Non-oriented electromagnetic steel sheet and method for producing the same

Abstract

The present invention relates to a non-oriented electrical steel sheet containing silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, and the balance of iron (Fe) and other inevitable impurities. Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, and the iron loss (W 10 / 400 ) is 12.0 W / kg or less. Provided is a non-oriented electrical steel sheet characterized by having the above properties.

Description

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and more particularly, to a high-efficiency non-oriented electrical steel sheet and a method for manufacturing the same.

Background Art

[0002] Electrical steel sheets can be classified into oriented electrical steel sheets and non-oriented electrical steel sheets according to their magnetic properties. Oriented electrical steel sheets are manufactured so that magnetization is easy in the rolling direction of the steel sheet and have particularly excellent magnetic properties in the rolling direction. Therefore, they are mainly used as cores for large, medium-sized, and small-sized transformers that require low iron loss and high magnetic permeability. On the contrary, non-oriented electrical steel sheets have uniform magnetic properties regardless of the direction of the steel sheet, and thus are widely used as core materials for small electric motors, small power transformers, ballasts, and the like.

[0003] As a prior art document, there is Korean Patent Publication No. 10-2015-0001467.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technical problem to be achieved by the present invention is to provide a high-efficiency non-oriented electrical steel sheet and a method for manufacturing the same.

[0005] However, such problems are exemplary and do not limit the scope of the present invention.

Means for Solving the Problems

[0006] In order to solve the above problems, one aspect of the present invention provides a non-oriented electrical steel sheet containing 2.8 to 3.8 wt% silicon (Si), 0.2 to 0.5 wt% manganese (Mn), 0.5 to 1.5 wt% aluminum (Al), more than 0 to 0.003 wt% carbon (C), more than 0 to 0.015 wt% phosphorus (P), more than 0 to 0.015 wt% sulfur (S), more than 0 to 0.003 wt% nitrogen (N), more than 0 to 0.003 wt% titanium (Ti), and the remainder being iron (Fe) and other unavoidable impurities, wherein the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more among secondary phase particles constituting the microstructure is 60% or more, and the iron loss (W) is 12.0 W / kg or less. 10 / 400 ) is characterized by having.

[0007] In the non-oriented electrical steel sheet, among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more and less than 2.0 μm may be 20% or more, and the volume fraction of secondary phase particles having an average diameter of 2.0 μm or more may be 38% or more.

[0008] In the non-oriented electrical steel sheet, the secondary phase particles may include precipitate particles and inclusion particles.

[0009] The microstructure of the non-oriented electrical steel sheet may have an average crystal grain size of 80 to 160 μm.

[0010] According to one aspect of the present invention for solving the above problems, a method for manufacturing a non-oriented electromagnetic steel sheet includes: providing a steel material containing silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): 0.2 to 0.5% by weight, aluminum (Al): 0.5 to 1.5% by weight, carbon (C): more than 0 and 0.003% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.003% by weight or less, nitrogen (N): more than 0 and 0.003% by weight or less, titanium (Ti): more than 0 and 0.003% by weight or less, and the balance iron (Fe) and other inevitable impurities; hot rolling the steel material; performing a first annealing heat treatment on the hot-rolled steel material; cold rolling the steel material after the first annealing heat treatment; and performing a second annealing heat treatment on the cold-rolled steel material. The step of hot rolling includes a step of winding at a coiling temperature (CT) of 500 to 700°C after hot rolling. The step of performing the first annealing heat treatment includes a step of annealing at 940 to 1110°C. The step of performing the second annealing heat treatment includes a step of annealing at 900 to 1100°C.

[0011] In the method for manufacturing the non-oriented electromagnetic steel sheet, the step of hot rolling can be performed under the conditions of a reheating temperature (SRT) of 1110 to 1150°C and a finishing rolling temperature (FDT) of 800 to 900°C.

[0012] In the method for manufacturing the non-oriented electromagnetic steel sheet, the thickness of the hot-rolled steel material is 1.6 to 2.6 mm, and the thickness of the cold-rolled steel material may be 0.35 mm or less.

[0013] In the method for manufacturing the non-oriented electromagnetic steel sheet, after the step of performing the second annealing heat treatment, among the secondary phase particles constituting the microstructure, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more may be 60% or more.

Advantages of the Invention

[0014] According to an embodiment of the present invention, a high-efficiency non-oriented electromagnetic steel sheet and a method for manufacturing the same can be provided.

[0015] Of course, the scope of the present invention is not limited by such effects.

Brief Description of the Drawings

[0016]

Figure 1

Modes for Carrying Out the Invention

[0017] A method for manufacturing a non-oriented electromagnetic 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 the functions in the present invention, and the definitions of such terms must be made based on the content throughout this specification.

[0018] Generally, electromagnetic steel sheets are classified into oriented electromagnetic steel sheets and non-oriented electromagnetic steel sheets. In the case of oriented electromagnetic steel sheets, they are mainly used in static devices such as transformers, and non-oriented electromagnetic steel sheets are mainly used in rotating devices such as motors and generators. Recently, as a response to global environmental problems, technologies have been rapidly converted to hybrid electric vehicles (HEVs), electric vehicles (EVs), and hydrogen vehicles that replace existing internal combustion engines. The characteristics of electromagnetic steel sheet materials can be evaluated by magnetic flux density and iron loss. The magnetic flux density is B 50 , and in the case of iron loss, it is generally evaluated mainly by W 15 / 50 , but when high-frequency characteristics are required as in the case of electric vehicles, it is evaluated by W 10 / 400 iron loss. B 50 indicates the magnetic flux density at 5000 A / m, W 15 / 50 indicates the iron loss at 50 Hz and 1.5 T, and W 10 / 400 indicates the iron loss at 400 Hz and 1.0 T.

[0019] As typical methods for improving the magnetic properties of electromagnetic steel sheets, there are methods such as adding elements such as Si, Al, and Mn to increase the specific resistance or using thinner materials. However, when adding specific resistance increasing elements such as Si, Al, and Mn, the magnetic flux density decreases due to the addition of alloy elements, and rolling becomes difficult, making it difficult to reduce the thickness. The thinner the material, the more problems such as a decrease in productivity and an increase in cost occur.

[0020] In addition to Si, Al, and Mn, which are the main alloy elements of non-oriented electromagnetic steel sheets, impurity elements such as C, S, N, and Ti, which are inevitably added, can combine to form fine precipitates and inclusions. Such secondary phase particles hinder the movement of magnetic domains and deteriorate the magnetic properties. The finer such secondary phase particles are, the more they hinder the movement of magnetic domains and suppress the growth of crystal grains. Therefore, it is very important to control the size and fraction of secondary phase particles.

[0021] In the case of an example of a technique for controlling inclusions and precipitates to improve the magnetic properties of electromagnetic steel sheets, it can be produced through steps of slab reheating, hot rolling, annealing of hot rolled sheets, cold rolling, and finally annealing. In the above example, it is characterized by the difference between the average size of oxides and the average size of non-oxides among the precipitates and has the characteristics of adding Sb and Sn elements. However, rather than the ratio of the sizes of non-oxides and oxides affecting the magnetic properties, the amount and size of the precipitates affect the final magnetic properties. Therefore, it is difficult to see that the ratio of the sizes of oxides and non-oxides is related to the magnetic properties. In the case of Sb and Sn, they are grain boundary segregation elements, which are advantageous for improving the microstructure, but have the drawback that they can suppress the growth of crystal grains and deteriorate the rolling properties.

[0022] In the case of other examples of techniques for controlling inclusions and precipitates to improve the magnetic properties of electromagnetic steel sheets, Zn is added to improve the cleanliness of the molten steel, and Y is added as a segregation element. However, controlling inclusions only by the amount of Zn added has limitations and has the drawback of promoting the formation of fine precipitates depending on the added amount. And in the case of Y, like Sb and Sn, it is a grain boundary segregation element and has the drawback of suppressing the growth of grains and deteriorating the rolling properties.

[0023] In electromagnetic steel sheets, impurities are controlled to an extremely low level during steelmaking to minimize the formation of secondary phases that have an adverse effect on magnetic properties. However, inevitable impurities form secondary phases and have an unfavorable effect on magnetic properties. In the present invention, by controlling the variables in the winding process, hot rolling annealing process, and cold rolling annealing process, a method and product are proposed that can improve the magnetic properties of the final product of non-oriented electromagnetic steel sheets by controlling the size and volume fraction of secondary phase particles in the final product.

[0024] The slab is heated to 1110 - 1150°C and undergoes a hot rolling step. In the hot rolling step, after hot rolling the slab to 1.6 mm - 2.6 mm, it goes through a winding step. The temperature condition during winding is carried out within the range of 500 - 700°C to minimize the precipitation of secondary phases. The hot rolling annealing (APL) process serves to homogenize the elongated structure inside the hot rolled sheet formed during the hot rolling process, facilitate cold rolling, and homogenize the microstructure of the final product to improve magnetic properties. However, if the temperature condition of the hot rolling annealing (APL) is too high, fine precipitates may be formed due to the re - solution of alloy elements, which may hinder magnetic properties, so it is carried out within the range of 940 - 1110°C. Finally, the cold rolling annealing (ACL) process determines the quality of the final product by controlling the microstructure and precipitates of the cold rolled product, so it is carried out within the range of 900 - 1100°C. The present invention provides an electromagnetic steel sheet characterized in that by controlling the variables of the winding temperature, hot rolling annealing, and cold rolling annealing processes, it induces the volume fraction of secondary phase particles having a size of 1 μm or more in the product after the final process to account for 60% or more, thereby improving magnetic properties.

[0025] Figure 1 is a flowchart showing a method for manufacturing a non-oriented electromagnetic steel sheet according to an embodiment of the present invention.

[0026] Referring to Figure 1, a method for manufacturing a non-oriented electromagnetic steel sheet according to an embodiment of the present invention includes a step (S10) of providing a steel material containing silicon (Si), manganese (Mn), and aluminum (Al), a step (S20) of hot-rolling the steel material, a step (S30) of performing a first annealing heat treatment on the hot-rolled steel material, a step (S40) of cold-rolling the steel material that has been subjected to the first annealing heat treatment, and a step (S50) of performing a second annealing heat treatment on the cold-rolled steel material.

[0027] Steel material supply step (S10)

[0028] The steel material input into the hot-rolling process is a steel material for manufacturing a non-oriented electromagnetic steel sheet. For example, it contains silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, and the balance of iron (Fe) and other inevitable impurities.

[0029] Hereinafter, the roles and contents of exemplary components to which the method for manufacturing a non-oriented electromagnetic steel sheet according to the technical idea of the present invention can be applied will be described.

[0030] Silicon (Si): 2.8 - 3.8 wt%

[0031] Silicon (Si) is a component that increases the specific resistance and reduces iron loss (eddy current loss), and is a main additive element. When the addition amount of silicon is less than 2.8 wt%, it becomes difficult to obtain a desired high-frequency low iron loss value, and as the addition amount increases, the magnetic permeability and magnetic flux density decrease. Also, when the addition amount of silicon exceeds 3.8 wt%, brittleness increases, making cold rolling difficult and reducing productivity.

[0032] Manganese (Mn): 0.2 - 0.5 wt%

[0033] Manganese (Mn) increases the resistivity together with silicon and improves the structure. When manganese is added in an amount exceeding 0.5% by weight, coarse MnS precipitates are formed and the magnetic properties deteriorate, such as a decrease in magnetic flux density. Further, when the manganese content exceeds 0.5% by weight, the amount of reduction in iron loss is small compared to the addition amount, while a significant decrease in cold rolling property occurs. Further, when the manganese content is less than 0.2% by weight, the composition range of manganese can be adjusted to 0.2 to 0.5% by weight in that it can form fine MnS precipitates and suppress the growth of crystal grains.

[0034] Aluminum (Al): 0.5 - 1.5 wt%

[0035] Aluminum (Al) is a component that increases the resistivity together with silicon and reduces iron loss (eddy current loss), and is a major additive element. Aluminum plays a role in reducing magnetic anisotropy and reducing magnetic variation. Aluminum induces the precipitation of AlN when it meets nitrogen. When the aluminum content is less than 0.5% by weight, it is difficult to expect the above-described effects, and it may form fine nitrides and increase the variation in magnetic properties. When the aluminum content exceeds 1.5% by weight, a decrease in cold rolling property occurs, excessive nitrides are formed, the magnetic flux density decreases, and the magnetic properties deteriorate.

[0036] Carbon (C): More than 0 and 0.003 wt% or less

[0037] Carbon (C) is an element that forms carbides such as TiC and NbC and increases iron loss, and the less the better, and it is limited to 0.003% by weight or less. When the carbon content exceeds 0.003% by weight, magnetic aging occurs and the magnetic properties decrease, and when it is 0.003% by weight or less, the magnetic aging phenomenon is suppressed.

[0038] Phosphorus (P): More than 0 and 0.015 wt% or less

[0039] Phosphorus (P) is a grain boundary segregation element and an element that promotes the development of the microstructure. When the phosphorus content exceeds 0.015 wt%, the growth of the crystal grains is suppressed due to the segregation effect, the magnetic properties deteriorate, and the cold rolling property decreases.

[0040] Sulfur (S): More than 0 and 0.003 wt% or less

[0041] Sulfur (S) forms precipitates such as MnS and CuS, increasing the iron loss and suppressing the growth of crystal grains. Therefore, it is added as low as possible and limited to 0.003 wt% or less. When the sulfur content exceeds 0.003 wt%, the problem of increased iron loss occurs.

[0042] Nitrogen (N): More than 0 and 0.003 wt% or less

[0043] Nitrogen (N) forms precipitates such as AlN, Tin, and NbN, increasing the iron loss and suppressing the growth of crystal grains. Therefore, it is added as low as possible and limited to 0.003 wt% or less. When the nitrogen content exceeds 0.003 wt%, the problem of increased iron loss occurs.

[0044] Titanium (Ti): More than 0 and 0.003 wt% or less

[0045] Titanium (Ti) forms fine precipitates such as TiC and TiN, suppressing the growth of crystal grains. Since the magnetic properties become inferior as titanium is added, it is added as low as possible and limited to 0.003 wt% or less. When the titanium content exceeds 0.003 wt%, the problem of deteriorated magnetic properties occurs.

[0046] Hot rolling step (S20)

[0047] The steel material having the above-described composition will undergo a hot rolling process. The step (S20) of hot rolling the steel material can be performed under the conditions of a reheating temperature (SRT): 1110 - 1150 °C and a finishing rolling temperature (FDT): 800 - 900 °C.

[0048] When the slab reheating temperature exceeds 1150°C, precipitates such as C, S, and N in the slab redissolve, and fine precipitates may form during subsequent rolling and annealing processes, suppressing the growth of crystal grains and potentially deteriorating the magnetic properties. When the slab reheating temperature is less than 1110°C, the rolling load may increase, and there may be a problem of high iron loss in the final product.

[0049] After performing the step (S20) of hot rolling the steel material, the thickness of the hot-rolled sheet may be, for example, 1.6 to 2.6 mm. The greater the thickness of the hot-rolled sheet, the greater the reduction ratio of cold rolling becomes, and the microstructure becomes inferior. Therefore, it is preferable to control the thickness to 2.6 mm or less.

[0050] The hot-rolled steel material may be coiled under the condition of a coiling temperature (CT): 500 to 700°C. When the coiling temperature is less than 500°C, there is no annealing effect on the steel material, so the crystal grains do not grow. When the coiling temperature exceeds 700°C, oxidation may increase during cooling, and the pickling property may deteriorate.

[0051] First annealing heat treatment step (S30)

[0052] The step (S30) of performing the first annealing heat treatment on the hot-rolled steel material can be carried out. The first annealing heat treatment is an APL (Annealing and Pickling Line) step of annealing and pickling the hot-rolled sheet, which can be understood as a preliminary annealing treatment or a hot-rolling annealing treatment.

[0053] The step (S30) of performing the first annealing heat treatment includes an annealing process in which the temperature is raised at a rate of 20°C / s or more and then annealing is started at a temperature of 940 to 1110°C and maintained for 30 to 180 seconds. After annealing, the steel material can be cooled at a cooling rate of 20°C / s or more. After cooling, a pickling treatment step can further be included.

[0054] After hot rolling, an annealing process of the hot-rolled sheet is carried out to ensure the uniformity of the microstructure and the cold rollability. The first annealing temperature is adjusted at 940 - 1110 °C so as to form a uniform fine microstructure in which the elongated casting structure is removed. When the first annealing temperature is too low, less than 940 °C, the elongated casting structure remaining after hot rolling may remain, inducing non-uniformity of the microstructure, and the crystal grains may be formed small, which may act as an obstructive factor for cold rolling. On the contrary, when the first annealing temperature is too high, exceeding 1110 °C, it induces variations in the aggregate structure of the final product, causing anisotropy of properties.

[0055] Cold rolling step (S40)

[0056] The step (S40) of cold rolling the steel material heat-treated by the first annealing is performed. The reduction ratio of cold rolling is 50 - 85%, and the thickness of the steel material after cold rolling may be 0.35 mm or less (strictly, 0.25 mm or less). In order to impart rollability, the plate temperature can be raised to 100 - 200 °C for warm rolling.

[0057] Second annealing heat treatment step (S50)

[0058] The cold-rolled steel material can be subjected to a second annealing heat treatment. The second annealing heat treatment is an ACL (Annealing and Coating Line) step of finally annealing the cold-rolled sheet, which can be understood as a cold-rolling annealing treatment. The step (S50) of performing the second annealing heat treatment may include a step of annealing under the conditions of a heating rate: 10 °C / s or more, an annealing temperature: 900 - 1100 °C, a holding time: 30 - 90 seconds, and a cooling rate: 30 °C / s or more.

[0059] The second annealing heat treatment is performed on the cold-rolled sheet obtained after cold rolling. Considering the improvement of iron loss and mechanical properties, the temperature for deriving the optimal grain size is applied. In order to prevent surface oxidation and nitridation during cold rolling annealing, heating is performed under the conditions of a mixed atmosphere. Through the mixed atmosphere of nitrogen and hydrogen, the surface state is made smoother. If the cold rolling annealing temperature is less than 900 °C, the grain size is fine, so the hysteresis loss may increase. If the cold rolling annealing temperature exceeds 1100 °C, the grain size becomes coarse and the eddy current loss increases.

[0060] On the other hand, after the final cold rolling annealing, a coating process can be performed to form an insulating coating layer. By forming the insulating coating layer, the punching property can be improved and the insulation can be ensured. The thickness of the insulating coating layers formed on the upper and lower parts of the cold-rolled material may be about 1 to 2 μm.

[0061] The non-oriented electrical steel sheet embodied by the above-described manufacturing method is a non-oriented electrical steel sheet containing silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): 0.2 to 0.5% by weight, aluminum (Al): 0.5 to 1.5% by weight, carbon (C): more than 0 and not more than 0.003% by weight, phosphorus (P): more than 0 and not more than 0.015% by weight, sulfur (S): more than 0 and not more than 0.003% by weight, nitrogen (N): more than 0 and not more than 0.003% by weight, titanium (Ti): more than 0 and not more than 0.003% by weight, and the balance of iron (Fe) and other inevitable impurities. Among the secondary phase particles constituting the fine structure, the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, and it has an iron loss (W 10 / 400 ) of 12.0 W / kg or less. The secondary phase particles may include precipitate particles and inclusion particles.

[0062] Among the secondary phase particles constituting the fine structure, the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more and less than 2.0 μm is 20% or more, and the volume fraction of secondary phase particles having an average diameter of 2.0 μm or more may be 38% or more.

[0063] In the microstructure, the average grain size may be 80 to 160 μm. The mechanical properties of the finally realized non-oriented electrical steel sheet are as follows: yield strength (YP): 400 MPa or more, tensile strength (TS): 500 MPa or more.

[0064] According to the non-oriented electrical steel sheet and its manufacturing method according to the embodiments of the present invention, by controlling the variables of the winding, APL, and ACL processes and controlling the volume fraction of secondary phase particles having a size of 1 μm or more to 60% or more, fine precipitates less than 1 μm that hinder the movement of magnetic domains, etc. can be minimized, and a non-oriented electrical steel sheet having excellent magnetic properties can be realized.

[0065] Experimental example

[0066] Hereinafter, preferred experimental examples are presented to assist in the understanding of the present invention. However, the following experimental examples are only for assisting in the understanding of the present invention, and the present invention is not limited by the following experimental examples.

[0067] 1. Composition of test piece

[0068] In this experimental example, test pieces having the composition of alloy elements in Table 1 (unit: wt%) are provided.

[0069]

Table 1

[0070] Referring to Table 1, the composition of the non-oriented electromagnetic steel sheet according to the experimental example is: silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, and the balance is iron (Fe). The slab having the above composition was reheated to 1130 °C, and hot rolling was performed under the condition that the finish rolling temperature (FDT) was 850 °C, and then a hot rolled sheet having a thickness of 2.0 mm was manufactured.

[0071] 2. Process conditions and evaluation of physical properties

[0072] Table 2 shows the coiling temperature and holding time, the first annealing heat treatment temperature and time, and the second annealing heat treatment temperature and time among the process conditions of this experimental example. In this experimental example, after hot rolling, the coiling process, the first annealing heat treatment process, and the second annealing heat treatment process were carried out at various temperatures. After the first annealing heat treatment, cold rolling was performed to produce a cold rolled sheet having a thickness of 0.25 t, and the second annealing heat treatment was applied. Thereafter, the final product was manufactured through a coating process. The final annealing atmosphere was carried out in a mixed atmosphere of 30% hydrogen - 70% nitrogen. At this time, the heating rate was 20 °C / s and the cooling rate was 30 °C / s. In Table 2, the CT temperature is the temperature of the coiling process, the CT time is the time for maintaining the coiling temperature after the steel material is coiled, the APL temperature is the annealing temperature in the first annealing heat treatment, the APL time is the annealing holding time in the first annealing heat treatment, the ACL temperature is the annealing temperature in the second annealing heat treatment, and the ACL time is the annealing holding time in the second annealing heat treatment.

[0073]

Table 2

[0074] Referring to Table 2, in Example 1, Comparative Example 1, and Comparative Example 2, the conditions of the first annealing heat treatment and the second annealing heat treatment are the same, but different winding conditions are applied. In Example 1, Example 2, Example 3, Comparative Example 3, Comparative Example 4, and Comparative Example 5, the winding conditions and the conditions of the second annealing heat treatment are the same, but different conditions of the first annealing heat treatment are applied. In Example 1, Example 4, Example 5, Example 6, Comparative Example 6, Comparative Example 7, and Comparative Example 8, the winding conditions and the conditions of the first annealing heat treatment are the same, but different conditions of the second annealing heat treatment are applied. Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 satisfy the winding temperature (CT): 500 - 700 °C, the annealing temperature of the first annealing heat treatment: 940 - 1110 °C, and the annealing temperature of the second annealing heat treatment: 900 - 1100 °C.

[0075] In contrast, Comparative Example 1 exceeds and does not satisfy the range of the winding temperature (CT): 500 - 700 °C, Comparative Example 2 exceeds and does not satisfy the range of the winding temperature (CT): 500 - 700 °C, Comparative Example 3 is below and does not satisfy the range of the annealing temperature of the first annealing heat treatment: 940 - 1110 °C, Comparative Example 4 exceeds and does not satisfy the range of the annealing temperature of the first annealing heat treatment: 940 - 1110 °C, Comparative Example 5 exceeds and does not satisfy the range of the annealing temperature of the first annealing heat treatment: 940 - 1110 °C, Comparative Example 6 is below and does not satisfy the range of the annealing temperature of the second annealing heat treatment: 900 - 1100 °C, and Comparative Example 7 and Comparative Example 8 exceed and do not satisfy the range of the annealing temperature of the second annealing heat treatment: 900 - 1100 °C.

[0076] Table 3 shows the grain size of the non-oriented electrical steel sheet, the volume fraction of the secondary phase particles, and the iron loss (W 10 / 400 ) embodied by this experimental example.

[0077]

Table 3

[0078] Referring to Table 3, Examples 1, 2, 3, 4, 5, and 6 satisfy all of the following: average grain size: 80 - 160 μm; volume fraction (A) of secondary phase particles with an average diameter of 1.0 μm or more and less than 2.0 μm among the secondary phase particles constituting the microstructure: 20% or more; volume fraction (B) of secondary phase particles with an average diameter of 2.0 μm or more among the secondary phase particles constituting the microstructure: 38% or more; volume fraction (A + B) of secondary phase particles with an average diameter of 1.0 μm or more among the secondary phase particles constituting the microstructure: 60% or more; iron loss (W 10 / 400 ): 12.0 W / kg or less. For example, Examples Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, and Ⅵ satisfy the following: volume fraction (A) of secondary phase particles with an average diameter of 1.0 μm or more and less than 2.0 μm among the secondary phase particles constituting the microstructure: 20% or more and 30% or less; volume fraction (B) of secondary phase particles with an average diameter of 2.0 μm or more among the secondary phase particles constituting the microstructure: 38% or more and 50% or less; volume fraction (A + B) of secondary phase particles with an average diameter of 1.0 μm or more among the secondary phase particles constituting the microstructure: 60% or more and 70% or less.

[0079] In contrast, Comparative Examples 1, 2, 3, 4, 5, 6, 7, and 8 do not satisfy the condition that the volume fraction (A + B) of secondary phase particles with an average diameter of 1.0 μm or more among the secondary phase particles constituting the microstructure is 60% or more. Comparative Example 6 does not satisfy the condition that the average grain size is in the range of 80 - 160 μm. Comparative Examples 7 and 8 do not satisfy the condition that the average grain size is in the range of 80 - 160 μm as they exceed this range.

[0080] According to the above-described experimental examples, by controlling the process variables based on each reference condition, a product having an excellent iron loss characteristic was ensured, with the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more satisfying 60% or more.

[0081] In contrast, for example, in Comparative Examples 1, 2, 4, 5, 7, and 8, since the process temperature is relatively high, after the precipitated elements redissolve during the process, fine precipitation occurs during cooling, resulting in a decrease in the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more, and the iron loss characteristics deteriorate.

[0082] In the case of Comparative Examples 3 and 6, since the process temperature is relatively low, the grain size is relatively fine, the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more decreases, and the iron loss characteristics deteriorate.

[0083] As described above, through the experimental examples of the present invention, by controlling the variables of the winding, APL, and ACL processes, and controlling the volume fraction of secondary phase particles having a size of 1 μm or more to 60% or more, it was confirmed that a non-oriented electrical steel sheet having excellent magnetic properties can be realized by minimizing fine precipitates less than 1 μm that hinder the movement of magnetic domains.

[0084] As described above, the embodiments of the present invention have been mainly described, but various changes and modifications can be made at the level of those skilled in the art. As long as such changes and modifications do not depart from the scope of the present invention, it can be said that they belong to the present invention. Therefore, the scope of the rights of the present invention must be determined by the appended claims.

Claims

1. An isotropic electromagnetic steel sheet containing silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): 0.2 to 0.5% by weight, aluminum (Al): 0.5 to 1.5% by weight, carbon (C): more than 0 and 0.003% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.003% by weight or less, nitrogen (N): more than 0 and 0.003% by weight or less, titanium (Ti): more than 0 and 0.003% by weight or less, and the balance iron (Fe) and other inevitable impurities, Among the secondary phase particles constituting the microstructure, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, Non-oriented electrical steel sheet characterized by having an iron loss (W １０／４００ ) of 12.0 W / kg or less.

2. Among the secondary phase particles constituting the microstructure, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more and less than 2.0 μm is 20% or more, and the volume fraction of the secondary phase particles having an average diameter of 2.0 μm or more is 38% or more. The isotropic electromagnetic steel sheet according to Claim 1.

3. The isotropic electromagnetic steel sheet according to Claim 1, wherein the secondary phase particles include precipitate particles and inclusion particles.

4. In the microstructure, the average grain size is 80 to 160 μm. The isotropic electromagnetic steel sheet according to Claim 1.

5. Providing a steel material containing silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): 0.2 to 0.5% by weight, aluminum (Al): 0.5 to 1.5% by weight, carbon (C): more than 0 and 0.003% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.003% by weight or less, nitrogen (N): more than 0 and 0.003% by weight or less, titanium (Ti): more than 0 and 0.003% by weight or less, and the balance iron (Fe) and other inevitable impurities; Hot rolling the steel material; Performing a first annealing heat treatment on the hot-rolled steel material; Cold rolling the steel material that has been subjected to the first annealing heat treatment; Including performing a second annealing heat treatment on the cold-rolled steel material, The step of hot rolling includes a step of winding at a coiling temperature (CT) of 500 to 700°C after hot rolling. The step of performing the first annealing heat treatment includes a step of annealing at 940 to 1110°C. The step of performing the second annealing heat treatment includes a step of annealing at 900 to 1100°C. A method for manufacturing an isotropic electromagnetic steel sheet.

6. The hot rolling step is carried out under the conditions of a reheating temperature (SRT): 1110 to 1150 °C and a finish rolling temperature (FDT): 800 to 900 °C, the method for manufacturing a non-oriented electrical steel sheet according to claim 5.

7. The thickness of the hot-rolled steel material is 1.6 to 2.6 mm, and the thickness of the cold-rolled steel material is 0.35 mm or less, the method for manufacturing a non-oriented electrical steel sheet according to claim 5.

8. After performing the step of the second annealing heat treatment, among the secondary phase particles constituting the fine structure, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, characterized in that, the method for manufacturing a non-oriented electrical steel sheet according to claim 5.

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