Non-oriented electrical steel sheet and method for producing same

Abstract

The invention provides a non-oriented electrical steel sheet and a manufacturing method thereof. This electrical steel sheet contains, in wt%, 0.005% or less of C, 2.50-4.50% of Si, 0.10-2.50% of Mn, 0.002-0.020% of P, 0.0010-0.0050% of S, 0.50-2.50% of Al, 0.0050% or less of N, and 0.0050% or less of Ti, with the balance being Fe and unavoidable impurities, Al, Si, and Mn satisfy a predetermined relational expression 1, and the microstructure of the steel sheet exhibits a precipitation component distribution satisfying relational expression 3.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a non-oriented electrical steel sheet mainly used as a core material for motors, generators, etc. as rotating devices and small transformers, etc. as stationary devices. More specifically, the present invention relates to a non-oriented electrical steel sheet having excellent high-frequency iron loss, which can be manufactured by controlling the composition of steel to an optimal level, optimizing manufacturing conditions, and appropriately controlling the distribution of precipitates. Background Art

[0002] In recent years, with the strengthening of global environmental protection policies, the demand for improving the efficiency of motors or generators, which are energy conversion devices for converting electrical energy into mechanical energy or converting mechanical energy into electrical energy, is increasing. Non-oriented electrical steel sheets are used as core materials in rotating devices such as these motors and generators and stationary devices such as small transformers, and are materials that have an important impact on efficiency. Therefore, the demand for improving the efficiency of motors or generators has led to a demand for improving the properties of non-oriented electrical steel sheets.

[0003] Representative magnetic properties of non-oriented electrical steel sheets are iron loss and magnetic flux density. As the iron loss decreases, the iron loss dissipated during the magnetization of the core decreases, thereby improving the efficiency. The higher the magnetic flux density, the larger the magnetic field can be induced at the same energy. To obtain the same magnetic flux density, a small current can be applied, so the energy efficiency can be improved. In addition, in recent years, high-frequency iron loss has become a more important property compared to the iron loss at commercial frequency (50 Hz) in iron loss. This is because as the rotational speed of the motor increases, high-frequency iron loss has a greater impact on efficiency compared to iron loss at commercial frequency. As a representative example, in the case of non-oriented electrical steel sheets used in drive motors applied to eco-friendly vehicles, etc., the high-frequency iron loss at 400 Hz is evaluated as a more important property. Therefore, considering such energy efficiency improvement policies and the usage direction of non-oriented electrical steel sheets in recent years, the development technology of non-oriented electrical steel sheets with excellent magnetic properties having low high-frequency iron loss and high magnetic flux density can be said to be essential.

[0004] Among the important properties of non-oriented electrical steel sheets, the most fundamental and effective methods for reducing iron loss include increasing the addition amounts of Si, Al, and Mn, which are elements with high specific resistance, or thinning the thickness of the steel sheets. Increasing the addition amounts of Si, Al, and Mn increases the specific resistance of the steel, reducing the eddy current loss in the iron loss of non-oriented electrical steel sheets, thus having the effect of reducing iron loss. In the case of high-frequency iron loss, the proportion of eddy current loss in the iron loss is larger, so it can be a very effective method for reducing high-frequency iron loss. However, its effect varies with the addition ratio. As the addition amount of alloying elements increases, the magnetic flux density deteriorates. Therefore, in order to ensure excellent iron loss and magnetic flux density, it is necessary to appropriately control the addition ratio between the appropriate addition amount and the addition amounts of Si, Al, and Mn. The method of thinning the thickness is also a method that significantly reduces eddy current loss and is very effective in reducing iron loss. However, steel sheets with a thin thickness have the disadvantages of reduced productivity and workability. However, from the perspective of recent energy efficiency, the demand for thinner products is increasing, and it is considered that future product development will move in the direction of gradually thinning the thickness.

[0005] As methods for reducing the iron loss and improving the magnetic flux density of non-oriented electrical steel sheets, techniques such as using special additive elements such as REM to improve the texture to enhance magnetic properties or introducing additional manufacturing processes such as warm rolling, secondary rolling, and secondary annealing have been reported. However, all of these techniques will result in an increase in manufacturing costs or difficulty in large-scale production. Therefore, it can be said that there is a need to develop a technology with excellent magnetism and easy commercial production. In addition, technologies for suppressing and controlling the formation of inclusions by minimizing the addition amount of impurities and adding elements such as Ca are being developed, but this also leads to an increase in manufacturing costs and the effect cannot be clearly ensured.

[0006] Continuous efforts have been made to solve this problem, and many technologies have been developed. In the prior art of non-oriented electrical steel sheets, Patent Document 1 proposed a method of improving magnetism by improving the texture by setting the compositional weight ratio (MnO / SiO2) of MnO and SiO2 in the oxide-based inclusions in the steel to 0.43 or less, performing finish rolling in the single-phase ferritic region where the friction coefficient between the steel and the roll is 0.2 or less and the finish rolling temperature is 700 °C or higher during hot rolling, and then performing hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. At this time, it is necessary to control the thickness of the hot-rolled sheet to 1.0 mm or less, so the productivity is reduced, and there are limitations in commercial production.

[0007] Patent Document 2 proposed a method of ensuring excellent magnetism by improving the texture of non-oriented electrical steel sheets by controlling the heating rate at final annealing to 50 °C / second or more. Although the texture can be improved by implementing rapid heating, the part where the magnetism may deteriorate due to the non-uniformity of the fine microstructure is not considered.

[0008] In addition, Patent Document 3 proposes a process which, in addition to the processes of hot rolling, annealing of hot-rolled sheets, cold rolling, and annealing of cold-rolled sheets, further performs skin pass rolling at a reduction ratio of 3 - 10% and then anneals again to manufacture a non-oriented electrical steel sheet having excellent magnetic properties in the rolling direction. However, this also has the problem of increased costs due to the additional processes.

[0009] Patent Document 4 proposes a method which can obtain a steel sheet with low iron loss by reducing specific impurity elements contained in the steel to a very low level and ensuring the ease of grain growth by increasing the skin pass rolling process. However, it has the disadvantage of increased costs due to the extremely low management of impurities.

[0010] Patent Document 5 proposes a technique in which the precipitation of MnS is suppressed by adding rare earth elements such as Ca or Mg and REM. Before stress removal, the grains are small, but grain growth occurs during stress removal annealing, so that excellent iron loss can be achieved. However, this also has the disadvantages of increased manufacturing costs due to the addition and control of additional elements, and it is difficult to ensure the effect when stress removal annealing is not performed.

[0011] [Prior Art Documents]

[0012] [Patent Documents]

[0013] (Patent Document 1) Japanese Unexamined Patent Application No. 2009 - 102739

[0014] (Patent Document 2) Japanese Unexamined Patent Application No. 2016 - 199787

[0015] (Patent Document 3) Japanese Unexamined Patent Application No. 2006 - 265720

[0016] (Patent Document 4) Japanese Unexamined Patent Application No. 2008 - 050686

[0017] (Patent Document 5) Korean Unexamined Patent Application No. 2001 - 0100866 Summary of the Invention

[0018] (1) Technical Problems to be Solved

[0019] An object of the present invention is to provide a non-oriented electrical steel sheet in which, by strictly controlling the composition of the steel and appropriately controlling the heat treatment time, heating rate, and cooling rate at the soaking temperature during the annealing process of the hot-rolled sheet according to the content of the components, the precipitates in the steel are controlled to be coarse, thereby having excellent magnetic properties.

[0020] In addition, the technical problems to be solved by the present invention are not limited to the above technical problems, and those skilled in the technical field to which the present invention pertains can clearly understand other technical problems not mentioned from the following description.

[0021] (2) Technical Solution

[0022] Therefore, one aspect of the present invention relates to a non-oriented electrical steel sheet, which, by weight %, comprises: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and inevitable impurities, and Al, Si and Mn satisfy the following relational expression 1, and a precipitation component distribution satisfying the following relational expression 3 is exhibited in the fine structure of the steel sheet.

[0023] [Relational Expression 1]

[0024] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00

[0025] Wherein, [Al], [Mn], and [Si] are the addition amounts (weight %) of Al, Mn, and Si, respectively.

[0026] [Relational Expression 3]

[0027] In the fine structure of the steel, the number ratio of sulfides and nitrides with a size of 0.2 μm or more in precipitates with a size of 0 - 0.5 μm ≥ 10%

[0028] The fine structure of the steel sheet may satisfy the following relational expression 4.

[0029] [Relational Expression 4]

[0030] In the fine structure of the steel, the number of nitrides with a size of 0.5 μm or more ≥ 100 pieces / mm 2

[0031] The specific resistance (ρ) of the non-oriented electrical steel sheet at room temperature may be 63 μΩcm or more.

[0032] The iron loss (W10 / 400) of the non-oriented electrical steel sheet may be 12.0 W / Kg or less, and the magnetic flux density (B50) may be 1.60 T or more.

[0033] Wherein, the iron loss W10 / 40 is the average loss (W / Kg) in the rolling direction and the direction perpendicular to rolling when a magnetic flux density of 1.0 Tesla (Tesla) is induced at a frequency of 400 Hz, and the magnetic flux density B50 is the size (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0034] The non-oriented electrical steel sheet may further contain one or more of Sn and Sb in the range of 0.2% or less.

[0035] The non-oriented electrical steel sheet may further contain one or more of Cu and Ni in the range of 0.05% or less.

[0036] The non-oriented electrical steel sheet may further contain Cr in the range of 0.1% or less.

[0037] The non-oriented electrical steel sheet may further contain one or more of Zr, Mo, and V in the range of 0.01% or less.

[0038] Furthermore, another aspect of the present invention relates to a method for manufacturing a non-oriented electrical steel sheet, characterized in that the manufacturing method includes the following processes: reheating a slab, which, by weight%, contains: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and unavoidable impurities; hot-rolling the reheated slab to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet and then performing hot-rolled sheet annealing or performing hot-rolled sheet annealing without cold-rolling; pickling the steel sheet after the hot-rolled sheet annealing and then air-cooling; cold-rolling the air-cooled hot-rolled steel sheet; and finally annealing the cold-rolled steel sheet after the cold-rolling, wherein Al, Si, and Mn satisfy the following relational expression 1, during the hot-rolled sheet annealing process, the soaking temperature is controlled within the range of 850 - 1100°C, the soaking time is controlled within the range of 30 - 300 seconds, and the heating rate (HR, °C / second (s)) from 600°C to the soaking zone temperature and the cooling rate (CR, °C / second) after soaking until 600°C are controlled to satisfy the following relational expression 2.

[0039] [Relational expression 1]

[0040] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00

[0041] Wherein, [Al], [Mn], and [Si] are the addition amounts (weight%) of Al, Mn, and Si, respectively.

[0042] [Relational expression 2]

[0043] 1.0 ≤ (HR + CR) / 1000{([Al] + [Mn]) ([N] + [S])} ≤ 10.0

[0044] Among them, [Al], [Mn], [N], and [S] are the addition amounts (weight %) of Al, Mn, N, and S, respectively.

[0045] In the electrical steel sheet after the final annealing, a precipitation component distribution satisfying Relational Expression 3 and Relational Expression 4 can be exhibited in the fine structure of the steel sheet. The specific resistance (ρ) at room temperature can be 63 μΩ·cm or more, the iron loss (W10 / 400) after the final annealing can be 12.0 W / kg or less, and the magnetic flux density (B50) can be 1.60 T or more.

[0046] [Relational Expression 3]

[0047] In the fine structure of the steel, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more in the precipitates with a size of 0 - 0.5 μm is ≥ 10%.

[0048] [Relational Expression 4]

[0049] In the fine structure of the steel, the number of nitrides with a size of 0.5 μm or more is ≥ 100 pieces / mm 2

[0050] (III) Beneficial Effects

[0051] According to the present invention, by controlling the composition of the steel, appropriately controlling the heat treatment time, the heating rate, and the cooling rate at the soaking temperature during the annealing process of the hot-rolled sheet according to the content of the components, and coarsening the precipitates in the steel, it is possible to effectively provide a non-oriented electrical steel sheet with excellent magnetic properties, having a specific resistance (ρ) at room temperature of 63 μΩ·cm or more, an iron loss (W10 / 400) after the final annealing of 12.0 W / kg or less, and a magnetic flux density (B50) of 1.60 T or more. Specific Embodiments

[0052] Hereinafter, the present invention will be described.

[0053] The present invention provides a method for manufacturing a non-oriented electrical steel sheet. Among them, in the composition system of the existing non-oriented electrical steel sheet, the addition amounts of Si, Mn, and Al, which are essential components, are set to 2.5 - 4.5%, 0.1 - 2.5%, and 0.5 - 2.5% respectively, and the components Al, Mn, and Si are in a composition relational expression 1 satisfying 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00.

[0054] In addition, when manufacturing non-oriented electrical steel sheets using the slab of the said composition system, through hot rolling, hot rolled sheet annealing, cold rolling, and cold rolled sheet annealing, the soaking heat treatment time in the hot rolled sheet annealing process is set to 30 seconds or more, and by means of the following relational expression 2, the heating rate (HR, °C / second) from 600°C to the soaking zone temperature during heating and the cooling rate (CR, °C / second) from after soaking until 600°C are appropriately controlled, so as to coarsen the distribution of precipitates in the fine structure of the steel sheet.

[0055] [Relational expression 2]

[0056] 1.0 ≤ (HR + CR) / 1000{([Al] + [Mn]) ([N] + [S])} ≤ 10.0

[0057] Specifically, the important elements whose addition amounts and contents need to be controlled in the present invention are Si, Al, Mn, N, and S. The most effective method for reducing iron loss is to increase the specific resistance of the steel by adding Si, Al, and Mn. In particular, in the high-frequency region, the proportion of eddy current loss in the iron loss further increases, and the effect of increasing the specific resistance becomes greater. However, as the addition amounts of Si, Al, Mn, etc. increase, the iron loss decreases, but the saturation magnetic flux density decreases, deteriorating the magnetic flux density, and it will also increase the brittleness of the material, deteriorating the cold rolling property and reducing the productivity. Therefore, in order to ensure the characteristics of low iron loss, high magnetic flux density, and productivity, not only the addition amounts of Si, Al, and Mn need to be controlled, but also the addition ratios of various elements need to be appropriately combined, and thus the said relational expression 1 is proposed.

[0058] In addition, it is well known that Al and Mn are elements that combine with N and S to form nitrides and sulfides. In non-oriented electrical steel sheets, when there are precipitates in the steel, the grain growth is inhibited and the hysteresis loss increases, thus deteriorating the magnetic properties. Therefore, when the addition amounts of Al and Mn increase, it is necessary to more actively control N and S, and to maximize the suppression of the deterioration of magnetic properties by forming coarser nitrides and sulfides, etc. For this purpose, not only in terms of composition control, but also in the manufacturing process, especially in the hot rolled sheet annealing process, which is very important for the formation and distribution of precipitates, it is necessary to strictly control the conditions. In this regard, the said relational expression 2 is proposed in the present invention.

[0059] The non-oriented electrical steel sheet of the present invention obtained from this viewpoint contains, by weight %: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and unavoidable impurities. Al, Si, and Mn satisfy the following relational expression 1, and a precipitation component distribution satisfying the following relational expression 3 is exhibited in the fine structure of the steel sheet. This electrical steel sheet of the present invention can exhibit excellent high-frequency iron loss and magnetic flux density, has a specific resistance (ρ) of 63 μΩcm or more at room temperature, an iron loss (W10 / 400) of 12.0 W / Kg or less, and a magnetic flux density (B50) of 1.60 T or more.

[0060] [Relational expression 1]

[0061] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00

[0062] Wherein, [Al], [Mn], and [Si] are the addition amounts (weight %) of Al, Mn, and Si, respectively.

[0063] [Relational expression 3]

[0064] In the fine structure of the steel, the proportion of the number of sulfides and nitrides of 0.2 μm or more in the precipitates having a size of 0 - 0.5 μm ≥ 10%

[0065] Hereinafter, the reasons for restricting the composition components and contents of the electrical steel sheet of the present invention will be described, where “%” represents weight %.

[0066] Si: 2.50 - 4.50% or less

[0067] The Si is a main element added to increase the specific resistance of the steel and reduce the eddy current loss in the iron loss. In order to ensure low iron loss, especially the low iron loss characteristics in the high-frequency region, it is necessary to add 2.50% or more. In addition, as the addition amount increases, the magnetic flux density decreases significantly, and the increase in brittleness results in poor rollability. Therefore, it is preferable to limit the addition amount of Si to 4.50% or less. More preferably, the addition amount of Si is limited to 3.00 - 4.00%.

[0068] Mn: 0.10 to 2.50% or less

[0069] The Mn is an element that, together with Si, Al, etc., increases the specific resistance and reduces the iron loss, and is also an element that improves the texture. However, when the addition amount of Mn is too small, fine sulfides are formed, and when the addition amount is too large, the magnetic flux density is significantly reduced. Therefore, the addition amount is limited to 0.10 - 2.50%. More preferably, the addition amount of Mn is limited to 0.50 - 2.00%.

[0070] Al: 0.50 - 2.50%

[0071] The Al, together with Si, plays an important role in increasing the specific resistance and reducing the iron loss, and is an element added to reduce the magnetic anisotropy to reduce the magnetic deviation between the rolling direction and the direction perpendicular to rolling. However, when the addition amount is small, the effect of reducing the iron loss is not significant, and when the addition amount is too large, the magnetic flux density deteriorates significantly. Therefore, the addition amount of Al is limited to 0.50 - 2.50%. More preferably, the addition amount of Al is limited to 0.60 - 2.00%.

[0072] C: 0.0050% or less

[0073] C combines with Ti, Nb, etc. to form carbides, thereby deteriorating the magnetism. When used after processing the final product into an electrical product, the iron loss increases due to magnetic aging, reducing the efficiency of the electrical device. Therefore, the content of C is preferably limited to 0.0050% or less.

[0074] S: 0.0010 - 0.0050%

[0075] S is an element that forms sulfides such as MnS, CuS, and (Cu, Mn)S that are harmful to the magnetic properties. Therefore, it is preferable to add as little S as possible. However, when the addition amount of S is less than 0.0010%, it is instead unfavorable for forming the texture, promoting the formation of fine sulfides and reducing the magnetism. Therefore, the content of S is set to 0.0010% or more. In addition, when the addition amount of S exceeds 0.0050%, the magnetism deteriorates due to the increase in sulfides. Therefore, the addition amount of S is set to 0.0010 - 0.0050%.

[0076] N: 0.0050% or less

[0077] N is an element harmful to the magnetism. For example, the N combines firmly with Al, Ti, Nb, etc. to form nitrides and inhibit grain growth, etc. Therefore, it is preferable to contain less N. In the present invention, the content of N is limited to 0.0050% or less.

[0078] Ti: 0.0050% or less

[0079] Ti combines with C and N to form fine carbides and nitrides, which inhibit grain growth, resulting in a deterioration of the magnetic flux density. As the addition amount increases, the texture deteriorates due to the increased carbides and nitrides, leading to a deterioration of the magnetism. Therefore, in the present invention, it is limited to 0.0050% or less.

[0080] P: 0.002 - 0.020%

[0081] P is a grain boundary and surface segregation element, which has the effect of improving the texture of steel. However, when the addition amount of P is less than 0.002%, the effect is very small. When the addition amount of P exceeds 0.02%, it inhibits grain growth, the iron loss deteriorates, and due to grain boundary segregation, the rollability deteriorates and the productivity also decreases. Therefore, the addition amount of P needs to be controlled within 0.002 - 0.020%. More preferably, the addition amount of P is limited to 0.003 - 0.010%.

[0082] In addition to the above elements, Sn and Sb are generally known as elements that improve the texture, and Sn and Sb can also be added to further improve the magnetism. However, when the addition amounts of Sn and Sb are excessive, they inhibit grain growth and deteriorate the magnetism. Therefore, in the present invention, one or more of Sn and Sb in the range of 0.2% or less can be further included.

[0083] In addition, in the case of Cu and Ni, although Cu and Ni can be added for reasons such as improving the magnetism, they react with impurity elements to form fine sulfides, carbides and nitrides, which may have an adverse effect on the magnetism. Therefore, in the present invention, one or more of Cu and Ni in the range of 0.05% or less can be further included.

[0084] In the case of Cr, it is similar to Cu and Ni, but has the effect of improving the magnetism by increasing the specific resistance. Therefore, Cr can be added in the range of 0.1% or less.

[0085] In addition, Zr, Mo, V, etc. are strong carbonitride-forming elements. Therefore, it is preferably not added as much as possible. In the present invention, one or a combination of two or more of Zr, Mo, and V in the range of 0.01% or less can be included.

[0086] Except for the above composition, the rest is composed of Fe and other inevitable impurities.

[0087] In addition, in the present invention, Si, Al, and Mn are added: Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, Al: 0.50 - 2.50%. The Al, Mn, and Si satisfy the following relational expression 1, and the specific reasons are as follows.

[0088] [Relational expression 1]

[0089] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00

[0090] Among them, [Al], [Mn], and [Si] are the addition amounts (weight %) of Al, Mn, and Si respectively.

[0091] The iron loss of non-oriented electrical steel sheets is divided into hysteresis loss and eddy current loss. If the specific resistance of the steel is increased by adding elements such as Si, Al, and Mn, the eddy current loss can be significantly reduced. In particular, as the frequency increases, the proportion of eddy current loss in the total iron loss increases. Therefore, in order to achieve excellent high-frequency iron loss, the specific resistance of the steel needs to be controlled above a certain level. It has been confirmed by the present invention that when the specific resistance (ρ) of the steel is 63 μΩ·cm or more, excellent properties can be ensured. Among Si, Al, and Mn, the element that most significantly increases the specific resistance of the steel is Si. However, an increase in the addition amount of Si will increase the brittleness of the steel, resulting in poor productivity. Therefore, in order to ensure the specific resistance of the steel is 63 μΩ·cm or more while ensuring productivity, it is necessary to add an appropriate amount of Al and Mn while adding Si. As a result of analyzing the appropriate addition ratio, the above-mentioned relational expression 1 is obtained. It is known that the effect of Al on increasing the specific resistance of the steel is greater than that of Mn, but it is not necessary to add more Al than Mn.

[0092] In addition, in the electrical steel sheet of the present invention, a precipitation component distribution satisfying the following relational expression 3 can be exhibited in the fine structure of the steel sheet.

[0093] [Relational expression 3]

[0094] In the precipitates with a size of 0 - 0.5 μm in the fine structure of the steel, the number ratio of sulfides and nitrides with a size of 0.2 μm or more ≥ 10%

[0095] More preferably, the fine structure of the steel can satisfy the following relational expression 4.

[0096] [Relational expression 4]

[0097] In the fine structure of the steel, the number of nitrides with a size of 0.5 μm or more ≥ 100 pieces / mm 2

[0098] The electrical steel sheet of the present invention exhibiting such a precipitate distribution can have a specific resistance (ρ) of 63 μΩ·cm or more at room temperature.

[0099] In addition, the iron loss (W10 / 400) can be 12.0 W / kg or less, and the magnetic flux density (B50) can be 1.60 T or more. Among them, the iron loss W10 / 40 is the average loss (W / kg) in the rolling direction and the direction perpendicular to rolling when a magnetic flux density of 1.0 tesla is induced at a frequency of 400 Hz, and the magnetic flux density B50 is the size (tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0100] Next, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail.

[0101] The method for manufacturing a non-oriented electrical steel sheet of the present invention is characterized by including the following processes: reheating a slab, which, by weight %, contains: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and unavoidable impurities; hot rolling the reheated slab to produce a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet and then performing hot-strip annealing or performing hot-strip annealing without cold rolling; pickling the steel sheet after the hot-strip annealing and then performing air cooling; cold rolling the hot-rolled steel sheet after the air cooling; and finally annealing the cold-rolled steel sheet after the cold rolling, wherein Al, Si, and Mn satisfy the relational expression 1, and during the hot-strip annealing process, the soaking temperature is controlled within the range of 850 - 1100°C, the soaking time is controlled within the range of 30 - 300 seconds, and the heating rate (HR, °C / second) from 600°C to the soaking zone temperature during heating and the cooling rate (CR, °C / second) after soaking until 600°C are controlled to satisfy the following relational expression 2.

[0102] That is, the non-oriented electrical steel sheet of the present invention can be manufactured by subjecting a steel slab having the above-described composition to normal reheating, hot rolling, hot-strip annealing, pickling followed by cold rolling, and cold-rolled sheet annealing. At this time, the cold rolling can be performed one or two times, and intermediate annealing is performed therebetween. The following description of the manufacturing conditions is representative of the implementation content and does not necessarily correspond only to the following conditions.

[0103] Preferably, the steel slab is reheated to 1200°C or less and then hot rolled. This is because when the reheating temperature is 1200°C or higher, precipitates such as nitrides, carbides, and sulfides present in the slab redissolve and then finely precipitate during hot rolling and annealing, inhibiting grain growth and thus reducing magnetism.

[0104] The hot-rolled plate after hot rolling is coiled at a temperature below 700°C and cooled in air. The coiled and cooled hot-rolled plate is subjected to hot-rolled plate annealing before cold rolling to ensure a recrystallized structure. The hot-rolled plate annealing conditions are very important processes for improving the texture in non-oriented electrical steel sheets and are also very important processes for controlling the distribution of precipitates. In non-oriented electrical steel sheets, the more precipitates there are, the worse the magnetic properties. As the existing precipitates become finer, the magnetic properties deteriorate significantly. In addition, in order to reduce iron loss, as the alloy addition amount increases, the precipitation temperature and distribution of precipitates also change, so it is necessary to control the hot-rolled plate annealing conditions suitable for the composition system. Therefore, it is necessary to control the precipitates in the hot-rolled plate annealing process, which is the final heat treatment process, that can control the distribution of precipitates before the final annealing.

[0105] As a result of various analyses by the present inventors, it was confirmed that by controlling the holding time at the soaking temperature, the heating rate from 600°C to the soaking temperature, and the cooling rate from the soaking heat treatment to 600°C in the hot-rolled plate annealing process according to the composition, the distribution of precipitates becomes coarse, and the deterioration of magnetic properties can be suppressed to the maximum extent, thereby ensuring excellent magnetic properties.

[0106] At this time, the holding time at the soaking temperature in the hot-rolled plate annealing process should be 30 seconds or more to form coarse precipitates. When the holding time is less than 30 seconds, fine precipitates are formed. When the holding time is too long, the grains become too coarse and the cold rolling property deteriorates. Therefore, it is judged that the holding time is preferably 300 seconds or less.

[0107] The soaking temperature in the hot-rolled plate annealing process is preferably in the range of 850 - 1100°C. When the hot-rolled plate annealing temperature is below 850°C, the grain growth is insufficient, the texture deteriorates, and the distribution of precipitates cannot be controlled. When the hot-rolled plate annealing temperature exceeds 1100°C, the grain growth becomes coarse, the cold rolling property deteriorates, and fine precipitates are precipitated, resulting in poor magnetic properties.

[0108] In addition, in the hot-rolled plate annealing process, when the sum of the heating rate (HR, °C / second) from 600°C to the soaking temperature and the cooling rate (CR, °C / second) from the soaking heat treatment to 600°C is too fast, fine precipitates are formed. On the other hand, when the sum of the heating rate (HR, °C / second) from 600°C to the soaking temperature and the cooling rate (CR, °C / second) from the soaking heat treatment to 600°C is too slow, the texture deteriorates. Therefore, it needs to be controlled within an appropriate range, and the appropriate range needs to be controlled according to the composition. As the composition content changes, it is necessary to reflect the behavior of precipitates to control the conditions. The range for ensuring the best magnetic properties is represented by the following relational expression 2.

[0109] [Relational expression 2]

[0110] 1.0 ≤ (HR + CR) / 1000{([Al] + [Mn]) ([N] + [S])} ≤ 10.0

[0111] Wherein, the [Al], [Mn], [N], and [S] are respectively the addition amounts (weight %) of Al, Mn, N, and S.

[0112] The heating rate from 600°C to the soaking temperature and the cooling rate after the soaking heat treatment until 600°C are preferably controlled respectively in the range of more than 5°C / second and less than 100°C / second to ensure a uniform fine microstructure and texture.

[0113] Next, in the present invention, the hot-rolled sheet annealed by the usual method is pickled and then cold-rolled.

[0114] The cold rolling is finally rolled to a thickness of 0.10 - 0.30 mm. The thickness of the final product has a great influence on the iron loss, and a considerable influence on the high-frequency iron loss. Therefore, in order to ensure excellent high-frequency iron loss, it should be 0.3 mm t or less. The cold rolling can be carried out by single cold rolling if necessary, or by double cold rolling with an intermediate annealing provided therebetween. In any case, the final reduction ratio should be in the range of 50 - 95% so as to ensure excellent magnetic properties by controlling an appropriate texture.

[0115] And the cold-rolled steel sheet is finally annealed as a cold-rolled sheet. In the process of annealing the cold-rolled sheet, there is no great limitation as long as the annealing temperature is the temperature usually applied to non-oriented electrical steel sheets.

[0116] The iron loss of the non-oriented electrical steel sheet is closely related to the grain size. The iron loss of the non-oriented electrical steel sheet can be divided into hysteresis loss and eddy current loss. The hysteresis loss decreases as the grain size increases, while on the other hand, the eddy current loss increases as the grain size increases. Therefore, there is an appropriate grain size at which the sum of the hysteresis loss and the eddy current loss becomes the minimum. Therefore, it is important to obtain and apply an annealing temperature that can ensure the optimum grain size, and the annealing temperature is preferably 850 - 1100°C. When the annealing temperature is lower than 850°C, the grains are overly fine and the hysteresis loss increases. When the annealing temperature exceeds 1100°C, the grains are overly coarse and the eddy current loss increases, and the iron loss may deteriorate.

[0117] The final annealed sheet is sent to the customer company after being treated with an insulating film. The insulating film can be treated with an organic, inorganic, and organic-inorganic composite film, or can be treated with other coating agents that can insulate. The customer company can directly use it after processing the steel sheet.

[0118] The fine structure of the non-oriented electrical steel sheet of the present invention manufactured by the above-described components and manufacturing process can exhibit a precipitate distribution that satisfies the following relational expression 3. Therefore, it is possible to impart excellent high-frequency iron loss characteristics with a specific resistance (ρ) of 63 μΩcm or more at room temperature, an iron loss (W10 / 400) of the steel sheet of 12.0 W / Kg or less, and a magnetic flux density (B50) of 1.60 T or more.

[0119] [Relational expression 3]

[0120] In the fine structure of the steel, the quantity ratio of sulfides and nitrides of 0.2 μm or more in precipitates having a size of 0 - 0.5 μm ≥ 10% Detailed implementation mode

[0121] Hereinafter, through examples, the manufacturing method of the non-oriented electrical steel sheet according to the present invention will be described in detail. However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited to the following examples.

[0122] (Example)

[0123] Steel ingots having the composition components described in Table 1 below are manufactured by vacuum melting. Each of the manufactured steel ingots is heated at 1180 °C and then hot-rolled to a thickness of 2.1 mm. Then, after winding, it is cooled in air. Thereafter, the cooled hot-rolled sheet is subjected to hot-rolled sheet annealing under the conditions of Table 2 below. Specifically, by changing the heating rate (HR, °C / second) from 600 °C to the soaking zone temperature and the cooling rate (CR, °C / second) after soaking until 600 °C according to the heat treatment time at the soaking temperature during hot-rolled sheet annealing and the contents of the steel components Si, Al, Mn, N, and S, the distribution of the formed precipitates and their influence on magnetism can be analyzed. In addition, the hot-rolled sheet after the hot-rolled sheet annealing is pickled and then cold-rolled to a thickness of 0.2 mm, and then it is finally subjected to cold-rolled sheet annealing at a temperature in the range of 900 - 1050 °C.

[0124] As described above, for each of the manufactured test pieces, the specific resistance at room temperature is measured, and the results are shown in Table 2 below. In addition, TEM replica test pieces are produced, and the distribution of precipitates such as sulfides and nitrides in the test piece structure is observed and analyzed, and the results according to relational expression 3 and relational expression 4 are shown in Table 2 below.

[0125] After processing the magnetic measurement test piece, the iron loss W10 / 400 and the magnetic flux density B50 were measured, and the results are shown in Table 2 below. In addition, in this experiment, the iron loss W10 / 400 represents 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 B50 represents the size (tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0126] [Table 1]

[0127]

[0128] In Table 1, the remaining components are Fe and unavoidable impurities, and Relationship 1 is ([Al] + [Mn]) / [Si].

[0129] [Table 2]

[0130]

[0131] In Table 2, Relationship 2 is (HR + CR) / 1000 {([Al] + [Mn]) ([N] + [S])}, the heating rate (HR) is the heating rate from 600 °C to the soaking temperature zone, and the cooling rate (CR) is the cooling rate from the soaking heat treatment until 600 °C.

[0132] And Relationship 3 refers to the quantity ratio (%) of sulfides and nitrides with a size of 0.2 μm or more in the precipitates with a size of 0 - 0.5 μm in the fine structure of the steel, and Relationship 4 refers to the quantity of nitrides with a size of 0.5 μm or more in the fine structure of the steel.

[0133] As shown in Tables 1 to 2, among the steels numbered 1 to 15 (inventive examples) that satisfy the composition and manufacturing process conditions of the electrical steel sheet of the present invention, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more in the precipitates with a size of 0 - 0.5 μm of Relationship 3 is 10% or more, and the quantity of nitrides with a size of 0.5 μm or more according to Relationship 4 all satisfies 100 pieces / mm 2 , and thus shows very excellent magnetic properties with an iron loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more after final annealing. In addition, the specific resistance at room temperature is 63 μΩcm or more.

[0134] On the other hand, the addition amount of Mn in the 16th steel and Relationship 1 do not satisfy the scope of the present invention. As a result, the quantity of nitrides with a size of 0.5 μm or more of Relationship 4 is less than 100 pieces / mm 2 , and the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0135] In addition, the addition amounts of Mn and Al in Steel No. 17 and the relational expression 1 do not meet the scope of the present invention. As a result, in the precipitates with a size of 0 - 0.5 μm in relational expression 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, and the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0136] In addition, for Steel No. 18, the addition amount of Al and the relational expression 1 deviate from the scope of the present invention, and the heat treatment time at the soaking temperature during hot rolled sheet annealing is too short. As a result, the requirements of relational expressions 3 to 4 are not met, and the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor. In addition, the specific resistance (ρ) at room temperature does not meet 63 μΩ·cm or more.

[0137] In addition, for Steel No. 19, the addition amounts of Mn and Al and the requirements of relational expression 2 are not met during hot rolled sheet annealing, and relational expression 3 is not met, and the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0138] In addition, for Steel No. 20, not only the addition amounts of Mn and Al and the relational expression 1 are not met, but also the requirements of relational expression 2 are not met during hot rolled sheet annealing. In the precipitates with a size of 0 - 0.5 μm in relational expression 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, and the number of nitrides with a size of 0.5 μm or more in relational expression 4 is less than 100 per mm 2 , so the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0139] For Steel No. 21 and Steel No. 22, Si, Mn, and Al do not meet relational expression 1. Further, during hot rolled sheet annealing, relational expression 2 is not met. As a result, in the precipitates with a size of 0 - 0.5 μm in relational expression 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, and the number of nitrides with a size of 0.5 μm or more in relational expression 4 is also less than 100 per mm 2 , so the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0140] For Steel No. 23, the composition components and the components meet relational expression 1, but the heat treatment time at the soaking temperature during APL annealing is not met. The number of nitrides with a size of 0.5 μm or more in relational expression 4 is less than 100 per mm 2 , and the iron loss W10 / 400 and the magnetic flux density B50 are shown to be poor.

[0141] Similar to Steel No. 23, Steel No. 24 is a case where the compositional components and compositional relationship formula 1 are satisfied, but the heat treatment time at the soaking temperature during APL annealing does not meet the requirements of formula 2. In the precipitates with a size of 0 - 0.5 μm in formula 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, and the number of nitrides with a size of 0.5 μm or more in formula 4 is less than 100 per mm 2 , and the iron loss W10 / 400 and magnetic flux density B50 are shown to be poor.

[0142] Steel No. 25 is a case where the contents of Si, Mn, and Al are within the scope of the present invention, but the requirements of formula 1 and formula 2 are not met. In the precipitates with a size of 0 - 0.5 μm in formula 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, and the number of nitrides with a size of 0.5 μm or more in formula 5 is less than 100 per mm 2 , and the iron loss W10 / 400 and magnetic flux density B50 are shown to be poor. And the specific resistance (ρ) at room temperature does not meet the condition of 63 μΩcm or more.

[0143] Steel No. 26, Steel No. 27, and Steel No. 28 are cases where the soaking time etc. are met during hot-rolled sheet annealing, but the requirements of formula 2 are not met. In the precipitates with a size of 0 - 0.5 μm in formula 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more is less than 10%, or the number of nitrides with a size of 0.5 μm or more in formula 4 is less than 100 per mm 2 , so the iron loss W10 / 400 and magnetic flux density B50 are shown to be poor.

[0144] Steel No. 29 is a case where not only Si, Mn, and Al do not meet formula 1, but also the soaking time condition of 30 - 300 seconds during hot-rolled sheet annealing and the requirements of formula 2 are not met. In the precipitates with a size of 0.5 μm in formula 3, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more does not meet the requirement of being less than 10%, and the number of nitrides with a size of 0.5 μm or more in formula 4 does not meet the requirement of being less than 100 per mm 2 , so the iron loss W10 / 400 and magnetic flux density B50 are shown to be poor.

[0145] In addition, Steel No. 30 is a case where not only Si, Mn, and Al do not meet formula 1, but also the soaking time condition of 30 - 300 seconds during hot-rolled sheet annealing and the requirements of formula 2 are not met. The number of nitrides with a size of 0.5 μm or more in formula 4 is less than 100 per mm 2 , and the iron loss W10 / 400 and magnetic flux density B50 are shown to be poor. In addition, the specific resistance (ρ) at room temperature does not meet the condition of 63 μΩcm or more.

[0146] The above has been described with reference to the embodiments. However, it should be clear that for those skilled in the art, within the scope of the basic idea of the present invention, various modifications and changes can be made to the present invention, and the scope of the rights of the present invention should be interpreted based on the scope of the claims.

Claims

1. An non-oriented electrical steel sheet, by weight %, the non-oriented electrical steel sheet comprises: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and inevitable impurities, Al, Si and Mn satisfy the following relational expression 1, and the precipitated component distribution satisfying the following relational expression 3 is exhibited in the fine structure of the steel sheet. [Relational expression 1] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.0 Among them, [Al], [Mn], and [Si] are the addition amounts of Al, Mn, and Si respectively, with the unit of weight %. [Relational expression 3] In the fine structure of the steel, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more in the precipitates with a size of 0 - 0.5 μm ≥ 10%.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The fine structure of the steel sheet satisfies the following relational expression 4. [Relationship 4] The number of nitrides with a size of 0.5 μm or more in the fine structure of steel ≥ 100 pieces / mm 2 .

3. The non-oriented electrical steel sheet according to claim 1, wherein, The specific resistance (ρ) of the non-oriented electrical steel sheet at room temperature is 63 μΩcm or more.

4. The non-oriented electrical steel sheet according to claim 1, wherein, The iron loss (W10 / 400) of the non-oriented electrical steel sheet is 12.0 W / Kg or less, and the magnetic flux density (B50) is 1.60 T or more. Among them, the iron loss W10 / 40 is the average loss in the rolling direction and the direction perpendicular to rolling when a magnetic flux density of 1.0 tesla is induced at a frequency of 400 Hz, with the unit of W / Kg, and the magnetic flux density B50 is the size of the magnetic flux density induced when a magnetic field of 5000 A / m is applied, with the unit of tesla.

5. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Sn and Sb in the range of 0.2% or less.

6. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Cu and Ni in the range of 0.05% or less.

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

8. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Zr, Mo, and V in the range of 0.01% or less.

9. A method for manufacturing a non-oriented electrical steel sheet, characterized in that, The manufacturing method includes the following processes: reheating a slab, by weight %, the slab comprises: C: 0.005% or less, Si: 2.50 - 4.50%, Mn: 0.10 - 2.50%, P: 0.002 - 0.020%, S: 0.0010 - 0.0050%, Al: 0.50 - 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, the balance being Fe and inevitable impurities; hot rolling the reheated slab to manufacture a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet and then performing hot-rolled sheet annealing or performing hot-rolled sheet annealing without cold rolling; pickling the steel sheet after the hot-rolled sheet annealing and then performing air cooling; cold rolling the hot-rolled steel sheet after the air cooling; and finally annealing the cold-rolled steel sheet after the cold rolling. Among them, the Al, Si, and Mn satisfy the following relational expression 1. During the annealing process of the hot-rolled sheet, the soaking temperature is controlled within the range of 850 - 1100 °C, the soaking time is controlled within the range of 30 - 300 seconds, and the heating rate (HR) from 600 °C to the soaking zone temperature and the cooling rate (CR) from the soaking temperature until 600 °C are controlled to satisfy the following relation 2. The unit of the cooling rate is °C / second. [Relation 1] 0.60 ≤ ([Al] + [Mn]) / [Si] ≤ 1.00 where [Al], [Mn], and [Si] are the addition amounts of Al, Mn, and Si respectively, with the unit of weight %. [Relationship 2] 1.0 ≤ (HR + CR) / 1000{([Al] + [Mn]) ([N] + [S])} ≤ 10.0 where [Al], [Mn], [N], and [S] are the addition amounts of Al, Mn, N, and S respectively, with the unit of weight %.

10. The manufacturing method of the non-oriented electrical steel sheet according to claim 9, wherein, The heating rate (HR) and the cooling rate (CR) are 5 - 100 °C / second respectively.

11. The manufacturing method of the non-oriented electrical steel sheet according to claim 9, wherein, In the electrical steel sheet after the final annealing, the precipitation composition distribution satisfying Relations 3 and 4 is exhibited in the fine structure of the steel sheet. The specific resistance (ρ) at room temperature is 63 μΩcm or more, the iron loss (W10 / 400) after the final annealing is 12.0 W / Kg or less, and the magnetic flux density (B50) is 1.60 T or more. [Relation 3] In the fine structure of the steel, the quantity ratio of sulfides and nitrides with a size of 0.2 μm or more in the precipitates with a size of 0 - 0.5 μm ≥ 10% [Relationship 4] The number of nitrides with a size of more than 0.5 μm in the fine structure of steel ≥ 100 pieces / mm 2 .

Images