Non-oriented electrical steel sheet and its manufacturing method

Abstract

Providing non-oriented electrical steel sheets with excellent magnetic properties [Solution] The steel sheet has a composition, by weight, of C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, with the balance being Fe and inevitable impurities, wherein Al, Si, and Mn satisfy the following relational expression 1, and the microstructure of the steel sheet exhibits a precipitate distribution that satisfies the following relational expression 3. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10%

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 manufacturing method for a non-oriented electrical steel sheet used mainly as a material for the iron cores of rotating machines such as motors and generators, and stationary machines such as small transformers. More specifically, the present invention relates to a non-oriented electrical steel sheet with excellent high-frequency iron loss that can be manufactured by optimally controlling the steel composition, optimizing the manufacturing conditions, and appropriately controlling the distribution of precipitates. [Background technology]

[0002] Recently, with the strengthening of environmentally friendly policies worldwide, there has been an increasing demand for improved efficiency in motors and generators, which are energy conversion devices that convert electrical energy into mechanical energy and mechanical energy into electrical energy. In such rotating devices such as motors and generators and stationary devices such as small transformers, non-oriented electrical steel sheets are used as iron core materials and have an important influence on efficiency. Therefore, the demand for improved efficiency in motors and generators is leading to a demand for improved properties of non-oriented electrical steel sheets.

[0003] The key magnetic properties of non-oriented electrical steel are iron loss and magnetic flux density. Lower iron loss reduces the iron loss lost during the magnetization process, improving efficiency. Higher magnetic flux density improves energy efficiency by enabling a stronger magnetic field to be induced with the same energy and requiring less current to achieve the same magnetic flux density. Recently, high-frequency iron loss has emerged as a more important iron loss characteristic than commercial-frequency (50 Hz) iron loss. This is because, as motor rotation speeds increase, high-frequency iron loss has a greater impact on efficiency than commercial-frequency iron loss. For example, in the case of non-oriented electrical steel used in drive motors for eco-friendly automobiles, high-frequency iron loss at 400 Hz is considered a more important characteristic. Therefore, given recent policies to improve energy efficiency and the trend toward the use of non-oriented electrical steel, it is essential to develop technology for non-oriented electrical steel that offers low high-frequency iron loss, high magnetic flux density, and excellent magnetic properties.

[0004] Among the important properties of non-oriented electrical steel sheets, the most basic and efficient ways to reduce iron loss are to increase the amount of Si, Al, and Mn, which are elements with high resistivity, or to reduce the thickness of the steel sheet. Increasing the amount of Si, Al, and Mn increases the steel's resistivity, thereby reducing eddy-current loss in the iron loss of non-oriented electrical steel sheets, thereby reducing iron loss. In the case of high-frequency iron loss, eddy-current loss accounts for a larger proportion of iron loss, making this a very effective method for reducing high-frequency iron loss. However, the effectiveness varies depending on the addition ratio, and the magnetic flux density decreases as the amount of alloying elements increases. Therefore, to ensure excellent iron loss and magnetic flux density, it is necessary to properly control the appropriate addition amounts and the addition ratio between Si, Al, and Mn. Reducing the thickness is also very effective in reducing iron loss by significantly reducing eddy-current loss, but thin steel sheets have the disadvantage of poor productivity and formability. However, with the recent increase in demand for thinner products due to energy efficiency, product development is expected to continue toward ever thinner thicknesses.

[0005] As a method for improving magnetic flux density while reducing iron loss in non-oriented electrical steel sheets, various techniques have been reported, including the use of special additive elements such as REM to improve texture and magnetic properties, and the introduction of additional manufacturing processes such as warm rolling, double rolling, and double annealing. However, all of these techniques increase manufacturing costs and make mass production difficult, so development of commercially viable technologies that provide excellent magnetic properties is essential. Furthermore, technologies have been developed to minimize the amount of added impurities and suppress and control the formation of inclusions by adding elements such as Ca, but these also increase manufacturing costs and make it difficult to clearly demonstrate their effectiveness.

[0006] Continuous efforts have been made to solve these problems, and many technologies have been developed. Patent Document 1, one of the prior art technologies for non-oriented electrical steel sheets, proposes a method for improving magnetic properties through texture improvement by setting the composition weight ratio (MnO / SiO2) of MnO to SiO2 in oxide-based inclusions in the steel to 0.43 or less, setting the friction coefficient between the steel and the roll during hot rolling to 0.2 or less, and performing finish rolling at a temperature of 700°C or higher in the ferrite single-phase region, followed by hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. However, this method has limitations, such as poor productivity and difficulty in commercial production, because the hot-rolled sheet thickness must be controlled to 1.0 mm or less.

[0007] Patent Document 2 proposes a method of controlling the heating rate during final annealing to 50°C / s or more in order to improve the texture of non-oriented electrical steel sheets and ensure excellent magnetic properties. However, although rapid heating can improve the texture, it does not take into consideration the fact that the microstructure becomes non-uniform and magnetic properties deteriorate.

[0008] In Patent Document 3, in order to manufacture a non-oriented electrical steel sheet having excellent magnetic properties in the rolling direction, a process of skin pass rolling at a reduction rate of 3 to 10% and re-annealing is further carried out in addition to the processes of hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. However, this additional process poses a problem of increased costs.

[0009] Patent Document 4 proposes a method for obtaining a steel sheet with low iron loss by reducing specific impurity elements contained in steel to an extremely low level and ensuring ease of grain growth by adding a skin pass process. However, this method has the drawback of causing an increase in cost due to the extremely low level of impurities.

[0010] Patent Document 5 proposes a technology in which rare earth elements such as Ca, Mg, and REM are added to suppress the precipitation of MnS, resulting in small crystal grains before stress relief, but the crystal grains grow during stress relief annealing, resulting in excellent core loss. However, this also has the drawback of increasing manufacturing costs due to the addition and control of additional elements, and of making it difficult to ensure the effect if stress relief annealing is not performed. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-102739 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-199787 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-265720 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-050686 [Patent Document 5] Korean Patent Publication No. 2001-0100866 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a non-oriented electrical steel sheet with excellent magnetic properties, which is obtained by strictly controlling the steel composition and appropriately controlling the heat treatment time at the soaking temperature and the temperature increase and cooling rates during the hot-rolled sheet annealing process according to the component contents, thereby controlling the size of precipitates in the steel to be coarse. Furthermore, the technical problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those having ordinary skill in the technical field to which the present invention pertains from the following description. [Means for solving the problem]

[0013] The non-oriented electrical steel sheet of the present invention is The steel sheet is characterized in that, by weight percent, it contains C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, wherein Al, Si, and Mn satisfy the following relational expression 1, and the microstructure of the steel sheet exhibits a precipitate distribution that satisfies the following relational expression 3. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10%

[0014] The microstructure of the steel sheet can satisfy the following relational expression 4. [Equation 4] Number of nitrides 0.5 μm or larger in the steel microstructure ≧ 100 / mm 2 The non-oriented electrical steel sheet preferably has a resistivity (ρ) of 63 μΩcm or more at room temperature. The iron loss of the above non-oriented electrical steel sheet (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) is preferably 1.60T or more. Here, iron loss W 10 / 40 is the average loss (W / Kg) in the rolling direction and perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B 50is the magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0015] The non-oriented electrical steel sheet may further contain at least one of Sn and Sb in an amount of 0.2% or less. The non-oriented electrical steel sheet may further contain at least one of Cu and Ni in an amount of 0.05% or less. The non-oriented electrical steel sheet may further contain Cr in the range of 0.1% or less. The non-oriented electrical steel sheet may further contain one or more of Zr, Mo, and V in an amount of 0.01% or less.

[0016] The method for producing a non-oriented electrical steel sheet of the present invention comprises: A method for producing a non-oriented electrical steel sheet, comprising the steps of: reheating a slab containing, by weight, C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities; hot-rolling the reheated slab to produce a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet and then hot-rolling the hot-rolled steel sheet, or hot-rolling the hot-rolled steel sheet without cold-rolling; pickling the hot-rolled-annealed steel sheet and then air-cooling it; cold-rolling the air-cooled hot-rolled steel sheet; and final annealing the cold-rolled cold-rolled steel sheet, The Al, Si, and Mn satisfy the following relational formula 1: During the hot-rolled sheet annealing process, the soaking temperature is controlled to a range of 850 to 1100°C, and the soaking time is controlled to a range of 30 to 300 seconds, and the heating rate (HR, °C / s) from 600°C to the soaking temperature during heating and the cooling rate (CR, °C / s) to 600°C after soaking are controlled to satisfy the following relational expression 2. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 2] 1.0≦(HR+CR) / 1000{([Al]+[Mn])*([N]+[S])}≦10.0 Here, the above [Al], [Mn], [N], and [S] are the amounts (wt %) of Al, Mn, N, and S added, respectively.

[0017] The final-annealed electrical steel sheet has a precipitate distribution in the microstructure of the steel sheet that satisfies the relations 3 and 4, and has a resistivity (ρ) of 63 μΩcm or more at room temperature, and an iron loss (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) is 1.60T or more. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10% [Equation 4] Number of nitrides 0.5 μm or larger in the steel microstructure ≧ 100 / mm 2 [Effects of the Invention]

[0018] According to the present invention, by controlling the steel composition and appropriately controlling the heat treatment time at the soaking temperature and the temperature increase and cooling rate during the hot-rolled sheet annealing process according to the component contents, the precipitates in the steel are coarsened, and the resistivity (ρ) at room temperature is 63 μΩcm or more and the iron loss (W) after final annealing is 100%. 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) of 1.60 T or more can be effectively provided. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described below. The present invention proposes a method for producing a non-oriented electrical steel sheet, in which the essential elements Si, Mn, and Al are added in amounts of 2.5 to 4.5%, 0.1 to 2.5%, and 0.5 to 2.5% to the chemical composition of conventional non-oriented electrical steel sheets, respectively, and the Al, Mn, and Si satisfy the compositional relation 1 of 0.6≦([Al]+[Mn]) / [Si]≦1.00. In addition, in the present invention, when a non-oriented electrical steel sheet is manufactured from a slab with the above-mentioned chemical composition, hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing are performed. In the hot-rolled sheet annealing process, the soaking heat treatment time is set to 30 seconds or more, and the heating rate (HR, °C / s) from 600°C to the soaking temperature during heating and the cooling rate (CR, °C / s) to 600°C after soaking are appropriately controlled according to the following Relational Formula 2, thereby coarsening the distribution of precipitates in the microstructure of the steel sheet. [Equation 2] 1.0≦(HR+CR) / 1000{([Al]+[Mn])*([N]+[S])}≦10.0

[0020] Specifically, the key elements whose amounts and contents must be controlled in this invention are Si, Al, Mn, N, and S. The most efficient way to reduce iron loss is to increase the resistivity of steel by adding Si, Al, and Mn. In particular, in the high-frequency range, the relative importance of eddy current loss in iron loss increases, making the effect of increasing resistivity even more pronounced. However, while increasing the amount of Si, Al, Mn, etc. reduces iron loss, it also reduces saturation magnetic flux density, degrading magnetic flux density, and increases material brittleness, degrading cold rolling ability and reducing productivity. Therefore, in order to achieve low iron loss, high magnetic flux density, and ensure productivity, it is necessary not only to control the amounts of Si, Al, and Mn added, but also to appropriately combine the addition ratios of each element. Therefore, we propose the above Relational Formula 1.

[0021] On the other hand, Al and Mn are well known to form nitrides and sulfides by combining with N and S. The presence of precipitates in non-oriented electrical steels inhibits grain growth, increases hysteresis loss, and deteriorates magnetic properties. Therefore, when the amount of Al and Mn added increases, N and S must be more actively controlled to maximize the suppression of magnetic deterioration by forming coarser nitrides and sulfides. To achieve this, not only is it necessary to control the composition, but the manufacturing process, particularly the hot-rolled sheet annealing process, which is a process that is quite important for the formation and distribution of precipitates, must also be strictly controlled. In light of this, the present invention proposes the above-mentioned Relation 2.

[0022] The non-oriented electrical steel sheet of the present invention obtained from this viewpoint comprises, by weight, C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, in which Al, Si, and Mn satisfy the following relational expression 1, and the microstructure of the steel sheet exhibits a distribution of precipitates that satisfies the following relational expression 3. The electrical steel sheet of the present invention has a resistivity (ρ) of 63 μΩcm or more at room temperature and an iron loss (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) can exhibit excellent high-frequency core loss and magnetic flux density of 1.60T or more. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10% The reasons for limiting the composition and content of the electrical steel sheet of the present invention will be explained below, where "%" means % by weight.

[0023] Si:2.50~4.50% or less The Si element is a major element added to increase the resistivity of steel and reduce eddy current loss in iron loss. To ensure low iron loss, especially in the high frequency range, 2.50% or more of Si must be added. However, as the amount of Si added increases, the magnetic flux density decreases significantly and the rollability deteriorates due to increased brittleness. Therefore, it is preferable to limit the amount of Si to 4.50% or less. More preferably, it is limited to 3.00 to 4.00%.

[0024] Mn: 0.10~2.50% or less The Mn element, together with Si and Al, increases resistivity and reduces iron loss, and also improves texture. However, if the amount added is too small, fine sulfides are formed, while if the amount added is excessive, the magnetic flux density decreases significantly. Therefore, the amount added is limited to 0.10 to 2.50%, and more preferably, to 0.50 to 2.00%.

[0025] Al: 0.50 to 2.50% The Al element plays an important role in increasing resistivity and reducing iron loss, along with Si, and is added to reduce magnetic anisotropy and magnetic deviation between the rolling direction and the direction perpendicular to the rolling direction. However, if the amount added is small, the iron loss reduction effect is not significant, while if the amount added is too large, the magnetic flux density significantly deteriorates. Therefore, the amount added is preferably limited to 0.50 to 2.50%, and more preferably to 0.60 to 2.00%.

[0026] C: 0.0050% or less C combines with Ti, Nb, etc. to form carbides, which deteriorates magnetic properties, and when processed into electrical appliances after use, increases iron loss due to magnetic aging, reducing the efficiency of electrical appliances. Therefore, it is preferable to limit C to 0.0050% or less.

[0027] S: 0.0010~0.0050% S is an element that forms sulfides such as MnS, CuS, and (Cu, Mn)S, which are harmful to magnetic properties, so it is preferable to add as little as possible. However, if S is added in an amount less than 0.0010%, it is actually detrimental to the formation of texture, promoting the formation of fine sulfides and reducing magnetic properties, so it is preferable to add 0.0010% or more. On the other hand, if S is added in an amount exceeding 0.0050%, the magnetic properties will be reduced due to the increase in sulfides. Therefore, it is recommended that S be added in an amount of 0.0010 to 0.0050%.

[0028] N: 0.0050% or less N is an element that is harmful to magnetism by forming nitrides by strongly bonding with Al, Ti, Nb, etc., and inhibiting grain growth, etc. Therefore, it is preferable that the N content be small, and in the present invention, it is preferable to limit it to 0.0050% or less.

[0029] Ti: 0.0050% or less Ti is an element that inhibits grain growth and reduces magnetic flux density by forming fine carbides and nitrides by combining with C and N. As the amount of Ti added increases, the texture becomes inferior due to the increased amount of carbides and nitrides, resulting in poor magnetic properties. Therefore, in the present invention, the amount of Ti is limited to 0.0050% or less.

[0030] P: 0.002 to 0.020% P is an element that segregates at grain boundaries and surfaces and has the effect of improving the texture of steel. However, if added in an amount less than 0.002%, this effect is minimal. On the other hand, if added in an amount exceeding 0.02%, it inhibits grain growth, thereby deteriorating iron loss, and grain segregation deteriorates rollability, resulting in reduced productivity. Therefore, its addition amount must be controlled to 0.002 to 0.020%. It is more preferable to limit it to 0.003 to 0.010%.

[0031] In addition to the above elements, Sn and Sb, which are generally known to improve texture, can be added to further improve magnetic properties. However, if added in excess, this will inhibit grain growth and deteriorate magnetic properties, so in the present invention, the content of at least one of Sn and Sb is limited to a range of 0.2% or less. Furthermore, Cu and Ni can be added to improve magnetic properties, but they may react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetic properties. Therefore, in the present invention, the amount of at least one of Cu and Ni is limited to a range of 0.05% or less.

[0032] Cr is similar to Cu and Ni, but has the effect of increasing resistivity and improving magnetic properties, so it can be added in the range of 0.1% or less. Furthermore, since Zr, Mo, V, etc. are elements that form strong carbonitrides, it is preferable to avoid their inclusion as much as possible. In the present invention, the amount of Zr, Mo, and V, either alone or in combination of two or more of them, is limited to 0.01% or less. In addition to the above composition, the remainder is composed of Fe and other unavoidable impurities.

[0033] On the other hand, in the present invention, Si, Al, and Mn are added in an amount of Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, and Al: 0.50 to 2.50%, and it is necessary that the above Al, Mn, and Si satisfy the following relational formula 1. The specific reasons for this are as follows. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively.

[0034] The core loss of non-oriented electrical steel sheets can be divided into hysteresis loss and eddy-current loss. Adding elements such as Si, Al, and Mn increases the resistivity of steel, significantly reducing eddy-current loss. In particular, as the frequency increases, the proportion of eddy-current loss in total core loss increases. Therefore, to achieve excellent high-frequency core loss, it is necessary to control the resistivity of steel above a certain level. Through this invention, we have confirmed that excellent properties can be achieved when the resistivity (ρ) of steel is 63 μΩcm or higher. Among Si, Al, and Mn, Si is the element that most significantly increases the resistivity of steel. However, increasing the amount of Si increases the brittleness of steel and reduces productivity. Therefore, to achieve a resistivity of 63 μΩcm or higher while also ensuring productivity, appropriate amounts of Al and Mn must be added along with Si. After investigating the appropriate addition ratio, we derived the above Relational Formula 1. It is known that Al has a greater effect on increasing the resistivity of steel than Mn, but adding more Al than Mn is undesirable.

[0035] Furthermore, the electrical steel sheet of the present invention exhibits a distribution of precipitates in the microstructure of the steel sheet that satisfies the following relational expression 3. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10% More preferably, the steel microstructure satisfies the following relation 4: [Equation 4] Number of nitrides 0.5 μm or larger in the steel microstructure ≧ 100 / mm 2 The electrical steel sheet of the present invention that exhibits such a precipitate distribution preferably has a resistivity (ρ) of 63 μΩcm or more at room temperature. In addition, iron loss (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) can be 1.60T or more. Here, iron loss W 10 / 40 is the average loss (W / Kg) in the rolling direction and perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B 50 is the magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0036] Next, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail. The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of reheating a slab containing, by weight, C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities; hot-rolling the reheated slab to produce a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet and then hot-rolling the hot-rolled steel sheet or hot-rolling the hot-rolled steel sheet without cold rolling; The method for producing a non-oriented electrical steel sheet includes a step of pickling a hot-rolled annealed steel sheet and then air-cooling it, a step of cold-rolling the air-cooled hot-rolled steel sheet, and a step of final annealing the cold-rolled cold-rolled steel sheet, wherein the Al, Si, and Mn satisfy the above-mentioned relational expression 1, and in the hot-rolled sheet annealing step, the soaking temperature is controlled to be in the range of 850 to 1100°C and the soaking time is controlled to be in the range of 30 to 300 seconds, and the heating rate (HR, °C / s) from 600°C to the soaking zone temperature and the cooling rate (CR, °C / s) to 600°C after soaking are controlled so as to satisfy the following relational expression 2:

[0037] That is, the non-oriented electrical steel sheet of the present invention can be produced by subjecting a steel slab having the above-described composition to the usual reheating, hot rolling, hot-rolled sheet annealing, pickling, followed by cold rolling and cold-rolled sheet annealing, and in this case, cold rolling may be carried out once or two or more times with intermediate annealing in between. The following description of the production conditions is a typical example and does not necessarily apply only to the following conditions. The steel slab can be reheated to 1200°C or below and then hot rolled. If the reheating temperature is 1200°C or higher, precipitates such as nitrides, carbides, and sulfides present in the slab are redissolved and then finely precipitate during hot rolling and annealing, suppressing grain growth and reducing magnetic properties.

[0038] After hot rolling, the hot-rolled sheet is coiled at temperatures below 700°C and cooled in air. The coiled and cooled hot-rolled sheet is then annealed to ensure a recrystallized structure before cold rolling. The annealing conditions are crucial for improving the texture of non-oriented electrical steel sheets and for controlling the distribution of precipitates. The magnetic properties of non-oriented electrical steel sheets deteriorate with increasing amounts of precipitates, and the finer the precipitates, the greater the deterioration. Furthermore, as the amount of alloying added to reduce iron loss increases, the precipitation temperature and distribution of precipitates change, so the annealing conditions for the hot-rolled sheet must be controlled to suit the composition. Therefore, the precipitation must be controlled in the hot-rolled sheet annealing process, which is the final heat treatment step before final annealing and allows for control of the distribution of precipitates.

[0039] As a result of various investigations, the present inventors have confirmed that, in the hot-rolled sheet annealing process, the holding time at the soaking temperature, the temperature increase rate from 600°C to the soaking temperature, and the cooling rate to 600°C after the soaking heat treatment can be controlled in accordance with the components, thereby coarsening the distribution of precipitates and minimizing deterioration of magnetic properties, thereby ensuring excellent magnetic properties. In this case, the holding time at the soaking temperature in the hot-rolled sheet annealing process must be 30 seconds or more so that coarse precipitates can be formed, and if it is less than 30 seconds, fine precipitates are formed. On the other hand, if the holding time is too long, the crystal grains become too coarse, resulting in poor cold rolling properties, so it was determined that the holding time should be 300 seconds or less.

[0040] The soaking temperature in the hot-rolled sheet annealing step is preferably in the range of 850 to 1100° C. If the hot-rolled sheet annealing temperature is 850° C. or less, the crystal grain growth is insufficient, the texture deteriorates, and the distribution of precipitates cannot be controlled. If the temperature exceeds 1100° C., the crystal grain growth becomes coarse, the cold rolling ability deteriorates, and the precipitates precipitate finely, resulting in a deterioration of magnetic properties.

[0041] Meanwhile, if the combined total of the heating rate (HR, °C / s) from 600°C to the soaking temperature during the hot-rolled sheet annealing process and the cooling rate (CR, °C / s) to 600°C after soaking heat treatment is too fast, fine precipitates will form, and conversely, if it is too slow, the texture will deteriorate, so they must be managed within an appropriate range, and this range must be controlled by the composition. As the composition content changes, the conditions must be controlled to reflect the behavior of the precipitates, so the range to ensure optimal magnetic properties is shown in Relation 2 below. [Equation 2] 1.0≦(HR+CR) / 1000{([Al]+[Mn])*([N]+[S])}≦10.0 Here, the above [Al], [Mn], [N], and [S] are the amounts (wt %) of Al, Mn, N, and S added, respectively. The heating rate from 600°C to the soaking temperature and the cooling rate to 600°C after the soaking heat treatment are preferably controlled within the range of 5°C / s to 100°C / s to ensure a uniform microstructure and texture.

[0042] Subsequently, the hot-rolled sheet annealed in the present invention is pickled in a conventional manner and then cold-rolled. Cold rolling is performed to a final thickness of 0.10 mm to 0.30 mm. The thickness of the final product has a significant effect on iron loss, especially high-frequency iron loss. To ensure excellent high-frequency iron loss, the thickness must be 0.3 mm or less. This cold rolling can be performed in a single pass, or in two passes with intermediate annealing, if necessary. In either case, excellent magnetic properties can be ensured through appropriate texture control only when the final reduction is in the range of 50 to 95%. The cold-rolled steel sheet is finally subjected to cold-rolled sheet annealing. In the process of annealing the cold-rolled sheet, the annealing temperature is not particularly limited as long as it is a temperature that is generally applied to non-oriented electrical steel sheets.

[0043] The iron loss of non-oriented electrical steel sheets is closely related to the grain size. The iron loss of non-oriented electrical steel sheets can be divided into hysteresis loss and eddy-current loss. Hysteresis loss decreases with increasing grain size, while eddy-current loss increases with increasing grain size. Therefore, there is an optimum grain size at which the sum of hysteresis loss and eddy-current loss is minimized. Therefore, it is important to determine and apply an annealing temperature that ensures the optimum grain size. The annealing temperature is preferably 850 to 1100°C. If the annealing temperature is lower than 850°C, the grains will be too fine, resulting in increased hysteresis loss. On the other hand, if the annealing temperature exceeds 1100°C, the grains will be too coarse, resulting in increased eddy-current loss and a deterioration in iron loss.

[0044] The final annealed steel sheets are then shipped to customers after being treated with an insulating coating. The insulating coating can be organic, inorganic, or an organic-inorganic composite coating, or it can be treated with other insulating coating agents. Customers can use the steel sheets as they are after processing.

[0045] The microstructure of the non-oriented electrical steel sheet of the present invention manufactured by the above-described composition and manufacturing process can exhibit a precipitate distribution that satisfies the following relational expression 3, and as a result, the resistivity (ρ) at room temperature is 63 μΩcm or more, and the iron loss (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) is 1.60 T or more, and excellent high-frequency iron loss characteristics can be achieved. [Equation 3] The number ratio of sulfides and nitrides of 0.2 μm or larger among precipitates of 0 to 0.5 μm size in the steel microstructure is ≥ 10% [Example]

[0046] The method for manufacturing a non-oriented electrical steel sheet according to the present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples. (Example) Steel ingots having the chemical composition shown in Table 1 below were produced by vacuum melting. Each produced steel ingot was heated to 1180°C, hot-rolled to a thickness of 2.1 mm, coiled, and cooled in air. The cooled hot-rolled sheet was then hot-rolled under the conditions shown in Table 2 below. Specifically, the distribution of precipitates formed and their influence on magnetic properties were analyzed by varying the heat treatment time at the soaking temperature during hot-rolled sheet annealing, as well as the heating rate (HR, °C / s) from 600°C to the soaking temperature and the cooling rate (C, °C / s) to 600°C after soaking, depending on the contents of the steel sheet components Si, Al, Mn, N, and S. The hot-rolled sheet was then pickled and cold-rolled to a thickness of 0.2 mm, followed by final cold-rolled sheet annealing at a temperature ranging from 900 to 1050°C.

[0047] The room temperature resistivity of each test specimen prepared as described above was measured, and the results are shown in Table 2 below. In addition, TEM replica test specimens were prepared, and the distribution of precipitates such as sulfides and nitrides in the test specimen structure was observed and analyzed. The results according to Relation 3 and Relation 4 are shown in Table 2 below. After processing the magnetic test piece, the iron loss W 10 / 400 and magnetic flux density B 50 The results are also shown in Table 2 below. 10 / 400 indicates the average loss (W / Kg) in the rolling direction and perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B 50 indicates the magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0048] [Table 1] *The remaining components in Table 1 are Fe and unavoidable impurities, and the relationship 1 is ([Al] + [Mn]) / [Si].

[0049] [Table 2] *Relationship 2 in Table 2 is (HR+CR) / 1000{([Al]+[Mn])*([N]+[S])}, where the heating rate (HR) is the rate at which the temperature rises from 600°C to the soaking temperature, and the cooling rate (CR) is the rate at which the temperature is cooled to 600°C after the soaking heat treatment.

[0050] Relational formula 3 represents the percentage of sulfides and nitrides with a size of 0.2 μm or more among precipitates with a size of 0 to 0.5 μm in the steel microstructure, and relational formula 4 represents the number of nitrides with a size of 0.5 μm or more in the steel microstructure. As shown in Tables 1 and 2 above, the 1-15 steel (invention example) that satisfies the conditions of the electrical steel sheet composition and manufacturing process of the present invention has a number ratio of sulfides and nitrides that are 0.2 μm or larger among the precipitates of 0 to 0.5 μm size according to Relational Formula 3 of 10% or more, and the number of nitrides that are 0.5 μm according to Relational Formula 4 is 100 / mm 2 By satisfying all of the above, the iron loss after final annealing (W 10 / 400 ) is 12.0W / Kg or less, and the magnetic flux density (B 50 ) showed excellent magnetic properties of over 1.60 T. In addition, the resistivity at room temperature was over 63 μΩcm.

[0051] In contrast, in the case of No. 16 steel, the amount of Mn added and relational expression 1 do not satisfy the ranges of the present invention, and as a result, the number of nitrides having a size of 0.5 μm or more in relational expression 4 is 100 pieces / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. In addition, in the case of No. 17 steel, the amounts of Mn and Al added and the relational expression 1 do not satisfy the ranges of the present invention, and as a result, the number ratio of sulfides and nitrides having a size of 0.2 μm or more among the precipitates of 0 to 0.5 μm size in the relational expression 3 is less than 10%, and the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. In addition, in the case of No. 18 steel, not only are the amount of Al added and Relational Formula 1 outside the range of the present invention, but the heat treatment time at the soaking temperature during hot-rolled sheet annealing is too short, so the requirements of Relational Formula 3 and Relational Formula 4 are not met, and the iron loss W 10 / 400 and magnetic flux density B 50In addition, the resistivity (ρ) at room temperature did not meet the requirement of 63 μΩcm or more.

[0052] In addition, No. 19 steel is a case where the amount of Mn and Al added and the requirements of relational expression 2 were not satisfied during the annealing of the hot-rolled sheet, and relational expression 3 was not satisfied, resulting in iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. In addition, No. 20 steel not only does not satisfy the amount of Mn and Al added in relation to Relation 1, but also does not satisfy the requirements of Relation 2 during hot-rolled sheet annealing. The number ratio of sulfides and nitrides with a size of 0.2 μm or more among the precipitates of 0 to 0.5 μm size in Relation 3 is less than 10%, and the number of nitrides with a size of 0.5 μm or more in Relation 4 is 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated.

[0053] In the case of steels No. 21 and No. 22, the contents of Si, Mn, and Al do not satisfy relational expression 1. Furthermore, during the annealing of the hot-rolled sheet, relational expression 2 is not satisfied. Therefore, the number ratio of sulfides and nitrides of 0.2 μm or more among the precipitates of 0 to 0.5 μm size in relational expression 3 is less than 10%, and the number of nitrides of 0.5 μm or more in relational expression 4 is also less than 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. No. 23 steel satisfies the composition and chemical formula 1, but the heat treatment time at the soaking temperature during APL annealing was not met. The number of nitrides with a size of 0.5 μm or more as specified in formula 4 was 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated.

[0054] Steel No. 24, like Steel No. 23, satisfied the compositional elements and elemental relation 1, but did not satisfy the requirements of relation 2, as well as the heat treatment time at the soaking temperature during APL annealing. The number ratio of sulfides and nitrides with a size of 0.2 μm or more among the 0-0.5 μm precipitates of relation 3 was less than 10%, and the number of nitrides with a size of 0.5 μm or more of relation 4 was 100 / mm2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. No. 25 steel is a case where the contents of Si, Mn, and Al are within the range of the present invention, but do not satisfy the requirements of Relational Formula 1 and Relational Formula 2. The number ratio of sulfides and nitrides of 0.2 μm or more among precipitates of 0 to 0.5 μm size in Relational Formula 3 is less than 10%, and the number of nitrides of 0.5 μm or more in Relational Formula 5 is 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 Furthermore, the specific resistance (ρ) at room temperature did not meet the requirement of 63 μΩcm or more.

[0055] Steels No. 26, No. 27, and No. 28 were cases where the soaking time, etc., was met during hot-rolled sheet annealing, but the requirements of Relational Formula 2 were not met, and the number ratio of sulfides and nitrides of 0.2 μm or more among the 0-0.5 μm size precipitates of Relational Formula 3 was less than 10%, or the number of nitrides of 0.5 μm or more of Relational Formula 4 was 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated. No. 29 steel not only does not satisfy the relational expression 1 in terms of Si, Mn, and Al, but also does not satisfy the condition of a 30-300 second soaking time during hot-rolled sheet annealing and the requirement of relational expression 2. The ratio of sulfides and nitrides of 0.2 μm or larger among the 0.5 μm-sized precipitates of relational expression 3 is less than 10%, and the number of nitrides of 0.5 μm or larger in relational expression 4 is 100 / mm 2 Less than, not all are satisfied, iron loss W 10 / 400 and magnetic flux density B 50 has deteriorated.

[0056] On the other hand, No. 30 steel not only does not satisfy the relationship 1 in terms of Si, Mn, and Al, but also does not satisfy the condition of a soaking time of 30 to 300 seconds during hot-rolled sheet annealing and the requirement of relationship 2. In addition, the number of nitrides with a size of 0.5 μm or more in relationship 4 is 100 / mm 2 is less than the iron loss W 10 / 400 and magnetic flux density B 50In addition, the specific resistance (ρ) at room temperature did not meet the requirement of 63 μΩcm or more.

[0057] Although the present invention has been described with reference to the preferred embodiments, those skilled in the art may make various modifications and changes to the present invention within the scope of the basic concept of the present invention. The scope of the present invention is to be interpreted based on the claims.

Claims

1. A non-oriented electrical steel sheet comprising, by weight, C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, wherein Al, Si, and Mn satisfy the following relational expression 1, and the microstructure of the steel sheet exhibits a precipitate distribution that satisfies the following relational expression 3: [Relationship 1] 0.60≦([Al]+[Mn]) / [Si]≦1.0 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Relationship 3] The number ratio of sulfides and nitrides of 0.2 μm or more among precipitates of 0 to 0.5 μm size in the steel microstructure is ≧10%

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the microstructure of the steel sheet satisfies the following relational expression 4: [Relationship 4] The number of nitrides of 0.5 μm or more in the steel microstructure is ≧100 / mm ２

3. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a resistivity (ρ) of 63 μΩcm or more at room temperature.

4. The iron loss (W １０／４００ ) is 12.0 W / Kg or less, and the magnetic flux density (B ５０ 2. The non-oriented electrical steel sheet according to claim 1, wherein the tensile strength is 1.60T or more. Here, iron loss W １０／４０ is the average loss (W / Kg) in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B ５０ is the magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

5. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of Sn and Sb in an amount of 0.2% or less.

6. The non-oriented electrical steel sheet according to claim 1 , further comprising at least one of Cu and Ni in an amount of 0.05% or less.

7. The non-oriented electrical steel sheet according to claim 1, further comprising Cr in a range of 0.1% or less.

8. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of Zr, Mo, and V in an amount of 0.01% or less.

9. A method for producing a non-oriented electrical steel sheet, comprising: a step of reheating a slab containing, by weight, C: 0.005% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, with the balance being Fe and inevitable impurities; a step of producing a hot-rolled steel sheet by hot-rolling the reheated slab; a step of cold-rolling the hot-rolled steel sheet and then hot-rolling the hot-rolled steel sheet, or a step of hot-rolling the hot-rolled steel sheet without cold-rolling; a step of pickling the hot-rolled-annealed steel sheet and then air-cooling it; a step of cold-rolling the air-cooled hot-rolled steel sheet; and a step of final annealing the cold-rolled cold-rolled steel sheet, The Al, Si, and Mn satisfy the following relational formula 1: a soaking temperature in the range of 850 to 1100°C and a soaking time in the range of 30 to 300 seconds during the hot-rolled sheet annealing step, and a heating rate (HR, °C / s) from 600°C to the soaking zone temperature during heating and a cooling rate (CR, °C / s) to 600°C after soaking are controlled so as to satisfy the following relational expression 2. [Relationship 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Relationship 2] 1.0≦(HR+CR) / 1000 {([Al]+[Mn])*([N]+[S])}≦10.0 Here, the above [Al], [Mn], [N], and [S] represent the amounts (wt %) of Al, Mn, N, and S added, respectively.

10. The method for producing a non-oriented electrical steel sheet according to claim 9, wherein the heating rate (HR) and the cooling rate (CR) are each 5 to 100°C / s.

11. The final-annealed electrical steel sheet has a precipitate distribution that satisfies Relational Formula 3 and Relational Formula 4 in the microstructure of the steel sheet, a resistivity (ρ) of 63 μΩcm or more at room temperature, and an iron loss (W １０／４００ ) is 12.0 W / Kg or less, and the magnetic flux density (B ５０ 10. The method for producing a non-oriented electrical steel sheet according to claim 9, wherein the tensile strength is 1.60T or more. [Relationship 3] The number ratio of sulfides and nitrides of 0.2 μm or more among precipitates of 0 to 0.5 μm size in the steel microstructure is ≧10% [Relationship 4] The number of nitrides of 0.5 μm or more in the steel microstructure is ≧100 / mm ２

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