hot-rolled sheet annealing, cold-rolling the slab to a cold-rolled sheet of the final thickness (product thickness), finish-annealing the slab, and then applying an insulating coating. Note that the step that differs between the first embodiment and the second embodiment of the present invention is the step of applying an insulating coating to the steel sheet after the above-mentioned finish-annealing. This will be specifically described below.

[0055] First, the steel material (slab) used to manufacture the non-oriented electrical steel sheet of the present invention can be produced by melting steel having the above-described chemical composition suitable for the present invention through a commonly known refining process using a converter, electric furnace, vacuum degasser, etc., and then by a conventional continuous casting method or an ingot making-blooming rolling method. Note that thin cast pieces having a thickness of 100 mm or less may also be produced by a direct casting method.

[0056] The slab is then hot-rolled by a known method to produce a hot-rolled sheet. The slab is usually reheated to a predetermined temperature in a heating furnace before hot-rolling, but it may also be hot-rolled immediately after casting without reheating. Furthermore, in the case of a thin cast slab, hot rolling may be performed, or the hot rolling may be omitted and the slab may proceed directly to the subsequent steps.

[0057] The hot-rolled sheet annealing following hot rolling is preferably performed at a soaking temperature in the range of 800 to 1100°C. If the annealing temperature is less than 800°C, the effect of hot-rolled sheet annealing is small and sufficient improvement in magnetic properties cannot be obtained. On the other hand, if the annealing temperature exceeds 1100°C, the crystal grains become coarse, which promotes brittle fracture (sheet breakage) during cold rolling and is disadvantageous in terms of manufacturing costs. In addition, from the viewpoint of ensuring productivity, the soaking time is preferably 3 minutes or less. More preferably, the soaking temperature is 850 to 1000°C and the soaking time is 1 minute or less.

[0058] Next, the steel sheet that has been subjected to the hot rolling or hot-rolled sheet annealing after the hot rolling is cold-rolled to a final thickness by one cold rolling or two or more cold rollings with intermediate annealing in between. The finished thickness (final thickness) of the cold rolling is not particularly limited, but is preferably in the range of 0.10 to 0.35 mm. This is because if it is less than 0.10 mm, productivity decreases, while if it exceeds 0.35 mm, iron loss increases as shown in Figure 4.

[0059] The cold-rolled sheet having reached the final thickness is then subjected to finish annealing. This condition is preferably continuous annealing, in which the sheet is soaked at a temperature of 700 to 900°C for 1 to 300 seconds. If the soaking temperature is less than 700°C, recrystallization does not proceed sufficiently, resulting in poor magnetic properties. Furthermore, the shape correction effect of continuous annealing is not fully achieved. On the other hand, if the temperature exceeds 900°C, the crystal grain size becomes coarse and the strength decreases. From the viewpoint of ensuring the strength required for the rotor core after finish annealing, it is desirable to set the finish annealing conditions to a temperature as low as possible and a short time as long as possible within the range in which shape correction is possible.

[0060] The steel sheet subjected to the above-mentioned finish annealing is finally coated with a coating agent that will become an insulating coating on at least the surface of the steel sheet piece, and then heated and baked to form an insulating coating, resulting in a finished steel sheet. The type of insulating coating is not particularly limited, but it is preferable that the solid content of the insulating coating is made of an inorganic material or that the solid content is made of an organic resin and an inorganic material. The inclusion of an inorganic material can ensure weldability and heat resistance, and the inclusion of an organic resin can improve press formability, so it is preferable to select an appropriate type depending on the application. Note that when an organic resin is included in the insulating coating, the proportion of the organic resin in the solid content after baking is preferably 70 mass% or less. This is because a proportion of the organic resin exceeding 70 mass% can cause a deterioration in heat resistance.

[0061] The type of organic resin is not particularly limited, and conventionally used known resins can be used, such as acrylic resins, alkyd resins, styrene resins, polyolefin resins, epoxy resins, phenolic resins, urethane resins, polyester resins, melamine resins, etc. The type of inorganic material is also not particularly limited, and one or more may be selected from oxides, hydroxides, carbonates, carbides, etc. of Si, Al, Ti, Zr, Cr, etc.

[0062] Other components that may be contained in the insulating coating include, for example, rust inhibitors, surfactants, lubricants, antifoaming agents, antioxidants, and the like, which are added to improve the properties and uniformity of the insulating coating. Known color pigments, extender pigments, and functional pigments may also be included. These components may be contained within a range that does not impair the performance of the insulating coating, specifically, within 5 mass% or less of the solid content after baking.

[0063] Various methods can be used to apply the insulating coating, such as roll coating, flow coating, knife coating, spraying, etc. The coating weight to be applied is determined taking into consideration that sufficient insulation properties can be obtained and that a sufficient nitriding suppression effect can be obtained. Specifically, the coating weight after baking is 0.1 g / m per side. ２ It is preferable to apply the coating amount to 0.2 g / m or more. ２ However, as the coating weight increases, the cost of the coating material increases and the space factor decreases when the core is made, so the upper limit is set to 10 g / m per side. ２ More preferably, it is 5 g / m ２ More preferably, 2 g / m or less ２ The following is the result.

[0064] The baking method after the coating agent is applied is not particularly limited, and commonly used baking methods such as hot air, infrared heating, and induction heating can be applied. The baking temperature may also be within a commonly used temperature range, and for example, a maximum temperature of about 80 to 350°C is preferred for the steel sheet. The heating time from the start to the end of heating is preferably in the range of 0.1 to 60 seconds, and more preferably in the range of 1 to 30 seconds.

[0065] Here, the most important aspect of the present invention is to form a coating layer (nitriding-suppressing layer) having nitriding suppression ability on the surface of the steel sheet after the above-mentioned finish annealing. The method of forming this coating layer differs between the first embodiment, in which nitriding suppression ability is imparted to an insulating coating formed on the surface of the steel sheet substrate, and the second embodiment, in which an intermediate layer having nitriding suppression ability is formed between the steel sheet substrate surface and the insulating coating. The methods are described in detail below.

[0066] [First embodiment] In a first embodiment of the present invention, an insulating coating is formed on the surface of a steel sheet substrate after finish annealing, and is used as a coating layer having nitriding suppression ability. The insulating coating contains at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi to impart the nitriding suppression function. By including these elements in the insulating coating, the density and adhesion of the insulating coating are improved, and the insulating coating can be imparted with a nitriding suppression effect.

[0067] The method for incorporating at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi into the insulating coating is not particularly limited. Examples of suitable inorganic compounds include dissolving or dispersing the element in the coating material for the insulating coating. Those that are soluble in the coating material are dissolved, while those that are difficult to dissolve are mixed and dispersed. Any form of inorganic compound can be used, including oxides, carbides, hydroxides, carbonates, chromates, and phosphates. The amount of these elements is preferably 0.001 mass% or more in total in terms of elemental ratio in the baked coating film. However, excessive addition can cause deterioration in corrosion resistance and coating adhesion, so the upper limit is preferably about 10 mass%.

[0068] [Second Embodiment] The second embodiment of the present invention is an embodiment in which an insulating coating is formed on the surface of a steel sheet after finish annealing, and an intermediate layer having nitriding suppression properties is formed between the insulating coating and the surface of the steel sheet substrate. The intermediate layer contains at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi. By including these elements in the intermediate layer, not only can the intermediate layer have a nitriding suppression effect, but it can also be expected to have insulating and rust-preventing effects. Furthermore, the combined thickness of the intermediate layer and the insulating coating can be made thinner than the insulating coating of the first embodiment, thereby improving the space factor (core magnetic flux).

[0069] Furthermore, to improve the scratch resistance of the insulating coating during core manufacturing, it is necessary to strengthen the bond of the insulating coating itself, and if the insulating coating contains a large number of elements, this bond tends to weaken. However, in the second embodiment, there is no need to impart the nitriding suppression function to the insulating coating, and the elements contained in the insulating coating can be limited to a minimum, so that strong bonding can be maintained and excellent scratch resistance can be obtained.

[0070] The method for forming the intermediate layer containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is not particularly limited. Examples include a method in which a treatment solution containing the above elements is applied to the steel sheet surface by immersion or spraying, or is applied to the steel sheet surface by roll coating or the like, followed by drying. The conditions for forming the intermediate layer (temperature and time) are not particularly limited. Considering productivity, however, it is preferable to select a method that allows the treatment to be performed at room temperature for 10 seconds to 10 minutes. Other methods, such as plating or a dry process using a CVD or PVD method, may also be used. The number of intermediate layers formed may be two or more.

[0071] Next, the motor core of the present invention and its manufacturing method will be described. Motor cores are typically composed of a rotor core, which requires high strength, and a stator core, which requires low iron loss and high magnetic flux density. The former rotor core is used as a motor core in its current state after finish annealing, in which steel sheets coated with an insulating film are formed into a core shape by punching or other processing, laminated, and fixed. The latter stator core is typically used as a motor core after finish annealing, in which steel sheets coated with an insulating film are formed into a core shape by punching or other processing, laminated, and fixed. Furthermore, it is further subjected to stress relief annealing to improve magnetic properties.

[0072] The above-mentioned stress relief annealing is carried out in an atmosphere of Ar gas or N ２ It is preferable to perform the stress relief annealing in an inert gas atmosphere such as gas under the conditions of 800 to 950°C x 0.5 to 3 hours. If the stress relief annealing temperature is less than 800°C and the time is less than 0.5 hours, the grain growth effect of the stress relief annealing is small and the iron loss improvement effect cannot be obtained sufficiently. １０ / ８００ However, there is a risk that the iron loss standard value defined by the above-mentioned formula (2) will not be satisfied. On the other hand, if the stress relief annealing temperature exceeds 950°C and the time exceeds 3 hours, it becomes difficult to ensure insulation between the laminated steel sheets. More preferable stress relief annealing conditions are in the range of 800 to 875°C x 1 to 2 hours.

[0073] The steel sheet after the above-mentioned stress relief annealing has an appropriate amount of Zn added to the steel material and further has a coating layer on the steel sheet surface that has the ability to suppress nitriding, so that nitriding during stress relief annealing is suppressed, and therefore the concentration of N (Na as AlN) present as AlN in the layer from one side surface to 1 / 20 of the sheet thickness layer (1 / 20 sheet thickness layer) of the steel sheet after stress relief annealing can be made 100 mass ppm or less (0.0100 mass% or less). As a result, the steel sheet of the present invention can suppress an increase in iron loss due to AlN precipitated in the 1 / 20 sheet thickness layer, so that even after stress relief annealing, the following formula (2): W １０／８００ = 15 + 80 × t (2) It is possible to clear the iron loss standard value defined by the following.

[0074] Slabs having various elemental compositions shown in Table 1, with the balance being Fe and unavoidable impurities, were heated at a temperature of 1120°C for 30 minutes, and then hot-rolled to a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled sheet was annealed at 930°C for 30 seconds, pickled, descaled, and then cold-rolled to a cold-rolled sheet having the final thickness shown in Table 2. Next, H was added to the cold-rolled sheet in a vol% ratio. ２ :N ２ After finish annealing at 820°C for 10 seconds in an atmosphere of SiO2 = 20:80, a coating agent for an insulating coating, which was a combination of the components A to G shown in Table 3 in the composition shown in Table 2, was applied to both sides of the steel sheet using a roll coater so that the coating weight per side was the value shown in Table 2, and the steel sheet was baked in a hot air drying furnace under the conditions shown in Table 2 to obtain a finished sheet.

[0075] Test pieces of 280 mm in length and 30 mm in width were taken from the product plate thus obtained coated with the insulating coating in the rolling direction (L direction) and in the direction perpendicular to the rolling direction (C direction). ２ After stress relief annealing was performed under the conditions shown in Table 2 in an atmosphere of 0.5% by volume, the iron loss W １０／８００ The steel sheets after stress relief annealing were analyzed by electrolytic extraction for the concentration of N (Na as AlN) present as AlN in the 1 / 20 layer of the sheet thickness. Two test pieces, each 100 mm wide and 200 mm long, with the length direction in the rolling direction (L direction), were taken from the product sheets coated with the insulating coating under each condition. The two test pieces were stacked together and subjected to a pressure of 1 kg / cm. ２After sliding for 10 seconds at a relative speed of 2 cm / s with the applied pressure, the test piece surface was visually inspected for the presence or absence of scratches, and the scratch resistance was evaluated according to the following criteria. <Evaluation criteria for scratch resistance> ⊚: Almost no scratches were observed (pass) ◯: Some scratches were observed (pass) ×: Scratches were clearly observed (fail) Furthermore, two test pieces, each 100 mm wide and 200 mm long, with the rolling direction (L direction) as the length direction were taken from the product plates coated with the insulating coating described above, for each condition. Cellophane adhesive tape was applied to the test surface, and the steel plate was bent 180° using a 5 mm diameter round rod with the test surface as the compression side. The cellophane adhesive tape was then peeled off, the peeled area of ​​the coating was calculated, and the coating adhesion was evaluated according to the following criteria. <Coating adhesion judgment criteria> ◎: Film peeling area <5% (pass) ○: 5%≦film peeling area <10% (pass) ×: film peeling area ≧10% (fail)

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] The above results are also shown in Table 2, and it can be seen that all of the steel sheets manufactured under conditions suitable for the present invention have excellent core loss characteristics, scratch resistance, and coating adhesion.

[0084] Slabs having various elemental compositions shown in Table 4, with the balance being Fe and unavoidable impurities, were heated at a temperature of 1120°C for 30 minutes, and then hot-rolled to a thickness of 2.0 mm. These were then annealed at 930°C for 30 seconds, pickled, descaled, and cold-rolled to a final thickness shown in Table 5. Next, H was added to the cold-rolled sheet in a vol% ratio. ２ :N ２After finish annealing at 820°C for 10 seconds in an atmosphere of SiO2 = 20:80, treatment agent A or B shown in Table 6 was applied and dried to form an intermediate layer having a film thickness of 5 to 100 nm after drying. Subsequently, a coating agent for an insulating coating, which was a combination of components C to G shown in Table 6 in the composition shown in Table 5, was applied to both surfaces of the steel sheet using a roll coater so that the coating weight on one side was the value shown in Table 5, and the steel sheet was baked in a hot air drying furnace under the conditions shown in Table 5 to obtain a finished sheet.

[0085] Test pieces measuring 280 mm in length and 30 mm in width were taken from the product plate having the intermediate layer and the insulating coating thus obtained in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction). ２ After stress relief annealing was performed under the conditions shown in Table 5 in an atmosphere of 0.5% by volume, the iron loss W １０／８００ The steel sheets after stress relief annealing were analyzed by electrolytic extraction for the concentration of N (Na as AlN) present as AlN in the 1 / 20 layer of the sheet thickness. Two test pieces, each 100 mm wide and 200 mm long, with the rolling direction (L direction) as the length direction, were taken from the product sheets having the intermediate layer and the insulating coating under each condition. The two test pieces were stacked together in the same manner as in Example 1, and subjected to a pressure of 1 kg / cm. ２ After sliding for 10 seconds at a relative speed of 2 cm / s with the applied pressure, the test piece surface was visually inspected for the presence or absence of scratches, and the scratch resistance was evaluated according to the following criteria. <Evaluation criteria for scratch resistance> ⊚: Almost no scratches were observed (pass) ◯: Some scratches were observed (pass) ×: Scratches were clearly observed (fail) Furthermore, two test pieces, each 100 mm wide and 200 mm long, with the rolling direction (L direction) as the length direction were taken from the product plates coated with the insulating coating described above, for each condition. Cellophane adhesive tape was applied to the test surface, and the steel plate was bent 180° using a 5 mm diameter round rod with the test surface as the compression side. The cellophane adhesive tape was then peeled off, the peeled area of ​​the coating was calculated, and the coating adhesion was evaluated according to the following criteria. <Coating adhesion judgment criteria> ◎: Film peeling area <5% (pass) ○: 5%≦film peeling area <10% (pass) ×: film peeling area ≧10% (fail)

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] The above results are also shown in Table 5. All of the steel sheets manufactured under conditions consistent with the present invention exhibit excellent iron loss characteristics. Furthermore, a comparison with Table 2 reveals that the provision of an intermediate layer with a nitriding-suppressing effect between the insulating coating and the surface of the steel sheet substrate further improves scratch resistance and coating adhesion.

[0094] The technology of the present invention has the effect of improving the strength of the insulating coating, and therefore can be applied not only to the field of non-oriented electrical steel sheets but also to grain-oriented electrical steel sheets.