Non-oriented electrical steel sheet and method for producing same

Abstract

The present invention provides a non-oriented electrical steel sheet comprising: 2.8 wt% to 3.8 wt% of silicon (Si), 0.2 wt% to 0.5 wt% of manganese (Mn), 0.5 wt% to 1.5 wt% of aluminum (Al), 0 wt% to 0.003 wt% (excluding 0) of carbon (C), 0 wt% to 0.015 wt% (excluding 0) of phosphorus (P), 0 wt% to 0.003 wt% (excluding 0) of sulfur (S), 0 wt% to 0.003 wt% (excluding 0) of nitrogen (N), 0 wt% to 0.003 wt% (excluding 0) of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities. Wherein, among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles having an average diameter of at least 1.0 [mu] m is at least 60%, and the non-oriented electrical steel sheet has an iron loss (W10 / 400) of at most 12.0 W / kg.

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 exhibit excellent magnetic properties particularly in the rolling direction of the steel sheets because they are manufactured to be easily magnetized in the rolling direction, and are therefore mostly used as cores for large, medium, and small transformers requiring low iron loss and high magnetic permeability. On the other hand, non-oriented electrical steel sheets have uniform magnetic properties regardless of the orientation of the steel sheets, and are therefore generally used as core materials for small motors, small power transformers, stabilizers, and the like.

[0003] Related art includes Korean Patent Publication No. 2015-0001467A. Summary of the invention

[0004] Technical issues

[0005] The present invention provides a high-efficiency non-oriented electrical steel sheet and a method for manufacturing the same.

[0006] However, the above description is only an example, and the scope of the present invention is not limited thereto.

[0007] Technical Solution

[0008] According to one aspect of the present invention, there is provided a nonoriented electrical steel sheet, comprising: 2.8 wt % to 3.8 wt % of silicon (Si), 0.2 wt % to 0.5 wt % of manganese (Mn), 0.5 wt % to 1.5 wt % of aluminum (Al), more than 0 wt % to not more than 0.003 wt % of carbon (C), more than 0 wt % to not more than 0.015 wt % of phosphorus (P), more than 0 wt % to not more than 0.003 wt % of sulfur (S), more than 0 wt % to not more than 0.003 wt % of nitrogen (N), more than 0 wt % to not more than 0.003 wt % of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities; wherein, among the secondary phase particles constituting the microstructure of the nonoriented electrical steel sheet, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, wherein the iron loss (W) of the nonoriented electrical steel sheet is less than 0.003 wt %. 10 / 400 ) is 12.0W / kg or less.

[0009] Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles having an average diameter equal to or greater than 1.0 μm 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 is 38% or more.

[0010] The secondary phase particles may include precipitate particles and inclusion particles.

[0011] The microstructure may have an average grain size of 80 microns to 160 microns.

[0012] According to another aspect of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet, the method comprising: providing a steel material, the steel material comprising: 2.8 wt % to 3.8 wt % of silicon (Si), 0.2 wt % to 0.5 wt % of manganese (Mn), 0.5 wt % to 1.5 wt % of aluminum (Al), greater than 0 wt % and not more than 0.003 wt % of carbon (C), greater than 0 wt % and not more than 0.015 wt % of phosphorus (P), greater than 0 wt % and not more than 0.003 wt % of sulfur (S), greater than 0 wt % and not more than 0. 0.003 wt. % nitrogen (N), greater than 0 wt. % and not more than 0.003 wt. % titanium (Ti), and the balance iron (Fe) and other inevitable impurities; hot rolling the steel; primary annealing the hot-rolled steel; cold rolling the steel after the primary annealing; and secondary annealing the cold-rolled steel; wherein the hot rolling includes coiling at a coiling temperature (CT) of 500°C to 700°C after the hot rolling, the primary annealing includes annealing at 940°C to 1110°C, and the secondary annealing includes annealing at 900°C to 1100°C.

[0013] The hot rolling may be performed under the conditions of a slab reheating temperature (SRT) of 1110°C to 1150°C and a finishing outlet temperature (FDT) of 800°C to 900°C.

[0014] The thickness of the hot-rolled steel may be 1.6 mm to 2.6 mm, and the thickness of the cold-rolled steel may be 0.35 mm or less.

[0015] After the secondary annealing is performed, the volume fraction of secondary phase particles having an average diameter of 1.0 micrometer or more among the secondary phase particles constituting the microstructure of the nonoriented electrical steel sheet may be 60% or more.

[0016] Beneficial Effects

[0017] According to the embodiments of the present invention, a highly efficient non-oriented electrical steel sheet and a method for manufacturing the same can be provided.

[0018] However, the scope of the present invention is not limited to the above-mentioned effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The method for manufacturing a nonoriented electrical steel sheet according to an embodiment of the present invention will now be described in detail. The terms used herein are selected according to their functions in the present invention, and the definitions of these terms should be combined with the context of the entire specification.

[0021] Electrical steel sheets are generally divided into oriented electrical steel sheets and non-oriented electrical steel sheets. Oriented electrical steel sheets are mostly used in stationary machinery such as transformers, and non-oriented electrical steel sheets are often used in rotating machinery such as motors and generators. Currently, in order to cope with global environmental issues, existing internal combustion engine vehicles are rapidly being replaced by hybrid electric vehicles (HEV), electric vehicles (EV) and hydrogen vehicles. The performance of electrical steel sheet materials can be evaluated based on magnetic flux density and iron loss. Magnetic flux density is mostly measured by B 50 Evaluation, iron loss is generally based on W 15 / 50 However, if high frequency characteristics are required in EV, press W 10 / 400 Evaluate. B 50 Indicates the magnetic flux density at 5000A / m, W 15 / 50 represents the iron loss at 50Hz and 1.5T, W 10 / 400 It represents the iron loss at 400Hz and 1.0T.

[0022] A representative method for improving the magnetic properties of electrical steel sheets is to increase the resistivity by adding elements such as silicon (Si), aluminum (Al) and manganese (Mn), or to reduce the material thickness. However, when elements such as Si, Al and Mn are added to increase the resistivity, the magnetic flux density decreases and the rolling property deteriorates, making it difficult to reduce the material thickness. In addition, the reduction in material thickness leads to a decrease in productivity and an increase in production costs.

[0023] In addition to the main alloying elements of non-oriented electrical steel sheets, namely Si, Al and Mn, impurity elements such as carbon (C), sulfur (S), nitrogen (N) and titanium (Ti) that are inevitably added combine to form fine precipitates and inclusions. These secondary phase particles hinder the movement of magnetic domains, thereby deteriorating magnetic properties. The smaller the secondary phase particles are, the more they hinder the movement of magnetic domains or inhibit grain growth. Therefore, it is critical to control the size and amount of secondary phase particles.

[0024] According to one embodiment of the technology of controlling inclusions or precipitates to improve the magnetic properties of electrical steel sheets, electrical steel sheets can be manufactured by slab reheating, hot rolling, hot rolled sheet annealing, cold rolling, and then final annealing. The above embodiment is characterized by the difference between the average size of oxides and the average size of non-oxides in the precipitates and the addition of elements such as antimony (Sb) and tin (Sn). However, since the final magnetic properties are affected by the number and size of precipitates rather than the size ratio between non-oxides and oxides, it is not easy to regard the size ratio between oxides and non-oxides as being related to the magnetic properties. Although Sb and Sn can improve the texture as grain boundary segregation elements, they inhibit grain growth and deteriorate the rolling quality.

[0025] According to another embodiment of the technology for controlling inclusions or precipitates to improve the magnetic properties of an electrical steel sheet, zinc (Zn) is added to improve the cleanliness of the steel, and yttrium (Y) is added as a segregation element. However, the addition of Zn has limitations in controlling inclusions, and depending on the amount of addition, the addition of Zn promotes the formation of fine precipitates. Like Sb and Sn, Y is a grain boundary segregation element that inhibits grain growth and deteriorates rolling quality.

[0026] When manufacturing electrical steel sheets, the addition of impurities is controlled at very low levels to minimize the formation of secondary phases that have a serious impact on magnetic properties. However, unavoidable impurities may be added to form secondary phases and deteriorate magnetic properties. The present invention proposes a method and product that can improve the magnetic properties of the final product of non-oriented electrical steel sheets by controlling the size and volume fraction of secondary phase particles in the final product by controlling the process variables of coiling, hot annealing and cold annealing.

[0027] The slab is reheated to 1110°C to 1150°C and hot rolled. In the hot rolling process, the slab is hot rolled to 1.6 mm to 2.6 mm and then coiled. The coiling process is performed in a temperature range of 500°C to 700°C to minimize the precipitation of secondary phases. The thermal annealing process (e.g., annealing and pickling line (APL)) facilitates cold rolling by homogenizing the elongated structure formed inside the hot rolled slab during the hot rolling process, and improves the magnetic properties by homogenizing the microstructure of the final product. However, when the thermal annealing (e.g., APL) temperature condition is too high, fine precipitates may be formed, and the magnetic properties may be hindered due to the redissolution of alloying elements. Therefore, the thermal annealing process is performed in the range of 940°C to 1110°C. Finally, the cold annealing process (e.g., annealing and coating line (ACL)) determines the quality of the final product by controlling the microstructure and precipitates of the product after cold rolling, and is therefore performed in the range of 900° C. to 1100° C. The present invention provides an electrical steel sheet with improved magnetic properties by controlling the coiling temperature and the hot annealing and cold annealing variables to achieve a volume fraction of secondary phase particles having a size of 1 micron or more in the final product of 60% or more.

[0028] Figure 1 is a flow chart of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0029] Reference Figure 1 , a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: providing a steel material containing silicon (Si), manganese (Mn) and aluminum (Al) (S10); hot rolling the steel material (S20); performing primary annealing on the hot-rolled steel material (S30); cold rolling the primary annealed steel material (S40); and performing secondary annealing on the cold-rolled steel material (S50).

[0030] Provide steel (S10)

[0031] The steel material provided to the hot rolling process is a steel material for manufacturing a non-oriented electrical steel sheet, which contains, for example, 2.8 to 3.8 wt% of Si, 0.2 to 0.5 wt% of Mn, 0.5 to 1.5 wt% of Al, more than 0 wt% and not more than 0.003 wt% of carbon (C), more than 0 wt% and not more than 0.015 wt% of phosphorus (P), more than 0 wt% and not more than 0.003 wt% of sulfur (S), more than 0 wt% and not more than 0.003 wt% of nitrogen (N), more than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities.

[0032] The functions and contents of exemplary components applicable to the method for manufacturing a nonoriented electrical steel sheet according to the technical features of the present invention will now be described.

[0033] Silicon: 2.8 wt% to 3.8 wt%

[0034] Si is a main element added as a component to reduce iron loss (or eddy current loss) by increasing resistivity. When the content of Si is less than 2.8 wt%, it is not easy to achieve the low iron loss value required at high frequencies, and when the content increases, the magnetic permeability and magnetic flux density decrease. When the content of Si is greater than 3.8 wt%, brittleness increases, making cold rolling difficult and reducing productivity.

[0035] Mn: 0.2 wt% to 0.5 wt%

[0036] Mn increases resistivity and improves texture together with Si. When Mn is added in excess of 0.5 wt%, coarse MnS precipitates are formed, causing deterioration of magnetic properties, such as reduced magnetic flux density. In addition, when the content of Mn is greater than 0.5 wt%, the reduction in iron loss is small compared to the amount added, and cold rolling properties are significantly deteriorated. When the content of Mn is less than 0.2 wt%, fine MnS precipitates may be formed to inhibit grain growth. Therefore, the content of Mn can be controlled within the range of 0.2 wt% to 0.5 wt%.

[0037] Al: 0.5 wt% to 1.5 wt%

[0038] Al is a main element added together with Si as a component to reduce iron loss (or eddy current loss) by increasing resistivity. The role of Al is to reduce the change in magnetic properties by reducing magnetic anisotropy. Al induces AlN precipitation when combined with N. When the content of Al is less than 0.5 wt%, the above effect may not be easily expected, and fine nitrides may be formed to increase the change in magnetic properties, while when the content of Al is more than 1.5 wt%, cold rolling properties deteriorate, and excessive nitride generation occurs, resulting in a decrease in magnetic flux density and deterioration of magnetic properties.

[0039] C: greater than 0 wt% and not more than 0.003 wt%

[0040] C is an element that increases iron loss by forming carbides such as TiC and NbC, and the less the better. The content of C is limited to 0.003 wt% or less. When the content of C is more than 0.003 wt%, magnetic aging occurs and the magnetic properties deteriorate, while when the content of C is 0.003 wt% or less, magnetic aging is suppressed.

[0041] P: greater than 0 wt% and not more than 0.015 wt%

[0042] P is an element that develops texture as a grain boundary segregation element. When the content of P is greater than 0.015 wt%, grain growth is inhibited, magnetic properties deteriorate, and cold rolling properties are reduced due to the segregation effect.

[0043] S: greater than 0 wt% and not more than 0.003 wt%

[0044] S increases iron loss and inhibits grain growth by forming precipitates such as MnS and CuS, so the less the better. The S content is limited to 0.002 wt% or less. When the S content is more than 0.003 wt%, the iron loss increases.

[0045] N: greater than 0 wt% and not more than 0.003 wt%

[0046] N increases iron loss and inhibits grain growth by forming precipitates such as AlN, TiN, and NbN, so the less the better. The content of N is limited to 0.003 wt% or less. When the content of N is greater than 0.003 wt%, iron loss increases.

[0047] Ti: more than 0 wt% and not more than 0.003 wt%

[0048] Ti inhibits grain growth by forming fine precipitates such as TiC and TiN. Ti deteriorates magnetic properties, so the less the better. The content of Ti is limited to 0.003 wt% or less. When the content of Ti is greater than 0.003 wt%, magnetic properties deteriorate.

[0049] Hot rolling (S20)

[0050] The steel material of the above composition is hot rolled. The step of hot rolling the steel material (S20) may be performed under the conditions of a slab reheating temperature (SRT) of 1110°C to 1150°C and a finishing outlet temperature (FDT) of 800°C to 900°C.

[0051] When the SRT is higher than 1150°C, precipitates such as C, S and N in the slab may be redissolved, and fine precipitates may be formed in subsequent rolling and annealing processes, thereby inhibiting grain growth and deteriorating magnetic properties. When the SRT is lower than 1110°C, the rolling load may increase and the final product may show high iron loss.

[0052] After the steel is hot rolled (S20), the thickness of the hot rolled sheet may be, for example, 1.6 mm to 2.6 mm. Since the reduction rate of cold rolling increases and the texture deteriorates when the hot rolled sheet is thicker, the thickness may be controlled to 2.6 mm or less.

[0053] The hot-rolled steel may be coiled at a coiling temperature (CT) of 500° C. to 700° C. When the CT is below 500° C., the steel does not undergo annealing effects and thus grain growth does not occur, whereas when the CT is above 700° C., excessive oxidation occurs during cooling and thus pickling properties may deteriorate.

[0054] Primary annealing (S30)

[0055] The hot-rolled steel may be subjected to primary annealing (S30). Primary annealing is an annealing and pickling line (ACL) process for annealing and pickling the hot-rolled sheet, which may be understood as preliminary annealing or thermal annealing.

[0056] The primary annealing step (S30) includes increasing the temperature at a heating rate of 20°C / s or more, starting annealing at a temperature of 940°C to 1110°C, and maintaining the annealing process for 30 seconds to 180 seconds. After the annealing process, the steel material may be cooled at a cooling rate of 20°C / s or more. After the cooling process, pickling may be further performed.

[0057] After hot rolling, the hot rolled sheet is annealed to ensure uniformity of microstructure and cold rollability. The primary annealing temperature is controlled between 940°C and 1110°C to form a uniform microstructure by eliminating the elongated cast structure. When the primary annealing temperature is too low (below 940°C), the elongated cast structure may remain after hot rolling, resulting in an uneven microstructure, and grains may be formed in a small size, thereby hindering cold rolling. On the other hand, when the primary annealing temperature is too high (above 1110°C), texture imbalance may occur in the final product, resulting in anisotropic properties.

[0058] Cold rolled (S40)

[0059] The steel material after primary annealing is cold rolled (S40). The reduction ratio of cold rolling may be 50% to 85%, and the thickness of the steel material after cold rolling may be 0.35 mm or less (more strictly, 0.25 mm or less). In order to improve rollability, the plate temperature may be increased to 100° C. to 200° C. for hot rolling.

[0060] Secondary annealing (S50)

[0061] The steel material after cold rolling may be subjected to secondary annealing. Secondary annealing is an annealing and coating line (ACL) process for final annealing of the cold rolled sheet, which may be understood as cold annealing. The secondary annealing step (S50) may include annealing at a heating rate of 10°C / s or more, an annealing temperature of 900°C to 1100°C, and a holding time of 30 seconds to 90 seconds, and cooling at a cooling rate of 30°C / s or more.

[0062] The cold-rolled sheet obtained after cold rolling is subjected to secondary annealing. A temperature that can achieve an optimum grain size is applied in consideration of iron loss reduction and mechanical properties. Heating is performed under mixed atmosphere conditions to prevent surface oxidation and nitration during cold annealing. The surface is further smoothed using a mixed atmosphere of nitrogen and hydrogen. When the cold annealing temperature is lower than 900°C, fine grains may be formed to increase hysteresis loss, and when the cold annealing temperature is higher than 1100°C, coarse grains may be formed to increase eddy current loss.

[0063] Meanwhile, a coating process may be performed after the final cold annealing to form an insulating coating. By forming the insulating coating, stampability may be improved and insulation may be ensured. The thickness of the insulating coating formed on and under the cold-rolled material may be about 1 micron to 2 microns.

[0064] The non-oriented electrical steel sheet prepared by the above method is a non-oriented electrical steel sheet comprising 2.8 wt% to 3.8 wt% of Si, 0.2 wt% to 0.5 wt% of Mn, 0.5 wt% to 1.5 wt% of Al, more than 0 wt% to not more than 0.003 wt% of C, more than 0 wt% to not more than 0.015 wt% of P, more than 0 wt% to not more than 0.003 wt% of S, more than 0 wt% to not more than 0.003 wt% of N, more than 0 wt% to not more than 0.003 wt% of Ti, and the balance of Fe and other inevitable impurities. Among the secondary phase particles constituting the microstructure of the non-oriented electrical steel sheet, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, and the iron loss (W) of the non-oriented electrical steel sheet is less than 0.003 wt%. 10 / 400 ) is 12.0 W / kg or less. The secondary phase particles may include precipitate particles and inclusion particles.

[0065] Among the secondary phase particles constituting the microstructure, the volume fraction of secondary phase particles having an average diameter equal to or greater than 1.0 μm 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 is 38% or more.

[0066] The microstructure may have an average grain size of 80 micrometers to 160 micrometers. The mechanical properties of the finally produced non-oriented electrical steel sheet are as follows: a yield point (YP) of 400 MPa or more, and a tensile strength (TS) of 500 MPa or more.

[0067] Based on the non-oriented electrical steel sheet and the manufacturing method thereof according to the embodiment of the present invention, by controlling the winding, APL and ACL process variables, the volume fraction of the secondary phase particles with a size of 1 micron or more is controlled to be 60% or more, and the fine precipitates less than 1 micron that hinder the movement of the magnetic domains can be minimized, so that a non-oriented electrical steel sheet with excellent magnetic properties can be manufactured.

[0068] Test Example

[0069] Test examples will now be described in order to better understand the present invention. However, the following test examples are only used to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0070] 1. Sample composition

[0071] The samples provided in this test example have the alloy element composition shown in Table 1 (unit: weight %).

[0072] [Table 1]

[0073] Si Mn Al C P S N Ti margin 3.3 0.32 0.73 0.0025 0.0052 0.0014 0.0018 0.0011 Fe

[0074] Referring to Table 1, the composition of the non-oriented electrical steel sheet according to the test example satisfies Si: 2.8 wt% to 3.8 wt%, Mn: 0.2 wt% to 0.5 wt%, Al: 0.5 wt% to 1.5 wt%, C: greater than 0 wt% and not more than 0.003 wt%, P: greater than 0 wt% and not more than 0.015 wt%, S: greater than 0 wt% and not more than 0.003 wt%, N: greater than 0 wt% and not more than 0.003 wt%, Ti: greater than 0 wt% and not more than 0.003 wt%, and the balance is Fe. The slab of the above composition was reheated to 1130°C and hot rolled at an FDT of 850°C, thereby manufacturing a hot rolled sheet with a thickness of 2.0 mm.

[0075] 2. Process conditions and performance evaluation

[0076] Table 2 shows the CT temperature and time, the primary annealing temperature and time, and the secondary annealing temperature and time in the process conditions of this test example. In this test example, coiling, primary annealing, and secondary annealing are performed at various temperatures after hot rolling. After the primary annealing, cold rolling is performed to obtain a cold-rolled sheet with a thickness of 0.25t, and secondary annealing is performed. Then, a coating process is performed to manufacture the final product. The final annealing is performed in a mixed atmosphere of 30% hydrogen-70% nitrogen. In this example, the heating rate used is 20°C / s and the cooling rate is 30°C / s. In Table 2, the CT temperature represents the coiling temperature, the CT time represents the holding time of the steel at the coiling temperature after coiling, the APL temperature represents the primary annealing temperature, the APL time represents the primary annealing holding time, the ACL temperature represents the secondary annealing temperature, and the ACL time represents the secondary annealing holding time.

[0077] [Table 2]

[0078]

[0079]

[0080] Referring to Table 2, Embodiment 1 and Comparative Examples 1 and 2 adopt the same primary annealing and secondary annealing conditions, but different winding conditions. Embodiments 1, 2 and 3 and Comparative Examples 3, 4 and 5 adopt the same winding and secondary annealing conditions, but different primary annealing conditions. Embodiments 1, 4, 5 and 6 and Comparative Examples 6, 7 and 8 adopt the same winding and primary annealing conditions, but different secondary annealing conditions. Embodiments 1, 2, 3, 4, 5 and 6 meet CT of 500°C to 700°C, primary annealing temperature of 940°C to 1110°C, and secondary annealing temperature of 900°C to 1100°C.

[0081] On the other hand, Comparative Example 1 exceeds and does not satisfy the CT of 500°C to 700°C, Comparative Example 2 exceeds and does not satisfy the CT of 500°C to 700°C, Comparative Example 3 is lower than and does not satisfy the primary annealing temperature of 940°C to 1110°C, Comparative Example 4 exceeds and does not satisfy the primary annealing temperature of 940°C to 1110°C, Comparative Example 5 exceeds and does not satisfy the primary annealing temperature of 940°C to 1110°C, Comparative Example 6 is lower than and does not satisfy the secondary annealing temperature of 900°C to 1100°C, and Comparative Examples 7 and 8 exceed and do not satisfy the secondary annealing temperature of 900°C to 1100°C.

[0082] Table 3 shows the grain size, volume fraction of secondary phase particles and iron loss (W) of the non-oriented electrical steel sheet manufactured according to this test example. 10 / 400 ).

[0083] [Table 3]

[0084]

[0085] Referring to Table 3, embodiments 1, 2, 3, 4, 5 and 6 all satisfy: the average grain size is 80 μm to 160 μm; the volume fraction (A) of secondary phase particles with an average diameter of 1.0 μm or more and less than 2.0 μm in the secondary phase particles constituting the microstructure is 20% or more; the volume fraction (B) of secondary phase particles with an average diameter of 2.0 μm or more in the secondary phase particles constituting the microstructure is 38% or more; the volume fraction (A+B) of secondary phase particles with an average diameter of 1.0 μm or more in the secondary phase particles constituting the microstructure is 60% or more; the iron loss (W 10 / 400 ) is 12.0 W / kg or less. For example, embodiments 1, 2, 3, 4, 5 and 6 satisfy: the volume fraction (A) of secondary phase particles with an average diameter of 1.0 micrometer or more and less than 2.0 micrometers in the secondary phase particles constituting the microstructure is equal to or greater than 20% and equal to or less than 30%; the volume fraction (B) of secondary phase particles with an average diameter of 2.0 micrometers or more in the secondary phase particles constituting the microstructure is equal to or greater than 38% and equal to or less than 50%; the volume fraction (A+B) of secondary phase particles with an average diameter of 1.0 micrometer or more in the secondary phase particles constituting the microstructure is equal to or greater than 60% and equal to or less than 70%.

[0086] On the other hand, Comparative Examples 1, 2, 3, 4, 5, 6, 7 and 8 are lower than and do not satisfy the volume fraction (A+B) of secondary phase particles having an average diameter of 1.0 μm or more in the secondary phase particles constituting the microstructure of 60% or more; Comparative Example 6 is lower than and does not satisfy the average grain size of 80 μm to 160 μm, and Comparative Examples 7 and 8 exceed and do not satisfy the average grain size of 80 μm to 160 μm.

[0087] According to the above test examples, by controlling the process variables based on the reference conditions, it is ensured that the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more in the product satisfies 60% or more, thereby obtaining excellent iron loss performance.

[0088] In contrast, for example, according to Comparative Examples 1, 2, 4, 5, 7 and 8, since the process temperature is relatively high, the precipitate elements are redissolved during the process and then cooled to form fine precipitates, the volume fraction of secondary phase particles having an average diameter of 1.0 μm or more is reduced, and the iron loss performance is deteriorated.

[0089] According to Comparative Examples 3 and 6, since the process temperature is relatively low, the grain size is relatively small, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is reduced, and the iron loss performance is deteriorated.

[0090] The test examples of the present invention have demonstrated that by controlling the winding, APL and ACL process variables, the volume fraction of secondary phase particles having a size of 1 μm or more is controlled to 60% or more, and the fine precipitates less than 1 μm that hinder the movement of magnetic domains can be minimized, thereby manufacturing a non-oriented electrical steel sheet with excellent magnetic properties.

[0091] While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the claims.

Claims

1. A nonoriented electrical steel sheet comprising: 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), more than 0 wt% and not more than 0.003 wt% of carbon (C), more than 0 wt% and not more than 0.015 wt% of phosphorus (P), more than 0 wt% and not more than 0.003 wt% of sulfur (S), more than 0 wt% and not more than 0.003 wt% of nitrogen (N), more than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities; in, Among the secondary phase particles constituting the microstructure of the nonoriented electrical steel sheet, the volume fraction of the secondary phase particles having an average diameter of 1.0 μm or more is 60% or more, and Wherein, the iron loss (W 10 / 400 ) is 12.0W / kg or less.

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 equal to or greater than 1.0 μm 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 secondary phase particles include precipitate particles and inclusion particles.

4. The non-oriented electrical steel sheet according to claim 1, wherein: The microstructure has an average grain size of 80 microns to 160 microns.

5. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: Provided is a steel material comprising: 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), more than 0 wt% and not more than 0.003 wt% of carbon (C), more than 0 wt% and not more than 0.015 wt% of phosphorus (P), more than 0 wt% and not more than 0.003 wt% of sulfur (S), more than 0 wt% and not more than 0.003 wt% of nitrogen (N), more than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities; Hot rolling of steel; Performing primary annealing on the hot-rolled steel; Cold rolling the steel after primary annealing; as well as Perform secondary annealing on the cold-rolled steel; The hot rolling includes coiling at a coiling temperature (CT) of 500° C. to 700° C. after the hot rolling, the primary annealing includes annealing at 940° C. to 1110° C., and the secondary annealing includes annealing at 900° C. to 1100° C.

6. The method according to claim 5, wherein: The hot rolling is performed under the conditions of a slab reheating temperature (SRT) of 1110°C to 1150°C and a finishing outlet temperature (FDT) of 800°C to 900°C.

7. The method according to claim 5, wherein: The thickness of the steel after hot rolling is 1.6 mm to 2.6 mm, and the thickness of the steel after cold rolling is 0.35 mm or less.

8. The method according to claim 5, wherein: After the secondary annealing is performed, the volume fraction of secondary phase particles having an average diameter of 1.0 micrometer or more among the secondary phase particles constituting the microstructure of the nonoriented electrical steel sheet is 60% or more.

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