Non-oriented electrical steel sheet and method for manufacturing 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 non-oriented electrical steel sheets and methods for manufacturing the same, and more particularly to high-efficiency non-oriented electrical steel sheets and methods for manufacturing the same. [Background technology]

[0002] Electrical steel sheets can be classified into grain-oriented and non-oriented types based on their magnetic properties. Grain-oriented electrical steel sheets are manufactured to be easily magnetized in the rolling direction of the steel sheet, and have particularly excellent magnetic properties in the rolling direction. Therefore, they are mainly used as core materials for large, medium, and small transformers where low iron loss and high permeability are required. In contrast, non-oriented electrical steel sheets have uniform magnetic properties regardless of the orientation of the steel sheet, and are therefore widely used as core materials for small electric motors, small power transformers, ballasts, and other devices.

[0003] Prior art document includes Korean Published Patent No. 10-2015-0001467. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The technical problem that this invention aims to solve is to provide a highly efficient non-oriented electrical steel sheet and a method for manufacturing the same.

[0005] However, these challenges are illustrative and do not limit the scope of the present invention. [Means for solving the problem]

[0006] A non-oriented electrical steel sheet according to one aspect of the present invention to solve the above problems is a non-oriented electrical steel sheet containing silicon (Si): 2.8~3.8 wt%, manganese (Mn): 0.2~0.5 wt%, aluminum (Al): 0.5~1.5 wt%, carbon (C): greater than 0.003 wt% or less, phosphorus (P): greater than 0.015 wt% or less, sulfur (S): greater than 0.003 wt% or less, nitrogen (N): greater than 0.003 wt% or less, titanium (Ti): greater than 0.003 wt% or less, and the remaining iron (Fe) and other unavoidable impurities, wherein the volume fraction 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, and the iron loss (W) is 12.0 W / kg or less. 10 / 400 It is characterized by having ).

[0007] In the non-oriented electrical steel sheet, the volume fraction of secondary phase particles constituting the microstructure, where the average diameter is 1.0 μm or more and less than 2.0 μm, is 20% or more, and the volume fraction of secondary phase particles where the average diameter is 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] In the microstructure of the non-oriented electrical steel sheet, the average grain size may be 80 to 160 μm.

[0010] A method for manufacturing non-oriented electrical steel sheets according to one aspect of the present invention to solve the above problems is to provide 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): greater than 0.003% by weight or less, phosphorus (P): greater than 0.015% by weight or less, sulfur (S): greater than 0.003% by weight or less, nitrogen (N): greater than 0.003% by weight or less, titanium (Ti): greater than 0.003% by weight or less, and the remaining iron (Fe) and other unavoidable impurities; and the steel The process includes the steps of: hot rolling a material; first annealing treatment of the hot-rolled steel material; cold rolling of the first annealed steel material; and second annealing treatment of the cold-rolled steel material, wherein the hot rolling step includes winding at a winding temperature (CT) of 500 to 700°C after hot rolling; the first annealing treatment step includes annealing at 940 to 1110°C; and the second annealing treatment step includes annealing at 900 to 1100°C.

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

[0012] In the method for manufacturing the non-oriented electrical steel sheet, the thickness of the hot-rolled steel material may be 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 electrical steel sheet, after performing the second annealing heat treatment step, the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more among the secondary phase particles constituting the microstructure may be 60% or more. [Effects of the Invention]

[0014] According to embodiments of the present invention, a highly efficient non-oriented electrical 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 explanation of the drawing]

[0016] [Figure 1] This flowchart shows a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. [Modes for carrying out the invention]

[0017] A method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention will be described in detail. The terms described below are terms that have been appropriately selected considering the function in the present invention, and the definitions of such terms must be based on the content throughout this specification.

[0018] Generally, electrical steel sheets are divided into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. Grain-oriented electrical steel sheets are mainly used in static equipment such as transformers, while non-oriented electrical steel sheets are mainly used in rotating equipment such as motors and generators. Recently, in response to global environmental issues, technology is rapidly shifting from existing internal combustion engines to hybrid electric vehicles (HEVs), electric vehicles (EVs), and hydrogen vehicles that replace them. The properties of electrical steel sheet materials can be evaluated by magnetic flux density and iron loss, and magnetic flux density is B 50 In the case of iron loss, generally W 15 / 50 While primarily evaluated, when high-frequency characteristics are required, such as in electric vehicles, W 10 / 400 It is evaluated based on iron loss. B 50 This indicates the magnetic flux density at 5000 A / m, W 15 / 50 This shows the iron loss at 50Hz, 1.5T, W 10 / 400 This shows the iron loss at 400Hz and 1.0T.

[0019] As a representative method for improving the magnetic properties of electromagnetic steel sheets, there are methods of adding elements such as Si, Al, Mn to increase the specific resistance, or reducing the thickness of the material. However, when adding specific resistance-increasing elements such as Si, Al, Mn, the addition of alloying elements reduces the magnetic flux density and makes rolling difficult, which makes it harder to reduce the thickness of the material. Moreover, the greater the thickness reduction, the more problems there are such as decreased productivity and increased production costs.

[0020] In addition to Si, Al and Mn, which are the main alloying elements of non-oriented electrical steel sheets, impurity elements that are unavoidably added such as C, S, N, and Ti can combine to form fine precipitates and inclusions. Such secondary phase particles hinder the movement of magnetic domains and reduce magnetic properties. The finer the secondary phase particles are, the more they hinder magnetic domain movement and inhibit grain growth. Therefore, it is very important to control the size and fraction of secondary phase particles.

[0021] As an example of technology for controlling inclusions and precipitates to improve the magnetic properties of electromagnetic steel sheets, the steel sheet can be produced through steps of slab reheating, hot rolling, hot rolled sheet annealing, cold rolling, and final annealing. Said example is characterized by the difference between the average size of oxides and the average size of non-oxides in precipitates, and has the characteristic of adding Sb and Sn elements. However, rather than the size ratio of non-oxides to oxides affecting magnetic properties, it is the amount and size of precipitates that affect the final magnetic properties, so it is difficult to conclude that the size ratio of oxides to non-oxides is related to magnetic properties. In the case of Sb and Sn, although they are grain boundary segregation elements and are advantageous for improving texture, they have the disadvantage of inhibiting grain growth and potentially degrading rolling properties.

[0022] In another example of a technique for controlling inclusions and precipitates to improve the magnetic properties of electrical steel sheets, Zn is added to improve the cleanliness of molten steel, and Y is added as a segregation element. However, there is a limit to controlling inclusions only by the addition amount of Zn, and it has the disadvantage that the addition amount rather promotes the formation of fine precipitates. And in the case of Y, like Sb and Sn, it is a grain boundary segregation element, which suppresses the growth of crystal grains and has the disadvantage of degrading rolling properties.

[0023] In electrical steel sheets, impurities are controlled to an extremely low level during steelmaking to minimize the formation of secondary phases that adversely affect magnetic properties, but unavoidable impurities form secondary phases that adversely affect magnetic properties. The present invention aims to provide a method and a product capable of improving the magnetic properties of a final product of non-oriented electrical steel sheet by controlling variables in a coiling step, a hot-rolled annealing step, and a cold-rolled annealing step to control the size and volume fraction of secondary phase particles in the final product.

[0024] The slab undergoes a step of heating to 1110~1150°C and then hot rolling. In the hot rolling step, after the slab is hot rolled to a thickness of 1.6 mm to 2.6 mm, it undergoes a coiling step. The temperature condition during coiling is within the range of 500 to 700°C to minimize the precipitation of secondary phases. The hot-rolled annealing (APL) process homogenizes the stretched structure inside the hot-rolled sheet formed during the hot rolling process, thereby facilitating cold rolling, homogenizing the microstructure of the final product, and improving magnetic properties. However, if the temperature condition of hot-rolled annealing (APL) is too high, fine precipitates may be formed due to re-dissolution of alloy elements, which impairs magnetic properties, so the hot-rolled annealing is performed within the range of 940~1110°C. Finally, the cold-rolled annealing (ACL) process determines the quality of the final product by controlling the microstructure and precipitates of the cold-rolled product, so it is performed within the range of 900~1100°C. The present invention provides an electrical steel sheet characterized in that by controlling variables of coiling temperature, hot-rolled annealing and cold-rolled annealing processes, after the final process, the volume fraction of secondary phase particles having a size of 1 μm or more in the product is induced to account for 60% or more, and the magnetic properties are improved.

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

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

[0027] Steel material supply step (S10)

[0028] The steel material fed into the hot rolling process is steel material for manufacturing non-oriented electrical steel sheets, and for example, it contains silicon (Si): 2.8-3.8% by weight, manganese (Mn): 0.2-0.5% by weight, aluminum (Al): 0.5-1.5% by weight, carbon (C): greater than 0% or less than 0.003% by weight, phosphorus (P): greater than 0% or less than 0.015% by weight, sulfur (S): greater than 0% or less than 0.003% by weight, nitrogen (N): greater than 0% or less than 0.003% by weight, titanium (Ti): greater than 0% or less than 0.003% by weight, and the remaining iron (Fe) and other unavoidable impurities.

[0029] The following describes the roles and contents of exemplary compositional components to which the method for manufacturing non-oriented electrical steel sheets according to the technical concept of the present invention can be applied.

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

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

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

[0033] Manganese (Mn), along with silicon, increases resistivity and improves texture. Adding more than 0.5% by weight of manganese degrades magnetic properties, such as the formation of coarse MnS precipitates and a decrease in magnetic flux density. Furthermore, when the manganese content exceeds 0.5% by weight, while the reduction in iron loss is small compared to the amount added, a significant decrease in cold rolling properties occurs. Moreover, when the manganese content is less than 0.2% by weight, it can form fine MnS precipitates and suppress grain growth; therefore, the manganese composition can be adjusted to a range of 0.2-0.5% by weight.

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

[0035] Aluminum (Al), along with silicon, is a major additive element that increases resistivity and reduces iron loss (eddy current loss). Aluminum also plays a role in reducing magnetic anisotropy and decreasing magnetic variability. Aluminum combines with nitrogen to induce the precipitation of AlN. If the aluminum content is less than 0.5% by weight, the above effects are unlikely to be achieved, and fine nitrides may form, increasing the variability of magnetic properties. If the aluminum content exceeds 1.5% by weight, cold rolling properties decrease, excess nitrides are formed, the magnetic flux density decreases, and the magnetic properties deteriorate.

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

[0037] Carbon (C) is an element that increases iron loss by forming carbides such as TiC and NbC, and it is preferable to have less of it, limiting it to 0.003% by weight or less. If the carbon content exceeds 0.003% by weight, magnetic aging occurs and the magnetic properties decrease, and if it is 0.003% by weight or less, the magnetic aging phenomenon is suppressed.

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

[0039] Phosphorus (P) is a grain boundary segregating element that promotes the development of texture. When the phosphorus content exceeds 0.015% by weight, the segregation effect inhibits grain growth, degrades magnetic properties, and reduces cold rolling properties.

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

[0041] Sulfur (S) forms precipitates such as MnS and CuS, increasing iron loss and inhibiting grain growth. Therefore, its addition should be kept as low as possible, limiting it to 0.003% by weight or less. If the sulfur content exceeds 0.003% by weight, the problem of increased iron loss will occur.

[0042] Nitrogen (N): Greater than 0% by weight and less than or equal to 0.003% by weight

[0043] Nitrogen (N) forms precipitates such as AlN, Tin, and NbN, increasing iron loss and inhibiting grain growth. Therefore, its addition should be kept as low as possible, limited to 0.003% by weight or less. If the nitrogen content exceeds 0.003% by weight, the problem of increased iron loss will occur.

[0044] Titanium (Ti): Less than 0% by weight

[0045] Titanium (Ti) inhibits grain growth by forming fine precipitates such as TiC and TiN. Since the magnetic properties deteriorate as titanium is added, it should be added as little as possible, limiting it to 0.003% by weight or less. If the titanium content exceeds 0.003% by weight, problems arise with the deterioration of magnetic properties.

[0046] Hot rolling step (S20)

[0047] The steel material having the above-described composition undergoes a hot rolling process. The hot rolling step (S20) of the steel material may be carried out under the conditions of a reheating temperature (SRT): 1110~1150°C and a finish rolling temperature (FDT): 800~900°C.

[0048] If the slab reheating temperature exceeds 1150°C, precipitates such as C, S, and N in the slab may redissolve, leading to the formation of fine precipitates in subsequent rolling and annealing processes, suppressing grain growth and potentially degrading magnetism. If the slab reheating temperature is below 1110°C, the rolling load may increase, resulting in high iron loss in the final product.

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

[0050] The hot-rolled steel material may be wound at a winding temperature (CT) of 500 to 700°C. If the winding temperature is below 500°C, there is no annealing effect on the steel material, and therefore no grain growth occurs. If the winding temperature exceeds 700°C, oxidation may increase during cooling, which may result in poor pickling properties.

[0051] First annealing heat treatment step (S30)

[0052] The hot-rolled steel material can be subjected to a first annealing heat treatment (S30). The first annealing heat treatment is an APL (Annealing and Pickling Line) step in which the hot-rolled sheet is annealed and pickled, and can be understood as a pre-annealing treatment or a hot-rolling annealing treatment.

[0053] The first annealing heat treatment step (S30) includes an annealing process in which the temperature is raised at a heating rate of 20°C / s or more, followed by initiating annealing at a temperature of 940 to 1110°C and maintaining it 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, the step of pickling may be further included.

[0054] After hot rolling, the hot-rolled sheet is annealed to ensure uniformity of the microstructure and cold-rollability. The first annealing temperature is adjusted to 940-1110°C to form a uniform microstructure from which the stretched cast structure has been removed. If the first annealing temperature is too low (below 940°C), the stretched cast structure remaining after hot rolling will persist, inducing microstructure non-uniformity, resulting in smaller grain sizes, which can hinder cold rolling. On the other hand, if the first annealing temperature is too high (above 1110°C), it can induce variations in the texture of the final product, leading to anisotropy in its properties.

[0055] Cold rolling step (S40)

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

[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 in which the cold-rolled sheet is final annealed, and can be understood as a cold-rolling annealing treatment. The second annealing heat treatment step (S50) may include a step of annealing under the conditions of heating rate: 10°C / s or more, annealing temperature: 900~1100°C, and holding time: 30~90 seconds, and a step of cooling under the conditions of cooling rate: 30°C / s or more.

[0059] The second annealing heat treatment is performed on the cold-rolled sheet obtained after cold rolling. The temperature is applied to derive the optimal grain size, taking into consideration the improvement of iron loss and mechanical properties. To prevent surface oxidation and nitriding during cold rolling annealing, heating is performed under mixed atmosphere conditions. The surface is further smoothed by passing it through a mixed atmosphere of nitrogen and hydrogen. If the cold rolling annealing temperature is below 900°C, the grain size is fine, which may increase hysteresis loss, and if the cold rolling annealing temperature exceeds 1100°C, the grain size becomes coarse, and eddy current loss increases.

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

[0061] The non-oriented electrical steel sheet produced by the manufacturing method described above is a non-oriented electrical steel sheet containing silicon (Si): 2.8-3.8 wt%, manganese (Mn): 0.2-0.5 wt%, aluminum (Al): 0.5-1.5 wt%, carbon (C): greater than 0 and less than 0.003 wt%, phosphorus (P): greater than 0 and less than 0.015 wt%, sulfur (S): greater than 0 and less than 0.003 wt%, nitrogen (N): greater than 0 and less than 0.003 wt%, titanium (Ti): greater than 0 and less than 0.003 wt%, and the remaining iron (Fe) and other unavoidable impurities. Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more is 60% or more, and the iron loss (W) is 12.0 W / kg or less. 10 / 400 The secondary phase particles may include precipitate particles and inclusion particles.

[0062] Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles with 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 with an average diameter of 2.0 μm or more may be 38% or more.

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

[0064] By using the non-oriented electrical steel sheet and its manufacturing method according to the embodiment of the present invention, the volume fraction of secondary phase particles having a size of 1 μm or more is controlled to 60% or more by controlling the variables of the winding, APL, and ACL processes, thereby minimizing fine precipitates smaller than 1 μm that hinder the movement of magnetic domains, and thus realizing a non-oriented electrical steel sheet with excellent magnetic properties.

[0065] Experimental example

[0066] The following are preferred experimental examples to aid in understanding the present invention. However, these experimental examples are merely for the purpose of aiding in understanding the present invention, and the present invention is not limited to these experimental examples.

[0067] 1. Composition of the test specimen

[0068] In this experimental example, test specimens having the alloying elemental composition (in weight %) shown in Table 1 are provided.

[0069] [Table 1]

[0070] Referring to Table 1, the composition of the non-oriented electrical steel sheet in the experimental example satisfies the following conditions: silicon (Si): 2.8-3.8 wt%, manganese (Mn): 0.2-0.5 wt%, aluminum (Al): 0.5-1.5 wt%, carbon (C): greater than 0 and less than 0.003 wt%, phosphorus (P): greater than 0 and less than 0.015 wt%, sulfur (S): greater than 0 and less than 0.003 wt%, nitrogen (N): greater than 0 and less than 0.003 wt%, titanium (Ti): greater than 0 and less than 0.003 wt%, and the remaining iron (Fe). A slab having the above composition was reheated to 1130°C, and hot-rolled at a finishing rolling temperature (FDT) of 850°C to produce a hot-rolled sheet with a thickness of 2.0 mm.

[0071] 2. Evaluation of process conditions and physical properties

[0072] Table 2 shows the process conditions for this experimental example, specifically the winding temperature and holding time, the first annealing heat treatment temperature and time, and the second annealing heat treatment temperature and time. In this experimental example, after hot rolling, the winding process, the first annealing heat treatment process, and the second annealing heat treatment process were performed at various temperatures. After the first annealing heat treatment, a cold-rolled sheet with a thickness of 0.25t was produced by cold rolling, and the second annealing heat treatment was applied. Subsequently, the final product was manufactured through a coating process. The final annealing atmosphere was a mixed atmosphere of 30% hydrogen and 70% nitrogen. At this time, the heating rate was 20°C / s and the cooling rate was 30°C / s. In Table 2, CT temperature is the temperature during the winding process, CT time is the time the steel material is maintained at the winding temperature after winding, APL temperature is the annealing temperature in the first annealing heat treatment, APL time is the annealing maintenance time in the first annealing heat treatment, ACL temperature is the annealing temperature in the second annealing heat treatment, and ACL time is the annealing maintenance 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 were the same, but different coiling conditions were applied. In Example 1, Example 2, Example 3, Comparative Example 3, Comparative Example 4, and Comparative Example 5, the coiling conditions and the conditions of the second annealing heat treatment were the same, but different conditions of the first annealing heat treatment were applied. In Example 1, Example 4, Example 5, Example 6, Comparative Example 6, Comparative Example 7, and Comparative Example 8, the coiling conditions and the conditions of the first annealing heat treatment were the same, but different conditions of the second annealing heat treatment were applied. Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 satisfy the following requirements: the coiling temperature (CT) is 500 to 700°C, the annealing temperature of the first annealing heat treatment is 940 to 1110°C, and the annealing temperature of the second annealing heat treatment is 900 to 1100°C.

[0075] On the contrary, in Comparative Example 1, the coiling temperature (CT) exceeds the range of 500 to 700°C and does not satisfy the requirement; in Comparative Example 2, the coiling temperature (CT) exceeds the range of 500 to 700°C and does not satisfy the requirement; in Comparative Example 3, the annealing temperature of the first annealing heat treatment is below the range of 940 to 1110°C and does not satisfy the requirement; in Comparative Example 4, the annealing temperature of the first annealing heat treatment exceeds the range of 940 to 1110°C and does not satisfy the requirement; in Comparative Example 5, the annealing temperature of the first annealing heat treatment exceeds the range of 940 to 1110°C and does not satisfy the requirement; in Comparative Example 6, the annealing temperature of the second annealing heat treatment is below the range of 900 to 1100°C and does not satisfy the requirement; in Comparative Example 7 and Comparative Example 8, the annealing temperature of the second annealing heat treatment exceeds the range of 900 to 1100°C and does not satisfy the requirement.

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

[0077]

Table 3

[0078] Referring to Table 3, Examples 1, 2, 3, 4, 5, and 6 have the following characteristics: average grain size: 80-160 μm, volume fraction (A) of secondary phase particles constituting the microstructure with an average diameter of 1.0 μm or more and less than 2.0 μm: 20% or more, volume fraction (B) of secondary phase particles constituting the microstructure with an average diameter of 2.0 μm or more: 38% or more, volume fraction (A+B) of secondary phase particles constituting the microstructure with an average diameter of 1.0 μm or more: 60% or more, iron loss (W 10 / 400 All of the following conditions must be met: 12.0 W / kg or less. For example, Examples 1, 2, 3, 4, 5, and 6 satisfy the following conditions regarding the volume fraction (A) of secondary phase particles constituting the microstructure with an average diameter of 1.0 μm or more and less than 2.0 μm: 20% or more and 30% or less, the volume fraction (B) of secondary phase particles constituting the microstructure with an average diameter of 2.0 μm or more: 38% or more and 50% or less, and the volume fraction (A+B) of secondary phase particles constituting the microstructure with an average diameter of 1.0 μm or more: 60% or more and 70% or less.

[0079] In contrast, Comparative Examples 1, 2, 3, 4, 5, 6, 7, and 8 all fell below the range of 60% or more in volume fraction (A+B) of secondary phase particles with an average diameter of 1.0 μm or more that constitute the microstructure. Comparative Example 6 fell below the range of 80-160 μm in average grain size and did not meet the requirement. Comparative Examples 7 and 8 exceeded the range of 80-160 μm in average grain size and did not meet the requirement.

[0080] According to the experimental examples described above, by controlling process variables based on each standard condition, a product with excellent iron loss characteristics was secured, satisfying the requirement that the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more be 60% or more.

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

[0082] In Comparative Examples 3 and 6, the relatively low process temperature results in a decrease in the volume fraction of secondary phase particles, which have a relatively fine grain size and an average diameter of 1.0 μm or more, leading to a deterioration in iron loss characteristics.

[0083] Through the experimental examples of the present invention described above, it has been confirmed that by controlling the variables of the winding, APL, and ACL processes to control the volume fraction of secondary phase particles having a size of 1 μm or more to 60% or more, it is possible to minimize fine precipitates smaller than 1 μm that hinder the movement of magnetic domains, thereby realizing non-oriented electrical steel sheets with excellent magnetic properties.

[0084] The above description has focused on embodiments of the present invention, but various modifications and variations can be made at the level of those skilled in the art. Such modifications and variations can be said to fall within the scope of the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the rights of the present invention must be determined by the appended claims.

Claims

1. This is a non-oriented electrical steel sheet consisting of silicon (Si): 2.8-3.8 wt%, manganese (Mn): 0.2-0.5 wt%, aluminum (Al): 0.5-1.5 wt%, carbon (C): greater than 0 and 0.003 wt% or less, phosphorus (P): greater than 0 and 0.015 wt% or less, sulfur (S): greater than 0 and 0.003 wt% or less, nitrogen (N): greater than 0 and 0.003 wt% or less, titanium (Ti): greater than 0 and 0.003 wt% or less, and the remaining iron (Fe) and other unavoidable impurities. Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles with an average diameter of 1.0 μm or more is 60% or more. Iron loss of 12.0 W / kg or less (W １０／４００ ) has, The non-oriented electrical steel sheet is characterized in that the secondary phase particles are precipitate particles or inclusion particles.

2. The non-oriented electrical steel sheet according to claim 1, wherein, 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 is 20% or more, and the volume fraction of secondary phase particles having an average diameter of 2.0 μm or more is 38% or more.

3. The non-oriented electrical steel sheet according to claim 1, wherein the average grain size in the microstructure is 80 to 160 μm.

4. A step of providing a steel material comprising: 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): greater than 0 and 0.003 wt% or less, phosphorus (P): greater than 0 and 0.015 wt% or less, sulfur (S): greater than 0 and 0.003 wt% or less, nitrogen (N): greater than 0 and 0.003 wt% or less, titanium (Ti): greater than 0 and 0.003 wt% or less, and the remaining iron (Fe) and other unavoidable impurities; The steps include: hot rolling the aforementioned steel material, The steps include: performing a first annealing heat treatment on the hot-rolled steel material; The first step of cold rolling the annealed steel material, The step includes a second annealing heat treatment of the cold-rolled steel material, The hot rolling step includes a step of winding at a winding temperature (CT) of 500 to 700°C after hot rolling, the first annealing heat treatment step includes a step of annealing at 940 to 1110°C, and the second annealing heat treatment step includes a step of annealing at 900 to 1100°C. After performing the second annealing heat treatment step, the volume fraction 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. The non-oriented electrical steel sheets manufactured have an iron loss of 12.0 W / kg or less (W 10 / 400). A method for manufacturing non-oriented electrical steel sheets, wherein the secondary phase particles are precipitate particles or inclusion particles.

5. The method for manufacturing a non-oriented electrical steel sheet according to claim 4, wherein the hot rolling step is performed under the conditions of a reheating temperature (SRT) of 1110 to 1150°C and a finish rolling temperature (FDT) of 800 to 900°C.

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 4, wherein 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.

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