Non-oriented electrical steel sheet and its manufacturing method

Abstract

An object of the present invention is to provide a non-oriented electrical steel sheet in which the occurrence of rust during motor production is suppressed by adjusting the steel composition and the atmospheric conditions for annealing the cold-rolled sheet, and a method for producing the same. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.5-4.5% Si, 0.04-1.4% Mn, 0.2-1.1% Al, 0.0005-0.003% Bi, 0.0005-0.003% Zr, 0.0005-0.004% As, with the balance being Fe and unavoidable impurities, and is characterized in that the length from the surface of the steel sheet inward to the innermost part containing 5% O is 5 μm or less.

Description

[Technical field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more specifically, to a non-oriented electrical steel sheet and a manufacturing method thereof in which the occurrence of rust during motor manufacturing is suppressed by adjusting the steel composition and the atmospheric conditions for annealing the cold-rolled sheet. [Background technology]

[0002] Electrical steel sheets are used as materials for transformers, motors, and electrical equipment, and are functional products that emphasize electrical properties, unlike ordinary carbon steels, which emphasize workability such as mechanical properties. Required electrical properties include low iron loss, high magnetic flux density, magnetic permeability, and space factor. Electrical steel sheets are again divided into oriented and non-oriented. Grain-oriented electrical steel sheets have a Goss texture ({110} <001> Non-oriented electrical steel sheets have a uniform magnetic property in all directions on the surface of the rolled sheet. Duplex non-oriented electrical steel has uniform magnetic properties in all directions and is generally used as a material for motor cores, generator cores, electric motors, and small transformers. The representative magnetic properties of non-oriented electrical steel are core loss and magnetic flux density. The lower the core loss of non-oriented electrical steel, the less core loss that occurs during the magnetization of the core, improving efficiency. The higher the magnetic flux density, the larger the magnetic steel can be induced with the same energy, and less current can be applied to obtain the same magnetic flux density, reducing copper loss and improving energy efficiency. However, the improvement of properties of non-oriented electrical steel based on conventional metallurgical techniques has reached its limit, and the deterioration of core loss of non-oriented electrical steel that is not subjected to stress relief annealing after processing cannot satisfy the energy efficiency regulations that require strict core loss and the requirements of industries related to the production, transmission, conversion, and utilization of electrical energy. Accordingly, there is an increasing need for technology to improve magnetic properties.

[0003] Meanwhile, in the manufacture of motors, non-oriented electrical steel sheets are processed in various ways. One of the most commonly used methods is to process non-oriented electrical steel sheets into the desired shape and size by punching, blanking, or other methods alone or in combination, and then laminating them. In this case, if oxidation occurs on the surface of the raw material non-oriented electrical steel sheet or on the processed shear / fracture surface, causing rust, this can cause a defect in the motor manufacturing process called a "shortage." The highest quality non-oriented electrical steel sheets, which have low iron loss and high magnetic flux density, contain a high content of Si in their composition, which increases the probability of rust generation due to the base material. Recently, with the strengthening of energy efficiency regulations, there is a demand for the development of non-oriented electrical steel sheets with reduced rust generation in the manufacture of motors with higher efficiency. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention aims to provide a non-oriented electrical steel sheet and a manufacturing method thereof. The present invention aims to provide a non-oriented electrical steel sheet and a manufacturing method thereof in which the occurrence of rust during motor manufacturing is suppressed by adjusting the steel composition and the atmospheric conditions for annealing the cold-rolled sheet. [Means for solving the problem]

[0005] The non-oriented electrical steel sheet of the present invention is characterized in that it contains, by weight, 2.5 to 4.5% Si, 0.04 to 1.4% Mn, 0.2 to 1.1% Al, 0.0005 to 0.003% Bi, 0.0005 to 0.003% Zr, 0.0005 to 0.004% As, with the balance being Fe and unavoidable impurities, and the length from the surface of the steel sheet inward to the innermost part containing 5% O is 0.5 μm or less.

[0006] The non-oriented electrical steel sheet of the present invention further contains one or more of Sn: 0.001 to 0.08% by weight, Sb: 0.001 to 0.08% by weight, and P: 0.001 to 0.03% by weight.

[0007] The non-oriented electrical steel sheet of the present invention further contains one or more of Cr: 0.010 to 0.150 wt %, Cu: 0.01 to 0.20 wt %, S: 0.004 wt % or less, C: 0.004 wt % or less, N: 0.004 wt % or less, and Ti: 0.004 wt % or less.

[0008] When the non-oriented electrical steel sheet of the present invention is exposed to an environment with a humidity of 50% or more and a temperature of 15° C. or more for 48 hours, rust may not occur.

[0009] The non-oriented electrical steel sheet of the present invention has an iron loss W15 / 50 (W / kg) that is equal to or less than the value calculated by the following formula 1.

[0010] [Formula 1] 2.9-2×(0.5-t)-0.58×([Si]-2.5)-0.45×([Al]-0.2) (In formula 1, t represents the thickness (mm) of the electrical steel sheet, [Si] and [Al] represent the Si and Al contents (wt%) in the steel sheet, respectively.)

[0011] The non-oriented electrical steel sheet of the present invention has a magnetostriction deterioration degree (λ 0-p,p -λ 0-p,e ) / λ 0-p,e The value is less than or equal to 0.25. (The above λ 0-p,e is the magnetostriction caused by the electric discharge machining, and the λ 0-p,p is the magnetostriction caused by punching)

[0012] The method for producing a non-oriented electrical steel sheet of the present invention is characterized by including a step of producing a hot-rolled sheet by hot-rolling a slab containing, by weight, 2.5-4.5% Si, 0.04-1.4% Mn, 0.2-1.1% Al, 0.0005-0.003% Bi, 0.0005-0.003% Zr, 0.0005-0.004% As, with the balance being Fe and unavoidable impurities, a pickling step of pickling the hot-rolled sheet two to four times, a step of cold-rolling the pickled hot-rolled sheet to produce a cold-rolled sheet, and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0013] In the cold-rolled sheet annealing step, the annealing is performed at a temperature of 600°C or higher, in an atmosphere where the oxygen partial pressure is 10 mmHg or lower and the dew point is 10°C or lower.

[0014] After the step of producing the hot-rolled sheet, the method further includes a first hot-rolled sheet annealing step and a second hot-rolled sheet annealing step of annealing the hot-rolled sheet.

[0015] The first hot-rolled sheet annealing step is a step of maintaining the temperature at 980 to 1150° C. for 60 to 150 seconds, and the second hot-rolled sheet annealing step is a step of maintaining the temperature at 900 to 950° C. for 60 to 90 seconds.

[0016] In the cold-rolled sheet annealing step, the cracking temperature is 800 to 1070°C. Effect of the Invention

[0017] The non-oriented electrical steel sheet of the present invention suppresses rust generation during motor manufacturing and has excellent magnetic properties, thereby ultimately improving the efficiency of a motor in which the non-oriented electrical steel sheet is used.

[0018] The non-oriented electrical steel sheet of the present invention can provide a non-oriented electrical steel sheet in which the residual stress remaining after punching and shearing has a small effect on magnetostriction.

[0019] Moreover, according to the present invention, a non-oriented electrical steel sheet having excellent core loss properties can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Terms such as first, second and third are used to describe various parts, components, regions, layers and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Thus, a first part, component, region, layer or section described below can be referred to as a second part, component, region, layer or section without departing from the scope of the present invention. The terminology used herein is merely for the purpose of referring to specific embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the text clearly indicates otherwise. As used herein, the meaning of "comprises" is intended to embody certain properties, regions, integers, steps, operations, elements and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements and / or components. When an element is described as being "on" or "above" another element, it may be exactly on or above the other element, or it may have other elements therebetween. In contrast, when an element is referred to as being "directly on" another element, there are no other elements between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined.

[0021] Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0022] In an embodiment of the present invention, the term "additionally containing an additional element" refers to the additional amount of the additional element replacing the remaining iron (Fe).

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a schematic diagram of a method for manufacturing a semiconductor device according to the present invention;

[0024] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 2.5-4.5% Si, 0.04-1.4% Mn, 0.2-1.1% Al, 0.0005-0.003% Bi, 0.0005-0.003% Zr, 0.0005-0.004% As, and the remainder being Fe and unavoidable impurities.

[0025] First, the reasons for limiting the components of non-oriented electrical steel sheets will be explained.

[0026] Si:2.5~4.5wt% Silicon (Si) is a major element added to increase the non-resistance of steel and to reduce eddy current loss during iron loss. If too little Si is added, the iron loss deteriorates. Therefore, increasing the Si content is advantageous from the perspective of iron loss, but if too much Si is added, the brittleness of the material increases, sheet breakage occurs during coiling and cold rolling, and rolling productivity may drop sharply. Therefore, Si can be included within the above-mentioned range. More specifically, Si can be included in an amount of 2.5 to 3.7 wt%.

[0027] Mn:0.04~1.40wt% Manganese (Mn) plays a role in increasing the non-resistance of the material, improving core loss, and forming sulfides. If the amount of Mn added is too small, sulfides may precipitate finely, reducing magnetic properties. Conversely, if the amount of Mn added is too much, it may promote the formation of {111} texture, which is unfavorable to magnetic properties, reducing magnetic flux density. Therefore, Mn may be contained within the above-mentioned range. More specifically, Mn may be contained in an amount of 0.30 to 1.00 wt%.

[0028] Al: 0.2~1.1% by weight Aluminum (Al) plays an important role in increasing resistivity and reducing iron loss together with Si, and also improves rollability to improve workability during cold rolling. If the amount of Al added is too small, it is ineffective in reducing high-frequency iron loss, the precipitation temperature of AlN is lowered, and fine nitrates are formed, which may reduce magnetic properties. Conversely, if the amount of Al is too much, excessive nitrates are formed, which may deteriorate magnetic properties, cause problems in all processes such as steelmaking and continuous casting, and greatly reduce productivity. Therefore, Al can be contained within the above-mentioned range. More specifically, it can be contained in 0.5 to 0.8 wt %.

[0029] Bi:0.0005~0.0030wt% Bismuth (Bi) segregates to the grain boundaries as a segregation element, thereby reducing the grain boundary strength and suppressing the shape in which the potential is fixed to the grain boundaries. This has the effect of suppressing the increase in processing stress during shearing and punching, and reducing the processing stress depth at which magnetic properties become inferior due to the processing stress, but if the amount added is too large, it may suppress the grain growth and reduce the magnetic properties. Therefore, Bi can be added within the above-mentioned range. More specifically, Bi can be contained in an amount of 0.0010 to 0.0025 wt %.

[0030] Zr: 0.0005 to 0.0030% by weight and As: 0.0005 to 0.0040% by weight Since zirconium (Zr) or arsenic (As) can contribute to the formation of precipitates, suppress the formation of fine precipitates, and play a role in reducing the density of fine precipitates that cause residual stress due to processing, the Zr content can be 0.0005 to 0.0030 wt%, and the As content can be 0.0005 to 0.0040 wt%. More specifically, the Zr content can be 0.0010 to 0.0025 wt%, and the As content can be 0.0010 to 0.0030 wt%.

[0031] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain at least one of Sn: 0.001 to 0.08 wt %, Sb: 0.001 to 0.08 wt %, and P: 0.001 to 0.03 wt %.

[0032] Sn:0.001~0.080wt% Tin (Sn) segregates at the grain boundaries and surface to improve the texture of the material and inhibit surface oxidation, and can be added to improve magnetic properties. If the amount of Sn added is too small, the effect is insignificant. If the amount of Sn added is too large, grain boundary segregation becomes severe, surface quality deteriorates, hardness increases, and cold-rolled sheet breaks occur, which may reduce rollability. Therefore, Sn can be added within the above-mentioned range. More specifically, Sn can be further contained in an amount of 0.005 to 0.050 wt %.

[0033] Sb:0.001~0.080wt% Antimony (Sb) segregates at the grain boundaries and surface to improve the texture of the material and inhibit surface oxidation, and can be added to improve magnetic properties. If the amount of Sb added is too small, the effect is insignificant. If the amount of Sb added is too large, grain boundary segregation becomes severe, the surface quality deteriorates, and the hardness increases, which may cause the cold-rolled sheet to break and the rollability to deteriorate. Therefore, Sb can be added within the above-mentioned range. More specifically, Sb can be further contained in an amount of 0.005 to 0.050 wt %.

[0034] P:0.001~0.030wt% Phosphorus (P) not only plays a role in increasing the non-resistance of the material, but also plays a role in improving the texture by segregating at the grain boundaries, increasing the non-resistance, and reducing iron loss. If the amount of P added is too small, the amount of segregation may be too small and there may be no effect of improving the texture. If the amount of P added is too large, it may result in the formation of a texture unfavorable to magnetism, there may be no effect of improving the texture, and there may be excessive segregation at the grain boundaries, which may reduce rollability and workability, making production difficult. Therefore, P can be added within the above-mentioned range. More specifically, P can be contained in an amount of 0.005 to 0.015 wt %.

[0035] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of Cr: 0.010 to 0.150 wt%, Cu: 0.01 to 0.20 wt%, S: 0.004 wt% or less, C: 0.004 wt% or less, N: 0.004 wt% or less, and Ti: 0.004 wt% or less.

[0036] Cr:0.010~0.150wt% Chromium (Cr) segregates on the surface when the annealing conditions are appropriately adjusted. Segregation is performed appropriately by including Cr in the above-mentioned range. If the amount is less than the range, there is no surface segregation effect, and if the amount is too much, the brittleness of the material is enhanced, which may cause problems. More specifically, Cr can be included at 0.010 to 0.100 wt%.

[0037] Cu:0.01~0.20wt% Copper (Cu) plays a role in forming sulfides together with Mn. When Cu is further added, if the amount added is too small, CuMnS may precipitate finely, which may deteriorate the magnetic property. If the amount of Cu is too much, high-temperature brittleness may occur, which may cause cracks to form during continuous casting or hot rolling. More specifically, Cu may be further contained in an amount of 0.01 to 0.10 wt %.

[0038] S: 0.004% by weight or less Sulfur (S) forms fine sulfides inside the base material, inhibiting grain growth and weakening iron loss, so the lower the content, the better, and if the content exceeds 0.004 wt%, it can combine with Mn etc. to inhibit grain growth and increase the degree of deterioration of magnetic properties after processing. More specifically, S can be further contained at 0.0001 to 0.0030 wt%.

[0039] C: 0.004% by weight or less Carbon (C) suppresses the growth of ferrite crystal grains during annealing, increases the degree of deterioration of magnetic properties during processing, and can combine with Ti etc. to make magnetic properties inferior, so the content of C can be set to 0.004% by weight or less. More specifically, C can be contained in an amount of 0.0001 to 0.0030% by weight.

[0040] N: 0.004% by weight or less, Nitrogen (N) not only combines with Al, Ti, etc. to form fine, long precipitates inside the base material, but also combines with other impurities to form fine nitrates, which inhibit grain growth and worsen iron loss, so it can be further contained in an amount of 0.004 wt% or less. More specifically, N can be further contained in an amount of 0.0001 to 0.003 wt%.

[0041] Ti: 0.004% by weight or less Titanium (Ti) is an element that has a strong tendency to form precipitates in steel, and forms fine carbides or nitrates inside the base material to inhibit grain growth. The more Ti is added, the more carbides and nitrates are formed, which deteriorates iron loss and impairs magnetic properties, so it can be further contained in an amount of 0.004% or less. More specifically, Ti can be further contained in an amount of 0.0001 to 0.0030 wt%.

[0042] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less. These react with the inevitably contained C, S, N, etc. to form fine carbides, nitrates, or sulfides, which may adversely affect magnetic properties, so the upper limit can be limited as described above.

[0043] The balance is composed of Fe and unavoidable impurities. The unavoidable impurities are impurities that are mixed in during the steelmaking step and the manufacturing process of the non-oriented electrical steel sheet, and are widely known in the art, so a detailed description will be omitted. In addition of elements other than the alloy components described above in one embodiment of the present invention, various elements may be included within a range that does not impair the technical concept of the present invention. When an additional element is further included, it is included in place of the balance Fe.

[0044] In the non-oriented electrical steel sheet according to an embodiment of the present invention, the length from the surface of the steel sheet to the innermost part containing 5% O in the inward direction may be 0.5 μm or less. The surface of the steel sheet means the outermost surface of the steel sheet when no insulating coating is present, and means the boundary surface between the steel sheet substrate and the insulating coating when an insulating coating is present on the surface of the steel sheet substrate. The method for measuring the length to the innermost part containing 5% O is not particularly limited, and glow discharge spectroscopy (GDS) may be used. The length may vary depending on the measurement position of the steel sheet, and may be measured at five or more positions to reduce measurement errors, and the average value of the measurements may be used as the length. More specifically, the length from the surface of the steel sheet to the innermost part containing 5% O in the inward direction may be 0.05 to 0.5 μm.

[0045] When a large amount of O penetrates the surface of a steel sheet, additional oxygen penetrates through the O, causing rust during motor manufacturing. Meanwhile, in one embodiment of the present invention, rust does not occur during motor manufacturing. That is, when exposed to an environment with a humidity of 50% or more and a temperature of 15°C or more for 48 hours, rust does not occur. Rust is distinguished from general steel sheets with a silver-gray color in that it is mainly composed of Fe-based oxides and is red in color, and in one embodiment of the present invention, rust can be detected by exposing a steel sheet having an area of ​​305 mm x 30 mm or more to the above-mentioned environment and confirming the presence of rust of 1000 μm or more in size.

[0046] The non-oriented electrical steel sheet according to an embodiment of the present invention may have an iron loss W15 / 50 (W / kg) equal to or less than the value calculated by the following Equation 1.

[0047] [Formula 1] 2.9-2×(0.5-t)-0.58×([Si]-2.5)-0.45×([Al]-0.2) (In formula 1, t represents the thickness (mm) of the electrical steel sheet, [Si] and [Al] represent the Si and Al contents (wt%) in the steel sheet, respectively.)

[0048] It is generally known that the iron loss is smaller as the thickness of the steel sheet is smaller and the Si and Al contents are higher. In one embodiment of the present invention, the iron loss is further lower than the reflected value even when the thickness and Si and Al contents of the steel sheet are reflected. This can be obtained by adjusting the steel composition and annealing the cold-rolled sheet at a low oxygen partial pressure and a low dew point. The iron loss (W15 / 50) is the iron loss when a magnetic flux density of 1.5 T is induced at a frequency of 50 Hz. More specifically, it can be the average value of the iron loss measured in the rolling direction and the direction perpendicular to the rolling direction.

[0049] Non-oriented electrical steel sheets have a low degree of magnetostriction deterioration (λ 0-p,p -λ 0-p、e ) / λ 0-p,e The value may be less than or equal to 0.25. (The above λ 0-p,e is the magnetostriction caused by the electric discharge machining, and 0-p,p is the magnetostriction caused by punching)

[0050] Specifically, the magnetostrictive deterioration degree value may be 0.01 to 0.23, more specifically, 0.05 to 0.17.

[0051] Said λ 0-p,p The value is 7.0×10 -6 Specifically, it may be 3.0×10 -6 ~6.65×10 -6 , more specifically 3.26×10 -6 ~5.37×10 -6 may be also possible.

[0052] A method for producing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of hot rolling a slab containing, by weight, 2.5-4.5% Si, 0.04-1.4% Mn, 0.2-1.1% Al, 0.0005-0.003% Bi, 0.0005-0.003% Zr, 0.0005-0.004% As, with the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, cold rolling the hot-rolled sheet to produce a cold-rolled sheet, and annealing the cold-rolled sheet.

[0053] First, the slab is hot-rolled to produce a hot-rolled sheet. The reason for limiting the addition ratio of each component in the slab is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation will be omitted. Since the composition of the slab does not substantially change during the manufacturing processes such as hot rolling, cold rolling, and cold-rolled sheet annealing described below, the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same.

[0054] Before the step of producing the hot-rolled sheet, a slab heating step of heating the slab at a temperature range of 1100 to 1250°C for 0.1 to 3 hours may be further included. If the slab heating temperature is too high, precipitates such as AlN and MnS present in the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, which may inhibit grain growth and reduce magnetic properties. Specifically, a heating step at a temperature range of 1150 to 1200°C for 0.5 to 3 hours may be further included.

[0055] In the step of producing the hot-rolled sheet, the thickness of the hot-rolled sheet may be 1.6 to 3.0 mm. Specifically, the thickness of the hot-rolled sheet may be 1.8 to 2.5 mm.

[0056] In one embodiment of the present invention, after the step of producing a hot-rolled sheet, a first hot-rolled sheet annealing step and a second hot-rolled sheet annealing step of annealing the hot-rolled sheet may be further included.

[0057] The continuous annealing step may include a first hot-rolled sheet annealing step and a second hot-rolled sheet annealing step. The first hot-rolled sheet annealing step may be performed at 980 to 1150°C for 60 to 150 seconds. Specifically, the first hot-rolled sheet annealing step may be performed at 1030 to 1100°C for 60 to 100 seconds.

[0058] The secondary hot-rolled sheet annealing step can be carried out at 900 to 950° C. for 60 to 90 seconds.

[0059] Next, the hot rolled sheet is cold rolled to produce a cold rolled sheet. Depending on the thickness of the hot rolled sheet, a rolling reduction of 70-95% may be applied to cold roll the sheet to a final thickness of 0.2-0.7 mm. To match the rolling reduction, one cold rolling pass or two or more cold rolling passes with intermediate annealing may be performed. Cold rolling may be performed in 3-7 passes.

[0060] After the step of producing the cold-rolled sheet, the cold-rolled sheet is annealed. In the cold-rolled sheet annealing step, the annealing is performed in an atmosphere where the annealing temperature is 600°C or more, the oxygen partial pressure is 10 mmHg or less, and the dew point is 10°C or less. This can suppress O permeation of the finally produced electrical steel sheet, which plays a role in suppressing rust generation during motor manufacturing. Since oxygen permeation is fully performed at an annealing temperature of 600°C or more, the oxygen partial pressure and dew point temperature at 600°C or more are limited. More specifically, the oxygen partial pressure can be 1 to 9 mmHg, and the dew point can be -50 to 5°C.

[0061] The step of annealing the cold-rolled sheet may be performed at 800 to 1070°C, and the annealing time may be 10 seconds to 5 minutes. More specifically, it may be 900 to 1050°C.

[0062] Thereafter, a step of forming an insulating layer may be further included. A method of forming an insulating layer is widely known in the technical field of non-oriented electrical steel sheets, and therefore a detailed description thereof will be omitted.

[0063] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples.

[0064] Working Example A slab having the composition shown in Table 1 below was heated to approximately 1120°C. It was hot rolled to the thickness shown in Table 2 below. The hot rolled steel sheet cooled in air was subjected to a first hot rolled sheet annealing for 90 seconds at the temperature shown in Table 2 below, and a second stage hot rolled sheet annealing for 80 seconds at 930°C. The material after the hot rolled sheet annealing was pickled and then cold rolled to the thickness shown in Table 2. Then, cold rolled sheet annealing was performed at the crack temperature shown in Table 2 below.

[0065] The iron loss was measured by Epstein test, where the Epstein test pieces each had a size of 305 mm × 30 mm.

[0066] The length from the surface of the steel sheet to the innermost part containing 5% O in the inward direction was measured at five points on the test piece by GDS, and the innermost position where the oxygen content was 5% was measured.

[0067] The above test pieces were left in a thermo-hygrostat with a humidity of 50% or more and a temperature of 15° C. or more for 48 hours or more, and then observed with the naked eye to determine whether rust was present or not.

[0068] In addition, to measure magnetostriction, test specimens were processed by shearing and electric discharge machining, and magnetostriction was measured at 50 Hz and 1.5 T. The magnetostriction was calculated using the average value in the rolling direction (RD direction) and the direction perpendicular to the rolling direction (TD direction). The magnetostriction value was measured using a device that can apply a magnetic field of 50 Hz and 1.5 T and is defined as (change in length / original length of test specimen). The magnetostriction value of the test specimen processed by electric discharge machining was λ 0-p,e , the magnetostriction caused by shearing and punching is λ 0-p,p The deterioration degree of magnetostriction is (λ 0-p,p -λ 0-p,e ) / λ 0-p、e Defined in.

[0069] The clearance for shearing and punching was set at 5%, and specimens were taken during shearing and punching. The clearance is the value obtained by dividing the distance between the upper and lower dies of the shearing or punching machine by the thickness of the plate of the workpiece.

[0070] The EDMed Epstein specimens were fabricated by EDMing the sheared specimens to 310mmx35mm to 305mmx30mm.

[0071] [Table 1]

[0072] [Table 2]

[0073] [Table 3]

[0074] As shown in Tables 1 to 3, it was confirmed that the invention examples that satisfied the alloy composition and manufacturing process conditions did not generate rust, had excellent iron loss values, and showed little deterioration in magnetostriction.

[0075] On the other hand, it was confirmed that in Comparative Examples 1 to 13, the oxygen partial pressure or dew point temperature during annealing of the cold-rolled sheet was not appropriately adjusted, and rust was generated. It was confirmed that in Comparative Examples 14 to 18, Bi, Zr, and As were not appropriately contained, and iron loss was relatively deteriorated, and the residual stress after punching and shearing due to punching had a large effect on magnetostriction.

[0076] The present invention is not limited to the above-mentioned embodiment, and can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention belongs can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, the above-mentioned embodiment should be understood to be illustrative in all respects and not restrictive.

Claims

1. The composition contains, by weight, 2.5-4.5% Si, 0.04-1.4% Mn, 0.2-1.1% Al, 0.0005-0.003% Bi, 0.0005-0.003% Zr, 0.0005-0.004% As, and the balance being Fe and unavoidable impurities; A non-oriented electrical steel sheet, characterized in that the length from the surface of the steel sheet inward to the innermost part containing 5% O is 0.5 μm or less.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of Sn: 0.001 to 0.08 wt %, Sb: 0.001 to 0.08 wt %, and P: 0.001 to 0.03 wt %.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cr: 0.010 to 0.150 wt %, Cu: 0.01 to 0.20 wt %, S: 0.004 wt % or less, C: 0.004 wt % or less, N: 0.004 wt % or less, and Ti: 0.004 wt % or less.

4. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet does not rust when exposed to an environment having a humidity of 50% or more and a temperature of 15° C. or more for 48 hours.

5. The non-oriented electrical steel sheet according to claim 1, characterized in that the iron loss W15 / 50 (W / kg) is equal to or less than the value calculated by the following formula 1. [Formula 1] 2.9-2×(0.5-t)-0.58×([Si]-2.5)-0.45×([Al]-0.2) (In formula 1, t represents the thickness (mm) of the electrical steel sheet, [Si] and [Al] represent the contents (wt%) of Si and Al in the steel sheet, respectively.)

6. The non-oriented electrical steel sheet has a magnetostriction deterioration degree (λ ０－ｐ，ｐ -λ ０－ｐ，ｅ ) / λ ０－ｐ，ｅ 2. The non-oriented electrical steel sheet according to claim 1, wherein the value is 0.25 or less. (The above λ ０－ｐ，ｅ is the magnetostriction caused by the electric discharge machining, and the λ ０－ｐ，ｐ is magnetostriction caused by punching)

7. A step of producing a hot-rolled sheet by hot rolling a slab containing, by weight%, 2.5 to 4.5% Si, 0.04 to 1.4% Mn, 0.2 to 1.1% Al, 0.0005 to 0.003% Bi, 0.0005 to 0.003% Zr, 0.0005 to 0.004% As, with the balance being Fe and unavoidable impurities; cold rolling the hot rolled sheet to produce a cold rolled sheet; and A cold-rolled sheet annealing step of annealing the cold-rolled sheet; The method for producing a non-oriented electrical steel sheet, wherein the cold-rolled sheet annealing step is performed at an annealing temperature of 600° C. or higher, an oxygen partial pressure of 10 mmHg or lower, and an atmosphere with a dew point of 10° C. or lower.

8. The method for producing a non-oriented electrical steel sheet according to claim 7, further comprising a first hot-rolled sheet annealing step and a second hot-rolled sheet annealing step of annealing the hot-rolled sheet after the step of producing the hot-rolled sheet.

9. The first hot-rolled sheet annealing step is a step of maintaining the temperature at 980 to 1150 ° C. for 60 to 150 seconds, The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the second hot-rolled sheet annealing step is a step of maintaining the temperature at 900 to 950° C. for 60 to 90 seconds.

10. The method for producing a non-oriented electrical steel sheet according to claim 7, characterized in that the cold-rolled sheet annealing step has a cracking temperature of 800 to 1070°C.

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