KR20240081966A - Non-oriented electrical steel sheet and manufacturing method of the same - Google Patents

Abstract

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preparatory step of reheating a semi-finished product, and a hot rolling step of hot rolling the semi-finished product with an upper roll and a lower roll to form a hot rolled steel sheet, and friction of the upper roll. The coefficient is different from the friction coefficient of the lower roll.

Description

Non-oriented electrical steel sheet and manufacturing method of non-oriented electrical steel sheet {NON-ORIENTED ELECTRICAL STEEL SHEET AND MANUFACTURING METHOD OF THE SAME}

The present invention relates to a non-oriented electrical steel sheet and a method of manufacturing a non-oriented electrical steel sheet. Specifically, the present invention relates to a non-oriented electrical steel sheet having low iron loss and high magnetic flux density without performing a preliminary annealing step in the hot rolling step. It's about how to do it.

Non-oriented electrical steel sheet is a material used as an iron core material for motors, generators, and small transformers. Specifically, non-oriented electrical steel is a material used to convert electrical energy into kinetic energy, change voltage, and other various energy conversions. Meanwhile, the use of high-efficiency electric motors is becoming mandatory to reduce energy consumption worldwide, and there is a need to develop non-oriented electrical steel sheets with excellent properties that can improve energy efficiency.

The characteristics required for non-oriented electrical steel sheets are low iron loss and high magnetic flux density.

In general, a method of increasing the resistivity of steel is used to reduce iron loss due to induced current generated during magnetization of the steel sheet, which is a loss occurring in a motor. By increasing the amount of silicon (Si), aluminum (Al), and manganese (Mn) added to steel, the resistivity of the steel increases and iron loss can be reduced. Because silicon is the most effective of these elements, a large amount of silicon is added to non-oriented electrical steel, and it has been called silicon steel (Si steel) for a long time.

Additionally, reducing impurities in non-oriented electrical steel is one of the main technologies for reducing power loss in the iron core. For example, elements such as C, N, Ti, and S combine with elements added for resistivity such as Al, Mn, and Cu in steel to form precipitates, forming fine precipitates that interfere with magnetic domain wall movement during magnetization. Therefore, it has a negative effect on iron loss, especially at high frequencies where there is a lot of movement of the domain walls. By lowering the content of elements such as C, N, Ti, and S, the iron loss of steel can be reduced. However, depending on the amount of Si, Al, and Mn added to the steel, the proportion of Fe atoms acting on magnetization in the same volume of steel decreases, so the magnetic flux density decreases.

The magnetic flux density is determined by the fraction of iron (Fe) atoms in the steel and the arrangement of the steel grains, which is due to the magnetic anisotropy of iron atoms. Due to magnetic anisotropy, magnetization occurs easily in the <100> structure of iron atoms, but it is difficult to magnetize the <110> structure and <111> structure, so the magnetization direction of the atomic arrangement in the steel is along the <100> axis. When made parallel to , the steel has a high magnetic flux density even in low magnetic fields. Since non-oriented electrical steel sheets are mainly used in motors with rotating axes, the direction of magnetization is not constant, so it is difficult to determine the orientation of the axis. However, since the direction of magnetization is mainly in the direction of the sheet surface, it is necessary to orient the axis that helps magnetize the sheet surface or to magnetize it. It is possible to obtain high magnetic flux densities at low magnetic fields using methods that do not orient the axes or axes, which is very difficult.

In the conventional method of manufacturing non-oriented electrical steel sheets, a technology for improving the texture through a hot-rolled steel sheet annealing process at the stage before cold rolling was widely used to improve iron loss and magnetic flux density characteristics. However, the addition of the hot-rolled steel sheet annealing process causes an increase in manufacturing costs, and when the crystal grains become coarse by annealing the hot-rolled steel sheet, there are problems such as poor cold rolling properties. Accordingly, if it is possible to manufacture a non-oriented electrical steel sheet with excellent magnetic properties without performing a hot-rolled steel sheet annealing process, the manufacturing cost can be reduced while also solving the problem of productivity caused by the hot-rolled sheet annealing process.

The present invention applies sufficient shear deformation to the semi-finished product by varying the friction coefficient of the upper rolling roll and the friction coefficient of the lower rolling roll in the hot rolling stage, thereby providing low core loss and high magnetic flux density characteristics without performing a hot rolled steel sheet annealing process. The purpose is to provide a method of manufacturing a non-oriented electrical steel sheet.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preparation step of reheating a semi-finished product; and a hot rolling step of hot rolling the semi-finished product using an upper roll and a lower roll to form a hot rolled steel sheet. It includes, and the friction coefficient of the upper roll is different from the friction coefficient of the lower roll.

In one embodiment, after the hot rolling step, the annealing step may be omitted and a coiling step of winding the hot rolled steel sheet may be further included.

In one embodiment, the coiling temperature in the coiling step may be 720°C or more and 770°C or less.

In one embodiment, after the coiling step, a cold rolling step of cold rolling the coiled hot rolled steel sheet to form a cold rolled steel sheet and a final annealing step of annealing and coating the cold rolled steel sheet may be further included.

In one embodiment, a friction reduction layer may be provided on the surface of any one of the upper roll and the lower roll.

In one embodiment, the friction reduction layer may include lubricant.

In one embodiment, the friction coefficient of one of the upper roll and the lower roll may be 0.3, and the friction coefficient of the other may be 0.1.

In one embodiment, immediately after the hot rolling step, the hot rolled steel sheet may satisfy Equation 1 below:

[Equation 1]

ε ₁₃ /ε ₁₁ > 0.5

In Equation 1, ε ₁₃ /ε ₁₁ is the hot rolling strain rate, ε ₁₃ is the shear strain rate of the hot rolled steel sheet, and ε ₁₁ is the plane strain rate of the hot rolled steel sheet.

In one embodiment, the semi-finished product has a silicon content of 2 wt% to 2.8 wt%, a carbon content of 0.002 wt% or less, a manganese content of 0.2 wt to 0.28 wt%, and an aluminum content of 0.32 wt to 0.45 wt. % by weight or less, the phosphorus content is 0.015% by weight or less, the sulfur content is 0.002% by weight or less, the nitrogen content is 0.002% by weight or less, the titanium content is 0.002% by weight or less, and the balance may include iron.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preparation step of reheating a semi-finished product; A hot rolling step of hot rolling the semi-finished product using an upper roll and a lower roll to form a hot rolled steel sheet; A winding step of winding the hot rolled steel sheet while omitting the annealing step; A cold rolling step of cold rolling the wound hot-rolled steel sheet to form a cold-rolled steel sheet; and a final annealing step of annealing and coating the cold rolled steel sheet to form a final product. Includes, and the coiling temperature is 720°C or more and 770°C or less.

In one embodiment, the coefficient of friction of the upper roll may be different from the coefficient of friction of the lower roll.

In one embodiment, the friction coefficient of one of the upper roll and the lower roll may be 0.3, and the friction coefficient of the other may be 0.1.

In one embodiment, one of the upper roll and the lower roll may be a non-lubricated rolling roll, and the other may be a lubricated rolling roll.

In one embodiment, immediately after the hot rolling step, the hot rolled steel sheet may satisfy Equation 1 below:

[Equation 1]

ε ₁₃ /ε ₁₁ > 0.5

In Equation 1, ε ₁₃ /ε ₁₁ is the hot rolling strain rate, ε ₁₃ is the shear strain rate of the hot rolled steel sheet, and ε ₁₁ is the plane strain rate of the hot rolled steel sheet.

In one embodiment, the semi-finished product has a silicon content of 2 wt% to 2.8 wt%, a carbon content of 0.002 wt% or less, a manganese content of 0.2 wt to 0.28 wt%, and an aluminum content of 0.32 wt to 0.45 wt. % by weight or less, the phosphorus content is 0.015 weight% or less, the sulfur content is 0.002 weight% or less, the nitrogen content is 0.002 weight% or less, the titanium content is 0.002 weight% or less, and the balance contains iron. Manufacturing method of steel plate.

In one embodiment, the iron loss (W _15/50 ) of the final product may be 2.55 W/kg or less, and the magnetic flux density (B ₅₀ ) may be 1.685T or more.

The non-oriented electrical steel sheet according to an embodiment of the present invention has, based on weight percent, C: 0.002 or less, Si: 2 or more and 2.8 or less, Mn: 0.2 or more and 0.28 or less, Al: 0.32 or more and 0.45 or less, P: 0.015 or less, S : 0.002 or less, N: 0.002, Ti: 0.002 or less, including the balance iron and inevitable impurities, and satisfies the following formula 1:

[Equation 1]

ε ₁₃ /ε ₁₁ > 0.5

In Equation 1, ε ₁₃ /ε ₁₁ is the hot rolling strain, ε ₁₃ is the shear strain, and ε ₁₁ is the plane strain.

In one embodiment, the iron loss (W _15/50 ) may be 2.55 W/kg or less.

In one embodiment, the magnetic flux density (B ₅₀ ) may be 1.685T or more.

In one embodiment, the shear strain of the quarter layer may be greater than the shear strain of the surface layer, and the shear strain of the surface layer may be greater than the shear strain of the central layer.

The method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention can provide a non-oriented electrical steel sheet that exhibits excellent magnetic properties without performing an annealing process for the hot rolled steel sheet.

The non-oriented electrical steel sheet according to an embodiment of the present invention may exhibit low iron loss and high magnetic flux density.

1 is a flowchart showing a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.
Figure 2 is a cross-sectional view showing a hot rolling step according to one embodiment.

All terms (including technical terms and scientific terms) used in this specification have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains.

Terms as defined in commonly used dictionaries are explicitly defined herein, and should be construed as having meanings consistent with their meanings in the context of the relevant technology, unless interpreted in an idealized or overly formal sense.

Terms such as first, second, and third are used to describe various components, regions, parts, or layers, but are not limited thereto. These terms are used to distinguish one component, region, portion or layer from another component, portion or layer.

In this specification, the fact that one part is “on” or “on” another part is not limited to the case where there is another part directly above the one part, but also includes the case where there is another part between one part and the other part. will be.

In this specification, further inclusion of an additional element means inclusion in place of the remaining iron (Fe).

Hereinafter, a method of manufacturing a non-oriented electrical steel sheet and the non-oriented electrical steel sheet according to an embodiment will be described in detail with reference to the drawings.

1 is a flowchart showing a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

Referring to Figure 1, the method (S10) of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preparation step (S100) of reheating a semi-finished product, a hot rolling step (S200) of forming a hot rolled steel sheet, and an annealing step. is omitted and includes a coiling step (S300) of winding the hot rolled steel sheet, a cold rolling step (S400) of forming a cold rolled steel sheet, and a final annealing step (S500) of annealing and coating the cold rolled steel sheet.

The preparation step for reheating the semi-finished product (S100, hereinafter referred to as the preparation step) may be a step for reheating the manufactured semi-finished product. For example, a semi-finished product may be a slab. The manufacturing process of the slab may be carried out by processes known in the art.

In one embodiment, the semi-finished product has a silicon content of 2 wt% to 2.8 wt%, a carbon content of 0.002 wt% or less, a manganese content of 0.2 wt to 0.28 wt%, and an aluminum content of 0.32 wt to 0.45 wt. % or less, the phosphorus content is 0.015% by weight or less, the sulfur content is 0.002% by weight or less, the nitrogen content is 0.002% by weight or less, the titanium content is 0.002% by weight or less, and the balance may include iron. However, the examples are not limited to this, and the semi-finished product may contain copper in an amount of 0.9% by weight or less, tin in an amount of 0.1% by weight or less, antimony in an amount of 0.1% by weight or less, and other unavoidable products. It may contain added impurities.

Hereinafter, the components of steel will be described in detail.

[Carbon (C)]

Carbon (C) is an element that combines with Ti and Nb to form carbides such as TiC and NbC and increases iron loss, which can deteriorate magnetism. Therefore, the smaller the carbon content, the more desirable it is, and it is limited to 0.002% by weight or less. If the carbon content exceeds 0.002% by weight, iron loss increases due to self-aging and may reduce the efficiency of electronic devices when applied to them. In the present invention, it is preferable to limit the carbon content to 0.002% by weight or less.

[Silicon (Si)]

Silicon (Si) may be an ingredient that increases specific resistance and reduces eddy current loss. Additionally, silicon is an effective element in improving the yield strength of steel and stabilizing ferrite and residual austenite at room temperature. If the silicon content is low, it may be difficult to obtain the desired low iron loss value. Additionally, if the silicon content is excessive, there is a problem of increasing the load of hot rolling, causing hot rolling cracks, and the amount of Si enriched on the surface after annealing increases, resulting in poor plating properties. Additionally, permeability and magnetic flux density decrease in electrical steel sheets. If silicon is added in excess of 4% by weight, brittleness increases and cold rolling becomes difficult. Therefore, an appropriate amount of silicon must be added, and in the present invention, it is preferable to limit the silicon content to 2% by weight or more and 2.8% by weight or less.

[Manganese (Mn)]

Manganese (Mn), along with silicon and aluminum, is an element that increases resistivity and lowers iron loss. If the amount of manganese added is small, the effect of increasing resistivity may be reduced.

Manganese is also an element that improves aggregate structure. Manganese is well known as a hardenability enhancing element that suppresses ferrite formation and makes austenite safe. Additionally, since manganese increases the solubility of nitrogen in steel, it must be present in an amount of 0.1% by weight or more to obtain the above-mentioned effect. If the manganese content is less than 0.1% by weight, fine MnS precipitates may be formed to inhibit grain growth. If the amount of manganese (Mn) added is excessive, coarse MnS precipitates may be formed and magnetic properties may deteriorate, such as reducing magnetic flux density. For example, if the manganese content is 0.5% by weight or more, the amount of reduction in iron loss is small and cold rolling properties may be reduced. In the present invention, it is preferable to limit the manganese content to 0.2% by weight or more and 0.28% by weight or less.

[Aluminum (Al)]

Aluminum (Al) is an element added for deoxidation in the steelmaking process and is a carbonitride forming element. Aluminum, along with silicon, is a major added element that increases resistivity and lowers eddy current loss. In addition, aluminum is an element that expands the ferrite region and has an advantageous effect in reducing annealing costs by lowering the transformation point. However, if the content exceeds 0.9% by weight, weldability deteriorates and at the same time, the amount of surface oxidation of aluminum increases during the annealing process, making it difficult to secure plating properties. Additionally, aluminum can form AlN precipitates when it meets nitrogen. Accordingly, if the aluminum content is excessive, cold rolling properties may decrease, magnetic flux density may decrease, and magnetic properties may deteriorate. In the present invention, it is preferable to limit the aluminum content to 0.32% by weight or more and 0.45% by weight or less.

[Copper (Cu)]

Copper (Cu) is an austenite stabilizing element that is effective in improving low-temperature toughness while stabilizing austenite along with manganese and carbon.

Copper has a very low solid solubility in carbides and slow diffusion in austenite, so it tends to concentrate at the interface between austenite and carbides. As a result, when a fine nucleus of carbide is generated, it surrounds it, slowing down the growth of carbide due to additional diffusion of carbon, and ultimately inhibiting the creation and growth of carbide. Because of this effect, it is preferable to use it together with chromium (Cr). In order to achieve the above-mentioned effect, it is preferable that copper is added in an amount of 0.1% by weight or more. On the other hand, if the content exceeds 0.9% by weight, there is a risk that the surface quality may deteriorate due to hot shortness defects. In the present invention, it is preferable to limit the copper content to 0.1% by weight or more and 0.9% by weight or less.

[P]

Phosphorus (P) is a grain boundary segregation element that develops texture. If the phosphorus content is excessive, segregation easily occurs, suppressing the growth of crystal grains and deteriorating magnetic properties. If the content exceeds 0.015% by weight, there is a problem that weldability deteriorates, castability deteriorates, cold rolling properties decrease, the risk of steel embrittlement increases, and the possibility of causing dent defects increases. In the present invention, it is preferable to limit the phosphorus content to 0.015% by weight or less.

[Hwang(S)]

Sulfur (S), like phosphorus, is an impurity element in steel and is an element that inhibits the ductility and weldability of steel. Sulfur can be added as low as possible because it forms sulfides such as MnS, CuS, and (Cu,Mn)S, which are harmful to magnetic properties, increases iron loss and suppresses the growth of crystal grains.

If the sulfur content is excessive, the magnetic properties may deteriorate due to an increase in fine sulfides and the properties of crystal grains may be suppressed. If the content exceeds 0.002% by weight, the likelihood of impairing the ductility and weldability of the steel increases. In the present invention, it is preferable to limit the sulfur content to 0.002% by weight or less.

[Nitrogen (N)]

Nitrogen (N) is an element that contributes to the strength and corrosion resistance of steel. Specifically, nitrogen, along with carbon, is an element that improves toughness by stabilizing austenite, and, like carbon, is an element that is particularly advantageous in improving strength through solid solution strengthening. However, nitrogen combines strongly with Al, Ti, Nb, etc. to form nitrides such as AlN, TiN, NbN, etc., which increases iron loss and suppresses the growth of crystal grains, so it can be added as low as possible. When nitrogen is added in excess of 0.002% by weight, coarse nitrides are formed, which causes the surface quality and physical properties of the steel to deteriorate. In the present invention, it is preferable to limit the nitrogen content to 0.002% by weight or less.

[Titanium (Ti)]

By combining with C and N, titanium (Ti) can form fine carbides such as TiC and nitrides such as TiN and suppress the growth of crystal grains. Titanium can reduce nitrogen in steel, but if the content of titanium is excessive, the texture may be inferior due to increased carbides and nitrides, which may result in inferior magnetic properties. The magnetic properties deteriorate as titanium is added, so it is desirable to add it as low as possible. In the present invention, it is preferable to limit the titanium content to 0.002% by weight or less.

In addition to the above elements, tin (Sn) and antimony (Sb), known as elements that improve the texture, may be added to further improve magnetism. However, if the amount added is too large, there is a problem of suppressing grain growth and lowering productivity, so the addition amount can be controlled to be 0.1% by weight or less.

In the case of Ni and Cr, which are elements inevitably added in the steelmaking process, they react with impurity elements to form fine sulfides, carbides, and nitrides, which have a detrimental effect on magnetism, so their content can be limited to 0.05% by weight or less.

In addition, since Zr, Mo, V, etc. are strong carbonitride forming elements, it is preferable not to add them as much as possible, and each can be contained in an amount of 0.01% by weight or less.

The balance includes Fe and inevitable impurities. As for unavoidable impurities, they are impurities mixed during the steelmaking stage and the manufacturing process of grain-oriented electrical steel sheets, and since these are widely known in the field, detailed descriptions will be omitted. In one embodiment of the present invention, the addition of elements other than the above-described 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. If additional elements are included, they are included by replacing the remaining Fe.

As described above, the steel composition and composition range of the steel plate according to one embodiment have been examined, and the fact that, in addition to the embodiment described above, the present invention can be embodied in other specific forms without departing from the spirit or scope of the present invention is known in the relevant technology. This is self-evident to those with ordinary knowledge.

That is, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description and may be modified within the scope of the appended claims and their equivalents.

The preparation step (S100) may be a step of manufacturing a semi-finished product that satisfies the above-mentioned ingredient range and then reheating the semi-finished product for a subsequent process. Since semi-finished products include a heating step during the manufacturing process, the process of heating again after manufacturing is completed can be understood as a reheating process. Specifically, the semi-finished product may be charged into a heating furnace and reheated. For example, semi-finished products can be reheated under SRT (Slab Reheating Temperature): 1,110℃ or higher and 1,150℃ or lower. When reheating semi-finished products, it is desirable to reheat at the lowest temperature possible to prevent re-dissolution of precipitates. If the SRT exceeds 1,150°C, precipitates formed by C, N, S, etc. in the semi-finished product are re-dissolved, and the precipitates may finely precipitate during hot rolling, which is a subsequent process, which may significantly reduce hot rolling properties. In addition, if the above precipitates are finely deposited, they may affect the final annealing of the steel sheet, which may result in poor grain growth during annealing, and may interfere with the movement of the domain wall during magnetization after annealing, thereby increasing iron loss, thereby playing a harmful role. will do. If the SRT is less than 1,110°C, the deformation resistance during hot rolling may become excessively large and the rolling load may increase. Therefore, it is necessary to heat the semi-finished product above 1,110℃ and below 1,150℃.

The hot rolling step (S200, hereinafter referred to as the hot rolling step) for forming a hot rolled steel sheet is a step of hot rolling a semi-finished product using an upper roll and a lower roll to form a hot rolled steel sheet. Specifically, the hot rolling step (S200) may include rough rolling the semi-finished product and finishing rolling the semi-finished product.

The step of crudely rolling the semi-finished product is a step of crudely rolling the reheated semi-finished product to manufacture it into a bar. For example, slabs with a thickness of 200 mm or more can be manufactured into bars with a thickness of 100 mm or more and 150 mm or less by hot rolling a steel plate at a reduction ratio of 50% to 65%.

Afterwards, the step of grinding the semi-finished product may proceed. It is desirable to carry out the finishing rolling so that the cumulative reduction ratio in the non-recrystallized area is 50 to 70%. If the cumulative reduction rate is less than 50%, it is difficult to secure a uniform and fine structure, which may lead to severe variations in strength and impact toughness. On the other hand, if the cumulative reduction ratio exceeds 70%, the rolling process time becomes longer and productivity decreases. FDT (Finishing Delivery Temperature) may be 860°C or more and 900°C or less. If the FDT is less than 860°C, rolling occurs in an ideal region and an uneven structure is formed, which can significantly reduce low-temperature impact toughness. Conversely, when the FDT exceeds 900°C, ductility and toughness are excellent, but there is a problem in that strength rapidly decreases. Therefore, FDT is preferably 860℃ or higher and 900℃ or lower.

Figure 2 is a cross-sectional view showing a hot rolling step according to one embodiment.

Referring to FIG. 2, in the hot rolling step (S200), the semi-finished product is rolled by the rolling rolls RL1 and RL2 and a hot rolled steel sheet (ST) is formed.

Generally, in the hot rolling step (S200), the thickness of the hot rolled steel sheet (ST) decreases from the first thickness (t1) to the second thickness (t2). In one embodiment, the second thickness t2 may be 1.8 mm or more and 2.6 mm or less. As the second thickness (t2) decreases, the recrystallized texture increases, thereby ensuring a uniform structure after annealing, and improving magnetic properties by reducing the cold rolling reduction rate. When the second thickness t2 increases, the cold rolling reduction rate increases and the texture may become inferior. Therefore, the second thickness t2 is preferably 2.6 mm or less. However, if the second thickness (t2) is excessively thin, the thickness of the cold rolled steel sheet obtained after the cold rolling process is not sufficient, which may cause shape defects when applied to products. Therefore, the second thickness t2 is preferably about 2.6 mm or less, and more preferably 1.8 mm or more and 2.6 mm or less.

Additionally, shear strain may be applied to the hot rolled steel sheet (ST) by the rolling rolls (RL1, RL2). The rolling rolls RL1 and RL2 include an upper roll RL1 and a lower roll RL2 arranged to face each other. The method of manufacturing a non-oriented electrical steel sheet of the present invention controls the friction coefficient of the upper roll (RL1) and the friction coefficient of the lower roll (RL2) differently in the hot rolling step (S200), thereby providing sufficient shear deformation to the hot rolled steel sheet (ST). can be applied.

In one embodiment, a friction reduction layer LO may be provided on the surface of either the upper roll RL1 or the lower roll RL2. The friction reducing layer (LO) may include lubricant. For example, one of the upper roll (RL1) and the lower roll (RL2) may be a non-lubricated rolling roll and the other may be a lubricated rolling roll. Accordingly, the friction coefficient of the upper roll (RL1) and the friction coefficient of the lower roll (RL2) become different, and one surface of the hot rolled steel sheet (ST) in contact with the upper roll (RL1) and the hot rolled steel sheet (ST) in contact with the lower roll (RL2) The surfaces of ST) are subjected to different frictional forces. For example, the friction coefficient of one of the upper roll (RL1) and the lower roll (RL2) may be 0.3, and the friction coefficient of the other may be 0.1.

As the hot rolled steel sheet (ST) is rolled by the upper roll (RL1) and lower roll (RL2) having different coefficients of friction, shear deformation may occur from the surface layer of the hot rolled steel sheet (ST) through the 1/4 layer to the central layer. Accordingly, the hot rolled steel sheet formed in the hot rolling step (S200) may have a uniform microstructure throughout the entire thickness layer.

In the present invention, the hot rolled steel sheet can satisfy Equation 1 below.

[Equation 1]

ε ₁₃ /ε ₁₁ > 0.5

In Equation 1 above, ε ₁₃ /ε ₁₁ is defined as the hot rolling strain.

ε ₁₃ is the shear strain rate of the hot rolled steel sheet. ε ₁₁ is the plane strain rate of the hot rolled steel sheet.

The hot rolled steel sheet of the present invention can satisfy Equation 1 above in the entire thickness layer. Specifically, Equation 1 above can be satisfied in each of the surface layer, quarter layer, and center layer.

The hot-rolled steel sheet of the present invention is rolled by the upper roll (RL1) and the lower roll (RL2) having different friction coefficients, so that the entire thickness of the hot-rolled steel sheet can be rolled while satisfying Equation 1 above. A hot-rolled steel sheet that satisfies Equation 1 has sufficient shear deformation in the entire thickness layer, has uniformly controlled microstructure, and can exhibit excellent magnetic properties. For example, the hot-rolled steel sheet of the present invention has further improved magnetism after completing the cold rolling process, final annealing, and coiling process, and the iron loss (W _15/50 ) is 2.55 W/kg or less and the magnetic flux density (B ₅₀ ) is 2.55 W/kg or less. It may be 1.685T or more.

After the hot rolling step (S200), the annealing step is omitted and a coiling step (S300, hereinafter referred to as the coiling step) of winding the hot rolled steel sheet is performed.

The conventional method of manufacturing a non-oriented electrical steel sheet involves performing a preliminary annealing process after the hot rolling process. At this time, if the preliminary annealing temperature is low, fine precipitates such as carbides and nitrides are formed from the surface layer, and the magnetism of the final product is inferior. On the other hand, if the pre-annealing temperature is too high, not only inclusions but also grains grow excessively, causing grain size deviation to increase and excessive oxidation to occur, adversely affecting the final product.

The method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes rolling a hot-rolled steel sheet with an upper roll (RL1) and a lower roll (RL2) having different coefficients of friction in the hot rolling step (S200), thereby achieving uniform fineness. A hot rolled steel sheet having a structure can be formed, and the preliminary annealing process can be omitted. As the preliminary annealing process is omitted, the method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention increases process efficiency and solves the problems caused by the preliminary annealing process described above.

In the winding step (S300), the hot rolled steel sheet is wound under the conditions of CT (Coilling Temperature): 720°C or more and 770°C or less. As CT satisfies the above range, grains can grow sufficiently even if the annealing step is omitted.

The coiling step (S300) may further include a pickling step of pickling the coiled hot rolled steel sheet. The pickling step may be a step in which the oxide layer formed on the surface of the hot rolled steel sheet is removed using a pickling solution.

Afterwards, a cold rolling step (S400, hereinafter referred to as cold rolling step) to form a cold rolled steel sheet is performed. The cold rolling step (S400) is a step of forming a cold rolled steel sheet by cold rolling the coiled hot rolled steel sheet. The cold rolling step (S400) is carried out for the purpose of forming a microstructure by cooling the hot-rolled steel sheet to 500°C or more and 540°C or less using a forced cooling method such as water cooling, thereby forming a microstructure and securing a low-temperature phase structure. The cold rolling step (S400) may be rolling the hot rolled steel sheet at a reduction ratio of 50% or more, for example, rolling at a reduction ratio of 80 to 85%. When the cold rolling step (S400) is completed, a cold rolled steel sheet is formed, and the thickness of the cold rolled steel sheet may be, for example, 0.35 mm or less.

Afterwards, a final annealing step (S500, hereinafter referred to as final annealing step) of annealing and coating the cold rolled steel sheet is performed. The final annealing step (S500) is a step of forming the final product by annealing and coating the cold rolled steel sheet. In one embodiment, the final annealing may be heat treating the cold rolled steel sheet at a temperature of 950°C or higher and 1,100°C or lower for 30 to 120 seconds. In order to prevent the surface of the cold rolled steel sheet from being oxidized or nitrided during the final annealing, the final annealing process is performed under a mixed atmosphere of nitrogen and hydrogen.

The final annealing temperature is set at a temperature that derives the optimal grain size considering reduction of iron loss and mechanical properties. When the final annealing temperature satisfies the above range, the grain size in the final product can grow from 80 ㎛ to 150 ㎛. If the final annealing temperature is less than 950°C, the grain size may not grow to an appropriate level and may be fine, resulting in increased hysteresis loss. If the final annealing temperature exceeds 1,100°C, the size of the crystal grains becomes coarse and eddy current loss increases. In addition, in the case of non-oriented electrical steel sheets with a silicon content of 2% by weight or less, if the final annealing temperature exceeds 1,100°C, heat treatment may proceed in the phase transformation region, i.e., the biphasic region or austenite single-phase region, and the magnetic properties of the texture may vary. . For example, if the final annealing temperature exceeds 1,100°C, the (001) orientation fraction rapidly decreases and the (111) orientation fraction increases in the final product, which may deteriorate the magnetic properties. Therefore, in the present invention, by setting the final annealing temperature to 950°C or more and less than 1,100°C, cold-rolled steel sheet can be heat treated in the ferrite single phase region and a final product having low iron loss and high magnetic flux density characteristics can be formed.

Meanwhile, when the final annealing temperature satisfies the above range, the yield strength (YP) of the final product may be 350 MPa or more and the tensile strength (TS) may be 450 MPa or more. However, the mechanical properties of the final product are not limited to this.

In the final annealing step (S500), the coating step is performed to secure punching and insulation properties. The coating step may be a step of forming an insulating film on the surface of the final annealed cold rolled steel sheet. Specifically, the insulating film may be formed of an organic, inorganic, organic-inorganic composite film, or other insulating film. After completing the coating step, the final product, non-oriented electrical steel sheet, can be manufactured.

The non-oriented electrical steel sheet formed by the above-described non-oriented electrical steel sheet manufacturing method may satisfy the above-described Equation 1 and exhibit excellent magnetic properties. Specifically, the non-oriented electrical steel sheet of the present invention has a hot rolling strain (ε ₁₃ /ε ₁₁ ) greater than 0.5, and accordingly, the non-oriented electrical steel sheet has an iron loss (W _15/50 ) of 2.55 W/kg or less, and a magnetic flux density ( B ₅₀ ) can exhibit low iron loss and high magnetic flux density characteristics of 1.685T or more.

In particular, the non-oriented electrical steel sheet of the present invention can satisfy the above-described equation 1 in the entire thickness layer, and specifically, the above-described equation 1 can be satisfied in each of the surface layer, 1/4 layer, and center layer of the non-oriented electrical steel sheet. there is. In one embodiment, shear strain occurs, where the shear strain rate of the quarter layer is greater than the shear strain rate of the surface layer, and the shear strain rate of the surface layer may be greater than the shear strain rate of the central layer.

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and should not be construed as limiting the present invention.

1. Fabrication of non-oriented electrical steel sheet

Non-oriented electrical steel sheets of Examples 1 to 4 and Comparative Examples 1 to 12 were manufactured by the following method.

A slab containing the steel components summarized in Table 1 below, the remaining iron, and other unavoidable impurities was manufactured. The slab was heated to 1140°C, and hot rolling was performed under FDT: 890°C conditions to manufacture a hot rolled steel sheet with a thickness of 2.0 mm. The hot rolling step was carried out to satisfy the above-mentioned equation 1.

For the non-oriented electrical steel sheets of Examples 1 to 4, Comparative Examples 1 to 8, Comparative Example 11, and Comparative Example 12, the preliminary annealing process was omitted. That is, the annealing process before cold rolling was omitted in the non-oriented electrical steel sheets of Examples 1 to 4 and Comparative Examples 1 to 8, Comparative Example 11, and Comparative Example 12. For the non-oriented electrical steel sheets of Comparative Examples 9 and 10, a preliminary annealing process was performed at 950°C.

After hot rolling, the non-oriented electrical steel sheets of Examples 1 to 4 and Comparative Examples 1 to 12 were wound under the CT conditions shown in Table 2 below.

Afterwards, the coiled hot-rolled steel sheet was cold-rolled to create a cold-rolled steel sheet with a thickness of 0.5 mm, and the final annealing process was performed at 950°C for 45 seconds. Afterwards, the final product was manufactured through a coating process. The final annealing process was performed under a mixed atmosphere of 30% hydrogen and 70% nitrogen. In the final annealing process, the temperature increase rate was 20°C/sec and the cooling rate was 30°C/sec. The magnetic properties of the final product were measured by measuring the iron loss and magnetic flux density values in the L and C directions using a single sheet tester (SST) and calculating the average values.

The coiling temperature (CT) in the manufacturing process of the non-oriented electrical steel sheets of Examples 1 to 4 and Comparative Examples 1 to 12 is shown in Table 2 below.

division C Si Al Mn S N Ti Example 1 0.0018 2.6 0.39 0.23 0.0017 0.0016 0.0011 Example 2 0.0017 2.5 0.42 0.22 0.0016 0.0015 0.0012 Example 3 0.0017 2.7 0.40 0.28 0.0018 0.0014 0.0015 Example 4 0.0018 2.6 0.37 0.26 0.0015 0.0013 0.0013 Comparative Example 1 0.0016 2.4 0.41 0.24 0.0017 0.0015 0.0012 Comparative Example 2 0.0019 2.5 0.39 0.22 0.0018 0.0016 0.0011 Comparative Example 3 0.0018 2.9 0.25 0.11 0.0016 0.0013 0.0014 Comparative Example 4 0.0018 2.1 0.65 0.35 0.0017 0.0014 0.0012 Comparative Example 5 0.0017 2.5 0.34 0.22 0.0017 0.0013 0.0013 Comparative Example 6 0.0019 2.4 0.39 0.27 0.0016 0.0015 0.0014 Comparative Example 7 0.0017 2.6 0.33 0.25 0.0016 0.0014 0.0011 Comparative Example 8 0.0017 2.7 0.37 0.23 0.0018 0.0013 0.0012 Comparative Example 9 0.0018 2.5 0.40 0.25 0.0015 0.0016 0.0013 Comparative Example 10 0.0018 2.4 0.37 0.25 0.0016 0.0015 0.0012 Comparative Example 11 0.0016 2.3 0.39 0.23 0.0017 0.0015 0.0013 Comparative Example 12 0.0017 2.4 0.38 0.27 0.0016 0.0014 0.0014

2. Evaluation of magnetic properties of non-oriented electrical steel sheet

Table 2 below shows the hot rolling strain (ε ₁₃ /ε ₁₁ ), coiling temperature (CT), and whether an annealing process is performed for the non-oriented electrical steel sheets of Examples 1 to 4 and Comparative Examples 1 to 12 having the compositions in Table 1. , iron loss, and magnetic flux density are shown. Specifically, the hot rolling strain (ε ₁₃ /ε ₁₁ ) is the hot rolling strain (ε ₁₃ /ε ₁₁ ) measured in each of the surface layer, quarter layer, and center layer of the non-oriented electrical steel sheet.

In addition, the non-oriented electrical steel sheets of Examples 1 to 4, Comparative Examples 1 to 4, and Comparative Example 10 were rolled under the condition that the friction coefficient of the upper roll = 0.3 and the friction coefficient of the lower roll = 0.1 in the hot rolling step. did.

The non-oriented electrical steel sheets of Comparative Examples 5 to 9 were rolled under the condition that the friction coefficient of the upper roll = 0.3 and the friction coefficient of the lower roll = 0.1 in the hot rolling step.

division Hot rolling strain (ε ₁₃ /ε ₁₁ )
winding temperature
(℃) Whether preliminary annealing process is in progress magnetic flux density
(B ₅₀ )
(T) iron loss
(W _15/50 )
(W/kg) surface layer 1/4th floor middle floor Example 1 0.75 1.13 0.71 720 X 1.688 2.54 Example 2 0.75 1.13 0.71 720 X 1.685 2.52 Example 3 0.75 1.13 0.71 720 X 1.688 2.54 Example 4 0.75 1.13 0.71 720 X 1.685 2.52 Comparative Example 1 0.75 1.13 0.71 610 X 1.651 3.02 Comparative Example 2 0.75 1.13 0.71 660 X 1.653 2.97 Comparative Example 3 0.75 1.13 0.71 720 X 1.661 2.68 Comparative Example 4 0.75 1.13 0.71 760 X 1.678 2.65 Comparative Example 5 0.86 0.84 0.05 610 X 1.648 3.77 Comparative Example 6 0.86 0.84 0.05 660 X 1.645 3.04 Comparative Example 7 0.86 0.84 0.05 720 X 1.650 2.97 Comparative Example 8 0.86 0.84 0.05 760 X 1.657 2.91 Comparative Example 9 0.86 0.84 0.05 610 O 1.681 2.62 Comparative Example 10 0.75 1.13 0.71 610 O 1.683 2.58 Comparative Example 11 0.75 1.13 0.71 700 X 1.679 2.59 Comparative Example 12 0.75 1.13 0.71 710 X 1.681 2.60

Referring to Table 1 and Table 2 together, the non-oriented electrical steel sheets of Examples 1 to 4 have a silicon content of 2% by weight or more and 2.8% by weight or less, and the entire thickness layer (surface layer, 1/4 layer, center layer) Since the hot rolling strain (ε ₁₃ /ε ₁₁ ) is greater than 0.5 and the coiling temperature (CT) satisfies 720℃ or higher and 770℃ or lower, excellent iron loss (W _15/50 ) and magnetic flux are achieved even without the final annealing process. Density (B ₅₀ ) is shown. Specifically, the non-oriented electrical steel sheets of Examples 1 to 4 showed an iron loss (W _15/50 ) of 2.55 W/kg or less and a magnetic flux density (B ₅₀ ) of 1.685T or more. Comparative Example 1 and Comparative Example 2 As the coiling temperature (CT) of the non-oriented electrical steel sheets of Examples 1 to 4 decreases below 720°C, the grains do not grow sufficiently and the iron loss (W _15/50 ) and magnetic flux density (B ₅₀₎ decrease. ) It is thought that the characteristics have deteriorated.

The non-oriented electrical steel sheet of Comparative Example 3 is believed to have reduced iron loss (W _15/50 ) and magnetic flux density (B ₅₀ ) characteristics as the main components of the steel are outside the scope of the present invention.

The non-oriented electrical steel sheets of Comparative Examples 5 to 9 were rolled so that the friction coefficients of the upper and lower rolls were the same in the rolling stage, so that the hot rolling strain (ε ₁₃ /ε ₁₁ ) in the center layer was less than 0.5. That is, in the non-oriented electrical steel sheets of Comparative Examples 5 to 9, the plane strain rate (ε ₁₁ ) in the central layer was higher than the shear strain rate (ε ₁₃ ), and shear strain did not sufficiently occur in the central layer. Accordingly, it is believed that the iron loss (W _15/50 ) and magnetic flux density (B ₅₀ ) characteristics were reduced compared to the non-oriented electrical steel sheets of Examples 1 to 4. In particular, the iron loss (W _15/50 ) and magnetic flux density (B ₅₀ ) characteristics of Comparative Examples 5 and 6 are thought to have further decreased compared to Comparative Examples 7 to 9 as the coiling temperature (CT) decreased below 720°C. . The non-oriented electrical steel sheet of Comparative Example 10 had a coiling temperature (CT) of less than 720°C, but final annealing was performed to reduce iron loss (W _15/50 ) and magnetic flux density (B ₅₀ ) among the non-oriented electrical steel sheets of Comparative Examples 5 to 9. It is thought to have the best characteristics.

The non-oriented electrical steel sheet of Comparative Example 10 has a coiling temperature (CT) of less than 720°C, but the final annealing process results in lower iron loss (W _15/50 ) and magnetic flux density (B ₅₀₎ compared to the non-oriented electrical steel sheets of Examples 1 to 4. ) Although the properties were deteriorated, it is believed that among the non-oriented electrical steel sheets of Comparative Examples 1 to 12, the iron loss (W _15/50 ) was measured to be the lowest and the magnetic flux density (B ₅₀ ) was measured to be the highest.

In the non-oriented electrical steel sheets of Comparative Examples 11 and 12, as the coiling temperature (CT) decreased below 720°C, the grains did not grow sufficiently and the iron loss (W _15/50 ) and magnetic flux density (B ₅₀ ) characteristics were thought to have decreased. do. It is believed that among the non-oriented electrical steel sheets of Comparative Examples 1 to 10, the iron loss (W _15/50 ) was measured to be the lowest and the magnetic flux density (B ₅₀ ) was measured to be the highest.

The method of manufacturing a non-oriented electrical steel sheet of the present invention is a process of controlling the friction coefficient of the upper roll and the friction coefficient of the lower roll differently in the hot rolling step, setting the coiling temperature to 720 ℃ or higher and 770 ℃ or lower, and performing final annealing. Even if omitted, the crystal grains grow sufficiently and a non-oriented electrical steel sheet with excellent magnetic properties can be manufactured. In particular, as the friction coefficient of the upper roll and the friction coefficient of the lower roll are different in the hot rolling stage, the hot rolling strain (ε ₁₃ /ε ₁₁ ) in the entire thickness layer of the steel sheet may be greater than 0.5.

In the non-oriented electrical steel sheet of the present invention, the hot rolling strain (ε ₁₃ /ε ₁₁ ) in the entire thickness layer is greater than 0.5, so the iron loss (W _15/50 ) is 2.55 W/kg or less and the magnetic flux density (B ₅₀ ) It can exhibit low core loss and high magnetic flux density characteristics of 1.685T or more.

In the above, the present invention has been described with reference to preferred embodiments, but those skilled in the art or have ordinary knowledge in the relevant technical field should not deviate from the spirit and technical scope of the present invention as set forth in the claims to be described later. It will be understood that various modifications and changes can be made to the present invention within the scope. Therefore, the technical scope of the present invention should not be limited to what is described in the description of the specification, but should be defined by the claims.

ST: hot rolled steel plate
RL1: Upper roll
RL2: lower roll

Claims (20)

Preparatory steps for reheating semi-finished products; and
A hot rolling step of hot rolling the semi-finished product using an upper roll and a lower roll to form a hot rolled steel sheet; Including,
A method of manufacturing a non-oriented electrical steel sheet wherein the friction coefficient of the upper roll is different from the friction coefficient of the lower roll. According to claim 1,
After the hot rolling step, the annealing step is omitted and the method of manufacturing a non-oriented electrical steel sheet further includes a winding step of winding the hot rolled steel sheet. According to clause 2,
A method of manufacturing a non-oriented electrical steel sheet in which the coiling temperature in the coiling step is 720°C or more and 770°C or less. According to clause 2,
After the coiling step, a cold rolling step of cold rolling the coiled hot rolled steel sheet to form a cold rolled steel sheet and a final annealing step of annealing and coating the cold rolled steel sheet. According to claim 1,
A method of manufacturing a non-oriented electrical steel sheet, wherein a friction reduction layer is provided on the surface of any one of the upper roll and the lower roll. According to clause 5,
The friction reducing layer is a method of manufacturing a non-oriented electrical steel sheet including lubricating oil. According to claim 1,
A method of manufacturing a non-oriented electrical steel sheet wherein the friction coefficient of one of the upper roll and the lower roll is 0.3, and the friction coefficient of the other is 0.1. According to claim 1,
Immediately after the hot rolling step, the hot rolled steel sheet is a method of manufacturing a non-oriented electrical steel sheet that satisfies the following equation 1:
[Equation 1]
ε ₁₃ /ε ₁₁ > 0.5
In equation 1 above,
ε ₁₃ /ε ₁₁ is the hot rolling strain,
ε ₁₃ is the shear strain rate of the hot rolled steel sheet,
ε ₁₁ is the plane strain rate of the hot rolled steel sheet. According to claim 1,
The semi-finished product has a silicon content of 2 wt% to 2.8 wt%, a carbon content of 0.002 wt% or less, a manganese content of 0.2 wt to 0.28 wt%, and an aluminum content of 0.32 wt to 0.45 wt%, A method for producing a non-oriented electrical steel sheet including a phosphorus content of 0.015% by weight or less, a sulfur content of 0.002% by weight or less, a nitrogen content of 0.002% by weight or less, a titanium content of 0.002% by weight or less, and the balance containing iron. Preparatory steps for reheating semi-finished products;
A hot rolling step of hot rolling the semi-finished product using an upper roll and a lower roll to form a hot rolled steel sheet;
A winding step of winding the hot rolled steel sheet while omitting the annealing step;
A cold rolling step of cold rolling the wound hot-rolled steel sheet to form a cold-rolled steel sheet; and
A final annealing step of annealing and coating the cold rolled steel sheet to form a final product; Including,
A method of manufacturing a non-oriented electrical steel sheet with a coiling temperature of 720°C or more and 770°C or less. According to claim 10,
A method of manufacturing a non-oriented electrical steel sheet wherein the friction coefficient of the upper roll is different from the friction coefficient of the lower roll. According to claim 10,
A method of manufacturing a non-oriented electrical steel sheet wherein the friction coefficient of one of the upper roll and the lower roll is 0.3, and the friction coefficient of the other is 0.1. According to claim 10,
One of the upper roll and the lower roll is a non-lubricated rolling roll, and the other is a lubricated rolling roll. According to claim 10,
Immediately after the hot rolling step, the hot rolled steel sheet is a method of manufacturing a non-oriented electrical steel sheet that satisfies the following equation 1:
[Equation 1]
ε ₁₃ /ε ₁₁ > 0.5
In equation 1 above,
ε ₁₃ /ε ₁₁ is the hot rolling strain,
ε ₁₃ is the shear strain rate of the hot rolled steel sheet,
ε ₁₁ is the plane strain rate of the hot rolled steel sheet. According to claim 10,
The semi-finished product has a silicon content of 2 wt% to 2.8 wt%, a carbon content of 0.002 wt% or less, a manganese content of 0.2 wt to 0.28 wt%, and an aluminum content of 0.32 wt to 0.45 wt%, A method for producing a non-oriented electrical steel sheet including a phosphorus content of 0.015% by weight or less, a sulfur content of 0.002% by weight or less, a nitrogen content of 0.002% by weight or less, a titanium content of 0.002% by weight or less, and the balance containing iron. According to claim 10,
The iron loss (W _15/50 ) of the final product is 2.55 W/kg or less, and the magnetic flux density (B ₅₀ ) is 1.685T or more. Based on weight percent, C: 0.002 or less, Si: 2 or more and 2.8 or less, Mn: 0.2 or more and 0.28 or less, Al: 0.32 or more and 0.45 or less, P: 0.015 or less, S: 0.002 or less, N: 0.002, Ti: 0.002 or less, Contains remaining iron and inevitable impurities,
Non-oriented electrical steel sheet that satisfies Equation 1 below:
[Equation 1]
ε ₁₃ /ε ₁₁ > 0.5
In equation 1 above,
ε ₁₃ /ε ₁₁ is the hot rolling strain,
ε ₁₃ is the shear strain rate,
ε ₁₁ is the plane strain. According to claim 17,
Non-oriented electrical steel sheet with iron loss (W _15/50 ) of 2.55 W/kg or less. According to claim 17,
Non-oriented electrical steel sheet with a magnetic flux density (B ₅₀ ) of 1.685T or more. According to claim 17,
The hot rolling strain (ε ₁₃ /ε ₁₁ ) in the 1/4 layer is greater than the hot rolling strain (ε ₁₃ /ε ₁₁ ) of the surface layer, and the hot rolling strain (ε ₁₃ /ε ₁₁ ) of the surface layer is greater than the hot rolling strain of the central layer. Non-oriented electrical steel sheet with a strain rate greater than (ε ₁₃ /ε ₁₁ ).

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