KR101329715B1 - Non-oriented electrical steel sheet with excellent magnetic properties after Stress Relief Annealing, and method for manufacturing the same - Google Patents

Abstract

The present invention relates to the production of non-oriented electrical steel sheet, in weight% Al: 1.0 ~ 3.0%, Si: 2.3 ~ 3.5%, Mn: 0.5 ~ 2.0%, N: 0.001 ~ 0.004%, S: 0.0005 ~ 0.004% , Remainder Fe and other unavoidable impurities, Al, Mn, N, S is (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤ 0.006, 300 ≤ (Al + Mn) / ( Provided is a high silicon non-oriented electrical steel sheet having excellent magnetic properties after SRA contained so as to satisfy all conditions of N + S) ≦ 1,400 and a method of manufacturing the same.
Accordingly, by optimizing the additive components of Al, Mn, N, S to increase the density of coarse inclusions, it is possible to stably manufacture the highest quality non-oriented electrical steel sheet having a grain size of 60 µm or more after SRA and a cube aggregate structure fraction of 3% or more. can do.

Description

Non-oriented electrical steel sheet with excellent magnetic properties after Stress Relief Annealing, and method for manufacturing the same

The present invention relates to a manufacturing technology of non-oriented electrical steel sheet, the additive composition of the steel is set optimally, the distribution density of coarse inclusions in the steel is high, and the growth of grains and the fraction of the cube aggregate structure during SRA treatment improves the magnetic properties after SRA It relates to an excellent high quality non-oriented electrical steel sheet and a method of manufacturing the same.

The present invention relates to the manufacturing technology of non-oriented electrical steel sheet mainly used as the iron core material of the rotating machine, the magnetic properties are very important because the non-oriented electrical steel sheet is used as an important component for converting electrical energy into mechanical energy . Mainly mentioned magnetic properties are iron loss and magnetic flux density. Iron loss is energy that disappears as heat during the energy conversion process, the lower the better, the higher the magnetic flux density is the power source of the rotor, the higher the better the energy efficiency.

Typically, Si is added as a main element to produce a non-oriented electrical steel sheet having low iron loss. However, when the Si content is excessively high, the magnetic flux density of the non-oriented electrical steel sheet decreases, and when the Si content exceeds 3.5%, the workability is lowered, which makes it difficult to cold roll. In addition, the die life is reduced when the customer punches.

Therefore, attempts have been made to improve the magnetic and mechanical properties by reducing the Si content and increasing the Al content, but are not yet commercialized due to the difficulty of the high-quality non-oriented electrical steel sheet and the difficulty in mass production process.

On the other hand, in order to obtain good magnetism in the non-oriented electrical steel sheet, it is necessary to control the impurities such as C, S, N, Ti in the steel to an extremely low level to improve the grain growth. However, it is not easy to manage impurities very low in a general electrical steel sheet manufacturing process, and there is a disadvantage in that an increase in cost occurs in the steelmaking stage.

Impurities not removed in the steelmaking stage exist in the form of nitrides or sulfides in the slab during continuous casting, and inclusions such as nitrides or sulfides are redissolved as the slab is reheated to a temperature above 1,100 ° C for hot rolling. At the end of rolling, fine precipitates again.

The inclusions MnS and AlN, which are precipitated in general non-oriented electrical steel sheets, are observed to have a fine size of about 50 nm, and the fine inclusions thus produced not only increase the hysteresis loss by inhibiting the growth of grains during annealing, but also during magnetization. It reduces the permeability by preventing the movement of the wall.

Therefore, in the manufacturing process of the non-oriented electrical steel sheet, it is important to properly control the impurities from the steelmaking stage so that such fine inclusions do not exist, and to suppress the remaining inclusions from being re-used during hot rolling to be deposited finer.

In addition, it is very important not only to improve impurities grain growth by controlling impurities in the electrical steel sheet, but also to form an aggregate structure that is advantageous for magnetism.

In order to improve the magnetism of the non-oriented electrical steel sheet, it is most ideal that the magnetization direction <100> lies in the direction perpendicular to the surface of the steel sheet, and the orientation (111) or (211) which is difficult to magnetize compared to <100>. Cotton is preferably low.

The formation of the texture is also determined by the alloy component system, but is closely related to the final annealing condition and the stress relief process (SRA). In general, as the grains grow after the final annealing, the magnetism is oriented to the magnetic field such as the orientation of the texture of the texture (<100> // ND orientation) in which the direction of magnetization lies in a direction perpendicular to the surface of the steel sheet. The fraction of favorable bearing decreases. Therefore, it is very important to make grain size favorable to the aggregate structure during final annealing and to further develop the aggregate structure in the SRA process. However, the technology that deals with the assembly of the highest quality non-oriented electrical steel sheet after SRA has not been proposed.

The present invention was created to solve all the problems of the prior art as described above, and manages the component ratios of Al, Si, Mn, which are alloy elements of steel, and N and S, which are impurity elements, under optimal conditions, thereby making them coarse in steel. It provides high-quality non-silicon non-oriented electrical steel sheet having excellent magnetic properties after SRA by increasing the distribution density of inclusions and reducing the incidence of fine inclusions, and increasing the fraction of aggregates which are advantageous for grain growth and magnetism during SRA treatment. It is intended to be.

The non-oriented electrical steel sheet having excellent magnetic properties after SRA of the present invention for solving the above problems is Al: 1.0 to 3.0%, Si: 2.3 to 3.5%, Mn: 0.5 to 2.0%, N: 0.001 to 0.004% , S: 0.0005 to 0.004%, the balance Fe and other inevitable impurities, Al, Mn, N, S is (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤ 0.006, 300 ≤ ([Al] + [Mn]) / ([N] + [S]) is contained so as to satisfy all the conditions of ≤ 1,400, the grain size is 60㎛ or more, characterized in that the cube aggregate tissue fraction is 3% or more.

The non-oriented electrical steel sheet of the present invention contains Al, Si, Mn to satisfy the conditions of 3.0≤ (Al + Si + Mn / 2) ≤6.5, 0.3≤Al / Si≤1.3, 1≤Al / Mn≤8 There is also a feature in being.

In the non-oriented electrical steel sheet of the present invention, inclusions of nitrides and sulfides alone or in combination thereof are formed in a steel sheet, and the distribution density of inclusions having an average size of 300 nm or more is 0.02 pieces / mm ² or more.

The method of manufacturing the non-oriented electrical steel sheet having excellent magnetic properties after SRA of the present invention is weight%, Al: 1.0-3.0%, Si: 2.3-3.5%, Mn: 0.5-2.0%, N: 0.001-0.004%, S: 0.0005% to 0.004%, balance of Fe and other inevitable impurities, Al, Mn, N, S is (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤ 0.006, 300 ≤ (Al + Mn) / (N + S) ≤1,400 The slab contained so as to satisfy all the conditions of 1,100 ~ 1,250 ℃ heated and hot-rolled, then hot-rolled sheet annealing or omitted, and then 70 ~ 95% reduction rate After cold rolling, the cold-rolled cold rolled sheet is finally annealed at a temperature range of 750 ~ 850 ℃, and then characterized in that the SRA heat treatment by maintaining a crack at 700 ~ 850 ℃ temperature for at least 60 minutes.

Method for producing a non-oriented electrical steel sheet of the present invention is characterized by controlling the grain size of the SRA heat-treated steel sheet to 60㎛ or more, and controlling the cube aggregate tissue fraction to 3% or more.

In the method for manufacturing a non-oriented electrical steel sheet of the present invention, the slab is Al, Si, Mn is 3.0≤ (Al + Si + Mn / 2) ≤6.5, 0.3≤Al / Si≤1.3, 1≤Al / Mn≤8 It is characterized by containing so as to satisfy the conditions.

The method for producing non-oriented electrical steel sheet of the present invention is also characterized by controlling the distribution density of inclusions having an average size of 300 nm or more to 0.02 pieces / mm ² or more.

In the manufacturing method of the non-oriented electrical steel sheet according to the present invention, 0.3 to 0.5% of Al is added to deoxidation, and then the remaining alloying elements are added. After the addition of the remaining alloying elements, the slab is maintained at a temperature of 1,500 to 1,600 ° C. There is also a feature in manufacturing.

According to the present invention, by appropriately managing the component ratios of Al, Si, Mn, which are alloy elements, and N, S, which are impurity elements, by increasing the distribution density of coarse inclusions, it is possible to increase grain growth and improve mobility of magnetic walls. Therefore, by securing the optimum grain size after SRA and increasing the fraction of the texture structure advantageous to magnetism, it is possible to manufacture the highest quality non-silicon non-oriented electrical steel sheet having excellent magnetism after SRA. In addition, it is possible to increase cost and productivity of customers, and to lower production costs of products.

1 is a view showing a composite inclusion in the non-oriented electrical steel sheet of the present invention.
FIG. 2 is a graph showing the distribution density of a huge composite inclusion having an average size of 300 nm or more with (N + S) as the horizontal axis and the vertical axis as the basis of 0.02 / mm ² or more.

Hereinafter, the present invention will be described in detail.

The non-oriented electrical steel sheet is most ideal if (100), which is a direction easily magnetized in the vertical direction (ND), is located on the surface of the steel sheet, among them, the cube-structured tissue (100). ) The higher the degree of integration of [001], the better the magnetic characteristics.

In general, in non-oriented electrical steel sheet, the fraction of orientations favoring magnetism such as cube texture {(100) [001]} during cold rolling and grain growth decreases to less than 3%.

Therefore, it is required to find an alloy component system having an integration degree of 3% or more of the cube texture structure which is advantageous for the magnetism after SRA.

In order to solve the above technical problem, the present inventors investigated the effects of the alloying elements, impurity elements and the relationship between the elements on the formation of the inclusions and the effects on the magnetic properties and workability, respectively, excellent grain growth after SRA The purpose of this study was to find a condition in which the fraction of aggregates favoring magnetism was increased.

As a result, the Al, Si, Mn and impurity elements N and S in the alloy elements added to the steel are appropriately set and Al / Si, Al + Mn, N + S, (Al + Mn) / (N By optimally managing the ratio of + S), it is possible to increase the distribution density of large composite inclusions having an average size of 300 nm or more in the steel sheet, and to increase the fraction of the grain structure which is advantageous for the excellent grain growth and magnetism during SRA treatment. The present invention has been completed by paying attention to the results of the magnetic properties of the electrical steel sheet being significantly improved.

The present invention is by weight, Al: 1.0 ~ 3.0%, Si: 2.3 ~ 3.5%, Mn: 0.5 ~ 2.0%, N: 0.001 ~ 0.004%, S: 0.0005 ~ 0.004%, balance Fe and other unavoidably incorporated And Al, Mn, N, and S are made of (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤ 0.006, 300 ≤ (Al + Mn) / (N + S) ≤ 1,400 It is characterized by being contained to satisfy.

As a result, the distribution density of nitrides and sulfides having an average size of 300 nm or more alone or incorporating them is increased to 0.02 pieces / mm ² or more, and the grain size is increased to 60 μm or more by SRA treatment, and the cube aggregate structure fraction is higher than 3%. It can be secured to the highest level and can manufacture high quality non-silicon non-oriented electrical steel sheet having excellent magnetic properties after SRA.

In addition, in the present invention, 0.3 to 0.5% of Al is first added in the steelmaking step so that deoxidation is performed, and then a residual alloy element is added, and after the addition of the remaining alloy element, the temperature of molten steel is maintained at 1,500 to 1,600 ° C. A slab having a composition of components is prepared, and the slab is heated to a temperature of 1,100 to 1,250 ° C., and then hot rolled, but hot finishing rolling is performed at 800 ° C. or higher, and the hot rolled hot rolled plate is hot rolled at a temperature range of 850 to 1,100 ° C. After annealing or omitting, pickling, cold rolling at a reduction ratio of 70 to 95%, and final cold annealing of the cold rolled cold plate at a temperature range of 750 to 850 ° C., and then cracking at a temperature of 700 to 850 ° C. for at least 60 minutes. It is characterized in that the high silicon non-oriented electrical steel sheet having excellent magnetic properties after SRA having a grain growth of 3% or more with good grain growth and magnetic properties by maintaining SRA heat treatment.

In the case of Al, Si, and Mn, which are alloying elements of steel, the alloying elements are elements added to lower iron loss of electrical steel sheets, but as the added content thereof increases, the magnetic flux density decreases and the workability of the material is also deteriorated. In addition, the content of these alloying components should be set appropriately to improve magnetic flux density as well as iron loss and maintain hardness at an appropriate level.

In addition, Al and Mn combine with the impurity elements N and S to form inclusions such as nitrides or sulfides. Since such inclusions have a great effect on the magnetism, the inclusion frequency is increased to minimize the deterioration of the magnetic properties. There is a need.

The inventors first discovered that when Al, Mn, Si, N, and S were contained so as to satisfy specific conditions, a huge composite inclusion composed of nitrides or sulfides was formed, and the workability was adjusted by adjusting the distribution density of such composite inclusions. The present invention has been proposed in view of the fact that the magnetism is greatly improved despite having a minimum amount of deteriorating alloying elements.

First, the reason for limiting the content ratio between the component elements constituting the present invention and the specific component elements will be described.

[Al: 1.0-3.0 wt%]

Al is added because it increases the specific resistance of the material, lowers iron loss and forms nitride, and is added in 1.0 to 3.0% to form coarse nitride. If the Al content is less than 1.0%, the inclusions cannot be sufficiently grown. If the Al content is more than 3.0%, the workability is degraded and problems occur in all processes such as steelmaking and continuous casting.

[Si: 2.3-3.5 wt%]

Si serves to lower the iron loss by increasing the specific resistance of the material, when contained less than 2.3%, there is no effect of reducing high-frequency iron loss, and when contained in more than 3.5%, the hardness of the material rises to increase productivity and breakability. It is not desirable because it is harmful.

[Mn: 0.5-2.0 wt%]

Mn improves iron resistivity and forms sulfides by increasing the specific resistance of the material, and the coarsening effect is exhibited when contained at 0.5% or more. When Mn is contained in an amount exceeding 2.0%, the content of Mn is preferably limited to 0.5 to 2.0% since it promotes formation of [111] aggregates, which is detrimental to magnetism.

[N: 0.001-0.004 wt%]

N is an impurity element, in which fine nitride is formed during the manufacturing process to suppress grain growth and inferior iron loss. Therefore, it is necessary to suppress the formation of nitride, but this requires additional cost and processing time, so it is not economical. It is more desirable to reduce the impact. In order to grow the inclusions in this manner, it is essential to control the N to 0.001% to 0.004%. If the N content exceeds 0.004%, coarsening of inclusions is not achieved, and iron loss is increased, and more preferable N content is less than 0.003%.

[S: 0.0005-0.004 wt%]

S is an impurity element, which forms fine sulfides during the manufacturing process, inhibits grain growth, and infers iron loss. Therefore, the formation of sulfides should be suppressed, but this requires additional cost and processing time, and thus it is not economical. Therefore, as described below, the inclusions are coarsely grown by using an element having a high affinity for S as an impurity element to crystal grain growth. It is more desirable to reduce the impact. In order to grow the inclusions in this way, it is essential to control the S in the range 0.0005 to 0.004%. If the S content exceeds 0.004%, coarsening of inclusions is not achieved, and iron loss is increased, and more preferable S content is less than 0.003%.

In addition to the above impurity elements, impurities inevitably mixed such as C and Ti may be included in the steel.

C is self-aging and should be limited to 0.004% or less. More preferred C content is 0.003% or less.

Ti promotes the growth of the [111] aggregate structure, which is an undesirable crystal orientation in non-oriented electrical steel sheet, and therefore, it should be limited to 0.004% or less. More preferred Ti content is 0.002% or less.

In the present invention, the total amount of Al and Mn (Al + Mn) is limited to 3.5% or less, which means that when the total amount of Al and Mn exceeds 3.5%, the fraction of the [111] aggregate structure, which is disadvantageous to magnetism, increases and the magnetic heat is increased. Because you lose. In addition, when the total amount of Al and Mn is less than 1.5%, nitrides, sulfides, or two complex inclusions are not coarse to form magnetic heat, but in the present invention, Al is contained in an amount of 1.0% or more, and Mn is 0.5% or more. It is contained in the total amount of Al and Mn is 1.5% or more, so that magnetic deterioration is prevented.

In the present invention, the total amount of N and S (N + S) is limited to 0.002 ~ 0.006%, because the inclusions grow coarse in this range. When the total amount of N and S exceeds 0.006%, the fraction of fine inclusions increases and the magnetism deteriorates.

In the present invention, Al, Mn, N, and S are contained so as to satisfy all the conditions of 300≤ (Al + Mn) / (N + S) ≤1,400. Within this range, iron loss is improved by increasing coarse inclusions and increasing the density of distribution of large composite inclusions, but outside this range, coarsening of inclusions is not achieved, formation frequency of huge composite inclusions is lowered, and it is disadvantageous to magnetic structure. Is formed.

1 is a view showing a composite inclusion in the non-oriented electrical steel sheet of the present invention.

As in the present invention, within the range in which the content of Al, Mn, N, and S is optimally managed, inclusions grow several times or more compared to conventional materials, and the frequency of formation of coarse composite inclusions having an average size of 300 nm or more is increased. As a result, fine inclusions having an average size of about 50 nm are reduced, thereby improving magnetic properties. When the distribution density of such a large composite inclusion is 0.02 pieces / mm ² or more, the magnetism of the non-oriented electrical steel sheet is greatly improved.

The formation of such coarse composite inclusions is assumed to occur in the steelmaking stage. The exact mechanism of formation thereof is not yet clear, but Al-based oxides and nitrides are formed by deoxidation during the initial introduction of Al in the steelmaking stage. Al-based oxides / nitrides are grown in the component system satisfying the Al, Mn, N, S component ratios identified in the present invention during addition and bubbling of additional alloying elements such as Al and Mn, and at the same time, Mn-based sulfides are deposited thereon. It is believed that this is due to

FIG. 2 is a graph showing (N + S) as the horizontal axis and (Al + Mn) as the vertical axis, based on whether or not the distribution density of a large composite inclusion having an average size of 300 nm or more is 0.02 / mm ² or more. .

2, (Al + Mn) is 3.5% or less, (N + S) is 0.002 ~ 0.006, while (Al + Mn) / (N + S) is 300 ~ 1,400 of the present invention In the range (inside the thick line), the inclusions are coarse and the distribution density of the large composite inclusions having an average size of 300 nm or more is higher than 0.02 pieces / mm ² , whereas the magnetic properties are excellent, whereas the coarse inclusions are not formed when out of the scope of the present invention. It can be seen that the distribution density of the large composite inclusions with an average size of 300 nm or more is lower than 0.02 / mm ² , resulting in inferior texture due to inferior texture.

Coarse inclusions have been observed to have an average size of 300 nm or more mainly due to the compounding of nitrides and sulfides, but also includes several nitrides or several sulfides having an average size of 300 nm or more, and nitrides or sulfides alone It can be included also grown to 300nm or more. Here, the average size of the inclusions is a value obtained by measuring the longest length and the shortest length of the inclusions in the cross section of the steel sheet and averaging them.

In the present invention, Al / Si is preferably limited to 0.3 ~ 1.3. This is because when the ratio of Al to Si is 0.3 to 1.3, the grain growth is excellent and the hardness of the material is lowered, thereby improving productivity and punchability. If Al / Si is less than 0.3, the inclusions do not grow significantly, and the growth of grains deteriorates, causing magnetism to deteriorate. If Al / Si exceeds 1.3, the texture of the material deteriorates and the magnetic flux density deteriorates.

In the present invention, Al / Mn is preferably limited to 1 to 8. This is because when the ratio of Al to Mn is 1 to 8, the inclusion loss is excellent and the iron loss characteristics are excellent. On the contrary, when the Al ratio is out of this range, the growth of the inclusion is lowered and the fraction of the texture that is favorable for magnetism is reduced.

Next, the ratio limitation of the alloy component related to a specific resistance is demonstrated. Recently, as the demand for eco-friendly cars increases rapidly, a product that can be used for a motor capable of rotating at high speed is required. As the number of revolutions of the motor increases, the fraction of eddy current loss among the losses in the inner core increases rapidly. In order to reduce this eddy current loss, the specific resistance should be increased, and it is desirable to secure a specific resistance of 47 (Ωm) or more. In addition, despite the recent development of cold rolling technology, when the specific resistance (intrinsic resistance) exceeds 87 (Ωm), the alloying element content increases, resulting in poor workability and the production of ordinary cold rolling is impossible, so the specific resistance is 87 (Ωm). The following is appropriate.

The relationship between the component system and the resistivity was calculated using the following empirical formula.

ρ = 13.25 + 11.3 (Al + Si + Mn / 2) (ρ: resistivity)

According to this empirical formula, Al + Si + Mn / 2 should be managed at 3.0 ~ 6.5% to satisfy specific resistivity 47 ~ 87 (Ωm) level, and thus non-oriented electrical steel sheet having a cross-section Vickers hardness (Hv1) of 225 or less. Can be obtained.

Hereinafter, a method of manufacturing a non-oriented electrical steel sheet according to the present invention. In the method for manufacturing a non-oriented electrical steel sheet of the present invention, it is preferable to first add 0.3 to 0.5% of the total Al content in the steelmaking step, and then add residual alloy elements to sufficiently deoxidize the steel. After the alloying element is added, the molten steel is maintained at a temperature of 1,500 to 1,600 ° C. so that the inclusions in the steel are sufficiently grown, and then solidified in a continuous casting process to manufacture the slab. Subsequently, the slab is charged to a heating furnace and reheated to a temperature of 1,100 ° C or more and 1,250 ° C or less. When the slab is heated to a temperature exceeding 1,250 ℃, the precipitate that harms the magnetic can be re-dissolved and finely precipitated after hot rolling, so the slab is heated at a temperature below 1,250 ℃.

Once the slab is reheated, it is then hot rolled. It is preferable to perform hot finishing rolling at the time of hot rolling at the temperature of 800 degreeC or more.

Hot rolled hot rolled sheet is annealed at a temperature of 850 ~ 1,100 ℃. If the hot-rolled sheet annealing temperature is less than 850 ℃, the structure does not grow or grow fine, the magnetic flux density is less synergistic effect, if the annealing temperature exceeds 1,100 ℃ magnetic properties are rather deteriorated, rolling workability due to the deformation of the plate shape Since this may worsen, the hot-rolled sheet annealing temperature range is limited to 850 ~ 1,100 ℃. The more preferable annealing temperature of a hot rolled sheet is 950-1,100 degreeC. Hot-rolled sheet annealing is performed in order to increase the crystal orientation favorable to magnetic as needed, but it is also possible to omit hot-rolled sheet annealing.

After the hot rolled sheet is annealed or omitted, the hot rolled sheet is pickled, and then cold rolled at a reduction ratio of 70 to 95% to prepare a cold rolled sheet having a predetermined sheet thickness. In the present invention, since the content of Si, Mn, Al alloy elements affecting the cold rolling is appropriately controlled and excellent in cold rolling, it is possible to apply a high rolling rate, so that only one cold rolling can be used as a thin plate having a thickness of about 0.15 mm. Manufacturing is possible. When cold rolling is required, two cold rolling including intermediate annealing may be performed, or two annealing may be applied.

The cold-rolled cold-rolled sheet is subjected to final annealing. If the final annealing temperature is less than 750 ℃ recrystallization does not occur sufficiently, if the final annealing temperature exceeds 850 ℃ because the fraction of the cube texture advantageous to the magnetic is reduced, the final annealing is preferably performed at a temperature of 750 ~ 850 ℃.

The final annealed steel sheet is shipped to the customer after insulation coating treatment in the usual way. When the insulation coating is applied, it is possible to apply a conventional coating material, and any of chromium-based (Cr-type) or chromium-free (Cr-free type) can be used without limitation.

Subsequently, customer heat treatment (SRA) is performed. SRA heat treatment may be performed in an atmosphere of 100% nitrogen or in a mixed gas atmosphere of LNG and air. SRA heat treatment may be performed by maintaining the crack at least 60 minutes at a temperature of 700 ~ 850 ℃. When the SRA heat treatment temperature exceeds 850 ° C., the fraction of cube aggregates may be lowered as a result of the <110> aggregates being encroached by the <111> aggregates. When the SRA heat treatment is performed in an oxidizing atmosphere, when the SRA heat treatment temperature exceeds 850 ° C., excessive oxidation may occur and core deformation and steel sheet coating layer deformation may occur. On the contrary, when the SRA heat treatment temperature is less than 700 ° C. or the SRA heat treatment time is less than 60 minutes, it is difficult to secure a grain size favorable to the aggregate structure by the SRA process and it is difficult to increase the cube aggregate structure fraction. Therefore, SRA treatment is preferably carried out at 700 ~ 850 ℃ 60 minutes or more.

Hereinafter, the present invention will be described in detail with reference to Examples. Unless stated otherwise in the examples below, the ingredient content is expressed in weight percent.

Were vacuum-melted in a laboratory to produce ingots having the compositions shown in Table 1 below. Impurities C, S, N, and Ti of the material were all controlled to 0.002%, and 0.3 to 0.5% of Al was added to the molten steel to promote the formation of inclusions, and then the remaining Al, Si, and Mn were added to prepare a steel ingot. . Each material was heated to 1,150 캜 and hot-rolled at 850 캜 to produce a hot-rolled sheet having a thickness of 2.0 mm. The hot rolled hot rolled sheet was annealed at 1,050 ° C. for 4 minutes and then pickled. Thereafter, cold rolling was performed to make the plate thickness 0.35 mm, followed by final annealing at 850 ° C. for 38 seconds. The final annealed steel sheet was coated and then subjected to the SRA process. SRA treatment was performed by cracking at 100% nitrogen atmosphere at 750 ° C. for 2 hours.

The aggregates of the samples thus obtained were observed by EBSD (Electron back scattered diffraction) in cross section (TD direction), and the fractions of the aggregates were obtained by using the obtained Orientation Distribution Function (ODF). The reason for obtaining the ODF from the aggregate data is to quantitatively analyze the observed aggregate.

Inclusion size and inclusion distribution density, iron loss, magnetic flux density and grain size for each, and the cube (Cube) assembly tissue fractions are measured in Table 2 below.

Sample preparation for observation of inclusions was performed using a replica method, which is a common method for steel materials, and a transmission electron microscope was used as a device. At this time, the acceleration voltage was applied to 200kV.

Steel grade Al Si Mn C S N Ti A1 3.0 2.3 1.0 0.002 0.002 0.002 0.002 A2 2.5 1.7 1.0 0.002 0.002 0.002 0.002 A3 1.0 2.3 1.0 0.002 0.002 0.002 0.002 A4 1.5 2.3 0.8 0.002 0.002 0.002 0.002 A5 2.0 2.7 0.8 0.002 0.002 0.002 0.002 A6 1.0 2.7 0.8 0.002 0.002 0.002 0.002 A7 0.5 2.7 0.8 0.002 0.002 0.002 0.002 A8 3.5 3.0 0.8 0.002 0.002 0.002 0.002 A9 2.5 3.0 0.8 0.002 0.002 0.002 0.002 A10 1.5 3.0 1.0 0.002 0.002 0.002 0.002 A11 3.0 3.2 1.0 0.002 0.002 0.002 0.002 A12 1.5 3.2 1.0 0.002 0.002 0.002 0.002 A13 3.0 2.5 1.0 0.002 0.002 0.002 0.002 A14 2.5 2.5 1.0 0.002 0.002 0.002 0.002 A15 1.0 2.5 1.0 0.002 0.002 0.002 0.002

Steel grade Al /
Si Al /
Mn Al + Mn N + S (Al + Mn)
/ (N + S) Al + Si
+ Mn / 2 Inclusion
size
(Nm) Inclusion
Distribution density
(1 / mm ² ) Iron loss
(W15 / 50;
W / Kg) Magnetic flux density
(B50;
Tesla) decision
Lip diameter
(탆) Cube
Fraction
(%) Remarks A1 1.3 3.0 4.0 0.0040 1000 5.8 250 0.01 2.2 1.63 45 2.8 Comparative Example A2 1.5 2.5 3.5 0.0040 875 4.7 200 0.01 2.3 1.63 35 2.8 Comparative Example A3 0.4 1.0 2.0 0.0040 500 3.8 300 0.10 2.2 1.69 65 4.5 Honor A4 0.7 1.9 2.3 0.0040 575 4.2 400 0.20 2.1 1.68 70 4.1 Honor A5 0.7 2.5 2.8 0.0040 700 5.1 500 0.15 2.0 1.70 80 4.5 Honor A6 0.4 1.3 1.8 0.0040 450 4.1 450 0.09 2.1 1.69 75 3.5 Honor A7 0.2 0.6 1.3 0.0040 325 3.6 50 0.01 2.5 1.65 45 2.5 Comparative Example A8 1.2 4.4 4.3 0.0040 1075 6.9 75 0.01 2.2 1.63 40 2.8 Comparative Example A9 0.8 3.1 3.3 0.0040 825 5.9 400 0.25 2.0 1.69 75 4.0 Honor A10 0.5 1.5 2.5 0.0040 625 5.0 600 0.10 2.1 1.69 85 4.5 Honor A11 0.9 3.0 4.0 0.0040 1000 6.7 250 0.005 2.5 1.62 48 2.5 Comparative Example A12 0.5 1.5 2.5 0.0040 625 5.2 400 0.15 2.0 1.69 87 4.5 Honor A13 1.2 3.0 4.0 0.0040 1000 6.0 75 0.01 2.4 1.62 58 2.6 Comparative Example A14 1.0 2.5 3.5 0.0040 875 5.5 400 0.10 2.0 1.67 70 5.2 Honor A15 0.4 1.0 2.0 0.0040 500 4.0 350 0.15 2.0 1.71 75 5.0 Honor

Steel grades A3 to A6, A9, A10, A12, A14 and A15 belonging to the scope of the present invention have coarse inclusions of 300 nm or more in size after SRA treatment, and their distribution density is higher than 0.02 (1 / mm ² ). Accordingly, the grain growth is excellent, the grain size is larger than 60㎛, the fraction of the cube aggregate structure is also higher than 3% is confirmed to be excellent magnetic properties.

On the contrary, in steel grades A1, A8, A11, and A13, inclusions having a size of 300 nm or more in which (Al + Mn) is out of the scope of the present invention were not observed. Steel grade A2 has a low Si content and no inclusions having a size of 300 nm or more were observed. Steel grade A7 had a low Al content, and no inclusions were observed in which Al / Mn and (Al + Mn) had a size of 300 nm or more outside the scope of the present invention. Si content, Al content, (Al + Mn), Al / Mn is not within the scope of the present invention all have a grain size of less than 60㎛, the fraction of the cube aggregate structure is less than 3% low magnetic properties Inferior.

Vacuum dissolution in the lab produced a steel ingot as shown in Table 3 below. At this time, the content was controlled by varying the content of impurities N and S of the material, and 0.3 to 0.5% of Al was added to the molten steel to promote the formation of inclusions, and then the remaining Al, Si, and Mn were added to prepare the steel ingot. It was. Manufacturing of the steel sheet was carried out in the same manner as in Example 1 except that the SRA treatment was performed in an atmosphere of 7: 1 air and LNG mixed. The reason why SRA atmosphere is mixed with air and LNG 7: 1 atmosphere is that most customers have similar atmosphere when heat treatment.

Steel grade Al Si Mn C S N Ti B1 1.0 2.3 0.5 0.0030 0.0010 0.0010 0.0020 B2 1.0 2.3 0.5 0.0030 0.0030 0.0030 0.0020 B3 1.0 2.5 1.0 0.0030 0.0020 0.0030 0.0020 B4 1.2 2.5 1.2 0.0030 0.0015 0.0020 0.0020 B5 1.2 2.7 1.0 0.0030 0.0005 0.0005 0.0020 B6 1.2 2.7 1.0 0.0030 0.0020 0.0040 0.0020 B7 2.0 2.7 2.0 0.0030 0.0020 0.0020 0.0020 B8 2.0 3.2 1.5 0.0030 0.0010 0.0015 0.0020 B9 2.0 3.2 1.5 0.0030 0.0020 0.0020 0.0020 B10 2.0 3.2 1.0 0.0030 0.0030 0.0040 0.0020 B11 2.0 3.2 1.5 0.0030 0.0030 0.0030 0.0020 B12 1.5 3.5 1.5 0.0030 0.0020 0.0025 0.0020 B13 2.5 3.5 1.0 0.0030 0.0005 0.0005 0.0020

Steel grade Al /
Si Al /
Mn Al + Mn N + S (Al + Mn)
/ (N + S) Al + Si
+ Mn / 2 Inclusion
size
(Nm) Inclusion
Distribution density
(1 / mm ² ) Iron loss
(W15 / 50;
W / Kg) Magnetic flux density
(B50;
Tesla) decision
Lip diameter
(탆) Cube
Fraction
(%) Remarks B1 0.4 2.0 1.5 0.0020 750 3.6 350 0.15 2.0 1.69 83 3.3 Honor B2 0.4 2.0 1.5 0.0060 250 3.6 75 0.01 2.3 1.65 43 2.8 Comparative Example B3 0.4 1.0 2.0 0.0050 400 4.0 400 0.20 2.0 1.70 80 3.5 Honor B4 0.5 1.0 2.4 0.0035 686 4.3 450 0.08 2.1 1.69 75 3.8 Honor B5 0.4 1.2 2.2 0.0010 2200 4.4 50 0.01 2.4 1.65 43 2.5 Comparative Example B6 0.4 1.2 2.2 0.0060 367 4.4 350 0.20 2.1 1.69 75 3.8 Honor B7 0.7 1.0 4.0 0.0040 1000 5.7 250 0.01 2.2 1.64 35 2.6 Comparative Example B8 0.6 1.3 3.5 0.0025 1400 6.0 450 0.12 2.0 1.68 75 4.2 Honor B9 0.6 1.3 3.5 0.0040 875 6.0 550 0.09 2.0 1.68 80 4.1 Honor B10 0.6 2.0 3.0 0.0070 429 5.7 250 0.01 2.3 1.64 50 2.5 Comparative Example B11 0.6 1.3 3.5 0.0060 583 6.0 500 0.15 2.0 1.68 78 4.1 Honor B12 0.4 1.0 3.0 0.0045 667 5.8 600 0.20 2.1 1.68 85 4.6 Honor B13 0.7 2.5 3.5 0.0010 3500 6.5 50 0.01 2.1 1.63 35 2.8 Comparative Example

As can be seen from Table 4, steel grades B1, B3, B4, B6, B8, B9, B11, and B12 belonging to the scope of the present invention have coarse inclusions of 300 nm or more after SRA treatment, and their distribution density is 0.02 (1 / mm ² ). Accordingly, the grain growth is excellent, the grain size is larger than 60㎛, the fraction of the cube aggregate structure is also higher than 3% is confirmed to be excellent magnetic properties.

On the contrary, in steel grades B5, B10 and B13, inclusions having a size of 300 nm or more in which (N + S) is outside the scope of the present invention were not observed. For steel grade B7, inclusions with (Al + Mn) outside the scope of the present invention having a size of 300 nm or more were not observed. In steel grades B2, B5, and B13, inclusions having a size of 300 nm or more in which (Al + Mn) / (N + S) were out of the scope of the present invention were not observed. Comparative examples in which (N + S), (Al + Mn) and (Al + Mn) / (N + S) did not fall within the scope of the present invention had a grain size smaller than 60 μm, and the fraction of cube-assembly was 3 Lower than%, the magnetic properties were inferior.

Claims (10)

By weight%, Al: 1.0-3.0%, Si: 2.3-3.5%, Mn: 0.5-2.0%, N: 0.001-0.004%, S: 0.0005-0.004%, C: 0.004% or less (excluding 0%) , Ti: 0.004% or less (except 0%), balance Fe and other inevitable impurities, Al, Si, Mn, N, S is (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤0.006, 300≤ (Al + Mn) / (N + S) ≤1,400, 3.0≤ (Al + Si + Mn / 2) ≤6.5, 0.3≤Al / Si≤1.3, 1≤Al / Mn≤8 It is contained so as to satisfy all of the conditions, the grain size is 60㎛ or more, the non-oriented electrical steel sheet excellent in magnetism after stress removal annealing, the cube aggregate structure fraction is more than 3%. delete delete The method according to claim 1,
The non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing, wherein the inclusions of nitrides and sulfides alone or in combination thereof are formed in the steel sheet, and the distribution density of inclusions having an average size of 300 nm or more is 0.02 pieces / mm 2 or more. By weight%, Al: 1.0-3.0%, Si: 2.3-3.5%, Mn: 0.5-2.0%, N: 0.001-0.004%, S: 0.0005-0.004%, C: 0.004% or less (excluding 0%) , Ti: 0.004% or less (except 0%), the balance Fe and other inevitable impurities, Al, Si ,, Mn, N, S is (Al + Mn) ≤ 3.5, 0.002 ≤ (N + S) ≤0.006, 300≤ (Al + Mn) / (N + S) ≤1,400, 3.0≤ (Al + Si + Mn / 2) ≤6.5, 0.3≤Al / Si≤1.3, 1≤Al / Mn≤ The slabs contained to satisfy all of the conditions of 8 were heated to a temperature of 1,100 to 1,250 ° C, followed by hot rolling, followed by annealing or omission of hot rolled plates, followed by cold rolling at a reduction ratio of 70 to 95%, followed by cold rolling. After the final annealing of the cold-rolled sheet in the temperature range of 750 ~ 850 ℃, cracks maintained at 700 ~ 850 ℃ temperature for 60 minutes or more stress relief annealing method for producing an excellent non-oriented electrical steel sheet after stress removal annealing. The method according to claim 5,
The method of manufacturing a non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing, characterized in that the control the grain size of the stress relief annealing heat-treated steel sheet to 60㎛ or more, and the cube aggregate structure fraction to 3% or more. delete delete The method according to claim 5 or 6,
A method for producing a non-oriented electrical steel sheet having excellent magnetic properties after stress relief annealing, characterized by controlling the distribution density of inclusions having an average size of 300 nm or more to 0.02 pieces / mm 2 or more. The method according to claim 5 or 6,
After deoxidation is performed by adding 0.3 ~ 0.5% of Al, the remaining alloy element is added, and after the addition of the remaining alloy element, the slab is manufactured by maintaining the temperature at 1,500 ~ 1,600 ° C. Method for producing this excellent non-oriented electrical steel sheet.

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