Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention comprises: 2.8-4.0 wt% of silicon (Si); 0.5-1.5 wt% of aluminum (Al); 0.2-0.5 wt% of manganese (Mn); more than 0 wt% but not more than 0.003 wt% of antimony (Sb); more than 0 wt% but not more than 0.003 wt% of tantalum (Ta); more than 0 wt% but not more than 0.003 wt% of niobium (Nb), and the remainder of iron (Fe) and other inevitable impurities, and satisfies equation 1, thus enabling implementation of a non-oriented electrical steel sheet with low core loss and a method for manufacturing the non-oriented electrical steel sheet.

Description

Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet.

[0002] In line with recent global policies to reduce carbon dioxide emissions to combat global warming, conventional internal combustion engine vehicles are rapidly being replaced by eco-friendly vehicles such as hybrid, electric, and hydrogen-powered vehicles. Eco-friendly vehicles utilize electric motors to generate the necessary driving force and significantly reduce harmful exhaust gas emissions, thereby minimizing environmental pollution.

[0003] As interest in and demand for eco-friendly vehicles grows, so does the demand for electric motors, which power these vehicles. Electric motors use electricity to generate the power needed for vehicles. These electric motors must be capable of delivering high output to replace the output of internal combustion engines, while also being energy efficient to enable longer operation times using the same amount of energy.

[0004] To improve the output and energy efficiency of electric motors, it is essential to improve the magnetic properties of non-oriented electrical steel used as the core material. Representative magnetic properties of non-oriented electrical steel include core loss and magnetic flux density. To improve the output and energy efficiency of electric motors, core loss must be reduced and magnetic flux density increased.

[0005] The core loss and magnetic flux density of non-oriented electrical steel sheets are affected by their grain structure. Generally, it is known that magnetic properties are the best when the grains have {001} planes based on the ND (Normal Direction) plane. On the other hand, magnetic properties are known to be inferior when the grains have {111} planes. Furthermore, it is known that magnetic properties are worse when the grains have {110} planes than when they have {001} planes, and more favorable when they have {111} planes.

[0006] Therefore, in order to have excellent magnetic properties, the growth of crystal grains with {111} planes, which are unfavorable for magnetic properties, must be suppressed, and crystal grains with {001} planes, which are advantageous for magnetic properties, must be grown.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] (Patent Document 1) Republic of Korea Patent No. 2653156

[0010] The present invention has been devised to solve the above problems, and the object of the present invention is to provide a non-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing a non-oriented electrical steel sheet by controlling the content of additive elements and the formation of inclusions to suppress the formation of aggregate structures having unfavorable magnetic properties.

[0011] The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention includes 2.8 wt% or more and 4.0 wt% or less of silicon (Si), 0.5 wt% or more and 1.5 wt% or less of aluminum (Al), 0.2 wt% or more and 0.5 wt% or less of manganese (Mn), 0 wt% or more and 0.003 wt% or less of antimony (Sb), 0 wt% or more and 0.003 wt% or less of tantalum (Ta), and 0 wt% or more and 0.003 wt% or less of niobium (Nb), with the remainder being iron (Fe) and other unavoidable impurities, and satisfying the following equation 1.

[0013] [Formula 1]

[0014] 10 ≤ [Sb]+[Ta]+[Nb] ≤ 90

[0015] (However, in the above formula 1, [Sb], [Ta], and [Nb] represent the contents of Sb, Ta, and Nb in ppm, respectively.)

[0016] In addition, the following equation 2 can be satisfied.

[0017] [Formula 2]

[0018] 3.0 ≤ [0.71(An * Av) + 0.29(Bn * Bv)]*100 ≤ 5.0

[0019] However, in the above formula 2, An represents the number of inclusions having a size of 150 nm or more and less than 330 nm, Av represents the average volume of inclusions having a size of 150 nm or more and less than 330 nm (the volume of a sphere converted based on the average diameter), Bn represents the number of inclusions having a size of 330 nm or more, and Bv represents the average volume of inclusions having a size of 330 nm or more (the volume of a sphere converted based on the average diameter).

[0020] Here, the average inclusion volume is defined as the average of all measured inclusion diameters, calculated as the diameter of a circle with the same area as the area of ​​the inclusion measured in the SEM image, and the volume when the inclusion is calculated as a sphere. Furthermore, the inclusion diameter referred to here can also mean the average of the converted diameters of all inclusions measured within a given unit area.

[0021] In addition, it may further include at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

[0022] Also, iron loss (W 10 / 400 ) may be less than 12.5 W / kg.

[0023] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a steel preparation step of preparing a steel sheet including the above-described alloy composition, a hot rolling step of hot-rolling the steel sheet to form a hot-rolled steel sheet, a hot-rolling annealing step of annealing the hot-rolled steel sheet, a cold-rolling step of cold-rolling the hot-rolled steel sheet subjected to the hot-rolling annealing step to form a cold-rolled steel sheet, and a cold-rolling annealing step of annealing the cold-rolled steel sheet at 800 to 1100°C for 30 to 120 seconds.

[0024] In addition, the steel may further include at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

[0025] According to one embodiment of the present invention, by controlling the contents of Sb, Ta, and Nb and the cold rolling annealing conditions to control the formation of crystal grains and inclusions, the formation of aggregate structures that are unfavorable to magnetic properties can be suppressed, thereby realizing a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties.

[0026] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0027] Figure 1 is a graph showing the change in iron loss according to the silicon (Si), aluminum (Al), and manganese (Mn) content.

[0028] Figure 2 is a graph showing the change in size when the inclusions are arranged in order of size.

[0029] Figure 3 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention is not limited or restricted by the following embodiments.

[0031] Additionally, when a component (or region, layer, portion, etc.) is referred to as being "on," "connected to," or "coupled to" another component, it means that it can be directly placed / connected / coupled to the other component, or that a third component may be placed between them.

[0032] Terms such as "include" or "have" should be understood to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0033] In order to clearly explain the present invention, a detailed description of a part that is irrelevant to the description or a related known technology that may unnecessarily obscure the gist of the present invention has been omitted, and when adding reference signs to components of each drawing in this specification, the same or similar reference signs are attached to the same or similar components throughout the specification.

[0034] In addition, terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0035] Unless otherwise specified, the notation 'A to B' for numerical values ​​A and B means 'A or more and B or less'. In such notation, if a unit is attached only to numerical value B, the unit shall also be applied to numerical value A.

[0036] Also, unless otherwise stated, 1 ppm is 0.0001 wt%.

[0037]

[0038] Non-oriented electrical steel sheet

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 2.8 wt% or more and 4.0 wt% or less of silicon (Si), 0.5 wt% or more and 1.5 wt% or less of aluminum (Al), 0.2 wt% or more and 0.5 wt% or less of manganese (Mn), 0 wt% or more and 0.003 wt% or less of antimony (Sb), 0 wt% or more and 0.003 wt% or less of tantalum (Ta), and 0 wt% or more and 0.003 wt% or less of niobium (Nb), with the remainder being iron (Fe) and other unavoidable impurities.

[0040] Hereinafter, the role and content of alloy elements included in a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0041]

[0042] Silicon (Si)

[0043] Silicon (Si) is an element that increases the resistivity of steel and reduces iron loss, making it a key additive in electrical steel. If the silicon content is too low, the iron loss improvement effect may be insufficient. Conversely, excessive silicon additions can lead to reduced magnetic flux density and increased brittleness. Therefore, it is important to appropriately control the silicon content.

[0044] As shown in Fig. 1, when the silicon content is less than 2.8 wt%, the iron loss improvement effect is insufficient, and when the silicon content exceeds 4.0 wt%, brittleness increases, which may cause plate breakage during rolling.

[0045] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain silicon in an amount of 2.8 wt% or more and 4.0 wt% or less.

[0046]

[0047] Aluminum (Al)

[0048] Aluminum (Al), along with silicon (Si), increases resistivity and reduces iron loss, making it a key additive in electrical steel. However, excessive addition of Al can combine with nitrogen (N) in the steel to form AlN particles. These AlN particles can hinder the formation of a magnetically favorable texture and hinder domain wall movement, thereby degrading magnetic properties.

[0049] As shown in Fig. 1, when the aluminum content is less than 0.5 wt%, the iron loss reduction is insufficient, and when the aluminum content exceeds 1.5 wt%, the iron loss may be deteriorated due to the formation of inclusions.

[0050] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain aluminum in an amount of 0.5 wt% or more and 1.5 wt% or less.

[0051]

[0052] manganese (Mn)

[0053] Manganese (Mn), like silicon (Si) and aluminum (Al), is an element that improves magnetic properties by increasing resistivity and reducing iron loss. It can also enhance the fraction of grain structures with favorable magnetic properties. If the manganese content is too low, the aforementioned effects cannot be achieved.

[0054] On the other hand, excessive manganese content can lead to the formation of fine inclusions. These fine inclusions can impede domain wall and grain boundary movement, hindering the formation of a texture favorable for magnetic properties, thereby degrading magnetic properties. Furthermore, if these inclusions grow coarsely, they can reduce mechanical strength.

[0055] As shown in Fig. 1, when the manganese content is less than 0.2 wt%, the iron loss improvement effect is insufficient, and when the manganese content exceeds 0.5 wt%, the iron loss may increase due to the formation of inclusions.

[0056] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain manganese in an amount of 0.2 wt% or more and 0.5 wt% or less.

[0057]

[0058] antimony (Sb)

[0059] Antimony (Sb), when employed in small amounts, can reduce the austenite region and improve magnetic properties. Furthermore, depending on the heat treatment temperature, it can segregate on the steel plate surface, forming inclusions. These segregated inclusions inhibit the growth of grains with {111} planes, which are detrimental to magnetic properties, and prevent excessive grain growth, which can lead to increased iron loss.

[0060] The above-described effects cannot be expected if antimony is not added. On the other hand, if antimony is added in excess of 0.003 wt%, the decrease in magnetic properties due to excessive segregation may be greater than the improvement in magnetic properties due to grain suppression, resulting in inferior magnetic properties.

[0061] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain antimony in an amount of more than 0 wt% and less than or equal to 0.003 wt%.

[0062]

[0063] Tantalum (Ta)

[0064] Tantalum (Ta) is a grain-refining element that can improve magnetic properties by suppressing the growth of grains with {111} planes, which are unfavorable for magnetic properties. However, it easily combines with carbon (C) in steel to form carbides, so it is important to appropriately control its content.

[0065] If the tantalum content exceeds 0.003 wt%, carbides may form, which may deteriorate magnetic properties. On the other hand, if no tantalum is added, the aforementioned effects cannot be expected.

[0066] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain tantalum in an amount of more than 0 wt% and less than 0.003 wt%.

[0067]

[0068] niobium (Nb)

[0069] Niobium (Nb), like tantalum (Ta), can refine grains. Furthermore, by increasing the grain growth temperature, it can suppress the excessive growth of grains with {111} planes, which are detrimental to magnetic properties. Furthermore, it can prevent iron loss degradation due to coarse grains. Without the addition of niobium, the aforementioned effects cannot be expected.

[0070] On the other hand, if the niobium content exceeds 0.003 wt%, excessive grain refinement may occur, which may result in poor iron loss. In addition, if added in excessive amounts, hardenability may be reduced and tempering brittleness may be reduced.

[0071] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain niobium in an amount of more than 0 wt% and less than or equal to 0.003 wt%.

[0072]

[0073] A non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following equation 1.

[0074] [Formula 1]

[0075] 10 ≤ [Sb] + [Ta] + [Nb] ≤ 90

[0076] However, in the above formula 1, [Sb], [Ta] and [Nb] represent the contents of antimony (Sb), tantalum (Ta) and niobium (Nb) in ppm content, respectively.

[0077] The above formula 1 is a formula for controlling the combined amount of antimony (Sb), tantalum (Ta), and niobium (Nb). Antimony (Sb), tantalum (Ta), and niobium (Nb) are key additive elements for controlling the growth of crystal grains, and by controlling their content, the growth of crystal grains with {111} planes, which are unfavorable for magnetic properties, can be suppressed, thereby improving magnetic properties.

[0078] This will be explained in more detail below.

[0079] Antimony (Sb) can suppress the movement and growth of grain boundaries and delay the recrystallization of the material, thereby inhibiting the growth of grains with {111} planes. Furthermore, tantalum (Ta) and niobium (Nb) have a grain refinement effect and can suppress the growth of grains with {111} planes by increasing the temperature at which grains grow.

[0080] In this way, by adding antimony (Sb), tantalum (Ta), and niobium (Nb), the growth of {111} planes, which are unfavorable to magnetic properties, can be suppressed, thereby preventing deterioration of iron loss.

[0081] At this time, if the combined amount of antimony (Sb), tantalum (Ta), and niobium (Nb) is less than 10 ppm, the growth of grains with {111} planes, which are unfavorable for magnetic properties, cannot be suppressed. In this case, grains with {111} planes, which are unfavorable for magnetic properties, may grow, increasing iron loss.

[0082] On the other hand, if the combined amount of antimony (Sb), tantalum (Ta), and niobium (Nb) exceeds 90 ppm, the grain size may become excessively small, which may increase iron loss and deteriorate magnetic properties. In addition, if additive elements such as antimony (Sb), tantalum (Ta), and niobium (Nb) are contained excessively, problems such as deterioration of magnetic properties due to surface segregation and deterioration of mechanical properties may occur.

[0083] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention can suppress the growth of crystal grains having a {111} plane, which is unfavorable to magnetic properties, by satisfying the above equation 1, thereby reducing iron loss and improving magnetic properties.

[0084]

[0085] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

[0086]

[0087] carbon (C)

[0088] Carbon (C) is an inevitable impurity element included during the steelmaking process, and can increase iron loss by combining with iron (Fe), niobium (Nb), titanium (Ti), etc. to form carbides. Furthermore, if the carbon content exceeds 0.003 wt%, self-aging can occur. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain carbon in an amount of 0.003 wt% or less.

[0089]

[0090] Person (P)

[0091] Phosphorus is a grain boundary segregation element, and if added excessively, problems such as grain growth inhibition, deterioration of magnetic properties, and reduction in cold rolling properties may occur due to the segregation effect. Therefore, it is preferable to add as little as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain phosphorus at 0.011 wt% or less.

[0092]

[0093] Yellow (S)

[0094] Sulfur (S) is an impurity element that is inevitably contained during the manufacturing process, and can combine with manganese (Mn) to form precipitates. If the sulfur content exceeds 0.003 wt%, the formed precipitates may impede the movement of the magnetic domain walls, resulting in deteriorated magnetic properties. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur in an amount of 0.003 wt% or less.

[0095]

[0096] Nitrogen (N)

[0097] Nitrogen (N) can combine with aluminum (Al) or titanium (Ti) to form nitrides such as AlN and TiN, which increase iron loss and thus deteriorate magnetic properties. In addition, when the nitrogen content exceeds 0.003 wt%, the formed nitrides can impede the movement of the magnetic domain walls, which can deteriorate magnetic properties. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain nitrogen in an amount of 0.003 wt% or less.

[0098]

[0099] Titanium (Ti)

[0100] Titanium (Ti) is an unavoidable impurity element contained during the steelmaking process. It reacts with dissolved elements within the steel to form inclusions. These inclusions can impede magnetic domain movement, potentially resulting in poor magnetic properties. Therefore, its content must be controlled, with a titanium content of 0.003 wt% or less being preferred.

[0101]

[0102] In addition to the aforementioned steel components, the remainder may contain iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the field, a detailed description will be omitted.

[0103] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are included, they may be included to replace the remaining Fe.

[0104]

[0105] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 2.

[0106] [Formula 2]

[0107] 3.0 ≤ [0.71(An * Av) + 0.29(Bn * Bv)]*100 ≤ 5.0

[0108] However, in the above formula 2, An represents the number of inclusions having a size of 150 nm or more and less than 330 nm, Av represents the average volume of inclusions having a size of 150 nm or more and less than 330 nm (the volume of a sphere converted based on the average diameter), Bn represents the number of inclusions having a size of 330 nm or more, and Bv represents the average volume of inclusions having a size of 330 nm or more (the volume of a sphere converted based on the average diameter).

[0109] Here, the average inclusion volume is defined as the average of all measured inclusion diameters, calculated as the diameter of a circle with the same area as the area of ​​the inclusion measured in the SEM image, and the volume when the inclusion is calculated as a sphere. Furthermore, the inclusion diameter referred to here can also mean the average of the converted diameters of all inclusions measured within a given unit area.

[0110] Below, the above equation 2 will be explained in more detail.

[0111] In the case of non-oriented electrical steel sheets, inclusions form within the steel sheet after cold rolling and annealing. These inclusions affect the magnetic properties depending on their size, number, and volume.

[0112] In general, coarse inclusions can impede domain wall movement, adversely affecting magnetic flux density. Furthermore, coarse inclusions themselves can act as weak points in the microstructure, degrading the mechanical properties of the steel sheet. Conversely, the formation of a large number of small inclusions can refine grain size, increasing iron loss.

[0113] In this way, the degree to which the inclusions affect the magnetic properties varies depending on their size, number, and volume.

[0114] As described above, magnetic properties can be controlled by controlling the number and volume of inclusions of different sizes. The present invention uses Equation 2 to control the number and volume of inclusions of different sizes.

[0115] Equation 2 is a formula for controlling the number and volume of inclusions of different sizes. (An*Av) is the small inclusion control variable, 0.71 is the weight assigned to the small inclusion control variable, (Bm*Bv) is the large inclusion control variable, and 0.29 is the weight assigned to the large inclusion control variable. Below, the method for measuring the size of the inclusion, the criteria for distinguishing between large and small inclusions, and the process of deriving the weights are sequentially explained with reference to Figure 2.

[0116] The size of the inclusions was determined as the average value of the sizes of the inclusions in the SEM images taken at three arbitrary points of the non-oriented electrical steel sheet of one embodiment. Specifically, the SEM images were taken at a magnification of 5000x so that 5 to 20 inclusions appeared in each image, and numbers were assigned in ascending order of the size of the inclusions in each of the taken SEM images, and the sum of the sizes of three inclusions with the same number was divided by 3 to derive the average value of the size of the inclusions.

[0117] Figure 2 is a graph listing inclusions in order of their size. Referring to Figure 2, it can be seen that the size of the inclusion changes rapidly in the range of 228.14 to 430.86 nm, which is between No. 10 and No. 11. 330 nm, which is the midpoint between the point where the rapid change in inclusion size begins (A) and the point where the rapid change in inclusion size ends (B), is used as the reference point (C), and inclusions with a size less than the reference point are defined as small inclusions, and inclusions with a size greater than the reference point are defined as large inclusions.

[0118] In one embodiment, the number of small inclusions in the non-oriented electrical steel sheet is confirmed to be 10, and the number of large inclusions is 4. Accordingly, the weight of the small inclusions is set to 0.71, which is the ratio of the number of small inclusions to the total number of inclusions, and the weight of the large inclusions is set to 0.29, which is the ratio of the number of large inclusions to the total number of inclusions. 0.71 is derived from 10 / 14, which is the "number of small inclusions / total number of inclusions," and 0.29 is derived from 4 / 14, which is the "number of large inclusions / total number of inclusions."

[0119] Through the above-described method, the characteristics of the inclusion can be quantified using the formula described in Equation 2.

[0120] In the above equation 2, when the value of [0.71(An * Av) + 0.29(Bn * Bv)] * 100 is less than 3.0, the formation of inclusions is insufficient, so the growth of crystal grains with {111} planes, which are unfavorable for magnetic properties, is limited, and the crystal grains grow excessively, increasing iron loss, etc., which may result in inferior magnetic properties.

[0121] On the other hand, if the value of [0.71(An * Av) + 0.29(Bn * Bv)]*100 in the above equation 2 exceeds 5.0, a large amount of inclusions may be formed, which may result in deterioration of magnetic properties due to excessive grain refinement. In addition, iron loss may increase due to some coarse inclusions.

[0122] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention can prevent deterioration of magnetic properties due to inclusions by satisfying the above equation 2.

[0123] More specifically, magnetic properties can be improved by suppressing the growth of grains with {111} planes, which are detrimental to magnetic properties, through appropriately formed inclusions, and by suppressing the increase in iron loss due to excessive grain growth. Furthermore, magnetic properties can be improved by preventing excessive grain refinement.

[0124] A non-oriented electrical steel sheet according to one embodiment of the present invention can have excellent magnetic properties. In addition, it can have good iron loss properties for use as an electric motor core material, and more specifically, it can have iron loss (W 10 / 400 ) may be less than 12.5 W / kg.

[0125] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0126]

[0127] Method for manufacturing non-oriented electrical steel sheet

[0128] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described with reference to FIG. 3.

[0129] Figure 3 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0130] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a steel preparation step of preparing steel, a hot rolling step of hot-rolling the steel to form a hot-rolled steel sheet, a hot-rolling annealing step of annealing the hot-rolled steel sheet, a cold-rolling step of cold-rolling the hot-rolled steel sheet that has undergone the hot-rolling annealing step to form a cold-rolled steel sheet, and a cold-rolling annealing step of cold-rolling the cold-rolled steel sheet.

[0131] At this time, the steel contains 2.8 wt% or more and 4.0 wt% or less of silicon (Si), 0.5 wt% or more and 1.5 wt% or less of aluminum (Al), 0.2 wt% or more and 0.5 wt% or less of manganese (Mn), 0 wt% or more and 0.003 wt% or less of antimony (Sb), 0 wt% or more and 0.003 wt% or less of tantalum (Ta), and 0 wt% or more and 0.003 wt% or less of niobium (Nb), and the remainder contains iron (Fe) and other unavoidable impurities, and satisfies the above formula 1.

[0132] In addition, the steel may further include at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

[0133] The alloy composition has been previously described, so a detailed explanation will be omitted. Furthermore, since the alloy composition does not substantially change during the manufacturing process described below, the alloy composition of the steel material and the alloy composition of the final product, the non-oriented electrical steel sheet, are substantially identical.

[0134] Hereinafter, each step of a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0135] The steel preparation step, which involves preparing steel, is a step for preparing semi-finished products for manufacturing the final product, non-oriented electrical steel sheet. More specifically, this step may involve designing alloy components within the alloy composition range according to one embodiment of the present invention to manufacture semi-finished products. The semi-finished products may be slabs, but are not necessarily limited thereto. Furthermore, the slabs may be manufactured using a steelmaking process known in the art, such as a casting process.

[0136] According to one embodiment of the present invention, a method for manufacturing a non-oriented electrical steel sheet may include, after the steel preparation step, performing a hot rolling step of hot-rolling the steel to form a hot-rolled steel sheet. The hot rolling step may include a reheating process, a hot rolling process, and a coiling process.

[0137] First, the reheating process may be performed prior to the hot rolling process to reheat the steel for subsequent processing. Specifically, this may be a step of loading the steel into a heating furnace and uniformly heating it, thereby facilitating plastic deformation.

[0138] At this time, if the reheating temperature is below 1000℃, the rolling load increases, which can make hot rolling difficult. On the other hand, if the reheating temperature exceeds 1250℃, precipitates formed by carbon (C), sulfur (S), nitrogen (N), etc. in the steel are re-dissolved, which can lead to the formation of fine precipitates during the subsequent rolling and annealing processes. These fine precipitates can inhibit grain growth and increase iron loss.

[0139] Therefore, the reheating process according to one embodiment of the present invention can be performed at a temperature of 1000 to 1250°C.

[0140] Next, a hot rolling process may be performed to form a hot-rolled steel sheet by hot-rolling the reheated steel. The hot rolling process may include rough rolling and finish rolling. Here, rough rolling may refer to forming the steel into a rolled material with an appropriate shape, thickness, and width, and finish rolling may refer to adjusting the steel to a specified thickness and width and rolling it at a finishing temperature suitable for the intended use to achieve a good surface and shape.

[0141] At this time, the finishing temperature of the hot rolling process may be carried out at a temperature for uniform tissue formation and appropriate strength enhancement, and preferably, the finishing temperature may be 850 to 1000°C. If the finishing temperature is lower than 850°C, dynamic recrystallization may not sufficiently occur, making it difficult to homogenize the microstructure, which may lower the uniformity of the final aggregate structure and result in inferior magnetic properties. If the finishing temperature exceeds 1000°C, the problem of rapid deterioration in the strength of the steel may occur.

[0142] Afterwards, a coiling process can be performed to coil the hot-rolled steel sheet formed through the hot rolling process. At this time, the coiling temperature is preferably 550 to 750°C. If the coiling temperature is below 550°C, brittleness increases, potentially leading to sheet fracture. Furthermore, the grain size decreases, preventing sufficient grain growth even after annealing. Conversely, if the coiling temperature exceeds 750°C, fine precipitates may form, increasing iron loss.

[0143] The thickness of the hot-rolled steel sheet formed through the above hot rolling step is preferably 1.8 to 3.5 mm. If the thickness of the hot-rolled steel sheet is excessively thin, less than 1.8 mm, the thickness obtained after cold rolling may be insufficient, which may cause shape defects during product application. On the other hand, if the thickness of the hot-rolled steel sheet exceeds 3.5 mm, the cold rolling reduction ratio increases, and the fraction of aggregate structures unfavorable to magnetic properties increases, which may result in inferior magnetic properties.

[0144] According to one embodiment of the present invention, a non-oriented electrical steel sheet can perform a hot rolling annealing step of hot rolling the hot rolled steel sheet after the hot rolling step.

[0145] The hot-rolled annealing step may be a hot-rolled annealing step performed to ensure uniformity of the microstructure of hot-rolled steel. When the silicon content is 2.8 wt% or more, hot-rolled annealing is preferably performed.

[0146] The reasons for performing hot-rolled annealing are as follows. When the silicon content exceeds 2.8 wt%, the α-ferrite single phase is maintained without phase transformation into a solid state during heating from room temperature to the melting point. However, dynamic recrystallization (DRX) does not occur during this process, resulting in the formation of elongated unrecrystallized parts. These unrecrystallized parts have high internal residual stresses and are unstable, which can lead to increased anisotropy and plate failure.

[0147] Therefore, the hot rolling annealing step may be a step of performing heat treatment at an appropriate temperature to promote recrystallization of unrecrystallized grains and thereby obtain a uniform equiaxed grain.

[0148] The appropriate temperature for hot-rolling annealing according to the present invention may be 900 to 1100°C. If the hot-rolling annealing temperature is below 900°C, the elongated cast structure may remain after hot rolling, causing microstructural inhomogeneity. Conversely, if the hot-rolling annealing temperature exceeds 1100°C, it may cause an imbalance in the final product's texture and deteriorate its magnetic properties.

[0149] Additionally, hot rolling annealing may include a heat treatment step for 10 to 180 seconds to form an appropriate grain size under the above temperature conditions. At this time, the heating rate to the heat treatment temperature and the cooling rate after the heat treatment may be 20°C / s or more.

[0150] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a shot blast and acid pickling process after the hot rolling annealing step.

[0151] Specifically, shot blasting can be performed by rotating fine particles with a size of 2 to 1200 μm at a speed of 2000 rpm or more and then spraying them at a high speed of 50 to 120 m / s. Pickling can be performed by supplying 18% hydrochloric acid to a pickling tank where it reacts with the steel plate, thereby reacting and removing fine residual scale that cannot be removed by mechanical methods.

[0152] Thereafter, the method for manufacturing a non-oriented electrical steel sheet according to the present invention may perform a cold rolling step of cold rolling the hot-rolled steel sheet that has undergone a hot-rolling annealing step to form a cold-rolled steel sheet. The cold rolling step may be a cold rolling process that further thins the thickness of the steel sheet by rolling the hot-rolled annealed hot-rolled steel sheet at a temperature below the recrystallization temperature.

[0153] More specifically, it may be a process of rolling a hot-rolled steel sheet to a thickness and width that meet the specifications of the final product. The cold rolling step according to the present invention may include a step of cold rolling a hot-rolled steel sheet to produce a cold-rolled steel sheet having a thickness of 0.15 to 0.30 mm. At this time, the reduction ratio may be 70 to 97%.

[0154] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may include performing a cold rolling annealing step, after a cold rolling step, of cold rolling the cold rolled steel sheet. The cold rolling annealing may be performed at an appropriate temperature to improve magnetic and mechanical properties.

[0155] At this time, the appropriate temperature for cold rolling annealing may be 800 to 1100℃. If the cold rolling annealing temperature is lower than 800℃, it is difficult to relieve residual stress due to the insufficient cold rolling annealing temperature, and the iron loss may be inferior. In addition, the grain size after annealing may be small, which may result in inferior magnetic flux density and iron loss. Furthermore, there is a concern that the inclusions formed during low-temperature annealing may grow, increasing the overall size of the inclusions, which may weaken the physical properties of the sheet.

[0156] On the other hand, if the cold rolling annealing temperature exceeds 1100℃, excessive grain growth may lead to increased eddy current loss, which may increase iron loss. Furthermore, precipitates may re-dissolve, forming fine precipitates, which may deteriorate magnetic properties.

[0157] In addition, the cold rolling annealing according to the present invention can be maintained for 30 to 120 seconds in the above-mentioned temperature range, the heating rate up to the above temperature can be 10°C / min or more, and the cooling rate after the heat treatment can be 20°C / s or more.

[0158] The cold-rolled annealing step can be performed in a mixed atmosphere containing hydrogen (H2) and nitrogen (N2) to prevent oxidation or nitriding of the surface of the cold-rolled steel sheet. This can improve the surface quality of the cold-rolled steel sheet.

[0159] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a coating step after the cold-rolled annealing step. The coating step may be performed to secure the insulation properties and improve the punchability of the non-oriented electrical steel sheet, and may mean forming an insulating film on the surface of the cold-rolled steel sheet after the cold-rolled annealing step. The coating step may be performed using any process known in the art.

[0160] According to one embodiment of the present invention, by suppressing the growth of crystal grains having {111} planes that are unfavorable for magnetic properties, a grain structure that is advantageous for magnetic properties can be formed. As a result, excellent magnetic properties can be achieved, and more specifically, iron loss (W 10 / 400 ) may be less than 12.5 W / kg.

[0161]

[0162] Experimental example

[0163] Below, the composition and operation of the present invention will be explained through experimental examples. However, these examples are provided to aid understanding of the present invention and are not intended to limit the present invention.

[0164]

[0165] (Method for measuring the properties of non-oriented electrical steel sheets)

[0166] 1. Volume and number of inclusions

[0167] In this experiment, SEM images were taken to measure the size of the inclusions. The magnification was 5000 times, and more than 3 random points were photographed so that the number of inclusions was in the range of 5 to 20. After that, the area of ​​the inclusions was measured in the photographed SEM images, and the average diameters of large and small inclusions were calculated based on the diameter of a circle with the same area as the area of ​​the inclusions. Then, the volume was calculated based on each calculated diameter and substituted into Equation 2. The calculated size was used as the volume of the inclusion, and the volume V = (π * average diameter 3 ) / 6 was calculated.

[0168] In this experiment, SEM images were taken at 5000x magnification and the number of inclusions present in the SEM images was measured.

[0169]

[0170] 2. Iron hand

[0171] Iron loss (W) of the non-oriented electrical steel sheet specimen of the present invention 10 / 400 ) was measured using SST (Single Sheet Tester). More specifically, it was measured based on the test method specified in the IEC 60404-3 standard.

[0172] In this experiment, non-oriented electrical steel sheet specimens were used, measuring 60×60 mm. 2 A specimen of the same size was manufactured, and the iron loss in the direction parallel to the rolling direction (RD) and the direction perpendicular to the rolling direction (TD, Transverse direction) was measured, and the average value was used as the iron loss value of the specimen.

[0173]

[0174] (Manufacturing method and evaluation results of non-oriented electrical steel sheet specimens)

[0175] In the present invention, an alloy composition capable of suppressing the growth of crystal grains having a {111} plane that is unfavorable to magnetic properties was established, and the following experiment was conducted to quantify the inclusion properties through the above equation 2.

[0176] First, the composition ranges of silicon (Si), aluminum (Al), and manganese (Mn), the major alloying elements of non-oriented electrical steel, were established. Next, the conditions for the major alloying elements established through previously conducted experiments were fixed, and changes in core loss due to additive elements and cold-rolled annealing conditions were examined. The additive elements can include antimony (Sb), tantalum (Ta), and titanium (Ti).

[0177]

[0178] 1. Composition of silicon (Si), aluminum (Al), and manganese (Mn)

[0179] First, the composition ranges of silicon (Si), aluminum (Al), and manganese (Mn) of the non-oriented electrical steel sheet specimen of the present invention were controlled as follows.

[0180] In order to control the main alloying elements of non-oriented electrical steel sheets, silicon (Si), aluminum (Al), and manganese (Mn), to an appropriate content, the iron loss (W) according to the content of each alloying element 10 / 400 ) value trend was confirmed.

[0181] At this time, the specimens of non-oriented electrical steel sheets used were manufactured using the following method.

[0182] A slab having the alloy compositions listed in Table 1 below was heated to 1130°C and hot rolled to produce a hot-rolled steel sheet having a thickness of 2.0 mm. The hot-rolled steel sheet was hot-rolled and annealed, and then cold-rolled to produce a cold-rolled steel sheet having a thickness of 0.25 mm. Thereafter, the cold-rolled steel sheet was cold-rolled and annealed in a mixed atmosphere of nitrogen (N2) and hydrogen (H2) in a ratio of 1:3, and heat-treated at 1000°C for 60 seconds. The heating rate was 10°C / s. The cold-rolled steel sheet subjected to cold-rolling annealing was coated to produce a specimen of a non-oriented electrical steel sheet.

[0183] At this time, impurity elements not listed in Table 1 were controlled as follows. Phosphorus (P) was controlled to 100 ppm (error range of 10 ppm or less), and carbon (C), nitrogen (N), sulfur (S), and titanium (Ti) were controlled to 25 ppm (error range of 5 ppm or less).

[0184] Hereinafter, a more detailed explanation will be provided with reference to Fig. 1 and Table 1.

[0185] Figure 1 is a graph showing changes in iron loss according to the contents of silicon (Si), aluminum (Al), and manganese (Mn), and Figures 1 (a), (b), and (c) are graphs showing changes in iron loss according to the contents of silicon (Si), aluminum (Al), and manganese (Mn), respectively.

[0186] [Table 1]

[0187]

[0188] Referring to Fig. 1 (b) and Table 1, it can be confirmed that when the aluminum content is less than 0.5 wt%, the iron loss does not satisfy 12.5 W / kg. Therefore, in the present invention, the lower limit of aluminum is limited to 0.5 wt%. On the other hand, it can be confirmed that as the aluminum content increases, the iron loss decreases and then increases at a point. The reason for the increase in iron loss is the formation of inclusions. Therefore, the upper limit of aluminum is set to a range where inclusions are not formed, and the upper limit is 1.5 wt%.

[0189] Referring to Fig. 1(c) and Table 1, it can be confirmed that when the manganese content is less than 0.2 wt%, the iron loss does not satisfy 12.5 W / kg or less. Therefore, in the present invention, the lower limit of aluminum is limited to 0.2 wt%. On the other hand, it can be confirmed that as the manganese content increases, the iron loss decreases and then increases at a point, which is due to the formation of inclusions. Therefore, the upper limit of manganese is set to a range where inclusions are not formed, and the upper limit is set to 0.5 wt%.

[0190]

[0191] 2. Additive element composition and cold rolling annealing conditions

[0192] The main alloy element composition range was controlled to ±0.01 wt% based on the median value of silicon (Si) 3.3 wt%, aluminum (Al) 1.0 wt%, and manganese (Mn) 0.4 wt%, and the change in iron loss according to the added elements and cold rolling annealing conditions was confirmed using steel.

[0193] At this time, the specimens of non-oriented electrical steel sheets used were manufactured using the following method.

[0194] Slabs having the alloy components listed in Tables 2 and 3 below were heated to 1130°C and hot rolled to produce hot-rolled steel sheets having a thickness of 2.0 mm. The hot-rolled steel sheets were hot-rolled and annealed, and then cold-rolled to produce cold-rolled steel sheets having a thickness of 0.25 mm. Thereafter, the cold-rolled steel sheets were cold-rolled and annealed in a mixed atmosphere with a nitrogen (N2) and hydrogen (H2) ratio of 1:3, and the cold-rolled annealing temperature and time were performed under the conditions listed in Tables 2 and 3 below. At this time, the heating rate was 10°C / s. The cold-rolled steel sheets subjected to cold-rolled annealing were coated to produce specimens of non-oriented electrical steel sheets.

[0195] At this time, impurity elements not listed in Table 1 were controlled as follows. Phosphorus (P) was controlled to 100 ppm (error range of 10 ppm or less), and carbon (C), nitrogen (N), sulfur (S), and titanium (Ti) were controlled to 25 ppm (error range of 5 ppm or less).

[0196] In Tables 2 to 4 below, ‘inclusions less than 330 nm’ refers to inclusions having a size of 150 nm or more and less than 330 nm.

[0197] [Table 2]

[0198]

[0199]

[0200] [Table 3]

[0201]

[0202]

[0203] [Table 4]

[0204]

[0205] Referring to Table 2 above, in the case of experimental examples that do not satisfy the lower limit of Equation 1 above, the iron loss (W 10 / 400) value does not satisfy 12.5 W / kg or less. In particular, in the case of the experimental example that does not satisfy the above equation 2, it can be confirmed that the growth of {111} plane crystal grains due to the inclusion is not suppressed, and the crystal grains become coarser, resulting in high iron loss.

[0206] Continuing with reference to Table 2, for experimental examples exceeding the niobium (Nb) content according to one embodiment of the present invention, the iron loss (W 10 / 400 ) value exceeds 12.5 W / kg. In addition, in the case of an experimental example exceeding each content of tantalum (Ta) and antimony (Sb) according to an embodiment of the present invention, the iron loss (W 10 / 400 ) It can be confirmed that the value does not satisfy 12.5 W / kg or less.

[0207] In the above Table 2, in the case of an experimental example that does not satisfy the upper limit of the above equation 1, the iron loss (W 10 / 400 ) can be confirmed to exceed 12.5 W / kg. In particular, in the case of the experimental example that does not satisfy the above equation 2, it can be confirmed that excessive inclusions are generated and the iron loss is high.

[0208] Referring to Table 3, in the case of an experimental example that satisfies the alloy composition according to one embodiment of the present invention but does not satisfy the above formula 2, the iron loss (W 10 / 400 ) can be confirmed to exceed 12.5 W / kg.

[0209] On the other hand, in the case of an experimental example satisfying the alloy composition according to one embodiment of the present invention, the iron loss (W 10 / 400 ) It can be confirmed that the value satisfies 12.5 W / kg or less. In addition, when the above equation 2 is satisfied, it can be confirmed that the iron loss deterioration due to inclusions is reduced, resulting in excellent magnetic properties.

[0210] Finally, referring to Table 4, it can be confirmed that when the ACL conditions are unsatisfactory, even though the composition is within the appropriate range, the inclusions are not properly controlled, and thus Equation 2 is not satisfied. As a result, it can be confirmed that the iron loss is deteriorated.

[0211] As described above, preferred embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms, in addition to the embodiments described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. Contains 2.8 wt% or more of silicon (Si) and 4.0 wt% or less, 0.5 wt% or more of aluminum (Al) and 1.5 wt% or less, 0.2 wt% or more of manganese (Mn) and 0.5 wt% or less, 0 wt% or more of antimony (Sb) and 0.003 wt% or less, 0 wt% or more of tantalum (Ta) and 0 wt% or less of niobium (Nb), and the remainder includes iron (Fe) and other unavoidable impurities. Non-oriented electrical steel sheet satisfying the following equation 1: [Formula 1] 10 ≤ [Sb]+[Ta]+[Nb] ≤ 90 (However, in the above formula 1, [Sb], [Ta], and [Nb] represent the contents of Sb, Ta, and Nb in ppm, respectively.) 2. In paragraph 1, Non-oriented electrical steel sheet satisfying the following equation 2: [Formula 2] 3.0 ≤ [0.71(An *Av) + 0.29(Bn * Bv)]*100 ≤ 5.0 (However, in the above formula 2, An represents the number of inclusions with a size of 150 nm or more and less than 330 nm, Av represents the volume of spheres converted based on the average diameter of inclusions with a size of 150 nm or more and less than 330 nm, Bn represents the number of inclusions with a size of 330 nm or more, and Bv represents the volume of spheres converted based on the average diameter of inclusions with a size of 330 nm or more.) 3. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

4. In paragraph 1, Iron Loss (W 10 / 400 ) Non-oriented electrical steel sheet having a strength of 12.5 W / kg or less.

5. Steel preparation stage for preparing steel; A hot rolling step of hot rolling the above steel to form a hot rolled steel plate; A hot rolling annealing step for annealing the above hot rolled steel sheet; A cold rolling step of forming a cold rolled steel sheet by cold rolling the hot rolled steel sheet that has undergone the above hot rolling annealing step; and It includes a cold rolling annealing step of annealing the above cold rolled steel sheet at 800 to 1100℃ for 30 to 120 seconds, The above steel is, Contains 2.8 wt% or more of silicon (Si) and 4.0 wt% or less, 0.5 wt% or more of aluminum (Al) and 1.5 wt% or less, 0.2 wt% or more of manganese (Mn) and 0.5 wt% or less, 0 wt% or more of antimony (Sb) and 0.003 wt% or less, 0 wt% or more of tantalum (Ta) and 0 wt% or less of niobium (Nb), and the remainder includes iron (Fe) and other unavoidable impurities. A method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] 10 ≤ [Sb]+[Ta]+[Nb] ≤ 90 (However, in the above formula 1, [Sb], [Ta], and [Nb] represent the contents of Sb, Ta, and Nb in ppm, respectively.) 6. In paragraph 5, The above steel is, A method for manufacturing a non-oriented electrical steel sheet further comprising at least one of carbon (C) exceeding 0 wt% and 0.003 wt% or less, phosphorus (P) exceeding 0 wt% and 0.011 wt% or less, sulfur (S) exceeding 0 wt% and 0.003 wt% or less, nitrogen (N) exceeding 0 wt% and 0.003 wt% or less, and titanium (Ti) exceeding 0 wt% and 0.003 wt% or less.

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