Non-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a non-oriented electrical steel sheet in which the iron loss in the direction perpendicular to the rolling direction is lower than the iron loss in the rolling direction at high frequencies, and a method for manufacturing the same. [Means for Solving the Problem] The present invention provides a steel sheet containing, by weight, 1.5 to 6.5% Si, 0.0005 to 3.5% Al, 0.01 to 3.0% Mn, 0.005 to 5.0% Cr, and 0.0005 to 0.03% S, with the balance being Fe and other unavoidable impurities, the Goss orientation fraction in the region from the surface to 1 / 10t (t: steel sheet thickness) in the thickness direction is 3 area % or less, and the Goss orientation fraction in the entire region in the thickness direction is 5 area % or less, The non-oriented electrical steel sheet may further contain one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%, and the non-oriented electrical steel sheet may further contain one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%), and Ti: 0.01% or less (excluding 0%).

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet in which the iron loss in the direction perpendicular to the rolling direction is lower than the iron loss in the rolling direction at high frequencies, and a manufacturing method thereof. [Background technology]

[0002] Electric vehicles and other forms of transportation are being used to replace internal combustion engines in order to reduce greenhouse gas emissions. Currently, more than 50% of all electrical energy generated is consumed by electric motors for power generation. Therefore, efficient use of electricity is crucial for the future replacement of internal combustion engines with electric motors. In particular, electric motors are becoming increasingly compact and lightweight, along with their improved performance. Motors that generate axial magnetic flux are gaining attention. These motors eliminate spatial constraints and improve performance in a variety of electric mechanisms, including existing electric vehicles, electric motorcycles, electric aircraft, and electric ships. Therefore, high efficiency is essential. Furthermore, technological advances and market changes are driving continued interest in improving the functionality and efficiency of high-efficiency motors for home appliances, robots, and industrial motors, leading to ever-increasing demand for more efficient use of electrical energy.

[0003] Meanwhile, optimizing all aspects of electric motor efficiency, from material selection to design, assembly, and control, is crucial. In terms of materials, the magnetic properties of electrical steel sheets are particularly important, with high demands for low iron loss and high magnetic flux density. For automobile drive motors and air conditioner compressor motors, which must operate not only in the commercial frequency range but also in the high-frequency range, low iron loss at high frequencies is crucial. Furthermore, for small, high-power motors with narrow yokes, high magnetic flux is generated not only in the motor's teeth but also in the yoke to generate high torque during motor operation. Therefore, improving iron loss at high frequencies and high magnetic flux is crucial to improving motor efficiency.

[0004] Typically, electrical steel sheets are manufactured by adding large amounts of resistive elements such as Si, Al, and Mn to reduce the grain size and eddy current loss. As the frequency increases, eddy currents pass only through the surface layer of the steel sheet, so high-frequency iron loss can be improved by increasing the resistivity of the elements in the surface layer. However, while this conventional manufacturing method is effective in controlling iron loss at magnetic fluxes around 1.0 T, no method is known for reducing iron loss at higher magnetic fluxes. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a non-oriented electrical steel sheet in which the iron loss in the direction perpendicular to the rolling direction is lower than the iron loss in the rolling direction at high frequencies, and a method for manufacturing the same. [Means for solving the problem]

[0006] The non-oriented electrical steel sheet of the present invention contains, by weight, 1.5 to 6.5% Si, 0.0005 to 3.5% Al, 0.01 to 3.0% Mn, 0.005 to 5.0% Cr, and 0.0005 to 0.03% S, with the remainder being Fe and other unavoidable impurities, and is characterized in that the Goss orientation fraction in the region from the surface to 1 / 10t (t: thickness of the steel sheet) in the thickness direction is 3 area % or less, and the Goss orientation fraction in the entire region in the thickness direction is 5 area % or less.

[0007] The non-oriented electrical steel sheet may further contain at least one of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

[0008] The non-oriented electrical steel sheet may further contain one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%), and Ti: 0.01% or less (excluding 0%).

[0009] The non-oriented electrical steel sheet may further contain one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%), and Mg: 0.0050% or less (excluding 0%).

[0010] The non-oriented electrical steel sheet may further contain one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2%, and Zn: 0.01% or less (excluding 0%).

[0011] The non-oriented electrical steel sheet may further contain one or more of Bi, Pb, Ge and As in an amount of 0.20% or less (excluding 0%), either individually or in total.

[0012] The non-oriented electrical steel sheet may have an iron loss (W10 / 600C) of 28 W / kg or less, an iron loss (W10 / 800C) of 43 W / kg or less, and an iron loss (W10 / 1200C) of 75 W / kg or less.

[0013] The non-oriented electrical steel sheet may have an iron loss (W10 / 600L) of 30 W / kg or less, an iron loss (W10 / 800L) of 48 W / kg or less, and an iron loss (W10 / 1200L) of 85 W / kg or less.

[0014] The non-oriented electrical steel sheet may have an iron loss (W15 / 600C) of 65 W / kg or less, an iron loss (W15 / 800C) of 95 W / kg or less, and an iron loss (W15 / 1200C) of 175 W / kg or less.

[0015] The non-oriented electrical steel sheet may have an iron loss (W15 / 600L) of 75 W / kg or less, an iron loss (W15 / 800L) of 105 W / kg or less, and an iron loss (W15 / 1200L) of 190 W / kg or less.

[0016] The non-oriented electrical steel sheet can satisfy the following relational expression 1.

[0017] [Equation 1] Iron loss (W10 / 600C) + Iron loss (W10 / 800C) + Iron loss (W10 / 1200C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L)

[0018] The present invention provides a method for manufacturing a steel sheet, the method comprising the steps of: heating a slab containing, by weight, 1.5 to 6.5% Si, 0.0005 to 3.5% Al, 0.01 to 3.0% Mn, 0.005 to 5.0% Cr, 0.0005 to 0.03% S, with the balance being Fe and other inevitable impurities, at 1050 to 1220°C; finish hot rolling the slab to obtain a hot-rolled sheet; hot-rolling the hot-rolled sheet at 850 to 1150°C for 30 to 300 seconds; and The present invention provides a method for producing a non-oriented electrical steel sheet, comprising the steps of cold-rolling to obtain a cold-rolled sheet, heating the cold-rolled sheet, and final-annealing the heated cold-rolled sheet, wherein the cold-rolling satisfies the following [Relational Formula 2], the heating is performed at a heating rate of 5 to 150°C / s in a temperature range of 300 to 500°C, and the final annealing is performed in a gas atmosphere consisting of, by volume, 15 to 99.99% hydrogen, 0.0001 to 0.0030% oxygen, and the balance being an inert gas.

[0019] [Equation 2] Maximum temperature on the surface of cold-rolled sheet during cold rolling <200 × cold rolling reduction / 100 + 60

[0020] The slab may further contain one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

[0021] The slab may further contain one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%), and Ti: 0.01% or less (excluding 0%).

[0022] The slab may further contain one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%), and Mg: 0.0050% or less (excluding 0%).

[0023] The slab may further contain one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2%, and Zn: 0.01% or less (excluding 0%).

[0024] The slab may further contain one or more of Bi, Pb, Ge and As in an amount of 0.20% or less (excluding 0%), either individually or in total.

[0025] The finish hot rolling can be performed at 700 to 1050°C.

[0026] The cold rolling may be performed at a cold reduction rate of 35 to 98%.

[0027] During the cold rolling, the maximum rolling speed in one or more of the first and second passes may be 3 m / s or more.

[0028] The final annealing may be performed at 600 to 1150° C. for 10 to 500 seconds. [Effects of the Invention]

[0029] According to the present invention, it is possible to provide a non-oriented electrical steel sheet in which the iron loss in the direction perpendicular to the rolling direction is lower than the iron loss in the rolling direction at high frequencies, and a method for manufacturing the same. DETAILED DESCRIPTION OF THE INVENTION

[0030] The non-oriented electrical steel sheet of the present invention will be described below. First, the alloy composition will be described. The contents of the alloy compositions described below are in weight percent unless otherwise specified.

[0031] Si: 1.5 to 6.5% Si plays a role in increasing the resistivity of the material and reducing iron loss. If the Si content is less than 1.5%, the effect of improving high-frequency iron loss is insufficient. If the Si content exceeds 6.5%, hardness increases, and productivity and punchability deteriorate. Therefore, the Si content is preferably in the range of 1.5 to 6.5%. The lower limit of the Si content is more preferably 1.8%, and even more preferably 2.0%. The upper limit of the Si content is more preferably 6.0%, even more preferably 5.0%, and most preferably 4.0%.

[0032] Al: 0.0005 to 3.5% Al increases the resistivity of the material and reduces iron loss. If the Al content is less than 0.0005%, the amount of Al required to remove oxygen during steel production is reduced, resulting in the formation of many inclusions in the steel, which may result in an ineffective reduction of high-frequency iron loss and the formation of fine nitrides on the surface, potentially reducing magnetic properties. If the Al content exceeds 3.5%, problems may arise in all processes, including steelmaking and continuous casting, significantly reducing productivity. Therefore, the Al content is preferably in the range of 0.0005 to 3.5%. The lower limit of the Al content is more preferably 0.15%. The upper limit of the Al content is more preferably 3.0%, even more preferably 2.5%, and most preferably 2.0%.

[0033] Mn: 0.01 to 3.0% Mn increases the resistivity of the material, improving iron loss, and plays a role in forming sulfides, stabilizing austenite. If the Mn content is less than 0.01%, fine sulfides, such as MnS, may precipitate in the steel, reducing magnetic properties. If the Mn content exceeds 3.0%, the annealing temperature range for obtaining an appropriate grain size for low high-frequency iron loss is limited. Furthermore, Mn may reduce the saturation magnetic flux of the material, particularly promoting the formation of a {111} texture that is unfavorable to ferromagnetism, resulting in a decrease in magnetic flux density. Therefore, the Mn content is preferably in the range of 0.01 to 3.0%. The lower limit of the Mn content is more preferably 0.2%. The upper limit of the Mn content is more preferably 2.5%, even more preferably 2.0%, and most preferably 1.5%.

[0034] Cr: 0.005 to 5.0% Cr increases the resistivity of the material and reduces iron loss. By appropriately controlling the cold rolling and final annealing conditions, Cr can concentrate on the surface to form a Cr-enriched layer. If the Cr content is less than 0.005%, the effect of Cr in increasing the resistivity is minimal, and Cr may combine with C and other elements to form carbides that are detrimental to magnetic properties. If the Cr content exceeds 5%, Cr is distributed uniformly throughout the entire thickness rather than on the surface, resulting in a decrease in magnetic flux density throughout the steel sheet. Therefore, the Cr content is preferably in the range of 0.005 to 5.0%. From the viewpoint of surface enrichment, the lower limit of the Cr content is more preferably 0.04%. From the viewpoint of preventing a decrease in magnetic flux density, the upper limit of the Cr content is more preferably 3.0%, even more preferably 1.0%, and most preferably 0.3%.

[0035] S: 0.0005 to 0.03% S is a strong segregating element and forms precipitates. When a titrated amount is added, it segregates to the surface and reacts with oxygen in the air during annealing, thereby suppressing the growth of Goss crystal grains on the surface. If the S content is less than 0.0005%, the surface segregation effect becomes insufficient. If the S content exceeds 0.03%, an FeS-enriched layer forms on the surface, significantly deteriorating the surface quality. Therefore, the S content is preferably in the range of 0.0005 to 0.03%. The lower limit of the S content is more preferably 0.001%. The upper limit of the S content is more preferably 0.015%, even more preferably 0.005%, and most preferably 0.0035%.

[0036] The remaining component is iron (Fe). However, in a normal manufacturing process, unintentional impurities may be inevitably mixed in from the raw materials or the surrounding environment, and this cannot be excluded. These impurities are known to anyone skilled in the normal manufacturing process, so this specification does not specifically mention all of them.

[0037] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

[0038] P: 0.005 to 0.08% P concentrates on the surface and plays a role in controlling the fraction of the internal oxide layer. If the P content is less than 0.005%, it may be difficult to form a uniform internal oxide layer. If the P content is more than 0.08%, the melting point of the Si-based oxide may fluctuate, which may lead to the rapid formation of the internal oxide layer. Therefore, the P content is preferably in the range of 0.005 to 0.08%. The upper limit of the P content is more preferably 0.07%.

[0039] Sn: 0.01 to 0.2% Sn segregates on the surface and grain boundaries of the steel sheet, suppressing surface oxidation during annealing and improving texture. If the Sn content is less than 0.01%, it may be difficult to fully achieve the above-mentioned effects. If the Sn content exceeds 0.2%, Sn segregates on the grain boundaries, reducing toughness and decreasing productivity relative to magnetic improvement. Therefore, the Sn content is preferably in the range of 0.01 to 0.2%. The lower limit of the Sn content is more preferably 0.02%. The upper limit of the Sn content is more preferably 0.15%, even more preferably 0.1%, and most preferably 0.07%.

[0040] The non-oriented electrical steel sheet of the present invention may further contain one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%), and Ti: 0.01% or less (excluding 0%).

[0041] C: 0.005% or less (excluding 0%) C reacts with N, Ti, Nb, V, etc. to form fine carbides, which play a role in hindering grain growth and magnetic domain movement, so the upper limit is limited to 0.005%.

[0042] N: 0.005% or less (excluding 0%) N combines with Ti, Nb, V, etc. to form nitrides, which act to reduce grain growth, so the upper limit is set to 0.005%.

[0043] O: 0.005% or less (excluding 0%) O reacts with Fe, Ti, Al, Mn, Cr, Si, V, etc. to form fine oxides, which play a role in hindering grain growth and magnetic domain movement, so the upper limit is limited to 0.005%.

[0044] Ti: 0.01% or less (excluding 0%) Ti combines with C, N, O, etc. to form fine nitrides or oxides, which plays a role in preventing magnetic domain movement, so the upper limit is limited to 0.01%.

[0045] The non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%), and Mg: 0.0050% or less (excluding 0%).

[0046] Mo: 0.1% or less (excluding 0%) Mo reacts with C, O, N, etc. to form fine carbides or nitrides, which adversely affect the magnetic properties, so the upper limit is set to 0.1%.

[0047] B: 0.0050% or less (excluding 0%) B reacts with C, O, N, etc. to form fine carbides or nitrides, which adversely affect magnetic properties, so the upper limit is set to 0.0050%.

[0048] V: 0.050% or less (excluding 0%) V reacts with C, O, N, etc. to form fine carbides or nitrides, which adversely affect magnetic properties, so the upper limit is set to 0.050%.

[0049] Ca: 0.010% or less (excluding 0%) Ca reacts with C, O, N, etc. to form fine carbides or nitrides, which have a negative effect on magnetic properties, so the upper limit is set to 0.010%.

[0050] Nb: 0.0050% or less (excluding 0%) Nb reacts with C, O, N, etc. to form fine carbides or nitrides, which adversely affect magnetic properties, so the upper limit is set to 0.0050%.

[0051] Mg: 0.0050% or less (excluding 0%) Mg reacts with C, O, N, etc. to form fine carbides or nitrides, which adversely affect magnetic properties, so the upper limit is set to 0.0050%.

[0052] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2%, and Zn: 0.01% or less (excluding 0%).

[0053] Sb: 0.1% or less (excluding 0%) Sb is an element that segregates at grain boundaries, suppressing the diffusion of nitrogen through the grain boundaries, suppressing the {111} texture that is detrimental to magnetic properties, and increasing the advantageous {100} texture, thereby improving magnetic properties. If the Sb content exceeds 0.1%, it will impede grain growth, reducing magnetic properties and deteriorating rolling properties. More specifically, the Sb content may be 0.001 to 0.1%. Even more specifically, the Sb content may be 0.005 to 0.08%.

[0054] Ni: 0.05% or less (excluding 0%) Ni reacts with impurity elements to form fine sulfides, carbides, and nitrides, which have a detrimental effect on magnetic properties, so its upper limit is limited to 0.05%. More specifically, the Ni content may be 0.0001 to 0.050%. Even more specifically, the Ni content may be 0.001 to 0.030%.

[0055] Cu: 0.005 to 0.2% Cu plays a role in forming sulfides together with Mn. If the Cu content is less than 0.005%, fine (Cu Mn)S precipitates, which may deteriorate the magnetic properties. If the Cu content exceeds 0.2%, high-temperature embrittlement may occur, which may cause cracks during continuous casting or hot rolling. More specifically, the Cu content may be 0.010 to 0.1%.

[0056] Zn: 0.01% or less (excluding 0%) Zn acts as an impurity and may deteriorate magnetic properties, so its upper limit is set to 0.01%. More specifically, the Zn content may be 0.0001 to 0.01%. Even more specifically, the Zn content may be 0.001 to 0.008%.

[0057] The non-oriented electrical steel sheet of the present invention may further contain one or more of Bi, Pb, Ge and As in an amount of 0.20% or less (excluding 0%), either individually or in total.

[0058] When the above-mentioned elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling, and in the subsequent recrystallization annealing process, <111> / / Improves magnetic flux density by suppressing recrystallization of ND-oriented crystal grains. When these elements are added appropriately, the above-mentioned effects can be further achieved. However, excessive addition can cause significant segregation, suppressing grain growth and potentially deteriorating magnetic flux density and core loss. More specifically, the alloy may contain one or more of Bi, Pb, Ge, and As, each in an amount of 0.0001 to 0.20%. Even more specifically, the alloy may contain one or more of Bi, Pb, Ge, and As, each in an amount of 0.001 to 0.10%.

[0059] In the non-oriented electrical steel sheet of the present invention, the Goss orientation fraction in the region from the surface to 1 / 10t (t: steel sheet thickness) in the thickness direction is preferably 3 area % or less, and the Goss orientation fraction in the entire region in the thickness direction is preferably 5 area % or less. The Goss orientation fraction can be the area fraction of crystal grains having an orientation within 10° from the Goss orientation. While the Goss orientation has excellent magnetic properties in the rolling direction, it has a significant adverse effect on magnetic properties in the direction perpendicular to the rolling direction. Therefore, to improve magnetic properties in the direction perpendicular to the rolling direction, it is very important to reduce the fraction of crystal grains having the Goss orientation. In particular, the surface layer has a greater effect on overall iron loss as the frequency increases. If the Goss orientation fraction in the region from the surface to 1 / 10t (t: steel sheet thickness) in the thickness direction exceeds 3 area %, it will have a significant adverse effect on magnetic properties in the direction perpendicular to the rolling direction. If the Goss orientation fraction in the entire region in the thickness direction exceeds 5 area %, it may have a negative effect on magnetic properties in the direction perpendicular to the rolling direction. While the Goss orientation provides excellent magnetic properties in the rolling direction, it has a significant adverse effect on magnetic properties in the direction perpendicular to the rolling direction. Therefore, reducing the fraction of Goss-oriented grains is crucial to improving magnetic properties in the direction perpendicular to the rolling direction. In particular, reducing the Goss orientation fraction in the surface layer is crucial because it has a significant effect on overall iron loss as the frequency increases. The Goss orientation fraction is measured by measuring the cross section of the steel sheet using conventional EBSD. To ensure statistical significance, the number of grains with a minimum grain size of over 5 μm and grain boundaries with a misorientation angle of 3° or more from surrounding grains must be at least 5,000 within the measurement area. For grains measured in a cut-out form within the measurement area, the fraction is calculated including the cut-out area.

[0060] The non-oriented electrical steel sheet of the present invention provided as described above may have an iron loss (W10 / 600C) of 28 W / kg or less, an iron loss (W10 / 800C) of 43 W / kg or less, and an iron loss (W10 / 1200C) of 75 W / kg or less. The iron loss (W10 / 600L) may be 30 W / kg or less, an iron loss (W10 / 800L) of 43 W / kg or less, and an iron loss (W10 / 1200L) of 85 W / kg or less. Furthermore, the iron loss (W15 / 600C) may be 65 W / kg or less, an iron loss (W15 / 800C) of 95 W / kg or less, and an iron loss (W15 / 1200C) of 175 W / kg or less. The iron loss (W15 / 600L) may be 75 W / kg or less, the iron loss (W15 / 800L) may be 105 W / kg or less, and the iron loss (W15 / 1200L) may be 190 W / kg or less. If these conditions are not met, the iron loss at high magnetic flux density will be poor, making it difficult to achieve the object of the present invention, which is to utilize the material to increase motor output and efficiency. Since the lower the iron loss value, the more advantageous it is, the present invention does not particularly limit the lower limit of the iron loss. However, the lower limits of the iron loss (W10 / 600C), iron loss (W10 / 800C), and iron loss (W10 / 1200C) may be 6 W / kg, 8 W / kg, and 15 W / kg, respectively. The lower limits of the iron loss (W10 / 600L), iron loss (W10 / 800L), and iron loss (W10 / 1200L) may be 6.5 W / Kg, 9 W / Kg, and 17 W / Kg, respectively. The lower limits of the iron loss (W15 / 600C), iron loss (W15 / 800C), and iron loss (W15 / 1200C) may be 12 W / Kg, 12 W / Kg, and 25 W / Kg, respectively. The lower limits of the iron loss (W15 / 600L), iron loss (W15 / 800L), and iron loss (W15 / 1200L) may be 13 W / Kg, 13 W / Kg, and 27 W / Kg, respectively. Meanwhile, the above W10 / 600, W10 / 800, and W10 / 1200 refer to iron losses measured by the Epstein method at 600 Hz, 800 Hz, and 1200 Hz, respectively, with a maximum magnetic flux of 1.0 T. The above W15 / 600, W15 / 800, and W15 / 1200 refer to iron losses measured by the Epstein method at 600 Hz, 800 Hz, and 1200 Hz, respectively, with a maximum magnetic flux of 1.5 T. L refers to the rolling direction, and C refers to the direction perpendicular to the rolling direction.

[0061] The non-oriented electrical steel sheet of the present invention preferably satisfies the following relational expression 1.

[0062] [Equation 1] Iron loss (W10 / 600C) + Iron loss (W10 / 800C) + Iron loss (W10 / 1200C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L)

[0063] By satisfying the above relational expression 1, the high-frequency iron loss in the direction perpendicular to the rolling direction is superior to that in the rolling direction, and therefore when manufacturing a motor that uses the magnetic flux in the direction perpendicular to the rolling direction, it is possible to drive the motor with high efficiency even at high speeds.

[0064] The non-oriented electrical steel sheet of the present invention may have a thickness of 0.03 to 0.35 mm.

[0065] The method for producing a non-oriented electrical steel sheet according to the present invention will be described below.

[0066] First, a slab having the above-mentioned alloy composition is heated at 1050 to 1220°C. If the slab heating temperature is less than 1050°C, the temperature difference between the surface and the interior of the slab becomes large during hot rolling, resulting in poor sheet passing properties during hot rolling and an insufficient reduction ratio during hot rolling. If the slab heating temperature exceeds 1220°C, precipitates may remelt and precipitate finely after hot rolling. The lower limit of the slab heating temperature is more preferably 1080°C, and even more preferably 1100°C. The upper limit of the slab heating temperature is more preferably 1200°C, and even more preferably 1180°C.

[0067] The slab is then finish hot-rolled to obtain a hot-rolled sheet. The finish hot-rolling can be performed at 700 to 1050°C. If the finish hot-rolling temperature is less than 700°C, the shape of the hot-rolled sheet will be poor, deformation will be concentrated on the surface, making hot-rolling of the steel sheet impossible, and Goss-like orientation will increase in the surface area. If the finish hot-rolling temperature exceeds 1050°C, the friction force between the rolling roll and the sheet surface will increase, increasing Goss-like orientation and resulting in poor sheet shape due to high-temperature deformation. The lower limit of the finish hot-rolling temperature is more preferably 730°C, even more preferably 750°C, and most preferably 780°C. The upper limit of the finish hot-rolling temperature is more preferably 1000°C, even more preferably 960°C, and most preferably 930°C. Meanwhile, the thickness of the hot-rolled sheet may be 0.8 to 3 mm.

[0068] The hot-rolled sheet is then annealed at 850 to 1150°C for 30 to 300 seconds. If the hot-rolled sheet annealing temperature is less than 850°C, the structure may not grow or may grow finely. If the hot-rolled sheet annealing temperature exceeds 1150°C, the magnetic properties may deteriorate and the rolling workability may be impaired due to deformation of the sheet shape. The lower limit of the hot-rolled sheet annealing temperature is more preferably 900°C, and even more preferably 950°C. The upper limit of the hot-rolled sheet annealing temperature is more preferably 1135°C, and even more preferably 1110°C. If the hot-rolled sheet annealing time is less than 30 seconds, the growth of the surface and internal crystal grains differs, resulting in a disadvantage that the Goss fraction in the surface portion of the final electrical steel sheet increases significantly. If the hot-rolled sheet annealing time exceeds 300 seconds, the crystal grains become coarse, resulting in a disadvantage that the Goss fraction in the entire thickness of the finally obtained electrical steel sheet increases significantly. The lower limit of the hot-rolled sheet annealing time is more preferably 60 seconds, and even more preferably 80 seconds. The upper limit of the hot-rolled sheet annealing time is more preferably 180 seconds, and even more preferably 150 seconds. The hot-rolled sheet annealing is performed as needed to increase the orientation advantageous for magnetic properties, and can be omitted.

[0069] Thereafter, the hot-rolled sheet that has been annealed is cold-rolled to obtain a cold-rolled sheet. During the cold rolling, it is preferable that the following [Relational Expression 2] is satisfied.

[0070] [Equation 2] Maximum temperature on the surface of cold-rolled sheet during cold rolling <200 × cold rolling reduction / 100 + 60

[0071] The temperature of the steel sheet may become high due to residual heat during the hot-rolled sheet production or annealing stage, heating due to mechanical friction of the steel sheet during rolling, or external heat supply. If the maximum temperature of the cold-rolled sheet surface during cold rolling is 200 x cold reduction / 100 + 60 or more, a large shear force acts during material deformation, greatly increasing the fraction of crystal grains with Goss orientation in the steel sheet.

[0072] The cold rolling can be performed at a cold reduction of 35 to 98%. If the cold reduction is less than 35%, the energy stored by processing is consumed during cold rolling, and recrystallization does not occur, which is a problem in that the magnetic properties deteriorate even after annealing. If the cold reduction is more than 98%, a highly processed microstructure is formed by rolling, and there is a problem that iron loss increases in both the rolling direction and the direction perpendicular to the rolling direction even after final annealing. The lower limit of the cold reduction is more preferably 55%, even more preferably 65%, and most preferably 73%. The upper limit of the cold reduction is more preferably 93%, even more preferably 88%, and most preferably 83%. Meanwhile, the cold rolling can be a single cold rolling or two or more cold rollings with intermediate annealing in between.

[0073] During the cold rolling, the maximum rolling speed in one or more of the first and second passes may be 3 m / s or more. If the maximum rolling speed in one or more of the first and second passes is less than 3 m / s, a strong shear force acts on the steel sheet surface during rolling, resulting in increased nucleation of Goss orientation grains, which may increase the fraction of crystal grains having the Goss orientation on the steel sheet surface during final annealing. In the present invention, the faster the maximum rolling speed in one or more of the first and second passes during cold rolling, the more advantageous it is, so there is no particular upper limit. However, the upper limit of the maximum rolling speed in one or more of the first and second passes during cold rolling may be 20 m / s.

[0074] The cold-rolled sheet is then heated to the final annealing temperature. The heating rate in the 300-500°C temperature range during heating is preferably 5-150°C / s. If the heating rate in the 300-500°C temperature range during heating is less than 5°C / s, recrystallization of crystal grains with orientation unfavorable for magnetic properties is promoted. If the heating rate in the 300-500°C temperature range during heating is more than 150°C / s, recrystallization of crystal grains with Goss orientation unfavorable for magnetic properties in the direction perpendicular to the rolling direction is greatly promoted. The lower limit of the heating rate is more preferably 7°C / s, and even more preferably 10°C / s. The upper limit of the heating rate is more preferably 120°C / s, even more preferably 100°C / s, and most preferably 50°C / s.

[0075] The heated cold-rolled sheet is then subjected to final annealing. The final annealing can be performed at 600 to 1150°C for 10 to 500 seconds. If the final annealing temperature is less than 600°C, there is a drawback that the Goss fraction inside the steel sheet increases significantly during recrystallization. If the final annealing temperature exceeds 1150°C, there is a drawback that coarse crystal grains are formed, resulting in a deterioration in high-frequency iron loss in the C direction. The lower limit of the final annealing temperature is more preferably 700°C, even more preferably 730°C, and most preferably 750°C. The upper limit of the final annealing temperature is more preferably 1120°C, even more preferably 1100°C, and most preferably 1050°C. If the final annealing time is less than 10 seconds, there is a drawback that the fraction of crystal grains having a Goss fraction in the entire sheet thickness increases significantly. If the final annealing time exceeds 500 seconds, there is a drawback that high-frequency iron loss increases significantly due to overgrowth of crystal grains. The lower limit of the final annealing time is more preferably 20 seconds, even more preferably 30 seconds, and most preferably 35 seconds, and the upper limit of the final annealing time is more preferably 400 seconds, even more preferably 300 seconds, and most preferably 200 seconds.

[0076] The gas atmosphere during the final annealing is preferably composed of, by volume, 15 to 99.99% hydrogen, 0.0001 to 0.0030% oxygen, and the remainder an inert gas. This control allows for a substantially oxygen-free steel sheet surface. A hydrogen fraction of less than 15% results in insufficient reducing power, leading to oxidation of the surface of the material of the present invention. While a hydrogen fraction of substantially 100% is ideal, industrial application of this is extremely difficult. Therefore, the hydrogen fraction is limited to 99.99%. An oxygen fraction of less than 0.0001% may result in a small portion of the steel sheet surface bonding with oxygen, forming a localized oxide layer and creating surface irregularities. An oxygen fraction of more than 0.0030% may result in a widespread oxide layer forming on the surface, degrading magnetic properties, promoting nucleation of Goss-oriented crystal grains on the surface, and increasing the surface area fraction. The present invention does not particularly limit the type of inert gas; any type commonly used in the art may be used. For example, nitrogen or argon can be used.

[0077] Meanwhile, the method may further include forming an insulating layer after the final annealing. The method of forming the insulating layer is widely known in the technical field of non-oriented electrical steel sheets, and therefore, detailed description thereof will be omitted. [Example]

[0078] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention. The scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0079] (Example) Slabs having the alloy compositions shown in Tables 1 and 2 below were prepared, and then non-oriented electrical steel sheets were produced using the production conditions shown in Tables 3 and 4 below. Meanwhile, the remainder of the gas atmosphere in the temperature range of 500 to 750°C during final annealing was nitrogen.

[0080] The Goss orientation fraction and electrical properties of the non-oriented electrical steel sheets thus produced were measured, and the results are shown in Tables 4 to 6 below.

[0081] The Goss orientation fraction in the surface layer (the region from the surface to 1 / 10t (t: steel plate thickness) in the thickness direction) and the entire region in the thickness direction was measured using EBSD. To confirm the Goss orientation fraction by thickness, the RD-ND plane was observed, and EBSD measurement surfaces were separated and analyzed for the top and bottom surfaces at 1 / 10 of the total thickness. To ensure statistical reliability, the cross sections of 100 samples were measured, and the texture by thickness was measured for each sample measurement and averaged, which was evaluated as the Goss orientation fraction at 1 / 10t.

[0082] Iron loss (W10 / 600C), iron loss (W10 / 800C), iron loss (W10 / 1200C), iron loss (W10 / 600L), iron loss (W10 / 800L), iron loss (W10 / 1200L), iron loss (W15 / 600C), iron loss (W15 / 800C), iron loss (W15 / 1200C), iron loss (W15 / 600L), iron loss (W15 / 800L), and iron loss (W15 / 1200L) were measured using the Epstein measurement method, which is commonly used for quantitative measurements of electrical steel sheets. Samples were cut using a cutting machine. The L-direction samples were 305 mm long and 30 mm long. The C-direction samples were 305 mm long and 30 mm long.

[0083] [Table 1]

[0084] [Table 2]

[0085] [Table 3]

[0086] [Table 4]

[0087] [Table 5]

[0088] [Table 6]

[0089] As can be seen from Tables 1 to 6 above, in the case of Examples 1 to 17 of the present invention, the alloy composition and manufacturing conditions of the present invention are satisfied, and the fine structure that the present invention aims to obtain is secured, and therefore excellent magnetic properties are secured.

[0090] In the cases of Comparative Examples 1 and 2, the alloy composition does not satisfy the alloy composition of the present invention, and the fine structure that the present invention aims to obtain cannot be obtained, but it is clear that excellent magnetic properties are obtained.

[0091] In the cases of Comparative Examples 3 to 6, the manufacturing conditions of the present invention were not satisfied, and the fine structure that the present invention aims to obtain could not be obtained, but it is clear that excellent magnetic properties were obtained.

Claims

1. The alloy contains, by weight, 1.5 to 6.5% Si, 0.0005 to 3.5% Al, 0.01 to 3.0% Mn, 0.005 to 5.0% Cr, and 0.0005 to 0.03% S, with the balance being Fe and other inevitable impurities; the Goss orientation fraction in a region from the surface to 1 / 10t (t: thickness of the steel plate) in the thickness direction is 3 area % or less, A non-oriented electrical steel sheet characterized in that the Goss orientation fraction in the entire region in the thickness direction is 5 area % or less.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of C: 0.005% or less (except 0%), N: 0.005% or less (except 0%), O: 0.005% or less (except 0%), and Ti: 0.01% or less (except 0%).

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Mo: 0.1% or less (except 0%), B: 0.0050% or less (except 0%), V: 0.050% or less (except 0%), Ca: 0.010% or less (except 0%), Nb: 0.0050% or less (except 0%), and Mg: 0.0050% or less (except 0%).

5. The non-oriented electrical steel sheet according to claim 1, further containing one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2%, and Zn: 0.01% or less (excluding 0%).

6. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Bi, Pb, Ge, and As in an amount of 0.20% or less (excluding 0%), either individually or in total.

7. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W10 / 600C) of 28 W / kg or less, an iron loss (W10 / 800C) of 43 W / kg or less, and an iron loss (W10 / 1200C) of 75 W / kg or less.

8. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W10 / 600L) of 30 W / kg or less, an iron loss (W10 / 800L) of 48 W / kg or less, and an iron loss (W10 / 1200L) of 85 W / kg or less.

9. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W15 / 600C) of 65 W / kg or less, an iron loss (W15 / 800C) of 95 W / kg or less, and an iron loss (W15 / 1200C) of 175 W / kg or less.

10. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W15 / 600L) of 75 W / kg or less, an iron loss (W15 / 800L) of 105 W / kg or less, and an iron loss (W15 / 1200L) of 190 W / kg or less.

11. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet satisfies the following relational expression 1: [Relationship 1] Iron loss (W10 / 600C) + Iron loss (W10 / 800C) + Iron loss (W10 / 1200C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L)

12. a step of heating a slab containing, in weight percent, 1.5 to 6.5% Si, 0.0005 to 3.5% Al, 0.01 to 3.0% Mn, 0.005 to 5.0% Cr, 0.0005 to 0.03% S, with the balance being Fe and other unavoidable impurities, at 1050 to 1220°C; finish hot rolling the slab to obtain a hot-rolled sheet; annealing the hot-rolled sheet at 850 to 1150°C for 30 to 300 seconds; cold-rolling the hot-rolled sheet after the sheet-rolling annealing to obtain a cold-rolled sheet; heating the cold-rolled sheet; and final annealing of the heated cold-rolled sheet; During the cold rolling, the following [Relationship 2] is satisfied, During the heating, the heating rate in the temperature range of 300 to 500°C is 5 to 150°C / s, The gas atmosphere during the final annealing is composed of, by volume, 15 to 99.99% hydrogen, 0.0001 to 0.0030% oxygen, and the remainder an inert gas. [Relationship 2] Maximum temperature of cold-rolled sheet surface during cold rolling < 200 × cold rolling reduction / 100 + 60

13. The method for manufacturing a non-oriented electrical steel sheet according to claim 12, wherein the slab further contains at least one of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

14. 13. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the slab further contains one or more of C: 0.005% or less (except 0%), N: 0.005% or less (except 0%), O: 0.005% or less (except 0%), and Ti: 0.01% or less (except 0%).

15. 13. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the slab further contains one or more of Mo: 0.1% or less (except 0%), B: 0.0050% or less (except 0%), V: 0.050% or less (except 0%), Ca: 0.010% or less (except 0%), Nb: 0.0050% or less (except 0%), and Mg: 0.0050% or less (except 0%).

16. 13. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the slab further contains one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2%, and Zn: 0.01% or less (excluding 0%).

17. 13. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the slab further contains one or more of Bi, Pb, Ge, and As in an amount of 0.20% or less (excluding 0%), either individually or in total.

18. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the finish hot rolling is performed at 700 to 1050°C.

19. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the cold rolling is performed at a cold reduction rate of 35 to 98%.

20. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the maximum rolling speed in at least one of the first pass and the second pass during the cold rolling is 3 m / s or more.

21. The method for producing a non-oriented electrical steel sheet according to claim 12, wherein the final annealing is performed at 600 to 1150°C for 10 to 500 seconds.

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