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

Abstract

The present invention provides 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 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities. In the final microstructure, the crystal grains having the {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and the crystal grains having the {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more.

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 and small 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 are widely used as core materials for small motors, small power transformers, ballasts, etc.

[0003] As a related 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 non-oriented electrical steel sheet having excellent high-frequency iron loss and uniform magnetic properties, 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] The non-oriented electromagnetic steel sheet according to one aspect of the present invention for solving the above problems contains silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance iron (Fe) and other inevitable impurities. In the final fine structure, the crystal grains having the {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and the crystal grains having the {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more.

[0007] In the non-oriented electromagnetic steel sheet, the iron loss (W 10 / 400 ) is 13.5 W / kg or less, and the standard deviation of the iron loss may be 0.725 W / kg or less.

[0008] In the non-oriented electromagnetic steel sheet, the average crystal grain size may be 80 to 150 μm.

[0009] 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 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance of 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 undergone the first annealing heat treatment; and performing a second annealing heat treatment on the cold-rolled steel material. The hot rolling step is carried out under the conditions of a reheating temperature of 1100 to 1200 °C, a finish rolling temperature of 800 to 1000 °C, and a coiling temperature of 560 to 600 °C. The first annealing heat treatment step is carried out under the conditions of a heating rate of 10 °C / s or more, an annealing start temperature of 900 to 1050 °C, an annealing holding time of 30 to 90 seconds, and a cooling rate of 20 °C / s or more. The second annealing heat treatment step is carried out under the conditions of a heating rate of 10 °C / s or more, an annealing start temperature of 900 to 1100 °C, an annealing holding time of 30 to 90 seconds, and a cooling rate of 30 °C / s or more.

[0010] In the method for manufacturing the non-oriented electromagnetic steel sheet, after the first annealing heat treatment, the average grain size may be 140 to 250 μm, and the volume fraction of grains having a <110> / / RD orientation in the central layer may be 20% or less.

[0011] In the method for manufacturing the non-oriented electromagnetic steel sheet, the cold rolling step may be carried out under the condition of a reduction ratio of 81 to 92%.

[0012] In the method for manufacturing the non-oriented electromagnetic steel sheet, the thickness of the steel material after hot rolling may be 1.6 to 2.6 mm, and the thickness of the steel material after cold rolling may be 0.1 to 0.3 mm.

Advantages of the Invention

[0013] According to an embodiment of the present invention, it is possible to provide a non-oriented electromagnetic steel sheet excellent in high-frequency iron loss and having uniform magnetic properties. For example, by adjusting the conditions of preliminary annealing after hot rolling, it is possible to provide a non-oriented electromagnetic steel sheet having a low average iron loss and a standard deviation. By restricting the temperature and grain size during preliminary annealing, an increase in production cost can be suppressed. By manufacturing a non-oriented electromagnetic steel sheet having a uniform fine structure and aggregate structure, uniform magnetic properties can be ensured.

[0014] Of course, the scope of the present invention is not limited by such effects.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0016] 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.

[0017] Generally, electromagnetic steel sheets are classified into grain-oriented electromagnetic steel sheets and non-oriented electromagnetic steel sheets. In the case of grain-oriented electromagnetic steel sheets, they are mainly used in static devices such as transformers, while non-oriented electromagnetic steel sheets are mainly used in rotating devices such as motors and generators. Recently, as a response to global environmental issues, technologies are rapidly shifting from existing internal combustion engines to hybrid electric vehicles (HEVs), electric vehicles (EVs), and hydrogen vehicles for replacement.

[0018] The non-oriented electromagnetic steel sheet used as the core material of a motor plays a role in converting electrical energy into mechanical energy in a rotating device. For energy saving, it is important to have its magnetic properties, that is, low iron loss and high magnetic flux density. Iron loss is the energy loss generated during the magnetization process, and magnetic flux density means the force that generates power. The magnetic flux density is B 50 , and in the case of iron loss, generally W 15 / 50 is mainly evaluated, 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 represents the magnetic flux density at 5000 A / m, W 15 / 50 represents the iron loss at 50 Hz and 1.5 T, and W 10 / 400 represents the iron loss at 400 Hz and 1.0 T.

[0019] In order to meet such required characteristics, the Si content, product thickness, grain size, microstructure, precipitates, etc. must be appropriately controlled. An increase in the Si content and a decrease in the product thickness are effective in reducing iron loss but have the drawback of reducing the magnetic flux density. To complement this, in the manufacturing process of non-oriented electromagnetic steel sheets, the control of grain size, microstructure, and precipitates is very important. Since the magnetic properties (iron loss, magnetic flux density) change very sensitively according to the grain size, microstructure, and precipitates, variations in the manufacturing process will lead to variations in the magnetic properties.

[0020] The motor core has a structure in which dozens to hundreds of non-oriented electrical steel sheets are laminated. When non-oriented electrical steel sheets with large variations in magnetic properties are applied to the manufacture of such a motor core, problems may occur in the operation of the motor.

[0021] The non-oriented electrical steel sheet for an automotive drive motor according to the present invention performs preliminary annealing after hot rolling and before cold rolling in order to achieve low iron loss and high magnetic flux density. The preliminary annealing is different from the final annealing performed after cold rolling.

[0022] According to related research, a method of cold rolling and final annealing with a grain size of 400 μm or more after preliminary annealing has been proposed, but this may cause problems with variations in magnetic properties due to non-uniformity of the microstructure and texture. According to other research, a technique for improving the texture through ensuring productivity by controlling the grain size to 150 μm or more after preliminary annealing has been proposed, but no limit was set on the grain size after preliminary annealing, and variations in magnetic properties due to non-uniformity of the microstructure / texture occurring thereafter were not considered.

[0023] In the present invention, by restricting an appropriate grain size and texture after preliminary annealing, a non-oriented electrical steel sheet having a uniform microstructure and texture after cold rolling and final annealing and a method for manufacturing the same are provided.

[0024] FIG. 1 is a flowchart showing a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0025] Referring to FIG. 1, a method for manufacturing a non-oriented electrical 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 first-annealed heat-treated steel material, and a step (S50) of performing a second annealing heat treatment on the cold-rolled steel material.

[0026] Steel material supply step (S10)

[0027] The steel material input into the hot rolling process is a steel material for manufacturing non-oriented electrical steel sheets. 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 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance of iron (Fe) and other inevitable impurities.

[0028] Hereinafter, the roles and contents of exemplary components to which the method for manufacturing a non-oriented electrical steel sheet according to the technical idea of the present invention can be applied will be described.

[0029] Silicon (Si): 2.8 to 3.8 wt%

[0030] Silicon (Si) is a component that increases the specific resistance and reduces the 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. Further, when the addition amount of silicon exceeds 3.8 wt%, the brittleness increases, making cold rolling difficult and reducing productivity.

[0031] Manganese (Mn): 0.2 to 0.5 wt%

[0032] Manganese (Mn) increases the specific resistance together with silicon and improves the microstructure. When manganese is added in an amount exceeding 0.5 wt%, coarse MnS precipitates are formed and the magnetic flux density decreases, etc., and the magnetic properties deteriorate. Further, when the content of manganese exceeds 0.5 wt%, the reduction amount of iron loss is small compared to the addition amount, while the decrease in cold rollability is remarkable. Further, when the content of manganese is less than 0.2 wt%, the composition range of manganese can be adjusted to 0.2 to 0.5 wt% in that it can form fine MnS precipitates and suppress the growth of crystal grains.

[0033] Aluminum (Al): 0.5 to 1.2 wt%

[0034] Aluminum (Al) is a component that, together with silicon, increases the resistivity and reduces the iron loss (eddy current loss), and is a major additive element. Aluminum plays a role in reducing magnetic anisotropy and decreasing the variation in magnetism. Aluminum reacts with nitrogen to induce the precipitation of AlN. When the content of aluminum is less than 0.5% by weight, it is difficult to expect the above-mentioned effects, and it may form fine nitrides and increase the variation in magnetic properties. When the content of aluminum exceeds 1.2% by weight, the cold rolling property deteriorates, excessive nitrides are formed, the magnetic flux density decreases, and the magnetic properties deteriorate.

[0035] Carbon (C): More than 0 and 0.002 wt% or less

[0036] Carbon (C) is an element that forms carbides such as TiC and NbC and increases the iron loss. The less the better, and it is limited to 0.002% by weight or less. When the content of carbon exceeds 0.002% by weight, magnetic aging occurs and the magnetic properties decrease. When it is 0.002% by weight or less, the magnetic aging phenomenon is suppressed.

[0037] Phosphorus (P): More than 0 and 0.015 wt% or less

[0038] Phosphorus (P) is an element that segregates at grain boundaries and develops the microstructure. When the content of phosphorus exceeds 0.015% by weight, the growth of grains is suppressed due to the segregation effect, the magnetic properties deteriorate, and the cold rolling property deteriorates.

[0039] Sulfur (S): More than 0 and 0.002 wt% or less

[0040] Sulfur (S) forms precipitates such as MnS and CuS and increases the iron loss and suppresses the growth of grains. Therefore, it is added as low as possible and limited to 0.002% by weight or less. When the content of sulfur exceeds 0.002% by weight, the problem of increasing iron loss occurs.

[0041] Nitrogen (N): More than 0 and 0.002 wt% or less

[0042] Nitrogen (N) forms precipitates such as AlN, TiN, etc., increasing iron loss and suppressing the growth of crystal grains. Therefore, it is added as low as possible and limited to 0.002 wt% or less. When the nitrogen content exceeds 0.002 wt%, the problem of increased iron loss occurs.

[0043] Titanium (Ti): More than 0 and 0.002 wt% or less

[0044] 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 more, it is added as low as possible and limited to 0.002 wt% or less. When the titanium content exceeds 0.002 wt%, the problem of deteriorated magnetic properties occurs.

[0045] Hot rolling step (S20)

[0046] 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 of 1100 - 1200 °C, a finish rolling temperature of 800 - 1000 °C, and a coiling temperature of 560 - 600 °C.

[0047] When the slab reheating temperature exceeds 1200 °C, precipitates such as C, S, and N in the slab redissolve, and fine precipitates occur in the subsequent rolling and annealing processes, suppressing the growth of crystal grains and possibly deteriorating the magnetism. When the slab reheating temperature is less than 1100 °C, the rolling load increases, and there may be a problem that the iron loss becomes high in the final product.

[0048] After performing the step (S20) of hot rolling the steel material, the thickness of the hot rolled sheet may be, for example, 1.6 - 2.6 mm. The thicker the thickness of the hot rolled sheet, the greater the reduction ratio in cold rolling becomes, and the microstructure becomes inferior. Therefore, it is preferable to control the thickness to 2.6 mm or less.

[0049] The hot-rolled steel material may be wound under the condition that the coiling temperature (CT) is 560 to 600 °C. When the coiling temperature is less than 560 °C, since there is no annealing effect on the steel material, the growth of crystal grains does not occur. When the coiling temperature exceeds 600 °C, oxidation may increase during cooling, and thus the pickling property may deteriorate.

[0050] First annealing heat treatment step (S30)

[0051] 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, and can be understood as a preliminary annealing treatment or a hot-rolled annealing treatment.

[0052] The step (S30) of performing the first annealing heat treatment includes an annealing process in which the temperature is raised at a rate of 10 °C / s or more and then annealing is started at a temperature of 900 to 1050 °C and maintained for 30 to 90 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.

[0053] After hot rolling, an annealing process of the hot-rolled sheet is carried out to ensure the uniformity of the microstructure and the cold-rolling property. The first annealing temperature is adjusted to 900 to 1050 °C so that a uniform microstructure in which the elongated cast structure is removed can be formed. When the first annealing temperature is too low, less than 900 °C, the elongated cast structure remaining after hot rolling remains and induces non-uniformity of the microstructure, and crystal grains are formed small, which may act as an interfering factor for cold rolling. On the contrary, when the first annealing temperature is too high, exceeding 1050 °C, it induces variation in the aggregate structure of the final product and causes anisotropy of properties.

[0054] After the first annealing heat treatment, the average grain size is 140 to 250 μm, and <110> / / The volume fraction of crystal grains having the RD orientation may be more than 0% and not more than 20%. Here, RD means the rolling direction, and the central layer means the central region (thickness 1 / 4 to 3 / 4) obtained by excluding t / 4 of the thickness (t) of the steel material from the surface portion of the steel material to the upper and lower portions.

[0055] Cold rolling step (S40)

[0056] The steel material that has undergone the first annealing heat treatment is subjected to a step (S40) of cold rolling. The reduction ratio of the cold rolling may be 81 to 92%, and the thickness of the steel material after cold rolling may be 0.1 to 0.3 mm. To impart rollability, the sheet temperature may be increased to 100 to 200°C and warm rolling may be performed.

[0057] Second annealing heat treatment step (S50)

[0058] The cold-rolled steel may be subjected to a second annealing heat treatment. The second annealing heat treatment is an ACL (Annealing and Coating Line) step of final annealing the cold-rolled steel sheet, and may be understood as a cold-rolling annealing treatment. The step of performing the second annealing heat treatment (S50) may include annealing at a temperature increase rate of 10°C / s or more, an annealing temperature of 900 to 1100°C, and a maintenance time of 30 to 90 seconds, and cooling at a cooling rate of 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 selected to derive the optimum grain size, taking into consideration the improvement of iron loss and mechanical properties. To prevent surface oxidation and nitridation during cold rolling annealing, the sheet is heated in a mixed atmosphere. A mixed atmosphere of nitrogen and hydrogen further smooths the surface. If the cold rolling annealing temperature is less than 900°C, the grain size will be fine, which may increase hysteresis loss. If the cold rolling annealing temperature is more than 1100°C, the grain size will become coarse, which may increase eddy current loss.

[0060] On the other hand, after final cold rolling and 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 portions 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 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities. In the final fine structure, the crystal grains having the {111} / / ND orientation have a volume fraction of more than 0 and 30% or less, and the average misorientation angle is 23° or more (for example, 23° or more and 40° or less), and the crystal grains having the {001} / / ND orientation have a volume fraction of 15% or more (for example, 15% or more and 50% or less), and the average misorientation angle is 48° or more (for example, 48° or more and 60° or less).

[0062] Here, the ND direction is a direction perpendicular to the rolling direction (RD) and is a direction perpendicular to the upper surface of the steel sheet. The crystal grains having the {111} / / ND orientation include crystal grains in which the test single surface is parallel to the {111} plane, and the crystal grains having the {001} / / ND orientation include crystal grains in which the test single surface is parallel to the {001} plane.

[0063] Steel materials are composed of numerous crystal grains, and each crystal grain has a different orientation. Such a distribution of orientations is called a texture. Adjacent crystal grains have their respective orientations. The difference in orientation angle between adjacent crystal grains is called the misorientation angle.

[0064] The larger the average misorientation angle, the more it means that there are no crystal grains with similar orientations in the vicinity, indicating a uniform microstructure. On the contrary, the smaller the average misorientation angle, the more it means that there are many crystal grains with similar orientations in the vicinity, indicating a non-uniform microstructure. The misorientation angle varies for each orientation and for each material.

[0065] In the final microstructure, the average crystal grain size may be 80 to 150 μm. The finally realized non-oriented electrical steel sheet has an iron loss (W 10 / 400 ) of 13.5 W / kg or less, and the standard deviation of the iron loss can be 0.725 W / kg or less.

[0066] According to the non-oriented electrical steel sheet and its manufacturing method according to the embodiments of the present invention, by adjusting the conditions of preliminary annealing after hot rolling, a non-oriented electrical steel sheet having a low average iron loss and a standard deviation can be provided. By restricting the temperature and crystal grain size in preliminary annealing, an increase in production cost can be suppressed. By manufacturing a non-oriented electrical steel sheet having a uniform microstructure and texture, uniform magnetic properties can be ensured.

[0067] Experimental example

[0068] 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.

[0069] [[ID=**17**]]1. Composition of test piece

[0070] In this experimental example, a test piece having the composition of alloying elements in Table 1 (unit: wt%) is provided.

[0071]

Table 1

[0072] Referring to Table 1, the composition of the non-oriented electrical 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 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance being 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 produced. For the hot-rolled sheet, the first annealing heat treatment (pre-annealing) was performed under the conditions of a heating rate of 15 °C / s, an annealing holding time of 50 seconds, and a cooling rate of 30 °C / s. After cold rolling, the second annealing heat treatment (final annealing) was performed under the conditions of a heating rate of 20 °C / s, an annealing start temperature of 1000 °C, an annealing holding time of 50 seconds, and a cooling rate of 30 °C / s. Thereafter, the final product was manufactured through a coating process. The final annealing atmosphere was a mixed atmosphere of 30% hydrogen - 70% nitrogen.

[0073] [[ID=**18**]]2. Evaluation of process conditions and physical properties

[0074] Table 2 shows the process conditions (pre-annealing temperature) of this experimental example and the results of physical property evaluation thereby. In the experimental examples of Table 2, the condition that the temperature of the final annealing was all 975 °C was applied. The iron loss was measured 10 times or more with a test piece having an area of 3000 mm 2 or more at different positions.

[0075] On the one hand, FIG. 2 is a photograph of the microstructure (IPF MAP) observed through the EBSD analysis technique for the non-oriented electromagnetic steel sheet according to Example 1 among the experimental examples of the present invention, and FIG. 3 is a photograph of the microstructure (IPF MAP) observed through the EBSD analysis technique for the non-oriented electromagnetic steel sheet according to Comparative Example 2 among the experimental examples of the present invention. (a) in FIGS. 2 and 3 is a photograph related to the microstructure after preliminary annealing (first annealing heat treatment), and (b) is a photograph related to the microstructure after final annealing (second annealing heat treatment).

[0076]

Table 2

[0077] Referring to Table 2, Examples 1 to 3 were subjected to the first annealing heat treatment under the conditions of a heating rate of 10 °C / s or more, an annealing start temperature of 900 to 1050 °C, an annealing holding time of 30 to 90 seconds, and a cooling rate of 20 °C / s or more. After the first annealing heat treatment, the average grain size satisfies the range of 140 to 250 μm, and the volume fraction of grains having the <110> / / RD orientation in the central layer is 20% or less. Further, after the final annealing (second annealing heat treatment), in the final microstructure, the grains having the {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and the grains having the {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more, and have an iron loss (W 10 / 400 ) of 13.5 W / kg or less, and it can be confirmed that the standard deviation of the iron loss is 0.725 W / kg or less. Examples 1 to 3 embody a microstructure advantageous for magnetism and have a small average iron loss value, but a uniform fine microstructure / microstructure develops, and the standard deviation can be controlled to 0.725 W / kg or less. Referring to FIG. 2, it can be confirmed that a uniform fine microstructure / microstructure develops.

[0078] In contrast, Comparative Example 1 fails to satisfy as the annealing start temperature in the preliminary annealing (first annealing heat treatment) is below the range of 900 to 1050 °C. As a result, after the first annealing heat treatment, the average grain size is below the range of 140 to 250 μm and is not satisfactory. The volume fraction of grains having the <110> / / RD orientation in the central layer exceeds the range of 20% or less and is not satisfactory. After the final annealing (second annealing heat treatment), in the final microstructure, the grains having the {111} / / ND orientation have a volume fraction exceeding the range of 30% or less and are not satisfactory. The grains having the {001} / / ND orientation have a volume fraction below the range of 15% or more and are not satisfactory. The iron loss (W 10 / 400の ) does not satisfy the range of 13.5 W / kg or less.

[0079] Comparative Example 2 fails to satisfy as the annealing start temperature in the preliminary annealing (first annealing heat treatment) is above the range of 900 to 1050 °C. As a result, after the first annealing heat treatment, the average grain size is above the range of 140 to 250 μm and is not satisfactory. After the final annealing (second annealing heat treatment), in the final microstructure, the average misorientation angle of the grains having the {111} / / ND orientation is below the range of 23° or more and is not satisfactory. The average misorientation angle of the grains having the {001} / / ND orientation is below the range of 48° or more and is not satisfactory. Although the iron loss (W 10 / 400 ) satisfies the requirement, it can be confirmed that the standard deviation of the iron loss does not satisfy the range of 0.725 W / kg or less. In Comparative Example 2, although a microstructure favorable for magnetism is realized and the average iron loss value is small, a non-uniform microstructure / aggregate structure has developed and the standard deviation exceeds 0.725 W / kg. Referring to FIG. 3, it can be confirmed that a non-uniform microstructure / aggregate structure has developed.

[0080] Comparative Example 3 is not satisfactory as the annealing start temperature in the preliminary annealing (first annealing heat treatment) is below the range of 900 to 1050 °C. As a result, after the first annealing heat treatment, the average grain size is below the range of 140 to 250 μm and is not satisfactory, and the volume fraction of grains having the <110> / / RD orientation in the central layer exceeds the range of 20% or less and is not satisfactory. After the final annealing (second annealing heat treatment), in the final microstructure, the grains having the {111} / / ND orientation have a volume fraction exceeding the range of 30% or less and are not satisfactory, and the grains having the {001} / / ND orientation have a volume fraction below the range of 15% or more and are not satisfactory, and the iron loss (W 10 / 400 ) does not satisfy the range of 13.5 W / kg or less.

[0081] Comparative Example 4 is not satisfactory as the annealing start temperature in the preliminary annealing (first annealing heat treatment) is above the range of 900 to 1050 °C. As a result, after the first annealing heat treatment, the average grain size is above the range of 140 to 250 μm and is not satisfactory. After the final annealing (second annealing heat treatment), in the final microstructure, the average misorientation angle of the grains having the {001} / / ND orientation is below the range of 48° or more and is not satisfactory. Although the iron loss (W 10 / 400 ) satisfies the requirement, it can be confirmed that the standard deviation of the iron loss does not satisfy the range of 0.725 W / kg or less. In Comparative Example 4, although a microstructure advantageous for magnetism is realized and the average iron loss value is small, a non-uniform microstructure / aggregate structure is developed and the standard deviation exceeds 0.725 W / kg.

[0082] In the 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 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance iron (Fe) and other inevitable impurities, In the final microstructure, the crystal grains having a {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and the crystal grains having a {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more. An isotropic electromagnetic steel sheet characterized by this.

2. Iron loss of 13.5 W / kg or less (W １０／４００ ), and the standard deviation of the iron loss is 0.725 W / kg or less, characterized by the non-oriented electromagnetic steel sheet according to claim 1.

3. The isotropic electromagnetic steel sheet according to claim 1, characterized in that the average crystal grain size is 80 to 150 μm.

4. 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 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% 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 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 is performed under the conditions of a reheating temperature of 1100 to 1200°C, a finish rolling temperature of 800 to 1000°C, and a coiling temperature of 560 to 600°C, The step of performing the first annealing heat treatment is performed under the conditions of a heating rate of 10°C / s or more, an annealing start temperature of 900 to 1050°C, an annealing holding time of 30 to 90 seconds, and a cooling rate of 20°C / s or more, The step of performing the second annealing heat treatment is performed under the conditions of a heating rate of 10°C / s or more, an annealing start temperature of 900 to 1100°C, an annealing holding time of 30 to 90 seconds, and a cooling rate of 30°C / s or more. A method for manufacturing an isotropic electromagnetic steel sheet.

5. The method for manufacturing a non-oriented electrical steel sheet according to claim 4, wherein after the first annealing heat treatment, the average crystal grain size is 140 to 250 μm, and the volume fraction of crystal grains having a <110> / / RD orientation in the central layer is 20% or less.

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 4, wherein the cold rolling step is performed under the condition of a rolling reduction rate of 81 to 92%.

7. The thickness of the steel material after hot rolling is 1.6 to 2.6 mm, The thickness of the steel material after cold rolling is 0.1 to 0.3 mm, The method for manufacturing a non-oriented electrical steel sheet according to claim 4.

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