KR20190077890A - Grain oriented electrical steel sheet method for manufacturing the same - Google Patents

Abstract

According to an embodiment of the present invention, a grain-oriented electrical steel sheet comprises: 0.005 wt% or less of C; 0.015-0.040 wt% of AI; 0.04-0.15 wt% of Mn; 0.001-0.02 wt% of N; 0.01 wt% or less of S; and the remainder of Fe and other unavoidable impurities. The grain-oriented electrical steel sheet further comprises secondary recrystallized texture which has an average α angle of 3 ° or less. The α angle means an angle of the direction [001] of the texture with a rolling direction axis when viewed from a rolled surface.

Description

TECHNICAL FIELD [0001] The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same. BACKGROUND ART [0002]

A directional electric steel sheet and a method of manufacturing a directional electric steel sheet. More particularly, the present invention relates to a directional electric steel sheet having excellent magnetic properties and a method for producing a directional electric steel sheet obtained by specifically controlling the rolling conditions during hot rolling.

Directional electrical steel sheets are used as core materials for static devices such as transformers, motors, generators and other electronic devices. The final product of the grain-oriented electrical steel sheet has an aggregate structure in which the orientation of the grain is oriented in the (110) [001] direction (or the {110} < 001 > direction) and has extremely excellent magnetic properties in the rolling direction. Therefore, it can be used as an iron core material for transformers, motors, generators, and other electronic devices. In order to reduce energy loss, iron loss is required to be low, and magnetic flux density is required for miniaturization of power generation equipment.

The grain-oriented electrical steel sheet inhibits the growth of the primary recrystallized grains and selectively grows the crystal grains of the (110) [001] orientation (hereinafter also referred to as Goss orientation) in the final annealing process among the crystal grains whose growth is suppressed, Which is an electrical steel sheet. The second recrystallization is referred to as secondary recrystallization. In order to perform secondary recrystallization, fine inhibitors such as MnS and AlN are uniformly dispersed in the steel sheet before the final high-temperature annealing, The second recrystallized grains can be grown while having a precise goss orientation while suppressing the growth of the recrystallized grains, and it is possible to obtain an effect of increasing magnetic flux density and iron loss, which are excellent magnetic properties.

In order to effectively control the secondary recrystallization to have a precise Goss orientation, it is very important to make good directional Goss orientations that become nuclei grown by secondary recrystallization in the primary recrystallized structure.

Therefore, Goss Nuclear Regulation should consider two major aspects. It is necessary to make a large amount of directional Goss which is the nucleus of the actual secondary recrystallization and to reduce the Goss which is somewhat inferior to the directivity which can not be achieved by the secondary recrystallization finally.

Conditions for making the Goss nuclei capable of causing such secondary recrystallization are known, for example, rapid temperature elevation technique, hot rolling reduction technique, and appropriate cold rolling rate.

Directional electrical steel sheet is made by Goss grain which can cause secondary recrystallization through hot rolling - hot - rolled sheet annealing - cold rolling - primary recrystallization annealing process. Only a well aligned (110) [001] orientation in the rolling direction must be grown by secondary recrystallization and it is necessary to carefully adjust the process parameters prior to cold rolling in order to effectively provide such driving force. It should be noted that such a Goss orientation is formed from the hot rolling, but Goss starts to be formed intensively on the surface portion of the hot-rolled sheet where shear deformation is concentrated. After a while, a very small part of them survive and exist in the primary recrystallization structure, which can be a nucleus causing secondary recrystallization.

In order to make precise Goss secondary recrystallization nuclei in the grain-oriented electrical steel sheet, it is important to maximize the goss texture formed on the sub-surface of the hot-rolled steel sheet.

A method of producing a directional electrical steel sheet is known in the range of rough rolling temperature and finishing rolling temperature in which hot rolling is carried out under a low temperature and high pressure depending on Si, C, and Ni components in a high temperature heating method in which a slab reheating temperature is high. However, this method has a limitation in that it can not be applied because of the phase transformation behavior and the phase fraction in the low temperature heating method.

There is also known a low temperature heating method for producing a grain-oriented electrical steel sheet in which decarburization annealing is not performed by controlling the reduction ratio of the final two passes during hot rolling to an appropriate range. However, this has limitations that can be applied only to extremely low carbon components in order to omit decarburization annealing.

To provide a directional electrical steel sheet and a method of manufacturing a directional electrical steel sheet. Specifically, it is intended to provide a method of manufacturing a grain-oriented electrical steel sheet and a grain-oriented electrical steel sheet in which the rolling conditions at the time of hot rolling are specifically controlled to improve the magnetic properties.

The grain-oriented electrical steel sheet according to an embodiment of the present invention may contain 2.5 to 4.0% of Si, 0.005% or less (excluding 0%) of C, 0.015 to 0.040% of Al, 0.04 to 0.15% of Mn, N: not more than 0.005% (excluding 0%) and S: not more than 0.01% (excluding 0%), the remainder including Fe and other unavoidable impurities, The average α angle of the tea recrystallized texture is less than 3 °.

At this time,? Angle means an angle formed by the [001] direction of the texture with the rolling axis (RD axis) when viewed from the rolling surface (RD surface).

The grain-oriented electrical steel sheet may have an area fraction of the secondary recrystallized texture having an α angle of 0 ° to 3 ° in the entire secondary recrystallized texture of 50% to 80%.

The average alpha angle and the average beta angle of the secondary recrystallized texture can satisfy the following formula 1. &lt; EMI ID = 1.0 &gt;

[Formula 1]

0.8? [Average alpha angle] / [average beta angle]? 1.5

(In this case, the β angle refers to the angle formed by the [001] direction of the texture with the rolling direction axis when viewed from the rolling vertical plane (TD plane).)

The grain-oriented electrical steel sheet may further include at least one of Sn: 0.03 to 0.12 wt%, Sb: 0.01 to 0.05 wt%, Cr: 0.02 to 0.15 wt%, and P: 0.01 to 0.05 wt%.

The grain-oriented electrical steel sheet may further include at least one of 0.01 to 0.05% by weight of Mo and 0.01 to 0.2% by weight of Cu.

A method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.5 to 4.0% of Si, 0.03 to 0.09% of C, 0.015 to 0.040% of Al, 0.04 to 0.15% of Mn, 0.006 % (Excluding 0%) and S: not more than 0.01% (excluding 0%), the remainder comprising Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed, wherein the step of producing the hot rolled sheet includes rough rolling and finish rolling, and the rough rolling step has a cumulative rolling reduction of from 0 to 40% or more, and 40% or more in the rolling step, and the rolling step includes at least 40% or more of the lowering pass at least twice.

The slab may further include at least one of Sn: 0.03 to 0.12 wt%, Sb: 0.01 to 0.05 wt%, Cr: 0.02 to 0.15 wt%, and P: 0.01 to 0.05 wt%.

The slab may further include at least one of Mo: 0.01 to 0.05% by weight, and Cu: 0.01 to 0.2% by weight.

The rough rolling step may be performed at 1000 to 1150 占 폚.

The descending path can be performed with the last pass of the rough rolling step.

In the rough rolling step, it is possible to include 0 to 3 passes before the depressurizing pass.

The cumulative rolling reduction of the finish rolling step may be from 64 to 80%.

The finishing rolling step can be carried out in two pass under pressure.

The finishing rolling step can be carried out at 950 DEG C or higher.

After the step of producing the hot-rolled sheet, the hot-rolled sheet may have a volume fraction of the aggregate structure having an orientation within 15 DEG from (110) [001] of 4% or more.

After the secondary recrystallization annealing step, the directional electrical steel sheet produced may have an average α angle of the secondary recrystallization texture of 3 ° or less.

The directional electrical steel sheet according to an embodiment of the present invention can precisely control the rolling conditions in the manufacturing process, especially the hot rolling process, so that the gusset texture in the final directional electrical steel sheet can be accurately arranged.

The grain oriented electrical steel sheet according to one embodiment of the present invention can further improve the magnetic property by accurately arranging the crystal orientation of the texture.

1 is a schematic perspective view of a directional electric steel sheet for explaining the concept of alpha (alpha), beta (beta) and delta (delta) angles.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "on" or "on" another portion, it may be directly on or over another portion, or may involve another portion therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Unless otherwise stated,% means% by weight, and 1 ppm is 0.0001% by weight.

In an embodiment of the present invention, the term further includes an additional element, which means that an additional amount of the additional element is substituted for the remaining iron (Fe).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The directional electrical steel sheet according to an embodiment of the present invention includes a secondary recrystallized texture and an average alpha angle of the secondary recrystallized texture is less than 3 DEG.

In this case,? Angle means an angle formed by the [001] direction of the texture with the rolling direction (RD direction) when viewed from the rolled surface (ND surface) of the steel sheet. Mean α angle refers to the arithmetic mean α angle with respect to the number of texture.

The concept of alpha angle is summarized in Fig. The directions RD, TD, and ND in FIG. 1 indicate the rolling direction, the rolling direction, and the rolling direction normal direction, respectively. In addition to the angle alpha, degrees of departure from the Goss orientation also exist, and angle beta and angle [theta] are also present. An embodiment of the present invention may be an α angle of 2 to 3 and a β angle of 1.5 to 2.5.

By controlling the relationship between the average alpha angle and the average beta angle in one embodiment of the present invention, the magnetic properties of the grain-oriented electrical steel sheet can be further improved. Specifically, Equation 1 can be satisfied.

[Formula 1]

0.8? [Average alpha angle] / [average beta angle]? 1.5

(In this case, the β angle refers to the angle formed by the [001] direction of the texture with the rolling direction axis when viewed from the rolling vertical plane (TD plane).)

The grain oriented electrical steel sheet according to one embodiment of the present invention can further improve the magnetic property by accurately arranging the crystal orientation of the texture.

More specifically, in the entire secondary recrystallized texture, the area fraction of the secondary recrystallized texture having an alpha angle of 0 to 3 can be 50 to 80%. By satisfying the above-described range, the crystal orientation of the texture can be accurately arranged and the magnetic property can be further improved. More specifically 55 to 75%.

The grain-oriented electrical steel sheet contains 2.5 to 4.0% of Si, 0.005% or less of C, 0.015 to 0.040% of Al, 0.04 to 0.15% of Mn, 0.005% or less of N and 0.01% or less of S, The remainder includes Fe and other unavoidable impurities.

The reasons for limiting the components of the grain-oriented electrical steel sheet will be described below.

Si: 2.5 to 4.0 wt%

Silicon (Si) plays a role in lowering the core loss, that is, the iron loss, by increasing the resistivity of the oriented electrical steel sheet material. When the Si content is less than 2.5% by weight, the resistivity is decreased and the iron loss is deteriorated. When the Si content is more than 4.0% by weight, the brittleness of the steel is increased and the toughness is decreased to increase the plate fracture occurrence rate during the rolling process, A load is applied to the cold rolling operation, the temperature falls below the plate temperature required for pass aging during cold rolling, and the formation of the secondary recrystallization becomes unstable. Therefore, Si may contain 2.5 to 4.0 wt%. More specifically from 3.0 to 3.5% by weight.

C: 0.005 wt% or less

Carbon (C) is an element that induces the formation of austenite phase, and ferrite-austenite phase transformation is activated during the hot rolling process as the C content increases. Also, as the C content increases, the elongated hot rolled steel strip structure formed during the hot rolling process increases, thereby suppressing the ferrite grain growth during the annealing process of the hot rolled steel sheet. In addition, as the C content increases, the texture of the hot rolled steel strip, which is higher in strength than that of the ferrite steel, and the initial grain size of the annealed hot rolled steel sheet, . It is considered that the effect of pass aging during cold rolling becomes large due to the residual C existing in the steel sheet after annealing the hot-rolled sheet, thereby increasing the goss fraction in the primary recrystallized grains. Therefore, the larger the C content, the longer the decarburization annealing time in decarburization annealing and deteriorates the productivity, and if the decarburization at the initial stage of heating is insufficient, the primary recrystallization grain becomes uneven and eventually makes the secondary recrystallization unstable. In addition, the magnetic properties can be defeated by the magnetic aging phenomenon. Therefore, the C content in the slab is limited to the range of 0.03 to 0.09 wt%. More specifically, the C content may be 0.04 to 0.06% by weight.

As described above, during the decarburization annealing process during the manufacturing process of the grain-oriented electrical steel sheet, C is partially removed, and the C content in the finally produced grain-oriented electrical steel sheet can be 0.005 wt% or less.

Al: 0.015 to 0.04 wt%

Aluminum (Al) forms a nitride of (Al, Si, Mn) N and AlN type, and plays a role of inhibiting strong grain growth. When the content is less than 0.015% by weight, the number and the volume fraction of the precipitates to be formed are low, and the effect of inhibiting grain growth may not be sufficient. If the Al content is too high, the precipitates grow to a great extent and the effect of inhibiting the growth of grain growth is reduced. Therefore, Al can be added in an amount of 0.015 to 0.04% by weight. More specifically, Al may be added in an amount of 0.02 to 0.035% by weight.

Mn: 0.04 to 0.15 wt%

Manganese (Mn) has an effect of reducing the iron loss by increasing the resistivity as Si. It is also an important element for causing secondary recrystallization by suppressing the growth of primary recrystallized grains by forming precipitates of N by reacting with nitrogen together with Si (Al, Si, Mn). However, when added in an amount exceeding 0.15% by weight, a large amount of (Fe, Mn) and Mn oxide are formed on the surface of the steel sheet in addition to Fe ₂ SiO ₄ to prevent formation of a base coat formed during secondary recrystallization annealing, In the hot-rolled sheet annealing process, unevenness of the phase transformation between the ferrite and the austenite is caused, so that the size of the primary recrystallized grains is uneven and, as a result, the secondary recrystallization becomes unstable. Therefore, Mn is 0.04 to 0.15% by weight. And more specifically 0.07 to 0.13% by weight.

N: 0.005 wt% or less

Nitrogen (N) is an element that reacts with Al or the like to refine the grain. When these elements are appropriately distributed, as described above, it is possible to appropriately fine-structure the structure after cold rolling to ensure proper primary recrystallization grain size. However, if the content is excessive, the primary recrystallization grain becomes excessively fine, As a result, due to the fine crystal grains, the driving force causing crystal grain growth during the secondary recrystallization becomes large, so that it can grow to the crystal grains of an undesirable orientation. If N is contained in an amount exceeding 0.005% by weight, the secondary recrystallization starting temperature is increased to deteriorate the magnetic properties. Therefore, N may be contained in an amount of 0.005% by weight or less. More specifically, N may be contained in an amount of 0.0005 to 0.005% by weight.

When the treatment for increasing the nitrogen amount is performed between the cold rolling step and the secondary recrystallization annealing step, it is sufficient that the content of N in the slab is 0.006% by weight or less.

S: not more than 0.01% by weight

It is preferable that sulfur (S) is not contained as an element having a high solid solution temperature during hot rolling and segregation, but it is a kind of impurities contained in steelmaking. Also, since S forms MnS and affects the primary recrystallized grain size, the content of S is preferably limited to 0.01 wt% or less. More specifically, the content of S may be 0.008 wt% or less.

The grain-oriented electrical steel sheet may further include at least one of Sn: 0.03 to 0.12 wt%, Sb: 0.01 to 0.05 wt%, Cr: 0.02 to 0.15 wt%, and P: 0.01 to 0.05 wt%.

Sn: 0.03 to 0.12 wt%

Tin (Sn) acts as a crystal growth inhibitor because it is an element that interferes with the movement of grain boundaries as a grain boundary segregation element. In addition, by increasing the grain fraction of the Goss orientation in the primary recrystallized texture, the size of the secondary recrystallized microstructure is reduced because the number of the Goss bearing nuclei growing in the secondary recrystallized texture structure is decreased. As the grain size becomes smaller, The iron loss of the final product is reduced. On the other hand, Sn plays an important role in suppressing grain growth through grain segregation in grain boundaries. This not only improves the suppressing effect of suppressing the crystal growth driving force of the microcrystallized first recrystallized microstructure, (Al, Si, Mn) during the annealing process, particles causing N grain growth inhibiting effect such as N and AlN are coarsened, thereby preventing the grain growth growth inhibiting ability from being reduced. On the other hand, when the content of Sn is less than 0.03 wt%, there is no effect of addition. When the content of Sn exceeds 0.12 wt%, the grain growth inhibiting ability is excessively increased and the crystal grain growth driving force is relatively increased. It is necessary to perform the decarburization annealing at a low temperature, and as a result, it is impossible to control with an appropriate oxide layer, so that a good surface can not be secured. From the viewpoint of mechanical properties, brittleness is increased due to excessive segregation of grain boundary segregation elements, which may cause sheet breakage during manufacturing. Therefore, the content of Sn may be 0.03 to 0.12% by weight. More specifically, the content of Sn may be 0.05 to 0.08% by weight.

Sb: 0.01 to 0.05 wt%

The antimony (Sb) has the effect of increasing the grain nuclei in the goss orientation generated during the cold rolling process and improving the fraction of the grains having the goss orientation in the primary recrystallized texture. In addition, the secondary recrystallization starting temperature of the grains having a goss aggregate structure is increased when segregating in the primary recrystallization grain boundaries and performing secondary recrystallization and high temperature annealing, so that the secondary recrystallization microstructure excellent in the degree of integration can be obtained and the magnetic flux density is increased. If the content is more than 0.05% by weight, the size of the primary recrystallized grains becomes too small to lower the secondary recrystallization initiation temperature to deteriorate the magnetic properties or inhibit the grain growth The secondary recrystallization may not be formed. Therefore, the content of Sb is in the range of 0.01 to 0.05% by weight.

Cr: 0.02 to 0.15 wt%

Chromium (Cr) is an element promoting oxidation formation, and if it is added in the range of 0.02 to 0.15 weight%, formation of a dense oxide layer in the surface layer is suppressed and a fine oxide layer is formed in the depth direction. With addition of Sb and Sn, addition of a Cr content in an appropriate range makes it easier to form a primary recrystallization with excellent uniformity. By adding Cr, the decarburization and sedimentation due to the upward Sb and Sn contents can be delayed to overcome the problem of nonuniformity of the primary recrystallized grains, and a primary recrystallized grain having excellent uniformity can be formed. Ultimately, it is an element that has the effect of improving magnetism. When the Cr content is added to the above range in accordance with the contents of Sb and Sn, the internal oxide layer is formed deeper and the rate of decay and decarburization is increased, which is effective in controlling the size and uniformity of the primary recrystallization. When the Cr content is lower than the lower limit, the effect is weak. When the Cr content exceeds the upper limit, the oxide layer is excessively formed and the effect thereof may be decreased.

P: 0.01 to 0.05 wt%

Phosphorus (P) is an element that exhibits similar effects to Sn and Sb. It plays an auxiliary role in inhibiting grain boundary migration and at the same time suppressing crystal grain growth by segregating in grain boundaries. In the microstructure, {110} <001> There is an effect of improving the organization. If the content of P is less than 0.01% by weight, the effect of addition is not exhibited. If the content of P is more than 0.05% by weight, the brittleness is increased and the rolling property is greatly deteriorated.

The grain-oriented electrical steel sheet may further include at least one of 0.01 to 0.05% by weight of Mo and 0.01 to 0.2% by weight of Cu.

Mo: 0.01 to 0.05 wt%

Molybdenum (Mo) plays an important role in suppressing grain growth by segregating in grain boundaries like Sn and plays a role to control the secondary recrystallization to occur at high temperature. Thereby increasing the magnetic flux density. Mo is a very effective inhibitor of grain growth inhibition because its atomic size is relatively large and its melting point is very high, so its diffusion rate in iron is low and it can maintain its segregation effect well to high temperature.

When the content of Mo is less than 0.01% by weight, the effect is insignificant, and the effect of improving the degree of integration of the goss texture is low, and since the effect of compensating the grain growth inhibition by grains existing in the matrix is small, The improvement effect is extremely small. On the other hand, when the content exceeds 0.05% by weight, the crystal grain growth inhibiting ability is excessively increased, and the grain size of the primary recrystallized microstructure is decreased in order to increase the grain growth driving force relatively. Therefore, the decarburization annealing must be performed at a low temperature , Which can not be controlled by an appropriate oxide layer, so that a satisfactory surface can not be obtained. Therefore, the Mo content is preferably 0.01 to 0.05% by weight.

Cu: 0.01 to 0.2 wt%

Copper (Cu) binds with S and precipitates into CuS. It mainly forms (Mn, Cu) S form by being mixed with MnS, and plays a role of inhibiting grain growth. In addition, as in the case of Mo, Cu causes a large amount of Goss grains having a precise orientation to be formed in the structure of the hot-rolled surface portion, thereby reducing grain size after secondary recrystallization and reducing eddy current loss, The magnetic flux density is also increased because the Goss particles of the magnetic layer grows much.

When the content is less than 0.01% by weight, the effect is not sufficient. When the content exceeds 0.2% by weight, precipitates grow to a great extent and the effect of suppressing grain growth is deteriorated.

Impurity element

In addition to the above elements, inevitably incorporated impurities such as Ni, Zr, and V may be included. Ni reacts with impurity elements to form fine sulfides, carbides, and nitrides, which have a detrimental effect on the magnetic properties. Therefore, these contents are limited to 0.05 wt% or less, respectively. Zr, V, and the like are also strong carbonitride-forming elements, so they are preferably not added as much as possible and are each contained at 0.01 wt% or less.

In one embodiment of the present invention, the magnetization can be further improved by accurately arranging the crystal orientation of the texture in the secondary structure of the secondary recrystallization texture with an average alpha angle of 3 DEG or less. Specifically, iron loss can be less than __W / kg at 1.7 Tesla and 50 Hz of directional electrical steel sheet. The magnetic flux density (B8) induced under the magnetic field of 800 A / m of the directional electric steel sheet may be 1.92 T or more. More specifically 1.93 to 1.95T.

A method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes heating a slab; Hot rolling the slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.

Hereinafter, each step will be described in detail.

First, the slab is heated.

Since each composition of the slab is described in detail in the above-described directional electrical steel sheet, a duplicate description will be omitted.

The heating of the slab is preferably carried out at a low temperature of 1,250 ° C or lower, more preferably 1,150 ° C or lower, to partially refine the precipitate. As the heating temperature of the slab becomes higher, the heating furnace can be repaired by melting the surface of the slab and the lifetime of the heating furnace can be shortened. In addition, if the slab is heated to a temperature of 1,250 ° C. or lower, more preferably 1,150 ° C. or lower, the columnar structure of the slab is prevented from being grown to a great extent, thereby preventing cracks from being generated in the width direction of the plate in the subsequent hot rolling process Thereby improving the error rate. When the temperature is less than 1000 占 폚, the hot rolling temperature is low and the deformation resistance of the steel sheet is increased, so that the rolling load is increased. Therefore, the heating temperature of the slab may be 1000 ° C to 1250 ° C.

Next, the slab is hot-rolled to produce a hot-rolled sheet.

In one embodiment of the present invention, precise control of the rolling conditions in the step of hot-rolling the hot-rolled steel sheet enables precise arrangement of the gusset structure in the final directionally oriented steel sheet. The magnetic properties of the oriented electrical steel sheet are ultimately improved.

Specifically, the step of manufacturing the hot rolled sheet includes rough rolling and finish rolling.

First, the rough rolling step includes a lowering step with a cumulative rolling reduction of 0 to 40% and a rolling reduction of 40% or more. At this time, the reduction rate is calculated as ([thickness of steel plate before passing] - [thickness of steel plate after passing]) / [thickness of steel plate before passing]. Cumulative rolling reduction means cumulative rolling reduction based on the thickness immediately before the rolling step. For example, the cumulative rolling reduction rate in the rough rolling step is calculated as ([thickness of steel sheet at the stage of rough rolling] - [thickness of steel sheet after rough rolling]) / [thickness of steel sheet at the stage of rough rolling].

When the cumulative reduction ratio is over 40%, the rough rolling structure may be too fine to reduce the goss formation effect due to the rolling. Therefore, after the cumulative reduction ratio of 0 to 40%, the lowering pressure includes the lowering pass. The number of passes can be taken from 0 to 3 times before the coercion-lowering pass. As the number of passes before coercion increases, the effect of goth formation can be reduced.

The lowering pass means a pass having a reduction ratio of 40% or more. When only a general pass having a reduction ratio of less than 40% is performed, the shear deformation is insufficient and the goss formation effect becomes insufficient. The lowering pass can be performed in the last pass in the rough rolling step. Also, the lowering pass can be performed once in the rough rolling step.

This rough rolling step may be performed at 1000 to 1150 占 폚. When the temperature is too high, the grain is excessively coarse, the unevenness becomes large and the improvement effect is reduced by half. When the temperature is too low, the finish rolling temperature becomes low and the improvement effect is reduced to heat the workability. As described above. More specifically, the step of rough rolling may be performed at 1000 to 1150 占 폚.

Next, the finishing rolling step includes two or more passes under a pressure drop of 40% or more. When the under-pressure pass is included in less than one pass, the average α angle may increase due to insufficient under-pressure effect. The finishing rolling step can be carried out in two pass under pressure.

The cumulative rolling reduction of the finish rolling step may be from 64 to 80%. If the cumulative reduction rate is too low, then the rolling load in cold rolling will be excessively increased and the effect of forming goss under low pressure will be reduced by half, which is not preferable. If the cumulative reduction ratio is too high, it is difficult to control the thickness and shape of the hot rolled steel and it becomes difficult to control the Goss orientation. Specifically, the cumulative rolling reduction of the finishing rolling step may be 64 to 75%.

This finish rolling step can be carried out at 950 DEG C or higher. When the finish rolling temperature is 950 DEG C or less, the temperature in the finishing rolling step is controlled as described above for the reason that the goss forming effect is reduced to half. More specifically, the finishing rolling step may be carried out at 950 to 1100 占 폚.

A hot rolled sheet having a thickness of 2.0 to 3.5 mm can be produced by hot rolling. The hot rolled sheet thus produced can exhibit the effect of improving the goss fraction by the characteristics of the texture. By controlling the texture characteristics of the hot-rolled steel sheet as described above, it is possible to precisely control the average α angle of the final directionally oriented steel sheet, and ultimately improve the magnetic properties of the grain-oriented steel sheet. Specifically, in the hot rolled plate, the volume fraction of the texture having the orientation within 15 DEG from (110) [001] may be 4% or more. More specifically, the hot-rolled sheet may have a volume fraction of an aggregate structure having an orientation within 15 DEG from (110) [001] of 5% or more.

The hot-rolled hot-rolled sheet can be subjected to cold-rolling without performing annealing of the hot-rolled sheet or annealing of the hot-rolled sheet if necessary. In the case of performing hot-rolled sheet annealing, the hot-rolled steel sheet can be heated to a temperature of 900 캜 or more, cooled and then cracked to make the hot-rolled steel sheet uniform.

Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet.

Cold rolling may be performed through one time of cold rolling and may be made through rolling to a final thickness of 0.15 to 0.35 mm.

Next, the cold-rolled cold-rolled sheet is subjected to primary recrystallization annealing. Primary recrystallization occurs in which the core of the goss grain is generated in the primary recrystallization annealing step. Decarburization and nitriding of the steel sheet can be performed during the primary recrystallization annealing process. For decarburization and nitriding, primary recrystallization annealing can be performed in a mixed gas atmosphere of steam, hydrogen, and ammonia.

Nitrogen ions are introduced into the steel sheet by using ammonia gas for nitriding to form nitrides such as (Al, Si, Mn) N and AlN which are precipitates, nitriding after decarburization, nitriding at the same time as decarburization There is no problem in exerting the effect of the present invention in either of the nitriding treatment simultaneously or the decarburization treatment in which the nitriding treatment is performed first.

The primary recrystallization annealing can be carried out in a temperature range of 800 to 900 占 폚.

Next, the cold-rolled sheet having undergone the primary recrystallization annealing is subjected to secondary recrystallization annealing. At this time, after the annealing separator is applied to the cold-rolled sheet having undergone the primary recrystallization annealing, secondary recrystallization annealing can be performed. At this time, the annealing separator is not particularly limited, and an annealing separator containing MgO as a main component may be used.

The purpose of the secondary recrystallization annealing is mainly to remove the impurities that damage the magnetic properties by formation of {110} < 001 > texture by secondary recrystallization, formation of vitreous film by reaction of MgO with oxide layer formed at decarburization . As a method of secondary recrystallization annealing, a secondary recrystallization is well developed by maintaining the nitride as a grain growth inhibitor by keeping it with a mixed gas of nitrogen and hydrogen at a temperature rising period before secondary recrystallization, and after completion of the secondary recrystallization, % Hydrogen atmosphere for a long time to remove impurities.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example

The balance of Fe and other inevitably contained impurities was added in an amount of 3.23 wt% of Si, 0.055 wt% of C, 0.0045 wt% of N, 0.028 wt% of Al, 0.1 wt% of Mn and 0.005 wt% of S, Lt; / RTI &gt; Subsequently, the slab was heated at a temperature of 1180 ° C for 210 minutes, and hot-rolled under the hot rolling conditions shown in Table 1 to prepare a hot-rolled steel sheet having a thickness of 2.3 mm. Under the rough rolling conditions, the number of passes before under pressure was 0 to 3.

The hot-rolled sheet was heated to 1080 占 폚, held at 920 占 폚 for 90 seconds, cooled to 760 占 폚, quenched in water, pickled, and then cold-rolled once to a thickness of 0.23 mm.

The cold-rolled cold-rolled sheet was maintained at a temperature of about 860 ° C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to perform primary recrystallization annealing including simultaneous decarburization and nitridation so that the carbon content was 50 ppm or less and the nitrogen content was 200 ppm Respectively.

The steel sheet was coated with MgO as an annealing separator and subjected to secondary recrystallization annealing in a coiled manner. The secondary recrystallization annealing was carried out in a mixed atmosphere of 25% nitrogen + 75% hydrogen until 1200 ° C. After reaching 1200 ° C, it was maintained in a 100% hydrogen atmosphere for 10 hours and then cooled. The magnetic properties measured for each condition and the orientation of the secondary recrystallized grains are summarized in Table 2 below.

The iron loss was measured at 1.7 Tesla and 50 Hz using a single sheet method and the magnetic flux density (Tesla) induced under a magnetic field of 800 A / m was measured. Each iron loss value represents the average by condition.

In addition, the structural characteristics of the hot rolled steel sheet after the rolling were measured by measuring the RD cross section using the EBSD equipment and calculating the gross (110) [001]) texture fraction, and the results are shown in Table 1 below.

Rough rolling condition Finish rolling condition Goss fraction of hot rolled sheet RD surface
(%) Coercion rate
(%) Commencement under pressure
Previous cumulative rolling reduction
(%) practice
Temperature
(° C) 1 pass
Reduction rate
(%) 2 passes
Reduction rate
(%) Finish rolling
Cumulative reduction rate
(%) Temperature
(° C) Inventory 1 43 16 1050 50 50 75 1000 6 Inventory 2 40 35 1000 48 50 74 1050 5.2 Inventory 3 42 13 1100 40 40 64 1000 5.4 Invention 4 42 34 1040 40 40 64 1050 5.8 Invention Article 5 40 0 1120 40 40 64 1000 5 Comparison 1 42 45 980 40 40 64 1050 3.5 Comparative material 2 Absenteeism Absenteeism Absenteeism 40 40 64 1000 3.8 Comparative material 3 43 16 1070 31 33 54 1050 3.5 Comparison 4 40 0 1200 40 40 64 1150 3.6 Comparative material 5 40 35 980 40 40 64 950 3.2 Comparative material 6 42 10 1050 40 40 64 900 3.3

Electric steel plate characteristics Magnetic flux density
B8 (T) Iron loss W17 / 50
(W / kg) Average
alpha angle Within 3 °
Area fraction (%) Average β angle
/ Average alpha angle Inventory 1 1.94 0.77 2.4 70 1.4 Inventory 2 1.93 0.76 2.8 65 1.2 Inventory 3 1.93 0.75 2.7 63 1.3 Invention 4 1.94 0.79 2.5 65 1.2 Invention Article 5 1.93 0.78 2.9 60 1.4 Comparison 1 1.90 0.89 4.0 40 1.8 Comparative material 2 1.90 0.88 3.9 42 1.8 Comparative material 3 1.89 0.90 4.0 39 1.7 Comparison 4 1.89 0.89 4.3 35 1.8 Comparative material 5 1.90 0.88 3.8 43 1.6 Comparative material 6 1.89 0.90 4.1 38 1.7

As can be seen from Tables 1 and 2, Inventive materials 1 to 5, in which the conditions of rough rolling and warp-rolling were properly controlled during hot rolling, were able to arrange the texture precisely as compared with comparative materials 1 to 6. It can also be seen that inventive materials 1 to 5 have remarkably improved iron loss and magnetic flux density as compared with comparative materials 1 to 6.

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 spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (16)

(Excluding 0%), Al: 0.015 to 0.040%, Mn: 0.04 to 0.15%, N: 0.005% or less (excluding 0%), And S: not more than 0.01% (excluding 0%), the balance comprising Fe and other unavoidable impurities,
Wherein the second recrystallization texture includes the secondary recrystallization texture and the average α angle of the secondary recrystallization texture is less than 3 °.
(In this case, the angle &amp;alpha; means the angle formed by the [001] direction of the texture with the rolling direction axis when viewed from the rolling surface). The method according to claim 1,
A directional electrical steel sheet having an area fraction of a secondary recrystallized texture having an α angle of 0 to 3 ° in the entire secondary recrystallized texture of 50% to 80%. The method according to claim 1,
Wherein the average α angle and the average β angle of the secondary recrystallization texture satisfy the following formula (1).
[Formula 1]
0.8? [Average alpha angle] / [average beta angle]? 1.5
(In this case, β angle refers to the angle formed by the [001] direction of the texture with the rolling direction axis when viewed from the vertical direction of the rolling direction.) The method according to claim 1,
Further comprising at least one of Sn: 0.03 to 0.12 wt%, Sb: 0.01 to 0.05 wt%, Cr: 0.02 to 0.15 wt%, and P: 0.01 to 0.05 wt%. The method according to claim 1,
Mo: 0.01 to 0.05% by weight, and Cu: 0.01 to 0.2% by weight. (Excluding 0%) and S: not more than 0.01% by weight (%), Si: 2.5 to 4.0%, C: 0.03 to 0.09%, Al: 0.015 to 0.040%, Mn: 0.04 to 0.15% (Excluding 0%), the remainder comprising Fe and other unavoidable impurities;
Hot rolling the slab to produce a hot rolled sheet;
Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed,
The step of producing the hot rolled sheet includes rough rolling and finish rolling,
Wherein the rough rolling step includes a step of lowering the cumulative rolling reduction to 10 to 40% and a rolling reduction of 40% or more,
Wherein the finishing rolling step includes a step of lowering the pressure down to 40% or more at least twice. The method according to claim 6,
Wherein the slab further comprises at least one of Sn: 0.03 to 0.12 wt%, Sb: 0.01 to 0.05 wt%, Cr: 0.02 to 0.15 wt%, and P: 0.01 to 0.05 wt%. The method according to claim 6,
Wherein the slab further comprises at least one of 0.01 to 0.05% by weight of Mo and 0.01 to 0.2% by weight of Cu. The method according to claim 6,
Wherein the rough rolling is performed at 1000 to 1150 캜. The method according to claim 6,
Wherein the step of lowering the pressure in the rough rolling step is performed at the last pass of the rough rolling step. The method according to claim 6,
Wherein the step of rough rolling includes 0 to 3 passes before the lowering pass. The method according to claim 6,
Wherein the cumulative rolling reduction of the finishing rolling step is 64 to 80%. The method according to claim 6,
Wherein the finishing rolling step comprises two passes of the step of lowering the pressure. The method according to claim 6,
Wherein the finishing rolling is performed at a temperature of 950 캜 or higher. The method according to claim 6,
The method of manufacturing a directional electrical steel sheet according to claim 1, wherein the hot-rolled sheet has a volumetric fraction of an aggregate structure having an orientation within 15 占 from (110) [001] of 4% or more. The method according to claim 6,
Wherein the directional electrical steel sheet produced after the secondary recrystallization annealing has an average α angle of the secondary recrystallized texture of 3 ° or less.
(Here, the? Angle means an angle formed by the [001] direction of the texture with the rolling direction axis when viewed from the rolling surface of the steel sheet).

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