KR20240013556A - Non-oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of (a) hot rolling a first steel material and a second steel material containing silicon (Si), manganese (Mn), and aluminum (Al); (b) forming a first laminated structure by laminating the hot rolled first steel material and the second steel material with an intermediate layer containing ferrosilicon interposed; (c) forming a second laminated structure by cold rolling the first laminated structure; and (d) heat treating the cold rolled second layered structure so that silicon constituting the ferrosilicon diffuses uniformly throughout the second layered structure.

Description

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

The present invention relates to a non-oriented electrical steel sheet and a method of manufacturing the same, and more specifically, to a non-oriented electrical steel sheet with excellent high-frequency iron loss and a method of manufacturing the same.

Electrical steel sheets can be divided into oriented electrical steel sheets and non-oriented electrical steel sheets depending on their magnetic properties. Oriented electrical steel sheet is manufactured to facilitate magnetization in the rolling direction of the steel sheet and has particularly excellent magnetic properties in the rolling direction, so it is mainly used as the iron core of large, small and medium-sized transformers that require low core loss and high magnetic permeability. . In contrast, non-oriented electrical steel sheets have uniform magnetic properties regardless of the direction of the steel sheet, so they are widely used as iron core materials for small electric motors, small power transformers, and stabilizers.

Republic of Korea Patent Publication No. 2015-0001467A

The technical problem to be achieved by the present invention is to provide a non-oriented electrical steel sheet with excellent high-frequency iron loss characteristics and a method of manufacturing the same.

However, these tasks are illustrative and do not limit the scope of the present invention.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention to solve the above problem includes (a) first and second steel materials containing silicon (Si), manganese (Mn), and aluminum (Al); Hot rolling each; (b) forming a first laminated structure by laminating the hot rolled first steel material and the second steel material with an intermediate layer containing ferrosilicon interposed; (c) forming a second laminated structure by cold rolling the first laminated structure; and (d) heat treating the cold rolled second layered structure so that silicon constituting the ferrosilicon diffuses uniformly throughout the second layered structure.

In the method of manufacturing the non-oriented electrical steel sheet, the ferrosilicon is made of silicon and iron, and may contain 50 to 70% by weight of silicon (Si) and the remainder may be iron (Fe).

In the method of manufacturing the non-oriented electrical steel sheet, the silicon content of the second laminated structure after the heat treatment may be higher than the silicon content of the first steel material and the second steel material.

In the method of manufacturing the non-oriented electrical steel sheet, the ferrosilicon intervened in step (b) may be provided in powder form.

In the method of manufacturing the non-oriented electrical steel sheet, the first steel material and the second steel material include carbon (C): more than 0 and less than or equal to 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight, and manganese (Mn): 0.1 to 0.1% by weight. 0.5% by weight, aluminum (Al): 0.3 to 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight , Titanium (Ti): may contain more than 0 and less than 0.005% by weight, and the remaining iron (Fe) and other inevitable impurities.

In step (d) of the method for manufacturing the non-oriented electrical steel sheet, the heat treatment may include maintaining the heat treatment at a temperature of 1150°C to 1250°C for 3 to 6 hours.

In the method of manufacturing the non-oriented electrical steel sheet, the silicon content of the second laminated structure after the heat treatment may be 5.0 to 7.0% by weight.

In the method of manufacturing the non-oriented electrical steel sheet, the second laminated structure after the heat treatment has a thickness of 0.20 mm or more and can satisfy the characteristics of iron loss (W _10/400 ): 10 W/kg or less.

The non-oriented electrical steel sheet according to an embodiment of the present invention to solve the above problem contains silicon (Si), manganese (Mn), and aluminum (Al), respectively, but has ferro ferrite between the first and second hot-rolled steels. A laminated structure laminated with an intermediate layer containing silicon is implemented by cold rolling and heat treatment.

In the non-oriented electrical steel sheet, the ferrosilicon is made of silicon and iron, and may be silicon (Si): 50 to 70% by weight and the remainder may be iron (Fe).

In the non-oriented electrical steel sheet, the silicon content of the second laminated structure after the heat treatment is 5.0 to 7.0% by weight, and may be higher than the silicon content of the first and second steel materials.

In the non-oriented electrical steel sheet, the first steel material and the second steel material include carbon (C): greater than 0 and less than or equal to 0.005 wt%, silicon (Si): 2.0 to 4.0 wt%, and manganese (Mn): 0.1 to 0.5 wt%. , Aluminum (Al): 0.3 to 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight, titanium ( Ti): may contain more than 0 and less than 0.005% by weight, and the remaining iron (Fe) and other unavoidable impurities.

In the non-oriented electrical steel sheet, the second laminated structure after the heat treatment has a thickness of 0.20 mm or more and can satisfy the characteristics of iron loss (W _10/400 ): 10 W/kg or less.

According to an embodiment of the present invention, a non-oriented electrical steel sheet with excellent high-frequency iron loss characteristics and a method for manufacturing the same can be provided.

Of course, the scope of the present invention is not limited by this effect.

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 diagram schematically illustrating a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.
Figure 3 is a diagram schematically illustrating the distribution of silicon content centered on the middle layer in a non-oriented electrical steel sheet according to an embodiment of the present invention.
Figure 4 is a diagram schematically illustrating the distribution of silicon content centered on the middle layer in a non-oriented electrical steel sheet according to a comparative example of the present invention.
Figure 5 is an experimental example of the present invention, in which an intermediate layer containing ferrosilicon is sandwiched between two hot rolled steel sheets and then cold rolled under conditions of a predetermined cold rolling reduction ratio, and electrical steel sheets according to heat treatment time at a predetermined heat treatment temperature of 1250°C. This shows the change in iron loss.

A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail. The terms described below are terms appropriately selected in consideration of their functions in the present invention, and definitions of these terms should be made based on the content throughout the present specification.

Generally, electrical steel is divided into oriented electrical steel and non-oriented electrical steel. Grain-oriented electrical steel sheets are mainly used in stationary equipment such as transformers, while non-oriented electrical steel sheets are mainly used in rotating equipment such as motors. The properties of electrical steel can be evaluated by magnetic flux density and iron loss. Magnetic flux density is mainly evaluated as B ₅₀ , and iron loss is generally evaluated as W _15/50 , but in cases where high frequency characteristics are required, such as in electric vehicles, it is evaluated as W _10/400 . there is. B ₅₀ represents the magnetic flux density at 5000A/m, W _15/50 represents the iron loss at 50Hz and 1.5T, and W _10/400 represents the iron loss at 400Hz and 1.0T.

Recently, as a response to global environmental issues, technology is rapidly changing to hybrid vehicles (HEV)/electric vehicles (EV)/hydrogen vehicles to replace existing internal combustion engines, and in the case of electric vehicles, High-efficiency, high-frequency iron loss (W _10/400 ) characteristics are required.

As a way to improve iron loss, it is possible to improve resistivity by adding elements such as silicon (Si), manganese (Mn), and aluminum (Al), or by making the material thinner. However, when alloy elements such as silicon (Si), manganese (Mn), and aluminum (Al) increase, rolling becomes difficult and thinning becomes difficult, and when the thickness of the electrical steel sheet is reduced, the production cost increases and productivity decreases. It has the disadvantage of decreasing

Figure 1 is a flow chart showing a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention, and Figure 2 is a diagram schematically illustrating a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. Figure 3 is a diagram schematically illustrating the distribution of silicon content centered on the middle layer in a non-oriented electrical steel sheet according to an embodiment of the present invention.

Referring to Figures 1 and 2, the method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes (a) a first steel material (11) containing silicon (Si), manganese (Mn), and aluminum (Al); ) and the second steel material 12, respectively, hot rolling (S100); (b) forming the first laminated structure 10 by laminating the hot rolled first steel 11 and the second steel 12 with an intermediate layer 13 containing ferrosilicon (S200) ); Cold rolling the first laminated structure to form a second laminated structure 20 (S300); and heat-treating the cold-rolled second laminated structure 20 so that silicon constituting the ferrosilicon spreads uniformly throughout the second laminated structure 20 (S400).

Hot rolling step (S100)

The first steel material 11 and the second steel material 12 are steel materials for manufacturing non-oriented electrical steel sheets, for example, carbon (C): more than 0 and less than 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight. %, manganese (Mn): 0.1 to 0.5% by weight, aluminum (Al): 0.3 to 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen ( N): more than 0 and less than 0.005% by weight, titanium (Ti): more than 0 and less than 0.005% by weight, and the remainder includes iron (Fe) and other inevitable impurities.

However, the method of manufacturing a non-oriented electrical steel sheet according to the technical idea of the present invention is not limited by this example of composition range, and can be expanded to any composition range that can perform the function of a non-oriented electrical steel sheet. Below, the role and content of exemplary composition components to which the method for manufacturing a non-oriented electrical steel sheet according to the technical idea of the present invention can be applied will be described.

Carbon (C): greater than 0 and less than or equal to 0.005% by weight

Carbon (C) is an element that increases iron loss by forming carbides such as TiC and NbC. The smaller the carbon, the more desirable it is, and it is limited to 0.005% by weight or less. If the carbon content exceeds 0.005% by weight, self-aging occurs and magnetic properties deteriorate, and if the carbon content is less than 0.005% by weight, the self-aging phenomenon is suppressed.

Silicon (Si): 2.0 to 4.0% by weight

Silicon (Si) is a major added element that increases resistivity and lowers iron loss (eddy current loss). If the amount of silicon added is low, less than 2.0% by weight, it becomes difficult to obtain the desired low iron loss value, and as the amount added, permeability and magnetic flux density decrease. Additionally, if the amount of silicon added exceeds 4.0% by weight, brittleness increases, making cold rolling difficult and productivity decreasing.

Manganese (Mn): 0.1 to 0.5% by weight

Manganese (Mn), along with silicon, increases resistivity and improves texture. When manganese is added in amounts of less than 0.1% by weight, it forms fine MnS precipitates, suppressing grain growth, and when added in excess of 0.5% by weight, coarse MnS precipitates are formed, which reduces magnetic flux density and deteriorates magnetic properties. Furthermore, when the manganese content exceeds 0.5% by weight, the reduction in iron loss is small compared to the addition amount, but cold rolling properties are significantly reduced.

Aluminum (Al): 0.3 to 0.9% by weight

Aluminum (Al) is a major added element that, along with silicon, increases resistivity and lowers iron loss (eddy current loss). Aluminum plays a role in reducing magnetic deviation by reducing magnetic anisotropy. Aluminum meets nitrogen and induces AlN precipitation. If the aluminum content is less than 0.3% by weight, it is difficult to expect the above-mentioned effect, and fine nitrides may be formed, which may increase the variation in magnetic properties. If the aluminum content exceeds 0.9% by weight, cold rolling properties are deteriorated, and Excessive nitride formation reduces magnetic flux density and deteriorates magnetic properties.

Phosphorus (P): greater than 0 and less than or equal to 0.015% by weight

Phosphorus (P) is a grain boundary segregation element that develops texture. If the phosphorus content exceeds 0.015% by weight, grain growth is suppressed due to the segregation effect, magnetic properties are deteriorated, and cold rolling properties are deteriorated.

Sulfur (S): greater than 0 and less than or equal to 0.005% by weight

Sulfur (S) increases iron loss by forming precipitates such as MnS and CuS, and suppresses grain growth, so its addition is limited to 0.005% by weight or less. If the sulfur content exceeds 0.003% by weight, the problem of increased iron loss occurs.

Nitrogen (N): greater than 0 and less than or equal to 0.005% by weight

Nitrogen (N) increases iron loss by forming precipitates such as AlN, Tin, and NbN, and suppresses grain growth, so its addition is limited to 0.005% by weight or less. If the nitrogen content exceeds 0.003% by weight, the problem of increased iron loss occurs.

Titanium (Ti): More than 0 and less than 0.005% by weight

Titanium (Ti) suppresses grain growth by forming fine precipitates such as TiC and TiN. The magnetic properties deteriorate as titanium is added, so the addition is limited to as low as possible and limited to 0.005% by weight or less. If the titanium content exceeds 0.005% by weight, the problem of magnetic properties deterioration occurs.

The first steel material 11 and the second steel material 12 having the above-described composition each undergo a hot rolling process.

The step of hot rolling the steel (S100) includes reheating the steel under reheating temperature (SRT) conditions of 1000 to 1200°C, hot rolling under finish rolling temperature (FDT) conditions of 860 to 900°C, and 550 to 650°C. It may include the step of winding at a coiling temperature (CT) of ℃.

If the slab reheating temperature exceeds 1200°C, precipitates such as C, S, and N in the slab may be re-dissolved and fine precipitates may be generated during the subsequent rolling and annealing process, suppressing grain growth and deteriorating magnetism. If the slab reheating temperature is less than 1000℃, the rolling load increases. More preferably, the slab reheating temperature can be set to 1000 to 1200°C.

The thickness (t1) of the hot rolled first steel material 11 and the second steel material 12 may be 1.6 to 2.6 mm, respectively. As the thickness of the hot-rolled sheet increases, the cold rolling reduction rate increases and the texture becomes inferior, so it is desirable to set the thickness to 2.6 mm or less.

First layered structure forming step (S200)

Referring to (b) of FIG. 2, a first laminated structure 10 is laminated between hot rolled first steel materials 11 and second steel materials 12 with an intermediate layer 13 containing ferrosilicon. forms. The thickness of the intermediate layer 13 may be, for example, 0.3 mm or more, and the thickness t2 of the first laminated structure 10 may be, for example, 3.5 to 5.8 mm.

The ferrosilicon is an iron alloy made of silicon and iron. For example, it may be made of silicon (Si): 50 to 70% by weight and the remainder is iron (Fe). The ferrosilicon may be provided, for example, in powder form.

Silicon constituting ferrosilicon may diffuse into the first steel material 11 and the second steel material 12 due to the subsequent heat treatment process. Meanwhile, in a modified embodiment of the present invention, the process by which silicon constituting ferrosilicon diffuses into the first steel material 11 and the second steel material 12 is partially performed in a hot rolling annealing and/or cold rolling annealing process in addition to the heat treatment process. It could be.

On the other hand, if the silicon content in the ferrosilicon constituting the middle layer 13 is less than 50% by weight, the target silicon content (5.0 to 7.0% by weight) in the non-oriented electrical steel sheet is lowered, resulting in the iron loss of the final non-oriented electrical steel sheet. The reduction effect may be minimal. If the thickness of the intermediate layer 13 containing ferrosilicon with a silicon content of less than 50% by weight is increased in order to achieve the target silicon content (5.0 to 7.0% by weight) in the non-oriented electrical steel sheet, the final non-oriented electrical steel sheet The thickness of the electrical steel sheet also increases, so the effect of reducing iron loss may be minimal.

If the content of silicon in the ferrosilicon constituting the middle layer 13 exceeds 70% by weight, surface brittleness increases due to excessive diffusion of silicon from the middle layer composed of ferrosilicon to the surface of the non-oriented electrical steel sheet, leading to problems of punching defects and coating defects. problems may appear.

The bonding force between the intermediate layer 13 containing ferrosilicon and the first steel material 11 or the second steel material 12 is such that silicon diffuses from the ferrosilicon in the hot rolling annealing process performed before the cold rolling process, forming ferrosilicon. This may be due to homogeneous joining in which the iron forming the first steel material 11 or the second steel material 12 is joined. According to this homogeneous bonding, in constructing the first laminated structure 10, the intermediate layer 13 containing ferrosilicon is introduced, thereby interposing the intermediate layer 13 between the first steel material 11 and the second steel material 12. A beneficial effect can be expected in that there is no need to additionally form a separate bonding layer.

On the other hand, if the middle layer 13 is composed of silicon oxide, which is a ceramic, rather than ferrosilicon, the bonding between silicon oxide, which is an insulating material, and the first steel material 11 or the second steel material 12 is due to instability of the interface due to heterogeneous bonding. It becomes defective. In the case of homogeneous bonding in which the middle layer 13 is made of ferrosilicon, the bonding force between the middle layer 13 and the first steel material 11 or the second steel material 12 is higher than in the case of heterogeneous bonding in which the middle layer 13 is made of silicon oxide. Significantly improved effects can be expected.

Second layered structure forming step (S300)

Referring to (c) of FIG. 2, the second laminated structure 20 can be formed by cold rolling the above-described first laminated structure 10. Cold rolling is performed on the first laminated structure 10 to a final thickness (t3) of about 0.2 mm to 0.35 mm. To facilitate rolling, warm rolling can be performed by raising the plate temperature to 100 to 200°C. The final reduction rate can be adjusted from 50% to 85%.

Heat treatment step (S400)

Referring to (d) of FIG. 2, the cold rolled second laminated structure 20 is heat treated. The heat treatment step (S400) includes maintaining the temperature at 1150°C to 1250°C for 3 to 6 hours. The heat treatment process may be a batch type heat treatment process rather than a heat treatment process in a continuous annealing equipment (ACL; Annealing and Coating Line). Since the heat treatment process is a long-term, high-temperature heat treatment process, it can be performed in an atmosphere containing 80 to 99% by volume of hydrogen and the remainder is nitrogen to suppress oxidation of the steel sheet.

Through the heat treatment, silicon constituting the ferrosilicon can spread uniformly throughout the second layered structure 20 (see FIG. 3). The uniformly diffused silicon content (5.0 to 7.0% by weight; exemplarily 5.5% by weight in FIG. 3) in the second laminated structure 20 after the heat treatment is the first steel material 11 and the second steel material 12. higher than the silicon content (2.0 to 4.0% by weight).

To reduce iron loss in non-oriented electrical steel sheets, there are methods of reducing sheet thickness or increasing resistivity. Among them, the specific resistance can be increased by increasing the silicon content, but there are problems with the decrease in cold rolling recovery rate due to the increase in silicon content and the decrease in productivity due to thin rolling and heat treatment. When cold rolling steel containing more than 4% by weight of silicon, Problems may arise where the steel plate breaks.

To overcome this problem, it was previously possible to increase the silicon content of the steel sheet by applying a method of coating silicon on the surface of the steel sheet and heat treating it. However, this method used a chemical vapor deposition method using silicon tetrachloride (SiCl ₄ ), etc. during silicon coating. Since (CVD) must be applied or powder containing silicon must be applied to the upper and lower surfaces of the steel sheet, there are many limitations in the process to sufficiently increase the silicon content, and there is a problem of using reaction gas that is harmful to the environment. In order to stably apply a high content of silicon material to the surface of a steel plate, the existing technology uses a colloidal silica solution, so a process of drying the solution must be added, making it difficult to apply a sufficient amount of the material. There is. Additionally, when a material is applied to the surface, an atmosphere with a high content of hydrogen and nitrogen is required to suppress oxidation of the silicon material during heat treatment.

The present invention can be expected to have the advantageous effects of suppressing oxidation and easily controlling the application amount by adding a silicone material to the inner layer of the steel sheet. Additionally, it has the advantage of not using reaction gases that are harmful to the environment.

Meanwhile, in a modified embodiment of the present invention, cold rolling annealing may be performed after the cold rolling and before the heat treatment process. The cold rolling annealing treatment can be performed in a continuous annealing device (ACL; Annealing and Coating Line), and annealing is performed under the following conditions: temperature increase rate: 10°C/s or more, annealing temperature: 900 to 1100°C, holding time: 30 to 90 seconds. Step, cooling rate: may include cooling under conditions of 30°C/s or more. The cold rolling annealing is performed with the cold rolled sheet obtained after cold rolling. The temperature that derives the optimal grain size is applied considering the improvement of iron loss and mechanical properties. In cold rolling annealing, heating is performed under mixed atmosphere conditions to prevent surface oxidation and nitriding. The surface condition is made smoother through a mixed atmosphere of nitrogen and hydrogen (hydrogen: 5 to 15% by volume, the remainder is nitrogen). If the cold rolling annealing temperature is less than 900°C, the grain size may be fine and hysteresis loss may increase, and if the cold rolling annealing temperature exceeds 1100°C, the grain size may become coarse and eddy current loss may increase.

However, in the method of manufacturing a non-oriented electrical steel sheet of the present invention, the heat treatment process is different from the cold rolling annealing process in terms of equipment, temperature, time, atmosphere, etc., and silicon constituting ferrosilicon is used in the second laminated structure 20. The phenomenon of uniform diffusion throughout is mainly realized by the heat treatment process.

After the heat treatment process, a coating process may be performed to form the insulating coating layer 15. By forming the insulating coating layer 15, improved punching properties and insulation properties can be secured. The thickness of the insulating coating layer 15 formed on the top of the second laminated structure 20 may be about 1 ㎛, and the thickness of the insulating coating layer 15 formed on the top of the second laminated structure 20 may also be about 1 ㎛.

The non-oriented electrical steel sheet implemented by the above-described manufacturing method contains silicon (Si), manganese (Mn), and aluminum (Al), but an intermediate layer containing ferrosilicon is interposed between the hot-rolled first and second steel materials. The laminated structure is implemented by cold rolling and heat treatment. The ferrosilicon is made of silicon and iron, and may contain 50 to 70% by weight of silicon (Si) and the remainder may be iron (Fe). The silicon content of the second laminated structure after the heat treatment is 5.0 to 7.0% by weight, and is higher than the silicon content of the first and second steel materials.

The crystal grain size of the final product is 120 ~ 200㎛, the magnetic flux density (B ₅₀ ) is 1.50T or more, and at a thickness of 0.2mm or more, the iron loss (W _10/400 ) is less than 14.5W/Kg, strictly less than 10.0W/Kg. You can. Mechanical properties can achieve yield strength (YP) of more than 400 MPa and tensile strength (TS) of more than 500 MPa.

The first steel material and the second steel material include carbon (C): greater than 0 and less than or equal to 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight, manganese (Mn): 0.1 to 0.5% by weight, and aluminum (Al): 0.3. ~ 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight, titanium (Ti): more than 0 and less than 0.005% by weight % or less and the remainder may contain iron (Fe) and other unavoidable impurities, respectively.

Experiment example

Below, preferred experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are only intended to aid understanding of the present invention, and the present invention is not limited by the following experimental examples.

1. Composition of the Psalm

In this experimental example, specimens having the alloy element composition (unit: weight%) shown in Table 1 are provided.

C Si Mn Al P S N Ti Bal. 0.0018 3.3 0.3 0.9 0.0055 0.0021 0.0019 0.0020 Fe

Referring to Table 1, the composition of the non-oriented electrical steel sheet according to the experimental example is carbon (C): more than 0 and less than 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight, manganese (Mn): 0.1 to 0.5% by weight. , Aluminum (Al): 0.3 to 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight, titanium ( Ti): exceeds 0 and satisfies 0.005% by weight or less and the remaining iron (Fe).

2. Evaluation of process conditions and physical properties

Table 2 shows the process conditions and physical properties in the method of manufacturing a non-oriented electrical steel sheet according to an experimental example of the present invention. In the experimental examples, hot rolling was performed on steel materials having the compositions in Table 1 under the same conditions of hot rolling reheating temperature (SRT): 1100°C, finish rolling temperature (FDT): 880°C, and coiling temperature (CT): 600°C.

In Table 2, among the cold rolling method items, in the single sheet cold rolling method, a hot rolled single steel sheet is cold rolled under the conditions of a predetermined cold rolling reduction rate without introducing an intermediate layer containing ferrosilicon, annealing temperature: 1150°C, holding time: 60 seconds. After cold rolling annealing, magnetic flux density (B ₅₀ , unit: T) and iron loss (W _10/400 , unit: W/kg) were measured. The silicon content in the steel sheet was measured after cold rolling annealing.

In Table 2, among the cold-rolling method items, in the two-ply cold-rolling method, an intermediate layer containing ferrosilicon is sandwiched between two hot-rolled steel sheets, as shown in Figure 1, and then cold-rolled under the conditions of a predetermined cold rolling reduction rate, and heat treatment at a predetermined heat treatment temperature. A heat treatment process was performed under time conditions to allow the silicon that makes up ferrosilicon to diffuse into the steel sheet, and then the magnetic flux density (B ₅₀ , unit: T) and iron loss (W _10/400 , unit: W/kg) were measured. The ferrosilicon has a composition range of silicon (Si): 50 to 70% by weight and the balance is iron (Fe). The steel sheet silicon content was measured after the heat treatment.

cold rolling
method heat treatment temperature
(℃) heat treatment time hot rolled thickness
(mm) faro
silicon
thickness
(mm) Cold rolling reduction rate
(%) final thickness
(mm) Si average of steel plate
(%) from the surface
full thickness
1/10th of the position
Si content (%) iron loss
magnetic flux
density
Experimental Example 1 veneer 1150 60 seconds 2.0 0 90.0 0.20 3.3 3.3 11.1 1.62 Experimental Example 2 veneer 1150 60 seconds 2.0 0 87.5 0.25 3.3 3.3 12.8 1.66 Experimental Example 3 2 layers 1150 60 seconds 4.3
(Hot rolled + ferrosilicon layer) 0.3 94.2 0.25 6.6 3.3 11.3 1.64 Experimental Example 4 2 layers 1100 3 hours 4.3
(Hot rolled + ferrosilicon layer) 0.3 94.2 0.25 6.6 5.4 8.5 1.61 Experimental Example 5 2 layers 1250 30 minutes 4.3
(Hot rolled + ferrosilicon layer) 0.3 94.2 0.25 6.6 4.1 11.0 1.62 Experimental Example 6 2 layers 1250 3 hours 4.1
(Hot rolled + ferrosilicon layer) 0.1 93.9 0.25 4.4 4.4 10.6 1.57 Experimental Example 7 2 layers 1250 3 hours 4.3 (Hot rolled + ferrosilicon layer) 0.3 94.2 0.25 6.6 6.6 5.7 1.52

Referring to Table 2, in Experimental Example 7, as an example of the present invention, a heat treatment process was performed at a temperature of 1150°C to 1250°C for 3 to 6 hours, and silicon (Si): 50 to 70% by weight and the remainder As a result of performing cold rolling and heat treatment with a thickness of 0.3 mm of ferrosilicon (Fe), the final electrical steel sheet with a thickness of 0.25 mm satisfied the characteristics of iron loss (W _10/400 ): 10 W/kg or less. It can be confirmed that the silicon content in the final electrical steel sheet is uniformly 5.0 to 7.0% by weight.

In Experimental Example 6, a heat treatment process was performed at a temperature of 1150°C to 1250°C for 3 to 6 hours, but the thickness of ferrosilicon, which contains 50 to 70% by weight of silicon (Si) and the remainder is iron (Fe), was 0.3 mm. As a result of performing cold rolling and heat treatment with a lower thickness of 0.1mm, it was confirmed that the final electrical steel sheet with a thickness of 0.25mm did not satisfy the characteristics of iron loss (W _10/400 ): 10 W/kg or less. .

In Experimental Example 5, cold rolling and heat treatment were performed using ferrosilicon containing 50 to 70% by weight of silicon (Si) and the remainder being iron (Fe) with a thickness of 0.3 mm, but the heat treatment process was carried out at a temperature of 1150°C to 1250°C. As a result of performing a heat treatment process lasting only 30 minutes (less than 3 hours), the silicon that makes up ferrosilicon was not sufficiently diffused into the electrical steel sheet, and the iron loss (W _10/400 ) in the final electrical steel sheet with a thickness of 0.25 mm was: It can be confirmed that the characteristics below 10 W/kg are not satisfied, and the silicon content in the final electrical steel sheet is not uniform.

In Experimental Example 4, cold rolling and heat treatment were performed using ferrosilicon containing 50 to 70% by weight of silicon (Si) and the remainder being iron (Fe) with a thickness of 0.3 mm, but the heat treatment process was carried out at a temperature of 1150°C to 1250°C. As a result of performing a heat treatment process maintained at a lower temperature of 1100°C for 3 hours, the final electrical steel sheet with a thickness of 0.25mm satisfies the characteristics of iron loss (W _10/400 ): 10 W/kg or less, but consists of ferrosilicon. It can be confirmed that the silicon content in the final electrical steel sheet is not uniform because the silicon is not sufficiently diffused into the electrical steel sheet.

In Experimental Example 3, cold rolling and heat treatment were performed using ferrosilicon containing 50 to 70% by weight of silicon (Si) and the remainder being iron (Fe) with a thickness of 0.3 mm, but the heat treatment process was carried out at a temperature of 1150°C to 1250°C. As a result of performing a heat treatment process lasting only 60 seconds, which is less than 3 hours, the silicon constituting ferrosilicon was not sufficiently diffused into the electrical steel sheet, and the iron loss (W _10/400 ) in the final electrical steel sheet with a thickness of 0.25 mm was: It can be confirmed that the characteristics below 10 W/kg are not satisfied, and the silicon content in the final electrical steel sheet is not uniform.

In Experimental Examples 1 and 2, a hot-rolled single steel sheet was cold-rolled under the conditions of a predetermined cold rolling reduction rate without introducing an intermediate layer containing ferrosilicon, and cold-rolled and annealed under the conditions of annealing temperature: 1150°C and holding time: 60 seconds. As a result, it can be confirmed that the final electrical steel sheet with a thickness of 0.20 mm or more does not satisfy the characteristic of iron loss (W _10/400 ): 10 W/kg or less.

Figure 3 is a diagram schematically illustrating the distribution of silicon content centered on the middle layer in the non-oriented electrical steel sheet according to an embodiment of the present invention, and Figure 4 is a diagram schematically illustrating the distribution of silicon content centered on the middle layer in the non-oriented electrical steel sheet according to the comparative example of the present invention. This is a diagram schematically illustrating the distribution of silicon content.

The distribution of silicon content in the electrical steel sheet in Experimental Example 7 is uniformly distributed across the thickness direction in the finally implemented electrical steel sheet, as shown in FIG. 3. On the other hand, the distribution of silicon content in the electrical steel sheet in Experimental Examples 3 to 6 is not uniformly distributed across the thickness direction in the finally implemented electrical steel sheet as shown in Figure 4, and the intermediate layer composed of ferrosilicon The silicon content gradually decreases in the direction from (13) to the first steel material (11) and from the intermediate layer (13) composed of ferrosilicon to the second steel material (12).

Figure 5 is an experimental example of the present invention in which an intermediate layer containing ferrosilicon is interposed between two hot rolled steel sheets, then cold rolled under the conditions of a predetermined cold rolling reduction rate, and electrical steel sheets according to heat treatment time at a predetermined heat treatment temperature of 1250°C. This shows the change in iron loss. The thickness of the middle layer containing ferrosilicon was 0.3 mm, and the thickness of each of the two hot rolled steel sheets was 2.0 mm.

Referring to Figure 5, it can be seen that when the heat treatment time for the silicon constituting ferrosilicon to diffuse into the electrical steel sheet is more than 1 hour, the iron loss of the electrical steel sheet decreases rapidly.

So far, the non-oriented electrical steel sheet and its manufacturing method according to the technical idea of the present invention have been described. In the electrical steel sheet manufacturing process, if more than 4% by weight of silicon is contained, workability is reduced and cold rolling is generally impossible. However, the silicon content of the steel sheet can be significantly increased through silicon diffusion from the intermediate layer placed inside, thereby reducing iron loss. It was confirmed that it exists. Additionally, it can be understood that more silicone material can be added by adding the silicone material in powder form to the intermediate layer rather than applying it in liquid form to the surface.

Although the above description focuses on the embodiments of the present invention, various changes and modifications can be made at the level of those skilled in the art. These changes and modifications can be said to belong to the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of rights of the present invention should be determined by the claims described below.

Claims (13)

(a) hot rolling first and second steel materials containing silicon (Si), manganese (Mn), and aluminum (Al), respectively;
(b) forming a first laminated structure by laminating the hot rolled first steel material and the second steel material with an intermediate layer containing ferrosilicon interposed;
(c) forming a second laminated structure by cold rolling the first laminated structure; and
(d) heat treating the cold rolled second layered structure so that the silicon constituting the ferrosilicon diffuses uniformly throughout the second layered structure;
Method for manufacturing non-oriented electrical steel sheet. According to claim 1,
The ferrosilicon is made of silicon and iron, with silicon (Si): 50 to 70% by weight and the balance being iron (Fe),
Method for manufacturing non-oriented electrical steel sheet. According to claim 1,
Characterized in that the silicon content of the second laminated structure after the heat treatment is higher than the silicon content of the first steel material and the second steel material,
Method for manufacturing non-oriented electrical steel sheet. According to claim 1,
Characterized in that the ferrosilicon intervened in step (b) is provided in powder form,
Method for manufacturing non-oriented electrical steel sheet. The method according to any one of claims 1 to 4,
The first steel material and the second steel material include carbon (C): greater than 0 and less than or equal to 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight, manganese (Mn): 0.1 to 0.5% by weight, and aluminum (Al): 0.3. ~ 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight, titanium (Ti): more than 0 and less than 0.005% by weight % or less and the remaining iron (Fe) and other unavoidable impurities, respectively,
Method for manufacturing non-oriented electrical steel sheet. According to claim 5,
In step (d), the heat treatment includes maintaining the heat treatment at a temperature of 1150°C to 1250°C for 3 to 6 hours.
Method for manufacturing non-oriented electrical steel sheet. According to claim 6,
Characterized in that the silicon content of the second laminated structure after the heat treatment is 5.0 to 7.0% by weight,
Method for manufacturing non-oriented electrical steel sheet. According to claim 5,
After the heat treatment, the second laminated structure has a thickness of 0.20 mm or more and satisfies the characteristics of iron loss (W _10/400 ): 10 W/kg or less,
Method for manufacturing non-oriented electrical steel sheet. A laminated structure containing silicon (Si), manganese (Mn), and aluminum (Al), respectively, and laminated with an intermediate layer containing ferrosilicon between the hot-rolled first and second steel materials is implemented by cold rolling and heat treatment. made,
Non-oriented electrical steel sheet. According to clause 9,
The ferrosilicon is made of silicon and iron, with silicon (Si): 50 to 70% by weight and the balance being iron (Fe),
Non-oriented electrical steel sheet. According to clause 9,
The silicon content of the second laminated structure after the heat treatment is 5.0 to 7.0% by weight, and is higher than the silicon content of the first and second steel materials,
Non-oriented electrical steel sheet. According to claim 11,
The first steel material and the second steel material include carbon (C): greater than 0 and less than or equal to 0.005% by weight, silicon (Si): 2.0 to 4.0% by weight, manganese (Mn): 0.1 to 0.5% by weight, and aluminum (Al): 0.3. ~ 0.9% by weight, phosphorus (P): more than 0 and less than 0.015% by weight, sulfur (S): more than 0 and less than 0.005% by weight, nitrogen (N): more than 0 and less than 0.005% by weight, titanium (Ti): more than 0 and less than 0.005% by weight % or less and the remaining iron (Fe) and other unavoidable impurities, respectively,
Non-oriented electrical steel sheet. According to claim 12,
After the heat treatment, the second laminated structure has a thickness of 0.20 mm or more and satisfies the characteristics of iron loss (W _10/400 ): 10 W/kg or less,
Non-oriented electrical steel sheet.